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HomeMy WebLinkAboutSoils Report 11.05.2007CTL !TI- OMPSON SOILS AND FOUNDATION INVESTIGATION AUSTIN RESIDENCE LOT 57, FOUR MILE RANCH GARFIELD COUNTY, COLORADO Prepared For: MR. BILL AUSTIN 750 Canyon Creek Drive Glenwood Springs, CO 81601 Project No. G505101-120 November 5, 2007 234 Center Drive !Glenwood Springs, Colorado 81601 Telephone: 970-945-2809 Fax: 970-945-7411 TABLE OF CONTENTS SCOPE 1 SUMMARY OF CONCLUSIONS 1 SITE CONDITIONS 2 PROPOSED CONSTRUCTION 2 SUBSURFACE CONDITIONS 2 EARTHWORK 3 FOUNDATION 4 FLOOR SYSTEM AND SLABS -ON -GRADE 5 BELOW -GRADE CONSTRUCTION 6 SURFACE DRAINAGE 8 LIMITATIONS g FIGURE 1 - APPROXIMATE LOCATIONS OF EXPLORATORY BORINGS FIGURE 2 - SUMMARY LOGS OF EXPLORATORY BORINGS FIGURES 3 THROUGH 6 - SWELL -CONSOLIDATION TEST RESULTS FIGURES 6 AND 7 - EXTERIOR FOUNDATION WALL DRAINS TABLE I - SUMMARY OF LABORATORY TEST RESULTS MR. BILL AUSTIN LOT 57, FOUR MILE RANCH CTLIT PROJECT NOt OS05101-120 S:10505101.000112012. ReportaG3805101 120 R1.doc SCOPE This report presents the results of our soils and foundation investigation for the Austin Residence proposed on Lot 57, Four Mile Ranch in Garfield County, Colorado. We conducted this investigation to evaluate subsurface conditions at the site and provide foundation recommendations for the proposed construction. Our report was prepared from data developed from exploratory borings, laboratory testing, engineering analysis and our experience with similar conditions and construction. This report includes a description of the subsurface conditions at the site, and presents recommendations for design and construction of foundations, floor systems, and criteria for details influenced by the subsoils. Construction plans were not developed at the time of our investigation. If actual building 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. SUMMARY OF CONCLUSIONS 1. Subsurface conditions encountered in our exploratory borings consisted of about 11 feet of sandy clay underlain by silty to clayey gravel with cobbles and lenses of sand and clay. Practical auger refusal occurred on cobbles in our borings at a depth of about 15 feet. Free ground water was not observed in our exploratory borings at the time of drilling. 2. The residence can be constructed on footing foundations with a minimum deadload that are supported by the undisturbed, natural soils. The soils at anticipated footing elevations exhibit a low swell potential. The most positive foundation to resist swelling soils is drilled piers. We can provide criteria for drilled piers, if requested. Care should be taken to prevent significant wetting of the soils below the building. Design and construction criteria for footings are presented in the report. 3. We judge potential for differential movement will be low for slabs -on - grade supported by the undisturbed, natural soils. If the supporting soils are wetted some slab heave and cracking will likely occur. Additional discussion is in the report. MR. BILL AUSTIN LOT 57, FOUR MILE RANCH CTLIT PROJECT NO. GS05101-120 S:IG505101.000%12012. Reports1GS05101 120 R1.doc 1 4. Surface drainage should be designed to provide for rapid removal of surface water away from the residence. A foundation drain should be installed around below -grade areas in the building. SITE CONDITIONS Four Mile Ranch is located east of County Road 117 (Four Mile Road) in Garfield County, Colorado. Lot 57 is west of the intersection of Red Cliff Circle and Sunrise Circle. Ground surface on the lot generally slopes gently at grades less than 5 percent. Vegetation on the lot consists of sparse grasses and weeds. PROPOSED CONSTRUCTION Building plans for the residence were not developed at the time of our investigation. If construction will differ significantly from the descriptions below, we should be informed so that we can adjust our recommendations and design criteria as necessary. We expect the proposed residence will be a two-story, wood -frame building with an attached garage. A basement and/or crawl space may be constructed below the building. Similar residences in the area are typically constructed with slab -on -grade floors in basement and garage areas. Maximum foundation excavation depths will likely be on the order of 7 to 9 feet if a basement is constructed. 