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HomeMy WebLinkAboutSoils Report 03.12.2003CHURCH & Associates, Inc. ENGINEERS & GEOLOGISTS SOILS AND FOUNDATION INVESTIGATION PROPOSED RESIDENCE 420 PINON DRIVE LOT 12, LOS AMIGOS RANCH, FILING 1 (a.k.a. ELK SPRINGS) GARFIELD COUNTY, COLORADO Prepared for: LAURIE AND PATRICK WINTERS 2240 RHODA PLACE SCOTCH PLAINS, NEW JERSEY 07076 JOB NO. 15664W MAY 12, 2003 DENVER 4501 Wadsworth Boulevard Wheat Ridge, CO 80033 303.463.9317 Fax: 303.463.9321 TABLE OF CONTENTS SCOPE 1 CONCLUSIONS 1 PROPOSED CONSTRUCTION 2 SITE CONDITIONS 2 INVESTIGATION 2 SUBSURFACE CONDITIONS 3 SITE PREPARATION 4 EXCAVATIONS 4 BUILDING FOUNDATIONS 5 SLAB -ON -GRADE CONSTRUCTION 6 LATERAL LOADS AND DRAINAGE 6 LIMITATIONS 7 FIGURE 1 -SITE PLAN AND LOCATIONS OF EXPLORATORY TEST PITS FIGURE 2 - LOGS OF EXPLORATORY TEST PITS FIGURES 3 AND 4 - GRADATION ANALYSIS TEST RESULTS APPENDIX A - IMPORTANT INFORMATION ABOUT THE REPORT 1 1 SCOPE This report presents the results of a soils and foundation investigation for the proposed residence to be located at 420 Pinon Drive, which is Lot 12, Los Amigos Ranch, Filing 1 (a.k.a Elk Springs), in Garfield County, Colorado. The purpose of our investigation was to evaluate subsurface conditions and provide geotechnical recommendations for the proposed construction. The report presents a description of subsurface conditions encountered at the site, recommended foundation system, and design and construction criteria influenced by the soils and bedrock. The report is based on data developed during the field and laboratory investigations and our experience. A summary of our findings and 1 recommendations is presented below. 1 CONCLUSIONS 1. Subsurface materials encountered in Test Pit 1 (TP -1) consisted of 3 inches of clayey topsoil and root zone, overlying severely weathered basalt (boulders in a slightly sandy clay matrix) to the maximum explored depth of 2 feet. Materials encountered in TP -2 consisted of 6 inches of clayey topsoil .and root zone, overlying severely weathered basalt (boulders in a slightly sandy clay matrix) to 1.5 feet. Underlying the boulders, slightly weathered basalt bedrock was encountered to the maximum explored depth of 3 feet. Practical backhoe refusal was encountered on the basalt in both test pits. 2. Free water was not encountered in the testit duringexcavation. Based on our observations, p ground water should not be an issue during construction. 3. The residence can be constructed with a spread footing foundation system on the native soil or basalt. The spread footing foundation system will have a low risk of movement due to expansive or collapsible soils. Design and construction criteria are presented in the body of the report. 4. Slab -on -grade construction .on the clay and/or basalt will have a low risk for movement due to expansive soils. For slab -on -grade construction, slabs should ideally be constructed as "floating" slabs. The slabs should be free to move in the vertical direction. 5. Positive drainage down and away from all foundation walls should be established and maintained at all times. 1 Soils and Foundation Investigation Job No. 15664W Page 2 PROPOSED CONSTRUCTION A residence with an attached garage is proposed at the location presented on Figure 1. The residence will be of concrete and wood frame construction and light to moderate construction loads are anticipated. It is understood that the residence will have a structural floor over a crawl space and below grade construction is not proposed. Detailed house plans were not available when this report was prepared. An approximate foundation depth of 3 below the existing ground surface elevation was assumed for this investigation. SITE CONDITIONS The site is located in a rural -residential area southeast of GIenwood Springs in Garfield County, Colorado. The site is located on the south side of Pinon Drive and will be accessed from Pinon Point along the northwestern edge of the property. The ground surface has an approximate 18 percent slope to the southwest. The ground surface in the building area has a sparse cover of native grass and weeds with a moderate covering of evergreen trees, juniper bushes, and sage brush. INVESTIGATION Subsurface conditions were investigated on May 2, 2003 by excavating two exploratory test pits at the locations presented on Figure 1. The test pits were excavated with a John Deere 710D rubber -tired backhoe. Bulk samples were obtained at selected intervals for laboratory testing. Penetration testing to determine the consistency or relative density