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Home My WebLink AboutB12-0278 Soils Report.pdfHEPWORTN-PAWLAK G�OTECHNlCAL 'Hep��rth-�'a�.t�l�a� Georecl�nical, Inc. �� OZi) C«imR' Ruael ] 5=} C.�iei.��vnotl Sprin;,», Colora�lo 8JC01 1'hone: 9"!��-9=��-79�58 Fax:970-945-8454 �fnaiL hpgeoC�ltpreotcch.�am SUSSOIL STUDY FOR FOUNDATION DESIGN PROP�SED RESIDENCE LOT 1Q, SLOCK 2, BIGHORN SUBDIVISION FIFTH ADDYTION 5056 MAIN GORE DRl VE NORTH VAIL, COLORADO JOB NO. 111326A NOVEMBER 30, 2011 PREPARED FOR: MR. ERIC SCHULTZ � 5056 MAIN GORE DRIVE NORTH VAIL, CULORADO $]657 Pa��lce�• �0_�-541-1119 � Colurado S�,rings 719-C3�-»C? � Sil��ex'tl�c��-n< <�i��-��6�.1�?S9 TABLE OF CONTENTS �URPO�E AND SCOPE OF STUDY ........................................................................ - 1- PROPOSED C�NSTRUCTION ........................ - - ......................................................... SITECONDITIONS ......................................•-�--.........:......-----•.................................. - 2 - FIELD EXPLQRATION - - ............................................................................................ 2 SUBSURFACE CONDITIONS.----•-� .......................................................................... - 2 - FOUNDATI4N BEARING CONDITION� ............................................................... - 3 - DESIGN RECOMMENDATrONS ............................................................................. - 3 - FOUNDATIONS.......................-•--••-•----�•-� ............................................................. - 3 - FOUNDATION AND RETAINING WALLS ......................................................... - 4- FLOORSLABS .......................................................................................�--------...... - 6 - UNDERDRAIN SYSTEM .......................... ............. - 6 - SURFACE DRA�iAGE ......................................................................................... - `7 - LIMITATIONS ................................................................... - ....................................... 7 REFERENCES ................................................................................... - 9 - ........................ FIGURE 1- LOCATION OF EXPLORATORY BORINGS FIGURE 2- LOGS OF EXPLOR.ATORY BORINGS FIGURE 3- LEGEND AND NOTES FIGURE 4- GRADAT�QN TE,ST RESULTS TABLE 1- SUMMA.RY 4F LABORATORY TEST RESULTS PURPOSE AND SCOPE 4F STUDY This report pre�ents the results of a subsoil study for a proposed resic�ence to be located on Lot 10, Btock 2, Bighorn Subdivisian Fifth Addition, 5056 Main Gore Drive North, Vail, Colorada. The pro�ect site is shown on Figuze 1. The purpose of the study was to develap recommendations for the foundation design. The study was conducted in accardance with our agreement for geotechnical engineering services to Eric �chultz dated October 1Z, 2011. A field exploration program consistizxg of exploratory borings was conducted to ob�ain inforrnation on the subsurface canditians. Samples of the subsoils obiained during the field exploration were tested in the laboratory to determine their classification, and other engineering characteristics. The results of t�e field exploration and labora#ory testing were analyzed to deveiop recornmendatiar� �or foundation types, depths and allowable pressures for the propased b�ilding foundation. This repart sumrnarizes �he data obtained during this study and presents our conclusions, design recommendations and ather geotechnical engineering consideraiions based on fhe proposed canstruction and the subsurface canditions encauntered. PROPOSED CONSTRUCT�ON The proposed residence wili b� a one or twa story slab-on-grade structure with a walkout basement. We assuFne relatively light foundation loadings, typical of the proposed type of construction. The existing residence on the siie will be razed prior to construction of the new reszdence. The �roposed residence will be located in the same general area as the �xisting residence. The building and driveway lacations are shown on Figure 1. Ifbuilding loadings, location or grading plans change significantly frozn those described above, we should be notified to re-evaluate the recammendations contained in this report. Job �10. l i 1 326A ��#�h -2- SITE CONDITIONS The site is currently accupied by a single �arn.ily residence with a walkout basement. Vegetatian car�sists o�lawn areas and various evergreen and aspen trees scattered around the propert�. At the time of ouz- field explaration about 2 to 6 inches of snow covered the ground. The ground surface was rnoderately sloped down to �he southwest with less than 5 feet of elevation difference in the building site. A review of the Town of Vail Natural Hazards Maps {2000A, 2004B and 2000C) irzdicates that the site does not fall in a mapped hazard zone for avalanche, rockfall ar debris flow. Rounded boulders �crere exposed on �he gz-ound surface of the Iots. FIELD EXPLORATION The field exploration for the project was conducied