Loading...
HomeMy WebLinkAboutPLATT PROPERTY PUD PRELIMINARY - 3 90B - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORTREPORT OF A GEOTECHNICAL INVESTIGATION FOR VILLAGES AT HARMONY WEST FORT COLLINS, COLORADO THE GROUP, INC. FORT COLLINS, COLORADO PROJECT NO. 8299-90 BY EMPIRE LABORATORIES, INC. 301 NORTH HOWES STREET FORT COLLINS, COLORADO 80521 shrinkage factor of fifteen percent (15%) to twenty percent (20%) may be used for the bedrock used as compacted fill. All excavations should be dug on safe and stable slopes, It is suggested that excavated soil slopes be on minimum grades of 1-1 /2:1 or flatter. The bedrock may be excavated on near -vertical slopes. The slope of the sides of the excavations should comply with local codes or OSHA regulations. Where this is not practical, sheeting, shoring and/or bracing of the excavation will be required. The sheeting, shoring and bracing of the excavation should be done to prevent sliding or caving of the excavation walls and to protect construction workers and adjacent structures. The side slopes of the excavation or sheeting, shoring or bracing should be maintained under safe conditions until completion of backfilling. In addition, heavy construction equipment should be kept a safe distance from the edge of the excavation. Where utilities are excavated below ground water, dewatering will be needed during placement of pipe and backfilling for proper construction. All piping should be adequately bedded for proper load distribution. Backfill placed in utility trenches in open and planted areas should be compacted in uniform lifts at optimum moisture to at least ninety percent (90%) of Standard Proctor Density ASTM D 698-78 the full depth of the trench. The upper four (4) feet of backfill placed in utility trenches under roadways and paved areas should be compacted at or near optimum moisture to at least ninety-five percent (95%) of Standard Proctor Density ASTM D 698-78, and the lower portion of these trenches should be compacted to at least ninety percent (90%) of Standard Proctor Density ASTM D 698-78. Addition of moisture to and/or drying of the subsoils may be needed for proper compaction. Proper placement of the bedrock as backfill may be difficult. Stripping, grubbing, subgrade preparation, and fill and backfill placement should be accomplished under continuous observation of the geotechnical engineer. Field density tests should be taken daily in the compacted subgrade, fill, and backfill under the direction of the geotechnical engineer. Laboratory resistivity tests, pH, oxidation-reduction potential and sulfide tests performed in the laboratory indicate that the subsoils at -7- the site are slightly corrosive, and protection of metal utility pipe, in our opinion, is recommended. Foundations In view of the loads transmitted by the proposed residential construction and the soil conditions encountered over the majority of the. site, it is recommended that the structures in the northern two-thirds of the property placed a minimum of three (3) feet above the bedrock stratum be supported by conventional -type spread footi.ngs 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 (30) inches below finished grade for frost protection. The structural fill should be constructed in accordance with the recommendations discussed in the "Site Grading, Excavation and Utilities" 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. Footings and/or grade beams founded at the above levels may be designed for a maximum allowable bearing capacity of two thousand (2000) 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 seven hundred fifty (750) pounds per square foot. The predicted settlement under the above maximum loading, as determined by laboratory consolidation tests, should be less than three -fourths (3/4) inch, generally considered to be within acceptable tolerances. Structures founded in or within three (3) feet of the bedrock stratum should be supported by a drilled pier foundation system. It is anticipated that structures founded in the southern one-third of the property in the area of Borings 6 and 10 through 12 will extend into or within three (3) feet of the bedrock and will require drilled pier foundations. Using this type of foundation system, the structure is -8- supported by piers drilled into the bedrock stratum and structural grade beams spanning the piers. Piers should be straight -shaft and should be drilled within plumb tolerances of one and one-half percent relative to the length of the pier. The piers are supported by the bedrock stratum partially through end bearing and partially through skin friction. It is recommended that all piers have minimum ten (10) foot lengths and that they he drilled a minimum of three (3) feet into the firm