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HomeMy WebLinkAboutSoils & Foundation Report 10.02.2012CTLLTHONIPSON SOILS AND FOUNDATION INVESTIGATION PURA VIDA RANCH COUNTRY HOUSE AND GREENHOUSE RIVER VALLEY RANCH CARBONDALE, COLORADO Prepared For: CHAIRPERSON, PURA VIDA HOLDINGS, L.L.C. c/o Poss Architecture and Planning 605 East Main Street Aspen, CO 81611 Attention: Mr. Stephen Holley Project No. GS05690-120 October 2, 2012 234 Center Drive I 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 3 SUBSURFACE CONDITIONS 3 SITE GEOLOGY 4 GEOLOGIC HAZARDS 5 SITE EARTHWORK 6 Structural Fill and Subexcavation 7 BACKFILL COMPACTION 7 FOUNDATION 8 Pressure Grouted Micropiles 9 Footings on Gravel (Country House) or Sand (Greenhouse) 10 FLOOR SYSTEM 11 EXTERIOR FLATWORK 11 BELOW -GRADE CONSTRUCTION 11 SUBSURFACE DRAINAGE 12 SURFACE DRAINAGE 12 CONCRETE 13 PRELIMINARY BRIDGE ABUTMENT RECOMMENDATIONS 14 Foundation 14 Scour 14 Abutment Lateral Loads 14 Approach Walls 15 CONSTRUCTION OBSERVATIONS 16 GEOTECHNICAL RISK 17 LIMITATIONS 17 FIGURE 1 -- VICINITY MAP FIGURE 2 — LOCATIONS OF EXPLORATORY BORINGS FIGURE 3 — SUMMARY LOG OF EXPLORATORY BORINGS FIGURE 4 — EXTERIOR FOUNDATION WALL DRAIN DETAIL APPENDIX A — LABORATORY TEST RESULTS CHAIRPERSON, PURA VIDA HOLDINGS, L.L.C. PURA VIDA RANCH PROJECT NO. GS05690.120 S MS05690.000412042. Reports4GS05690 120 R1.doc SCOPE This report presents the results of our soils and foundation investigation for the proposed Country House and Greenhouse on the Pura Vida Ranch (south parcel of the 360 Lot) of River Valley Ranch in Carbondale, Colorado. We conducted this investigation to evaluate subsurface conditions at the site and provide geotechnical engineering recommendations for the proposed construction. Our report was prepared from data developed during our field exploration, engineering analysis, and our experience with similar conditions. This report includes a description of the subsurface conditions observed in our exploratory borings and presents geotechnical engineering recommendations for design and construction of the foundation, floor system, below -grade walls, drain system, exterior flatwork and details influenced by the subsoils. Preliminary recommendations for construction of a bridge on the driveway alignment are included, Percolation Testing was included in our proposal, but removed from the scope at this time at the request of the architect. 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 found in our exploratory borings at the Country House location consisted of about 3 inches to 1 foot of clayey sand "topsoil" underlain by natural gravels with cobbles and boulders. Subsurface conditions found in our exploratory borings at the Greenhouse consisted of about 6 inches to 1 foot of silty sandy "topsoil" and about 9 to 18 feet of clayey sand underlain by gravels with cobbles and boulders. Free ground water was not observed in the exploratory borings at the time of this investigation. CHAIRPERSON, PURA VIDA HOLDINGS, L.LC. PURA VIDA RANCH PROJECT NO- GS05690-120 S:16505690.000112042. Roports4G505690120 RLdoc 1 2. 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 site is micropile foundation system atthe Country House and Greenhouse. The Country House could be constructed on footing foundations supported by the natural gravel if the owner accepts a greater risk of movement than would be expected with micropiles. The Greenhouse could be supported on footings on the natural sand. Design and construction criteria for micropiles and footing foundations are presented in the report. 3. We understand structurally supported floors above crawl spaces are desired in living areas of the residence. We judge potential differential movement of slabs -on -grade and exterior flatwork supported by the undisturbed, natural gravel will be low if soil moisture content does not increase substantially. We recommend removal of clay or sand soils, if encountered, to a depth of at least 3 feet below exterior flatwork or slabs -on -grade and replacementwith 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 buildings. 