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HomeMy WebLinkAboutHILL POND ON SPRING CREEK - Filed GR-GEOTECHNICAL REPORT/SOILS REPORT -REPORT OF A PRELIMINARY G€OTECHNICAL INVESTIGATION FOR HILL POND PROPERTY FORT COLLI NS, COLORADO PARSONS AND ASSOCIATES FORT COLLINS, COLORADO PROJECT NO. 7855-89 BY EMPIRE LABORATORIES, INC. 301 NORTH HOWES STREET FORT COLLINS, COLORADO 80521 TABLE OF CONTENTS Table of Contents Letter of Transmittal ii Report 1 Appendix A A-1 Test Boring Location Plan A-2 Key to Borings A-3: Log of Borings A-4 Appendix B B-1 Summary of Test Results B-2 1 Empire. Laboratories, Inc.CORPORATE OFFICE P.O.Box 503•(303)484-0359 GEOTECHNICAL ENGINEERING&MATERIALS TESTING 301 No.Howes•Fort Collins Colorado 80522 1 February 13, 1989 Parsons and Associates 432 South Link Lane Fort Collins, Colorado 80524 Attention: Mr. Don Parsons Gentlemen: We are pleased to submit our Report of a Preliminary Geotechnical Investigation prepared for the proposed residential development located on South Shields Street north and south of Spring Creek in south-central Fort Collins, Colorado. The accompanying report presents our findings in the subsurface and our recommendations based upon these findings for the preliminary phase of the project. Very truly yours, c F,ti ' EMPIRE LABORATO IES, INC.NC.4``'2 i W i I 4/..# 49/ s.t e R. herrod ti ' Senior Engineering Geologist \ c?"< r Reviewed by: ooulum d-7,,.. .4-•,,,,- -,",„------,,,,„-.,-;,#=' 4:.: 4,,,tt.a .::"..„,,-5•;:trs,oft Chester C. Smith, P.E. s 0 President a :0 4808 W Nil, c•oi t,i 0: Q 4r ac OF Cudo . P$ORATO Pi Branch Offices Gf y P.O.Box 16859 P.O.Box 1135 P.O.Box 1744 P.O..Box 5659 o. Colorado Springs,CO 80935 Longmont,CO 80502 Greeley,CO 80632 Cheyenne,WY 82003 303)597-2116 303)776-3921 303)351-0460 307)632.9224 Member of Consulting Engineers Council ii REPORT OF A PRELIMINARY GEOTECHNICAL INVESTIGATION SCOPE This report presents the results of a preliminary geotechnical evaluation prepared for the proposed residential development located adjacent to Hill Pond along Spring Creek in south-central Fort Collins, Colorado. The investigation included test borings and laboratory testing of samples obtained from these borings. The objectives of this study were to determine the geologic characteristics at the site and to determine the subsurface conditions at the site relative to the proposed construction. SITE EXPLORATION The field exploration, carried out on February 9, 1989, consisted of drilling, logging, and sampling six (6) test borings. The test borings were located by pacing from the existing street and fence lines by Empire Laboratories, Inc. The locations of the test borings are shown on the Test Boring Location Plan and Geologic Map included in Appendix A of this report. Boring logs prepared from the field logs are included in Appendix A. These logs show soils encountered, location of sampling, and ground water at the time of the investigation. The borings were advanced with a four-inch diameter, continuous- type, power-flight auger drill. During the drilling operations, a geotechnical engineer from Empire Laboratories, Inc. was present and made continuous observations of the soils encountered. 1- SITE LOCATION AND DESCRIPTION The proposed residential site is located east of South Shields Street north and south of Spring Creek in south-central Fort Collins, Colorado. More particularly, the site is described as a tract of land situate in the Northwest 1/4 of Section 23, Township 7 North, Range 69 West of the Sixth P.M. , City of Fort Collins, Larimer County, Colorado. The site consists of two parcels. One tract is located north of Spring Creek, east of South Shields Street and south of Hobbit Street. The other area is located south of Spring Creek and east of the Hill Pond residential area. Portions of the north area have been filled, and approximately five (5) feet of fill was encountered just north of Spring Creek on this tract. The north portion of the site is relatively flat to gently rolling and has major drainage to the east-southeast toward Spring Creek. This portion of the site is vegetated with grass and weeds. The southern portion of the site consists of open rolling terrain. Numerous small irrigation ditches are located through this portion of the site. The south and east property lines are fenced, and the area is vegetated with grass and weeds. Major drainage in the south portion of the site is to the northeast toward Spring Creek, which forms the north boundary of this portion of the property. LABORATORY TESTS AND EVALUATION Samples