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Home My WebLink AboutHORSETOOTH EAST BUSINESS PARK PUD - PRELIMINARY/FINAL - 43-94 - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORTSUBSURFACE EXPLORATION REPORT PROPOSED CHRIS WELLS DEVELOPMENT FORT COLLINS, COLORADO EEC PROJECT 1942050 .1 1 EARTH ENGINEERING CONSULTANTS, INC. ' ZIS WELLS DEVELOPMENT .1RT COLLINS, COLORADO PROJECT NO: 1942050 DATE: JULY 1994 LOG OF BORING B-3 SHEET 1 OF 1 RIG TYPE: TRACK RIG CME ?%?;?`:.`i%>.fii%%`;$:`£#;i;':;{ :;}ii':;:;,:>!#i#:! WATER DEPTH ELEV FOREMAN: SCK START DATE 719194 WHILE DRILLING 9. NIA AUGER TYPE: 4' CFA FINISH DATE 716194 AFTER DRILLING NIA NIA SPT HAMMER: MANUAL SURFACE ELEV NIA 24 HOUR NIA NIA SOIL DESCRIPTION TYPE 0 (FEET) N (BLOWLFT) ou (PSF) Mc (%) 00 (PCF) A•LNMrTS .200 1%) SWELL LL M PRESSURE % 500 PSF SANDY CLAY (CL) F Medium brown Moist Medium stiff FST FSS _ _ _ _ _ 5 S 19.4 4 500 NONE 10 9 1 21.6 15 GRAVELLY CLAYEY SAND Red Fss Saturated Dense 37 16.2 _ _ _ 20 HIGHLY WEATHERED CLAYSTONEISHALE Olive grayish brown Mottled -Slightly hard-Plastic ISS 39 19.6 BOTTOM OF BORING 20 FEET. 25 Earth Engineering Consultants UNI# SOIL CLASSIFICATION SYS* ` Soil CbaaHleatbn Crherla for Assigning Group Symbols and Group Names Using Laboratory Taste Group Symbol Group Namea Coarsa-Grained Soils more than Gravels more than 50% of coarse Clean Gravels Less than 5% finest Cu > 4 and i < Cc <3' GW Well -graded gravel a 50% retained on fraction retained on No. 200 sieve No. 4 sieve Cu < 4 and/or 1 > Cc > 36 GP Poorly graded grave Gravels with Fines more than 12% finest Fines classifyas ML or N1H GM Silty gravel,G,H Fines classify as CL or CH GC Clayey gravel'-g•" Sands 50% or more Clean Sands Less Cu > B and 1 < Cc < 31 SW Well -graded sand' of coarse fraction than 5% finest passes No. 4 sieve Cu < 6 and/or 1 > Cc > 3t SP Poorly graded sand' Sands with Fines Fines classify as ML or NIH SM Silty sand° -Hu more than 12% fines° Fines Classify as CL or CH SC ,t Clayey sand°•"'' Fine -Grained Soils Silts and Clays inorganic PI > 7 and plots on or above "A line' CL Lean clay'-L" 50% or more Liquid limit less passes the than 50 PI < 4 or plots below "A" line' ML siltK.LH No. 200 sieve organic Liquid limit - oven dried Organic clayK•L"." < 0.75 OL Liquid limit - not dried Organic siltK•ua•o Silts and Clays inorganic PI plots on or above "A" line CH Fat clay"L'" Liquid limit 50 or more PI lots below "A" line MH Elastic SiftK,l organic Liquid limit - oven dried Organic clayKA.)A.° < 0.75 OH Liquid limit - not dried Organic siftKL'a•G Highly organic soils Primarily organic matter, dark in color, and organic odor PT Peat ABased on the material passing the 3-in. _ Klf soil contains 15 to 29% plus No. 200, add (75-mm) sieve .aCu=D /D Cc . (D°07 with sand" or "with gravelwhichever is elf field sample contained cobbles or `° 10 O:o x Dao predominant boulders, or both, add "with cobbles or boulders, or both" to group name. [Gravels with 5 to 12% fines require dual 'If soil contains > 15% sand, add "with symbols: sand" to group name. GW-GM wail -graded gravel with silt clf fines classify as CL-ML, use dual symbol GW-GC well -graded gravel with clay GC -GM, or SC-SM. GP -GM poorly graded gravel with silt "If fines are organic, add "with organic fines" GP -GC poorly graded gravel with clay to group name. "Sands with 5 to 12% fines require dual 'If soil contains > 15% gravel, add "with symbols: gravel" to group name. SW-SIM well -graded sand with silt 'If Atterberg limits plot in shaded area, soil is SW -SC well -graded sand with clay a CL-ML, silty clay. SP-SM poorly graded sand with silt SP-SC poorly graded sand with clay M a 50 10 7 J 0 Llf soil contains > 30°% plus No. 200 predominantly sand, add "sandy" to group name. "If soil contains > 30% plus No. 200, predominantly gravel, add "gravelly" to group name. "PI > 4 and plots on or above "A" line. °PI < 4 or plots below "A" line. FPI plots on or above "A" line. oPl plots below "A" line. For claa,llludon of flnog wined aoits and Ilne-grained fraction of cgana grained foil, / I Equation of -A" - tine HonLontal at PI . 4 to LL . 25.5. then PI . 0.73 ILL - 201 Eoualion of -U- • line -- Vertical at LL " 16 to PI . 7, I then PI . 