5. A bridge on the driveway alignment can likely be supported on micropile or footing foundations. Preliminary recommendations are in the report. SITE CONDITIONS The Country House is planned at the east side of the south parcel of the 360 Lot located southwest of Crystal Bridge Drive in River Valley Ranch in Carbondale, Colorado. A vicinity map is provided on Figure 1. An existing residence, water tank, and solar field are located on the north parcel. The greenhouse is planned in the south central parcel where the driveway for the country house splits from the driveway for the existing residence. The building areas are generally flat with scopes less than 5 percent. Steeper slopes are present north and east of the planned buildings and where two ravines transect the lot. Vegetation consists of sage meadows and pinion juniper forests. CHAIRPERSON, PURA VIDA HOLDINGS, L,L.C, PURA VIDA RANCH PROJECT NO. GS05690-120 S:YOSOS690.ODOY12042, Reporls;GSO569O 120 R1.dac 2 We spoke with Paul Werner with Frontier Long Homes and visited the existing residence. We understand the existing residence on the north parcel was constructed in 2004 or 2005. We understand that several cracks developg n dry nca1L in different areas and one interior wall rotated about 1.5 inches out of plumb. One crack is present in the garage slab near where the floor system transitions from slab - on -grade in the garage to structural floors above a crawl space. We are not aware of investigations to determine the cause of cracking. PROPOSED CONSTRUCTION We were provided plans by the architect, Poss Architecture & Planning titled "Schematic Design", dated August 16, 2012. The Country House is planned as a one- story building with an attached garage. Structural floors above crawl spaces are planned in living areas and the garage. An auto court and a courtyard with a water feature are planned. The Greenhouse is planned as a one level structure with a structural floor. We expect maximum foundation excavation depths will be about 4 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. The driveway is planned with a gravel surface. A bridge is planned on the driveway alignment. 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 at the site were investigated by drilling four exploratory borings (TH-1 through TH-4) in the area of the Country House and two exploratory borings (TH-5 and TH-6) in the area of the Greenhouse. Borings were advanced with solid -stem auger and a track -mounted drill rig. Approximate locations of exploratory CHAIRPERSON, PURA VIDA HOLDINGS, L.L.C. PURA VIDA RANCH PROJECT NO. GS05690.120 5:4G505590.00012012. Reports,,G505690120 R1.dac 3 borings are shown on Figure 2. Subsurface conditions encountered in the borings were logged by our laboratory/field manager who obtained samples of the soils encountered. Graphic Togs of the soils observed in the exploratory borings are shown on Figure 3. Subsurface conditions found in our exploratory borings at the Country House location consisted of about 3 inches to 1 foot of clayey sand "topsoil" underlain by natural gravels with cobbles and boulders. Subsurface conditions found in our exploratory borings at the Greenhouse consisted of about 6 inches to 1 foot of silty sandy "topsoil" and about 9 to 18 feet of clayey sand underlain by gravels with cobbles and boulders. Free ground water was not observed in the exploratory borings at the time of this investigation. Samples obtained in the field were returned to our laboratory where field classifications were checked and samples were selected for pertinent testing. Samples of the gravel from borings at the Country House location contained 10 to 27 percent silt and clay sized particles (passing the No. 200 sieve). Gradation test results exclude cobbles and boulders. Samples of the clayey sand from borings at the Greenhouse location exhibited low swell (1.9 percent) to low compression (1 percent) when wetted under applied loads of 500 to 1,000 psf. Laboratory test results are included in Appendix A. SITE GEOLOGY The geology of the site was evaluated using our in-house collection of geologic maps (Geologic Map of the Carbondale Quadrangle, Garfield County, Colorado by Kirkham and Widmann, 2008). We interpret the surficial soils of the site as alluvial, debris flow and colluvium deposits underlain by Eagle Valley Evaporite bedrock. We did not encounter bedrock in our borings. Outcroppings of Eagle Valley Evaporite are present adjacent to the access drive to the parcel. The subsurface conditions observed in our borings are consistent with the mapping we reviewed. CHAIRPERSON, PURA VIDA HOLDINGS, L.L.C. PURA VIDA RANCH PROJECT NO. GSOS660-120 5:10506$90.000112052. Reports 5GS05690 120 R1.doc 4 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. 