The URL can be used to link to this page

Home My WebLink AboutGeotechnical Investigation 12.04.2006Geotechnical lnvestigation Lot D17, AsPen Glen 0062 Sweet Grass Drive Garfield GountY, Golorado Project No. 26-273 December 4, 2006 Prepared for: Mr. Brandon Exline Exline Custom Homes, LLC 1550 West Horizon Ridge Parkway, Suite B32B Henderson, Nevada 8901 2 ' PrePated bY: Yeh and Associates, lnc. 170 Mel RaY Road Glenwood SPrings, Colorado 81601 Phone: 970-384-1500Farc 970-384-1501 Lot D17, Aspen Glen Project No. 26-273 TABLE OF CONTENTS PURPOSE AND SCOPE ............... PROPOSED CONSTRUCTION SITË CONDITIONS SUBSURFACE CONDITIONS EXPANSIVE SOIL RISK........, SITE DEVELOPMENT FOUNDATION RECOMM ENDATIONS .. BELOW-GRADË CONSTRUCTION ....... SLABS-ON-GRADE... SUBSURFACE DRAI NAGE",,. SURFACE DRAINAGE LTMTTAT!ONS .....,....,. Appendices Appendix A - Test Hole Logs Appendix B - Laboratory Test Results Lot D17, Aspen Glen Project No. 26-273 PURPOSE AND SCOPE This report presents the results of our geotêchnical investigation and recommendations for design and construction of a residential duplex unit on Lot D17 within Aspen Glen Subdivision in Garfield County, Colorado. The subsurface investigation was conducted to provide recommendations for foundation' design, subsurface drainage, below grade construction, and backfitling/compaction procedures for the consiruction of the residential structure. The findings of our ìnvestigation and recommendations for construction of the proposed residence on the subject site are presented in this report. The site investigation consisted of geologic reconnaissanoe and exploratory drilling to investigate subsurface conditions. Two test holes were drilted within the buìlding footprint, A representatíve of Yeh and Associates observed drilling of the test holes. I he project personnel examined samples obtained during the field exploration and representative samples were subjected to laboratory testing to determine the engineering characteristics of materials encountered. Based on our investigation, Yeh and Associates completed an engineering analysis of the subsurface conditions. This'report summarizes our field investigation, the results of our analysis, and our conclusions and recommendations based on the proposed construction, site reconnaissance, subsurface investigation, and results of the laboratory testing. PROPOSED CONSTRUCTION We understand the proposed construction would consist of â two-story residential duplex unit. We anticipate the structures would be wood framed. The residences would likely be supported oh footing foundations. We understand basement areas are planned. Cuts on the order of B to 10 feet below existing grade are planned to achieve foundation elevation for the residences. We anticipate minor grading around the building to establish drainage and flatwork. SITE CONDITIONS The site is located on Lot D17 within Aspen Glen Subdivision in Garfield County, Colorado. The proposed building site is located on a vacant lot within a partially developed subdivision. A manmade pond is located on the east property line, A drainage from the pond flows from north to south and turns at the southeast property corner and flows from east to west. The site is bordered on the north by Sweet Grass Drive with a vacant lot beyond. Existing 1 Lot D17, Aspen Glen Project No. 26-273 residences are located to the south and east. A vacant lot is located to the west. Streets were paved, and utilities were ¡nstalled. The site gently slopes down to the southwest and west at grades of less than 5 percent. SUBSURFACE CONDITIONS Subsurface conditions were investigated by drilling two exploratory borings at fhe approximate locations presented on Figure 1. The test holes were drilled using a Dietrich D-50 to pre-determined depths where modified California samples were obtained, The results are shown on Appendix A. Modified California samples were collected using a 2-inch l.D. sampler driven into the subsoils with