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HomeMy WebLinkAboutSoils & Foundation Investigation 12.12.2006ffi CTL ITHONIPSON December 12,2006 Ms. Arianna Lightfoot {23 Rosewood Way Parachute, CO 81635 Subject:Soils and Foundation lnvestigation Lightfoot Residence Lot 9, Monument Ridge Garfield County, Colorado Project No. G504906-1 20 This report presents the results of our soils and foundation investigation for the Lightfoot Residence proposed on Lot 9, Monument Ridge in GarÍield County, Cotorado. We conducted this investigation to evaluate subsurface conditions at the site and provide foundation recommendations for the proposed residence. Our report was prepared from data developed during observation of subsurface conditions exposed in exploratory pits excavated at the site, engineering analysis and our experience with similar conditions. This report includes a description of the subsurface conditions observed in exploratory pits, recommendations and design criteria for the foundation and floor systems, and geotechnical and construction crlteria for details influenced by the subsoils. Recommendations contained in this report were developed based on our understanding of the planned construction. lf plans differ significantly from the descriptions contained in the report, we should be informed so that we can check that our recommendations and design criteria are appropriate. Site..Gonditions Lot 9 is northeast of the County Road 300 and Monument Ridge Road intersection. Access to the lot will be from Monument Ridge Road. The building lootprint witl be near the center of the lot. Grades at the lot are relatively flat and vegetation is a sparse cover of native ground flora' Proposed Construction We did not have building plans to prepare this report, We understand that the Lightfoot Residence will be a two-story, wood-frame building with an attached 234 Center Þrive lGlenwood Springs, Colorado I'1601 Telephone: 97 A-945-2809 Fax: 970"945-7 411 ffi garage. No basement \¡ìtlll be constructed. A crawl space will be below thê ma¡n floor living area. The garage floor will be a slah-on-grade. Maximum foundation excavatíon depths will likely be about 5 feet, Completed wall backfill depth may be slightly more than excavation depth as final grades are adJusted for drainage. Foundation loads are expected to vary between 1,000 and 3,000 pounds per lineal foot of foundation wall with maximum interior column loads of 30 kips. lf construction will differ significantly from the descriptions above, we should be informed so that we can adjust our recommendations and design criteria, if necessary. Subsurface Conditions We observed subsurface conditTons exposed in two exploratory pits (TP-1 and TP-2) excavated at the site. The approximate locations of our exploratory pits are shown on Figure l. Subsurface conditions observed in the pits were logged by our laboratory/field manager who obtained samples of the excavated soils. Graphic logs of the soils observed in the exploratory pits are shown on Figure 2. Subsurface conditíons observed in our exploratory pits consisted of about l2 inches of sandy clay "topsoil" underlain by silty sand with gravel and scattered cobbles to the total explored depth of 11 feet below existing ground sur-face. Free ground water was not observed in the exploratory pits at the time of excavation. A sample of the natural soil selected for gradation analysis contained 41 percent gravel, 26 percent sand, and 33 percent silt and clay size particles {passing the No. 200 sieve). Two samples of the soils were subjected to one dimensional consolidation tests. The samples were flooded while subjected to a .1,000 psf load. Both samples showed consolidation potential. Laboratory test resutts are shown on F¡gures 3 through 5. Site Ea.rthwork Excavations We anticipate excavations for the building foundation and utilities can be accomplished using conventional, heavy-duty excavation equipment. Excavation sides will need to be sloped or braced to meet local, state and federal safety regulations. We believe the natural sands will classify as a Type C soil based on OSHA standards governing excavations. Ternporary