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Home My WebLink About20170082.tiffGEOTECHNICAL INVESTIGATION FOR 5300 KIOWA DRIVE, WELD COUNTY, COLORADO FOR WESTERN CONSTRUCTION MANAGEMENT CDS ENGINEERING CORPORATION LOVELAND, COLORADO PROJECT NUMBER 15-7752 NOVEMBER 3, 2015 November 3, 2015 Project No. 15-7752 IZI. .eai.�at 'LIB:. 't,WAMTVIT 79. Mr. Steve Carrier Western Construction Management 724 Soaring Eagle Drive LaPorte, CO 80535 Dear Steve, Enclosed is the report you requested of the geotechnical exploration for the proposed residence to be located at 5300 Kiowa Drive, Weld County, Colorado. The site appears to be suitable for the construction of the proposed residence, provided the design criteria and recommendations given in this report are followed. If you have any further questions concerning the information in this report; please contact this office. Reviewed by: Enclosures ' Respectfully, FOR AND ON BEHALF OF CDS ENGINEERING CORPORATION V. 1 , Vos D. Eriz, gineering Technician • TABLE OF CONTENTS Letter of Transmittal Table of Contents Scope Site Investigation Site Location and Description Subsurface Conditions Foundation Recommendations - Drilled Pier (Caisson) and Grade Ream Foundation - Continuous Spread Footing and Isolated Pad Foundation Lateral Earth Pressures Slab Construction Foundation Drain System Conclusions ATTACHMENTS Location of Test Borings Symbols and Soil Properties Log of Borings Swell -Consolidation Test Results Summary of Test Results Post -Construction Site Preparation and Maintenance Typical Perimeter Drain Details Placement of Compacted Fill Materials ii Page i ii 1 1 2 2 2 3 4 5 5 7 7 Drawing No. I Figure No. 1 Figure No. 2 Figure Nos. 3 & 4 Table No. I Appendix 1 Appendix 2 Appendix 3 1 SCOPE This report presents the results of a geotechnical exploration for the proposed residential building to be located at 5300 Kiowa Drive, Weld County, Colorado, The building is anticipated to be of typical wood frame construction. Walkout basement construction is anticipated for this structure, with the anticipated foundation bearing depths to range from two (2) to seven (7) feet below grades which existed at the time of this exploration. This exploration was conducted to provide recommendations pertaining to the type and depth of foundation system, allowable soil bearing pressures, groundwater conditions, and to identify any complications that may be encountered during or after construction due to subsurface conditions. A preliminary geotechnical engineering report conducted by CDS Engineering Corporation, Project No. 14-6S36, dated June 3, 2014, was reviewed as part of this exploration. SITE INVESTIGATION The field investigation performed on October 15, 2015, consisted of drilling, logging, and sampling one (1) test boring within the approximate building envelope at the site. The boring was drilled to a depth of twenty (20) feet. The location of the Test Hole is shown on Drawing No. 1. The boring location was established by a representative of CDS Engineering Corporation based on stakes provided by the homeowner. Distances from the referenced features were made by pacing and angles were estimated. A graphical log of the boring is shown on Figure No. 2. The descriptions of the soils and/or bedrock strata are based, primarily, on visual and tactual methods which are subject to interpretation. The test boring was advanced using a truck mounted, four -inch (4") diameter, continuous flight auger drill rig. Laboratory samples were obtained by driving a two and one-half inch (2'/a") diameter California Barrel Sampler twelve (12) inches (or as shown) into undisturbed soils with a 140 -pound hammer falling thirty (30) inches. Bag samples of auger cuttings may have also been collected. Laboratory tests performed were - Swell -Consolidation, Natural Moisture, Natural Dry Densities, and Unconfined Compressive Strengths. All tests were conducted in accordance with 2 AS TM standards. A Summary of the Swell -Consolidation Test Results is shown on Figure Nos. 3 and 4. A Summary of Test Results is shown on Table No. 1. SITE LOCATION AND DESCRIPTION The site is located south of Greeley, south of 37th Street, east of Arrowhead Drive, at the east end of Kiowa Drive, Weld County, Colorado. The site is in a developed rural subdivision with paved roads and utilities, and vegetation consists primarily of grasses. The building site has a gentle to moderate slope to the northeast. There is a small creek and a wetlands area north of the building