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HomeMy WebLinkAboutHIGHLAND MEADOWS FILING 2 LOT 1 LEGAL.pdflnwn o 75 soulh tronlage road Yall, colorado 81657 (303) 476-7000 DESIGN REVIEW BOARD AGENDA July 17" 1985 2:00 p.m. Ho Sate'l I i te Dish Lot 1, Highland Meadows 2nd A*,*.,1 p- sJ#"S. -tl .1"^,^7. + ()ao.4-' .,o^lu'^!n ^iL . h^r*? Beard Residence Lot 46, Glen Lyon Site Visits: l 12::30 t.#2 2. 'W(*, #5 #7 #8 alLA q a*,a-^* 4. Strauss Garage Addition Lot 47 ' Vail Village 'Jest #2 5. Sonnenalp Flags 5. All Season's Parking Lot and Landscaping 7. lfural on the Lodge Employee Cafeteria Bldg. ottlce of communlty development #6 ";. .,,11':i* ,ll 1i ,Utlllty coniiintes Withln The f own of vair ' , 'l' ;| r:i . i' , !,.j,:i ;ir., ' ,,lli: t':,.. . .:.' I . -'i::i+rJ;1r il,i;t ' , John Ho I Uaiversal SatelLite Systems "tf1:,,1"" "lY..-t:to rne rowrr tt. :o" :, 1,,,i*lo:..i...,, ., '*$fffi :o,,f r.1.1""r11r .fatellite svstems . ,qii,i,1, ;lt,ffii,r1, 'rodehnent of a Satelltte Dlsh Into Utility Easenent'b.. ." 'iill1,i:, t.i l{i:'. --- on a-loit,ion of f,ot t, nighland Meadows 3i11ig: #2, ffit ffi. : ; fl r '"-,l':,,'ii li il'l::*"' . fit ,$r'' ,,,, I'The afore menitonea sateLllte arsh.vtU Intrude lnto eertain "ii,lr., itji ,it 'i. "irtillty easenentg on the above refbreneed property and are it{i; ' t,jr'i :.{;1" rl descrlbed on the ettaehed Slte P1anr. dated JuIy 12, 1985. In i] i,,.r,,,.,,.:"' i1', ,,,.,..on a'porplon of l,ot 1, Highland Meadows 3i11ng: #2, .f,'.iitl:l' {fi. I i'"1if,r., ':,:{' ., .I . Xagle County ColoraCo. ,C,,... ";$, ,: easements and sald lnstallatton of.rUttllty nec.essltates renoval i:".i.;'l ,', ii i, af ttra oq.}al1{ta A{cl,r ul.lla {r tho ltllltrr aaqomont narnnv.a'I qrrd .r::;' .f " i.; ;. ii'replacement of the dlsh shall be.at tbe sole dtscretlon and ,'tlexiense oi ttre property owner. Thls notlce does not honever, ili",-^--r..- l----^ r- ---l--r l- --It .| -- ^^ -^-^-4-lili :permtt danage to prope;ty outsldg..StllltV easements. tT,Dates -,Property Owner - Publte Serviee i.i Cross Eleetrlc t,aln Bell ;Weete-n Gas Catle Forv noun -&8t o o z g n c o {6 z !ttt a =-{ 'n 1t 8e 2= OGt 2Z 66)z {o @ m r! q.iif c3 e3 =-;.t qg m=<=3i 6€4o 68 n3 EE fi9 I !m tt ={ ntr& <m o l+ gEEIS EE" IH l=!nn 9z zo ;-{m llr l=o lr- O tco !l(tr <lo t1t !m !3 o tr m x m !{ o z L o @ I m O O f\)P o) -J o 1o -t{,+Pfi t,l , o 7) 9a ai_ 9! o. 2p ic EE d6 ,t .G =^E!-l c)o>70- C) 2n {m vz >m on -t>or 7 io ()- -{m c)-{ o €z m v ! t-o @ z =m CJ o z. o atr I m t-t- {rfl o /gF AC,()>'t- =5 :-{ 1' t3 lil ,{ .m |- Fl -{o t I 7 t m P lz n 3 dE 3l 1rl <l il nl Pl 'l I I !c -{o €z o .I P t-t m P z o !a 3 {o €z o .ll F t m I z I I ! e = .D -t UI o, at 0.t ct (D a-f (D o -{ F t ! ct F .o F JI { 3 P |- D m 8 G'o x o,\o f\) n ! c fD -t ltl a, an o d .D cn (D N o o (D - et =ct =D o o t EI lt,lt q -{ 0, ! c-o =T o 5o J J'I vr2 a+|ll ',.8 ;H -ru,J{l 9!" od3 +Eg .42 .t- j'- .+l N rDl N ID =-l |,,al 5 ='l ll IUF oi Efr io )D 'rl zo ao -2 ot4 t!Ei 6 z o=rn= !< 3 slllEl; q l6l3l= i ttt>tttt- n (+ .D - o- tn 5 ttl =t,cf oJ (D : l;l= ig { | r@ rO frl rI !; p l3t*ilr E lgrd F!5 e | ='e It5' E liliFl;!m u 3 -l Prolect Appllcatlon ."*\* . -r :i' "r Conlact Person and plp ,! i: .r Architect, Address arid Pthone Zone {z Commenls: Design Review Board t.o"t. r\ tr\8f DISAPPROVAL ;/-o 2" tPtn H", r\.lf E star Approval \\. d;-7 J*---* _ ._r..,L--**1 X. -., C'.,'if -- -s.cJ-., Jt FJa &r',\*Lo t(n +^t\,}-- \" .o LIST OF I'IATERIALS OE MME OF PROJECT: LEGAL DESCRIPTION: STREET ADDRESS: DESCRIPTION OF P Roof Siding 0ther Wall Materials PLANT IVIATERIALS: PROPOSED TREES EXISTING TREES BE REMOVED ea The following information is_required for submittal by the applicant to the Design Review Board before a final approval can be fiven: A. BUILDING I'IATERIALS: TYPE OF MATERIAL COLOR Fasci a Soffits l.li ndows tdindow Trim Doors Door Trim Hand or Deck Rails Fl ues Flashings.. Chimneys Trash Enc'losures Greenhouses Other B: LANDscAPINc: Name of Des i gner: phone: hpEe 2 a./ 1 I(FaogleP !R{pq1W flr,&l Lqykff,,N Botani'ca'l Name Comr6n Nane Quanity Size* 610r teqsge-6*. fututor-rl *Indicate caliper for deciducious trees. Indicate height for conjfers. Project Applicatlon tI o"," 6laolSf hu Proiecl Name: Proiect Descriplion: conracr person and ,^"^" &RA' BUr2dgr Qll -145'.1 Filing tlte*Wo ftlennw #), rar" ?lS Legal Description: t-ot -f-' gtocr ou/ner, Address and phone: f,\t+^t t+a $qb- 0r/$ Architect, Addr€ss and Phone: COLO. Comments: _e4 [oton l,rce* Fon' (t+T .forto l-to $rtra-tlr@ DLg+' BnCr Stoe oF VtEtl. fltotir( t{,ttco€ oF Ttu+ Bcgce ign Review Board r-t-- o*. ztz\gf DISAPPROVAL Town Planner tl o"t" 1\$K E Star Approval - {S . t� ;y ' . . �- 5� . v�t, :�, •.�;}��y, -a* 8 .:- -p�� t ��„s s � k k �t� ; �:.'Ti t � � �,y��-�,1�,a �� tir �� v �.���r e.� a ` � � `� '3 �� �..-�• � p '� '* l�5"''��I���I� a` 'S"'""4ti`' x :'c' t r��t.^s�fr.. gF •• T. � s V �.-� � � `` � a ��'i .� g ,,, �-_rs ��r!��,, :�t t - Fr.�- :, . _ . : ' . . � yv s� � ,y+,,;q�„'� a,�a a, _.?, � ¢ 4 � -L -' - � �'( �� ��F ^n- y�,y *:, �fts' .�, '�s��a ��C �s °` !^'.K{r'„ � �'" x°.�x,i ��,��i-,^r✓, '�a;,, �,r,�f.a a:�� , g,yr1!. '�F�y� ' .a' �y`e-_+ .-� �?.i`'r �fau'y�re.,?'�°. '`:e� t s�"�.�t �S.t..i �+3�{��r'}�a"'A��b,��" -�y Ra :t��• ��. �'°� k'"�'-T - . : '� ' `�k .. 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M..� ♦h�,e.., - .: . .. .� .-.. . ..: - .._:�.:' - ..�n. ,.. - %� . .. v � ' r�_' '.�.. �.-+f�,_ .r_H::..,, '_ x't.,:. .. .-' _ _ . .. . �.�. �.. .. .�._ . �t�r. Y7� _. -_ . . ' ..e --I I -!7 I I a-o FOX & ASSOCTATES OF COLORADO, tNC. CONSI,',LTIN G ENGINEEKT AND (IEOLOGISTS I DEN'ER oFFrcE flTfErTooTE!,o"t}to'""ff8lo"" I t I REpoRT oF GEorEcHNrcAL I ENGINEERING INVESTIGATION LOT 1, FILING 2 t HIGHLAND MEADors suBDIvIsIoN I vArL, C0L0RAD0 I t I prepared For I Sierra Federal Savings and Loan Association I t I I I I A Fox coMpaNy Job Nunber 1-1100-6643 March 22, 1985 I I I * t t t L t I I I I I I I I I I oo FOX & ASSOCIATES OF COLORAE O, lNC. CONSI,'LTING ENGINEEFS AND GEOLOGIISTS OENVER OFFICE 4765 INDEPENDENCE STREET WHEAT RIDGE, @LORAOO 8OO3a (3O3) 42zr-s578 Sierra Federal Savings and Loan Association 2730 South Wadsworth Boulevard Denver, Colorado 80227 Ronald F. Holcombe, P.E. Sr. Project Geotechnica'l Engineer RFH/pw: see.4 Copies: (5) Attention: Mr. Jack Musselman, Director of Insurance Subject: Report of Geotechnical Engineering Investigation for Lot 1, Highland Meadows Subdivision, Filing 2' Vail Colorado Reference: Work Order Confirmation and Letter Contract for the subject project by Fox and Associates of Colorado, dated February 26, 1985 Dear Mr . Musse'lman: At your request, we have completed a geotechnical engineering investigation for the subject property. The purpose of this study was to satisfy Town of Vail Ordinance 29 requirements. This report contains the data developed duri ng the course of the study, together with our analyses and recommendations for t6e structure. Since the structure is already structurally complete, this report should be provided to the structural engineer of record so he may verify that the design and construction cornply with our recommendations. If warranted, supplemental recommendations can be developed jf additional design or construction is i ndi cated. If you have any questions concerning this report, or if u,e can be of additional assistance, pl ease cal l. FOX & ASSOCIATES OF COLORADO, INC.Reviewed by: o'o March 22, 1985 Job Number 1-1100-6643 Donald R. Clark, P.E. Principal Geotechnical Engineer Q^"rZ 7 /ilA-^"/*n^6A0//^ A FOX COMPANY t * +il I il +il I I ? I I i il I I I t t to c-o Page Fi gure TABLE OF CONTENTS Letter of Transmittal INTRODUCTION SITE INSPECTION GEOLOGY Geologic Setting Bedrock Geology Surficial Deposits and Geomorphology Hydrol ogy Geologic Hazards SUBSURFACE CONDITIONS Data Acquisition Str at i gr aphy Ground l,later Soil Properties REGIONAL SLOPE STABILITY LOCAL SLOPE STABILITY FOUNDATIONS RETAINING WALLS UNDERDRAI NS L IMITATI ONS TEST HOLE LOCATION PLAN TEST HOLE LOG CRITICAL SLOPE CIRCLES ll I 2 3 3 4 5 6 6 I I 9 10 10 11 13 13 14 15 16 I 2 3 )-o Page Figure APPENDIX RISK IDEALIZED PROBABLISTIC DISTRIBUTION LOG OF TEST HOLE 3-1 LOG OF TEST HOLE HM-4 LOG OF TEST HOLE HM-19 REFERENCES A-1 A-1 A-2 A-3 A-4 @ INTRODUCTION ro oo A geotechnical study has been performed by Fox and Associates of Colorado, Inc. for Lot I of Highland Meadows Subdivision, Filing 2 in Vail, Co1 orado. An essentially complete, tri-level , duplex structure occupies the lot. l.le understand it has been vacant for about two years. The purpose of this study was to perform the necessary geotechnical analyses as required by Town of Vail 0rdinance 29, lo develop foundation and site development design criteria and make preliminary recorunendations for mitigative measures that may be indicated. To accomplish the above stated purpose, this study included: (a) a review of available construction documents and design reports; (b) a review of previous studies in the Highland Meadows Subdivision by Fox and Associates and other firms; (c) a geologic reconnaissance and literature review; (d) an inspection of the structure by a foundation engineer; (e) a fie'l d investigation including a test boring; (f) a regional slope analysis; (g) analysis of the subsurface conditions as they relate to foundations, drains, retaining walls and on-site s'lope stability. This report is a summary of the various phases of the study together with our concl usions and recommendati ons. Normally, a study of this type would be performed prior to structural design and construction. Since this study follows construction, we recommend that our report be reviewed by the structural engineer of record to determine if the design complies with our recommendations. Such a review may or may not indicate the need for mitigative measures or additional construction. The existing structure is a tri-leve1 duplex located on Lot 1of H'ighland Meadows Subdivision, Filing 2. Lot 1 is located to the north of Vernont Road -1- oa and overlooks Gore Creek. The strucutre is of wood frame construction with rock veneer,stucco, and wood siding. Each portion of the duplex has a garage on the south side with the floor between the middle and upper living levels. All three levels "dayl'ight" on the north side; however, only the upper level and a ha1f daylights to the south. The garage floor level and lowest port'ion of the driveway are approximately 11 feet'l ower that Vermont Road. Because of the proximity of the driveway to Vermont Road, a retaining wall has been constructed to the south of the driveway. The wall varies in height from approximately 2 to 4.5 feet. The backfill above the wa]l slopes approximately at a t horizontal to 1 vertical slope up to Vermont Road. The lot s1 opes down to the north toward Gore Creek at about a 2.1 horjzontal to L vertical slope. Ground cover was not visib'l e at the time of our study due to the snowpack. The structure has been stepped to conform to the natural ground slope. The maximum depth of cut for below ground 'living space is about 10 feet for the south portion of the lowest level . A culvert crosses Vermont Road near the east property l'ine of the lot and discharges on the eastern portion of the 1ot. lrle have been advised that discharge from this cu1 vert has caused some erosion jn the past, but that the discharge area has been stabilized with rock. SITE INSPECTION A sjte inspection was performed by the project geotechnical engineer to determine the condition of the structure with respect to foundation performance. A large portion of the exterior of the the foundation walls could not be observed because of the snowpack. The visible portion of the walls, which are faced wjth rock veneer, showed no distress. The only distress that was observed in the interior of the structure was smal'l cracking -2- oo in the ceramic tile grout around showers in the lower level . Thjs may be related to lateral movement of the foundation wall or minor foundation movements. There is a crawl space under the lowest level , so the cracking would not be the result of floor slab movement. There is no other evidence of foundation movement 'in the dryrall, which js typically very sensitive to foundation movement. 0n the exterior of the structure, the only vjsible distress was two cracks in the retaining wa'l I to the south of the driveway. The largest crack is at the high point of the wall. This crack is about 3/8 of an inch wide with a slight offset, with the southern portion tilting away from the backfil'l more. 0bservations with a carpenter's level indicate the wal'l is vertical . No other exterior distress was observed, however, several areas were ponding water from snowmelt. These were primarily near the front entrances adjacent to the driveway. These areas should be well sealed to prevent infiltration of water into the foundation wal 1 backfil'l . The ceramic tile cracking noted above may be related to such infiltrat'ion. GEOLOGY Geologic Settjng The geologic setting of the subject area is comp'lex, with many different geo'logic processes control'l ing the present site conditions. These processes include: marine and non-marine deposition, uplift, faulting, folding, glaciation, glacial deposition, mass wasting, and erosion. The geologic investigation included research of published Iiterature, field reconnaissance of the area surrounding the subject lot, our previous experience in thir and similar areasr and an on-site geologic inspection. -3- Bedrock Geology 0utcrops of bedrock were not observed within the boundaries of the lot. The bedrock unit immediately under'lying tire study area is the Minturn Formation, composed of grit, sandstone, conglomerate, and shale, with minor dolomite/limestone beds. The est'lmated thickness of the Minturn Formation beneath the site is approximately 3000 feet. underlying the Minturn in the study area is the Pennsylvanian Belden Formation of sjmilar composition, and a sequence of early Paleozoic sedinentary rocks overlying precambrian crystalline rocks composed of granites, gneisses, and schists. The subject I ot overl jes Cl astic Units D and E of the Minturn, approximately in the mjddle of the formation. These bedrock units are composed of interbedded and interlensed coarse, poorly sorted, micaceous quartzose, arkosic sandstones and conglomerates with micaceous siltstones and shales. The sandstones and conglomerates are friable to firmly cenented (carbonate) and weather to light brown or gray. The Minturn Formation dips at approximately 15 degrees to the north-northeast in the vicinjty of High'land Meadows. The site is located on the western flank of the vail syncline. The vail Syncline is a relatively shallow north trending syrcline, which pl unges toward the center from its northern and southern axial extent. The structure is exposed along the s'ides of the Gore Creek Val1ey as it transects the valley at Vail. The western flank of the syncline is the homoclinal eastern flank of the Sawatch Anticline of the Sawatch mountain range. l{o bedrock faults have been mapped beneath the site by the u.S. Geo] ogic Survey, although, at least two east-west trending normal faults have been mapped by Tweto in the bedrock units to the west of Highland Meadows, Filing 2. Tweto suggests that these fau'l ts originated in Precambrian tjme and were -4- .tlsr active in Laramide t'ime; the last mountain bu'ilding tectonic period that rormed the present Rocky Mountains. Fracturing within the bedrock mass appears to be both parallel to and at ,righ angles to the bedding. The bedding plane fractures are probab'ly caused ty overburden pressure release from glacial and eros'lonal processes and possibly structural extension associated with local faulting. High angle fractures within the sandstone are rough and open, and within the shale are smooth and often fil'l ed with carbonate cement. The high angle fractures are probably caused by structural re'lease associated with local faulting. Surfic'i al Deposits and Geomorphology Surficial deposition on-site can be linked to a series of geomorphic processes including glaciation, s'l ope failure, alluvial and gravity sheetwash colluvia'l processes and the ongoing weathering and erosional processes. At 'I east two glacial stades affected the area during the Plejstocene Epoch; the first, known as the Pre-Bul'l Lake age and the second, the Bull Lake glacial age. The blankets of glacial debris high on the Gore Creek Val'ley walls, above BulI Lake deposits, suggest the Pre-Bull Lake glaciation was more extensive than the recent glacial .period. This glacial stade probably eroded a large "U" shaped valley at Vail. The first stade of the Bull Lake glacial age deposited a lateral moraine at the site on which Lot 1 is situated. Samples recovered from exploration holes suggest that morainal deposition was as high as 200 feet above the present valley floor. Bul'l Lake glacial till is a mixture of large igneous, metarnorphic and sedimentary boulders within a matrix of c'l ayey sands and gravels. Deposits are poorly sorted, medium dense to dense, and moist to wet. 0ngoing erosion from subsequent, less significant glacial stades have removed much of this lateral moraine within the valley- -5- After the Bull Lake age glacial erosion and deposition, evidence suggests that a landsl'ide occurred within the overburden above the site due to glacial oversteepening of the valley. This slide deposited material on the present site and probably northward into the Gore creek valley. The site ls entirely under'lain by this landslide complex as mapped by Tweto (lg7l). The slide deposit includes very sandy, silty clays and c'l ayey sands with scattered gravels and a few cobbles and bou'lders. The presence of depos.its of clean to slightly silty and cl ayey sands and gravels with cobb'les suggest that Gore creek or a tributary may have crossed the site. As Gore creek meandered across the valley, it downcut through the slide mass to its present'location. This downcutting preserved a portion of the glacial deposit and the overlying slide mass which is the Highland Meadows Filing l terrace observed today. Lot 1of Filing 2 lies near the east edge of the steep terrace. Recent colluvial and alluvial deposit'ion appears to have added litt'le to the present terrace. Hydro l ogy No surface seeps vrere observed during the field investigation, however, the snowpack would probably have prevented observation of any that did exist. Further, no seeps have been reported on this lot by previous. investlgators. The granular portions of the subsoils typically contain perched water conditions, sometimes under pressure due to the sloping ground surface. These conditions often deve'l op during snonrmelt and spring rains and may last into the winter depending on the amount of water present and the degree of drying during the summer. Geologic Hazards Bedrock dips gently to the northeast and the ground slope is to -the -6- northeast. There are relatively weak shale beds within the rock with many fractures parallel and perpendicular to the bedding planes. These conditions tend to weaken the overall rock mass although the reduction in strength is not considered s'ignificant enough to allow for massive slope failure withing the bedrock units. Solution cavities, karst topography and related surface subsjdence are often associated with carbonate rocks similar to those present within the M'inturn Formation. No evidence of these features was found during our investigation, although their is some potential for their existence based on our experience in the area. Subsoils on tne the lot consist of three basic groups: glacia'l till composed of boulders and cobbles in a matrix of gravel , sand and clay (Un'ified Soil Classification Gp/GW/GC); slide mass composed of sand and clay with gravels (CLISC); and alluvium consisting of sand and gravel with cobbles and some clay (SM/ML). The glacia'l till generally is found at depths of more than 20 feet below the ground