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HomeMy WebLinkAboutSubsoil Study for Foundation Design 11.26.2004StxE-o52t-6832 n t i A -W * aì:-l-: * trrì W L,å. ( G lü? Ë. {i i"i f'i å ": ¡i L SI]BSOIL STUDY T'OR FOUNDATION DESIGN PROPOSED RESIDENCE LOT F'7, ASPEN GLEN GARFTELD COUNTY, COLORADO JOB NO. tL4 437A NOVEMBER.26,20t4 PREPARED FOR: }VOODBRIDGE MORTGAGE INTVESTMENT F',UND z,LLC ATTN: RICK SALVATO 22 CENTER STREET, FRONT SUITE IREEIIOLD, NEIV JERSEY A7728 ûi i:¡,!: (¿:":¡ !r!é"gq!) )1 TABLE OF CONTENTS PLJRPOSE ÂND SCOPE OF STUDY.................. PROPOSED CONSTRUCTION.......... SITE CONDITIONS SUBSIDENCE POTENTIAL .... FIELD EXPLORATION. SUB SURFACE CONDITIONS .. DESIGN RECOMMENDATIONS..........,...... FOLINDATIONS......... FOI-INDATION AND RETAININC WALLS. FLOOR SLABS TINDERDRAIN SYSTEM... SITE GRADING ................. SURFACE DRAINAGE ...... LIMITATIONS REFERENCES FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGIIRE 3 . LEGEND AND NOTES FIGURE 4 - GRADATION TEST RESI'LTS .-l- I 1 -) _ -?_ -?_ _o PURPOSE AND SCOPE OF STT"IDY This report presents the results ofa subsoil study for a proposed residence to be located at Lot F 7, Aspen Glen Subdivision, Garfield Countg 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 proposal for geotechnical engineering services to Woodbridge Mortgage Investment Fund 2,LLC dated october 2,2014. chen-Northern, Inc. (1991 and lgg3)previously conducted preliminary geotechnical engineering studies for the development and preliminary plat design. A fie1d exploration program consisting of exploratory borings was conducted to obtain information on the subsurface conditions. Samples of the subsoils obtained during the field exploration rvere 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 fires, depths and allowable pressures for the proposed building foundation. This report surnmarizes the data obtained dwing this study and presents our conclusions, design recommendations and other geotechnical engineering considerations based on the proposed construction and the subsurface conditions encor¡ntered, PROPOSED CONSTRUCTION Building plans for the proposed residence are conceptual. Typical residences in the area are one and two story wood frame above a basement or crawlspace with an attached garage. Ground floors are typically slab-on-grade. Grading for the proposed structure is assumed to be relatively minor with cut depths befween about 3 to 10 feet. We assume relatively light foundation loadings, typical of the assumed type of eonstruction. 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. JobNo. tl4437A eåBtec¡ ô SITE CONDITIONS The vacant property is locatcd at the cul-de-sac of River Park Lane. Vegetation consists of sparse grass and weeds. Topography at the site consists of relatively flat upper and lower terraces separated with by a steep slope. The terraces have a slight slope down to the northwest' Elevation difference bsfween the terraces is about 15 feet. A wetland area and drainage are located beyond the site to the northwest. The uppor terrace appears to have been graded with minor cuts during subdivision development and gravel and cobbles are exposed on the ground swface. A golf coursc fairway is located along the northern property line. SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanian age Eugle Valley Evaporite underlies the Aspen Glep development. These rocks are a sequence of gypsiferous shale, fine-grained sandstonelsiltstone and limestone with some massive beds of gypsum. There is a possibility that massive gypsum deposits associated with the Eagle Valley Evaporite underlie portions of the lot. Dissolution of the gypsum uncler certain conclitions can cause sinkholes to develop and canproduce areas oflocalized subsidence. Duringprevious studies in the area, sevsral broad subsidence areas and smaller size sinktrole areas were observed scattered throughout the Aspen Glen development, predominantly on the east side of the Roaring Fork Rivor (Chen-Northcrn,Inc., 1993). These siukhules äppeðr similar to others associated with the Eagle Valley Evaporite in areas of the Roaring Fork River valley. Lot F 7 is located just outside of one of the broad subsidence areas mapped by Chen- Northern. Signs of active ground movements have not been observed in the zubsidence area. The neârest sinkhole wâs mapped about 900 feet to the northeast of Lot F 7. Sinkholes were not observed in the immediate area of the subject lot. No evidence of cavities