site. SUBSURFACE CONDITIONS Based on the boring drilled within the proposed building footprint, the subsurface conditions at the site consist of silty sand overlying a clayey siltstone to the depths explord. Groundwater levels were recorded as the borings were advanced, after completion of the drilling operations, and the day after drilling operations were complete. During our field exploration groundwater was not encountered in the test boring. The groundwater table should be expected to fluctuate throughout the year depending on seasonal moisture variations. Refer to the Log of Borings, Figure No. 2, for additional details specific to each boring. FOUNDATION RECOMMENDATIONS The type of foundation best suited for a particular building site is dependant not only on the characteristics of the soil and rock but also depends on the type of structure, depth to groundwater, the proposed depth of excavation, and owner preference. The recommendations that follow are primarily based on the type of soil encountered. Based on the conditions observed in the field and laboratory tests, we recommend the foundation be a drilled straight shaft pier foundation. 3 As an alternative to the drilled pier foundation, a spread footing foundation bearing over a compacted structural soil mat could be utilized. However, it should be understood that this spread footing foundation is a flexible foundation. Foundation movement could still occur and may cause functional, architectural or structural damage. Drilled Pier (Caisson) and Grade Beam Foundation Due to the swell potential and the proximity of the bedrock strata, we recommend the use of a drilled pier (caisson) and grade beam foundation to support this structure. The piers should be designed for a maximum end bearing pressure of 15,000 pounds per square foot (dead load plus fall live load), and side shear of 1500 pounds per square foot for that portion of the caisson embedded in competent bedrock strata. Piers should be drilled a minimum length of twenty- three (23) feet with a minimum diameter of ten (10) inches and a minimum embedment into competent bedrock of ten (10) feet. All piers should be reinforced full-length with a minimum of two (2) #5 Grade 60 bars, or equivalent. This minimum is based on the anticipated tension loads applied to the piers by the surrounding soil. Piers may require additional reinforcement due to applied axial, lateral and/or uplift forces imposed. Additional reinforcement should be designed by a qualified structural engineer. A minimum six-inch (6") void is to be placed continuously between each pier under the grade beams. Pier caps or equivalent are recommended in the upper one (1) foot of the borings so as to maintain a circular, straight -shaft pier and prevent "mushrooming" of the pier. The recommended pier lengths are deeper than the test borings were drilled for this exploration. Subsurface conditions could be encountered that were not anticipated, such as groundwater or very hard strata. Additional borings could be drilled to the recommended pier depth if desired. Additional fees will apply. Reinforcement shall be placed in the borings prior to the placement of concrete. Concrete should be placed immediately after the borings have been cleaned and dewatered. In our opinion, casing and/or de -watering may be required. In the event that more than four (4) inches of water appears at the bottom of a shaft, concrete shall be placed from the bottom up with a pump truck or other approved method of displacing the water. A polyethylene moisture barrier 4 should be placed over the voids extending at least six (6) inches above and below the voids to help prevent excess moisture from migrating under slabs and in crawl space areas. The drilling operations for caisson installation should be observed by a representative of CDS Engineering Corporation to verify penetration into bedrock, and that the holes were properly cleaned and dewatered prior to placement of reinforcement and concrete. Continuous Spread Footing and Isolated Pad Foundation As an alternative to the drilled piers, the foundation could be a continuous spread footing and isolated pad foundation bearing on a structural soil mat. The foundation could be designed for a maximum allowable bearing capacity of 1500 pounds per square foot (dead load plus full live load) and a minimum dead load of 500 pounds per square foot to help counteract the swelling should the subsoils become wetted. The bottom of the footings should be kept a