bedrock stratum. Piers founded at the above level may be designed for a maximum allowable end bearing pressure of twenty thousand (20,000) pounds per square foot. It is estimated that a skin friction of two thousand (2000) pounds per square foot will be developed for that portion of the pier embedded three (3) feet into the firm bedrock stratum. To counteract swelling pressures which will develop if the subsoils become wetted, all piers should be designed for a minimum dead load of five thousand (5000) pounds per square foot. Where this minimum dead load requirement cannot be satisfied, it is recommended that skin friction from additional embedment into the firm bedrock be used to resist uplift. To help provide the required skin friction, the sides of the pier drilled into the bedrock stratum should be roughened.. All piers should be reinforced their full length to resist tensile stresses created by swelling pressures acting on the pier. It is recommended that all grade beams have a minimum four (4) inch void between the bottom of the beam and the subsoil below. The predicted settlement under the above maximum loading should be negligible. Drilled piers should be designed to resist all induced lateral forces. Since no free around water was encountered in the southern portion of the site where drilled piers are required, it is our opinion that temporary casing of the drill holes will not he required. It is recommended that all piers should have minimum ten (10) to twelve (12) inch diameters. It is strongly recommended that the geotechnical engineer be present during the drilling operations to (1) identify the firm bedrock stratum, (2) assure that proper penetration is obtained into the sound bedrock stratum, (3) ascertain that all drill holes are thoroughly roughened, cleaned and dewatered prior to placement of any foundation -9- concrete, (4) check all drill holes to assure that they are plumb and of the proper diameter, and (5) ensure proper placement of concrete and reinforcement. , .Basements, Dewatering_Systems and Slabs on Grade In view of the depth to ground water and/or bedrock encountered at the site, it is our opinion the majority of the site is suitable for basement construction. Due to the shallow depth to bedrock encountered in the southern third of the site, it is recommended that. complete dewatering systems be provided around any portion of structures placed in or within three (3) feet of the bedrock and/or ground water. The deinwatering system should contain a four (4) inch diameter perforated pipe, underslab gravel, a sump and pump, or other suitable drain outlet. The perforated pipe should be placed around the entire perimeter of the lower basement area. All piping in the perimeter trench should be surrounded by clean, graded gravel from three -fourths (3/4) inch to the #4 sieve in accordance with ASTM C 33-78, Size. No. 67 The gravel should extend from at least three (3) inches below the bottom of the pipe to a minimum of two (2) feet above the bedrock and/or ground water above the pipe, the full width of the trench. To minimize the cost of gravel backfill, it is suggested that the excavation be limited to the area necessary for construction; however, the trench should he a minimum of twelve (12) inches wide. The top of the gravel backfill adjacent to foundation walls should be covered with .an untreated building paper to help minimize clogging of the medium with earth backfill. To minimize the potential for surface water to enter the system, it is recommended that a clay backfill be placed over the system and compacted at or near optimum moisture to at least ninety-five percent (95%) of Standard Proctor Density ASTM D 698-78. (See Appendix C.) We recommend that the drainage pipe be placed at least one (1) foot below the finished slab and have a minimum grade of one -eighth (1 /8) inch per foot. All lower level slabs surrounded by perimeter drains should be underlain by a minimum of eight (8) inches of clean, graded gravel or crushed rock devoid of fines. The drainage -10- system should empty into a sewer underdrain should one adequately sized to accept the anticipated flows exist at the site, or the water from the drain should empty into a sump provided in the lower basement area. The sump should be a minimum of eighteen (18) inches in diameter and three (3). feet deep. A minimum of one (1) foot of clean, graded gravel meeting the above specifications should be placed adjacent to the bottom and sides of the sump. The sump should be provided with a pump designed to discharge all flow to the sump. Water from the sump should be disposed of by suitable means well beyond the foundation of the residence. Due to the swelling pressures exerted by the materials at subgrade, it is our