was encountered in the subsurface materials; however, the exploratory borings .lob No. 114 437A cåBtecrt -3 - \¡rere relatively shallow, for foundation design only. Based on our present knowledge of the subsu¡face conditions at the site, it cannot be said for certain that sir*holes will not develop. The risk of fi.rture ground subsidence an Lot F 7 throughout the service life of the proposed residence, in our opinion, is low but the site should not be considered totaily risk free. If furfher investigation of possibie cavities in the be&ock helow the site is desired, we should tre contacted. FIELD EXPLORATION The field exploration for the project was conducted on Octob er 7,2014. Two exploratory borings were drilled at the locations shom on Figure 1 to evaluate the subsur-face conditions. Tlie borings u/ere advanced witb 4 inch diameter continuous flight augeîs powered by a truck-mounted cME-458 drill rig. The borings were logged by a representative of Hepwortli-Pawlak Geotechnical, Inc. .À previous boring (B-5-g3) was drilled near the û'ont of the lot by Chen-Northerno Inc. Samples of the subsoils were taken with a 1% irich I.D. spoon sampler. The sanpler was driven into the subsoils at various depths with blows fiom a 140 pouncl hammer falling 30 inches. T'his test is similar to the standard penetration test described by ASTM Method D- 1586. The penetration resistance values a1'e an indication of the relative density or consistency of the subsoils. Depths at which the samples were taken and the penetration resistance values ate shown on the Logs of Exploratory Bcrings, Figure 2. The samples rvere retumed to our laboratory for review by the proiect enginecr an<l testing. SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. T'he subsoils encountered consist of silty sandy gravel with cobbles and boultiers. Results of gradation analyses performed on a small diameter drive sample {minus 1% inch fiaction) of the coarse granular subsoiis are shown on Figure 4. Drilling in the dense Job No. 114437A cåFte*t -4- granulil soils witfu uuger equipmsflt was dtfllcult tlue to the cobbles antl boulders and drilling refusal was encountered in the deposit at relatively shallow depths. No free water was encountered in the borings at the time of drilling and thc subsoils were slightly moist to moist. Chen-Northern, Inc. Boring 8-5-93 indicates the granular soils extend down to about 60 feet and are underlain by Eagle Valley Evaporite Bedrock. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the zubsurface conditions encountered in the exploratoryborings and the nature of the proposed construction, we recofirmend thc building be founded with spread footings bearing on the nafural granular soils. The design and construction criteria presented below should be observed for a spread fo oting foundation system. 1) Footings placed on the undisturbed natural granular soils should be designed for an allowable bearing plessure 'I3,S0O prf,- Based on experience, we expect settlement of footings designed and construeted as discussed in this section will be about I inch or less. 2) The footings shoultl have a minimum width of l6 inches for continuous walls and 2 feet for isolated pads. 3) .Exterior tbotings and footings beneath unheated areas should be provided with adequate soil cover above their bearing elevation for frost protection. Placement of foundations at least 36 inches below exterior grade is typically used in this area. r'-r-- 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 earthpressures as discussed in the "Foundation and Retaining Walls" section of this report. 5) All topsoil and any loose or disturbed soils should be removed and the footing bearing lcvcl extended down to the relatively dense natural .lcrh Nn, l14 437A cåFtectr -5- granular soils. The exposed soils in footing area should then be moistened and compacted. If water seepage is encountered, the footing areas should be dewatered before concrete placement. A representative ofthe geotechnical engineer should observe all foofing excavations prior to concrete placement to evaluate bearing conditions. FOLINDATION 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 43 pcf for backfill consisting of the on-site soils. Cantilevered retaining structures which are separate from the residence 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 soils. All foundation and retaining structures should be designed for appropriate hydrostatic and surcharge pressures such as