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. Completed wall backfill depth may be slightly more than excavation depth as final grades are adjusted for drainage. SUBSURFACE CONDITIONS Subsurface conditions at the site were investigated by drilling two exploratory borings (TH-1 and TH-2) in the building envelope. The approximate locations of the exploratory borings are shown on Figure 1. Exploratory drilling operations were directed by our representative who logged subsurface conditions encountered in the MR. BILL AUSTIN LOT 57, FOUR MILE RANCH CTLIT PROJECT NO. GS05101.120 S_IGSD5101.000112012. Reports1GS05101 120 R1.doc 2 borings and obtained samples of the soils. Graphic Togs of the soils encountered in our exploratory borings are shown on Figure 2. Subsurface conditions encountered in our exploratory borings consisted of about 11 feet of sandy clay underlain by silty to clayey gravel with cobbles and lenses of sand and clay. Practical auger refusal occurred on cobbles in our borings at a depth of about 15 feet. Observations during drilling operations and results of field penetration resistance tests indicated the clay was very stiff and the gravel was dense. Free ground water was not observed in our exploratory borings at the time of drilling. Exploratory borings were backfilled immediately after our field investigation was completed. Samples of the soils obtained from our exploratory borings were selected for laboratory testing. Three samples of clay selected for one-dimensional, swell - consolidation testing exhibited low swell potential when wetted under an applied pressure of 1,000 psf. Swell -consolidation test results are shown Figures 3 through 5 and laboratory test results are summarized on Table I. EARTHWORK 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 soils at this site will generally classify as Type B and Type C soils based on OSHA standards governing excavations. Temporary slopes deeper than 5 feet should be no steeper than 1 to 1 (horizontal to vertical) in Type B soils and 1.5 to 1 in Type C soils. Contractors should identify the soils encountered in the excavations and refer to OSHA standards to determine appropriate slopes. We do not anticipate excavations for foundations or utilities will encounter significant amounts of ground water. However, excavations should be sloped to a gravity discharge or to a temporary sump where water can be removed by pumping. MR. BILL AUSTIN LOT 57, FOUR MILE RANCH CTLIT PROJECT MO. GS05101.12O S:1GS05101.000112012. Rnport51GS05101 120 R1.doc 3 Ir The ground surrounding the excavations should be sloped as much as practical to direct runoff away from the excavations. Fill may be required to obtain subgrade elevations for the garage floor and exterior concrete flatwork. Areas which will receive fill should be stripped of vegetation, organic soils and debris. The on-site soils free of rocks larger than 6 inches in diameter, organic matter, and debris are suitable for use as fill. Fill should be placed in loose lifts of 10 inches thick or less, 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. Moisture content and density of fill should be checked by a representative of our firm during placement. Properly placed backfill adjacent to foundation wall exteriors is important to reduce infiltration of surface water and subsequent consolidation. Backfill placed adjacent to foundation wall exteriors should be free of organic matter, debris and rocks larger than 6 inches in diameter. Backfill should be moisture conditioned to within 2 percent of optimum moisture content and compacted to at least 96 percent of standard Proctor (ASTM D 698) maximum dry density. FOUNDATION We understand a footing foundation is preferred by the client. The clay soils below the building footprint exhibit a low swell potential. Footing foundations with a minimum Toad supported by the undisturbed, natural clay are appropriate. It is important that surface drainage and subsurface drainage recommendations are followed. If the clay moisture increases significantly the soils will heave and move footings. The most positive foundation to resist swelling soils is drilled piers. We can provide criteria for drilled piers, if requested. Care should be taken to prevent significant wetting of the soils below the building. Our representative should be called to observe conditions exposed in the completed foundation excavation to check that the exposed soils are suitable for support of the designed footings. Recommended design and construction criteria for footings are presented below. MR. BILL AUSTIN LOT 57, FOUR MILE RANCH CTLIT PROJECT NO. GS05101.120 5:1GS05101.000112012 Reports1GS05101 120 R1.doc 4 1. Footings supported by the natural soils should be designed for a maximum allowable soil bearing pressure of 3,000 psf and a minimum deadload of 800 psf or as high as practical. Soils loosened during excavation or the forming process for the footings should be removed or re -compacted prior to placing concrete. 