minimum of three (3) feet above the bedrock. The foundation is to bear on an imported soil mat, and not on unapproved fill, topsoil, or frozen ground. The bottom of all foundation components should be kept at least thirty (30) inches (or per local code) below finished grade for frost protection. The open excavation should not be left open for an extended period of time or exposed to adverse weather conditions. The completed open excavation should be observed by a representative of CDS Engineering Corporation in order to verify the subsurface conditions from test hole data. The compacted soil mat should be comprised of moisture and density controlled, imported materials approved by the engineer prior to delivery or placement. The mat should be at least three (3) feet thick and should extend, at a minimum, the thickness of the soil replacement, beyond the outside edge of the footings. We recommend that the excavation walls be cut at a 1:1 slope beyond the edged of the over -excavation, unless geometrically constrained by the size of the lot. The compacted soil mat could also be constructed under floor slab areas to reduce the amount of potential slab movement. Potential movement can be reduced but will not be completely eliminated. The deeper the soil replacement is conducted, the less risk of movement there will be. The soils that are to be used for the compacted soil mat shall be adequately broken, crushed and the moisture well blended prior to placement. The soils should be placed and compacted, 5 with compacted lifts not exceeding six (6) inches, to the moisture and density specifications described in Appendix 3 of this report. Each twelve (12) inches of the compacted soils should be tested and approved prior to placing the next lift. The Geotechnical Engineer shall be retained to supervise the placement of fill material. It is the contractor's responsibility to contact the engineer a minimum of 24 hours inadvance to schedule the testing. The fill shall be evaluated after placement is complete to verify the bearing values assigned above. Allow three to five business days for additional testing prior to placement of concrete. LATERAL EARTH PRESSURES Lateral earth pressures are forces exerted on earth retaining structures and foundation components, by the soil. The pressure exerted is influenced by wetting of the backfill soils, type and compaction of the backfill and the methods used to compact the backfill. For the soils, above the free groundwater surface at this site, we recommend the foundation components be designed using the following equivalent fluid pressures. + Active Pressure = 40 psf/ft • At Rest Pressure = 60 psf/ft These values assume that the positive drainage will be maintained throughout the life of the structure. It is our opinion that the on -site soils encountered could be used as backfill material against foundation walls. The bedrock could be used as fill material at this site. The soils shall be moisture conditioned and well pulverized so that all fragments are smaller than. six (6) inches. Refer to Appendix 1 for additional backfill information. If there is opportunity for the backfill soils to become saturated, we shall be notified to revise the minimum equivalent fluid density. These values do not include a factor of safety or take into account any surcharge loading. SLAB CONSTRUCTION Changes in the moisture contents may result in consolidation or swelling of the subsoil, resulting in differential slab movement. The bedrock encountered and tested at this site are anticipated to exhibit low to moderate swell potential as moisture contents are increased. According 6 to the Guideline for Slab Performance Risk Evaluation and Residential Basement Floor System Recommendations, developed by the Colorado Association of Geotechnical Engineers, slab performance risk at this site would be considered low to moderate. Slabs placed on the native, unaltered bedrock at this site may experience excessive heaving and cracking. We recommend that structural floors be constructed at this site, in place of slabs -on - grade, where these areas may or are to be finished. Areas with slabs placed within three (3) feet of the siltstone/claystone bederock at this site shall be considered non -habitable, and therefore should not be finished for risk of damage caused by slab movement. An alternative which could reduce the risk of potential slab movement would be to remove at least three (3) feet of soil beneath the slab and replace it with a moisture and