opinion that the only positive solution for construction of the slab where movement will not occur is a structural floor with a void beneath it. However, the cost of this type of system may be prohibitive. It is our opinion that, with certain precautions and knowing that some risk is involved, a floating floor slab may be a reasonable alternative. If the owner is willing to assume the risk of future slab movement and related structural damage, the following recommendations may reduce slab movement and its adverse effects. Subarade below slabs on grade at the upper level should be prepared in accordance with the recommendations discussed i.n the "Site Grading, Excavation and Iltilities" section of this report. If the subgrade below slabs on grade is allowed to dry below the required moisture, the subgrade should be rescarified and recompacted to two percent (2%) wet of optimum moisture to the required density just prior to placement of underslab gravel and concrete. Slabs on grade should be underlain by a minimum of four (4) inches of clean, graded gravel or crushed rock devoid of fines. Slabs surrounded by perimeter drains should be underlain by a minimum of eight (8) inches of clean, graded gravel or crushed rock devoid of fines. Garage slabs should be reinforced with wire mesh running through the control joints. Slabs on grade should be designed and constructed structurally independent of bearing members. To minimize and control shrinkage cracks which may develop in slabs on grade, we suggest that control joints be placed every fifteen (15) to -11- twenty (20) feet and that the total area contained within these joints be no greater than four hundred (400) square feet. In addition, if building construction is done during winter months, it is recommended that slabs on grade not be placed on frozen ground and that they be protected from freezing temperatures until they are properly cured. We further recommend that nonbearing partitions placed on floor slabs be provided with a slip joint (either top or bottom). Slip joints reduce pressure applied by heaving floor slabs and thus minimize damage to the portion of the structure above. It is emphasized that if the subsoils are kept dry, movement of slabs on grade should be minimal. However, if moisture is permitted to reach the subsoils below the slabs, heaving will probably occur. Pavement At the time this report was prepared, the locations of the proposed streets within the subdivision had not been determined. However, general recommendations for streets have been provided, and pavement thicknesses for a typical residential street are provided. Final pavement design will be provided after street locations are determined. It is our opinion that flexible pavement is suitable for the proposed street construction at the site. A flexible pavement alternate should consist of asphalt concrete underlain by crushed aggregate base course or asphalt concrete underlain by plant mix bituminous base course. The design criteria described below was utilized in determining the pavement thicknesses at the site. City of Fort Collins "Design Criteria and Standards for Streets" dated July 1986 "R" value - 6 Regional Factor - 1.0 Serviceability Index - 2.0 for residential streets and 2.5 for collector streets 20-Year Design Life -12- 18 kip Equivalent Daily Load Application - 10 assumed for typical residential street Residential Streets Asphalt Concrete 3" Crushed Aggregate Base Course 12" Total Pavement Thickness 15" Asphalt Concrete 2" Plant Mix Bituminous Base Course 5" Total Pavement Thickness 7" The crushed aggregate base course should meet City of Fort Collins Class 5 or 6 specifications. The subgrade below the proposed asphalt pavement should be prepared in accordance with the recommendations discussed in the "Site Grading, Excavation and Utilities" section of this report. Upon proper preparation of the subgrade, the base course should be placed and compacted at optimum moisture to at least ninety-five percent (95%) of Standard Proctor Density ASTM n 698-78. (See Appendix C.) It is recommended that the asphalt concrete and/or plant mix bituminous base course he placed in two (2) to three (3) inch Lifts. All plant mix bituminous base course and asphalt concrete shall meet City of Fort Collins specifications and should be placed in accordance with these specifications. The crushed aggregate base course shall have an "R" value between 70 and 77, the plant mix bituminous base course shall have an Rt value of 90 or greater, and the asphalt concrete shall have an Rt value of 95 or greater. The "R" value of the pavement materials Used should be verified by laboratory tests. Field density tests should be taken in the aggregate base course, bituminous base course, and asphalt