0.9 (LL - 6) G\' MH oA 0H; I L CL ML MLoFtOL-- 1 I i I I 0 10 16 20 30 40 so 60 70 60 90 100 Ila LIQUID LIMIT ILL) DR, ING AND EXPLORATION DRILLING & SAMPLING SYMBOLS: SS : Split Spoon - lVa' I.D., 2" O.D., unless otherwise noted PS : Piston Sample ST : Thin -Walled Tube - 2" O.D., unless otherwise noted WS : Wash Sample R : Ring Barrel Sampler - 2.42" I.D., 3" O.D. unless otherwise noted. PA : Power Auger FT : Fish Tail Bit HA : Hand Auger RB : Rock Bit DB : Diamond Bit = 4", N, B BS : Bulk Sample AS : Auger Sample PM : Pressure Meter HS : Hollow Stem Auger DC : Dutch Cone WB : Wash Bore Standard "N" Penetration: Blows per foot of a 140 pound hammer falling 30 inches on a 2-inch O.D. split spoon, except where noted. WATER LEVEL MEASUREMENT SYMBOLS: WL :Water Level WS :While Sampling WCI : Wet Cave in WD : While Drilling DCI : Dry Cave in BCR : Before Casing Removal AB : After Boring ACR : After Casting Removal Water levels indicated on the boring logs are the levels measured in the borings at the time indicated. In pervious soils, the indicated levels may reflect the location of groundwater. In low permeability soils, the accurate determination of groundwater levels is not possible with only short term observations. DESCRIPTIVE SOIL CLASSIFICATION Soil Classification is based on the Unified Soil Classification system and the ASTM Designations D-2487 and D-2488. Coarse Grained Soils have more than 50% of their dry weight retained on a #200 sieve; they are described as: boulders, cobbles, gravel or sand. Fine Grained Soils have less than 50% of their dry weight retained on a #200 sieve; they are described as: clays, if they are plastic, and silts if they are slightly plastic or non -plastic. Major constituents may be added as modifiers and minor constituents may be added according to the relative proportions based on grain size. In addition to gradation, coarse grained soils are defined on the basis of their relative in -place density and fine grained soils on the basis of their consistency. Example: Lean clay with sand, trace gravel, stiff (CL); silty sand, trace gravel, medium dense (SM). CONSISTENCY OF FINE-GRAINED SOILS Unconfined Compressive Strength, Ou, psf Consistency < 500 Very Soft 500 - 1,000 Soft 1,001 - 2,000 Medium 2,001 - 4,000 Stiff 4,001 - 8,000 Very Stiff 8,001 - 16,000 Very Hard RELATIVE DENSITY OF COARSE -GRAINED SOILS: N-Blows/ft Relative Density 0.3 Very Loose 4.9 Loose 10-29 Medium Dense 30-49 Dense 50-80 Very Dense 80 + Extremely Dense PHYSICAL PROPERTIES OF BEDROCK DEGREE OF WEATHERING: Slight Slight decomposition of parent material on joints. May be color change. Moderate Some decomposition and color change throughout. High Rock highly decomposed, may be extremely broken. HARDNESS AND DEGREE OF CEMENTATION: Limestone and Dolomite: Hard Difficult to scratch with knife. Moderately Can be scratched easily with knife, Hard Cannot be scratched with fingernail. Soft Can be scratched with fingernail. Shale, Siltstone and Claystone: Hard Can be scratched easily with knife, cannot be scratched with fingernail. Moderately Can be scratched with fingernail. H and Soft Can be easily dented but not molded with fingers. Sandstone and Conglomerate: Well Capable of scratching a knife blade. Cemented Cemented Can be scratched with knife. Poorly Can be broken apart easily with fingers. Cemented IIS WELLS DEVELOPMENT FORT COLLINS, COLORADO PROJECT NO: 1942050 F DATE: JULY 1994 LOG OF BORING BB SHEET 1 OF 1 RIG TYPE: TRACK RIG CME <ijg;d€:°i3;?;:2:$3i#;`;`.i>?;i;ifi;;j#i31};u;??};;ji?i<;;;>'E>? START DATE 719194 WATER DEPTH ELEV FOREMAN: SCK WHILE DRILLING 9. 'NIA AUGER TYPE: 4" CPA FINISH DATE 70$4 AFTER DRILLING NIA NIA SPT HAMMER: MANUAL SURFACE ELEV NIA 24 HOUR NIA NIA SOIL DESCRIPTION 0 N ou MC Do A{MTS .200 SWELL LL PI PRESSURE % 500 PSF TYPE (FEET) (BLOWSIFT) (PSFI 1%1 (PCF) 1%) SANDY CLAY (CL) Medium brown Moist to saturated _ Medium stiff to soft 5 10 _ SANDY GRAVEL (GP) Saturated Dense _ i i HIGHLY WEATHERED CLAYSTONEISHALE Slightly hard 15 Plastic 20 BOTTOM OF BORING 20FEET. _ 25 Earth Engineering consultants .RIS WELLS DEVELOPMENT FORT COLLINS, COLORADO DATE: JULY 1994 PROJECT NO: 1S42050 SHEET 1 OF 1 LOG OF BORING 8.7 TRACK RIG CME i>.;tiii.'.z?%>`;?:;i;.;i;+.?>;'.:`:.'•»#z;#?;>>:o :S:ciii is>.:'.,`.>'. START DATE 719194 FINISH DATE 7181% SURFACE ELEV NIA 24 WATER DEPTH ELEV RIG TYPE: FOREMAN: SCK AUGER TYPE: 4" CFA SPT HAMMER: MANUAL WHILE DRILLING AFTER DRILLING HOUR 7' NIA NIA NIA NIA NIA SOILDESCRIPTION o N ou Mc 00 A. =Ts •200 SWELL TYPE (FEET) (aLOWSIFT) (PSF) I%) (PCF) LL PI 1%) PRESSURE % 500 PEP SANDY GRAVELLY CLAY (CL) _ _ Medium brown — — Moist SS — — 9 Medium stiff — — 5 SANDY CLAY (CL) ST 5 20.2 Reddish brown — — Moist — — Medlum stiff — — 1SS 10 4 21.3 — — GRAVELLY SAND(SP) Red — — Saturated — — Medium dense — — — SANDY CLAY (CL) Gray — — Saturated SS 15 19 7.9 Medium stiff — BOTTOM OF BORING 15112 FEET. 20 25 tans Cf19Nleerrna —11a RIS WELLS DEVELOPMENT FORT COLLINS, COLORADO PROJECT NO: 1942050 DATE: JULY 1994 LOG OF BORING B-6 SHEET 1 OF 1 RIG TYPE: TRACK RIG CME ;,?.:;>;`.;`..i;,j;.y,;<t;;'.:;;'.Ei`.;'::;:.Ei£„>,;;i$'\i;.'