adjacent footings, fraffic, construction materials and equipment. The pressures recouìmended above assurne 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 skucture. An underdrain should be provided to prevent hydrostatic pressure buildup behind walls. Backfill should be placed in uniform lifts and cornpacted to at least 90% of the maximum standard Proctor density at a moisture content near optimum. Backfill in pavement and walkway areas should be compacted to at least 95o/o af themaximum standard Proctor density. Care should be taken not to overcompact the backfill or use large equipment near the wall, since this could cause sxcessive 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. 6) Job No. 114437A cåFtecr, -6- The latcral rcsistance of fouutlutiurr ur retainirg wall footings will be a combination of the sliding resistance of the footing on the foundation matorials anrl passive carth 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 plessure 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 includeri in the design to limit the strain which will occur at the ultimate strength, particularly in the casc of passive resistance. Fill placed against the sides of the footings to resist lateral loads should be compacted to at least 95olo of the maxímum standard proctor density at a moisfure content near optimum. FLOOR SLABS The natural on-site soils, exclusive of topsoil, are suitable to support lightly 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 unreshained vertical movement. Floor slab control joints should be used to reduce damage due to shrinkage cracking. The requiremsnts 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 basement level 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. AII 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 ofthe on-site granular soils devoid ofvegetation, topsoil and oversized rock. TINDERDRAIN SYSTEM Although free water was not cncountered durùrg our exploration, it has been our experience in the areathat local perched groundwater can develop during times of heavy JobNo.1l4437A cåFtecn a precipitation or seâsonal runoff. Frozen grouncl during spring runoff can also create a perched conclition. W'e recornmenci below-gpade construction, such as retaining walls, crawlspace and basemenl âreas, be protected from wetting and. hyclrostatic pressure buildup by an underdrain system The drains should consist of in the bottom of the wall backfill surrounded above the invert level with free-draining granular material. The drai' should be placed at each level of excavation and at least I fbot below lawest adjacent finish grade and sioped at a minimum lYo to a suitable gravity outlet. Free-drain.ing granular material used'in the underdrain system should contaiu less tha:r Z% passing the No. 2û0 sieve, less than 50% passing the No, 4 sieve and have a maximul size of Z inches. The drain gravel backfill shoulcl be at least l% feet <leep. SITE GRADING The risk of conskuction-induced siope instability at the site appears low pr-ovided cut and filI depths are limited. We assume the cut depths for the basement levei (if any) rviil ¡rot exceed one level, about 10 to 12 feet, Fills should be limitcd to about I to 10 feet tleep at the dnwnhili side of the residence where the slope steepens" Embankrne't fills shor¡ld be oompacted to at ieast 95o1a oT the maximum standarrl Proctor density near optimum mois{ure content. Prior to fill placement, the subgra<le should be carefully prepared by removing all vegetation and topsoii ancl cornpacting to at least g5yo af themaximum standard Proctor density. The fill shoulcl be benchecl into the portigns of the hiilsicle exceecii ng 20a/o gr ad,e. Pennanetrt unretained cut and fîll slopes should be graded at 2 hoúr-antal to 1 vertical or flatter and protecled against erosion by revegetation or other means. The ri.sk o{. slope instability will be increase¡l if seepage is encounteled in csfs and flatte¡ slopes may ¡e nscessary. Ifseepage is encountered inpennanent cuts, an investigation shoulcl be conducted to cletermine if the seepage will adversely affect the cqt stabiliiy. This officc should review site grading plans for the project prior to conshr¡cfion, Job No. 114 437A cåFtecr¡ -8- SURFACtr DRAINAOE The following tlrainage precautions should he observed dwing construction and maintained at all times after the residence has been completed: 1) Inundation of the foundation excavations and underslab areas should be avoided during construction. 