concrete under the direction of the geotechnical engineer. Rigid Pavement A feasible pavement alternate at the site would be rigid pavement. Using the eighteen (18) kip equivalent daily load application described -13- above, a modulus of subgrade reaction of one hundred (100) pounds per square inch per inch based on an "R" value of 6, a design life of twenty (20) years, and concrete designed with a modulus of rupture of six. hundred (600) pounds per square inch using the above assumed 18 kip EDLA of 10, a minimum pavement thickness of five (5) inches of nonreinforced concrete is recommended. Subgrade below proposed streets should be prepared in accordance with the recommendations discussed in the "Site Grading, Excavation and Utilities" section of this report. Concrete pavement should be placed directly on the subgrade that has been uniformly and properly prepared in accordance with the above recommendations. All concrete used in the paving shall meet ASTM specifications, and all aggregate shall conform to ASTM C-33 specifications. The concrete should be designed with a minimum modulus of rupture of six hundred (600) pounds per square inch in twenty-eight (28) days. It is recommended that laboratory mix designs be done to determine the proper proportions of aggregates, cement, and water necessary to meet these requirements. It is essential that the concrete have a low water -cement ratio, an adequate cement factor, and sufficient quantities of entrained air. Joints should be carefully designed and constructed in accordance with the City of Fort Collins "Design Criteria and Standards for Streets" to ensure good performance of the pavement. It is recommended that all concrete pavement be placed in accordance with City of Fort Collins specifications. If paving is done during cold weather, acceptable cold Weather procedures as outlined in the City specifications should be. utilized. The concrete pavement should be properly cured and protected in accordance with the above specifications. Concrete injured by frost should be removed and replaced. It is recommended that the pavement not be opened to traffic until a flexural strength of four hundred (400) pounds per square inch is obtained or a minimum of fourteen (14) days after the concrete has been placed. -14- GENERAL RECOMMENDATIONS (1) Laboratory test results indicate that water soluble sulfates in the soil are negligible, and a Type 1-II cement may be used in concrete exposed to subsoils. Slabs on grade subjected to de-icing chemicals should be composed of a more durable concrete with low water -cement ratios and higher air contents. (2) Finished grade should be sloped away from the structures on all sides to give positive drainage. Ten percent (10%) for the first ten (10) feet away from the structures is the suggested slope. (3) Rackfill around the outside perimeter of the structures should be mechanically compacted at optimum moisture to at least ninety percent (90%) of Standard Proctor Density ASTM D 698-78. (See Appendix C.) Puddling should not be permitted as a method of compaction. (4) Gutters and downspouts should be designed to carry roof runoff water well beyond the backfill area. (5) Underground sprinkling systems should be designed such that piping is placed a minimum of five (5) feet outside the backfill of the structures. Heads should be desiqned so that irrigation Water is not sprayed onto the foundation walls. These recommendations should be taken into account in the. landscape. planning. (6) Plumbing under slabs should be eliminated wherever possible since plumbing failures are quite frequently the source of free water which may cause slab heave. (7) Footing, grade beam and/or pier sizes should be proportioned to equalize the unit loads applied to the soil and thus minimize differential settlements. -15- (8) It is recommended that compaction requirements specified herein be verified in the field with density tests performed under the direction of the geotechnical engineer. (9) It is recommended that a registered professional engineer design the substructures and that he take into account the findings and recommendations of this report. GENERAL COMMENTS This report has been prepared to aid in the evaluation of the property and to assist the architect and/or engineer in the design of this project. In the event that any changes in the design of the structures or their locations are planned, the conclusions and recommendations contained in this report will not be considered valid unless said changes are reviewed and conclusions of this report modified or approved in writing by Empire Laboratories, Inc., the geotechnical engineer of record. Every effort was made to provide comprehensive site coverage through careful locations of the test