density controlled fill approved by the engineer prior to delivery or placement. This method may reduce the risk of potential slab movement, but it will not completely eliminate potential damage. Refer to Appendix 3 of this report for compaction guidelines. This method may also benefit garage slabs and exterior flatwork. If slabs -on -grade for non -habitable areas are chosen and the owner is willing to accept the risks of potential damage from slab movement, slabs should be constructed to be "free-floating" and isolated from all structural members of the foundation, utility lines, and partition walls. There should be a minimum two-inch (2") void constructed below partition walls located over slabs -on - grade. The void should be increased to four (4) inches for slabs placed on potentially expansive bedrock stratum. Eliminate under -slab plumbing where feasible. Where such plumbing is unavoidable, it should be pressure tested before and after slab construction to minimize leaks which would result in wetting of the subsoil. Failure to allow the slab to float independently could result in functional, structural, architectural, and utility line damage. All slabs should be scored into maximum 225 square foot areas or maximum dimensions of fifteen (15) feet with a minimum depth of one (1) inch to localize and control any cracking due to heaving. Slabs less than. thirty (30) square feet should be scored at least once in each direction. The minimum slab thickness should be four (4) inches, with four (4) inches of clean, washed gravel under the slab. Slabs should be reinforced with welded wire fabric, or equivalent, to help control cracking and separation. Fiber mesh shall not be considered an equivalent substitute for the welded wire fabric. Areas to be finished shall utilize a structural floor system or a compacted structural mat as described above. 7 FOUNDATION DRAIN SYSTEM A perimeter drain system shall be installed where below grade floors are constructed. The type of drain, interior, exterior or both should be determined at the time of the excavation observation. The drain system should contain a four (4) inch diameter perforated drainpipe surrounded by a minimum of twelve (12) inches of clean, washed rock. There should be a minimum of eight (8) inches of gravel over the top of the pipe, for the full width of the trench. The gravel shall be covered with untreated building paper or geotextile fabric to minimize clogging by backfill material. The drain should have a positive slope to a non -perforated sump pit or to daylight, well away from the foundation. The sump pit should be a minimum of twenty four (24) inches in diameter by two (2) feet deep and should be surrounded by at least six (6) inches of clean gravel similar to that provided around the drain. The sump pit shall be capable of positive gravity or mechanical drainage to remove any accumulated water. The drainage system shall discharge a minimum of five (5) feet beyond the backfill zone. The discharge area should be placed so that it does not interfere with adjacent properties. Typical drain details are provided in Appendix 2 of this report. CONCLUSIONS The soils and rock encountered at this site are anticipated to exhibit low to moderate swell potential as moisture contents are increased. Future owners should be cautioned that there may be some risk of future damage caused by introduction of excess water to the soils and/or rock. All new and future owners should be directed to those items under "Post -Construction Site Preparation and Maintenance" in Appendix 1, included in this report. Our experience has shown that damage to foundations usually results from saturation of the foundation soils caused by improper drainage, excessive irrigation, poorly compacted backfills, and leaky water and sewer lines, The elimination of the potential sources of excessive water will greatly minimize the risks of construction at this site. It is recommended that a copy or summary of this report be provided to any new or future owners of this property. A copy of A Guide to Swelling Soils for Colorado Homebuyers and Homeowners, Colorado Geological Survey Special Publication 43 should also be provided to any new or future owners of the property. 