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HomeMy WebLinkAboutSubsoil Study .pdf GLgStech Hcpworth.t iwl.tk Geotechnical,Inc. 5020 County Road 154 Glenwood Springs,Colorado 81601 Phone:970-945-7988 HEPWORTH-PAWLAK GEOTECHNICAL Fax:970-945-8454 email. hpgeo®hpgeoteeh.com SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 14,BLOCK 3,BIGHORN SUBDIVISION,5T11 ADDITION 5147 GORE CIRCLE VAIL, COLORADO JOB NO. 116 221A JUNE 13, 2016 PREPARED FOR: GREG CUMMINGS 4936 JUNIPER LANE VAIL, COLORADO 81657 (Jangreg89@gmail.cam) Parker 303-841-7119 • Colorado Springs 719-633-5562 • Silverthorne 970-468-1989 TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - PROPOSED CONSTRUCTION - I - SITE CONDITIONS - 2 - FIELD EXPLORATION - 2 - SUBSURFACE CONDITIONS -2 - DESIGN RECOMMENDATIONS - 3 - FOUNDATIONS - 3 - FOUNDATION AND RETAINING WALLS -4 - FLOOR SLABS - 5 - UNDERDRAIN SYSTEM -5 - SITE GRADING - 6 - SURFACE DRAINAGE -7 - LIMITATIONS - 7 - FIGURE 1 -LOCATION OF EXPLORATORY PIT FIGURE 2 -LOG OF EXPLORATORY PIT FIGURE 3 -GRADATION TEST RESULTS TABLE 1-SUMMARY OF LABORATORY TEST RESULTS Job No. 116 221A Gettec h PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located at Lot 14, Block 3,Bighorn Subdivision, 5'h Addition, 5147 Gore Circle, Vail, Colorado. The project site is shown on Figure 1. The purpose of the study was to develop recommendations for the foundation design. The study was conducted in accordance with our agreement for professional services to Greg Cummings dated May 31, 2016. We previously observed the excavation for a garage addition at the subject site for bearing conditions and presented our findings in a report date September 14, 2012, Job No. 112 299A. A field exploration program consisting of an exploratory pit was conducted to obtain information on the subsurface conditions. Samples of the subsoils obtained during the field exploration were tested in the laboratory to determine their classification and other engineering characteristics. The results of the field exploration and laboratory testing were analyzed to develop recommendations for foundation types, depths and allowable pressures for the proposed building foundation. This report summarizes the data obtained during this study and presents our conclusions, design recommendations and other geotechnical engineering considerations based on the proposed construction and the subsurface conditions encountered. PROPOSED CONSTRUCTION The existing residence on the lot will be razed for the new construction. The proposed residence will be a two story structure with a walkout basement. Ground floor will be slab-on-grade. Grading for the structure is assumed to be relatively minor with cut depths between about 3 to 8 feet. We assume relatively light foundation loadings, typical of the proposed type of construction. If building loadings, location or grading plans change significantly from those described above, we should be notified to re-evaluate the recommendations contained in this report. Job NIo. 116 22 I A Ggcrtedl l - 2 - SITE CONDITIONS The lot was occupied by the existing residence at the time or our site visit. The lot is situated in the Gore Creek Valley bottom and has a gentle slope down to the south with about 8 feet of elevation difference across the building location. Scattered cobbles were observed on the ground surface and vegetation was dominated by grass and weeds. FIELD EXPLORATION The field exploration for the project was conducted on June 6, 2016. One exploratory pit was observed at the location shown on Figure 1 for bearing conditions. The pit was logged by a representative of Hepworth-Pawlak Geotechnical, Inc. A sample of the subsoils was taken by disturbed sampling methods at the location shown on the Log of Exploratory Pit, Figure 2. The sample was returned to our laboratory for review by the project engineer and testing. SUBSURFACE CONDITIONS A graphic Iog of the subsurface conditions observed at the site is shown on Figure 2. The subsoils consist of about 12 foot of topsoil overlying relatively dense silty sand and gravel with cobbles. Laboratory testing performed on the sample obtained from the pit consisted of natural moisture content and gradation analyses. Results of gradation analyses performed on the sample of natural granular soils are shown on Figure 3. The laboratory testing is summarized in Table 1. Free water was observed in the pit at a depth of 5 feet. The subsoils were slightly moist in the top 2 feet becoming very moist with depth. Job No, 116 221A Gt tech - 3 - DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory pit and the nature of the proposed construction, we recommend the building be founded with spread footings