slopes deeper than 5 feet should be no steeper than 1.5 to I {horizontal to vertical} in Type C soils. Contractors should identify the soils encountered in the excavations and refer to OSHA standards to determine appropriate slopes. Soils removed from the excavation should not be stockpiled at the edge of the excavation. Excavated soils should be placed at a dístance from the top of the excavation equal to at least the depth of the exeavation. MS. AR¡ANNA LIGHTFOOT LIGHTFOOT RESIDENCE PROJECT NO, GS04906 145 sics04906,o00tl2ol3, Letler31c50490S 120 Ll doc 2 ffi Fill and Backfill Grading plans were not províded to us. We are providing criteria for footings supported on structural fill (see Foundation section). Fill may be required to obtain subgrade elevations for parts of the driveway. Areas which will receive fill should be stripped of vegetation, organic soils and debris. The on-site soils free of organic matter, debris and rocks larger than 3 inches in diameter can be used as structural fill below footings or as fill to achieve subgrade for exterior {latwork or the drivewaY. Fill should be placed in loose lifts of 10 inches thick or less and moisture conditioned to within 2 percent of optimum moisture content. Fill placed outside the building footprint should be compacted to at least 95 percent of standard proctor {ASTM D 69S) maximum dry density. Structural fill below footings or exterior flatwork should be compacted to at least 98 percent of ASTM D 698 maximum dry density. Moisture content and density of fill and structural fill should be checked by a representative of our firm during placement' Baekfill placed adjacent to foundation wall exteriors should be free of organic matter, debris and rocks larger than 3 inches in diameter. Backfill should be moisture conditioned to within 2 percent of optimum moisture content and compacted to at least 95 percent of standard Proctor (ASTM D 698) maximum dry density. Free ground water was not ohserved in the exploratory pits during our site visit We do not anticipate excavations for foundations or utilities will penetrate ground water, however, excavations should be sloped to a gravity discharge or to a temporary sump where water ,can be removed by pumping' The ground surrounding the excavations should be sloped as much as practical to direct runoff away from the excavations. Foundation Our exploratory pits indicate that natural silty sands are present at anticipated foundation elevations for the Lightfoot Residence. These soils are slightly moist to dry and are susceptíble to collapse and consolidatíon when wetted. Some increase in moisture should be assumed after the residence is completed and the yard is landscaped. We recommend constructing the residence on footing foundations. The footÍngs can be supported by either a minimum 3 feet of densely compacted structural fill (see Figure 6) or on the native soils in the in-situ state. The placement of densely compacted structural fill below footing will reduce the risk of footing settlement and the potential for differentÍal settlement of the building foundation. Our representative should be called to observe and check the placement of structural fill. We should also observe the compteted foundation excavation prior to placing forms, to confirm that the soil exposed is suitable for support of the designed footings. Recommended desfgn and construction criteria for footings âre presented below. M5, ARIANNA LIGHTFOOT LIGHTFOOT RESIDËNCE PRoJECT NO. GS049t6 '145 s:lGSû4906,000\12013, !ótterstGSo,1906 1 20 Ll.doc 3 # Footing foundatlon.s should be supported by structural fill or tho undlsturbed, natural soils, Soils loosened during excavation or the forming process forthe footings should he rernoved or the soils can be re-compacted prior to placing concrete. Footings supported by structural fill or the natural soils can be designed for a maximum allowable soil pressure of 3,000 psf. Gontínuous wall footings should have a mínimum width of at least 16 inches. Foundations for isolated columns should have minimum dimensions of 24 inches by 24 inches. Larger sizes may be required, depending upon foundation loads. 