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HomeMy WebLinkAboutSoils report 12.05.2012CTLITHOMPSON SOILS AND FOUNDATION INVESTIGATION LOTS 29 AND 30, ROARING FORK MESA ASPEN GLEN GARFIELD COUNTY, COLORADO Prepared For: PAUL GOLDSTEIN 5418 Oak Canopy Way Ft. Lauderdale, FL 33312 Project No. GS05714-120 December 5, 2012 TABLE OF CONTENTS SCOPE 1 SUMMARY OF CONCLUSIONS 1 SITE CONDITIONS 2 PROPOSED CONSTRUCTION 3 SUBSURFACE CONDITIONS 3 SITE GEOLOGY 4 GEOLOGIC HAZARDS 4 SITE EARTHWORK 6 Structural Fill 6 BACKFILL COMPACTION 7 FOUNDATION 8 Post -Tensioned Slab -on -Grade 8 Mat Foundation 10 Footings on Structural Fill 10 FLOOR SYSTEM AND SLABS -ON -GRADE 11 BELOW -GRADE CONSTRUCTION 12 SUBSURFACE DRAINAGE 13 SURFACE DRAINAGE 13 CONCRETE 14 CONSTRUCTION OBSERVATIONS 15 GEOTECHNICAL RISK 15 LIMITATIONS 16 FIGURE 1 — VICINITY MAP FIGURE 2 - LOCATIONS OF EXPLORATORY BORINGS AND PITS FIGURES 3 AND 4 — SUMMARY LOGS OF EXPLORATORY BORINGS AND PITS FIGURE 5 — SWELL -CONSOLIDATION TEST RESULTS FIGURE 6 — EXTERIOR FOUNDATION WALL DRAIN DETAILS TABLE I — SUMMARY OF LABORATORY TESTING PAUL GOLDSTEIN LOTS 29 & 39, ROARING FORK MESA PROJECT NO. GS05714.120 S:1GS05714.000112042. Reports10505714 120 R1.doc SCOPE This report presents the results of our soils and foundation investigation for the proposed residence on Lots 29 and 30, Roaring Fork Mesa in Aspen Glen in Garfield County, Colorado. We conducted this investigation to evaluate subsurface conditions at the site and provide geotechnical engineering recommendations for the proposed construction. We previously conducted a soils and foundation investigation on Lot 29 (CTL Project No. GS05063-120, dated September 12, 2007). Our report was prepared from data developed during our field exploration and a previous investigation on Lot 29, engineering analysis, and our experience with similar conditions. This report includes a description of the subsurface conditions observed in our exploratory borings and pits and presents geotechnical engineering recommendations for design and construction of the foundation, floor system, below - grade wails, drain system, and details influenced by the subsoils. Recommendations contained in this report were developed based on our understanding of the planned construction. If plans differ significantly from the descriptions contained in the report, we should be informed so that we can provide geotechnical engineering input and check that our recommendations and design criteria are appropriate. A summary of our conclusions is presented below. SUMMARY OF CONCLUSIONS 1. Subsurface conditions encountered in our exploratory borings and pits varied significantly. Subsurface conditions encountered in our exploratory borings and pits consisted of about 0.5 to 1 foot of sandy clay "topsoil" and silty sand or silty to clean gravel to the total explored depth of 25 feet. The silty sand was encountered from about 3 to 9.5 feet in TP -1 and 1 to 4 feet in TP -2. The silty sand was encountered from about 0.5 to 4 feet in TH-3 and 8 to 12 feet and 18 to 25 feet in TH-2. Practical auger refusal occurred at multiple depths in TH-1 and TH-3. Foundation and floor construction needs to consider the non-uniform soils at the site. Free ground water was not observed in the exploratory pits at the time of excavation or the borings at the time of drilling. PAUL GOLDSTEIN LOTS 29 & 30, ROARING FORK MESA PROJECT NO. GS05714-120 S:1GS05714.000112012. ReportaGS05714 120 R1.doc 1 2. Differential settlement may occur if foundations are supported by the different types of soils found on the lots. We recommend subexcavation and replacement with structural fill to a depth of at least 5 feet below footings and replacement with structural fill. The potential for sinkhole formation exists on this lot. We judge that the risk to structures from sinkhole formation is low to moderate on this lot. A positive foundation alternative on this lot to reduce the potential for damage to the residence if a sinkhole forms is a structural mat (raft) foundation or a post -tensioned slab -on -grade foundation supported on at least 3 feet of structural fill or the natural gravel. A micropile foundation system Is also a positive alternative. These types of foundations are also less susceptible to damage from differential movement. Design and construction criteria for foundations are presented in the report. 