surface. Hydrol ogic conditions present important constraints to development. Seasonal 1y high ground water reduces the effectjve stress of granular soi1s, and softens cohesive soils. In addition, the ground water can add add'itional 'l ateral pressure to wal I s and increase the settl ement potenti al of foundat i ons. There were no active faults identified on, or in close proximity to the site. The site lies within the northern Rio Grande Rift subprovince which suggests a maximum credjble earthquake magnitude of 6 or 7 on the Modified I'lercall i Sca'le. This correlates to a seismic acceleration of approximately 0.07 times the acce'leration of gravity (.07g) The most obvious geologic hazard associated with the Highland Meadows Terrace is the stiUitity of the steeper slopes. The strength of the surficial -7 - deposits available for resisting failure is relatively small, particularly when saturated. The shear strength of the underlying glacial till is significantly more than the surficial deposits, although the possibility of failure still exists. The strength and orientation of the bedrock units appear to present only a very minor hazard. Solifluction is the slow, downward movement of fine grained surficial soils due to the loss of shear strength resu'l ting saturation and seasonal freeze and thaw. No evidence of solifluction was observed during our field investigation; although, it has been proposed by other investigators that sol ifl uction potential does exist. SUBSURFACE CONDITIONS Data Acquisition A field investigation rras initiated to obtain site specific subsurface information to develop on-site design criteria. In addition, available information from other studies was used to construct a regional subsurface model for use in regional slope analyses. The locations of test ho1es drilled for Lot I, Filing 2 and nearby lots (except for Test Hole HM-4) are shown on Figure 1, Test Hole Location PIan. The test holes were drilled with a continuous flight augers. In the later test continuous cone penetrometer soundings were are presented as Figure 2, and F'igures A-2 drilled in conjunction- with this study; Test Filing 2; and Test Holes HM-4 and HM-19 respectively of Highland Meadows Filing l. The test holes were logged in the truck mounted dri ll ing rig using holes (Test Holes I and 3-1), also made. Logs of the test holes through A-6. Test Ho'le 3-1 was Hole 3 in conjunction with Lot 3, in conjunctjon with Lots 4 and 19 field by a field engineer, -rnd -8- representative samples of the various strata encountered were collected. Descriptions of the subsurface materials that were encountered, together with standard penetration test, cone penetrometer test, and ground water data are presented on the test hole 1ogs. The del'ineation of the strata encountered is approximate as the actual transition may be gradual . The cone penetrometer test was used jn severa'l of the test holes to provide a large quantity of in-situ shear strength data. Previous studies in the Highland Meadows area have encountered difficulties in eva'l uating soil shear strength because of sample d'isturbance, the presence of rock fragments and boulders, and the s'l ightly over-consolidated nature of the surficial colluvial stratun. The cone penetrometer used in this investigation was a 1.9 inch diameter steel point. It was driven by blows of a 140 pound weight falling 30 inches. The penetration resistance is the number of blows required to drive the cone 12 inches, and is reported on the right hand portion of the test hole log. Str at i gr aphy Four generalized subsurface strata were encountered in the test holes located in close proximity to the site. The uppermost stratum is man made fill used to construct Vermont Road, and in the case of Test Hole HM-4, an access road. No fill was encountered in Test Hole HM-19. The fill is generally re-worked colluvium, which is described below. The depth of the fil'l varied from 11 to 13 feet jn Vermont Road to only 3 feet on Lot 4, Filing 1. Beneath the fill, a colluvial stratum was next encountered. The colluvium consists of silty clay to clayey silt with rock fragments and occasional boulders and sand lenses. The colluvium extends to depths of 17 to -9- 29 feet below ground surface, and is underlain by glacial til'l consisting of clayey sand and gravel with rock fragments, cobbles and boulders. Test Holes HM-4 and HM-19 penetrated this stratum and encountered shale and sandstone bedrock at depths of 40.5 to 44.5 feet. The bedrock extends past the maximum depth explored of 69.0 and 53.6 for Test Ho'les Hlrl-4 and Htil-l9 respective'ly. Ground Water Ground water was generally encountered be'l ow a depth of 20 feet. Our experience in the Highland Meadows area suggests that numerous seeps and perched water conditions occur at shallower depths. 0n Lot 4 of Filing 1, an artesian condition tras encountered at a depth of 26 feet. In addition, severa'l cases of slope fai'l ures in road cuts in Highland Meadows have been observed due to oversteepening of the natural slopes and intercepting seeps or perched water. No evidence of this type of condition was observed near the site. It was noted that the road embankment fill adJacent to the site was moist to wet. Portions of this fjll are highly permeablen and a perched water condition cou'l d easily develop during wet weather per.iods. So'i I Properties The results of this and previous studies, and observations of' various slope failures in the llest Vail area indicate that the shear strength of the colluvium is highly dependent on its moisture content. tthen dessicated, the colluvium has a relatively high shear strength; however, the relatively weak molecu'l ar bonds are broken upon saturation and shear strength is significantly reduced. The shear strength parameters used in the s'l ope stability analyses for this study are based on the cone penetration resistances.measured jn the field. In order for these values to remain applicable, good surface-and -10- subsurface drainage must be maintained to prevent softening of the colluviun. This a'lso applies to road embankments constructed of col 'l uvial soils. The underlying glacial till stratum has very high shear strength and is below the permanent ground water. The ground water has no effect on its shear strength parameters; however, a significant rise in the permanent ground water could create greater pore water pressures, thus reducing the strength of this stratun. Our experience indicates that this does not occur. Rather, perched water conditions are observed in the more granular zones in the overlying col'l uvium as the snow melts. As evidence of this, the artesian condjtjon jn the glacial tilI stratun on Lot 4, Filing t has remained relatively constant over a period of over a year and a half. The selected parameters for the slope stability analyses are presented on Figure 3, Crit'ical S'l ope Circles. Two sets of parameters are presented for the colluvjum and fill: (l) the average cohesion of the colluvium which is designated AVERAGE in the shear strength parameters tab'l e; and (2) the min'imum anticipated cohesion which is designated as MINIMUM. The shear strength of the glacial till is not tabu1 ated because the critical slope failure circles intersected only the co'l luvium and fill. The glacial till was modeled using zero cohesion and an internal frictjon angle of 45 degrees. REGIONAL SLOPE STABILITY It is our experience that regional slope stability is the primary concern for safe construction in the l,fest Vail area. This based on several factors: (1) the catastrophic nature of a failure should one occur; (2) regional slope prob'l ems are not easily mitigated, even at great expense; (3) problems would not necessarily be confined to a single lot; and (4) the relative safety of regional slopes is difficu'l t to predict. Our previous studies in this area -11 - concluded that the combination of steepness of slope, subsurface stratigraphy, particularly the depth to bedrock and the shear strength of the colluvium are the most significant factors in determining the rel ative safety of a slope. The regiona'l sl ope stability analysis for this study was made for a section paral'lel to the eastern and western property lines and midway through the lot. This section is essentially north-south trending, and represents the steepest portion of the site and surrounding area. The slope was investigated using both average and mjnimum anticipated shear strength propertjes of the colluvium. The critical failure circles and computed factors of safety are presented on Figure 3. The factors of safety that were computed are z.7g for the average shear strength case, and 1.68 for the minimum case. The failure circles for both cases were identical in location and radius. Since the critical failure circ'les did not intersect the 91 acial ti'l 'l stratum, the depth to bedrock was not a significant factor for this site. In analyzing the s1ope, a higher ground water case was used to determjne if pore i{ater pressure in the glacial till rlas a factor. The result was that the critical circles still only intersected the col luvium. Our experience has shown that natural slopes, particu'l arly. those covered with col 'l uvium should posses a higher computed factor of safety than control'l ed fill embankments, for which the soil properties are know wjth a greater certainty. lde recommend that natural slopes have factors of safety of at least 2.0 for the average shear strength case and 1.5 for the minimum shear strength case in order to be consjdered safe. It shou'l d be noted that, even if a slope meets these eriteria, it is not safe in an absolute sense. Refer to the section According RISK in the Appendix. the above reconmended criteria, the site is reasonably safe -12- on to Local slope stability is concerned with the performance walls, minor embankment fills, depths of cuts, and erosion with respect to regional slope stability. The lack of evidence of any distress or movement of the