bearing on the natural granular soils. The design and construction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on the undisturbed natural granular soils should be designed for an allowable bearing pressure of 2,500 psf. Based on experience, we expect settlement of footings designed and constructed as discussed in this section will be about 1 inch or less. 2) The footings should have a minimum width of 16 inches for continuous walls and 2 feet for isolated pads. 3) Exterior footings and footings beneath unheated areas should be provided with adequate soil cover above their bearing elevation for frost protection. Placement of foundations at least 48 inches below exterior grade is typically used in this area. 4) Continuous foundation walls should be reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 10 feet. Foundation walls acting as retaining structures should also be designed to resist lateral earth pressures as discussed in the "Foundation and Retaining Walls" section of this report. 5) All existing fill,debris, topsoil and any loose or disturbed soils should be removed and the footing bearing level extended down to the relatively dense natural granular soils. The exposed soils in footing area should then be compacted. If water seepage is encountered, the footing areas should be dewatered before concrete placement. Job No. 116 22 1 A t ,� -4- 6) A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. FOUNDATION AND RETAINING WALLS Foundation walls and retaining structures which are laterally supported and can be expected to undergo only a slight amount of deflection should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 45 pcf for backfill consisting of the on-site granular soils. Cantilevered retaining structures which are separate from the building and can be expected to deflect sufficiently to mobilize the full active earth pressure condition should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 40 pcf for backfill consisting of the on-site granular soils. Backfill should not contain organics, debris or rock larger than about 6 inches. All foundation and retaining structures should be designed for appropriate hydrostatic and surcharge pressures such as adjacent footings, traffic, construction materials and equipment. The pressures recommended above assume drained conditions behind the walls and a horizontal backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain should be provided to prevent hydrostatic pressure buildup behind walls. Backfill should be placed in uniform lifts and compacted to at least 90%of the maximum standard Proctor density at a moisture content near optimum. Backfill placed in pavement and walkway areas should be compacted to at least 95% of the maximum standard Proctor density. Care should be taken not to overcompact the backfill or use large equipment near the wall, since this could cause excessive lateral pressure on the wall. Some settlement of deep foundation wall backfill should be expected, even if the material is placed correctly, and could result in distress to facilities constructed on the backfill. Job No, 116 22I A Ggrrtech - 5 - The lateral resistance of foundation or retaining wall footings will be a combination of the sliding resistance of the footing on the foundation materials and passive earth pressure against the side of the footing. Resistance to sliding at the bottoms of the footings can be calculated based on a coefficient of friction of 0.50. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 400 pcf. The coefficient of friction and passive pressure values recommended above assume ultimate soil strength. Suitable factors of safety should be included in the design to Iimit the strain which will occur at the ultimate strength, particularly in the case of passive resistance. Fill placed against the sides of the footings to resist lateral loads should be a granular material compacted to at least 95% of the maximum standard Proctor density at a moisture content near optimum. FLOOR SLABS The natural on-site soils, exclusive of topsoil, are suitable to support Iightly loaded slab- on-grade construction. To reduce the effects of some differential movement, floor slabs should be separated from all bearing walls and columns with expansion joints which allow unrestrained vertical movement. Floor slab control joints should be used to reduce damage due to shrinkage cracking. The requirements for joint spacing and slab reinforcement should be established by the designer based on experience and the intended slab use. A minimum 4 inch layer of free-draining gravel should be placed beneath interior slabs to facilitate drainage. This material should consist of minus 2 inch aggregate