3. We judge potential differential movement of slabs -on -grade supported by the undisturbed, natural gravel will be low. We recommend removal of sand or clay soils to a depth of at least 3 feet below slabs -on -grade and replacement with granular structural fill. Additional discussion is in the report. 4. It is critical that surface drainage be designed to provide for rapid removal of surface water away from the residence. Foundation wall drains should be provided around below -grade areas of the residence. SITE CONDITIONS Aspen Glen is located west of Highway 82 between Glenwood Springs and Carbondale in Garfield County, Colorado (see Figure 1). Roaring Fork Mesa is located near the center of the development northeast of County Road 109. Lots 29 and 30 are east of Royal Coachman (see Figure 2). A drainage that was dry at the time of our investigation is north of the lot. The Aspen Glen golf course driving range is to the north and residential lots are to the east and south. Ground surface on the Tots drop down to the north at grades of about 5 percent. Vegetation on the lot consists of sparse grass and weeds. PAUL GOLDSTEIN LOTS 29 & 30, ROARING FORK MESA PROJECT NO. GS05714-120 S:4505714.000112012, Repor1slG505714 120 R1.d00 2 PROPOSED CONSTRUCTION We expect the residence will be a one or two-story, wood -frame building with an attached garage. A crawl -space below the residence may be provided in living areas. Slab -on -grade floors are likely the desired floor system in the garage. We expect, maximum foundation excavation depths will be about 3 to 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 linear foot of foundation wall with maximum interior column loads of 30 kips. If 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 Subsurface conditions encountered in our exploratory borings and pits varied significantly. Subsurface conditions encountered in our exploratory borings and pits consisted of about 0.5 to 1 foot of sandy clay "topsoil" and silty sand or silty to clean gravel to the total explored depth of 25 feet. The silty sand was encountered from about 3 to 9.5 feet in TP -1 and 1 to 4 feet in TP -2. The silty sand was encountered from about 0.5 to 4 feet in TH-3 and 8 to 12 feet and 18 to 25 feet in TH-2. Practical auger refusal occurred at multiple depths in TH-1 and TH-3. Foundation and floor construction needs to consider the non-uniform soils at the site. Free ground water was not observed in the exploratory pits at the time of excavation or the borings at the time of drilling. Subsurface conditions encountered in the borings and pits were logged by our field representative who obtained samples of the soils encountered in our exploratory borings and pits. Graphic logs of the soils observed in the exploratory borings and pits are shown on Figures 3 and 4. Our observations during excavation indicated the sand was loose to medium dense and the gravel was dense to very dense. The PAUL GOLDSTEIN LOTS 29 & 30, ROARING FORK MESA PROJECT NO. GS05714.120 S:5GS05714AQ9112912, IR poAs1GS05714 120 R1.doc 3 borings and pits were backfilled immediately after drilling and excavation operations were completed. Samples obtained in the field were returned to our laboratory where field classifications were checked and samples were selected for pertinent testing. Two samples of the gravel contained 8 and 22 percent silt and clay sized particles (passing the No. 200 sieve). Gradation test results exclude cobbles and boulders. Samples of the silty sand contained 40 to 45 percent silt and clay sized particles and exhibited a liquid limit 19 and a plasticity index of 2. A sample of the silty sand selected for swell - consolidation testing exhibited 2.2 percent compression when wetted under an applied pressure of 1,000 psf. Swell -consolidation test results are shown on Figure 5. Laboratory test results are summarized on Table I. SITE GEOLOGY The geology of the site was evaluated using our in-house collection of geologic maps (Geologic Map of the Cattle Creek Quadrangle, Garfield County, Colorado by Kirkham et. al., 1996). We interpret the surficial soils of the site as younger debris flow and colluvium deposits underlain by the Eagle Valley Formation. We did not encounter bedrock in our borings and pits. The subsurface conditions observed in our borings and pits are consistent with the mapping we reviewed. GEOLOGIC HAZARDS Colorado is a challenging location to practice geotechnical engineering. The climate is relatively dry and the near -surface soils are typically dry and relatively stiff. These soils and related sedimentary bedrock formations