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. Our interpretation of the site geology is that the surficial soils on the lot consist of terrace and pediment gravel. The Colorado Geologic Survey has mapped sinkhole, subsidence and soil -collapse features and locations in the area near this lot. Mapping by the Colorado Geologic Survey, "Collapsible Soils and Evaporite Karst Hazard, Map of the Roaring Fork River Corridor, Garfield, Eagle and Pitkin Counties, Colorado" (2002) shows small sinkholes near the site just north of Bowels Gulch. The site is mapped as alluvial terrace deposits which have potential for compression or collapse upon wetting. Some increase in subsurface moisture must be assumed due to the effects of site development, We compared moisture content and dry density verses collapse potential based on a rating system described in "Engineering Geology 14, Collapsible Soils in Colorado" (see Figure A-4). Based on the rating CHAIRPERSON, PURAVIDA HOLDINGS, L.L.C. PURA VIDA RANCH PROJECT NO. GS05690-120 S:1GSO5690.000112012. Repvrls1GS05690 120 1R1.dac 5 system, the soils exhibit lot to moderate collapse potential. Samples tested in our laboratory exhibited low collapse to low swell when wetted under loads of 500 or 1,000 psf. Based on our experience in the area, laboratory testing and published data, we consider the clayey sand soils at this site to have a low to moderate collapse potential. Engineered design of foundations, slabs -on -grade, pavements and surface drainage can mitigate, but not eliminate potential affects of collapse -prone soils. In approximately 2008, a debris flow event occurred at Bowels Gulch, which crosses the north parcel. Holland Gulch is located south of the lot, and is also susceptible to debris flow. 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 moderate potential for sinkhole formation or collapse of the soils due to wetting after construction. SITE EARTHWORK Based on information from our exploratory borings, we anticipate that the majority of the excavation for the proposed Country House will in the natural gravel soils. Excavation at the Greenhouse will likely be in silty sand. 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 sand or clay soils may classify as a Type B soil based on OSHA standards governing excavation; the natural granular soil 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. CHAIRPERSON, PURA VIDA HOLDINGS, L.L.C. PURA VIDA RANCH PROJECT NO. GS05690-120 5:4G505090.000112042, Repori55G505690 120 R1 An 6 Free ground water was not observed in the exploratory borings during drilling 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 and Subexcavation Excavations for the Country House will likely encounter gravel soils at elevation of the foundation, and exterior flatwork. Removal of boulders may result in voids. We recommend the clay or sand soils, if encountered, be removed from below the Country House footprint. Excavations at the Greenhouse will likely encounter sand at foundation elevations. Areas which will receive fill should be stripped of vegetation, organic soils and debris. The on-site gravel soil free of organic matter, debris and rocks larger than 3 inches in diameter can be used as structural fill. Import fill should consist of a CDOT 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 at least 98 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. 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 CHAIRPERSON, PURA VIDA HOLDINGS, L.L.G. PURA VIDA RANCH PROJECT NO. GS05690-120 5:5GS05690.000112012. Reporis1GS05690 120 R1,doC 7 density increases the risk of cracking the concrete wall. 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. FOUNDATION Our exploratory borings indicate that the natural gravel with cobbles and boulders are present at anticipated foundation elevations for the proposed Country House. Our borings indicate natural clayey sand is present at the Greenhouse location. The natural soils on this site are underlain by Eagle Valley Evaporite 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 potential risk of sinkhole formation, a positive alternative is to support the Country House on a micropile foundation system. A micropile foundation system may mitigate a "sinkhole", if encountered, below the building footprint by filling the sinkhole with grout. Post -tensioned slab or mat (raft) foundation systems are other positive alternatives, but would likely preclude construction of a crawl space. We can provide criteria for post -tensioned slabs or amt foundation, if desired. Footings supported on the natural gravel