8 The findings and recommendations of this report have been obtained in accordance with accepted professional engineering practices in the field of Geotechnical Engineering. However, standard Geotechnical Engineering practices and related government regulations are subject to change. The recommendations provided in this report are only valid as of the date of this report. If the construction is at a later date, we would be glad to review the information presented in this report with regard to updated governmental requirements or industry standards. There is no other warranty, either expressed or implied. We do not guarantee the performance of the project in any respect, but only that our engineering work and judgments rendered meet the standard of care of our profession. This report applies only to the type of construction anticipated in the area tested. The current technology is not at a stage where a guarantee of "absolutely no damage" can be assured by design and construction practices. 37TH STREET 100 0 100 MINN SCALE 1"100' 1 r Client: Western Construction Management Project: 5300 Kiowo Drive, Weld County, Colorado LOCATION OF TEST BORING Scale: 1" = 100' Date: 11/03/2015 Engineering Corporation Project No. 15-7752 Dwg. No.: 1 165 2nd St. S.W. Loveland, CO 80537 Tele: (970) 667-8010 Symbols & Sol FIGURE NO. 1 Fill Gravel Sand / Silt / Silty Clay , Clay Weathered Bedrock —`~ Siltstone Claystone Sandstone i iIf Limestone y Igneous & Metamorphic ' 'Properties N/12 CALIFORNIA N/12 SPLIT SPOON THIN WALLED (SHELBY) BAG SAMPLE PITCHER SAMPLE Penetration Resistance and Strength Classifications are Based on The Standard Penetration Test Number of Blows Per foot (N)* 0-4 4-10 10-30 30-50 50+ Relative Density Cohesionless Soils Consistency Cohesive Soils Approximate Cohesion ksf** Very Loose Soft Less than 0.5 Loose Firm 0,5-1.0 Medium Stiff 1,0-2.0 Dense Very Stiff 2.0-4.0 Very Dense Hard Greater than 4.0 * BLOWS PER FOOT - BLOWS OF 140 LB. HAMMER DROPPED 30 IN. TO DRIVE SPLIT SPOON OR CALIFORNIA SAMPLER 12' (IN.) (ASTM DL5B5-67) ** EQUIVALENT TO PP/2 AND QU/2 Engineering 165 2nd St. S.W.. Corporation Loveland, (970CO67-8010 5 FT. 10 FT. 15 FT. 20 FT, 25 FT. 30 FT. 35 FT, 0 FT. TH-1 PTH-1 • 23/12 50/12 50/10 0 FT. 50/11 SAND: silty, sl. moist, brown, loose SILTSTONE/CLAYSTONE: interbedded siltstone and cloystone bedrock, dk. grey/brown, weathered to competent 5 FT. 10 FT. 15 FT. 20 FT. 25 FT. 30 FT. 35 FT. Borings drilled 10/15/15 on using a 4" diameter, continuous flight truck mounted drilling rig. = Groundwater © drilling = Groundwater on 10/16/15 All soil and/or rock contacts shown on boring logs are approximate and represent subsurface conditions at time of drilling, Boring logs and information presented an logs are subject to discussion and limitations of this report. LOG OF BORINGS CLIENT: Western Construction Management PROJECT NO. 15-7752 PROJECT LOCATION 5300 Kiowa Drive, Weld County, Colorado Fig. No.: 2 Engineering Corporation 165 2nd St. S.W. Loveland, CO 80537 Tele: (970) 667-8010 SWELL / CONSOLIDATION TEST CURVES Client: Western Construction Management Project: 5300 Kiowa Project No.: 15-7752 Boring: TH-1 Description: Weathered siltstone, w. claystone, sl. mosit, it. tiro Depth, ft: 2' Water Content: 9.3% Swell (%):* 2,7 Dry Density, pcf: 97.7 Approximate Swell Pressure, psf: 2000 Volume Change, % 100 6 Pressure, psf 1000 10000 5 _ 4 _ 3 _ 2 _ E _ 0 i _ -1 _ .2 _ -3 _ -4 _ Boring: TH-1 Depth, ft: 10' Description: Clayey sand, w. caliche, tan, moist Water Content: 13.1% Swell (%):* 1,7 Dry Density, pcf: 110.7 Approximate Swell Pressure, psf: 3800 Volume Change, % 100 6 5 4 3 2 as _ -1 -2 -3 -4 Pressure, psf 1000 10000 -5 -6 CDS Engineering Corporation * negative values indicate consolidation Figure 3 SWELL / CONSOLIDATION TEST CURVES Client: Western Construction Management Project: 5300 Kiowa Project No.: 15-7752 Boring: TH-1 Description: Claystone, w. siltstone, olive/brown, sl. moist Depth, ft: 20' Water Content: 19.5% Swell (%)* 1.9 Dry Density, pcf: 108.9 Approximate Swell Pressure, psf: 3500 100 G 5 4 3 -3 -4 -5 -6 Pressure, psf 1000 10000 • _ 1 _ * negative values indicate consolidation CDS Engineering Corporation Figure 4 SUMMARY OF TEST RESULTS TABLE NO. Z Project No.: 15-7752 boring No. Depth (ft) # of blows/ penetration Natural Moisture (%) Natural Dry Density (pcf) Swell' (%) 2 23/12 9.3 97.7 2.7 1 10 50/10 13.1 110.7 1.7 Swell Pressure @ 1000 psf Surcharge 3800 Swell Pressure @ 500 psf Surcharge 20O0 Atterberg Limits LL (%) PI (9 76) Unconfined Compressive Strength (pat') Unconfined Compressive Strength"{psf) Passing #4 1 #200 Seive (%) Description Siltstone aystr es' Siltstone 9 1 } "Swell due to wetting under a 500 psf or 1000 psf surcharge - Negative values indicate consolidation '"'Unconfined