borings, while keeping the site investigation economically viable. Variations in soil and ground water conditions between test borings may be encountered during construction. In order to permit correlation between. the "reported subsurface conditions and the actual conditions encountered during construction and to aid in carrying out the plans and specifications as originally contemplated, it is recommended that Empire Laboratories, Inc. he retained to perform continuous construction review during the excavation and foundation phases of the work. Empire Laboratories, Inc. assumes no responsibility for compliance with the recommendations included in this report unless they have been retained to perform adequate on -site construction review during the course of construction. -16- No Text No Text TEST BORING LOCATION PLAN! TIF M. NDKTV PW 6d�-f - 9 FH EL: W D Plo.,z ® Mao s N6. 4 No.7 w AS i KEY TO BORING LOGS i�T] TOPSOIL v•� GRAVEL FILL SAND & GRAVEL SILT i SILTY SAND & GRAVEL CLAYEY SILT op COBBLES DSANDY SILT -'.a• SAND, GRAVEL & COBBLES VLA CLAY ® WEATHERED BEDROCK SILTY CLAY SILTSTONE BEDROCK SANDY CLAY CLAYSTONE BEDROCK SAND SANDSTONE BEDROCK i.'. SILTY SAND ® LIMESTONE CLAYEY SAND "` GRANITE SANDY SILTY CLAY ❑ SHELBY TUBE SAMPLE. fl, STANDARD PENETRATION DRIVE SAMPLER WATER TABLE 72 hrs. AFTER DRILLING C 4 .. HOLE CAVED 5/12 Indicates that 5 blows of a 140 pound hammer falling 30 inches was required to penetrate 12 lncha._- A= EMPIRE LAI = Ms ft v VA PM o� F" M® 100 95 90 85 Zol LOG OF BOW1GS No. !D I WIRE tABORATORIW INC. 6. No Text .81 .aa .79 4 rH-. .78 z A .77 .76 .75 .7 7 CONSOLIDATION TEST PRO. 8299 1111111-0-11111111111i'DEP7H, BORING NO.: I ��■��IryI�II�V��111 �IIIII����I ■■�11111�■■�INY 0.1 4.0 0.25 0.5 1.0 5 10 APPLIED PRESSURE TSF 0.1 0.25 0.5 1.0 5 10 APPLIED PRESSURE - TSF EMPIRE LABORATORIES INC. .43 .43 .42 .42 4 .41 A .41 a .4 .4 •3 3 CONSOLIDATION TEST PRO. 8299 ME R-111111M =NOR3,1111M u�u MEM11111 Mommill1 ■wAn �■■gnu, ■inn ■■Nn�■nnn ■unui�■■�nm . 0.1 0.25 4.0 0.0 0.1 0.5 1.0 5 APPLIED PRESSURE - TSF 0.25 0.5 1.0 5" 10 APPLIED PRESSURE - TSF EMPIRE LABORATORIES INC. B' 3 - J. LLI 4.0 uk: ,,, 0.0 Z'. -4.0 T 8.0 J. 0 ff) Z 12.0 -16.0 0.1 SWELL - CONSOLIDATION TEST PRO, 8M 0.25 0. 5 1.0 5 APPLIED PRESSURE - TSF AD13ED Empire Laboratories, Inc. GEOTECHNICAL ENGINEERING 8 MATERIALS TESTING January 18, 1990 The Group, Inc. 323 South College Avenue Fort. Collins, Colorado 80524 Attention: Ms. Linda Hopkins Gentlemen: CORPORATE OFFICE P.O. Box 503 • 301 No. Howes Fore Collins, Colorado eos22 (303) 484-0359 FAX No. (303) 484-0454 We are pleased to submit our Report of a Geotechnical Investigation prepared for the proposed residential development located on Seneca Street in southwest Fort Collins, Colorado. Based upon our findings in the subsurface, it is our opinion the site is suitable for the proposed construction, providing the design criteria and recommendations set forth in this report are met. The accompanying report presents our findings in the subsurface and our recommendations based upon these findings. Very truly yours, EMPIRE LABORATORIES INC 71 Neil R. herrod Senior Engineering Geologist Reviewed by: F L�2i'���T/�1 � t• S S� Chester C. Smith, P.F. a N 4806 i President oy cic '?F OF COV ::raeu(oslaua -` Branch Of em P.O. Boa I M59 P.O. Box 1135 P.O. Box 17" P.O., Box 5869 Colorado SPrin946 CO So935 Longmont, CO 80602 Greeley, CO 80632 Cheyenne, WY 82003 tiff)) 597-2116 (303) 770.3921 (303) 351.0480 (307) OU-9224 Member of ConstibV Engineers Council RESISTRNCE R-VHLUE'HND EXPRNSION PRESSURE OF COMPACTED SOIL RSTM — D 2844 CLIENT: THE GROUP. INC. PROJECT: THE VILLAGES AT HARMONY WEST LOCATION OF SAMPLE: COMPOSITE SAMPLE BORING NO. 9 @ 0.5' - 3.5' SAMPLE DATA TEST SPECIMEN I. 2. 3 COMPACTION PRESSURE - PSI 0 0 20 DENSITY - PCF 95.1 97.6 104.4 MOISTURE - % 28.0 25.5 21.0 EXPANSION PRESSURE - PSI 0.08 0.00 0.00 HORIZONTAL PRESSURE @ 160 psi 155 148 139 SAMPLE HEIGHT - in.. 2.52 2.56 2.56 EXUDATION PRESSURE - PSI 111 219 358 UNCORRECTED R-VALUE 1.6 4.0 8.2 CORRECTED R-VALUE 1.6 4.1 8.4 R-VALUE AT 300 PSI EXUDATION PRESSURE = 5.8 100 402 W 60 J 2 m 40 20 dai 260 300 400 500 600 EXUDATION PRESSURE — psi EMPIRE LABORATORIES INC. 0 B-5 SUMMARY OF TEST RESULTS Boring Depth Me lsturs Dry Density Compressive Strength Swell Pressure Soluble Sulfates PH Liquid Limit Plasticity Index ' G►ouP Index ClessHication AASHTO Resistivity (OHM�M) Penetration Blows/in. IFt.I I %1 IPCFI IPSFI IPSF) 1%1 1%1 1%1 LISCS 1 0.5-1.5 18.9 18/12 3.0-4.0 18.7 90.8 820 4.0-5.0 17.9 4/12 7.0-8.0 19.2 107.6 2370 8.0-9:0 18.3 7/12 14.0-15.0 19.0 12/12 Composi Sample' e 0.5-3.5 44.3 21.6 15.7 OL A-7(16) 2 0.5-1.5 17.8 21/12 3.0-4.0 16.7 107.8 3400 155 4.0-5.0 18.8 7/12 7.0-8.0 16.2 106.4 1900 8.0-9.0 18.8 5/12 14.0-14.7 12.9 50/8 3 0.5-1.5 19.5 22/12 &.0-4.0 23.1 89.7 2430 .0025 4.0-5.0 22.3 5/12 7.0-8.0 13.5 118.2 1900 8.0-9.0 10.1 13/12 14.0-15.0 13.3. 