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HomeMy WebLinkAboutFoundation RecommendationsHuddleston -Berry Engineering & Testing, LLC JP Construction P© Box 1880 Lyons, Colorado 80540 Attention: Mr. John Prater Subject: Foundation Recommendations and ISDS Design Mills Residence 19190 County Road 204 DeBeque, Colorado Dear Mr. Prater, 640 White Avenue Grand Junction, CO 81501 Phone: 970-255-8005 Fax: 970-255-6818 HuddlestonBerry@bresnan.net www.HBET-GJ.com August 21, 2012 Project#01199-0001 At your request, Huddleston -Berry Engineering & Testing, LLC (HBET) conducted a geotechnical investigation for the Mills Residence near DeBeque, Colorado. The site location is shown on Figure 1 — Site Location Map. The proposed construction is anticipated to include of a single-family residence. The scope of our investigation included evaluating the subsurface conditions at the site to aid in developing foundation recommendations for the proposed construction and to permit design of an Individual Sewage Disposal System (ISDS) at the site. Site Conditions At the time of the investigation, the site was generally open with gentle to moderate slopes up to the north and northwest. Vegetation consisted of short to tall grasses and weeds with numerous medium to large trees in the southern portion of the site. Thick Juniper trees and brush was observed on the hills surrounding the site. Several abandoned structures were observed at the site. The site was bordered by County Road 204 to the south and by open land to the north, east, and west. Subsurface Investigation The subsurface investigation included two test pits in the vicinity of the house and three test pits in the vicinity of the proposed ISDS absorption field. The locations of the test pits are shown on Figure 2 — Site Plan. The test pits were excavated to depths of between 3.0 and 9.0 feet below the existing ground surface. Typed test pit logs are included in Appendix A. Mills Residence 1101199-0001 08/21/12 Huddleston -Berry ea;c::,ing. Tr.:ins, I i C Test Pit TP -1, conducted north of the proposed house location, encountered 1.0 foot of clayey sand with gravel and organics topsoil above purple to tan to white, dry, very dense clayey sand with gravel to a depth of 3.0 feet. Below the sand, black to gray to white to purple, soft to medium hard, highly weathered bentonite extended to the bottom of the excavation. Groundwater was not encountered in TP -1 at the time of the investigation. Test Pit TP -2, conducted west of the proposed house location, encountered 1.0 foot of clayey sand with shale and organics topsoil above brown, dry to moist, medium dense to dense clayey sand with gravel and shale to the bottom of the excavation. Groundwater was not encountered in TP -2 at the time of the investigation. Test Pit TP -3, conducted in the vicinity of the proposed absorption field, encountered 4.0 feet of gravel fill materials above brown, dry to moist, medium dense to dense clayey sand with gravel and shale to the bottom of the excavation. Groundwater was not encountered in TP -3 at the time of the investigation. Test Pit TP -4, also conducted in the vicinity of the proposed absorption field, encountered 1.5 feet of clayey sand with shale and organics topsoil above brown, dry to moist, medium dense clayey sand with gravel and shale to the bottom of the excavation. Groundwater was not encountered in TP -4 at the time of the investigation. Test Pit TP -5, conducted in the vicinity of the proposed absorption field, encountered 1.5 feet of clayey sand with shale and organics topsoil above brown, dry to moist, medium dense clayey sand with gravel and shale to the bottom of the excavation. Groundwater was not encountered in TP -5 at the time of the investigation. Laboratory Testing Laboratory testing was conducted on samples of the native soils and bentonite collected in the test pits. The testing included grain -size analysis, Atterberg limits determination, natural moisture content determination, and swell/consolidation. The laboratory testing results are included in Appendix B. The laboratory testing results indicate that the native