a 14O-pound hammer falling 30 inches. The nurnber of blows needed to drive the sampler constitutes the blow count. For example, a value on the log (Appendix A) of 14112 indicates the sampler was driven 12 inches with 14 blows of the hammer. The blow count can be used as a relatively measure of material stiffness or density. The collected samples were transported to our laboratory where they were examined and classified. Laboratory tests included noisture content, dry density, swell/consolidation, grain size analysis and Atterberg limit testing, The subsoils encountered in the test holes consisted of 12.5 to 17 feet of clay and silt underlain by clean gravels with abundant cobbles and boulders. The clay and silt were stiff to very stiff and the gravel was very dense. Bedrock was not encountered in any of the test holes. Practical drill rig refusalwas encountered in both test holes TH-1 and TH-2 at depths of 21 and 17 feet, respectively. The clay samples tested had 81 to 90 percentfines (material passing the No. 200 sieve). Aiterberg limit test results indicated the clay had liquid tirnits of 27 to Sl.percent and plasticity indices of 6 to 9 percent. The silt sample tested had 81 percent fines and was nonliquid and non-plastic. The gravel sample tested had 3 percent fines. One clay sample exhibited moderate swell of 2.2 percent and one silt sample exhibited low swell of 0,0 percent swell when wetted under an applied pressure of 1,000 psf. The laboratory test results are presented in Appendix B and are summarized in the Summary of Laboratory Test Results table. Groundwater was not encountered in any of the test holes, and the subsoils were slightly moist. Variations in groundwater conditions may occur seasonally. The magnitude of the variation will be largely dependent upon the amount of spring snowmelt, duration and intensity 2 Project No. 26-273 Lot Dl7, AsPen Glen of precipitation, local landscape irrigation practices, site grading changes' and the surface and subsurfacedrainagecharacteristicsoftheSurroundingarea'Theex¡stingpondwhenfilledwith water could be a source of groundwater that could impact the proposed structure depending on planned etevations. Perched water tables may be present' but were not encountered in any of the test holes EXPANSIVE SOIL RISK The site aPPeared suitablefortheproposedconstruction.Potentiallyexpansivesoilswill require particular attention in the design and construction'We believe there is a moderate risk ils. We estimate of poor slab-on-grade Perfo rmance due to swelling or collaPsible so of basement slabs and exterior flatwork of about I lo 2 inches could occur movements wetting these soils lncrease ln Expansive soils are stable at current moisture conditions'Upon volume and could cause movement of slabs-on-grade' The amount of movement is dependent on the availability of water due to landscape irrigation and surface drainage and the structural tolerances to movement' construction fo r basement or garage areas is considered accePtable Slab-on-grade movement. The expansive soils can be rovided the owner accePts the risk of P otential slab mitigated bY subexbavation. Subexcavation consists of removal of the exPansive soils, moisture conditioning of the soils and placement as a moisture conditioned, controlled fill' lf selected' we recommend subexcavation to a depth of B feet below foundation or slab level or to the gravel soils, whichever is shallower' Subexcavation can also be performed by removing 3 feet of the expansive clay below improvements and repla cing the materialwith a non-expansive granular fill. We estimate potential movements of less th an 1-inch, if subexcavation is performed SITE DEVELOPMENT we anticipate cuts of about B to 10 feet from existing grade may be necessary to reach foundation level. Fill placement should be minor' Areas to receive fill should be stripped of vegetation, organic soits and debris. The on-site soils free of organic matter' debris and rocks