tend to react to changes in moisture conditions. Some of the soils swell as they increase in moisture and are called expansive soils. Other soils can settle significantly upon wetting and are referred to as collapsing soils. Most of the land available for development east of the PAUL GOLDSTEIN LOTS 29 & 30, ROARING FORK MESA PROJECT N0. GS05714-120 5010505714.000112012. Roports1GS05714 120 111.doe 4 Front Range is underlain by expansive clay or claystone bedrock near the surface. The soils that exhibit collapse potential are more common west of the continental divide; however, both types of soils occur all over the state. Covering the ground with houses, streets, driveways, patios, etc., coupled with lawn Irrigation and changing drainage patterns, leads to an increase in subsurface moisture conditions. As a result, some soil movement is inevitable. It is critical that all recommendations in this report are followed to increase the chances that the foundations and slabs -on -grade will perform satisfactorily. After construction, owners must assume responsibility for maintaining the structure and use appropriate practices regarding drainage and landscaping. Some increase in subsurface moisture must be assumed due to the effects of site development. We compared moisture content and dry density from a sample from the site to collapse potential based on a rating system described in "Engineering Geology 14, Collapsible Soils in Colorado". Based on the rating system, the soils exhibit moderate to high collapse potential. A sample tested in our laboratory exhibited moderate collapse when wetted under loads of 1,000 psf. Based on our experience in the area, laboratory testing and published data, we consider the upper soils at this site to have collapse potential. Engineered design of foundations, slabs - on -grade, pavements and surface drainage can mitigate the effects of collapse -prone soils. Lots 29 and 30 of Roaring Fork Mesa are located on a young debris -flow alluvial fan over Eagle Valley bedrock. The Colorado Geologic Survey has mapped sinkhole, subsidence and soli -collapse features and locations in the area near this lot (Collapsible Soils and Evaporite Karst Hazards Map of the Roaring Fork River Corridor, Garfield, Eagle and Pitkin Counties, Colorado by Jonathan L. White, 2002). We did not observe obvious visual evidence of sinkhole/subsidence formations in the immediate area surrounding the lot; however, we judge the lot has a low to moderate potential for sinkhole formation or collapse of the soils due to wetting after construction. PAUL GOLDSTEIN LOTS 29 & 30, ROARING FORK MESA PROJECT NO. GS05714-120 S: SGS05714.000%1201.2. R.por1 1GS05714 120 R1.doc 5 SITE EARTHWORK Based on information from our exploratory borings and pits, we anticipate that the excavation for the proposed residence will be through sand and gravel soils. We anticipate excavation of the soils can be accomplished using conventional, heavy duty excavating equipment. Sides of excavations need to be sloped to meet local, state and federal safety regulations. The silty sand soils may classify as a Type B soil based on OSHA standards governing excavation; the natural gravel will likely classify as Type C soil. Temporary slopes deeper than 4 feet that are not retained should be no steeper than 1 to 1 (horizontal to vertical) in Type B soils or 1.5 to 1 in Type C soils. Excavations into the gravel may encounter boulders and significant amounts of cobbles. Contractors should identify soils encountered and ensure that applicable standards are met. Contractors are responsible for site safety and maintenance of the work site. Free ground water was not observed in the exploratory borings and pits during exploratory operations. 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, if necessary. We should be contacted if ground water is encountered to provide additional permanent subsurface drain recommendations. Structural Fill Excavations for the residence will likely encounter sand and gravel soils at foundation or slab elevations. Differential settlement of the residence is likely if the foundations are supported on different soils. We recommend the sand soils be removed from below the building footprint. As a minimum, we recommend removal of the sand to a depth of at least 3 feet below mat or post -tensioned slab -on -grade foundations and slab -on -grade and replacement with densely compacted, granular PAUL GOLDSTEIN LOTS 29 & 30, ROARING FORK MESA PROJECT NO. GS05714.120 