sand soils are moderately plastic. In addition, the sand soils were shown to be slightly collapsible at their existing density with up to approximately 0.6% collapse measured in the laboratory. However, based upon the Atterberg limits of the native sand soils and presence of shale in the sands, HBET anticipates that the native clayey sand soils have the potential for expansion when compacted and introduced to excess moisture. The native bentonite materials were determined to be moderately to highly plastic. Based upon the Atterberg limits of these materials, the bentonite is anticipated to be moderately to highly expansive. W:\2008 ALL PROJECTs101199 - JP Construction101199-0001 Mills Residence1200 - Geo101199-0001 LR082112.doc 2 Mills Residence #01199-0001 08/21/12 Hiuddleston-Berry Foundation Recommendations Based upon the results of the subsurface investigation and nature of the proposed construction, the recommended foundation alternatives include spread footings, voided spread footings, isolated pads and grade beams, structural ribbed (waffle) slab, or monolithic (turndown edge) structural slab. However, as indicated above the native sand soils are anticipated to be slightly collapsible at their existing density and slightly expansive when compacted. In addition, the native bentonite materials are anticipated to be moderately to highly expansive. Therefore, to Iimit the potential for excessive differential movements, it is recommended that the foundations be constructed above structural fill. In general, it is recommended that spread footing, voided spread footing, or isolated pad and grade beam foundations be constructed above a minimum of 30 -inches of structural fill. It is recommended that a monolithic (turndown edge) slab foundation be constructed above a minimum of 42 -inches of structural fill. It is recommended that a ribbed slab foundation be constructed above structural fill extending to the base of the ribs. The depth of the ribs should be determined by the structural engineer to ensure rigidity of the slab. However, it is recommended that all foundations be separated from the bentonite a minimum of five feet. As a result, the final thickness of structural fill will be dependent upon the actual location of the house. Due to their potential for expansion, the native clayey sand soils are not suitable for reuse as structural fill. Imported structural fill should consist of a granular, non -expansive, non free draining material such as pit -run with high fines content, crusher fines, or CDOT Class 6 base course. However, if pit -run is used for structural fill, a minimum of six inches of crusher fines or Class 6 base course should be placed on top of the pit run to prevent large point stresses on the bottoms of the foundations due to large particles in the pit -run. Prior to placement of structural fill, it is recommended that the bottom of the foundation excavation be proofrolled to the Engineer's satisfaction. Structural fill should extend laterally beyond the edges of the foundation a minimum of 24 -inches. Structural fill should be moisture conditioned, placed in maximum 8 -inch loose lifts, and compacted to a minimum of 95% of the standard Proctor maximum dry density for fine grained soils and 90% of the modified Proctor maximum dry density for coarse grained soils, within ± 2% of the optimum moisture content as determined in accordance with ASTM D698 and D1557C, respectively. For structural fill consisting of imported granular materials, and foundation building pad preparation as recommended, a maximum allowable bearing capacity of 2,000 psf may be used. However, a minimum dead -load of 500 psf is recommended for spread footing, voided spread footing, or isolated pad and grade beam foundations. Where the minimum dead -load is not achievable, such as for interior foundations, the dead -load should be maximized to the extent practical. Footings should not be less than 12 -inches wide to limit the potential for a punching shear bearing capacity failure. For pit -run, base course, or crusher fines, a modulus of subgrade reaction of 250 pci may be used. Footings