largerthan6inchescanbeusedinfills.Fillshouldbeplacedinthin,looseliftsofBinchesthick or less, moisture conditioned to 0 to 3 percent above optimum moisture content and compacted to at least g5 percent of maximum standard proctor dry density (ASTM D 698)' Granular soils can be moisture conditioned to within 2 percent of optimum moisture content' Placement and p ? Project No. 26'273 Lot Ð17, Aspen Glen compâction of fill should be observed and tested by a representative of the geotechnical engtneer alternatives are Presented below Footings with Minimum Deadload l.Foundationsshouldbeconstructedonundisturbed.naturalsoils'Loose, disturbed *o¡f" åncãrntered at founáät¡on tevet should be removed and replaced with compacted äil ü; iounout¡on =ñouu uu extended io undisturbed soils' 2. Footing foundations can be designed for a maximum altowable soil pressure of 3,0û0 psf. The footing foundation *h"rià be designed with a minimum deadload pressure of 1,000 Psf' 3.Continuouswatlfootingsshouldhaveamin'ilumwidthofatleastl6inches' Foundation p;* f* ¡sälateo columns should have a minimum dimension of 20 inches bY 20 inches' 4'lnordertomaintaintheminimumdeadloadplessure,itmaybenecessaryto design "no "àn"äu*t-" "Vrt"* "f gt"d- Ëãrns un6 isolated footing pads' To maintain the minimum dead load p";;;; ;; footings, a minimum 4 inch void space shoutd be provided Ueneatl'iñå gtuU* beami between footing pads (if utilÌzed)' S.Resistancetoslidingatthebottomofthefootingcanbecalculatedbasedona coefficient of friction of 0.30. p"r*iv" prussure against the side of the footíng can atso be considered for the sliding iåri*turr." if it is properly compacted' Passive pressure can be estimated Ua"eO'oÃ ãn àquivaleni fluid density of 250 pcf for a level backfill 4 Project No. 26^273 l.ot D17, AsPen Glen 6. Grade beams and foundation walts should be reinforced to span undisclosed looseorsoftsoilareas,WerecommendreinforcementSufficÎenttospanan l-nsupporte¿ distance of at least 10 feet' 7. The soils below exterior footings or exterior edges of slabs should be proiected from freezing, W;';;;;m*"nã tne noitom of t-ootings be constructed at least 3 feet berow finisheJ exterior grade or as required by tocal municipal code' B.Allfoundationexcavationsshouldbeobservedbyanexperiencedengineering geologist o, g"ot"".îniàãr ånò¡n"ur prior to placement of concrete' Drílled Friction Píers l.Foraxialcompressionloads,piersmaybedesignedforamaximumend-bearing pressure ot ré,óóo pounds. p""quäîä tã"ì tp"O and'skin friction of '1'500 psf' The axial capacity of the pit'* *uiî; il-*ä+A by 1/3 or as allowed by tocal code when "on*iä"t¡ng wiñd ano/or seismic loading' 2.Allpiersrequiresufficientdeadloadtoresistthepotentialupliftoftheexpansive materials. All piers shoutd n. o"igñ"J-r* ä *ini*um dead load pressure of 10,000 Psf, based uPon Pier end area' 3'Piersshouldhaveaminimumlengthof20feetinbasementareasand2Sfeetin non-basement areas. pier length ä ä;"1"; rãt¡o stloutO not exceed 30 unless aPProved bY the engineer' 4.Piersshouldbeconsideredtoworkinagroup.acjiglitthehorizontalspacingis tess than 3 pier diameters. Th" ;;Ëñy-oi in¿iuiuuut piers must be reduced when pier spacing is less than 3 pieiä¡amåters to accouni for the effects of group action. capacity reduction i. u trñcön'ot pi"t spacing and the number of piers withinagroup.lfgroupactionanalysesarenecessary,capacityreduction fàctors "aá bt'provided for the analyses' 5. ïo reduce potentiat uplift forces on piers., use. of long grade beam spans to increase individual pier loading uni*'tiåff ãiameter pierJaie recommended' For this projecr, ;ä;i ã *¡n¡*urn pi"r aìä*åtãiot lo inches is recommended' A 4- inch or greater void space *hgyld îä piovioeo beneath grade beams between piers. The ";id "ä*t"r srrouro å; ;;;t;bte sirengtì to support the weight of fresh concrete used in grade #;; *""liuct¡on a-no to avoid collapse when foundation backfill is Placed' 6.Allpiersshouldbereinforcedfulldepthfortheappliedaxial,lateralanduplift stresses imposed. The amount