with at least 50% retained on the No. 4 sieve and less than 2% passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 95% of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of the on-site granular soils devoid of vegetation, topsoil and oversized rock. UNDERDRAIN SYSTEM Free water was encountered at a depth of 5 feet below ground surface in the exploratory pit. This is not unexpected and groundwater level is generally known to be shallow in Job NN- 116 221 A Gcligtech -6- this area. Additionally, it has been our experience in the area that water level can rise and that perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can create a perched condition. We recommend below-grade construction, such as retaining walls, crawlspace and basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain system. The drains should consist of drainpipe placed in the bottom of the wall backfill surrounded above the invert level with free-draining granular material. The drain should be placed at each level of excavation and at least 1 foot below lowest adjacent finish grade and sloped at a minimum 1% to a suitable gravity outlet. Free-draining granular material used in the underdrain system should contain less than 2% passing the No. 200 sieve, less than 50% passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at least 1' feet deep. The under slab gravel should be connected to the perimeter underdrain with interior lateral subdrains. SITE GRADING The risk of construction-induced slope instability at the site appears low. We assume the cut depths for the basement level will be kept relatively shallow and not exceed about 8 feet. Fills should be limited to about 8 to 10 feet deep. Embankment fills should be compacted to at least 95% of the maximum standard Proctor density near optimum moisture content. Prior to fill placement, the subgrade should be carefully prepared by removing all vegetation, topsoil and existing debris and compacting to at least 95% of the maximum standard Proctor density. The fill should be benched into slopes that exceed 20% grade. Permanent unretained cut and fill slopes should be graded at 2 horizontal to I vertical or flatter and protected against erosion by revegetation or other means. The risk of slope instability will be increased if seepage is encountered in cuts and flatter slopes may be necessary. If seepage is encountered in permanent cuts, an investigation should be )ob No. 116 221 A Ggrytech - 7 - conducted to determine if the seepage will adversely affect the cut stability. This office should review site grading plans for the project prior to construction. SURFACE DRAINAGE Positive surface drainage is an important aspect of the project to help prevent wetting of lower building areas. The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: 1) Inundation of the foundation excavations and undersiab areas should be avoided during construction. 2) Exterior backfill should be adjusted to near optimum moisture and compacted to at least 95% of the maximum standard Proctor density in pavement and slab areas and to at least 90% of the maximum standard Proctor density in landscape areas. 3) The ground surface surrounding the exterior of the building should be sloped to drain away from the foundation in all directions. We recommend a minimum slope of 12 inches in the first 10 feet in unpaved areas and a minimum slope of 3 inches in the first 10 feet in paved areas. Free-draining wall backfill should be capped with about 2 feet of the on- site finer graded soils to reduce surface water infiltration. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 5) Landscaping which requires regular heavy irrigation should be located at least 5 feet from foundation walls. LIMITATIONS This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this area at this time. We make no warranty either express or implied. The conclusions and recommendations submitted in this report are based upon the data obtained from the exploratory pit excavated at the location indicated on Figure 1, the proposed type of construction and our experience in the area. Our services do not include determining the presence, prevention or possibility of mold or Job No. 116 221A _..... _._ Ggi;tt - $ - other biological contaminants (MOBC) developing in the future. If the client is concerned about MOBC, then a professional in this special field of practice should be consulted. Our findings include interpolation and extrapolation of the subsurface conditions identified at the exploratory pit and variations in the subsurface conditions may not become evident until excavation is performed. If conditions encountered during construction appear different from those