obtained from the test borings were subjected to testing in the" laboratory. Moisture contents, dry unit weights, unconfined compressive strengths, swelling potentials, and the Atterberg limits were determined. A summary of the test results is included in Appendix B. SOIL AND GROUND WATER CONDITIONS The soil profile at the site consists of strata of materials arranged in different combinations. In order of increasing depths, they are as follows: 2- 1) Fill Material and Silty Topsoil: A one (1) to five and one-half 5-1 /2) foot layer of fill material was encountered at the surface of Borings 1, 2, 3 and 6. The fill consists of a mixture of silty clay, sandy silty clay and sand and gravel. It is not known whether the fill has been uniformly or properly compacted. Therefore, it should not be used as a foundation soil. A six (6) inch layer of silty topsoil was encountered at the surface of Borings 4 and 5 and below the fill in Boring 1 . The topsoil has been penetrated by root growth and organic matter and should not be used as a bearing soil or as a fill and/or backf I l material. 2) Sandy Silty Clay: This stratum underlies• the topsoil and/or fill and extends to the sand and gravel below. The brown to red silty clay is plastic, contains varying amounts of sand and minor amounts of gravel and exhibits low to moderate bearing characteristics in its dry to damp in situ condition. When wetted, the drier upper portions of the clay stratum exhibit moderate swell potential. 3) Silty and/or Clayey Sand and Gravel: The sand and gravel was encountered below the upper clays in all test borings at depths of three (3) to thirteen (13) feet below the surface and extends to the bedrock below and/or the depths explored. The sand and gravel contains varying amounts of silt and/or clay, is poorly graded,"is loose to medium dense and exhibits low to moderate bearing characteristics in its moist to saturated condition. 4) Siltstone-Sandstone _ Bedrock: The bedrock was encountered below the sand and gravel layer in Borings 3 through 6 at depths of four (4) to fourteen (14) feet below the surface and extends to greater depths. The upper two (2) feet of the bedrock is highly weathered; however, the underlying siltstone 3- interbedded with sandstone is firm and exhibits high to very high bearing characteristics. 5) Ground Water: Twenty-four hours after drilling, free ground water was encountered in the northern portion of the site at depths of nine and one-half (9-1 /2) to ten and one-half 10-1 /2) feet below the surface and in the southern portion of the site at depths of two (2) to six (6) feet below the surface. Water levels in this area are subject to change due to seasonal variations, irrigation demands on and/or adjacent to the site and the volume of flow of Spring Creek through the project area. GEOLOGY The proposed site is located within the Colorado Piedmont section of the Great Plains physiographic province. The Colorado Piedmont, formed during Late Tertiary and Early Quaternary time (approximately sixty-five million (65,000,000) years ago) , is a broad, erosional trench which separates the Southern Rocky Mountains from the High Plains. Structurally, the property lies along the western flank of the Denver Basin. During the Late Mesozoic and Early Cenozoic Periods approximately seventy million (70,000,000) years ago) ,. intense tectonic activity occurred, causing the uplifting of the Front Range and the associated downwarping of the Denver Basin to the east. Relatively flat uplands and broad valleys characterize the present-day -topography of the Colorado Piedmont in this region. The site is underlain by the Cretaceous Pierre Formation. The Pierre formation is overlain by residual and alluvial soils of Pleistocene and/or Recent Age. . Siltstone and claystone bedrock of the Pierre formation was encountered in the southern portion of the site at depths of four (4) to fourteen (14) feet below the surface. It is anticipated that bedrock underlies the northern portion of the site at depths of approximately twenty (20) feet below the surface. The bedrock in this area dips slightly to the east. Seismic activity in the area is anticipated to be 4- low• therefore, from a structural standpoint, the property should be relatively stable. Due to the relatively flat to gently-sloping nature of the site, mass movement due to gravity, such as mudflows, landslides, etc. , are not anticipated on the property. With proper site grading around proposed structures and streets, erosional problems should be minimal. Construction should not