are an option for the Country House. Footings supported on the natural sand would be appropriate for the Greenhouse. The owner must be willing to accept the increased risk of movement of a footing foundation system. Our representative should be called to observe conditions exposed in the completed foundation excavations to confirm that the exposed soils are as anticipated and suitable for support of the foundation as designed. Subexcavation and placement of structural fill should be observed and tested by our representative. Our experience indicates that maximum total settlement will be 1 inch and differential settlement about 3/4 Inch for footings constructed on structural fill, natural gravels or natural sand. If the soil moisture content increases significantly greater settlement CHAIRPERSON, PURA VIDA HOLDINGS, L.L.C. PURA VIDA RANCH PROJECT NO. GSOS690-120 S:4GS45696.000112042. ReporlsIGS05690 124 R1.doc 8 would be expected. We would anticipate about one-half as much movement for a micropile or post -tensioned slab or mat foundation. No foundation system can provide mitigation of building damage if a sinkhole forms below the building. Recommended design and construction criteria for footing and micropile foundations are presented below. Pressure Grouted Micropiles Micropiles should be designed to meet specified loading conditions, as indicated by the structural engineer. The micropiles can be designed using the Load Resistance Factor Design (LRFD) procedures contained in the FHWA "Micropile Design and Construction Guidelines Manual", Report No. FHWA-SA-97-070 dated June 2000 or "Micropile Design and Construction Reference Manual" number FHWA- NHI-05-039, dated December 2005. We can design the micropiles or be available to assist in the designs and specifications developed by others. General recommendations for micropiles are provided below. 1. Four distinct classifications of micropiles have been standardized based on various drilling and grouting techniques. A description of the various micropile types (A, B, C, and D) is provided in the previously referenced manual. The selection of micropile type should be left to the discretion of the designer and/or contractor. Based on the soil type encountered in our exploration, we recommend a "Type B" micropile be utilized. This type of micropile would be temporarily cased full length at the time of drilling. Neat cement grout is placed into the hole under pressure (typically 100 to 200 psi) as the temporary casing is withdrawn. We recommend a minimum micropile hole diameter of 4 inches and a total length of at least 15 feet. The reinforcement bar in the micropile should extend full length. 2. Values for the grout -to -ground nominal bond strength are commonly based on experience of local Contractors and Geotechnical engineers. Table 5-2 on page 5-16 of the "Micropile Design and Construction Guidelines Manual" presents ranges of typical values of the nominal bond strength for various installation methods and ground conditions. For initial design calculations and to allow development of foundation plans, we suggest assuming a grout to ground nominal bond stress of 30 psi for the gravel and cobble. In accordance with the FHWA design manual, a resistance factor of 0.6 should be used. CHAIRPERSON, PURA VIDA HOLDINGS, L.L.C. PURA VIDA RANCH PROJECT NO. GS05690-120 S4GS05690.0001120\2. Reports1GS05690 120 R1.doc 9 3. One compression verification Toad test to two times the factored load should be performed on a pre -production micropile. This testing is usually performed as the first order of work under the construction contract. The purpose of the pre -production testing is to verify whether design assumptions concerning bond zone strength are appropriate and the adequacy of the contractor's installation method. Production micropiles are approved only after the design assumptions and the adequacy of the contractor's installation method have been verified. Proof testing may not be practical also be performed on production piles. 4. We recommend, as a minimum, the upper 5 feet of the micropile contain permanent casing to provide a sound connection from the micropile to the foundation system. This upper section of permanent casing may also be required for lateral Toad considerations. 