S:\GS05714.0001120V2. Raparls1GS05714 120 R1.dac 6 structural fill. We recommend subexcavation of the sand and gravel to a depth of 5 feet below footings and replacement with structural fill. Areas which will receive fill should be stripped of vegetation, organic soils and debris. We recommend structural fill consisting of imported COOT Class 6 aggregate base course or similar soil. Structural fill should be placed in loose lifts of 10 inches thick or less and moisture conditioned to within 2 percent of optimum moisture content. Structural fill should be compacted to 100 percent of ASTM D 698 maximum dry density. Moisture content and density of structural fill should be checked by a representative of our firm during placement. BACKFILL COMPACTION We recommend foundation wall backfill be placed and compacted to reduce settlement. However, compaction of the backfill soils adjacent to concrete walls may result in cracking of the wall. The potential for cracking can vary widely based on many factors including the degree of compaction achieved, the weight and type of compaction equipment utilized, the structural design of the wall, the strength of the concrete at the time of backfill compaction, and the presence of temporary or permanent bracing. Our experience indicates wall backfill soils that have been moisture conditioned to within 2 percent of optimum moisture content and compacted to at least 90 percent of maximum standard Proctor dry density (ASTM D 698) are typically sufficiently dense to reduce settlement. Compacting the backfill soils to higher density increases the risk of cracking the concrete wail. Particles in excess of 3 inches in diameter should be excluded from the backfill soils. Frost or frozen soils should not be used for backfill. PAUL GOLDSTEIN LOTS 29 & 30, ROARING FORK MESA PROJECT NO. GS95714.120 5:56505714.0 0 01120l2. ReporlslG005714 120 111.doc 7 FOUNDATION Our exploratory borings and pits indicate that natural gravel with cobbles and boulders and sand are present at anticipated foundation elevations for the proposed residence. The silty sand soils have the potential to collapse when wetted. The natural soils on this site are underlain by Eagle Valley Formation bedrock. The potential for subsurface voids and related sinkholes exists on the site. We did not observe evidence of sinkholes on the site. We judge that the risk of foundation damage from sinkholes on this site is low to moderate. Due to the variable soils, geologic setting, and the risk of sinkhole formation, we recommend that the residence be supported on a post -tensioned slab or mat (raft) foundation system. A post - tensioned slab or mat foundation system may allow mitigation of distress from a sinkhole prior to extensive structural damage. These foundations also reduce the potential for building damages from differential movement. A micropile foundation system is another positive alternative. We will provide recommendations for micropiles, if requested. Footings supported on a minimum thickness of 5 feet of granular structural fill are an option, if the owner is willing to accept the increased risk of movement. Our representative should be called to observe conditions exposed in the completed foundation excavation to confirm that the exposed soils are as anticipated and suitable for support of the foundation as designed. Our experience indicates that maximum total settlement will be 1 inch and differential settlement about 3/4 inch for footings constructed on structural fill. We would anticipate about one-half as much movement for a post -tensioned slab or mat foundation. Recommended design and construction criteria for post -tensioned slabs and a mat (raft) foundation are presented below. Post -Tensioned Slab -on -Grade The post -tensioned, slab -on -grade foundation may be constructed on the undisturbed, natural gravel soils. The silty sand should be removed to a depth of at least 3 feet and replaced with structural fill. If soft or PAUL GOLDSTEIN LOTS 29 & 30, ROARING FORK MESA PROJECT NO, G905114-120 S:4GS05744..000\120\2. Roporls5GR05714 120 R1.dos 8 loose soils are exposed in excavations, the soft soils should be removed and recompacted to at least 100 percent of standard Proctor maximum dry density (ASTM D 698) within 2 percent of optimum moisture content prior to placing concrete. 