2. Continuous wall footings should have a minimum 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. 3. Grade beams and foundation walls should be well reinforced, top and • bottom, to span undisclosed loose or soft soil pockets. We recommend reinforcement sufficient to span an unsupported distance of at least 12 feet. Reinforcement should be designed by the structural engineer. 4. The soils beneath exterior 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 frost protection. FLOOR SYSTEM AND SLABS -ON -GRADE Similar residences in the area are typically constructed with slab -on -grade floors in garage and basement areas. Based on our laboratory test data and experience, we judge slab -on -grade construction can be supported by the undisturbed, natural soils with low risk of differential movement and associated damage. As stated recommendations regarding surface and subsurface drainage to reduce wetting below the slabs is important. Some fill may be required below the garage floor slab and exterior concrete flatwork. Fill should be in accordance with the recommendations outlined in the EARTHWORK section. We recommend the following precautions for slab -on -grade construction at this site. 1. We recommend against placing a gravel or sand layer below slabs because it increases the potential for wetting of the soils below the slabs. g"=. __ _L AUSTIN -. FOUR MILE RANCH =ROJECT NO. G505101-120 •_Z _'.01.0 0 0112012. Report51GS05101 120 R1.doc 5 2. Slabs should be separated from exterior walls and interior tea-:-; members with slip joints which allow free vertical movement slabs. 3. Underslab plumbing should be pressure tested for leaks befa- - =T slabs are constructed. Plumbing and utilities which pass throw:- s.ad_ should be isolated from the slabs with sleeves and provided flexible couplings to slab supported appliances. 4. Exterior patio and porch slabs should be isolated from the res,c _ - :- These slabs should be well -reinforced to function as independer:: z 5. Frequent control joints should be provided, in accordance �. American Concrete Institute (ACI) recommendations. to r=z.-_- problems associated with shrinkage and curling. Our expert_--__ indicates panels which are approximately square generally per=_ -- better than rectangular areas. 6. The 2003 International Building Code (IBC) or 2003 Interra:-a Residential Code (IRC) may require a vapor retarder be placed ba -o* e= - the base course or subgrade soils and the concrete slab-on-o-e:e floors. The merits of installation of a vapor retarder below floor s =_s and PT slabs depend on the sensitivity of floor coverings and to moisture. A properly installed vapor retarder (10 mil miniri -- more beneficial below concrete slab -on -grade floors where = = coverings, painted floor surfaces or products stored on the floc:- sensitive to moisture. The vapor retarder is most effective n -e- concrete _- concrete is placed directly on top of it. A sand or gravel leveling _c --._ should not be placed between the vapor retarder and the floor s __ The placement of concrete on the vapor retarder may increase t --e. -s • of shrinkage cracking and curling. Use of concrete with re:_:== shrinkage characteristics including minimized water cc-:= = maximized coarse aggregate content, and reasonably low slur--~ reduce the risk of shrinkage cracking and curling. Consideratiors recommendations for the installation of vapor retarders below cc- slabs are outlined in Section 3.2.3 of the 2003 report of Arne- _ Concrete Institute (ACI) Committee 302, "Guide for Concrete Slab Construction (ACI 302.R-96)". BELOW -GRADE CONSTRUCTION Foundation walls which extend below -grade should be designed ft; earth pressures where backfill is not present to about the same extent on be:- s of the wall. Many factors affect the values of the design lateral earth pressure. `-_:e factors include, but are not limited to, the type, compaction, slope and drainage MR. BILL AUSTIN LOT 57, FOUR MILE RANCH CTLIT PROJECT NO. GS05101-120 S:IGS05101.000%12012. Reports1GS05101 