on November 2, 2011. Two exploratory borings were drilled at the locations shown on Figure 1 to e�aluate the subsurface canditions. The borings were advanced vvith 4 inch diameter continuous flight augers powered by a CME-45B tnzck-�nountecl drill rig. Th.e bozix�gs were logged by a representative of Hepworth-Paw�ak Geotechnical, Inc. Sa�nples of the subsoils vvere taken with a 13/8 inch I.D. spoon sampler. The sampler was driven into t�e subsoils at various depths with blaws frorri a 140 pound hat�mer falling 30 inches. This test is similar to �he standard perzetration test described by ASTM Met�od D-1586. The penetration resistance values are an indication of �he relative density or consistency of the subsoils. Depihs at which the samples were taken and the penetration resis#ance values axe sk�own on the Logs of Explora#ory Borings, Figure 2. The samp�es �rere returned to our labaratory for review by the projeci engineer and iesting. SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils consist of about 6 inches of topsoil averlying silty sandy gravel and cobbles Job No. t 11 32GA HG�Ch -3- with boulders and silty gravelly sand layers. Drilling in the dense granular soils with auger equipment was difficult due ta the cobbles and boulders and c�rilling refusai was encoun.tered in the initial two atternpts at advancing Boring 2. Laboraiory testing performed on sazx�ples obtained from the borings included natural moisture content and gradation analyses. Results of gradation analyses performed an small diameter drive samples (minus 11/z inch fraciion} of the coarse granuiar subsoils are shown on Figure 4. The labora�ory testing is summarized in Table 1. Free water was encountered in the borings at tihe time of drilling at depths of approximately 9 to 10 feet and at 11 feet �in. Boring 1 when checked 8 days later. FOUNDATION BEARTNG COND�TTONS The natural silty sand and gravel subsoils encountered at the site are adequate fox support of spread footing fauz�dations with relatively Iow settlement potential. All fill material and debris from previous site development should be removed from beneath proposed building areas. DE,SIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratary borings and the nature of the proposed construction, we recommend the building be founded with spread footings bearing on the natural granu�ar soils. The design and construction criteria presented below shauId be observed for a spread faoting foundation systern. 1) Footings placed on the undisturbed natural gran.ular soils should be designed for an allowab�e bearing pressure of 2000 psf. Based on Job No. I 11 326A ��i,.� � experience, we expect settlement of foofiings designed and constructed as d�scussed in this section will be about 1 inch or less. 2} The footings shauld have a minimum width of 16 inches for continuous walls and 2 feet foz- isolated pads. 3) Exteriar %otings and footings beneath unheated areas should be provided with adequate soil caver above their bearing elevatian for frost proiection. Placement of founciations at least 48 rnches belo�v exterior grade is typically used in this area. 4) Continuous foundation walls should be reinforced top and bottorrx to span local anomalies such as by assuming an unsupported length o� at Ieast 10 feet. Foundation walls acting as re#aining structures should also be designed to resist latera� earth pressures as discussed in the "Foundatian and Retaining Wa11s" section of this report. 5} All existing fill, topsoil, debris and any loose or disturbed soils should be removed and the footing bearing level extended down to the xelatively dense nat�ral granular soils. The exposed soils in footizig area should then be maistened and co�npacted. Voids at bearing level from boulder removal should be backfilled with cancrete or structural gzanular soil co�npacted to at least 9$% of standard Proctor densrty. If water seepage is encountered, the foo�ing areas should be dewatere�d bEfore concrete placement. 6) A representative of the geotechnical engineer �hould observe alI footing excavations prior to concrete placement to e�aluate bearing conditzons. FOUNDATION AND RETAiNING WALLS Foundation wa11s and retaining structures �crhich are laterally supported and can be expected to undergo only a slight amount of deflection should be designed for a lateral earth pressure compuied on the basis of an equivalent fluid unit weight oiat least 45 pcf �oz backfill cansisting ofthe on-site or import granulaz- soxls. Cantilevered retaining struciures which are separate from the structure and can be expected to deflect suf�ciently �o rnobiiize the fiill active earth pressnre conditzon should be designec� for a Job No. 111 326A GEU�tGCh -5- lateral Earth pressure computed on the basis of an eq�ivalent fluid unit weight of at least 40 pcf far backfili consisting of the on-site granuiar soils. A11 foundation and retaining structures should be designed for appropriate hydrostatic and surcharge pressures such as adjacent