.,>..3>£j<}?;>`5;vi,>:;`2>:5 WATER DEPTH ELEV FOREMAN: SCK START DATE 718M WHILE DRILLING 9. NIA AUGER TYPE: 4' CFA FINISH DATE 718194 AFTER DRILLING NIA NIA SPT HAMMER: MANUAL SURFACE ELEV NIA 24 HOUR NIA NIA SOIL DESCRIPTION TYPE D (FEET) N (BLOWSIFT) ou (ISF) Mc (%I DotMTS•200 ()CF) 1%) SWELL PRESSURE % 500ISF Fss SANDY CLAY(CL) Medium brown Moist Medium stiff to soft EsT FSS _ _ _ _ 5 12 16.9 78.8 0 10 4 22.6 _ _ _ _ _ 15 SANDY LEAN CLAY (CL) Tan and Olive Mottled Saturated FSS Medium stiff to stiff 12 14.4 _ _ _ _ _ _ _ _ 20 �I GRAVELLY SAND Red -Saturated -Dense HIGHLY WEATHERED CLAYSTONEISHALE Mottled Slightly hard Plastic SS M - 20.9 25 BOTTOM OF BORING 20 V2 FEET. tarrtn tngineering LeunsumanL5 'HRIS WELLS DEVELOPMENT FORT COLLINS, COLORADO PROJECT NO: 1942050 DATE: JULY 1994 LOG OF BORING B5 SHEET 1 OF 1 RIG TYPE: TRACK RIG CME ::;i::?::;'::::;£:?33<.isry5>.;;i77 WATER DEPTH ELEV FOREMAN: SCK START DATE 718194 WHILE DRILLING NONE NIA AUGER TYPE: 4" CFA FINISH DATE 7I8I94 AFTER DRILLING NIA NIA SPT HAMMER: MANUAL SURFACE ELEV NIA 24 HOUR NIA NIA SOIL DESCRIPTION TYPE o (FEET) N (BLOWSIFT) au IPSFI sa (%) no (PCF) A -Lours -200 I%) SWELL LL PI PRESSURE %500 PSF SANDY CLAY (CL( Dark brown SS Moist Son ST _ _ _ _ 5 8 20.7 2 27.9 _ 10 R BOTTOM OF BORING 5 1l2 FEET. 15 - _ 20 25 Earth Engineering Consultants IRIS WELLS DEVELOPMENT rORT COLLINS, COLORADO PROJECT NO: 1942060 1 DATE: JULY 1994 LOG OF BORING B4 SHEET 1 OF 1 RIG TYPE: TRACK RIG CME •':,2Fi;;£`k':>:>#?t;r;:??:::'•?'iYi;:%>;`:?>;:£5??'?i':'?%`i::::i>.>;: WATER DEPTH ELEV FOREMAN: SCK START DATE 718I94 WHILE DRILLING NONE NIA AUGER TYPE: 4' CFA FINISH DATE 718191 AFTER DRILLING NIA WA SPT HAMMER: MANUAL SURFACE ELEV NIA 24 HOUR NIA NIA SOIL DESCRIPTION TYPE 0 (FEET) N (ELOWSIFT) au (PSF) we (%) 00 IPCF) A -LINTS -200 (%) SWELL LL PI PRESSURE Is 0 500 PSF SANDY CLAY (CL) Medium brown SS Moist Medium stiff to soft ST — — — — — _ 5 8 22.5 2 28.3 10 d BOTTOM OF BORING 5 V2 FEET. 15 20 — — 25 CBRfI Ciigine6fllly L VllQ,UlWllLQ 'RIS WELLS DEVELOPMENT rORT COLLINS, COLORADO PROJECT NO: 1942050 DATE: JULY 1994 LOG OF BORING B-2 SHEET 1 OF 1 RIG TYPE: TRACK RIG CME <:#::£##:;::S:i:;:?i;:::%;u#>.£;iE _`::�?<::£::>:£s;: START DATE 7M94 WATER WHILE DRILLING DEPTH 9' ELEV NIA FOREMAN: SCK AUGER TYPE: 4"CFA FINISH DATE 7WS4 AFTER DRILLING NIA r' NIA SPT HAMMER: MANUAL SURFACE ELEV NIA 24 HOUR NIA NIA SOIL DESCRIPTION TYPE D (FEET) N (BLOWLFT) oU (PSF) Mc 1%) Do IPCF) A•LDBTs .200 (%) HELL LL PI PRESSURE % 0 S00 PSP SS SANDY CLAY (CL) Medium brown Moist Medium stiff Wet Fss SS _ _ _ _ _ _ 5 6 16.3 r r 3 31.1 10 6 22.6 SANDY LEAN CLAY (CL) Son Weathered SS _ 1s 15 16.2 _ _ _ 20 GRAVELLY SAND (SP) Brownish red Saturated - Medium dense HIGHLY WEATHERED CLAYSTONEISHALE Grayish brown Mottled Slightly hard Plastic FSS 39 19.9 BOTTOM OF BORING 20 FEET. 25 Earth tngmeering consultants RIS WELLS DEVELOPMENT FORT COLLINS, COLORADO PROJECT NO: 1942050 DATE: JULY 1994 LOG OF BORING B-1 SHEET 1 OF 1 RIG TYPE: TRACK RIG CME `++ +":^'%""'%"''""'><ri�`:';i.3i>5%.>.>>?:,k;'.>%;! " WATER DEPTH ELEV FOREMAN: SCK START DATE 7M94 WHILE DRILLING 9' NIA AUGERTYPE: 4'CFA FINISH DATE 71&94 AFTER DRILLING NIA NIA SPT HAMMER: MANUAL SURFACE ELEV NIA 24 HOUR NIA NIA SOIL DESCRIPTION TYPE D (FEET) N (SLOWSIFT) oU (PSF) RIC I%) DD (PCF) A-UMTS .200 (%) SWELL LL I PI PRESSURE % 500 ►SF SS SANDY CLAY (CL) Medium brown Moist Medium stiff Wet F ss _ _ _ 5 12 16.0 35 15 79.9 3 22.0 10 2 25.3 _ _ 15 CLAYEY GRAVELLY SAND(SP) Brown Saturated Dense Ss 43 14.0 _ _ _ _ _ _ _ 20 SANDY CLAY (CL) Tanish brown Mottled Saturated - Soft HIGHLY WEATHERED CLAYSTONEISHALE Tallish brown Mottled Slighty hard Plastic Iss 25 for 4' 20.2 BOTTOM OF BORING 20 FEET. 25 Earth Engineering Consultants BORING LOCATION DIAGRAM CARIS WELLS DEVELOPMENT FORT COLLINS, COLORADO JULY 1994 N NOT TO SCALE rth F,ngineerinu Cnnsultnnts Earth Engineering Consultants, Inc. Proposed Chris Wells Development July 25, 1994 Page 12 This report has been prepared for the exclusive use of W.W. Reynolds for specific application to the project discussed and has been prepared in accordance with generally accepted geotechnical engineering practices. No warranty, express or implied, is made. In the event that any changes in the nature, design or location of the project as outlined in this report are planned, the conclusions and recommendations contained in this report shall not be considered valid unless the changes are reviewed and the conclusions of this