structure further suggests the slopes are stable. As discussed above, proper drainage of the colluvial soils is necessary to maintain the safety of the slopes. Refer to the section UNDERDRAINS. LOCAL SLOPE STABILITY retai ni ng the ground surface. Based on our field investigation and review of the construction plans that have been provided to us, there are no embankment fills on the site and all cuts that have been made are supported by structura'l walls. we understand that some erosion problems have been observed at the outfalI of the culvert along the eastern property line, but that this has been corrected. t,Je could not observe this condition because of the snowpack present at the time of our field investigation. In order to maintain loca'l slopes in a stable manner, the wal ls supporting them should be designed in accordance with the criteria given in the section RETAINING wALts. underdra'ins should be used to provide proper subsurface drainage as discussed in the section UNDERDRAINS. Undisturbed slopes should be 'l andscaped to protect from erosion and to divert surface water away from the structure. FOUNDATIONS Based on our analysis of the subsurface conditions, the foundation subgrade soils have a maximum bearing capacity of 2500 psf providing.adequate underdrains have been insta] led. conventional spread or pad type footings would adequately support the structura'l loads. The subgrade soils have gery of of -13- little to no swell potentia'l and settlements should be I imits. Our site inspection indicates the foundations sati sfactori I y. Active Pressure At-rest Pressure Passive Pressure within tolerable are performing Typically, foundation settlements on soils such as are present at foundation level occur relatively rapidly with the addition of load. Experience indicates that as much as 75 percent of total long term settlement occurs within one year after constructjon. Since the structure is about two years old, little or no additiona'l sett'lement is anticipated. This presumes properly designed and functioning underdrains adjacent to the foundations. RETAINING WALLS Two types of retaining wal 1s are present at the site: (l) foundation walls for the building; and (z) the wal'l to the north of Vermont Road. The performance of these walls to date was one of the obJectives of our field investigation. Since the foundation walls for the structure are covered, they could not be checked for distress. The lack of distress of other structural components suggests they have performed adequately. There is visible distress associated with the retaining wal I between the driveway and Vermoht Road as discussed above. Even though it is presently vertical , .its performance is questionable and shou'l d be evaluated by the structural engineer. The retaining wa1 ls should be checked with respect to several criteria: (1) lateral earth pressure including surcharge loading; (z) ttre maximum toe pressure with respect to soi'l bearing capacity; and (3) underdra.in design. l'le reconmend using the following equivalent fluid pressures to analyze retaining wal'ls: LeveI Backfill Sloping Backfill 115 L25 200 85 100 200 -14- I I The 'level backfill case may be used for the foundation walls for the structure. Since these walls are restrained at the top, they should be checked using at-rest conditions. The wall adJacent to Vermont Road should be checked using the sloping backfill parameters and either active or at-rest conditions, depending on whether the wall is flexible enough to develop active conditjons. The presence of the existing cracks, and the fact that the wall is still vertical , suggests that at-rest conditions are present. l,lhen checkjng the stabi'l ity of the wal'l s the naximum toe pressure shou'l d not exceed the maximum a'l lowab] e bearing capacity of 2500 psf. underdrains should be provided behind all wa'l 1s to relieve hydrostatic pressures, or the fu11 hydrostatic pressure should be applied to the wall. For conpacted backfill on the passive side of the wall, the recommended passive pressure may be used in stability computations. The passive pressure includes a factor of safety of 2.0 with respect to soil shear strength. The wal|s should also be checked for base sliding. l'|e reconrnend using a coefficient of base sl iding of 0.4. UNDERDRAI NS Review of the Cl aycomb report and our fie'l d investigation indicate that regional underdrains are not required for this lot. Local underdrains are recommended for all foundation and retaining wa'l 'l s to prevent buildup of hydrostatic pressures and to maintain the shear strength of the colluvial foundation soils. Our review of the construction plans provided to us indicates that drains were designed for foundation walIs. He have no information about drains for the retaining wa1 I adjacent to vermont Road, nor could an outfall or weep holes be found during our field investigation._ l,le recommend that the structural engineer of record evaluate the stability of all ! I I t -15- walls utith respect to lateral pressures and underdrains. Several areas along the south wall of the structure water at the time of our fie'l d investigation. This water enter the wall backfill or foundation subgrade. If these graded to drain, then drains should be installed or positive maintained to prevent jnfiltration. L IMIIATI ONS were ponding melt could potential ly areas cannot be seals should be I I I I I I I I I l I This report has been prepared excl usively to provide a detailed geotechnical evaluation of Lot 1, Filing 2 of Highland Meadows Subdivision, as required by Town of vail 0rdinance zg, lt has been based on widely spaced test holes, geologic interpretation, and our experience with sjmjlar projects in the vail area. It was performed in accordance with general ly accepted soil and foundation engineering practices. No other warranty, either expressed or imp'l ied is made. The structure for the subject site has already been designed and constructed. Therefore, the structural engineer of record did not have the benefit of recorunendations contained in this report during design. !{e recorrnend that the structural engineer be provided with this report to verify that our recommendations have been implemented in the design and construction. If instances are found where they have not, supplemental design and/or construction may be required. l.le are available to assist in this phase, shou'l d it be necessary. It cannot be over-emphasized that all mountain construction has inherent risks associated with it. tle have quantified these risks within the limitations of available analytical methods. P1ease refer to the Appendix for a discussion regarding risk. -15- Please cal'l if you have any questions concerning this report orif we may be of add'itional assistance. FOX & ASSOCIATES OF COLORADO, INC.Reviewed by: 8^r4?,U*-L A"algolL Ronald F. Holcombe, P.E. Sr. Project Geotechnical RFH/pr{ Copies:5 Engi neer Donald R. Clark, P.E. Principal Geotechnical Engineer =-'"ffi -17- -\ *Nl:*r*,- \ \ \ \ \\, \ \ $' ) I ^r' I /ll i\l \l a \ \i,s \ Y \ -#a -/ \- \ />r on-Zlo-j -21- \\\$\\\t)\rt { \ \l ' \l \l t \ )l \l \l \JI \ i o o Etevatlon: 8039 3 Teot Hol€ No.: 1 DEPTH (Fect) *DESCRIPTION PENETBATION RESISTANCE (Blowe/Foot) t0 20 ll 30 40 tl 5 10 15 20 25 u *' tr Medlum denee, darl brourn, gravelly, sllty SAND MAN-MADE FILL, molet to very molet (SP) .frost io a deprh of 4' A A A Sttlf brown sandy. sllty CLAY to clayey SLND, slth rock tragments, rnotst to v€ry molst (CLISC) A A A A Very dence brown clayey SAND AND GRAVEL ulth cobbles and boulders (GP/GW/GC) Borlng t€rmlnated at 2l fcet Pcnetr!tlon Rerl6trnc€ Legcnd O Strndard tpllt b.rrcl O Modtlled C.llto.nh b!.rel A 1.9 In€h cone p€netromatet * Sample lnt€.v.1 Legcnd + 2/t2/a4 W6ier level lnrl Dlte ff Drtvr .anrplcr I st"toy ruu" lll Rocl tore barret TEST HOLE LOG Job tlo 1-1100-5643 Date' 3/18/85 2 Fipre t2o0r v E150 E100 N R =142' F.S.=2.78 (avcrage) / - _. F.S.= 1.68 (mlnlmum) /\ /\ / --,. $ 8050 o t!t o El Booo 7950 79001 50 100 150 200 250 300 350 Dlctance, feet SOIL PARAMETERS COHESION. pcf FRICTION ANGLE, UNIT WEIGHT,LAYER Average Mlntmum degreec pcl I 500 300 . 2 2000 1250 3 2500 1500 20 o 0 110 r20 12s CRITICAL SLOPE CIBCLES Job l.lo: 1-1100-6643 Date: 3/18/85 3 F(rure I I I il t I I I I t t I APPEND IX I I I I I I I RISK The notion of risk is an important aspect of any geotechnical investigation. The primary reason for this is that the investigative and analytical methods used to deve'l op geotechnica'l recommendations do no comprise an exact science. The analytical tools wtrich are used are generally emperical and must be tempered by engineering judgement and experience. Therefore, the solutions or recommendations presented in any geotechnical study should not be considered risk-free and, more importantly, are not a guarantee that the proposed structure will perform satisfactorily. tlhat the engineering recorrnendations do constitute, is the geotechnical engineer's best estimate of those measures that are necessary to make the structure perform satisfactori'ly based on 'l imited subsurface information. The purpose of the following paragraphs is to discuss the concept of risk, so the owner, who must ultimately decide what is an acceptable risk, can better apply the findings of this study. Factor of Safety As discussed above, the most critical geotechnical consequence of this study is considered to regional s'lope stability. The stability of a portion of a slope is expressed as a factor of safety. It is important to note thdt the concept of factor of safety is a derived value, and not an intrinsic property of the slope. The accuracy with which that factor of safety for a given slope can be determined, is based on a number of factors, the most significant of trftich are I i sted be'l ow: 1. variability of surface conditions 2. variability and type of subsurface conditions. 