footings, traffic, construction materials and eq�ipment. The pressures recammended above assurne drained conditions behind the wa11s and a horizontal backfiil surface. The buildup of water behind a wall or an upward sloping backfi�l surface will increase the lateral pressure imposed on a foundation wali or retaining structure. Ara underdrai� should be provided to prevent hycl�-ostatic pressure buildup behiund walls. Wall backfill should be placed in uniform lifts and compacted �o at least 90% of the maximurn standaxd Proctor density at a moisture cantent near optimum. Backfill in pavexzient and wallcway areas should be compacted to at least 95% of th.e maximum staridard Proctor density. Care should be taken not to aver-compact the backfill or use large equipment near the wall, since this could cause excessive Iateral pressuze an the wa11. Some settlement of deep foundation wall backfill shauld be expected, �ven if the materiat is plac�d correctly, and could result in disfiress to facilities constructed on the bac�fzli. We recornmend �creened on-site or imported free-draining granular soils for backfilling foundation walls and retaining structures because their use results in lower lateral earth pressu�res az�d the backfill can be incorpora�ed izzto the underdrain system. Subsurface drainage recornmendations are discussed in more detail in the "Underdrain System" section ofthis report. Imported granular wa11 back�ll should contain less than 15% �assing the No. 200 sieve and have a maximum size of 6 inches. The lateral resistance of foundation or retaining wall footings �vill be a combinatian of ihe sliding resistance of the footing on the foundation maferials and passive earth pressure againis� the side of the foating. Resistance to slidir�g at the bottoms of the footings placed on the natural granular soils can be ca�culated based on a coeificient af friction af 0.45. Passive pressure of coza�pacted backfill agai.nst the sides ofthe footir�gs can be calculated Job No. 111 3Z6A �� using an equivalent fluid unit weight of 400 pc£ The coefficient of fricfion and passive pressure values recomrnended abave assume uitimate soil strength. Suitable factors at� safety should be included in the design to limit the strain vvhich will occur at the ultimate strength, particu�arly in ihe case of passiv� resistance. Fill placed against ihe sides of the footings to resist Iateral Ioads should be a granular material connpacted to at least 95% of the maximum standard Proctor density at a moisture can�ent near optimum. FLOOR SLABS The natural on-szte soil�, exclusive oftopsoil, are suita�le to support lightly loaded slab- on-grade construction. To xed�ce the effects of some differential movement, floar slabs should be separated from all bearing waIls ar�d columns with exparision }oints nvhich a11ow �nrestrained vertical movement. Fioor slab control joints should be used to reduce damage due to shrinkage cracking. The requirements �or joint spacing and slab reizlforcement should be established by the designer based on experience and the intended slab use. A mini�um 4 inch layer of fr�e-draining gra�el should be placed beneath basement level slabs to facilitate drainage. This material shou�d cansist of minus 2 inch aggregate with at least 50% retained an the No. 4�ieve and less than 2% passing the No. 200 sieve. All fill materials for support of floor slabs should �e compacted to at least 95% of rnaxirnuzx� siandard Proctor density at a maisture content near o�timum. Required fill can consist of the on-site granuIar soils devoid af vegeta�ian, tflpsoil and oversized roc�. UNDERDRAIN SYSTEM Free water was encountiered d�'ing our exploration and it has been our experience in mountainous area� that the water level caam seasonally rise and local perched groundwater can develop during times of heavy precipitation or seasonal runoff. Froz�n ground during spring runo�Fcan create a perched conditiion. We reco�nenc� below-grade construction, �uch as retainirig walls, crawl�pace and basement areas, be pz-atected from wetiin� and hydrostatic paressure buiidup by an und�rdrarr� system. 7oh No. 111 326A ��h -�- The drains should consist of drainpipe placed in the bo�tom of the wa11 backfill surrounded abo�re the irivert level with free-drair�ing grar�ular material. The drain should b� placed at each level ofexcavation and at least 1 foot below �awest adjacent finish grade and sloped at a mininnum l% to a suitable gravity outlet. The underslab gravel shauld have a positive cox�ection with th.e outside perimeter underdrain. Free-draining gran�alar material used in the underdrarn system shou�d contain less than 2% passing the No. 200 sieve, less than Sd% passing the Na. 4 sieve and have a ma�imum size af 2 inches. The drain gravel backfill should be at least 11/z feet deep. SURFACE DRAINAGE The followirig drainage precautions should be observed during construction and rnair�tained at all ti�es aftex the residence has been completed: 1) Inundation of the foundation ea�cavations and underslab areas should be avoided during construction. 