5. A grout with admixtures that thicken the grout to resist grout Toss is sometimes utilized. Footings on Gravel f Country House) or Sand (Greenhouse) 1. The Country House can be supported by footing foundations on the natural gravel. The Greenhouse can be supported on footing foundations on the natural sand. Soils loosened during the forming process for the footings should be removed or re -compacted prior to placing concrete. Void should be filled with densely compacted structural fill. 2. Footings on the natural gravel or sand can be sized using a maximum allowable bearing pressure of 1,500 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. 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. CHAIRPERSON, PURA VIDA HOLDINGS, L.L.C. PURA VIDA RANCH PROJECT NO. G505690-126 S:4GS65690.000112012. Reports1G505690 420 R1.doe 10 FLOOR SYSTEM We understand structural floors supported by the foundation system are desired. If a mat foundation or post -tensioned slab is constructed, the foundation will act as the floor slab. If an interior slab -on -grade is desired, we should be contacted to provide additional recommendations. EXTERIOR FLATWORK Exterior patios, courtyards and auto courts are planned at the Country House. A water feature is also planned. We recommend constructing patios, courtyards, the auto court and other exterior flatwork on the natural grave!. All topsoil or areas of clay or sand encountered should be removed and replaced with structural fill. A leveling course of densely compacted Class 6 aggregate base course should be provided below flatwork. We recommend a drain to a positive gravity outlet be provided below the water feature in the event Teaks develop. BELOW -GRADE CONSTRUCTION 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. CHAIRPERSON, PURA VIDA HOLDINGS, L.L.C. PURA VIDA RANCH PROJECT NO. GS05690-126 5:10506690.00011201.2. ReportslGS05690 120 R14oc 11 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. 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 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 gravity outlet or sump pit where water can be removed by pumping. A typical foundation drain detail is presented on Figure 4. SURFACE DRAINAGE Surface drainage is critical to the performance of foundations, floor slabs and concrete flatwork. 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. CHAIRPERSON, PURA VIDA HOLDINGS, L,L.C. PURA VIDA RANCH PROJECT NO. GS65690 12O 5:46505690.0 0 011 2012. Reports\G505690 120 R1.doc 12 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-attalning 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 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. Water-soluble sulfate concentrations in two samples from this site were 0.00 percent. For this level of sulfate concentration, ACI 332-08 Code Requirements for Residential Concrete indicates there are no special requirements for sulfate resistance. 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. CHAIRPERSON, PURA VIDA HOLDINGS, L.L.C. PURA VIDA RANCH PROJECT NO. OS05690.120 S:1GS0SG90.0001,12012. Reparls5GS05690 120 R1.doc 13 PRELIMINARY BRIDGE ABUTMENT RECOMMENDATIONS A bridge is being considered where the driveway crosses a ravine. We understand the bridge span may be about 60 feet. We should be provided with plans when available. Foundation Foundations for the bridge abutments and retaining walls can likely be constructed using the recommendations for the residence and greenhouse. We will need to verify soil conditions prior to final design. Depending on the size of the bridge, we may need to provide criteria for lateral loading and closely spaced pier reduction factors. Scour The bridge and retaining wall foundation design should consider the potential for scour of supporting soils. The ravine did not contain flowing water at the time of our site visit. Abutment Lateral Loads Lateral earth pressures are dependent upon the type, compaction and slope of backfill, the geometry and friction angle between the abutment and backfill, and the magnitude and direction of the abutment wall deflections. Bridge abutments should be backfilled with densely compacted, structural fill consisting of a CDOT Class 1 aggregate or similar soil. Recommendations for placement and compaction of backfill were presented in the Site Earthwork section. We recommend a total density of 130 pcf and a friction angle of 36 degrees be used to calculate the appropriate lateral earth pressures in the design of the abutments. For the lateral earth pressure CHAIRPERSON, PURA VIDA HOLDINGS, L.L.C. PURA VIDA RANCH PROJECT NO. GS05690-120 S:1GS05590.000112012. Reports 1GS05690 120 R1.doc 14 calculation, "AASHTO Standard Specifications