50/12 emrmc Lgeun.a 1 umca. 1.uc SUMMARY OF TEST RESULTS Boring Dopth Moisturo Dry Density Compressive Strength Swell Pressure Soluble Sulfates 1IiH Liquid Limit Plasticity Index Group Index Classification AASHTO USCS Resistivity (OHM CM) Penetration Blows/In. No. IFt (%) (PCF) IPSFI IPSFI 1%1 4 0.5-1.5 11.0 20/12 3.0-4.0 13.8 *285 4.0-5.0 4.3 28/12. 7.0-8.0 9.8 18/12 14.0-15.0 11.9 36/12 Composi: Sample e 0.5-3.5 31.3 12.7 1.7 SL A-6 (2) 5 0.5-1.5 12.6 22/12 3.0-4.0 6.3 4.0-5.0 5.6 6/12 %0.8.0 10.1 114.6 310 8.0-9.0 14.4 4/12 14.0-15.0 12.5 30/12 6 0.54.5 22.0 9/12 3.0-4.0 9.2 120.3 6050, 280 4.0-5.0 7.1 25/12 7.0-8.0 4.5 8.0-:9.0 11.5 48/12 14.0-14.3 12.2 *1290 50/4 e o remolded samplg cmrinc UMWwn..1 • SUMMARY OF TEST RESULTS Boring Depth Moisture Density .Compressive Strength Swell Pressure Soluble Sulfat Sulfate pH PH Liquid Limit Plasticity Index Group Index Cls wfwittion AASHTO Resistivity (OHM4m) Penetration Blows/In. No. > IFt.I 1%) IPCFI (PSFI (PSF) 1%) M (%1 USCS 7 0.5-1.5 13.8 24/12 3.0-4.0 10.0 94.3 3710 4.0-5.0 11.2 17/12 7..0-8.0 10.3 97.1 2360 .0031 8.0-9.0 6.0 30/12 14.0-14.7 10.5 50/8 8 0.5-1.5 13.4 17/12 3.0-4.0 10.4 88.3 3530 1060 4.0-5.0 10.5 18/12 8.0-9.0 3.0 24/12 14.0-14.3 6.2 50/4 9 0.5-1.5 8.9 16/12 3.0-4.0 17.9 98.1 1630 4.0-5.0 15.9 7/12 7.0-8.0 7.0 8.0-9.0 2.9 20/12 14.0-15.0 14.8 .0017 20/12 cmpos j e. Simple' '` Q.5-3.5 36.1 16.,5 7.5 CL A-6(7.5) ;,;... IL EMPIRE LAaURA I UNIC6.1N6. SUMMARY OF TEST RESULTS Boring Depth. moisture Dry Density Compressive Stronpth Swell Pressure Soluble Sulfates pH Liquid Limit Plasticity Index Group Index Classification AASHTO Resistivity (OHM -CM) penetration Blowslln. hto. IFt.) 1%) IPCF) IPSF) IPSF) I%) 1%1 I%1 IISCS 10 0.5-1.5 9.9 22/12 3.0-4.0 8.3 104.5 1850 4.0-5.0 8.5 50/12 8.0-8.7 11.1 50/8 14.0-14.3 10.5 50/3 11 0.5-1.5 17.4 15/12 3.0-4.0 7.4 4.0-5.0 4.3 50/12 7.0-7.7 9.1 750 50/8 14.0-14.3 8.2 50/3 Composi e Sample 0.5-1.5 41.4 21 10 CL A-700) 12 0.5-1.5 8.6 I 19/12 3.0-4.0 7.9 106.5 1980 4.0-5.0 8.4 5/12 7.0-8.0 15.4 99.3 1600 8.0-9.0 11.7 31/12 14.0-14.7 -------------- 9..5 50/8 CMromr. Lj%ounot 1 Vngra. Irvb. Boring No. Depth (ft.) SUMMARY % Moisture OF TEST RESULTS Resistivity ohm/cm Oxidation -Reduction Sulfide pH Potential (MV) 1 0.5-3.5 23.7 1200 255 trace 7.7 9 0.5=3.5 25A 2400 218 trace 7 5 No Text APPENDIX C. Suggested Minimum Specifications for Placement of Compacted Earth Fill and/or Back-fill.s 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 backfiil 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 beginning of the disposed of by subgrade. The suitable means prior to preparation subgrade shall be scarified a minimum depth of six (6) inches, moisture conditioned as necessary and compacted in a suitable fill material. Fill shall not be placed until manner prior to approval by the. placement of geotechnical engineer or his representative: and in -no case, shall fill material be placed on frozen or unstable ground. require the use of imported granular Subgrade which is not stable may material, geotextiles or other methods for stabilization as approved by the geotechnical engineer. FILL PLACEMENT Fill material shall not be placed during unfavorable.. weather fill shall be approved by the conditions. Material engineer proposed for use as or his representative prior to use. Proposed import. his geotechnical material shall be approved by the geotechnical Fill engineer or material shall be.. representative prior to hauling to the project site. C=2 ,.. uniformly mixed such as to preclude the formation of lenses ofmaterial 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 bemade 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 REPORT OF A GEOTECHNICAL INVESTIGATION This report presents the results of a geotechnical evaluation prepared for the proposed residential development located west of the Pleasant Valley and Lake Canal between Troutman Parkway and Wake. Robin Lane in southwest Fort Collins, Colorado. The investigation included test borings and laboratory testing of samples obtained from these borings. The objectives of this study were to (1) evaluate the subsurface conditions at the site relative to the proposed construction, (2) make recommendations regarding the design of the substructures; (3) recommend certain precautions which should be taken because of adverse soil and/or ground water conditions, and (4) make recommendations regarding pavement types and thicknesses for the proposed streets to be constructed at the site. SITE EXPLORATION The field exploration, carried out on January 10, 19.90, consisted of drilling, logging, and sampling twelve (12.) test