3. validity of the analytical method 4. validity of simplifying assumptions A-1 o 5. intensity of study 6. certainty of the des'ign loading condition occurring Depending on how well the above factors can be assessed determines what minimum factor of safety would be required to have a reasonable degree of con- fidence that a failure will not occur. It is the geotechical engineer's respon- sibility to assess these condit'ions and advise the owner as to a minimum accept- able factor of safety. Probability of Failure Theoretically, a factor of safety of 1.0 indicates that a slope is on the verge of failing. Therefore, any lower factors of safety should result in failure and any higher factor of safety should theoretica'l ly represent a safe s1ope. However, due to the uncertainty of the factors discussed in the preceed- ing paragraphn all slopes, even those with factors of safety greater than 1.0, have some potential for failure. The higher the computed factor of safety is for a given slope, the lower its probability of failure will be. In recent years' approaches have been developed to relate computed factor of safety to probability of failure. This approach is called a 'probabilistic analys'i s' and can be performed at a relatively great expense. Although such an analysis was beyond the scope of this study, it is believed that the concept of a probabilis- tic analys'is of failure is very important. An example of the relationship be- tween computed factor of safety and probability of failure is presented on Figure A-1, Idealizeo Probabilistic Distribution. This figure indjcates two curves representing the results of probabilist'ic analyses for two different slopes. 0n this example, a factor of safety of 2.5 was used to show the differ- .ence betwen curve A and curve B. For the site represented by curve A, a factor of safety of 2.5 would result in a probability of failure of abbut t in g. How- A-? ever, for the site represented by Curve B, a factor of- safety of 2.5 would result in a probability failure of about 1 in 2000. This illustrates graphically that the value of factor of safety cannot be cons'idered in absolute terms. For the slope represented by Curve A, a much higher minimum factor of safety would be required to provide a reasonable degree of safety than for the site repre- sented by Curve B. It should be emphasized that the data in Figure A-1 is for illustration purposes only and was not based on data pertaining to this study. A-3 CURVE A F rlJ q. o Il.o tr o l-(J lr o IrJ F A =o o CURVE B 10-l to-z 1o-3 PBOBABILITY OF FAILURE (LOG SCALE) TDEALIZED PROBABLISTIC DISTBTBUTION Job No:' 1-1100-6643 Consuhing Engineers and Geologists Date: 3/t9/85 A-1 Figure Elevatlon: 3070:Test Hole No.: I & lA DEPTH (Fectl I rJ DESCRIPTION PENETRATION RESISTANCE (Blows/Foot) r0 20 30 40 ltrl l0 20 ut4tl,I 30 40 45 t:I :o:16.. $t HAI.I-HAOE FILL .l ^t A/ A ! ^A AA A A A A 4 A A A A Stlff to very stiff brown, sllty sdndy CLAY to c'ldyey !M with roik fragnrents, nolst-to veiy-fr6'Ts t (CLlitLj A A A A A A A A A a+ Dense to very dense, dark brorn to dark gray, clayey SAND and GRAVEL Hith snale fraq,nents, cobbles and boul ders. rEi st (GP/G'.I/GC) 8orin9 termi nated I39.0'. Note: Test Hole 1A consisted of cone penetromler testing only. Readings are lndicated as:A Penetrdlion Rcslstance Legend O Stondard .trtlt b.tr.l El Modlfled Cltttoml! blrrel A 1.9 lnch aonc penet.o|netel * Ssmple Intervll L€gcnd =2/ 12/84 Water lcvcl rnd Data Drlvr llrrrp['r Shelby tub€ RocL co.e brrrel TEST HOLE LOG Job No r'1101{086-01 Date 8/29/84 2 F('ure Figure A-2 Prorect Prorcct l-l l0r-5916 Highland lleadc{s !t Vsll ProJect Manager Ron Holconbe Fleld Engr./Geol. Hike A. Brodn Drlll Rlg - -. -- 1.55 Drlllcr Steve crav Dri led with 4" so auger cB 6t6 7t6 5T 300 psi cB 7t6 7t6 l{o sample taken set surface castng f^ 'la^rh 2n f6ar Drilled }Jith 3-718 inch dlaneter rock bit sPT 1416 t3l6 20t6 Artesian water at depth 26.0 feet. Flowlng at apDrorjnately I gprn at surface cB 30/10 sPr l8/6 3l/6 30/6 Hole caving at depth 36 feet. Artesi flot' increased to approrimately l0 No, Borlng No. Totrl Depth Hl'l-4 69.4 Surface Elevatlon .verya , tlea- gprn, Cannot advance hole lrith tlonal rotary dri llIng method sPI 2016 30.5 off-set hole l0 feet southrest Redrill r'lth hollow s tern augers. sPT 50/5 - - sPT 50/6 - - thered, probablv d ispl aced: Claystone. 5 i I tslone, nicaceous, this distorted beddingi intennitant discontinuous sandstone I en ses, Bedding interrupted bJ faulting or mass fdilure. nediun!htrd to hard. noist. green to broi{n 5 '10 20 25 30 40 45 50 l{AN-llAoE FlLt, temporary placement tor CIAY, very sandy, si1ty, scattered gravels. SAIID, clayey lenses, stiff to very stiff, noist, brorn (CL-SC) Sedimentary rocl fraglpnts GRAVEL & SAll0 in CLAY lratrlx, run,lrrge boulders. cobbles, SAND (SP) seams, nedi um dense to dense, wet, brown (GC-SC) Sedimentary and l{etarorphic rock fragments SAMPLE SYMBOLS CB'Callfornla Barrel Olow!/lnch) SPT'standard Penetrltlon Test (blosr/lDchl ST. Thln Walled Shelby Tube NX- Core, dlsmerer 2.155 lnches LOG OF EXPLORATION HOLE Consulting Engineers and Geologisrs Date: 9/14/83 Figure A-3a pro1ect @ Protect Manager ----&!-xokg!Qg Ptoj.ct No, l-l l0l '5916 Fleld Engr,/Geol. --U-14.@ Eorlng No. Hl'l-4 (cont lnued)Drtrt Rtg --l!!Tonl Depth 69 '4 Drltler steve GraY Surtacc Elcv!tlon Dcprh Log Sarnple ,% Rec. RQD Llthology Notes 50 ot 70 sPT 18/6 36/6 - sPl 23/6 27t5 - sPr 50/4 - SHALE & SANDSToIIE conti nued SPT 5PT 5PT Total Depth 69.4 feet SAMPLE SYMBOLS CB. Calllornla Barrcl SPT- Standard Penclrallon Tcsi (blosr./lncb) ST. Thln Walled Shelby Tube NX- Core. dhmerer 2.t55 Inches LOG OF EXPLOBATION HOLE Consulting Engineers and G€ologists Date: 9/14183 Flgure: Al-3 Figure A'Sb ProJect Manager Fleld EngrJGcol. Ron Holcolbe Pror?ct No. Eorlng No' l-ll0l-59t6 Hfi- l9 Drlll Rls Total DcDth 53,6 Drlllct Steve Gray Surfsc. Elcv!tlon Depth Log Sample * Rsc. Datn Lltholosy Notes 0 :5 . : : -aJ : : - l- Jl -L I t Foo r I t- t-l- 45 I l- so I CB 131t2 ST psl 300 psl 12t6 .E l0l6 CB r s/6 9t6 SPT 16/6 24t6 t6/6 1416 916 |t6 Auger refusal at begain core r un. depth 4 3.0 feet, ToDsoi I 'tk , W:', 9t r?' CLAY, very sandJr, silty, few gravels stl ff. molst, bro{n (CL) CLAY, silty SILT, clEyey' lnterbedded, grades to SAND, clayey below depth 15.0 feet, stiff to very stiff, molst, brown (cl-ilL-sc)ST ST CB GRAVEL t SAND in CLAY nrtrlx, large boulders, cobbles, nedlum dense, r,Elst to !ret, brown (Gc-sc ) Rock fragmerts of sedinentarY, Igneous and netanorphi c orJgln. CB 5Pl SPT SANDSToNE. rEdinr to coarse grai ned, well cenented, delomltlc cement, nassive, mderately fractured, slightly oxidlzed' hard' nolst, light ^--., .- k--..6 tcdl :"' NX qn 25 orre ! rotrlvlc rrsr r!l terbedded sandstone I enses, nlcaceous. thlnly bedded, sl i ghtly carbonqceous,very fractured alonq beddinE 9lanes (+lDo dlgl. metal silfides.-hbrd. inols dark qray (1.11-CL) SAMPLE SYMBOLS CB. Callfo/nla Blrrcl Glos./ttrch..) SPT' Standard Penctrallon Tc6l Glo!,rrl lnch..) ST- Thln Walled Shetby Tube NX' Core, dlameter 2.155 Inches LOG OF EXPLORATION HOLE Drte: 9/14/93 Flgure: A1-4 Figure A'4a -.:8 ProJ€ci -!!9!Ls@-g!-!9!!ProlcctNo. l-ll0l-5916 Borlng No.tlH- l9 (conl lnued ) Totll Dcpth 53'6 Surface Elcvatlon Pror€cl lrlanlg€r Ron Holconbe Fleld Engr ./Geol. -Hlte-A-8rom Drlll Rls Drltler Stevp Grev Deprh Log Sanple , Bec. RQD Lltholosy Notca i t- F L F tr F t_ : : : l : - : : : NX 94 21 SHALE contlnued Iotal lbDth 53.5 feet 9AMPLE SYMBOLS CB' Calllornlc Barrel ST- Thln Walled Shelby Tube SPT. Standard Pcnetlatlon Tcsl NX- Core. dlameter 2.155 lnches LOG OF EXPLORATION HOLE Consulting Engineers and Geologists Dite: 9llqlg3 Flgure: A1-5 Figure A'4b REFERENCES 1. 'rGeotechnical Study for Highland Meadows Filing No. 1 and High'l and Park, Vail, Colorado" by Fox and Associates of Colorado, Inc., dated November 4, 1983, Job Number 1-1101-5916. 2. 'rDrainage and Slope Stability Analysis, Highland Meadows and Vajl Village West Subdivisions" by Claycomb Engineering Associates, Inc., dated August 17, 1982, Job Number 1845.001. 3. "Pre'liminary Plan Submitta'l for Highland Meadows Filing 2" by KKBNA, Inc., dated June 30, 1978. 4. "Phase II Geotechnical Study, Lots 3 and 26, Highland Meadows Filing No. 2, West Vai1, Colorado" by Fox and Associates of Colorado, Inc., dated September 10, 1984, Job Number 1-1101'6086-01. 5. "Soi'l s and Foundation Investigation for Proposed Residence, Lot 1, Highl and Meadows, Fi ling No. 2, Eagle County, Colorado" by Inter-Mountain Engineering, Ltd. dated June 9, 1980, Project Number v- 0043c. 6. Sheets 3, 7, and 8 of structural plans by Nova Design and Development, undated. 7. "Topographical Study" by Inter-Mountain Engineering, Ltd., Sheet 1 of 1, dated May 19, 1981, Project Number V-10975. u,F ;5#.l I I t' \.1 ,,tl I-r I I tlr,IF I I I rtt u, UJ rt E E € UJ o- J <l FI ol FI U' trJ u- F E c t.lJ =r&l o.0 z E t- o ttl o A z u, (, o =lrl u.t z |r! g, ul tt z o ts UJ ()rtl e z o F o z () !!o ttt F ll tl lf ltt 2 .f z \P- o o E o o (t I I 3 C'4 _l -l ul 3 o ilr llE k <l llol IFl totl totl l<ll t^tl t-tl r=ll =ll <u Gtl FqJ ll Jll <tl o =\l o tt z I .E 4 o z o 5 E F (, F.ta EcJ ( r- t+- H€O ..; e€Jcl. i|' - l!q- E *,-55 553*14(rEc, o 3'i or -{Pt r4t !t- i ;sts I EEFE I il;gJ FTtrFd =F </IE :{tr-sf- 'i h- =!r-.C- u-u.l o€ .E< tr:F H'< =<toiF f tEr,--b; uuu !is:El ;=-fi| - i tutl s$: frFl 5F$ F([ A;E E* tr}DD *fl t o E-q o !t @ =, c 5 E E o (, o o, E rg C't t- 'o)o,(-n \z- L ol 3l e3 - €"s]^ lioJ;u" (Op+;"..1 ) !"lnJ-" PVC ConJ,;t\-==-Norl\ SiJe o1 4i< . A DC :o qt,cl t.ll.'- - ( f'ro t\,''-e t\oi t>, I o.l4:c+dFs o* d;"h erJ J2" o rrra q roc^r -l ]7" $.o- tlJ,r,-€nJ 6roun) le re I { F gLle \ S'l'.e- BrVC Cr,.^ooJo.,4r,..!o-i-L e-,Js )lSt " c^borz .1, o,rr.)jo8" ]r, n coa]Jc,;+ e."J \ k & &ese 1 4 a T:*$L: I __l I I 4" \ -l^,tsc,J Holc 3G"*,Jr' '.+t l"ra. proo.,'t* ,r" i \3'l I Ii"li tt 4l\i t\tt\ -l f_l Y R- E"1 'r\^- lnwn 75 soulh frontage road rall, colorado Bl6Sz (303) 476-7000 August '1 , .