be placed within the one hundred 100) year flood plain of Spring Creek. RECOMMENDATIONS AND DISCUSSION It is our understanding the site is to be developed for single-family residential construction. Site Grading Specifications pertaining to site grading are included below. It is recommended that the upper six (6) inches of topsoil below building, filled and paved areas be stripped and stockpiled for reuse in planted areas. All existing fill should be removed from below all building and paved areas and stockpiled for reuse. Topsoil encountered below the fill should be stripped. The upper six (6) inches of the natural subgrade below building, paved and filled areas should be scarified and recompacted two percent (2%) wet of optimum moisture to at least ninety-five percent (95%) of Standard Proctor Density ASTM D 698-78. Where this subgrade compaction cannot be obtained due to saturated or unstable subsoil conditions, the subgrade should be stabilized by use of granular pit-run material, geotextiles, lime, fly ash or by other suitable means. Finished subgrade below building and paved areas should be placed a minimum of three (3) feet above existing ground water. Fill should consist of the on-site soils, existing fill devoid of debris, or imported granular material approved by the geotechnical engineer. Fill should be placed in uniform six (6) to eight (8) inch Lifts and mechanically compacted two percent (2%) wet of optimum moisture to at least ninety-five percent (95%) of Standard Proctor Density ASTM D 698-78. 5- Foundations In view of the loads transmitted by the proposed residential construction and the soil conditions encountered at the site, it is recommended _ that the structures be supported by conventional-type spread footings and/or grade beams. All footings and/or grade beams should be founded on the original, undisturbed soil or on a structural fill extended to the undisturbed soil a minimum of thirty r30) inches below finished grade for frost protection. In no case should footings be founded on the existing fill encountered at the site. The structural fill should be constructed in accordance with the recommendations discussed in the "Site Grading" section of this report. The structural integrity of the fill as well as the identification and undisturbed nature of the soil should be verified by the geotechnical engineer prior to placement of any foundation concrete. Based on preliminary test results, footings and/or grade beams founded at the above levels may be designed for a maximum allowable bearing capacity of between one thousand (1000) to three thousand (3000) pounds per square foot (dead load plus maximum live load) . To counteract swelling pressures which will develop if the subsoils become wetted, all footings and/or grade beams should be designed for a minimum dead load of between two hundred fifty (250) to seven hundred fifty (750) pounds per square foot. Basements and Slabs on Grade In' view of the depth of ground water encountered in tPe northern portion of the site, it is our opinion that basement construction is feasible in this portion of the property. Basement slabs should be placed a minimum of three (3) feet above existing ground water. Ground water was encountered at depths of two (2) to six (6) feet in the southern portion of the site. In view of the shallow depths to ground water, it is our opinion that basement construction is not feasible in this portion of the property without construction of complete dewatering systems, area drains or filling of the area to effectively lower water levels. It is recommended that conventional crawl-space, 6- garden-level or slab-on-grade construction be considered for the southern portion of the property. All lower level slabs should be placed a minimum of three (3) feet above existing ground water, or the structures should be provided with complete dewatering systems. Subgrade below slabs on grade should be prepared in accordance with the recommendations discussed in the "Site Grading" section of this report. It is recommended that slabs on grade founded on the expansive clays be designed structurally independent of bearing members. GENERAL COMMENTS It should be noted that this was a preliminary investigation and that the bearing capacities recommended in this report are based on preliminary tests. Due to variations in soil and ground water conditions and swelling pressures encountered at the site, it is recommended that additional test borings be made prior to construction. Samples obtained from the borings should be tested in the laboratory to provide a basis for evaluating subsurface conditions. 