subject to frost should be at least 36 -inches below the finished grade. W:12008 ALL PROJPCTS101199 - JP Construction101199-0001 Mills Residence1200 - Geo \01199-0001 LR082112.doc 3 Mills Residence #p01199-0001 08/21/12 Huddleston -Berry fryL,,,ringS Train;, I. I.0 Lateral Earth Pressures Any stemwalls, basement walls, or retaining walls should be designed to resist Iateral earth pressures. For backfill consisting of the native sand soils or imported granular, non free draining, non -expansive material, we recommend that the walls be designed for an equivalent fluid unit weight of 60 pcf in areas where no surcharge loads are present. Lateral earth pressures should be increased as necessary to reflect any surcharge loading behind the walls. Floor Slab and Exterior Flatwork Recommendations As mentioned above, expansive soils are present at the site. Due to the fact that slabs -on -grade do not generate sufficient loads to resist heave, differential movement of slabs -on -grade should be anticipated. However, to help limit the magnitude of movement, it is recommended that floor slabs be constructed above a minimum of 18 -inches of structural will with subgrade preparation and fill placement in accordance with the Foundation Recommendations section of this report. It is recommended that exterior slabs -on -grade be constructed above a minimum of 12 -inches of structural fill. Drainage Recommendations Grading around the structure is critical to the performance of the foundations and grading should be designed to carry precipitation and runoff away from the structure. It is recommended that the finished ground surface drop at least twelve inches within the first ten feet away from the structure. Downspouts should empty beyond the backfill zone. It is also recommended that landscaping within five feet of the structure include primarily desert plants with low water requirements. In addition, it is recommended that irrigation within ten feet of foundations be minimized or controlled with automatic shut off valves. If a structural floor and crawlspace and/or basement are proposed, perimeter foundation drains are recommended. In general, the perimeter foundation drains should consist of prefabricated drain materials or perforated pipe and gravel systems with the flowlines of the drains at least one foot below the bottoms of the foundations (at the highest point). The perimeter drain should slope at a minimum of 1.5% to daylight or to a sump. In addition, the gravel or other prefabricated drainage materials should extend along the basement walls to within 36 -inches of the finished ground surface. A geomembrane or other moisture barrier is also recommended along the footings/stemwalls and below the perimeter drains to limit the potential for surface moisture to penetrate down to the expansive soils and/or bedrock. Individual Sewage Disposal System Percolation testing was conducted in the vicinity of the proposed ISDS in TP -3, TP -4, and TP -5. The percolation rate in the native sand soils was determined range from 8 to 17 minutes -per -inch with an average of approximately 13 minutes -per -inch. The percolation testing data are included in Appendix C. In general, a percolation rate of between 5 to 60 minutes -per -inch is required for soils to be deemed suitable for on-site sewage disposal. Therefore, based upon the results of the percolation testing, the native clayey sand soils are suitable for on-site sewage disposal. W:12008 ALL PROJECTS101199 - JP Construction101199-0001 Mills Residence1200 - Geo101199-0001 LR082112.doc 4 Mills Residence #01199-0001 08/21/12 Audd[eston-Berry fry �.L Te. in,, I. I In addition to the percolation rate of the subsurface materials, the seasonal high groundwater elevation is an important factor in determining the suitability of the site for Individual Sewage Disposal Systems. For ISDS suitability, the seasonal high groundwater elevation should be at least four feet below the bottom of the proposed absorption bed. As discussed previously, groundwater was not encountered in the test pits in the vicinity of the ISDS at the time of the investigation. Due