o' *ñöt;ing itu*iånoulO be determined by the tensile force created by the upr¡n íoiJ"'ån ã"Ën pi"t with allowance for dead load' For piers þ;ih;;ãó ¡n"n,j" in'ï¡ãmeter, it is recommended that a minimum reinforceme"i"i y' pãitànt of the pier cross section be'used' 7. Free-fall concrete placement in piers witl only be- acceptable if provisions are taken to avoid striking the concriä Ë ;¡åä" of the hole or reinforcing steel' The use of a bottom-dump rìoppui ;; il elephant's trunk discharging near the 5 Lot D17, AsPen Glen bottom of the hole \Mhere recommended. ProJect No. 26-273 concrete segregat¡on will be minímized' is S.Pierbearingsurfacesmustbecleanedpriortoconcreteplacement representatiu. ot t'nïéåoi"ðñnir.r engineer should observe pier installation' BELOW.GRADE CONSTRUCTION A basement is planned for this residence' Foundation walls that extend below grade should be designed for lateral earth pressure where backfill is not present at about the same level on both sídes of the wall. watts that can deflect or rotate about 0'5 to 1 percent of the wall height can be designed for "active" earth pressure conditions' For a very rigid wall where negligible deflection will occur, ân "at-resf' lateral earth pressure condition can be used' Typically, below-grade walls in residences can rotate under normat design loads' and deflections result in acceptable performan ce' lf on-site soils are used as backfill, we recommend using an equivalent fluid density of 50 pcf for design of below grade walls foI "active" conditions' This value assumes that some minor cracking is acceptable. lf negligible deflections are desired, a higher ("at resf') equivalent fluid density should be used for design. For "at rest" conditions' an equivalent fiuid density of ô0 pcf can be used for design. These equivalent fluid densities do not account for sloping backfill' surcharges or hydrostatic pressure' A SLABS.ON-GRADE Based on our investigatio n, gärage and driveway slabs will likely be underlain by low to moderate swelling clay and silt soils' grade Perform ance due to swelling could occur if subgrade soils are saturated. lf a finished base ment is Planned for the inches should be given to useof clays, consideration residence, given the engineering characteristics modification,such as subexcavation above. The on-site soils, free of organics and debris, are suitable to support lightly loaded slabs-on-grade' Slabs should be separated from all load bearing walls and columns with expansion joints that allow at least 2 inches of vertical movement' Control joints should be used to reduce damage from shrinkage cracking'Allfillbelowslabsshouldbecompactedtoatleastgspercent Proctor dry density at 0 to 3 percent above optimum moisture content' t) of maximum standard Project No. 26-273 Lot D17, AsPen Glen SUBSURFACE DRAINAGE Surfacewatertypicallyflowsthroughpermeablewallbackfillandcollectsatthebackfill and naturar soir interface resurting in saturated foundation soils and/or wet basement conditions' To reduce water accumulation outside foundation walls and in basement areâs' a foundation drain should be installed around the exterior or interior of the foundation walls' The drain should consist of a 4-inch diameter, perforated pipe encased in free draining gravel. The gravel should beY,tto 1.5-inch washed rockwith less than 5 percentfines' The drain should be provicled with a gravity discharge such as a sump pit where water can be removed by pumping or daylighted. The pipe should be sloped at a minimum of 0'5 percent and beinstalled12lol|inchesawayfromandparalleltothefootingfoundation.Theboitomofthe pipeshouldbeatleast4inchesbelowthebottomoffootinglevelatthehighpoint.Crawlspace areas should also be provided with adequate ventilation' SURFACE DRAINAGE ' surface drainage is crucial to the performance of foúndations and flatwork' we recommend the ground surface surrounding the buitding be sloped to drain away from the structure. we recommend a slope of at least 6 inches