2. The foundations should be designed for a maximum allowable soil pressure of 1,500 psf. 3. Based on our subsurface information and assuming a depth of 3 feet for stiffening beams, we estimate the total settlement in the center of the building may be 3/4 inch. Our experience indicates differential settlement between the center and the edges may be 0.5 inches. The structural engineer should consider designing the slab to bridge voids in the event a sinkhole forms. 4. We understand the PTI design method assumes the slab is somewhat flexible. Some above -grade construction is not as flexible, such as drywall and brick or stucco. We are aware of situations where minor differential slab movement has caused distress in finish materials. One way to enhance performance would be to place reinforcing steel in the bottom of stiffening beams. The structural engineer should evaluate the merits of this approach and other potential alternatives. 5. Soils may cave or slough during trench excavation for the stiffening beams. Disturbed soils should be removed from trench bottoms prior to placement of concrete. Formwork or other methods may be required for proper stiffening beam installation. 6. Exterior stiffening beams must be protected from frost action. Normally 36 inches of frost cover is assumed in the area. The Garfield County Building Department should be consulted regarding required frost protection depth. 7. For slab tensioning design, a coefficient of friction value of 0.75 or 1.0 can be assumed for slabs on a polyethylene sheeting or a sand layer, respectively. A coefficient of friction of 1 should be used for slabs supported on the natural soils. 8. A representative of our firm should observe the completed foundation excavation. A representative of the structural engineer or our firm should inspect the placement of the reinforcing tendons and reinforcement prior to placing the slabs and beams. 9. Underslab plumbing should be pressure tested before the slab is constructed. PAUL GOLDSTEIN LOTS 29 & 30, ROARING FORK MESA PROJECT NO. GS05714.120 S.1G505714.000112012. Reporjs1G505714 120 R 1.doc 9 Mat Foundation 1. The reinforced concrete mat foundation can be constructed on the undisturbed gravel soils. Silty sand soil should be removed to a depth of at least 3 feet and replaced with structural fill. 2. The mat foundation should be designed for a maximum allowable soil pressure of 1,500 psf if constructed on the natural sand and gravel soils. 3. Modulus of subgrade reaction (Ks) is normally used for mat foundation design. The modulus of subgrade reaction is dependent upon the compressibility of the foundation soils and the size (or effective loaded area) of the foundation. If the entire mat foundation is uniformly loaded, then a Ks value of 150 pci should be used for the natural sand and gravel soils. 4. To resist lateral Toads, a coefficient of friction of 0.40 can be used for concrete in contact with the natural sand and gravel soils. Lateral Toads can be resolved by evaluating passive resistance using an equivalent fluid density of 300 pcf for the natural soils, provided the backfill is compacted and is not removed. A moist unit weight of 130 pcf can be assumed for backfill soils. These values have not been factored; appropriate factors of safety should be applied in design. 5. Soil beneath the foundation must be protected from freezing. We recommend the bottom of the foundation be constructed at a depth of at least 36 inches below finished exterior grades. The applicable building department should be consulted regarding required frost depths. Footings on Structural Fill 1. The building can be supported by footing foundations on a minimum 5 foot thickness of densely compacted granular structural fill. The structural fill should extend at least 3 feet horizontally from the bottom of the footings. Soils loosened during the forming process for the footings should be removed or re -compacted prior to placing concrete. 2. Footings on the structural fill can be sized using a maximum allowable bearing pressure of 2,000 psf. 4. 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. PAUL GOLDSTEIN LOTS 29 & 30, ROARING FORK MESA PROJECT NO, GS05714-120 S 1GS05714.0001120'12. Reporls1GS05714 12D FR1.d0e 10 5. 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. 