borings_ The test. borings were located by Empire Laboratories, Inc. from existing street intersections using conventional chaining methods. The locations of the test borings are shown on the Test Boring Location Plan included in Appendix A of this report. Boring logs prepared from the field logs are shown in Appendix A. These logs show soils encountered, location of sampling, and ground water at the time of the exploration. The borings were advanced with a four -inch diameter, continuous - type, power -flight auger drill. During the drilling operations, a geotechnic.al 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 bordered by Seneca Street. on the west, Regency Drive on the southwest, Wake Robin Lane on the south, proposed Troutman Parkway on the north and the Pleasant Valley and Lake Canal on the east in southwest Fort Collins, Colorado. More particularly, the site is described as a tract of land situate in the Southeast 1 /4 of Section 34, Township 7 North, Range 69 West of the Sixth P.M., City of Fort Collins, Larimer County, Colorado. The site consists of a large vacant tract of land with gently rolling terrain. Major drainage is slight to the east and northeast. The area is currently vegetated with grass and weeds. The south and west portions of the site are bordered by ditches. A large culvert is located at the intersection of Regency Drive and Seneca Street. A large stockpile is located at the southeast corner of the site and is approximately 100 feet long, 25 feet wide and 5 to 10 feet in height. The northern part of the property is bordered by an existing fence, and the eastern portion of the property is bordered by the Pleasant Valley and Lake Canal, which forms the east property line. A new elementary school is located to the northwest, and a junior high school is currently under construction west of the property. Open land is located to the north and east, and residential areas are Located to the south. LABORATORY TESTS AND EVALUATION Samples obtained from the test borings were subjected to testing in the laboratory to provide a sound basis for evaluating the physical properties of the soils encountered. Moisture contents, dry unit weights, unconfined compressive strenaths, water soluble sulfates, pH, sulfides, laboratory resistivity, oxidation-reduction potential, swelling potentials, and the Atterberg limits were determined. A summary of the test results is included in Appendix B. Consolidation, swell -consolidation and Hveem stabilometer characteristics were also determined, and curves showing this data are included in Appendix B. -2- 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: (1) Silty Topsoil: The majority of the area tested is overlain by a six (6) inch layer of silty topsoil. 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 backfill material. It is recommended that the topsoil be stripped and stockpiled for reuse in planted areas. (2) Silty Clay: A layer of brown silty clay underlies the topsoil and surface and extends to depths of one (1) to four and one-half (4-1 /2) feet below the surface. The silty clay is plastic, contains minor amounts of sand and traces of gravel and exhibits moderate bearing characteristics in its dry to damp natural condition. When wetted, the clay stratum exhibits moderate to high swell potential. (3) Sandy and/or Sandy Gravelly Silty Clay: This stratum underlies the upper clays and extends to the bedrock below and/or the depths explored:, The lower silty clay stratum is red to tan, contains varying amounts of sand and gravel and lenses of silty sand and gravel and is damp to moist in situ. When wetted, the lower clay stratum exhibits slight to moderate swell potential; and upon loading, consolidation occurs. (4) Siltstone-Sandstone . Bedrock: The bedrock was encountered below the upper clays in Borings 2 through 7 and 9 through 12 at depths of three (3) to fourteen and one-half (14-1/2) feet below the surface and extends to greater depths. The bedrock was encountered at relatively shallow depths of three (3) to nine (9) feet in the southern third of the property in the area -3- of Borings 6 and 10 through 12. The; upper one and one-half (1-1 /2) to two (2) feet of the bedrock is highly weathered; however, the underlying siltstone interbedded with minor amounts of sandstone is dense and exhibits very high bearing characteristics. When wetted, the siltstone portion of the bedrock stratum exhibits high swell potential. (5) Ground Water: At the time of the investigation, free ground water was encountered in Boring 2 at a depth of eleven (11 ) feet below the surface. No free ground water was encountered in the remaining borings drilled at the site to the depths explored. 