120 R1.doc backfill, and the rigidity 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 that typical basement walls can deflector rotate slightly under normal design loads, and that this deflection results in satisfactory wall performance. Thus, the earth pressures on the walls will likely be between the "active" and "at -rest" conditions. If the on-site soils are used as backfill, we recommend design of below -grade walls using an equivalent fluid density of at least 45 pcf for this site. This equivalent density does not include allowances for sloping backfill, surcharges or hydrostatic pressures. The recommended equivalent density assumes deflection; some minor cracking of walls may occur. If very little wall deflection is desired, a higher equivalent fluid density may be appropriate for design. Our recent experience indicates most basement and below -grade walls designed with 45 pcf to 50 pcf equivalent fluid density have performed satisfactorily. Backfill should be placed and compacted in accordance with the recommendations outlined in the EARTHWORK 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 wetting of the soils below the building and wet or moist conditions in basement and crawl space areas after construction. We recommend provision of a foundation drain around below -grade areas in the building. The drain should consist of a 4 -inch diameter, slotted PVC pipe encased in free draining gravel. The drain should lead to a positive gravity outfall, or to a sump pit where water can be removed by pumping. Typical foundation drain details are presented on Figures 6 and 7. Ventilation is important to maintain acceptable humidity levels in crawl spaces. The mechanical systems designer should consider the humidity and temperature of x= SILL AUSTIN __7 57, FOUR MILE RANCH PROJECT NO.,GS05101-120 3505101.000112012. RaportstGS05101 120 R1.doc 7 air, and air flow volumes, during design of crawl space ventilation systems. It may be appropriate to install a ventilation system that is controlled by a humidistat. SURFACE DRAINAGE Surface drainage is critical to the performance of foundations, floor slabs and concrete flatwork. We recommend the following precautions be observed during construction and maintained at all times after the residence is completed: 1. •The ground surface surrounding the exterior of the residence should be sloped to drain away from the residence in all directions. We recommend providing a slope of at least 12 inches in the first 10 feet around the residence, where possible. In no case should the slope be less than 6 inches in the first 5 feet. 2. Backfill around the exterior of foundation walls should be placed in maximum 10 inch thick loose lifts, 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. 3. The residence should be provided with roof gutters and downspouts. Roof downspouts and drains should discharge well beyond the limits of all backfill. Splash 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. 5. Impervious 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 borings drilled at the site provide a reasonably accurate picture of subsurface conditions. Variations in the subsurface conditions not MR. BILL AUSTIN LOT 57, FOUR MILE RANCH OTLIT PROJECT NO,. GS05101-120 S.tGS05101.000112012. ReportslGS06101 120 R1.doc 8 2 indicated by the borings will occur. A representative of our firm should be called to observe subsoils exposed in the completed foundation excavation to check that the soil are as anticipated and suitable for support of the footings as designed. This investigation was conducted in a manner consistent with that level of care and skill ordinarily exercised by engineering geologists and geotechnical engineers currently practicing under similar conditions in the locality of this project. No other warranty, express,- ar implied, is made. If we can be of further service in discussing the contents of this report or in the analysis of the influence of the subsoil conditions on the design•of the structure, please call. CTL 1ITHi}MPSON, INC. John Nipching, P.E. BranchiVlari�ir JM:cd 11 i1 (5 copies sent) MR. BILL AUSTIN LOT 57, FOUR MILE RANCH CTLIT PROJECT NO: GS05101-120 S::0505101.000%12012. Reporte1GS05101 120 R1.doc 9 NOT TO SCALE Lot 51 Lot 24 8 C/ �. Lot 23 Lot 4 Lot 5 Lot 6 Mr. 8111 Austin Austin Residence Lot 51,Four We Ranch Project No. G605101-120 Lot 7 Lot 10 Approximate Locations of Exploratory Borings Fig. 1 Project No. 0S05101-120 10 13 20 TH-1 17/12 16/12 29/4 TH-2 1 9/1 2 17/12 50/9 SUMMARY Lf mmN 20 LEGEND: NOTES: Clay, sandy, very stiff, moist, brown. (CL) Growl, silty to clayey, cobbles, lenses of sand and clay, dense, moist, rust, brown. (GC—GM, GM, SM, CL—ML) Drive sample. The symbol 17/12 Indicates that 17 blows of a 140 pound hammer falling 30 inches were required to drive a 2.5 inch 0.D. California sampler 12 inches. Indicates practical auger refusal. 