7- APPENDIX A. TEST BORING LOCATION PLAN e Avg: s lAp. to RE AGtoUs I f'it . F*Mrcj loll Ioo?. FLAI O i•L4 µ41 E K 140.2 s. sot A-2 EMPIRE LABORATORIES, INC. KEY TO BORING LOGS 0 TOPSOIL GRAVEL y= i FILL e••SAND&GRAVEL BE SILT SILTY SAND&GRAVEL i:•. CLAYEY SILT o 0 v.COBBLES y, ,. e SANDY SILT moo• SAND,GRAVEL&COBBLES CLAY WEATHERED BEDROCK 102 SILTY CLAY SILTSTONE BEDROCK SANDY CLAY MEM CLAYSTONE BEDROCK SAND SANDSTONE BEDROCK SILTY SAND mom LIMESTONE i. . ims PeA CLAYEY SAND Ern intim GRANITE META SANDY SILTY CLAY Hx SHELBY TUBE SAMPLE STANDARD PENETRATION DRIVE SAMPLER WATER TABLE 24 HRS. AFTER DRILLING C HOLE CAVED 5/12 Indicates that 5 blows of a 140 pound hammer falling 30 inches was required to penetrate 12 inches. A-3 EMPIRE LABORATORIES,INC LAG. OF BORINGS J 22/12 _r _.. tasiAMr 8/12 n264 4 12 Mg 10/12 e r®e ice® Ira 10 3/12 . Pre Wn17 .1111ZIE:P 4 12 _EVfrWAIMIIII2 16 16 12 1111.11111MBEISIE 10/12 A-4 EMPIRE LABORATORIES, INC. Of 90111,466 To Pe›. 1.10.10 0 3/12 , . 10/12 24/12 10/12 ' ? .. 2/12 • 5 5/12 '/•• 10 39/12 3/12 12/12 j 15 50/12 4_ .11/12 50/12 --,. ._ A 5 EMPIRE LABORATORIES, INC. APPENDIX B. N N N N N N N N N N N N N N, r rl 11-1 F-1 .4 .--4 .--1 •-i r1 .-I .-4 ri 1--4 1. 1 c.e M t0 CO CO Liz N O et O th O 0" O G• m r-1 1 •--1. N rt Cr) L0 t 2 x2 CC C J u.0 C-) 1.1UI w is U t0 t Q et o$ cq 0 e h P. x O 1I.0 4 a. r-r Z'E2 01 N H J y) z W _ vI1t H E C W .. F„ i' Q U. a C a. 4. iy in V) to d.'6. toLr) L. msLL O O' O C) O 0 E .- 01 CO • et' N 4- t.) r LL t0 tl) CO CI- 1 CO t0 I-- 01rn t... al p-- O 0) O 4 O O 1 ra r: r1- U) 1-, Cr) N .--4 O N. N. N. C!) Lc) 0 .4' t0 00 Cr' 1.0 .4- Lr) L[) 1-... e.. O t0 ii n CV N. C) d1 1--- COI--) CO tD COCV to M Q1 ri N N N rc .--4 N r1 • CV N M N CV r4 r-1' O O 0 0 0 0 0 0 0 O O • • 0 O O 0 • • 1.0 CI CI C) C)• • L 0 • • 0 LC) - • • • • C) Lc) 0 Ln 0 LC) 4- L[) t0 .--t r• CV U) t0 r1 1-1 r-1 Gt L0 r1 r! .-1- (r) d- r1 rl u. 1 1 1 1 1 1 1 1 1 1 1 I I I 1 I 1 1 1 1 1 G"" 0 CD 0 O O O 0 0 O 0 0 LO 0 O O- O .LO C) O. O C 0 • N d- LC) 0) it' O CV - Lr) C) O co d- 0) d- co N Cr) 01 d- I 1 r rt co biz .•-1 N Cr) to B_2 eo'e N N N N N N N N go:. r-4 .--1 .--I •=1 r+ 4-1 .--1 .-1 or X eL m O of GO N CV .N- 4 ` p 2 Ira ep aea'~Sq Ct as LI vo C7 9 a. Ea ca JJ J y CC LU S v n u Cl) C C tRCC 'u 2 _ 'ill:LL y N N .-G. m ro u O O eu) y. h E a r^ Ct a I, 0 O t CI LC) q 1h. C) r-i tD N 0 n• tf) cY) .n 0I CO O O 0 LC) O C) •- • L) O O • • O Lc) Q CC) 4; 4-1 I LC) ram' •"-I' ri Cr) Ct' .--r' .--C m..1L. 11 I I 1 1 1 I C"" LC) O O. O O LC) CD CO CD CD o- • O cr) Cm - O N ri rn 4: me o 0 2 Lc) to B-3 APPENDIX C. APPENDIX C. Suggested Minimum Specifications for Placement of Compacted Earth Fill and/or Backfills GENERAL The geotechnical engineer shall be the owner's, architect's, engineer's or contractor's representative to observe placement of compacted fill and/or backfill on the project. The geotechnical engineer or his representative shall approve all earth materials prior to their use, the method of placement and the degree of compaction. MATERIALS Soils used for all compacted fill and backfill shall be approved by the geotechnical engineer or his representative prior to their use. Fill material shall be free from organic matter, frozen material and other unsuitable substance and shall not contain rocks or lumps having a diameter greater than six (6) inches. SUBGRADE PREPARATION All topsoil, vegetation, trees, brush, timber, debris, rubbish and all other unsuitable material shall be removed to a depth satisfactory to the geotechnical engineer or his representative. The material shall be disposed of by suitable means prior to beginning preparation of the subgrade. The subgrade shall be scarified a minimum depth of six (6) inches, moisture conditioned as necessary and compacted in a suitable manner prior to placement of fill material. Fill shall not be placed until approval by the geotechnical engineer or his representative; and in no case, shall fill material be placed on frozen or unstable ground. Subgrade which is not stable may require the use of imported granular material , geotextiles or other methods for stabilization as approved by the geotechnical engineer. FILL PLACEMENT Fill material shall not be placed during unfavorable weather conditions. Material proposed for use as fill shall be approved by the geotechnical engineer or his representative prior to use. Proposed import material shall be approved by the geotechnical engineer or his representative prior to hauling to the project site. Fill material