report modified or verified in writing by the geotechnical engineer. Earth Engineering Consultants, Inc. Proposed Chris Wells Development July 25, 1994 Page 11 ■ Subgrade soils which are allowed to become wetted could result in premature failure of the pavement section. We recommend a minimum slope away from the structure of 1 inch per foot for the first 10 feet. In addition, roof drains should be designed to discharge at least 5 feet beyond the perimeter of the building. Lawn sprinkling system should also be installed at least 5 feet beyond the perimeter of the building and designed to avoid spraying water directly on the foundation walls. Plantings which are water intensive should not be planted immediately adjacent to the buildings. A detention pond will be constructed in the southeast corner of the site. Materials excavated from that area could likely be used as general site fill for the project. We anticipate groundwater at a relatively shallow depth in that area of the site. Fill materials will likely need to be dried prior to placement. Excavations extending near the groundwater table may be 4 unstable and scrapers or similar heavy equipment may not be suitable for the excavations. GENERAL COMMENTS The analysis and recommendations presented in this report are based upon the data obtained from the soil borings performed at the indicated locations and from any other information. discussed in this report. This report does not reflect any variations which may occur between borings or across the site. The nature and extent of such variations may not become evident until construction. If variations appear evident, it will be necessary to re-evaluate the recommendations of this report. It is recommended that the geotechnical engineer be retained to review the plans and specifications so that comments can be made regarding the interpretation and implementation of our geotechnical recommendations in the design and specifications. It is further recommended that the geotechnical engineer be retained for testing and observations during earthwork and foundation construction phases to help determine that the design requirements are fulfilled. Earth Engineering Consultants, Inc. Proposed Chris Wells Development July 25, 1994 Page 10 PAVEMENTS A R-value of 8 was determined to be appropriate for the site materials based on laboratory testing of a near surface soil sample. Pavement sections have been evaluated for this project based on that R-value and the 1986 American Association of State Highway and Transportation Officials (AASHTO) "Guidelines for Design of Pavement Structures". Traffic in the paved drive and parking areas was assumed to consist of low volumes of light vehicles including mostly automobiles and light trucks. If the pavements are to be used on a regular basis by heavier vehicles, the pavement section recommendations provided in this report should be reevaluated. Alternatively, if the pavements will be used exclusively by automobiles, a lighter pavement section may be considered. Based on the consideration of the subgrade soils and anticipated traffic loadings, we recommend the site pavements consist of 3 inches of asphaltic concrete wearing surface overlying 6 inches of aggregate base course. The wearing surface should consist of asphaltic concrete consist with City of Fort Collins recommendations for SC-1 or SC-2 blends. Aggregate base course should be compatible with Colorado Department of Transportation (CDOT) recommendations for clags 5 or 6 base. Stabilization of pavement subgrades could be considered to reduce the required pavement section and provide stronger, uniform subgrades. For this procedure, Class C fly ash or a similar material would be blended with the site soils to develop a stabilized subgrade. Each inch of stabilized subgrade would replace approximately 1 inch of aggregate base. We would be pleased to provide additional recommendations concerning subgrade stabilization, if desired. OTHER CONSIDERATIONS Positive drainage should be developed away from the proposed building and across and away from pavement edges to avoid wetting of the bearing or subgrade materials. Bearing soils which are allowed to become wetted could result in unacceptable settlement of the site structure. Earth Engineering Consultants, Inc. Proposed Chris Wells Development July 25, 1994 Page 9 were encountered in the subgrades. The moisture content of those materials should be adjusted to develop a stable subgrade. Those moisture contents may be lower than recommended above. Scarification and recompaction of the subgrade soils in the basement areas