6. The soils under 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. The Carbondale building department should be consulted regarding required frost protection depth. FLOOR SYSTEM AND SLABS -ON -GRADE If a mat foundation or post -tensioned slab is constructed, the foundation will act as the floor slab. If a footing foundation on granular structural fill is chosen, a slab -on -grade may be constructed in the garage area. Structural floors with a crawl space below are a positive alternative from a geotechnical perspective. Based on our laboratory test data and our experience, we judge slab -on -grade construction supported by undisturbed, natural gravel or an at least 3 foot thickness of densely compacted granular structural fill will have a low to moderate risk of differential movement and associated damage. Structural fill placed to attain subgrade elevations for the floor slab and exterior concrete flatwork should be in accordance with the recommendations outlined in the Structural Fill section. We recommend the following precautions for slab -on -grade construction at this site. These precautions will not prevent movement from occurring; they tend to reduce damage if slab movement occurs. 1. Slabs should be separated from exterior walls and interior bearing members with slip joints which allow free vertical movement of the slabs. 2. The use of underslab plumbing should be minimized. Underslab plumbing should be pressure tested for leaks before the slabs are constructed. Plumbing and utilities which pass through slabs should PAUL GOLDSTEIN LOTS 29 & 30, ROARING FORK MESA PROJECT NO. GS05714-120 S:0GS05714. 000412042 Repe1ts1GS05714 120 R1.doc 11 be isolated from the slabs with sleeves and provided with flexible couplings to slab supported appliances. 3. Exterior patio and porch slabs should be isolated from the building. These slabs should be well -reinforced to function as independent units. Movements of these slabs should not be transmitted to the building. 4. Frequent control joints should be provided, in accordance with American Concrete Institute (ACI) recommendations, to reduce problems associated with shrinkage and curling. BELOW -GRADE CONSTRUCTION We understand below -grade areas, with the exception of a crawl space, are not planned. If constructed, foundation walls which extend below -grade should be designed for lateral earth pressures where backfill 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, but are not limited to, the type, compaction, slope and drainage of the 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 that 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 basement walls in residences deflect or 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 50 pcf for this site. This equivalent density does not include allowances for compaction energy, sloping backfill, surcharges or hydrostatic pressures. Backfill should be placed in accordance with the recommendations contained in the BACKFILL COMPACTION section. PAUL GOLDSTEIN LOTS 29 & 30, ROARING FORK MESA PROJECT NO. GS05714-120 S:5GS05714.000112012. Reports1G505714 120 R1.dac 12 SUBSURFACE DRAINAGE 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 foundation soils, hydrostatic pressures on below -grade walls, and wet or moist conditions in below -grade 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 sump pit where water can be removed by pumping. A typical foundation dram detail is presented on Figure 6. SURFACE DRAINAGE Surface drainage is critical to the performance of foundations, floor slabs and concrete flatwork. Infiltration of water can cause sinkhole formation in Evaporite bedrock and settlement of collapsible soils. Estimated movements in this report are based on effective drainage for the life of the structure and cannot be relied upon if effective drainage is not maintained. 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 6 inches in the first 5 feet around the residence. 2. Backfill around the exterior of foundation walls should be placed as described in the BACKFILL COMPACTION section. Increases in the moisture content of the backfill soils after placement often results in settlement. Settlement is most common adjacent to north facing walls. Re -attaining proper slopes away from the residence may be necessary. 3. The residence should be provided with roof gutters and downspouts. Roof downspouts and drains should discharge well beyond the limits PAUL GQLDSTEIN LOTS 29 & 30, ROARING FORK MESA PROJECT NO. GS05714-120 S[GS05714.000%12012. RepodeLG505714 120 R1.tiot 13 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 residence. 