for Highway Bridges" may be referenced. Alternatively, the on-site granular soils less than 4 inches in diameter can be used as structural fill for the bridge approaches; however, increased settlement of the fill soils may occur. For well compacted backfill using the on-site soils, we recommend a total density of 130 pcf and a friction angle of 30 degrees be used to calculate lateral earth pressures. Approach Walls Approach walls may be constructed on the sides of each abutment. We recommend the approach walls be designed and constructed separate from the abutments and be sufficiently flexible so "active" earth pressure conditions can be used in design. Generally, geogrid reinforced MSE wall or a cantilever type retaining wall with slip joints between the wail and abutment will meet these requirements. Approach walls can be constructed on foundations using the criteria discussed previously. Recommendations presented in the Site Earthwork section should be followed. If a foundation key is required, the key can be designed using a "passive" earth pressure of 300 pcf equivalent fluid weight. We do not recommend the approach walls be designed using passive earth pressures from soils in front of the walls. The soils in front of the walls may slope away from the wall and could be eroded or scoured by the Creek in the future. The backfill behind the approach walls may slope upwards. Table C presents "active" earth pressures for granular backfill at various slope ratios. These recommended values do not include allowances for the surcharge loads such as hydrostatic pressure, traffic loads, and loads from fill compaction efforts during construction. Approach walls should be backfilled with densely compacted, structural fill as discussed in the Site Earthwork section. CHAIRPERSON, PURA VIDA HOLDINGS, L.L.C. PURA VIDA RANCH PROJECT NO. GS05680-120 S:1GS05690.000112012, Reports%GS05690 120 Ri doc 15 TABLE C RECOMMENDED DESIGN LATERAL EARTH PRESSURE BACKFILL SLOPE" (Hotizontal Vertical) I..ATERAL' EARTH PRESSURE (pcf, Equivalent Fluid Pressure) Granular Backfill 2:1 55 3:1 45 6:1 40 Level 35 We recommend drains be installed behind approach walls to reduce the risk of hydrostatic pressures developing behind the walls. The drains should consist of a free -draining gravel layer and weep holes or slotted pipe to drain water from behind the walls. Miradrain or similar manufactured drain products can be used Erosion protection, such as riprap, should be provided in areas that will be subject to scour action. CONSTRUCTION OBSERVATIONS This report has been prepared for the exclusive use of Chairperson, Pura Vida Holdings, L.L.C. 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 CHAIRPERSON, PURA VIDA HOLDINGS, L.L.C, PURA VIDA RANCH PROJECT NO. GS05690-120 5:1G505690.000112042. Repori510S05690 120 RI.doc 16 with those found during this investigation. If others perform these observations, they must accept responsibility to judge whether the recommendations in this report remain 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 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 on the lot provide a reasonably accurate picture of subsurface conditions. Variations in the subsurface conditions not indicated by the borings will occur. This investigation was not performed to identify potential sink holes on the lot. An investigation to attempt to identify sink holes was previously performed at River Valley Ranch by others. 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 CHAIRPERSON, PURA VIDA HOLDINGS, L.L.C. PURA VIDA RANCH PROJECT NO. GS05690-120 S:4G505S90.000%12012. Raports1GS05690 120 Ri.dac 17 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. Craig A. 8 Project Ma echling, P.E. ch Manager cc: Via email to sholleyybiliposs.com CHAIRPERSON, PURA VIDA HOLDINGS, L.L,C. PURA VIDA RANCH PROJECT NO, GS05690.120 5:1G505690.000112012, Repods4G505690 120 R1.doc 18 jr SCALE: V = 610001 Pura Vlda Ha'dEngs, LLC Pura Vide Ranch Project No. GS05690-120 Vicinity Map Ffg. 1 Awl ilzo/ot za`aa1vsa — -- 10 - 20 — Y5 25 TH-1 50/11 50/0 TH-2 PO 04 Po 04 044 044 50/10 TH-3 50/6 TH-4 pp • 0�e 04 50/6 TH-5 TH-6 LEGEND: t�• 04. g 25/12 48/12 50/10 0 — 50/12 5 50/12 10 15 — 20- - 0— .. 30 30 - 35 Project No. GS05690-120 35— SUMMARY 5— SUMMARY LOGS OF EXPLORATORY BORINGS • 5 • Clayey to silty sand 'topsoil'. medium dense, slightly moist to moist. brown. 