would not be required. However, consideration should be given to installation of under -slab drain system in this area. For development of an underslab drain system, the in -place materials would be removed to a depth of 6 to 12 inches below subgrade elevation in the basement area. The soil subgrade at that elevation would be sloped to drained to perforated drain lines spaced periodically across the building. An interior perimeter drain line would also be installed at approximate foundation bearing level. The area around the drain lines and the over excavated zone beneath the floor slab should be backfilled with free draining granular fill. The entire system should be sloped to a sump area where water can be removed without reverse flow into the system. The drain line should also be tied to the exterior perimeter at least two locations as previously recommended. Fill required to develop floor slab or pavement subgrades should consist of approved, low - volume change material, free from organic matter and debris. Normally, soils with a liquid limit of 40 or less and plasticity index of 18 or less could be used as low volume change fill. The near surface site cohesive soils could be used as low volume change fill beneath the floor slabs and pavements. J Fill materials in the floor slab and pavement areas should be placed in ,loose lifts not to exceed 9-inches thick, adjusted in moisture content as recommended for the sacrificed materials and compacted to at least 95 percent of the material's standard Proctor maximum dry density. After placement of the fill materials, care should be taken to prevent disturbance of the prepared subgrades. Materials which are loosened or disturbed by construction activities, or materials which become dry and desiccated or wet and softened should be removed and replaced or reworked in place. Earth Engineering Consultants, Inc. Proposed Chris Wells Development July 25, 1994 Page 8 backfill in these areas. However, soft/wet zones were noted in those materials and aeration drying of the soils would likely be required prior to use as backfill. We recommend the backfill materials be placed in loose lifts not to exceed 9-inches thick, adjusted in moisture content and compacted to at least 90 percent of the material's maximum dry density as determined in accordance with ASTM specifications D-698, the standard Proctor procedure. The moisture content of the reworked soils should be adjusted to be within the range of ±2% of standard Proctor optimum moisture. In the areas where the backfill materials will support floor slabs, pavements, steps, sidewalks or similar improvement, the backfill materials should be compacted to at least 95 percent of standard Proctor maximum dry density. The top 2 feet of material around the perimeter of the building should be an essential cohesive soil to help reduce surface infiltration. For design of below grade walls where appropriate steps have been taken to use low volume change materials and eliminate the buildup of hydrostatic loads, we recommend using an equivalent fluid pressure of 50 pounds per cubic foot. The equivalent fluid pressure is based on an at -rest stress distribution which assumes the walls have been restrained from lateral movement. Placement of the first floor of the structure should be considered to reduce the potential for displacement of the basement walls during backfilling. The recommended equivalent fluid pressure does not include an allowance for hydrostatic loading nor does it include a factor of safety. FLOOR SLAB SUBGRADES All existing vegetation and/or topsoil should be removed from beneath the floor slabs and pavements. After stripping and completing all cuts and prior to placement of any fill or floor slabs, we recommend the in -place soils be scarified to a minimum depth of 9 inches, adjusted in moisture content and compacted to at least 95 percent of the material's maximum dry density as determined in accordance with ASTM Specification D-698, the standard Proctor procedure. The moisture content of the scarified soils should be adjusted to be within the range of ±2 percent of standard Proctor optimum moisture. Occasional zones of higher silt content soils Earth Engineering Consultants, Inc. Proposed Chris Wells Development July 25, 1994 Page 7 for the portion of the drilled shaft extending greater than 5 feet into the site bedrock. The total load pressure includes both live and dead loads of the building, as well as deadload of the foundation. Exterior grade beams for the structure should be extended to at least 30 inches below adjacent exterior grade for frost