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 in the. Pleasant Valley and Lake Canal located adjacent to the site. In addition, it is our opinion that surface Water may percolate through the upper subsoils and become trapped on the relatively impervious bedrock stratum, forming a perched ground water condition. GEOLOGY The proposed subdivision is located in 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 Rasin 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 shale is overlain by alluvial and colluvial clays and gravels of Pleistocene and/or Recent Age. z2 Bedrock underlies the site at depths of three (3) to approximately twenty (20) feet below the surface. The dip of the bedrock in this area is slight and in an easterly direction. Seismicactivity in the area is anticipated to be low; therefore, from a structural standpoint, the property should be relatively stable. Due to the generally flat to gently rolling nature of the property, geologic hazards due to mass movement, such as landslides, mudflows, etc., are not anticipated on the property. The site lies within the drainage basin of Mail Creek, which is a tributary of Fossil Creek. Drainage of a tributary of Mail Creek is directed along the southwest corner of the site, below Seneca Drive and into two large concrete pipes just north of the its intersection with Regency Drive. The 100 year flood plain of this intermittent tributary should be established, and residential construction should be elevated above or placed beyond the flood plain of this drainage.. RECOMMENDATIONS AND DISCUSSION It is our understanding the site is to be developed for single-family residential construction. Due to the topography of the site, minor site grading of the area is anticipated. At the time of the site exploration, the locations of the residential lots and streets were not known. The test borings were placed to determine representative subsurface conditions throughout the site. Recommendations for pavement thicknesses of streets will be provided after the locations of the streets are determined and traffic data can be obtained from the City of Fort Collins. Pavement thicknesses for typical residential streets are provided in this report. Site Grading, Excavation and Utilities Specifications pertaining to site grading are included below and in Appendix C of this report. It is recommended that the upper six (6) inches of topsoil penetrated by root growth and organic matter below building, filled and paved areas he stripped and stockpiled for reuse in planted areas. The upper six (6) inches of the subgrade below -5- building, paved and filled areas should be scarified and recompacted between optimum moisture and two percent (2%) wet of optimum moisture to a minimum of ninety-five percent (95%) of Standard ProctorDensity ASTM D 698-78. (See Appendix C.) Finished subgrade below streets and paved areas should be placed a minimum of three (3) feet above the bedrock stratum, and this should be taken into account in the site grading plan proposed for the site. If the finished street subgrade is placed within three (3) feet of the bedrock, subdrains may be required to intercept potential perched ground water. nue to the clayey nature of the upper subsoils, unstable conditions may occur in the street subgrade during construction and/or under proof_rolling. Should this occur, stabilization may be required. The use of lime, geotextiles, pit run, kiln dust or fly ash could be used to provide the proper stabilization. Fill should consist of the on -site soils 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 between optimum moisture and two percent (2%) wet of optimum moisture to a minimum of ninety-five percent (95%) of Standard Proctor Density ASTM D 698-78. The material stockpiled on -site should be evaluated to determine if it is suitable for use as structural fill. If it is determined the material is not suitable, it should be wasted from the property or used in open and planted areas. Bedrock encountered at the site may be used as fill material in selected areas. Heavy-duty construction equipment equivalent to a track mounted excavator having a gross weight of ninety thousand (90,000) pounds or a D-8 tractor and ripper tooth may be needed to excavate the firm bedrock. Bedrock used as fill should be broken into pieces less than six (6) inches in diameter. Proper placement of the bedrock as fill may be difficult, and a disc or other mixing equipment may be needed to obtain uniform moisture and proper compaction. The bedrock should be used in open and planted areas or in the Lower portion of fill below paved areas. In computing earthwork quantities, an estimated shrinkage factor of eighteen percent (18%) to twenty-three percent (23%) may be used for the on -site clays compacted to the above -recommended density. A -6-