described in this report, we should be notified so that re-evaluation of the recommendations may be made. This report has been prepared for the exclusive use by our client for design purposes. We are not responsible for technical interpretations by others of our information. As the project evolves, we should provide continued consultation and field services during construction to review and monitor the implementation of our recommendations, and to verify that the recommendations have been appropriately interpreted. Significant design changes may require additional analysis or modifications to the recommendations presented herein. We recommend on-site observation of excavations and foundation bearing strata and testing of structural fill by a representative of the geotechnical engineer. Respectfully Submitted, HEPWORTH- PAWLAK GEOTECHNICAL, INC. Tom C Brunner--Staff Engineer Reviewed by: Steven L. Pawlak, P. E. flit.t 16222 t TCB/ksw • kx5igt#rix% se lit ...... o$I_ . F COG 7nb Nn. 116 221A -G tech APPROXIMATE SCALE 1 30 8602 8504 \ — — r , _.11 _. 8598 \ . . , - ..._ , _ _ 1 , Z — — — --. PIT1 \\ I w 0 8596 I ' ~ ` PROPOSED \ LOT 13 w — \ RESIDENCE —v cc \ F.F.= 8604.0' 0 \ 5147 GORE CIRCLE Ih I \\ I // / 1 � \ s. �'` �\ 1 I L \\ 6°0 �ti E / \ 1 / 8 �\ \\, \ \\ � , ,/ —8696 S`96 1 � _ — _ _ _ II - a594 GORE CIRCLE 116 221A ga PC "'1 LOCATION OF EXPLORATORY PIT Figure 1 HEPWGRTH•PAWLAK GEOTECHNICAL PIT 1 ELEV. 8598. 0 0 — 01.0.• — 0u- cu — : _, WC.5,1 -- 5 4 1 +449 u_ t = ti -J 5-200 a5 10 r o. — — a a)C _ o 10 10 LEGEND: '-`1 TOPSOIL; sandy, silty, dark brown. F... . SAND AND GRAVEL(SM-GM); silty, with cobbles, dense, siight;y most top 2 fest, free water at 5 feet, brown i i Disturbed bulk sample. _J — Free water level in pit at time of observation NOTES: 1. The exploratory pit was observed on June 6, 2016 and had been excavated with a backhoe. 2. The exploratory pit was located by the client. 3. The exploratory pit elevation was obtained by interpolation between contours on the site plan provided. 4. The exploratory pit location and elevation should be considered accurate only to the degree implied by the method used. 5. The lines between materials shown on the exploratory pit log represent the approximate boundaries between material types and transitions may be gradual. 6. Water level reading shown on the log was made at the time and under the conditions indicated Fuctuation in water level may occur with time. 7. Laboratory Testing Results: WC = Water Content(%) +4 = Percent retained on the No.4 sieve -200 = Percent passing No.200 sieve 116 221A �'1 c. ljec '� LOG OF EXPLORATORY PIT Figure 2 HEPWORTH•PAWLAK GEOTECHNICAL HYDROMETER ANALYSIS S EVE ANALYSIS I q Hq q TIME READINGS U S STANDARD SERIES I CLEAR SQUARE OPENINGS 0 45 MIN 15 MIN 60MIN19MIN.4 MIN 1 MIN #200 #100 #50 #30 #16 #8 #4 318' 314' 1 112' 3 5'6' 8- 100 --- ....... —1- --..... ---moi.—r r— ......—.......-- —1 M.MIM — a s --- — rr- - -- — — —a 1 S ......--- ------.rI ......--� ---15 ......--- ------1-- --- --.�—--1! 90 10 --- 1--r— ......—.......—— ---.'—1- - — ---rte—r- -- �a- -� �all MEM IIIM e--1— .. Il•.--1` a — M. --1.a—�1MI 60 20 --- —_—_,— — — ........ ----_1— ......—.......— �..I--51_ — — ----- 1— ......—.......—! MI--S—1! ......--— --MMa—.-1! ......--- --.�=—__a_ 70 30a........ ._—a1a --� ..!II!! ......—.......-- --f!—'1!II --!-1 !1.....I ......—.......—— —MUM!—Mi!11!II ......--- —_I--_1_ 0 111 LI ao = __a Z Z MIMI!= !lion!'!I __p V----!1! 1/ h --. _-- _aa --- —_ _--_ _I----iMe! N martii — — AIDS—S—_1a a_ LL !II r!a!a_...!!1! --- -..-----!!//M1! 50 I- 1– 50 ��— __----___a Z s-- •------! Cr 1! Li Q- 60 — -- Ai------S_r !...-- .— !Mt— !MI.......—.— .-------!Mt m !.IMI!! —!.!—!MI a --! I —.r1i MMi 70 — O--,Aa-------... IMatt!Il 30 —, . �� psi --� m... -1- - -1! —�1 -!—.*------- -MN— 20 ao • C-- 1....--.w---sa —err----- -------:a —1— 11-----_a —1a ^NME=---__ — IPM--1S 10 _----- !1— !w— !I.-- !1M --- ----!MI MI! 0 100--- ---a•.r.--r! 001 002 005 009 .019 .037 .074 .150 .300 600 1 18 2 36 4 75 9.5 19 0 37.5 76.2 152 203 12.5 127 DIAMETER OF PARTICLES.N M'LL METERS SANO CLAY:0'y i FINE I k OE RAN I COARSE MEGRAM COARSE COBBLES GRAVEL 49 % SAND 41 % SILT AND CLAY 10 % LIQUID LIMIT % PLASTICITY INDEX % SAMPLE OF: Siity Sand and Gravel FROM:Pit 1 at 4 to 5 Feet H 116 221A ec]''1 GRADATION TEST RESULTS Figure 3 14EPWORTH-PAWLAK GEOTECHNICAL 4-- . Q T 11N W co a et r 0 x C7 O JO i z N a rs _a wG - m rs cn rn CI W u,00 Ci' paw W a a Z J ON U J V) U Q W 1- Cl, U IX 5gZe Z I— CD 0 U W w W Y w aI- w O a =,71 • ,- a W IX x-00 Q J O ZZOW aa UCC NNu, O n_ W _ H0 )- cZ CC —,ra ` O Q O � 0 a a J = Co ¢ a• ON 0 J m a Nc. 0 r0z a a c Z W < z aDW e z S OW S. 7r a 0 U O J W J 0. as a _ Cl)