of the soils was not performed, but based on observations of the test pit excavations, the soils appeared to be generally stiff and the bedrock very hard. The very hard bedrock limited excavations. Logs of the soils encountered are presented on the Logs of Exploratory Borings, Figure 2. Samples were returned to the laboratory where they were visually classified and testing was assigned to evaluate the engineering properties of the soil. Laboratory testing consisted of natural Soils and Foundation Investigation Job No. 15664W Page 3 moisture content and gradation analyses. The results of the laboratory testing are presented on Figures 2 through 4. SUBSURFACE CONDITIONS Subsurface materials encountered in Test Pit 1 (TP -1) consisted of 3 inches of clayey topsoil and root zone, overlying severely weathered basalt (boulders in a slightly sandy clay matrix) to the maximum explored depth of 2 feet. Materials encountered in TP -2 consisted of 6 inches of clayey topsoil and root zone, overlying severely weathered basalt (boulders in a slightly sandy clay matrix) to 1.5 feet. Underlying the boulders, slightly weathered basalt bedrock was encountered to the maximum explored depth of 3 feet. Practical backhoe refusal was encountered on the basalt in both test pits. Free water was not encountered in either test pit during excavation. Based on our observations, ground water should not be an issue during construction. Additional subsurface details are presented on Figure 2. The surficial deposits are colluvium and sheetwash, and the underlying bedrock is Miocene age basalt based on the geologic map for the area, Geologic Map of the Carbondale Quadrangle. Garfield County. Colorado Open -File report 97-3, Kirkham and Widmann, Colorado Geological Survey, 1997. The site is on the flanks of the Carbondale Collapse Center, which is an area where regional collapse is occurring due to dissolution and/or flowage of relatively shallow evaporitic rocks below the surficial deposits. The unit underlying the basalt, the Eagle Valley Evaporite, contains beds of gypsum, anhydrite, and halite (rock salt) which dissolve when exposed to water. This means that a risk of ground loss exists in the area. We did not observe any sinkholes or other evidence of near -surface dissolution or collapse on the site, so the risk of detrimental ground loss during the life of the structure (assumed to be 100 years) appears to be low. It should be noted that several collapse structures are present in the area of the Colorado Mountain College campus located approximately 1 mile east of the property. The geotechnical practice in Colorado uses a relative scale to evaluate swelling potentials. When the sample is wetted under a surcharge pressure of 1000 pounds per square foot (PSF), the Soils and Foundation Investigation Job No. 15664W Page 4 measured swell is classified as low, moderate, high, or very high. It is important to note that measured swell is not the only criteria for slab -on -grade recommendations and additional factors are considered by the geotechnical engineer when evaluating the risk for slab -on -grade and foundation construction. Based on the limited amount of soil present and the presence of basalt boulders, the swell risk is assumed to be low for this property. Additional information regarding geotechnical risk is included as Appendix A. SITE PREPARATION Organic material and debris should be removed from the foundation area and wasted off site or used for non structural purposes. Any required structural fill should be placed in 8 -inch uncompacted thickness lifts and compacted to 95 percent of the standard Proctor maximum dry density (MPD) within 2 percent of the optimum moisture content. Uncontrolled fill at foundation elevations should be removed and replaced with structural fill. Structural fill is a non -expansive material that classifies as sand according to the Unified Soil Classification System possessing a silt and clay fraction less than 35 percent, a liquid limit less than 40 and a plasticity index less than 20. Structural fill should be placed as recommended above. Any soils loosened by the excavation or forming process should be removed from the footing areas prior to placing concrete or compacted as recommended above. A geotechnical engineer should review earthwork placement activities. EXCAVATIONS Excavations should not remain open for extended periods of time, permitting wetting or drying of the bearing materials. Moisture changes of the bearing materials may increase the risk for movement. The materials on site are categorized