1021 Sand, clayey, medium dense to very �� dense, slightly moist, red—brown. (SC) Gravel, sandy to silly, cobbles and boulders, very dense, slightly moist, brown. (CM) In Drive sample. The symbol 50/11 Indicates that 50 blows of a 140 pound hammer falling 30 inches wore required to drive a 2.0 inch 0.D. standard sampler 11 Inches. Drive sample. The symbol 25/12 Indicates that 25 blows of a 140 pound hammer falling 30 Inches were required to drive a 2.5 inch O.D. California sampler 12 Inches. Indicates practical auger refusal. T Symbols above the bottom of borings T indicates that boring location was moved to advance auger farther. NOTES: 1. Exploratory borings were drilled on September 14, 2012 with 4—inch diameter. continuous—flight solid—stem auger and a track—mounted drill rig. 2. Locations of exploratory borings are approximate. 3. No free ground water was found in our exploratory borings at the time of drilling or 3 days later. 4. These exploratory borings are subject to the explanations, limitations and conclusions as contained In this report. Fig. 3 SLOPE PER OSHA COVER ENTIRE WIDTH OF GRAVEL WITH NON -WOVEN GEOTEXTILE FABRIC (TENCATE MIRAFI 140N OR EQUIVALENT). ROOFING FELT IS AN ACCEPTABLE ALTERNATIVE. SLOPE PER REPORT BACKFILL BELOW -GRADE WALL ATTACH PVC SHEE111NG TO FOUNDATION WALL 8' MIN. OR BEYOND 1:1 SLOPE FROM BOTTOM OF FOOTING (WHICHEVER IS GREATER) MINIMUM 4 -INCH DIAMETER PERFORATED RIGID DRAIN PIPE. THE PIPE SHOULD BE PLACED IN A TRENCH WITH A SLOPE OF AT LEAST 1/B -INCH DROP PER FOOT OF DRAIN. SPACERAWLE OR VOID SEE NOTE 2 MICROPILE, 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 1 0 -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. A RATE SLAB MAY ALSO BE PROVIDED. Chairperson, Pura Vida holdings, L.L.C. Pura Vida Ranch Project Na. GS05690-120 Exterior Foundation Wall Drain Fig. 4 APPENDIX A LABORATORY TEST RESULTS CHAIRPERSON, PURA VIDA HOLDINGS, L.L.C. PURA VIDA RANCH PROJECT NO. GS05690-120 S:1GS05000,000H2O12. Reports1GS05690120 A1.doc COMPRESSION % EXPANSION 0 -B EXPANSION UNDER CONSTANT PRESSURE DUE TO WETTING 0.1 1.0 10 100 APPLIED PRESSURE - KSF Sample of SAND, CLAYEY (SC) DRY UNIT WEIGHT- 110 PCF From TH 5 AT 4 FEET MOISTURE CONTENT= 8.3 % Chairperson, Pura Vida Holdings, L.L.C. Pura Vida Ranch PROJECT NO. GS05690-120 S:1GS0569D.Q061i2G16. Calcs\GS05690-120SNELL.x1s Swell Consolidation Test Results FIG. A-1 COMPRESSION % EXPANSION 7 6 5 4 3 2 0 -1 -2 -3 -4 -5 -6 -7 -g ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING • 0.1 APPLIED PRESSURE - KSF Sample of SAND, CLAYEY (SC) From TH 5 AT 9 FEET Chairperson, Pura Vida Holdings, L.L.C. Pura Vida Ranch PROJECT NO. GS05690-120 S:1GS05690.0001120l6. Calcs1GS05690.120SWELL.xIs 1.0 10 100 DRY UNIT WEIGHT= 117 PCF MOISTURE CONTENT= 4,9 Swell Consolidation Test Results 04 FIG. A-2 COMPRESSION % EXPANSION 7 6 5 4 3 2 0 -1 -2 -3 -4 -5 -6 -7 -S ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 0.1 APPLIED PRESSURE - KSF Sample of SAND, CLAYEY(SC) From TH 5 AT 14 FEET Chairperson, Pura Vida Holdings, L.L.C. Pura Vida Ranch PROJECT NO. GS05690-120 5:1G5055 0.000412016. CalcslG505690.1205WELL.x1s 1.0 10 100 DRY UNIT WEIGHT= 115 PCF MOISTURE CONTENT= 3.7 % Swell Consolidation Test Results FIG. A-3 Dry Density (pcf) 135 125 Plot of M -D Data Overlayed on Proposed Collapse -Susceptibility Boundaries - -Laiiv to no potential Ilapse -ow-to-modeto collapse potential 85 75 65 --- 0.0 Modelate to high L 5.0 10.0 15.0 20.0 25.0 30.0 35.0 Chairperson, Pura Vida Holdings, L.L.C. Pura Vida Ranch PROJECT NO. GS05690-120 Moisture Content CY4 Note: proposed collapse -susceptibility boundaries estimated from "Engineering Geology 14, Collapsible Soils in Colorado" Colorado Geologic Survey, 2008. Figure 4-13 Fig. A - 4 TABLE A -I SUMMARY OF LABORATORY TESTING PROJECT NO. GS05690-120 TEST HOLE DEPTH (FEET)_ MOISTURE CONTENT (%) DRY DENSITY (PCF) ATTERBERG LIMITS ' PASSING NO. 200 SIEVE (%) SOLUBLE SULFATES (%) DESCRIPTION LIQUID LIMIT (%) PLASTICITY INDEX (%) SWELL (%) TH-1 4 0.611.2 0.00 Gravel, silty (GM) r t TH-2 4 0.4 9.9 Gravel, silty (GM) TH-3 4 4.0 26.6 Gravel, silty (GM) TH-4 4 2.1 NL NP 9.6 Gravel, silty (GM) TH-5 4 8.3 110 1.9 Sand, Clayey (SC) TH-5 9 4.9 117 -0.4 Sand, Clayey (SC) TH-5 14 3.7 115 -1.0 Sand, Clayey (SC) TH-6 4 6.7 116 29 15 48.7 0.00 Sand, Clayey (SC) r * SWELL MEASURED WITH 1000 PSF APPLIED PRESSURE, OR ESTIMATED IN-SITU OVERBURDEN PRESSURE. NEGATIVE VALUE INDICATES COMPRESSION. Page 1 of 1 SUBJECT:• Prrv�e, ccws � JOB NO: G• S S 6� (j DATE V 1 CTL I THOMPSON 0 b LS ael BY: PAGE OF i PAik 6 s- Conenl,rv�ti►e. 4 bra y.) s l c ac. z at \-% \;)