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. CONCRETE Concrete in contact with soil can be subject to sulfate attack. Our information on nearby Tots in the Aspen Glen area indicates low sulfate concentrations. For low levels of sulfate concentration, ACI 332-08 Code Requirements for Residential Concrete indicates there are no special requirements for sulfate resistance. Do to time constraints; sulfate testing was not complete at this writing. We will provide revised recommendations if sulfate testing, when complete, indicates otherwise. In our experience, superficial damage may occur to the exposed surfaces of highly permeable concrete, even though sulfate levels are relatively low. To control this risk and to resist freeze -thaw deterioration, the water-to-cementitious materials ratio should not exceed 0.50 for concrete in contact with soils that are likely to stay moist due to surface drainage or high water tables. Concrete should have a total air content of 6% +1- 1.5%. We recommend all foundation walls and grade beams in contact with the subsoils (including the inside and outside faces of garage and crawl space grade beams) be damp -proofed. PAUL GOLDSTEIN LOTS 29 & 30, ROARING FORK MESA PROJECT NO. GS05714.120 S \G50571,1 000112012. ReportO\G$05714 120 R1.doc 14 CONSTRUCTION OBSERVATIONS This report has been prepared for the exclusive use of Mr. Paul Goldstein and the design team for the purpose of providing geotechnical design and construction criteria for the proposed project. The information, conclusions, and recommendations presented herein are based upon the consideration of many factors including, but not limited to, the type of structure proposed, the geologic setting, and the subsurface conditions encountered. The conclusions and recommendations contained in the report are not valid for use by others. Standards of practice change continuously in the area of geotechnical engineering. The recommendations provided are appropriate for about three years. If the proposed structure is not constructed within about three years, we should be contacted to determine if we should update this report. We recommend that CTL 1 Thompson, Inc. provide construction observation services to allow us the opportunity to verify whether soil conditions are consistent with those found during this investigation. If others perform these observations, they must accept responsibility to judge whether the recommendations in this report are appropriate. GEOTECHNICAL RISK The concept of risk is an important aspect of any geotechnical evaluation. The primary reason for this is that the analytical methods used to develop geotechnical recommendations do not comprise an exact science. The analytical tools which geotechnical engineers use are generally empirical and must be tempered by engineering judgment and experience. Therefore, the solutions or recommendations presented in any geotechnical evaluation should not be considered risk-free and, more importantly, are not a guarantee that the interaction between the soils and the proposed structure will perform as desired or intended. What the engineering recommendations presented in the preceding sections do constitute is our estimate, based on the information generated during this and previous evaluations and our PAUL GOLDSTEIN LOTS 29 S 39, ROARING FORK MESA PROJECT NO. GS05714.120 SAGSO5714.990112O\2. RapadslGS05714 12D 111.doe 15 experience in working with these conditions, of those measures that are necessary to help the residence perform satisfactorily. The developer, builder, and future owners must understand this concept of risk, as it is they who must decide what is an acceptable level of risk for the proposed development of the site. LIMITATIONS The exploratory borings and pits on the lots provide a reasonably accurate picture of subsurface conditions. Variations in the subsurface conditions not indicated by the pits will occur. This investigation was not performed to identify potential sink holes on the lot. We can perform an investigation to attempt to identify sinkhole, if desired. A representative of our firm should be called to test structural fill placement and to observe the completed foundation excavation to confirm that the exposed soils are suitable for support of the footings as designed. Post -tensioned slab installation should be inspected by a qualified inspector. We should observe and test placement of fill. This investigation was conducted in a manner 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. If we can be of further service in discussing the contents of this report, please call. CTL 1 THOMPSON, INC. Reviewed by: Craig A. Burger, P.E. Project Manager _ CAB:JM:cd cc: Via email to mcstein@gate.net PAUL GOLDSTEIN LOTS 29 8 30, ROARING FORK MESA PROJECT NO. GS05714.120 S'. 