compressive strength estimated using a pocket penetrometer Sheet 1 of 1 APPENDIX 3 GENERAL SPECIFICATIONS FOR THE PLACEMENT OF COMPACTED FILL MATERIAL PLACED BELOW A STRUCTURE Moisture -Density Determination Representative samples of the materials to be used for fill shall be furnished by the contractor at least seventy two (72) hours prior to compaction testing. Samples with higher moisture contents will require extra time for test results due to the required drying for sample preparation. Tests to determine the optimum moisture and density of the given material will be made using methods conforming to the most recent procedures of ASTM D698 (standard Proctor) or other approved methods, whichever may apply. Copies of the Proctor Curves will be furnished to the contractor. These test results shall be the basis of control for the field moisture/density tests. Materials The soils used for compacted fill shall be selected or approved by the Engineer. The material shall be free of vegetation, topsoil or any other deleterious materials. The material should be relatively impervious and non -swelling for the depth specified in the soils report with no material greater than six (6) inches in diameter. Site Preparation All timber, logs, trees, brush and rubbish shall be removed from the area and disposed in a manner approved by the local governing agency. All vegetation and a substantial amount of topsoil shall be removed from the surface upon which the fill is to be placed. Where applicable, the surface shall then be scarified to a depth of at least six (6) inches, moistened or dried as necessary to allow for uniform compaction by the equipment being used. The scarified surface shall be compacted to not less than 95% of maximum dry density based on ASTM D698, or to such other density as may be determined appropriate for the materials and conditions and acceptable to the Engineer. Fill shall not be placed on frozen or muddy ground. Moisture The fill material, while being compacted should contain, as nearly as practical (typically +/- 2%), the optimum amount of moisture as determined by the Standard Proctor Test ASTM D698, or other approved method. The moisture shall be uniform throughout the fill material. The effort required for optimum compaction will be minimized by keeping soils near optimum moisture contents. Freezing temperatures andlor inclement weather conditions may impede moisture control and compaction operations. Placement of Fill The Geotechnical Engineer shall be retained to supervise the placement of fill material. The fill material shall be placed in unifoturi layers and be compacted to not less than 95% of maximum dry density based on ASTM D698, or to such other density as may be determined appropriate for the materials and conditions and acceptable to the Engineer, Prior to compacting, each layer shall have a maximum loose layer height of twelve (12) inches (or as dictated by the compaction equipment and/or soil conditions) with the surface relatively level. Test areas are recommended to determine the optimum layer thickness. Thinner lifts may be necessary in order to achieve the required compaction. Compacted layer thickness shall not exceed six (6) inches. Each twelve (12) inches of compacted fill shall be approved by the Engineer prior to placing succeeding lifts. Fill shall be compacted with machinery appropriate for the type of earthen material being installed. Granular materials shall be compacted with vibratory type machinery. Clay and silt material shall be compacted with a sheepsfoot or other segmented pad type compaction equipment. "Wheel rolling" is not considered an appropriate method to achieve the recommended compaction specifications. "Wheel rolling" is not recommended for extensive areas or depths and cannot be relied upon to give uniform results. Moisture and Density Testing It is the contractor's responsibility to contact the Engineer with a minimum of 24 -hours notice to schedule compaction testing. The density and moisture content of each layer of compacted fill will be determined by the Engineer, or qualified technician, in accordance with ASTM D6938 (nuclear method), or other approved method. If the tests show inadequate density, that layer, or portion thereof, shall be reworked until the required conditions are obtained. Additional layers shall not be placed until each underlying lift has been approved. The results of all density tests will be furnished to both the owner and the contractor by the Engineer. Hello