to the fact that the subsurface investigation was completed during the irrigation season, HBET believes that the seasonal high groundwater elevation is deeper than 9.0 feet below the existing ground surface elevation. Seepage Bed Design The design of the absorption system generally follows the requirements of the State of Colorado and Garfield County. The proposed construction at the site is anticipated to include an approximately 2,400 square -feet main house with five bedrooms. A clothes washer and garbage disposal are also anticipated. For conservatism, a soil percolation rate of 30 minutes -per -inch will be utilized for the absorption field design. Based upon information provided to HBET, Infiltrator Systems Quick4 Standard Chambers will be used for the absorption bed. As a result, a 40% reduction in the bed area is permitted. The maximum daily flow of the sewage disposal system is calculated below. Base Residential Flow = (5 bedrooms)(2 persons/bedroom)(75 GPD/person) = 750 GPD Average Daily Flow = (750 GPD)(1.0+0.4+0.2) = 1,200 GPD Maximum Daily Flow — (1,200 GPD)(1.5) = 1,800 GPD Standard Bed Area = [(1,800 GPD)(30 min/in)°']/5 1,972 Square Feet Reduced Area = (1,972 ft2)(0.40) = 789 Square Feet # of Quick4 Chambers = (789 / 9.2) = 86 Chambers Minimum A plan and profile of the ISDS absorption field is included as Figure 3. System Installation The installation of the septic tank, plumbing lines, absorption bed, etc. should be completed in accordance with the State of Colorado and Garfield County regulations. In addition, the following construction procedures are recommended: • The septic tanks and distribution box should be placed level over native soils that have been scarified to a depth of 8 to 12 inches, moisture conditioned, and recompacted to a minimum of 95% of the standard Proctor maximum dry density, within J2% of optimum moisture content. However, up to 3 -inches of washed rock or pipe bedding passing the 1 -inch sieve may be used as a leveling course under the septic tanks and/or distribution box. • The bottoms of trenches and backfill around the septic tanks and distribution box which will support sewer or effluent lines should be compacted to at least 90 percent of the standard Proctor maximum dry density, within ±2% of optimum moisture content. Pipe bedding should have a maximum particle size of 1 -inch. W:12008 ALL PROJECTS101199 - JP ConstrtLction101199-0001 Mills Residence \200 - Geo101199-0001 LR082112.doc 5 Mills Residence #01199-0001 08/21/12 Huddleston -Berry [n,liunin,d h4init. 1 1 C • Vehicular or heavy equipment traffic and placement of structures should not encroach within 10 feet of the septic tanks or distribution box. Inspection Schedule Huddleston -Berry Engineering & Testing LLC should be retained to monitor the construction of the ISDS. The following schedule of observation and/or testing should be followed: • Observe the absorption bed excavation prior to placement of gravel and disposal lines. • Observe placement of the septic tank, distribution box, and all connecting sewer and effluent lines prior to backfill. Verify proper fall between inverts. • Observe and verify installation of the absorption bed prior to placement of cover and backfill. General Notes The recommendations included above are based upon the results of the subsurface investigation and on our local experience. These conclusions and recommendations are valid only for the proposed construction. As discussed previously, the subsurface conditions at the site were observed to be slightly variable. However, the precise nature and extent of any subsurface variability may not become evident until construction. Therefore, it is recommended that HBET be contracted to provide engineering oversight during construction. It is important to note that the use of structural fill below slabs and foundations will reduce, but not eliminate, the potential for structural movement as a result of collapse and/or swelling of the native sand soils or swelling of the native bentonite materials. However, where excess moisture is permitted to infiltrate into the subsurface due to poor