|985 Thomas A. Braun Town Planner TAB: bpr olflce of communlty development Mr. John Ho 20]0 West Vermont Road Vail, Colorado 81657 Re: Satellite Dish Dear Mr. Ho, Il lgyi:*ilg your application for a sate'[ite dish instat]ation, the ueslgn Review Board required the installation of landscaping as wel 1 as the painting of the didh as part of ttre ippiJvi.i.'-ih;;;"imirovements were originally to have been comple!"d !.y July'24th. rnii-aite ilas agreed upon bv Greg-Burnett of Unversat'TVR. rhe weittrdr in ilii-paJi-flw weeks has obviously presented problems.with_the painping or Cne'oiirr. - pii*iriiy-for this reason, a n6w deadline of Augirst 7 his been estab'lished for the S:3pl-".t;:l-gf tl.,11!n!!ng ag,'tandscipins as was. gpproved oy irre o"sign Kevlew Eoaro. r have contacted Greg concerning this deadline and want6d to notify you as well. L.I::ld.rllongly encourage you to see that this work is completed by the Augusr / creadline so as to avoid further action by the Town. pleasl do not hesitate to call me with any questions you ma! have.-'ihanr you for your cooperation. Si n cerely, lnwn 75 south lronlage road yall, colorado 8t652 (303) 476-7000 August I, 1985 ofllce ol communlty deyelopment Mr. Greg Burnett Universal TVR Box 5520 Avon, Coloiado 8.|620 Re: Dear Greg: An adequate amount of^time has pas.sed in_which to complete the required improvements for the. Beckley anb Ho satel'tite aiin-in!iiiiations. I am requesting that this work be completed by the following-dead'lines: Beckley Installation As you know, citations were issued in early ,luly over failure to .qgTpl"!g requi.red Design Review Board impr6vere-nti'ior'irrii Jiir,.wnr re the landscaping is in, the paint used on the dish is incon-sistent with that'ap[roved 6y the'Board. t wouio-ue'[uppv to dis-miss the charges against you and Travis Beckley p"ouiJ"l the dish is painted th6 appioved g6ior. bt.wiranesaiv, Arsuii'i.--iour arraignment . has been rescheduld.to Aqsugt -gth to att6w vou-in uaotiionut weel- --'- to complete this_work. If-the painting is ci,mpteteJ-6v'nugust'i[ii I will see that the charges are'dismisied. _If'nJi,-t[i, ctrirges'witt be heard at your arraignfrent on the Bth ;f nuguli.' -"- Ho Instal lation ,As was discussed,.the required landscaping and paintinq was to have been completed within ond week after the isiuinie'i'i'if," uutiarng'-permit for this installation. . The permit was issued on-,luiv rzr-1985. .The heavy rain we have had oier the'last-rew-wi"ts nus obviously ' created prob'lems,with the_painting of this dish. Howev.", this should-not have affected,the ability to_install the required-iiniscaptng.I have set a deadrine of Augirst 7 for the,compidlion-oi-ttris wor[,as well. I encourage you to complete this work by the deadlines that have been Universal TVR Augqst l, l98S Page 2 established. In obtaining approva'rs for-these instalrations, you and your clients have acceptei tirb reiponsiLiriiy 91 ;;;i;;;;; the instanations as proposed. This inciudes the painiins ui i.ii ;;"'ih;"i;;dscape improvements.This has put me in a position Jr'"nio..ing..th.t"_;pp;;.i;";nd seeing that this work is comir]etea-ir-;pil;;;;: t,thire I wourd hope to avoid additional citations beins i.isuea: ih;;; dii';.*tl'i."i5' arternative if the work is not complei"d-Jn-iirJ.'-'itrere trail'n-6oi[ cises oeen arnpre time to allow the compietion oi inii'work and we wiil hope to see it done bv next Hbonesdav. trinli i;;l;; ili.i;"il'.oiiJ"ition. Sincerely, Thomas A. Braun Town P'lanner TAB: bpr G*o\. \ -fl\'A ,,..*ra-'r,.- J.$r. o.* <-.5.".., .^ { ^\ =t-Q\rrc \ rr*- t\..*"(4.1 -il',.i*t: &.^. O.r{- {.p \" s.-z- (Jr[^.arl't".{ 4'*..- Johnson, Kunkel ?nrro.iates, Inc. LANO SURVEYING . CIVTL ENGINEERING. MAPPTNG March 25, 1985 Ms. Diane !{eehan 391L Bighorn Road Vail, CoLorado 81657 Re: Lot l-, Highland Meadows #2 JKl85/0L2 Dear Diane: I have reviewed the Geotechnical Engineering investi-gation for Lot 1, riling No. 2, Highland Meadows Subdivision performed. by Fox Consulting Engineers and Geologists, dated March 18, 1985. The report suggested that the structural engineer of record verify that the reports recornrnendations have been implemented in the design and construction of the retaining wal-ls. In review of the drawings and. d.esign calculations for the building wa1ls, I found that the wall-s were adequately designed. Holvever, it shouLd be noted that I cannot attest to the actual construction since we were not present during the construction phase. Although specified reinforcing steel, waLl thicknesses and peripheral drains were indicated, the true "as built' conditions are unknown.The Town of Vail Building Department should have records of foundation inspections which should confirm the drawing requirements. The Fox report al-so guestions the adequacy of the retaining wa1l located between the structure and vermont Road. This was a short wall, 2 Eo 5 feet high al-ong the driveway. I cannot attest to the adequacy of this wall since we were no! reguested to provide a design or details for the waLL. I woul-d suggest that you contact Dave lrwin of NOVA Designs concerning this walI. il, U-t ,'{(Lx */l I P.O. Box 409 . ll3 East 4th Street Eagle, Colorado 81631 . Phone: (303) 32&6368 / Mv senera, "or,.Q"ion- from rhe r.ox report ?.n". .n. ::f::t:I:^::_i"_:_.911!iv3rv. safe area. rirat-no-sisns of major distress are evident other than minor -ricting or the driveway retaining warl. That surface arainige nust be -properJ-y controJ.led, such as no ponding Ue p";litted and that an underdrain around the Uirifaini ,u"[-i..r. o"",properly installed. A11 surface arainite'"i:^""ia"i"ve been diverted awav from the buirdi"g-u" quic[ry .. fo""iuru.Also the natirrar ar"i""l"-r"y'-irJ"g the East property rine should be adequately liiea t-o p."rrent erosion problems. Should you have any questions please advise. Sincerely, /n*/4^^"W . MacKown, piE.Structural Engineer of Record ': ': -.- ,. .- - -ii't - --: ' = iil f'j I il I I I t l I I I FOx & ASSOCTATESOFCOLORADO, tNc. CONST'LTING EIVGINEERS AND GEOLOGTSTS OETWER OFF|CE 4765 INOEPENDENCE STFEET WHEAT RIDGE. COLORADO AOO3:} (3I)31 424-ss7a FOX & ASSOCIATES OF COLORADO, INC. Eng i neer March 22, 1985 Job Number 1-1100-6643 Reviewed by: Donald R. Clark, p.E. Principal Geotechnical Eng.ineer Slerra Federal Savings and Lojn Association 2730 South lladsworth-Boulevard Denver, Colorado 90227 Attention: Mr. Jack Musselman, Director of Insurance Subject: Report of Geotechnical Engineer.ing.Investigation for Lot l, Highland Meadows Subdivision, Filiig Z, Vail Colorado Reference: work 0rder confirmation and Letter contract for the subject proJect by Fox and Associates of colorado, oiiea reuruiiy zo,-isgi Dear Mr. Musselman: At your request, we-!1yg-comp]eted a geotechnical engineering' investigation for the subject Droperty. 'The purpoie of this stuoy"*ai-to satisfy Town of vail 0rdinance 29 iequireirents. 'Thi;- report contains the data deveroped 9ltif'p the course of.the study, together wiin-ori-iniiyi.r".no recomnendatjons for the structure. since the structure .is _arready structuralr.y comp'rete, this report shourd be provided to the structural .enginEer of record-so rri mai've"try tn.t the design and construction compry with-our reionmendations. ii-wii.anted, supplementar recommendations can be developed if aOOiiionit-'Oesign-'0. construction is indi cated. I{.ry have qnl quest_ions concerning this report, or if we can be of additional assistance, please cal I . Q^"rZ 7 ttl4-*f L6Ao//- Rona]d F. Holcombe. p.E. Sr. Project Geotechnical RFH/pw: see.4 Copies: (5) a- A FOX COMPANY l: l" ii 1 2 3 3 4 5 6 6 8 8 9 10 10 11 13 13 14 15 l6 1 2 3 I t T I il il il il Letter of Transmittal INTRODUCTION SITE If'|SPECTION GEOLOGY Geologic Setting Bedrock Geology Surficial Dep6iits ano Hydrol ogy Geologic Hazards SUBSURFACE CONDITIONS Data Acquisition Str at i gr aphy Ground l.later Soil Properties REGIONAL SLOPE STABILITY LOCAL SLOPE STABILITY FOUNDATIONS RETAINING I.,ALLS UNDERDRAINS LIMITATIONS TEST HOLE LOCATIOI,I PLAN TEST HOLE LOG CRITICAL SLOPE CIRCLES TABLE OF CONTENTS Geomorphol ogy Page T Fi gure ict I I APPENDT' f, RI'K Pase A-1 IDEALIZED PR0BABLISTIC DISTRIBUTION Figure A-l I LoG oF TEsr H'LE 3-r A-z f LoG 0F TEST HoLE HM-4 A-3 t Loc oF TEsr HoLE HM-19 A-4 I REFERET{CES N I I I I I I I I I I il N II{TRODUCTION A geotechnicar study has been performed by Fox and Associates of colorado, Inc. for Lot I of Highland r,feadows subdivisron, Filing 2 in vail,colorado' An essentially complete, trl-level , duplex structure occupies the lot. t{e understand it has been vacant for about two years. The purpose of this study ',as to perform the necessary geotechnical analyses as required by Town of vair Ordinance 2g, to deverop foundation and site deveropment design criteria and make preliminary reconmendations for mitigative measures that mav be indicated. To accomprish the above stated purpose, this study included: (a) a review of avai'l able construction documents and design reports; (b) a review of previous studies ln the Highland Meadows Subdivlsion by Fox and Associates and other firms; (c) a georogic reconnarssance and literature review; (d) an lnspection of the structure by a foundation engineer; (e) a field investigation incruding a test boring; (f) a regionar srope anarysis; (s)analysis of the subsurface conditions as they rerate to foundations, drarns,retaining wails and on-site srope stability. This report is a summary of the various phases of the study together with our conclusions and recormendat ion s. Normally, a study of this type would be performed prlor to structural design and construction. since this study foilows construction,.we, recommend ihat our report be reviewed by the structural engineer of record to determine lf the ,the design'complies wittr our recomnendatlons. such a revrew mailo, mir,,, indicate the need r-,itieut,,. ;J;";;;":;;,r;,;il::,':" ,]u' not The existing structure is a tri-level duplex rocated on Lot l of Highrand l'readows Subdivision, Firing 2. Ldt 1 is located to the north of vermont Road I I .:b i. ,Ir -l- I I I I I I I I I N il I I I I @oo 'and overlooks Gore Creek- The strucutre ls of rood frame construction with rock veneer,stucco, and wood siding. Each porfion of the duplex has a garage on the south srde with the floor between the middre and upper Ilvrng levels. All three levels ndaylight" on the north srde; however, onry the upper level and a half daylights to the south. The garage froor level and lowest portion of the driveway are approximately 11 feet lower that Vermont Road. Because of the proximity of the drlveway to vermont Road, a retaining wail has been constructed to the south of the driveway. The wa'll varies in height from approximately 2 to 4.5 feet. The backfill above the wall slopes approximately at a I horizontal to I vertical slope up to Vermont Road. The lot slopes down to the north toward Gore creek at' about a z.L horizontal to I vertical slope. Ground cover was not visible at the time of our study due to the snowpack. The structure has been stepped to conform to the natural ground slope. The maximum depth of cut for below ground living space is about 10 feet for the south portlon of the lowest level . A culvert crosses Vermont Road near the east property line of thelot and discharges on the eastern portion of the lot. iiJ'have been advised that discharge from this , culvert has caused some erosion in the past, but that the dlscharge area has ,:been stablllzed with rock.'