as Type 13 overlying stable rock according the Occupational Safety and Health Administration (OSHA). Based on published OSHA guidelines, the temporary excavations in the Type B soils can have a maximum temporary slope of 1:1 horizontal:vertical (H:V). Excavations Soils and Foundation Investigation Job No. 15664W Page 5 in the rock can be vertical. This inclination is reasonable for the conditions at the site. Exceeding this inclination will increase the chance of deformation, especially over a long time period. Some localized pdeformation of the bank may occur, especially during wet weather, loading or with vibrations. Care should be taken when working near the sides of the excavation at all times, and the slopes should be monitored by onsite personnel during construction for evidence of sloughing, bulging or toppling of the sidewalls or cracking at the ground surface. Surcharge loading at the top of the cut by equipment, materials. or vehicles must be avoided, since surcharge loading will increase the risk of caving. Spoils of ' the excavation must be placed a minimum of 2 horizontal feet from the edge of the excavation. A geotechnical engineer should observe the completed excavation prior to foundation installation. BUILDING FOUNDATIONS ' The soils at the anticipated foundation elevations of 3 feet below the ground surface consist of basalt boulders in a slightly sandy clay matrix and basalt bedrock. The proposed residence can be constructed with a spread footing foundation system founded on either the native soil or the basalt ' bedrock. The footings should be designed for a maximum allowable soil bearing pressure of 2,500 ' pounds per square foot (PSF). A spread footing foundation system should be designed and constructed to meet the following criteria. ' 1. All footings must be supported by native clayey soils or bedrock. Soils loosened by the excavation or forming process should be removed from the footing areas prior to placing 1 concrete. If structural fill is required below foundations, it should be placed as detailed above in the Site Preparations section of this report. The footing excavations should be observed by a geotechnical engineer to confirm footings are supported by suitable material. 2. Recommended minimum footing widths should be at least 16 inches for continuous footings, and 20 inches square for concrete pads, which support columns. Larger sized footings may be necessary depending on the load of the structure. 3. Continuous foundation walls should be reinforced to span local anomalies in the subsoil. A minimum reinforcement of at least two, No. 5 grade 60 bars top and bottom in all foundation walls is recommended; however, steel reinforcement should satisfy the structural plans. Walls should be reinforced to span an unsupported length of 10 feet, 1 1 Soils and Foundation Investigation Job No. 15664W Page 6 4. Footings must be protected from frost action. Footings should be covered with a minimum of 3 feet of soil for frost protection. SLAB -ON -GRADE CONSTRUCTION The boulders in a slightly sandy clay matrix and the basalt encountered near the ground surface is suitable for support of slab -on -grade construction with a low risk of movement due to expansive soils. The slabs should ideally be constructed as "floating" slabs, which are free to move in the vertical direction. The slabs should not be attached to interior or exterior bearing members. If needed for lateral resistance or other reasons, slabs can be connected to the foundation walls, with a low risk of cracking or movement. If fill soils are used, a structural fill should be used and compacted and placed as detailed in the "Site Preparations" section of this report. The following design and construction details are recommended for slab -on -grade construction. 1. Slabs should be separated from exterior walls and interior bearing members. Vertical movement of the slabs should not be restricted. 2. Slab bearing partitions should be minimized. Where such partitions are necessary, a slip joint should be constructed to allow free vertical movement of the partitions. Slip joints should allow at least 1 inch of vertical movement in both directions. 3. Underslab plumbing should be eliminated where feasible. Where such plumbing is unavoidable it should be thoroughly pressure tested during construction. 