4.Grade beams and foundation walls should be well reinforced, top and bottom, to span undisclosed loose or soft soil pockets. We recornmend reinforcement sufficient to span an unsupported distance of at least 12îeet Reinforcement should be designed by a qual ified structural engineer. The soils beneath exteríor footings should be protected from freezing. We recommend the bottom of footings be constructed at a depth of at least 36 inches below finished exterior grades for soil frost protection. Floor Svstem and Slabs-On-Grade We understand the main level living area will be constructed with a crawl space below the floor. From a geotechnical perspective structural floors are very positive. We understand that the garage floor is planned as a slab-on-grade. Based on our experience, we judge slab-on-grade construction can be supported by the undisturbed, natural soils with a low to moderate risk of differential movoment and associated damage, The potential for slab-on-grade settlement can be reduced by the placementof atleast {2 inches of structural fill belowthe slab, $tructural fill placed to attain subgrade elevations for exterior concrete flatwork should be in accordance with the recommendations outlined in the Fill and Backfill section. We recommend the following precautions for slab-on-grade construction at this site. Slabs should be separated from exterior walls and interior bearing members with slip joints which allow free vertical movement of the slaÞs. Underslab plumbing should be pressure tested for leaks before the slabs are constructed. Plumbing and utílíties whích pass through MS. ARIANNA LIGHTFOOT LIGHTFOOT RESIÐENCE PROJECT NO. GS04906 145 slËS04906'Ù00\120\3. LettsrE\G504906'l 20 L1,doc 1 2. 3. 5 1 2. 4 ffi slabs should be isolated from the slabs with sleeves and provided with flexible couplings to slab supported appliances. Exterior patio and porch slabs should be isolated from the residence. These slabs should be well-reinforced to function as independent units. Frequent control joints should be provided, in accordance with American Concrete lnstítute (ACl) recommendatíons, to reduce problems associated with shrinkage and curling. B rade Constru ction Foundation walls which extend below-grade should be designed for lateral earth pressures where backfíll is not present to about the same extent on both sides of the wall. Many factors affect the values of the design lateral earth pressure. These factors include, þut are not limited to, the type, compaction, slope and drainage of the backfill, and the rigidi$ of the wall against rotation and deflection. For a very rigid wall where negligible or very little deflection will occur, an "at-rest" lateral earth pressure should be used in design. For walls which can deflect or rotate 0.5 to 1 percent of wall height (depending upon the backfill types), lower "active" lateral earth pressures are appropriate. Our experience indicates typical foundatíon walls can deflect or rotate slightly under normal design loads, and that this deflection results in satisfactory wall performance. Thus, the earth pressures on the wallg will likely be between the "active" and "at-rest" conditions. lf the on-site soils are used as backfill, we recommend design of below- grade walls using an equivalent fluid density of at least 50 pcf for this site, This equ¡valent density does not include allowances for sloping backfill, surcharges or hydrostatic pressures. The recommended equ¡valent density assumes deflection; some minor cracking of walls may occur. lf very little wall deflection is desired, a higher equivalent fluid density may be appropriate for design. Our recent experience indicates most below-grade walls designed with 45 pcf to 55 pcf equivalent fluid density have performed satisfactorily. Backfill should be placed in accordance with recornmendations in the Fill and Backfill section. Water from rain, snow melt and surface irrigation of lawns and landscaping frequently flows through relatively permeable backfill placed adjacent to a residence and collects on the surface of relatively impermeable soils occurring at the bottom of the excavation. This can cause wet