2) E��exior backfill should be ad�usted io near optimum moistuz�e and compacted to at least 95% ofthe maxiinum standard Proctor d�nsity in pavement and slab areas and to at least 90% ofthe maxirnum standard Proctar density in landscape areas. 3) The ground surface surrounding the �xterior of the building shauld be sloped to dzain away fro�xa. the �oun.dation in all directions. We recom�nend a rninimum slope of 12 iu�ches in the f�rst 10 feet in unpaved areas and a minimum slope of 3 inches in the �'irst 10 feet in paved areas. Free-draining wall backfill should be capped with about 2 feet ofthe on- site finer graded soils to reduce surface watez- i�filtration. 4) Roof dawnspouts and drains should discharge we�l beyond the lirnits of al� backfill. LIM�TATIONS This study has been conducted in accordance with generally accepted geatechnical engineering principles and practices in this area at this time. We make no warranty either expres� or implied. The conclusions and recammendations submitted in this report are Job 3�Io. 111 326A �[�t�Ch : based upon th� data obtained fram the exploratory borings drilled at the locations indicated on Figure 1, the proposed type af construction and our experience in the area. Our services do not includ� determining the presence, prevention or possibility of mold ar other biologicai contaminants (MOBC) developing in the future. If the client is concerned ahout MOBC, then a�rofessional in this special �eld ofpractice should be consulted. Our fmdings include interpolation and extrapolation af the subsurface conditions identified at the explaratory borings and variations in the subsuxface conditions may not became evident until excavation is performed. If conditions encountered during construction appear different from those described in this report, we should be notx�ed so that re-evaluation of the recommendations may be made. This report has been prepared for the exclusive use by aur client for design purposes. We are not responsibl� far technical interpretations by others of our information. As the projec� evolves, we should provide continued consultation and field services during construction to review and monitar the implementation of our recommendations, and to verify that tihe recomrnendations have been appropriately interpreted. Significant design changes may require additional analysis or modifications to the recommenda�tions presented herein. W� recommend on-site observation of excavations and foundation bearing strata and testing of structural fi11 by a represeniative of the geotechnical engineer. Respectfully Subnr�itted, HE�WO TH - �AWLAK GEOTECHNICAL,INC. Janraes . Paz-ker, PG, EIT Reviewed by: � �t�ven L. Pa�crlak, P�t; 15 2 2 2 : JAP/ksw p,�� f' � �'l:•.sf�NR� � Job l*Io. 111 326A ��h � REFERENCES Town of Vail, 2000A. Official Rockfall HazaYd Map, Town of Vail. Prepared by the Town of Vail, Vail, Calorado (Adopted by the Town Council on October 17, Zaoo}. Town of Vail, 20QOB. Official Debris Flow Hazard Map, Tawn of Vail. Prepared by the Town of Vail, Vail, Colarado (Adopted by the Tawn Council on 4ctober �7, 2040). Town of Vail, 2000C. OfficiaiAvalanche Hazard Map, Town of Pail. Prepared by the Tawn of Vail, Vail, Calorado (Adopted by the Tawn Council on 4ctober 17, 2004). Job No. 11 I 326A ��h LEGEND: N � :� Tapsoil; organic siity sand, moist, dark brown. Gravel & Cobbles (GM-GP}; Slighlty silty to silty, sandy with gravelly sand layers, probable baulders, medium to dense ta dense, moist to w�t with depth, brown, subangular ta raunded rock. brive sample; standard penetration test (SP'�, 1 318 inch I.D. split spoon sample, ASTM Q-�586. 38/12 �ri�e sample blow caunt; indicates that 38 blows of a 140 pound hammer falling 3d inches were required to dri�e the SPT sampler 12 inches. 0,2 � �� NOTES: Free water level in baring and number of days follawing dril�ing measurement was taken. Indicates slotted PVC pipe installed in boring to c�epih shown, Prac#ical drilling refusaE. Where shawn above bottom of log, indicates #hat multiple attempts were made to ad�ance t�e boring. 1. Explaratory borings wer� drilled on Na�ember 2, 2011 with 4-ir�ch diameter con#inuous flight power auger, 2. Locafions ofi exploratory borings were measured approximately by pacing firorr� fea#ures shown n� the si�e plan provided. 3. Elevatior�s af exploratory bor�ngs were obtained by instrument Isvel and refer to the Bench Mark shown on Figure 1 4. The explaratory E�oring locations and elevations should �e considered accurate only to the degree impli�d by #he method used. 5. The lines be#ween materials shown on the exploratory boring logs represent the a�proximate baundaries betw�en material types and transitions may be gradual. 6. Water le�el readir�gs shown an the logs were made at the time and under the conditions indicated. FluctuatEans in water levei may occur with time. 7. 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