1. Exploratory borings were drilled on October 17, 2007 with 4—inch diameter, solid—stem auger and a track—mounted drill rig. Exploratory borings were backfilled immediately after drilling operations were completed. 2. Locations and elevations of exploratory borings are approximate. 3. No free ground water was found in our exploratory borings at the time of drilling. 4. These exploratory borings are subject to the explanations, limitations and conclusions as contained in this report. 3 OF EXPLORATORY BORINGS Fig. 2 7 6 5 4 3 2 0 -1 -2 -3 z O -4 a. X -5 !l1 z O -6 vi F� w 0- -• 7 2 0 U } .1 .4. EXPANSION UNDER CONSTANT . PRESSURE DUE TO WETTING »l}_,_1 -1••4 I. 7 1 _ 0 0 0 1.•.-T.. s I. f 1 • ........ .........1.......... Y .... 1..... ISS . 0.1 APPLIED PRESSURE - KSF Sample of CLAY (CL) =rom TH-1 AT 9 FEET 1.0 ' . AUSTIN TIN RESIDENCE •LJECT NO. GS 6101 uclmenb and SeltlngsljmecMInggMy DocumemMMBWELLxIs 10 10C DRY UNIT WEIGHT= 105 PCF MOISTURE CONTENT= 11.7 % Swell Consolidation Test Results FIG- 3 7 6 5 4 3 2 0 .1 -2 -3 z O -4 z a 6 -5 z • .6 w N w a -• 7 2 0 V -B 0.1 4 • .S.• EXPANSION UNDER CONSTANT PRESSURE DUE TO WETTING i -4..• - • 1 n APPLIED PRESSURE - KSF Sample of CLAY (CL) From TH-2 AT 4 FEET 1.0 BILL AUSTIN AUSTIN RESIDENCE PROJECT NO. GS 5101 C:lDoeumcnb and SatingsVmechling%My DocumentstSWELLxIs 10 DRY UNIT WEIGHT= MOISTURE CONTENT= 100 116 PCF 13.4 % Swell Consolidation Test Results FIG. 4 SLOPE PER OSHA SLOPE pFR RFPlR't 2-3' BACKFILL i MOM PREFABRICATED DRAINAGE COMPOSITE (MIRADRAIN 6000 OR EQUIVALENT) COVER GRAVEL WITH FILTER FABRIC Y NOTE: DRAIN SHOULD BE AT LEAST 2 INCHES BELOW BOTTOM OF FOOTING AT THE HIGHEST POINT AND SLOPE DOWNWARD TO A POSMVE GRAVITY OUTLET OR TO A SUMP WHERE WATER CAN BE REMOVED BY PUMPING. PROVIDE POLYETHYLENE SHEETING GLUED TO FOUNDATION WALL TO REDUCE MOISTURE PENETRATION BELOW GRADE WALL REINFORCING STEEL PER STRUCTURAL DRAWINGS PROVIDE POSITIVE SUP JOINT BETWEEN SLAB AND WALL FLOOR SLAB • aim �v mom 2" MINIMUM 8" MINIMUM OR BEYOND 1:1 SLOPE FROM BOTTOM OF FOOTING. (WHICHEVER IS GREATER) FOOTING OR PAD 4—INCH DIAMETER PERFORATED DRAIN PIPE. THE PIPE SHOULD BE LAID IN A TRENCH WITH A SLOPE RANGING BETWEEN 1/8 INCH AND 1/4 INCH DROP PER FOOT OF DRAIN. ENCASE PIPE IN WASHED CONCRETE AGGREGATE (ASTM C33. NO. 57 OR NO. 67). EXTEND GRAVEL TO AT LEAST 1/2 HEIGHT OF FOOTING. 'roject No. GS05101-120 Exterior Foundation Wall Drain SLOPE PER OSHA SLOPE FIF IZ RF'PORT 2-3' BACKFILL {aiposmw AND compAcnom PER REPOIMA PREFABRICATED -. DRAINAGE COMPOSITE (MIRADRAIN 6000 OR EQUIVALENT) COVER GRAVEL WITH RLTER FABRIC NOTE: DRAIN SHOULD BE AT LEAST 2 INCHES BELOW BOTTOM OF FOOTING AT THE HIGHEST POINT AND SLOPE DOWNWARD TO A POSITIVE GRAVITY OUTLET OR TO A SUMP WHERE WATER CAN BE REMOVED BY PUMPING. STRUCTURALLY SUPPORTED FLOOR REINFORCING STEEL ER STRUCTURAL DRAWINGS WM TO OM 2" MINIMUM 8" MINIMUM — OR BEYOND 1:1 SLOPE FROM BOTTOM OF FOOTING. (WHICHEVER IS GREATER) CRAWL SPACE BOTTOM OF EXCAVATION PROVIDE POLYETHYLENE SHEETING GLUED TO FOUNDATION WALL TO REDUCE MOISTURE PENETRATION 4–INCH DIAMETER PERFORATED DRAIN PIPE. THE PIPE SHOULD BE LAID IN A TRENCH WITH A SLOPE RANGING BETWEEN 1/8 INCH AND 1/4 INCH DROP PER FOOT OF DRAIN. ENCASE PIPE IN WASHED CONCRETE AGGREGATE (ASTM C33, NO. 57 OR NO. 67). EXTEND GRAVEL TO AT LEAST 1/2 HEIGHT OF FOOTING. ±-oject No. 3505101-120 Exterior Foundation Wall Drain Fig. 7 PriOJCCT'NO. US0f101..i25 SUMMARY OF LABORATORY TEST RESULTS 0 BORING DEPTH (FEET) NATURAL MOISTURE (°t) NATURAL DRY DENSITY (PCF) SWELL" (%) ATTERBERG LIMITS GRADATION TESTS ' UNCONFINED COMPRESSION (PCF) PASSING NO. 200 SIEVE (%) SOIL CLASSIFICATION LIQUID LIMIT (%) PLASTICITY INDEX (%) PERCENT GRAVEL (%) PERCENT SAND (%) TH-1 4 11.1 106 CLAY,SANDY (CL) TH-1 9 11.7 105 0.7 CLAY,SANDY (CL) TH-1 14 7.5 95 53 CLAY,SANDY (CL) TH-2 4 13.4 116 0.9 CLAY,SANDY (CL) TH-2 9 14.4 118 0.7 CLAY,SANDY (CL) r Y "Nr,i.r fwr,fl dim lo wnttina unednr an implied Toad of 1.000 psf Negative values indicate consolidation I %lip. I id I