or moist conditions in below- grade areas after construction. To reduce the likelihood water pressure will develop outside foundation walls and reduce risk of accumulation of water in tlre crawl space, we recommend provision of a foundation drain. The drain should consist of a 4-inch díameter, slotted pipe encased ín free draining gravel. The drain should lead to a positive gravity outfall, or to a sump pit where water can be removed by pumping. A typical foundation drain detail is presented on Figure 7. ln addítfon, adequate crawlspace ventilation should be provided. MS. ARIANNA LìGHTFOOT LIGHTFOOT RESIDENCE PRoJEcr No. Gs04906 145 sloso4906.00O\12013. Lsllers\G$04906 t20 Ll doc 3 4- 5 tr Surface D-rqinsgg Surface drainage is critical to the pefformance of foundations, floor slabs and concrete flatwork. We recommend the following precautions be observed during construction and maintained at alltimes after the residence is completed: The ground surface surrounding the exterior of the residence should be sloped to drain away from the residence in afl directions. We recommend providing a slope of at least f 2 inches in the first l0 feet around the residence, where possible. ln no case should the slope be less than 6 inches in the first 5 feet. Backfill around the exterior of foundation walls should be placed in maximum 10 inch thick loose lifts, moisture cond¡t¡oned to within 2 percent of optimum moisture content and compacted to at least 95 percent of standard Proctor {ASTM D 698} maximum dry density. The residence should be provided with roof gutters and downspouts. Roof downspouts and drains should discharge well beyond the limits of all backfill. $plash blocks and downspout extensions should be provided at all discharge points. 4.Landscaping should be carefully designed to minimize irrigation. Plants used near foundation walls should be limited to those with low moisture requirements; irrigated grass should not be located within 5 feet of the foundation. Sprinklers should not discharge within 5 feet of the foundation and should be directed away from the building. lmpervious plastic membranes should not be used to cover the ground surface immediately surrounding the residence. These membranes tend to trap moisture and prevent normal evaporation from occurring. Geotextile fabrics can be used to control weed growth and allow some evaporation to occur. Limitations The exploratory pits provide a reasonably accurate picture of subsurface conditions. Variations in the subsurface conditions not indicated by the pits will occur. Our representative should be called to observe and check fill placement and to observe the completed foundation excavation to confirm the soil exposed is suitable for support of the footings as designed' ThÍs investigation was conducted in a mânner consistent with that level of care and skill ordinarily exercised by geotechnical engineers currently practicing under similar conditions in the locality of this project. No warranty, express or implied, is made. lf we can be of further service in discussing the contents of this MS. ARIANNA LIGHTFOOT LIGHTFOOT RESIDENCE PROJECT HO. GS04900 145 S lGâ04906.000\120\3. Letlerslcs04906 120 Ll.doc 1 2 3. 5 6 ffi report or in the analysls of the influonce of the subsoll condltlons on the deslgn of the structure, please call. Very Truly Yours cTL ITHOMPSON, lNC. J l" i-.;,: J 'r (5 copies sent) MS. ARIANNA LIGHTFOOT LIGHTFOOT RESIDENCE PROJECT NO. GS04906 1a5 S:\GS01906,000112013. Lolt6rslcs04006 l¡0 Ll.dæ 7 SGALE: 1'o 1(XÌ rNT 2091 I l\ts. Arlanna Ughflbot Lþhtfrpt FaCdsnos l-ot9, l/lonlrnãtRldgo ProJect No. G9O49O6-1 2O LOT 5 7.117 AC. r FENCE LOT 9 6.555 AC. t WELL FOR LOTS 9 AND 10, PERMIT _ I NO. 57703F TP-2 I ïP-r FENCE COUNTY ROAD 5OO È ıJ trTP-1 TP-2 00 IoE :r I aloo ool¡. ç sêoÕ 5 10 1ã 5 t0 l5 LEGEND:NOTES: El SondYbC moisl, oloy "topsoll", orgonlcs, brown. 1. Explor.olory pÌis nÇrc ôxcovolcd with o bockhos on December 6, 2006. Plls wero bockfillad immediolely ofler axcovolion operollons wer€ compleled. 2. No free ground wotsr wos obscrvcd ln lhc explorotory pÍls of lhe llme of excovolion, 3. Locolions of explorotory pits ore opproximole. 