shall be C-2 uniformly mixed such as to preclude the formation of lenses of material differing from the surrounding material. All clods shall be broken into small pieces. The contractor shall construct the fill in approximately horizontal lifts extending the entire length of the fill. The thickness of the layers before compaction shall not be greater than eight (8) inches. Fill being placed on slopes or hillsides shall be benched into the existing slope. A minimum two (2) foot horizontal bench shall be cut into the existing excavated slope for each four (4) feet vertical of fill, or each lift should be benched slightly into the existing grade. MOISTURE CONTROL Prior to and during compaction operations, the fill material being placed shall be maintained within the range of optimum moisture specified. A general recommendation is to maintain the fill material within two percent (2%) plus or minus of optimum moisture so that proper compaction to the specified density may be obtained with a minimal effort. In building pad and paved areas, material exhibiting swelling potential shall be maintained between optimum moisture and two percent (2%) wet of optimum moisture content. The moisture content of the fill material shall be maintained uniform throughout the fill. The contractor may be required to add necessary moisture to the fill material and to uniformly mix the water with the fill material if, in the opinion of the geotechnical engineer, it is not possible to obtain uniform moisture content by adding water on the fill surface. If, in the opinion of the geotechnical engineer, the material proposed for use in the compacted fill is too wet to permit adequate compaction, it shall be dried in an acceptable manner prior to placement and compaction. Uniform mixing may require discing, blading or other methods approved by the geotechnical engineer or his representative. Adjustments of moisture content shall be made on the basis of determinations of moisture content by field tests as construction progresses. COMPACTION The contractor shall furnish and operate the necessary types and kinds of equipment to perform the operations required to obtain the specified compaction. This equipment may include approved tamping rollers, rubber tired rollers, smooth wheeled rollers and vibratory rollers. If a sheepsfoot roller is used, it shall be provided with cleaner bars so attached as to prevent the accumulation of material between the tamper feet. Fill areas which are not accessible to full-sized construction equipment shall be placed in maximum four (4) inch lifts and compacted with power tampers to the specified density. C-3 Compaction should meet the minimum percentages of maximum density as set forth in the project specifications or the recommendations of the report. The contract specifications supercede the recommendations given in this report. MOISTURE DENSITY RELATIONSHIP DETERMINATION Samples of representative fill materials to be placed shall be furnished by the contractor to the geotechnical engineer for determination of maximum density and optimum moisture or relative density. Sufficient laboratory moisture density or relative density curves will be made to determine the optimum moisture content and maximum density for the various soils placed as fill. Tests for this determination will be made using the appropriate method conforming to the requirements of ASTM D 698 (Standard Proctor) , ASTM D 1557 (Modified Proctor) or ASTM D 4253, D 4254 (Relative. Density). The materials used for fill shall be classified in accordance with ASTM D 2487 in order to permit correlation between the moisture density relationship data and the material being placed and compacted. Copies of the results of these tests will be furnished to the client and others as directed by the client. These test -results shall be the basis of control for all compaction effort. FIELD DENSITY AND MOISTURE TESTS The in-place density and moisture content of compacted fill will be. determined by the geotechnical engineer or his representative in accordance with ASTM D 1556 (sand cone method) or ASTM D 2922, D 3017 (nuclear methods). Material not meeting the required compaction and/or moisture specifications shall be recompacted and/or, moisture conditioned until the required percent compaction and/or moisture content is obtained. Sufficient compaction tests shall be made and submitted to support the geotechnical engineer's or his representative's recommendations. The results of density tests will also be furnished to the client and others as directed. C-4