protection. The near surface site soils have low expansion potential so that construction of a void space beneath the building grade beams would not be required. Soil and groundwater conditions vary at the boring locations; we anticipate temporary casing would be required to prevent an influx of soil and groundwater into the open bore holes. We recommend the drilled pier foundations have a minimum diameter of 12-inches. We estimate the long term settlement of drilled pier foundations designed and constructed as recommended above would be small less than 1/2-inch. BELOW GRADE AREAS The, .below grade walls for the office building will be subjected to unbalanced lateral earth forces. We recommend the below grade area be designed with a perimeter drain to help remove surface infiltration water from adjacent to the below grade walls and help reduce the lateral loads on the walls. In general, a perimeter drain system would consist of perforated metal or plastic pipe placed at approximate foundation bearing level around the perimeter of the below grade areas. The drainline should allow for the free flow of water to a sump area where it can be removed without reverse flow into the system. The drainline should be surrounded by a minimum of six inches of appropriately sized permeable filter soil and either the granular filter soil or the drainline should be surrounded by an appropriate filter fabric to reduce potential for an influx of fines into the system. The exterior drain system should be tied into the underslab floor drain system (subsequently described in this report) at least two locations. Backfill placed above the drain system should consist of approved, low -volume change materials, free from organic matter and debris. The near surface cohesive site soils could be used as Earth Engineering Consultants, Inc. Proposed Chris Wells Development July 25, 1994 Page G In completing the excavations required for construction footings in the basement areas, some softer material zones may be encountered. The bearing soils should be closely observed and tested at the time of construction to see that footing foundations are not supported on or immediately above the soft cohesive materials. As a minimum, hand auger borings should be performed at random locations along continuous footing lines and should be completed at each column location. Soft or loose zones observed during construction would require removal and replacement prior to placement of the footings. The extent of the over excavation and backfill will vary with the consistency of the materials encountered and with the size of the footing. Those conditions can best be addressed during construction. m Care should be taken to avoid disturbing the bearing materials. The soil's at basement depth may be easily disturbed so that extra care will be needed. Soils which are loosened or disturbed by construction activities or materials which become dry and desiccated or wet and softened should be removed from the foundation excavations prior to placement of reinforcing steel and foundation concrete. We estimate the long-term settlement of lightly loaded footing foundations designed and constructed as recommend above would be small, less than 3/4-inch. Additional settlement could be caused by placement of overlot fill. We recommend overlot grading be completed as far in advance of building construction as possible. DRILLED PIER FOUNDATIONS For more heavily loaded foundations, consideration should be given to the use of deep foundations. Drilled pier foundations could be used for support of the proposed heavier column loads for the flex -space building. We recommend those drilled -pier foundations extend through the overburden soils to bear a minimum of 5 feet into the underlying bedrock. The 5 foot penetration is recommended so the drilled pier foundations extend through any soft, weathered materials near the surface of the bedrock. For design of drilled pier foundations bearing a minimum of 5 feet into the highly weathered to weathered bedrock, we recommend using a total load end bearing pressure not the exceed 20,000 psf. A friction value of 2000 psf could be used Earth Engineering Consultants, Inc. Proposed Chris Wells Development July 25, 1994 Page 5 ANALYSIS AND RECOMMENDATIONS FOUNDATIONS Based on materials observed at the boring locations, it is our opinion the proposed lightly loaded foundations for the basement and non -basement portions of the office building could be supported on conventional footing foundations. Deep foundation types may be necessary for more heavily loaded foundations as expected