2) Exterior backfill should be a-djusted 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 l0 feet in unpaved areas and a minimum slope of 3 inches in the first l0 feet in paved areas. Free-draining wall backfill should be capped with about 2 feet of the on- site soils to reduce surface water infilftation. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 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 er(fresñ nr implied. The conclusions and recommondations submittcd in this rcport æc based upon the data obtained from the exploratory borings drilled at the locations 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 other biological contaminants (MOBC) developing in the future. If the client is concerned about MOBC, then a professional in this special ñeld of practice should be consulted' Our findings include interpolation and extrapolation of the subswface conditions identified at the exploratoryborings and variations in the subsurface conditions may not become evidetrt until excavation is performed. If conditions JobNo. l14417A eåStecr¡ 9- 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 servicçs during construction to review and monitor the implernentation 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 presenfed herein. We recommend on-site observation of excavations and foundation bearing shata and testing of structural fill by a representative of the geotechnical engineer. Respectfully Submitted, HEPWORTH - PAWLAK GEOTECHNICAL, INC Louis E. Eller Reviewed by: Daniel E. Hardin, P.E LEE/ksw REFERENCES chen-Northern, rnc., 1991, Prelimínary Geotechnícal Engineeríng study, proposed Aspea Glen Development, Garfield counfii, colorado, prepared for Aspen Glen Company, dated December 20, Tggl,Job No. 4 ll2 gZ. Chen-Northem, Inc., 1993, Geoîechnical EngÌneering Studjtfor Preliminary PIat Design, Aspen Glen Development, Gørfield county, colorado, prepared for Aspen Glen Company, dated }lday 28,1993, Job No. 4 n2 gZ, JobNo. ll4437A ceFtecr' IWEÏLANDSI \ \ \\ (o {1v-z v¿\LOÏF7 )-""-""á. \\ a BORING 2 \ BENCH MAFK: GROUND AT PROPERTY CORNER; ELEV. : 100.0', ASSUMED. ) \ \ a BoRtNGT LOTF6 B-s-gg o - LOTFB APPROXIMATE SCALE'1": 50'RIVEB PARK I.ANE 114 4374 LOÇATION OF EXPLORATORY BORINGS Figure 1 BORING 1 ËLEV.= 102.3' BORING 2 ELEV,: 99.5' 105 105 100 100 0) {DLL Ic 'ãı q) LLI tril ry 21,50/3 +4-54 -200:11 o(Þ LL ¡ Co-E (ú d) UJ s0/6 95 95 90 90 Note: Explanation of symbols is shown on Figure 3. 114 4374 LOGS OF EXPLORATORY BORINGS Figure 2 LEGEND: leþ.{ ffi GRAVEL, COBBLES AND BOUTDEHS (GP-GM); sandy, silty, dense, slightly moist, brown, subrounded rocks. i Drive sample; standard penetration test (SPT), 1 3/8 inch l.D. split spoon sample, ASTM D-1586. 39112 î Drive sample blow count; indicates that 39 blows of a 140 pound hammer falling 30 inches were required io drive the SPT sampler 12 inches. Practical drilling refusal NOTES: 1. Exploratory borings were drilled on October 7,2014 with 4-inch diameter continuous flight power auger. 2. Locations of exploratory borings were measured approximately by pacing lrom fealures shown on the site plan provided. 3, Elevations of exploratory borings were measured by instrument level and refer to the Bench Mark shown on Figure 1 4. The exploratory boring locations and elevations should be considered accurate only to the degree implied by the method used. 5. The lines between materials shown on the exploratory boring logs represent the approximate boundaries between rnaterial types and transitions may be gradual, 6. No Tree water was encountered in the borings at the time of drilling. Fluctuation in water level may occur with time. 7. Laboratory Testing Results: +4 : Percent retained on the No. 4 sieve -200 : Percent passing No. 200 sieve 1 l4 4374 LEGEND AND NOTES Figure 3 24 HF. 7 HR o 45 MlN. 15 MtN. TIME BEADINGS U.S. STANDARD SERIES 00 #50 #30 #16 #8 CLEAR SOUARE OPEN¡NGS 3/8" 3/4' 1 112', 3', 5'6u60MtN19MtN.4MtN. 1MrN. #204 #1 #4 8',100 10 90 80 30 7Q bU 50 oul 40z. l¿¡ É. Þ50zIJ C)El¡Jo- 60 (Jz(n U' ù t- L bJov. l¡JfL 70 80 40 30 20 1090 100 0 00j .OO2 .00s.009 .01s .0S7 .O74 .150 .900 .6üû l.l8 2.36 DIAMETER OF PARTICLES IN MILLIMETERS 4.75 9.5 1S.0 37 .5 12.5 76.2 152 2A3 127 ctÀYTo srlf I SAND I GRA\,IL II |INE I MED,UM I COAFSE I FINE I ruffi I coBBr,Es GRAVEL 54 %SAND 35 %SILT AND CLAY 11 % LIOUID LIMIT %PLASTIC|TY INDEX % FROM:Boring2aì0Feet -t+ ---t--*- SAMPLE OF: Slightly Silty Sandy Gravel 114 4374 GRADATION TEST RESULTS Figure 4