-: rP ,. iJ SITE INSPECTION A slte inspection was performed by the project geotechnical engineer to determine the condition of the structure with respect to foundation performance. A large portion of the exterior of the the foundation walls could not be observed because of the snowpack. The visible portion of the walls, which are faced with rock veneer, showed no distress. The gnryr distress that was observed in tie interior of the structure was smalI cracking -2- I I I I l'ould not be the result of floor slab movenent. There ls no other evidence of foundation movement in the dryral 1, which is typically very sensitive to foundation movement. 0n the exterior of the structure, the only visible distress was two cacks il.jhe retainins wan ro rhe .ortili},.' o.ir."*. jin" ru"n.r. ....r' is at the high point of the wa'l'|. This crack is about 3/g of an inch wide with a slight offset' with the southern portion tilting away from the backfill more. Observations with a carpenter's level indicate the wall is vertical . No other exterior dlstress was observed, however, Gverit areas were oondJnq l \ j {44 +'+i+ -.J' water from snouamelt. i These were primarily near the front entrances adJacent to the driveway. These.areas should be well sea'led to prevent lnflltration ot ,, water lnto the foundation wall backfillrl' ,n. ceramlc tile cracking noted above may be related to such infiltrution. GEOLOGY Geologic Setting The geologic setting of the subject area ls complex, with many different geologic processes controlling the present site condjtions. These processes include: marine aird non-marine deposition, uplift, faulting, folding, glaciation, glacial deposition, mass wasting, and erosion. The geol ogic investigation incl uded research of publ ished I iterature, field reconnaissance of the area surrounding the subject lot, our previous experience in this and similar dreiSr and an on-site geologic inspection. I I F il il t I I I I I -3- I I I I I I I il il I I I I I I I t Bedrock Geoloqy outcrops of bedrock were not observed within the boundaries of the lot. The bedrock unit immedlately underlying the study area is the Minturn Formation, composed of grit, sandstone, congromerate, and share, with minor dolomite/limestone beds. The estimated thlckness of the trlinturn Formation beneath the site ls approximately 3ooo feet. underlying the l{inturn ln the study area is the Pennsylvanian Belden Formation of similar composition, and a sequence of early paleozoic sedimentary rocks overlying precambrian crystalline rocks composed of granites, gneisses, and schists. The subject lot overlies clastic units D and E of the Minturn, approximately in the middle of the formation. These bedrock units are conposed of interbedded and interlensed coarser poorly sorted, micaceous quartzose' arkosic sandstones and conglomerates with micaceous siltstones and shales. The sandstones and conglomerates are friable to firmly cemented (carbonate) and weather to light brown or gray. The Minturn Formation dips at approximately 15 degrees to the north-northeast in the vicinity of Highland Meadows. The site is located on the western flank of the vail syncline. The vail Syrcline is a relatively shal'low north trending syrcline, which plunges toward the center from its northern and southern axial extent. The structure ls exposed along the sides of the Gore Creek Va.lley as it transects the valley at Vail. The western flank of the sytcline is the homoclinal eastern flank of the Sawatch Anticline of the Sawatch mountain range. No bedrock faults have been mapped beneath the site by the u.s. Geologic survey, although, at least two east-west trending normal faults have been mapped by Tweto in the bedrock units to the west of Highland Meadows, Filing 2. Tweto suggests that these faults originated in Precambrian time and were -4- I I I I @o last actlve in Laramide time; the last formed the present Rocky Mountains. mountain building tectonic period that I I Fracturing withrn the bedrock mass appears to be both paralrer to and at high angles to the bedding. The bedding plane fractures are probably caused by overburden pressure release from glaclal and eroslonar processes and posslbly structural extension associated with local faulting. High angle fractures within the sandstone are rough and open, and withrn the shale are smooth and often filled with carbonate cement. The high angle fractures are probably caused by structurar re'rease associated with rocar faurting. SUificl al Dpnnsits end Aonrnnr.rh,..I '.,,., surficial deposition on-site can be rinked to a series of geomorphic processes lncluding glaciation' slope failure, alluvial and gravity sheetwash colluvial processes and the ongoing weathering and erosionar processes. At least two glacial stades affected the area during the pleistocene Epoch; the first, known as the pre-Buil Lake age and the second, the Bull Lake glacial age. The blankets of glacial debris high on the Gore creek va.lley walls, above Bull Lake deposits, suggest the pre-Buil Lake graciation was more extenslve than the recent gracial period. This g'raciar stade probabry eroded a large "u'r shaped valley at vail. The first stade of the Bu.ll Lake glacial age deposited a lateral moraine at the site on which Lot I is situated. Samples recovered frbn exploration holes suggest that morainal deposition |vas as high as 200 feet above the present valley floor. Bull Lake glacial till is a mixture of large igneous, metamorphic and sedimentary boulders withjn a matrix of clayey sands and gravels. Deposits are poorly sorted, medium dense to dense, and moist to wet. 0ngoing erosion from subsequent, .ress significant glacia'l stades have removed much of this lateral moraine within the valley- I I I T il E il I I -5- I I I I I ! I I il fl il il il After the Bull Lake age graciar erosion and deposition, evidence suggests that a landslide occurred within the overburden above the site due to glaclal oversteepening of the valley. This slide deposited material on the present site and probably northward lnto the Gore creek valley. The site is entirely underlain by this landslide complex as mapped by Tweto (lgll). The slide deposit includes very sandy, sllty clays and clayey sands with scattered gravels and a few cobbles and boulders. The presence of deposits of clean to slightly si'lty and clayey sands and grave'ls with cobbles suggest that Gore creek or a tributary may have crossed the site. As Gore creek meandered across the valley, it downcut through the s'l ide mass to its present location. This downcutting preserved a portron of the graciar depos.it and the overrying sllde mass which is the Highland f4eadows Filing l terrace observed today. Lot l of Fi'l ing 2 lies near the east edge of the steep terrace. Recent colluvial and alluvial deposition appears to have added little to the present terrace. Hydrol ogy No surface seeps were observed during the field investigation, however, the snowpack would probably have prevented observatlon of any that dld exist.) Further, no seeps have been reported on this lot by previous investigators. The granular portions of the subsoils typically contain perched water conditions, sometimes under pressure due to the sloping ground surface. These conditions often develop during snowmelt and spring rains and may last into the winter depending on the amount of water present and the degree of drying during the summer. Geologic Hazards Bedrock dips gently to the no.rtheast and the ground slope ls to -the il I I I -6- f, f f, f, il fl il il il northeast. There are relatively weak sha'le beds rithin the rock with many fractures parallel and perpendicular to the beddlng planes. These conditions tend to weaken the overall rock rnass although the reduction in strength is not considered significant enough to allow for massive slope fallure withing the bedrock units. Solution cavities, karst topography and related surface subsidence are often assoclated with carbonate rocks similar to those present nithin the Minturn Formation. No evidence of these features was found during our investigation, although -rn..,tr.. t: toT_ ?otlnrt.t..lol. their existence based:r on our experience in the area.