4. Plumbing and utilities, which pass through the slab, should be isolated from the slab. 5. If a forced air heating system is used and the furnace is located on the slab, we recommend provision of a collapsible connection between the furnace and the duct work. LATERAL LOADS AND DRAINAGE Below grade finished space is not proposed. If information regarding lateral loads or subsurface drainage is needed, our office should be contacted. If foundations or finished living space below 3 feet or retaining walls are planned, our firm should be contacted for additional recommendations. The risk for wetting of foundation soils and "wet crawl space" conditions can be reduced by carefully planned Soils and Foundation Investigation Job No. 15664W Page 7 and maintained surface drainage. The following precautions should be observed during construction and be maintained at all times after the structure is completed. 1. Excessive wetting or drying of open foundation excavations should be avoided as much as possible during construction. 2. Backfill at foundation walls should be moistened and compacted. Any settlement of backfill after completion of the structure should be immediately filled and positive drainage reestablished. 3. The ground surface surrounding the structures should be sloped to drain away from the structure in all directions. A minimum slope of 12 inches in the first 5 to 10 feet should be developed and maintained after construction. Irrigation should be avoided within 5 to 10 feet of the foundation walls. 4. Roof downspouts and drains should discharge to the surface well beyond the limits of all backfill. 5. Plastic membranes should not be used to cover the ground surface immediately surrounding the structure. These membranes can trap moisture and prevent normal evaporation from occurring. Geotextile fabrics are a suitable option to control weed growth and allow some evaporation. LINIITATIONS Although the test pits were located to obtain a reasonably accurate determination of foundation conditions, variations in the subsoil conditions are possible. Our firm should be contacted if conditions different from those described are encountered in the excavations. Excavations should be observed by a representative of our firm. The cost of construction observations is not included in this investigation. An environmental assessment of the property is outside our scope of work for this project. Soils and Foundation Investigation Job No. 15664W Page 8 If we can be of further service in discussing the contents of this report, or in the analysis of the influence of subsurface conditions on the design of the structures. please call. CHURCH & Associates, Inc. Reviewed by C. Steven Compton' Mark J. VesseIy, P.E. Project Geologist Geotechnical Group Manage MJV/csc 3 copies sent 1 copy to: •aliiirmw silliMMINIMMIma IIIIINMMINMNINND PROPOSED RESIDENCE LOT 12, LOS AMIGOS RANCH, FILING 2, (AKA ELK SPRINGS) GARFIELD COUNTY, COLORADO SCALE 1" = 60' ri PARTIAL SITE PLAN AND LOCATION OF JOB NO. 15664W EXPLORATORY TEST PITS FIGURE 1 w w 2 Q_ 0w --0 2 3 4 EXPLANATIONS: TP -1 ® TOPSOIL; CLAYEY, MOIST, BROWN WC=20,6 -200 = 66 TP -2 WC = 15.1 -200 = 69 jrIV SEVERELY WEATHERED BASALT, BOULDERS UP TO 1'X2 X3' IN A SLIGHTLY SANDY, CLAY MATRIX, SLIGHTLY MOIST, TAN \\ill BASALT BEDROCK, SLIGHTLY WEATHERED, JOINTED, VERY HARD. BLACK INDICATES DEPTH TO PRACTICAL BACKHOE REFUSAL INDICATES THAT A BULK SAMPLE WAS COLLECTED NOTES: 1. THE EXPLORATORY TEST PITS WERE EXCAVATED ON 5-2-2003 USING A JOHN DEERE 710D 4X4 RUBBER -TIRED BACKHOE 2 NO FREE WATER WAS ENCOUNTERED AT THE TIME OF EXCAVATION. 3. WC = WATER CONTENT(%) -200 = PERCENT OF FINES PASSING THE NUMBER 200 SIEVE. !no 1. Ir., a cf`!_•A4A: LOGS OF EXPLORATORY TEST PITS DEPTH - FEET Percent Passing 100 0 90 0 80-0 70.0 60.0 50 0 40 0 30 0 20 0 100 0.0 CHURCH & Associates, Inc. Engineers & Geologists Denver Metro Colorado 303-463-9317 Pine Junction ? Evergreen Colorado 303-816-1455 Castle Rock, Colorado 303-660-4358 Loveland, Colorado 970-663-2124 Gradation Test Results #200 #100 #50 #30 #1G #8 #4 318" .1" 1- /r 3" 0 00I 0. 1 Diameter or Particle in Millimeters DESCRIPTION: Clay, sandy, gravelly, nloi$tr brown, roots 10 GRAVEL 17% HOLE 1 SAMPLE TP -1 SAND 17% DEPTH 1' FINES 66°lo LIQUID LIMIT N/A MOISTURE 20.6% PLASTICITY INDEX N/A DRY DENSITY (pcf) NIA DATE: JOB NAME: Pinon Dr JOB NUMBER: 15664 10 20 30 40 50 60 70 80 90 100 100 FIGURE 3 Percent Retained 111111 111 1111111r411 II ISA 4 ill 1111111 inill ' 1111111111 1 1111111111111 II - 111 1 11E 1111 00I 0. 