in the flex space building. Recommendations for these foundation types are provided below. Over excavation and backfill procedures could also be considered for light to moderate loads. We will provide additional recommendations concerning those alternatives, if desired. FOOTING FOUNDATIONS 31 We recommend the footing foundations extend through all existing vegetation and/or topsoil and bear in natural, stiff cohesive soils. We understand site grading will be such that non -basement footings will be supported at or very near existing ground surface elevations. Basement footing for the office building would extend to depths of approximately 6 to 7 feet below present ground surface. At those anticipated elevations and for footings bearing on natural, stiff cohesive soils, we recommend the foundations be designed using a net allowable total load soil bearing pressure not to exceed 1,500 psf. The net bearing pressure refers to the pressure at foundation bearing level in excess of the minimum surrounding overburden pressure. Total load refers to full dead and live loads. Exterior foundations and foundations in unheated areas should be located a minimum of 30 inches below final adjacent exterior grades to provide frost protection. We recommend formed continuous footings have a minimum width of 16 inches and isolated column foundations have a minimum width of 30 inches. Trenched foundations (grade beam foundations) could be used in soils similar to the near surface cohesive materials. If used, we recommend those trenched foundations have a minimum width of 12 inches. Earth Engineering Consultants, Inc. Proposed Chris Wells Development July 25, 1994 Page 4 siltstone/claystone was colored brown and was soft to moderately hard. Those materials were weathered near ground surface and became less weathered with depth. The stratification boundaries indicated on the boring logs represent the approximate location of changes in soil and rock types; in -situ, the transition of materials may be gradual and indistinct. Classification of the bedrock was based on visual and tactual observation of disturbed samples and auger cuttings, as well as observation of drilling progress. Coring and/or petrographic analysis may reveal other rock types. WATER LEVEL OBSERVATIONS Observations were made while drilling and immediately after completion of the borings to detect the 'presence and depth to groundwater. At the time of drilling, free water was encountered at a depth of approximately 7 to 9 feet below ground surface. Similar water level depths were observed shortly after drilling activities were concluded. Based on those observed groundwater levels and on the moisture content of the subgrade soils, it is our opinion that the hydrostatic groundwater table was at a depth of approximately 7 to 9 feet at the time the subsurface exploration was performed. Fluctuations in groundwater levels can occur over time depending on variations in hydrologic conditions and other conditions not apparent at the time of this report. In addition, zones of perched and/or trapped water may be encountered in more permeable zones in the subgrade soils and this condition is often encountered in the soils immediately over lying less permeable bedrock. The location and amount of perched water can also vary over time depending"on. variations in hydrologic conditions and other conditions not apparent at the time of this report. Earth Engineering Consultants, Inc. Proposed Chris Wells Development July 25, 1994 Page 3 As a part of the testing program, all samples were examined in the laboratory by an engineer and classified in accordance with the attached General Notes and the Unified Soil Classification System, based on the soils texture and plasticity. The estimated group symbol for the Unified Soil Classification System is shown on the boring logs and a brief description of that classification system is included with this report. SITE AND SUBSURFACE CONDITIONS The proposed development site is located south of Bighorn Drive and west of Timberline Road in Fort Collins, Colorado. Site drainage is generally to the south with maximum difference in ground surface elevations across the site on the order of 5 feet. The site is presently vegetated and evidence of prior building construction was not observed at the site by EEC field personnel. An EEC field geologist was on site during drilling to evaluate the subsurface materials encountered and direct the drilling activities. Field logs were prepared by the EEC geologist base¢, visual and tactual observation of disturbed samples and auger cuttings. Final boring