-'-i' -" -:-".'rr'- . ''''r r'' " ' - ''t'J Subsoils on the the lot consist of three basic groups: glaciar till composed of boulders and cobbles in a matrix of gravel , sand and clay (unified soil classification GplG|,|/Gc); slide nass composed of sand and clay with gravels (CL/SC); and a'lluvjum consisting of sand and gravel with cobbles and some clay (SM/ML). The glacial till generally is found at depths of more than 20 feet below the ground surface. ' Hydrologic conditions present lmportant constraints to development.; Seasonally high ground water reduces the effective stress of granu'l ar soils, and softens cohesive soils. In addition, the ground water can add additional lateral pressure to walls and increase the settlement potential of foundat ions. There were no active faults identified on, or in close proximity to the site. The site lles within the northern Rio Grande Rift subprovince which suggests a maximum credible earthquake magnitude of G or 7 on the lilodified l'lercalli Scale. This correlates to a seismic acceleration of approximately 0.07 times the acceleration of gravity (.OZg1. The most obvious geologic hazard associated with the Highland Meadows Terrace is the stiuitity of the steeper slopes. The strength of the surficia] t il il t I -7- I I I I I I f, f, t il il il I I deposits available for resisting failure ls relatively small, particularly when saturated. The shear strength of the underlying glacial till is significantly more than the surflcial deposlts, although the posslbility of failure still exists. The strength and orientatlon of the bedrock units appear to present only a very minor hazard. solifluction is the slow, downward movement of fine grained surficial soils due to the loss of shear strength resulting saturatlon and seasonal freeze and thaw. l{o evidence of solifluctjon was observed during our field investigation; although, it has been proposed by other investigators that,t sollflucilon potential does exist. i SUBSURFACE CONDITIONS Data Acquisition A field investigation was initiated to obtain site specific subsurface information to develop on-site design criteria. In addition, avail able information from other studies was used to construct a regional subsurface model for use in regional slope analyses. The locatjons of test holes drilled for Lot 1, Fi'ling 2 and nearby tots (except for Test Hole HM-4) are shown on Figure 1, Test Hole Location plan. The test holes were drllled with a continuous flight augers. In the later test continuous cone penetrometer soundings were are presented as Figure Z, and Figures A-2 dri'lled in conJunction with this study; Test Filing 2; and Test Holes HM-4 and HM-19 respectively of Highland Meadows Filing l. The test holes were logged in the il I I t t truck mounted drilling rig using holes (Test Holes 1 and 3-l), also made. Logs of the test holes through A-6. Test Ho'le 3-1 was Hole 3 in conjunction with Lot 3, in conjunction with Lots 4 and 19 field by a fie'ld engineer, -rnd -8- I I I I I fl H oo representative samples of the various strata encountered rere collected. Descriptions of the subsurface materials that were encountered, together with standard penetration test, cone penetrometer test, and ground water data are presented on the test ho'l e logs. The delineation of the strata encountered is approximate as the actual transition may be gradual . The cone penetroneter test was used in severar of the test hores to provide a large quantlty of in-situ shear strength data. previous studies in the Highland Meadows area have encountered difficulties in evaluating soil shear strength because of sample disturbance, the presence of rock fragments and boulders, and the slighily over-consoridated nature of the surficiar col'l uvial stratum. The cone penetrometer used in this investigation was a 1.9 inch diameter steel point. tt was driven by brows of a 140 pound weight falling 30 inches. The penetration resistance is the number of blows required to drive the cone 12 inches, and is reported on the right hand portion of the test hole log. Strat i graphy Four generalized subsurface strata were encountered in the test holes located in close proxlmity to the site. The uppermost stratum is man made fill used to construct Vermont Road, and in the case of Test HoIe HM_4, an access road. No fill was encountered in Test Hole HM-lg. The filr is generally re-worked colluvium, which is described bel,ow, The depth of the fill varied from ll to 13 feet in vermont Road to only 3 feet on Lot 4, Fiting 1. Beneath the fil.r , a coiluviar stratum ,,as next encountered. The colluvium consists of silty clay to clayey silt with.rock fragments and occasional boulders and sand lenses. The colluvium extends to depths of 17 to il H fl il T T I I t I I -9- I I I I I I il il il il il il I il 29 feet below ground surface, and is underrain by graciar tiil consisting of clayey sand and gravel with rock fragments, cobbles and boulders. Test Holes HM-4 and Hl'l-19 penetrated this stratum and encountered shale and sandstone bedrock at depths of o.5 to 44.5 feet. The bedrock extends past the maximun depth explored of 69.0 and 53.6 for Test Holes HM-4 and HM-19 respectively. Ground l{ater Ground water ''as generalry encountered berow a depth of 20 feet. ()ur experience in the H'ightand Meadows area suggests that numerous seeps and perched water conditions occur at shallower depths. on Lot 4 of Filing l, an artesian condition was encountered at a depth of 2G feet. In addition, several cases of slope failures 'in road cuts in Highland r,leadows have been observed due to oversteepening of the natural slopes and intercepting seeps or perched water. No evidence of this type of condition Has observed near the site' It was noted that the road embankment fill adjacent to the site was moist to wet.--Fbitions of this fill are highly permeable, and a perched water. condition could easily develop during wet weather periodsj Soil Properties The results of this and previous studies, and observations of various slope failures in the I'test Vajl area indicate that the shear strength of the colluvium is highly dependent on its moisture content. Uhen dessicated, the colluvium has a relatively high shear strength; however, the relative.l y weak molecular bonds are broken upon saturation and shear strength is significantly reduced. The shear strength parameters used in the slope stability analyses for this study are based on the cone penetration resistances-measured in the field. In order for these varues to remain appricabre, good surface-and t I I I I -10- I I I I t t fl f, il il il il I t I I subsurface drainage mus o tbe maintained to prevent softening of the colluvium. This a'l so applles to road embankments constructed of colluvial soils. The underlying glacial tlll stratum has very high shear strength and is below the permanent ground water. The ground water has no effect on its shear strength parameters; however, a significant rise in the permanent ground water could create greater pore water pressures, thus reducing the strength of thls stratum. ()ur experience indicates that this does not occur. Rather, perched vrater conditions are observed in the more granular zones in the overlying colluv'ium as the snow melts. As evidence of this, the artesian condition in the glacia'l till stratum on Lot 4, Filing t has remained relatively constant over a period of over a year and a half. The selected parameters for the slope stability analyses are presented on Figure 3, Critical Slope Circles. Two sets of parameters are presented for the col I uvium and fil I : (1) the average cohesion of the col I uvium which is designated AVERAGE in the shear strength parameters tab'le; and (2) the minirnum antic'ipated cohesion which is designated as MINIMUM. The shear strength of the glacial ti'tl is not tabulated because the critical slope failure circles intersected only the colluvium and fill. The glacial till was modeled using zero cohesion and an internal frictjon angle of 45 degrees. REGIONAL SLOPE STABILITY It is our experience that regional slope stability is the primary concern for safe construction in the I'lest Vail area. This based on several factors: (1) the catastrophic nature of a failure should one occur; (2) regiona.l slope problems are not easily mitigated, even at great expense; (3) problems would not necessarily be confined to a single lot; and (a) the relative safety of regional s] opes is difficult to predict. Our previous studies in this area I I -11 - � � : Fox . � � � . concluded that the combination of steepness of slope, subsurface stratigraphy, particularly the depth to bedrock and the shear strength of the colluvium are � the most significant factars in determining the relative safety of a slope. � The regional slape stabiiity analysis for this study was made for a section parallel to the eastern and western property iines and midway through Ithe 1ot. This section is essentially north-south trending, and represents the steepest portion of the site and surraunding area. The slope was investigated � using both average and minimum anticipated shear strength properties of the � coltuvium. The critical failure circles and camputed factors af safety are presented on ffgure 3, The factors of safety that were computed are 2.78 for the average shear strength case, and 1.68 for the minimum case. The faiiure circles for both � cases were identical in location and radius. Since the critica] failure � circles did not intersect the glacial ti11 stratum, the depth to bedrock was not a significant f actor for this site. Ir� analyzing the slope, a higher � ground water case was used to determine if pore water pressure in the glacial till was a factor. The result was that the critical circles still only � intersected the colluvium. � Qur experience has shown that natural slopes, particularly thos�e covered with calluvium should posses a higher computed factor of safety than � contralled fill embankments, for which the sail properties are knaw with a ' greater certainty. We recommend that natural slopes have factors of safety of � at least 2.0 for the average shear strength case and 1.5 for the minimum shear strength case in order to be considered safe. It should be noted that, even � if a slope meets these criteria, it is not safe in an absolute sense. Refer to the section on RISK in the Appendix. � _ � . According to the above recommended criteria, the site is reasonably safe • � - I2 - ' • �