in the first 10 feet for landscape areas' paved areas can be sloped at a minimum of 0.5 percent away from the structure' Backfill around foundations should be moisture conditioned and compacted as recommended in the slTE DEVELOPMENT section. Roof downspouts and drains should discharge beyond the backfill area. LIMITATIONS The analyses and recommendations presented in this report are based upon our data obtained from the test hores at the indicated rocations, fierd observations, raboratory testing, our understandingoftheproposedconstructionandotherinformationdiscussedinthisreport.ltis possible that subsurface conditions may vary between or beyond the points explored' The nature and extent of such variations may not become evident untir construction. rf variations appear, we should be contacted immediately so we can review our report in light of the variaiions and provide supplemental recommendations as necessary' we should also review the report if the scope of the proposed construction, including the proposed loads' finished elevations or structure locations, change frorn those described in this report' The conclusions 7 Proiect No. 26-273 Lot D17, AsPen Glen and recommendations conta¡ned in this report shall not be considered valid unless Yeh and Associates reviews the changes and either verifies or mod¡fies the conclusions of this report in writing. The scope of services for this project did not include, specifically or by implication' any environmental or biological (e.g., mold, fungi, bacteria) assessment of the site or identification or prevention of pollutants, hazardous materials or conditions or biological conditions' If the owner is concerned about the potential for such contamination, conditions or pollution, other studies should be undertaken. The report was prepared in substantial accordance with the generally accepted standards of practice for geotechnical engineering as exist in the site area at the time of our investigation. No warranties, express or implied, are intended or made' The recommendatÎons in this report are based on the assumption that Yeh and Associates will conduct an adequate program of construction testing and observation to evaluate compliance with our recommendations' Respectful lY Submitted, YEH AND ASSOCIATES, INC Richard D. Johnson, P'E. Senior Geotechnical Engineer I APPENDIX B LABORATORY TEST RESU LTS Project No:26-273asEULK - lndicates bulk sample from augerNL - lndicates non-liquid'NP - lndicates non-Plastic'YEH & ASSOCIATES,lNcSummary of Laboratory TestResultsProject Name:Lot D17, AsPen GlenGravel, clean (GP)Silt, sandY (ML)tlaY, siliY (CLML)Clay, sandy (CL)Clay, sandY (CL)Soil DescriPtionComp.StrengthU2.27o Swell (+) /ConsolÍdation (-)under 1000 Psf6INPPINP2122PLNL2731LLıJJ818'1s0Fines#2042Sand(%)95Gravel>M1C31071091M.0(pcr,lDry'1.04.38.810.4o.oMoistureGontent(%)CABULKÇASamPleTYPe14-17I14.04I(ft)DepthTH.2TH-1TestHolecuttings.Page 1 of 1 nity Map Not to Scale Drive eet Ctrø gS g{{ SCALET 1" = 4B' 0 Legend: TH-1 lndicates Approximate Locations O of ExPloratory Borlngs Locations of Exploratory Borings TH.1 Lat D17 TH-2 Project No.26-273 Figure 1 APPENDIXA TEST HOLE LOGS No. A-1Lot D17, AsPen GlenNumber: 26-273ProjectrflYEH AND AssoGlATF$* lNc'bãorLcHfuìınf e¡r-b r¡r ÈeRt NG co N su urRNrsTH.1TH-2101Èo2A1N1214t1211t121AtlZ5o,ts14t1250/l Project; Lot D17, AsPen Glen Proiect Number: 26273YEH AhlD ASSOGIATEST !i!c.- sËòiÈcuNrcx- ENcINEERING coNSULTANTS Legend for symbols used on Borehole Logs Sample TYPes K Modified Calífornla Sampler' The symbÖl 16/12 indicates that 16 blows from a 140 pound hammer falling 30 inches was úiãã t" ãiiuu zinch l'D' sampler 12 inches' lndicates bulk sample from auger cuttings' Soil LithologY % m ffi I CLAY, silty to sandy, slightly moist, stiff lo very sliff' red-brown (CL' CL-ML)' SILT, sandy, slightly moist, stiff, red-brown (ML)' GRAVEL, clean, cobbles and boulders, sl¡ghtty moist, very dense' brown {GP). lndicates practical drill rig refusal No.26-273 A-2