1 Diameter or Particle in Millimeters DESCRIPTION: Clay, sandy, gravelly, nloi$tr brown, roots 10 GRAVEL 17% HOLE 1 SAMPLE TP -1 SAND 17% DEPTH 1' FINES 66°lo LIQUID LIMIT N/A MOISTURE 20.6% PLASTICITY INDEX N/A DRY DENSITY (pcf) NIA DATE: JOB NAME: Pinon Dr JOB NUMBER: 15664 10 20 30 40 50 60 70 80 90 100 100 FIGURE 3 Percent Retained Percent Passing 100.0 90 0 80 0 70.0 60 0 50 0 400 30 0 20 0 100 00 CHURCH & Associates, Inc. Engineers & Geologists Denver Metro Colorado 303-463-9317 Pine !unction / Evergreen Colorado 303-816-1455 Castle Rock, Colorado 303-660-4358 Loveland_ Colorado 970-663-2124 17.200 Gradation Test Results #100 1750 #10 1116 if8 44 319" 3M" 1-112' 3" F-- 0 10 20 ,130 0,01 0.1 1 Diameter of Particle in Millimeters DESCRIPTION: Clay, sandy, gravelly, moist, brown, roots GRAVEL SAND FINES MOISTURE 10 HOLE 1 SAMPLE TP -2 DLPTH 1' LIQUID LIMIT N./A PLASTICITY INDEX N/A DRY DENSITY (pcf) N/A 40 50 60 70 80 90 100 100 DATE: 5(2/03 JOB NAME: Pinon Dr JOB NUMBER: 15664W FIGURE 4 Percent Retained Appendix A Important Information About The Report The data collected by Church & Associates during this investigation was used to provide geotechnical information and recommendations regarding subsurface conditions on the site investigated, the effect of those conditions on the proposed construction, and the foundation type for the named client. The stratification lines indicated on the boring log are approximate, and subsurface conditions encountered during construction may differ from those presented herein. This uncertainty cannot be eliminated because of the many variabilities associated with geology. For example, material and engineering characteristics of soil and bedrock may change more gradually or more quickly than indicated in this report, and the actual engineering properties of non -sampled soil or rock may differ from interpretations. Quantitative conclusions regarding the performance of geotechnical structures prior to construction are not possible because of the complexity of subsurface conditions. Rather, engineering judgments and experience are used to estimate likely geotechnical performance and provide the necessary recommendations. Put another way, we cannot be sure about what is not visible, so the collected data and our training and experience are used to develop predictions and recommendations. There are no guarantees or warranties implied or expressed. The owner and/or client must understand that uncertainties are associated with geotechnical engineering, and they, the owner and/or client, must determine the level of risk they are willing to accept for the proposed construction. The risks can be reduced, but not eliminated, through more detailed investigation, which costs more money and takes more time, and through any appropriate construction which might be recommended as a result of that more detailed investigation. To reduce the level of uncertainty, this report was prepared only for the referenced client and for the proposed construction indicated in the report. Unless authorized by Church & Associates in writing, the owner will assume additional geotechnical risk if this report is used for any construction that differs from that indicated in the report. Our firm should be consulted well before changes in the proposed construction occur, such as the nature, size, configuration, orientation, or location of any improvements. Additionally, the knowledge and experience of the local geotechnical practice is continually expanding and it must be understood the presented recommendations were made according to the standard of practice at the time of report issuance. If the construction occurs 1 or more years after issuance of the report, the owner and/or client should contact our firm to determine if additional investigation or revised recommendations would be advisable. Post -construction landscaping and owner maintenance will greatly affect structures on expansive or collapsible soils and bedrock. Typically, irrigated landscaping increases the soil moisture content above the pre -construction water content. Slabs, pavements, and structures significantly reduce evaporation of soil moisture. Therefore, post -construction soil movement and resulting damage to buildings and other improvements are likely to occur on sites with expansive or collapsible soils because of the high probability that subsurface moisture content will increase as the property and surrounding area is developed. Poor owner maintenance, such as negative slopes adjacent to foundation walls and irrigated landscaping adjacent to the foundation, also will significantly increase the risk of damage from soil movement. The property owner, and anyone he or she plans to sell the property to, must understand the risks associated with construction and also must assume responsibility for maintenance of the structure.