16505714.600\l20't2, Rep0rt3\GS05714 120 RI,doc Sohn Mechling, P.E. Branch Manager 16 �� SCALE:1' PAUL GOLDSTEIN LOTS 29 AND 30, ROARING FORK MEGA Project No. GS05714-120 Flg. 1 Vicinity Map SCALE: 1' = 50' OM I 1 I I ZM m M 1:ti PAUL GOLDSTEIN LOTS 29 AND 30, ROARING PORK MESA ASPEN GLEN Project No. GS05714-120 ROTE: Locations of exploratory borings and pits ars approximate. Locations of Exploratory Borings and Pits Fig. 2 o. Project No. GS05714—f 20 10 15 20 25 30 TH-1 0/13. 30/0 TH-2 15/12, 28/6 11/18 43/12 9/12 ///J� 115/12 TH-3 TP -1 TP -2 35/16 Anticipated Foundation Elevatlon SUMMARY LOGS OF EXPLORATORY BORINGS AND PITS 0 5 10 15 20 25 30 064 ui 144100 Fig. 3 LEGEND: El Sandy clay "topsoil`, organics, moist, brown, rust. grg Gravel, clean to silty. cobbles and boulders, dense to very dense, slightly moist, brown, nut. (CP -014) Sand, silty, occasional gravel, loose to medium dense, slightly moist to moist, rust. brown. (SM) Drive sample. The symbol 3D/13 Indicates that 30 blows of a 140 pound hammer falling 30 inches were required to drive o 2.5 Inch 0.D. California sampler 3 inches. Project No. GS05714-120 F Drive sample. The symbol 15/12 Indicates that 15 blows of a 140 pound hammer falling 30 Inches were required to drive a 2.0 Inch 0.D. standard sampler 12 inches. indicates bulk sample. Indicates hand drive sample. lndlcates practical auger refusal. Symbols above the bottom of borings Indicates that boring location was moved to advance auger farther. SUMMARY LOGS OF EXPLORATORY BORINGS AND PITS NOTES: 1. Exploratory borings were drilled on August 28, 2007 with 4—Inch diameter. solid—stem auger and o track—mounted drill rig. Exploratory pits were excavated on December 4, 2012. Exploratory borings and pits were backfilled immediately after exploratory operations were compteted. 2. Locations of exploratory borings and pits are approximate. 3. No free ground water was found In our exploratory borings or plts at the time of exploratory operations. 4. These exploratory borings and pits are subject to the explanations. limitations and concluslons as contained In this report. Flg. 4 COMPRESSION % EXPANSION -a ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING L1 10 1❑ 100 APPLIED PRESSURE - KSF Sample of SAND, SILTY (SM) DRY UNIT WEIGHT= 101 PCF From TP -2- AT 3.5 FEET MOISTURE CONTENT= 3.6 % Paul Goldstein Lots 29 A. 30 Roaring Fork Mesa, Aspen Glen PROJECT NO. GS05714-120 S.1GS05714.000112016. CaIcs1GS05714-1205WELL.xIs Swell Consolidation Test Results FIG. 5 SLOPE PER REPORT BACKFILL BELOW -GRADE WALL STRUCTURAL FLOOR SLOPE . ATTACH POLYETHYLENE PER SHEETING TO FOUNDATION OSHA WALL COVER ENTIRE WIDTH OF GRAVEL WITH NON -WOVEN GEOTEXTILE FABRIC (TENCATE MIRAFI 140N OR EQUIVALENT). ROOFING FELT IS AN ACCEPTABLE ALTERNATIVE. 8' MIN. OR BEYOND 1:1 SLOPE FROM BOTTOM OF FOOTING (WHICHEVER I5 GREATER) 4' MINIMUM 4 -INCH DIAMETER PERFORATED RIGID DRAIN PIPE. THE PIPE SHOULD BE PLACED IN A TRENCH WITH A SLOPE OF AT LEAST 1/8 -INCH DROP PER FOOT OF DRAIN. CRAWL SPACE OR VOID SEE NOTE 2 FOOTING OR PAD ENCASE PIPE IN 1/2' TO 1-1/2' WASHED GRAVEL EXTEND GRAVEL LATERALLY TO FOOTING AND AT LEAST 1/2 HEIGHT OF FOOTING. FILL ENTIRE TRENCH WITH GRAVEL. NOTES: 1) THE BOTTOM OF THE DRAIN SHOULD BE AT LEAST 4 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. 2) TO HELP CONTROL THE HUMIDITY IN THE CRAWL SPACE, A MINIMUM 10 -MIL POLYETHYLENE VAPOR RETARDER MAY BE PLACED OVER THE CRAWL SPACE SOILS, AT THE BUILDER'S OPTION. THE RETARDER SHOULD BE ATTACHED TO CONCRETE FOUNDATION ELEMENTS AND EXTEND UP FOUNDATION WALLS AT LEAST 8 INCHES ABOVE TOP OF FOOTING. OVERLAP JOINTS 3 FEET AND SEAL PAUL GOLDSTEIN LOTS 2S AND 30, ROARING FORK MESA Protect No. GS05714-120 Exterior Foundation Wall Drain Flg. 6 PROJECT NO. GS05714.120 TABLE 1 SUMMARY OF LABORATORY TEST RESULTS BORING 1 OR PIT I DEPTH (FEET) NATURAL MOISTURE (%) NATURAL DRY DENSITY (PCF) SWELL' (%) ATTERBERG LIMITS SOLUBLE SULFATES (%) GRADATION TESTS PASSING NO. 200 SIEVE (%) SOIL CLASSIFICATION LIQUID LIMIT (%) PLASTICITY INDEX (%) PERCENT GRAVEL (%) PERCENT SAND (%) TH-2 4 1.9 22 GRAVEL, SILTY (GM) TH-2 9 7.6 19 2 45 SAND, SILTY (SM) TH-2 14 2.2 8 GRAVEL, CLEAN TO SILTY (GP -GM) TP -1 7-9 4.1 8 52 40 SAND, SILTY (SM) TP -2 3.5 3.6 101 -2.2 SAND, SILTY(SM) TP -2 2-4 3.9 13 47 40 SAND, SILTY (SM) "Note: Swell due to wetting under an applied load of 1,000 psf. Negative values indicate compression. Page 1 of 1