grading and drainage, irrigation leak, utility leak, or other cause, significant structural movements are likely. While the foundation recommendations above are consistent with generally accepted engineering practices in areas of swelling soils and/or bedrock, HBET cannot predict long-term changes in subsurface moisture conditions and/or the precise magnitude or extent of swelling or swelling pressures. We are pleased to be of service to your project. Please contact us if you have any questions or comments regarding the contents of this report. Respectfully Submitted: Huddleston -Be ry Engineering and Testing, LLC • t� •c, ". . :2 3 0 0 501. IPPON t Michael A. Berry, P.E. Vice President of Engineering W:12008 ALL PROJECTS101199 - JP Construction101199-0001 Mills Residence1200 - Geo\01199-0001 LR082112.doc 6 FIGURES -.-• County Line -- Geog Twp Line Lot Line Misc Line — Mon Linear — Parcel Line Parcel Line Leg Desc w.,, Po1 Corp Line — Pol Twp • Line -Railroad Centerline --Railroad ROW Road Centerline Road ROW ---Section Line Sub Line100 Sub Line400 -_. Sub Ref Strip — Unknown Linear --Water Line T6'5 R 1 GQ;'. T,_ R1if','2 1626 Feet Site Location Hrsriaolcue Owner Information MILLS, PAUL H & JULIA L, TRUSTEES OF THE MILLS FAMILY TRUST DTD 7-27-90 24535 OVERLAKE EL TORO, CA 92630-3639 parcel Number: 216530100016 Site Information Acres: 320 Account Number: R290161 T73 R9 96' FIGURE 1 Site Location Map 4-1 V) CO l9 clz ABSORPTI'ION BED PLAN ESTABLISH VEGETATIV 4' MAX BURIAL QUICK4 STANDARD (TYP.) -16.15 FT 6 -IN. MIN 34" I RESIDENTIAL STRUCTURE :PTIC TANK; MINIMUM 1,500 ALLAN CAPACITY BOX WITH FIVE Berry esting, LLC 0 2 4 nue, Unit B ,CO 81501 MILLS RESIDENCE FIGURE 3 - SEPTIC SYSTEM PLAN AND PROFILE APPENDIX A Typed Test Pit Logs 0 0 ❑ Z_ 0 a ui 0 z 0 uJ a 0 S 0, 0 z 2 J 0 0 CD 2 S 0 EU 0 0 w oN -� CLIENT PROJECT e",, .; co+970-255-6818 JP Huddleston -Berry Engineering & Testing, LLC 640 White Avenue, Unit B Grand Junction, CO 81501 970-255-8005 Construction PROJECT NAME LOCATION TEST PIT NUMBER TP -1 PAGE 1 OF 1 Mills Residence NUMBER 01199-0001 PROJECT DeBeque, CO DATE EXCAVATION EXCAVATION LOGGED NOTES STARTED BY 7/31/12 COMPLETED 7/31/12 GROUND ELEVATION WATER LEVELS: TIME OF EXCAVATION END OF EXCAVATION EXCAVATION TEST PIT SIZE CONTRACTOR Hi -River GROUND dry METHOD Mini -Excavator AT AS CHECKED BY MAB AT dry AFTER --- o DEPTH (ft) GRAPHIC LOG MATERIAL DESCRIPTION SAMPLE TYPE NUMBER RECOVERY % (RQD) BLOW COUNTS (N VALUE) POCKET PEN. (tsf) z m >- re n MOISTURE CONTENT (%) ATTERBERG LIMITS FINES CONTENT (%) LIQUID LIMIT PLASTIC LIMIT PLASTICITY INDEX ''. ` ii..;i.f; r,...sC I/. Clayey SAND with Gravel and Organics (TOPSOIL), reddish purple, dry 2.5 f !. Claa SAND with Sandstone Gravel(sc?), reddish purple, tan and white, dry, very dense -I 5.0 BENTONITE, black, gray, greenish gray, white and dark purple, soft to medium hard, highly hi hl weathered GB 1 12 57 18 39 - � A `j GB 2 12 45 16 29 Bottom of test pit at 7.0 feet. �NGSNEfR�,f,C -:•=aoke CLIENT PROJECT JP Huddleston -Bevy Engineering & Testing, LLC 640 White Avenue, Unit B Grand Junction, CO 81501 970-255-8005 970-255.6818 Construction PROJECT NAME LOCATION TEST PIT NUMBER TP -2 PAGE 1 OF 1 Mills Residence NUMBER 01199-0001 PROJECT DeBeque, CO DATE EXCAVATION EXCAVATION LOGGED NOTES STARTED BY 7/31/12 COMPLETED 7/31/12 GROUND ELEVATION WATER LEVELS: TIME OF EXCAVATION END OF EXCAVATION EXCAVATION TEST PIT SIZE CONTRACTOR Hi -River GROUND dry METHOD Mini -Excavator AT AS CHECKED BY MAB AT dry AFTER =-- m a = w " O 0.0 GRAPHIC LOG MATERIAL DESCRIPTION SAMPLE TYPE NUMBER RECOVERY % (RQD) BLOW COUNTS (N VALUE) POCKET PEN. (tsf) DRY UNIT WT. (pcf) MOISTURE CONTENT (%) ATTERBERG LIMITS FINES CONTENT (%) LIQUID LIMIT PLASTIC LIMIT PLASTICITY INDEX _ _...`5 •: •` i,.;i.4:• 1 I' ',l Clayey SAND with Shale fragments and Organics (TOPSOIL), brown, dry 2.5 Clayey SAND with Gravel and Shale fragments (SC), with large gravel lenses and thin sand lenses, brown to orangish brown, dry to moist, medium dense to dense, abundant sulfates G61: Lab Classified 5.0 drYt_ 11 GB1 13 38 24 14 48 1 MC 1 92 17 7.5 Bottom of test pit at 8.0 feet.