4. These explorolory pits ore subJecl lo lhe explonofions, llrnilotlons qnd conclusions os contslned ln lhis report. Ø L þ Sqnd, silty, grovel' cobbles, occoelonol bouldcrs, mcdiurn dcnss to d¡nsc, slighlly moisl to dry, lighl ton, whlle. (SM-Gl,l) lndlcotes hond drìve somPle. lndlcotss bulk somPle. SUMMARY LOGS OF EXPLORATORY PITS Projecl No. GS04906-145 Flg. 2 trF 7 ô 5 4 J ¿ -1 zI(nz o-xIu \9 zIûo trlÉ 0.Eo(J 0 -2 -3 4 -6 -8 0.1 1.0 APPLIED PRESSURE. KSF 10 NATURAL DRY UNÍT WEIGHT= NATURAL MOISTURE CONTENT= 100 71 10.1 PCF o/o Somple ol SAND, SILTY (SM) FTom TP.1 AT 3 FEET Swell Consolidation Test Results Frc 3 ,/i ,/i DUE INTOREWETT ON UNDER i PROJECT NO, G504906-120 ffi 7 6 5 4 -1 zItf,z o-x t¡¡ szI u,6 uJu o- Eoo o -a -J 1 -5 -6 7 .B 0,1 Somple of SAND, SILTY (SM) 1.0 APPLIED PRESSURE . KSF 10 NATURAL DRY UNIT WEIGHT= NATUR TMOISTURECONTENT= 100 PCF FTOM TP.2 AT4 FEET 7A 10.9 o/. Swell Gonsolidation Test Results FrG 4 ¡ : ADDITfONA CONST G o N DUE TOE I I I i PROJECT NO, GSO4906-120 --frir.- -J,l-fä' ïrlï- SANBS GRAVEI FINE MEÐIUM COARSE FINE COARSE CÔBBtESçLAY {PTÁSTIC) TO SILT {NON.FLASTIC) SIEVE ANALYSISHYDROMETER ANALYSIS 90 ao 7A 60 50 40 30 2t 10 .005 _oos .01s .037 .c74 .149 .297 _ __.590 1.19 2.0 2.38 4.76 9.52 19.1 36.1 76.2 't27-,2O0o.42 152 DIAMET€R OF PARTICLE IN À'ILLIMETERS :- l-- l-''-l', ,.1.-, i.---,.-J--:--'J "-'-l'-":-_. -- l.:-----f:-.::-.'l -.---- l-.. .l:---:.rr.l - ì..-. - -l , .-'--..-l----- _l_l .__ . -.----.-t_ ,__t._-.___--. ---t-____ .--:l-__: 1y,. ? 2 @oÈ d CLEÁR a d& tszd úuÀ 0.002 3/a'xt4" s0 lnn TIME 1Ul STANDARD SERIES ,50-40'30.1ô.1Ô,s6û MtN. re MrN. 4 MlN. 1 MlN. '200 '100 2g HR. 7 HR, d5 MtN. 15 MlN. Somple of From GR4VEL, CLAYEY, SILTY {Gç-GM) TP-1 AT 10.11 FEET GRAVEL 41 o/o srlr & CLAY ,,_qx % PLASTICITY INDEX SAND 26% Lte u ¡ o-I I lr¡ tî---l o/o - o/o SANDS GRÂVÊt fINE MEDIUM coARsÉ FINE coARsËCLAY {PI-ESTIC} TO SILT (ÑON-PLASTIC) COBBLÉS HYDROMËTER ANATYSIS SIEVE ANALYSIS 45 MtN. 15 MtN. 60 MrN. le MlN. 4 MlN. I MtN. '200 ',100 '50 '40 '30 *16 '10 '8 '4 sls" 314" lW 3' .5',6" 8" 1û0 90 8û 7A 60 50 40 30 2D 10 o.o02 .005 -009 .0'19 .O37 .074 .'l4S .rg o.oi*O 1.19 2.0 2.38 4.76 DIAMËTER OF PARTICLE IN M'LLIMËTERS .___I____-t,. -._i_ z À tszUoÉ! od2a EFz !t¡ d 60 70 80 90 100s.52 19.1 38-1 25 HR 7 HR. 0 ì0 20 30 40 50 1Ë.2 12f 2æ 152 Somple of From GRAVEL % SANÞ % stlr & ciÃY---% LleutD r-rrr¡rr % PLASIC|TY l¡¡-orx -- % Gradation Test ResultsPROJECT NO, GSO49O6-120 FIG.5 ffi 't D (MrN. 3 ¡ 2 P1 SIRIP FOOTING B+D DD)lI .=-,B P 2= F B+D SQUARË COLUMN FOCITING E'tr¡l''r=-Eu' FP= 2 o t Þ (e+D) 2 Distriþution of Pregsure q STRUCTURAL FILL B ; I \_*--\ p Project No. GSO49O6-120 Below Footings Flg,6 NOTË; DRAIN SHOULD BE AT LEAST 2 INCHES BELOW BOTTOM OF FOOTING AT THT HIGHEST POINT AND SLOPE DOWNWARD TO A POSITIVT GRAVITY OUTLfi OR TO A SUMP WHERE WATËR CAN BE REMOVED BY PUMPING. sr_oPE BELOW GRADE WALL PROVIDI PVC SHTilING GLUTD TO FOUNDATION WALL TO REDUCE MOISTURE PINT|RAÏON. REINFORCED STEEL PIR STRUCTURAL DRAWINGS SLOPE PER OSHA ENCASE PIPE lN WASHED CCINCRETE ACGREGATE (ASTM c53, NO. s7 0R NO. 67) EXTEND GRAVI TO AT LEASÏ 1/2 HîlGHr or FoorlNG I\ ror*r,rr ---- ICOMPOSIrION AND \ òoupncro¡r p¡R nEponD\ COVER GRAVEL WITH FILTER FABRIC MINIMUM 8" MINIMUM OR BEYOND 1:1 SLOPË FROM BCITTOM OF FOOTING, {wHtcHEVER lS GREATER) EOTTOM OF EXCAVATIÖN PVC DRAIN PIPE NETWORK IMBEDDED CRAI#L I t) J IN WASHED CONCRII-T AGGRIGATE 4-INCH DIAMETER PTRFORATED DRAJN PIPE. THE PIPE SHOULD BT PI-ACED IN A TRENCH WiÏH A sLoPE RANGE BETWEEN 1/8 INCH AND 1/4 |NCH DROP PtR FOOT OF DRAIN. êu .l ¡ .ç Ê Exterlor Foundation Wall Drain SUPFORTED $totE ro oR¡,¡N Project No. GSO4906-1 20 Flg.7 TABLE ISUMMARY OF LABORATORY TEST RESULTSPROJECT NO. GS04906-120SOIL CLASSIFICATIONSAND. SILry iSMìGRAVEL. CLAYEY, SILTY (GC-GM)SAND, SILTY (SM)PAliT'INGNO.200SIËVE('/")33'N TESTSPËRCENTSAND(o/ot¿ôGRADATI(PERCENTGRAVEL(o/o\41:RG LIMITSPLASTICITYINOEX(%\ATTËRBLIAUIDLIMIT(%jSWELL-(d/o\-1 .4-2.4NATURALDRYDENSITY(PCF)t170NATURALMOISTURË(a/o)10.18.310.9DEPTI.I(FEET)10-l 14BORINGI t -1TP-1TP.2'Note: swell due to wetting under en applied load of 1,00o psf" Negative values ¡ndicate consôlidationPage 1 of 1