logs included with this report may contain modifications to the field logs based on the results of laboratorytesting and evaluation. Based on result s of our field an g d laboratory services, subsurface conditions can be generalized as follows. Approximately 3 to 4 inches of vegetation and/or topsoil were encountered at the surface at the boring locations. The topsoil/vegetation was underlain by sandy lean clay which contained varying amounts of silt. Those soils were colored light brown to brown. The cohesive soils near ground surface were stiff and those materials became softer with depth. The cohesive soils extended to depths of approximately 10 to 15 feet. The cohesive soils at some locations were underlain by fine and fine to medium sand whic'p contained varying amounts of silt, gravel and occasional cobbles. The granular soils were medium dense and extended to depths in the order of 13 to 18 feet. Below those depths, the subsurface materials consisted of highly weathered siltstone/claystone bedrock. The 0 Earth Engineering Consultants, Inc. Proposed Chris Wells Development July 25, 1994 Page 2 EXPLORATION AND TESTING PROCEDURES The boring locations were selected in the field by Earth Engineering Consultants, Inc. (EEC) personnel. Those field locations were established by pacing and estimating angles from the references indicated on the attached boring location diagram. The boring locations should be considered accurate only to the degree implied by the methods used to make the field measurements. The borings were performed using a truck mounted, rotary -type drill rig equipped with a ! hydraulic head employed in drilling and sampling operations. The boreholes were advanced using 4-inch nominal diameter continuous flight augers and samples of the subsurface materials encountered were obtained using thin -walled tube and split barrel sampling procedures in general accordance with ASTM Specifications D-1587 and D-1586, respectively. In the thin -walled tube sampling procedure, a seamless steel tube with a sharpened cutting edge is push into the ground with hydraulic pressure to obtain a relatively undisturbed sample of cohesive or moderately cohesive material. In the split barrel sampling procedure, a standard 2-inch O.D. split barrel spoon is driven into the ground by means of a 140 pound hammer falling a distance of 30 inches. The number of blows required to advance the split barrel sampler is recorded and is used to estimate the in -situ relative density of cohesionless soils and, to a lesser degree of accuracy, the consistency of cohesive materials. Additional bulk samples were obtained from the auger cuttings. All samples obtained in the field were sealed and returned to the laboratory for further examination, classification and testing. Moisture content, and where appropriate, dry density and unconfined compressive strength tests were performed on representative portions of the discreet samples. In addition, Atterberg limits, washed sieve analysis, and swell/consolidation tests were performed on selected samples to evaluate the soil's tend to change volume with variation in moisture content. Hveem stabilometer R-value tests were also performed on a representative portion of one of the near surface bulk samples to provide subgrade strength information required for pavement design. Results of the outlined tests are indicated on the attached boring logs. SUBSURFACE EXPLORATION REPORT PROPOSED CHRIS WELLS DEVELOPMENT FORT COLLINS, COLORADO EEC PROJECT NO. 1942050 INTRODUCTION The subsurface exploration for the proposed Chris Wells Development located south of Bighorn Drive and west of Timberline Road in Fort Collins, Colorado, has been completed. Eight (8) soil borings extending to depths ranging from approximately 5 to 20 feet below present site grades were advanced to develop information on existing subsurface conditions in the development area. Individual boring logs and a diagram indicating the approximate boring locations are included with this report. We understand the proposed Chris Wells Development will include an approximate 7,000 sq feet office building and an approximate 24,000 to 30,000 sq feet flex space unit. The approximate plan locations of those structures are indicated on the attached boring location diagram. The proposed office building will be a single story wood frame structure which will contain a full basement. The flex space unit will be a single -story, slab -on -grade structure, probably of steel frame construction. Foundation loads for the office building will be light with continuous wall loads less than 3 kips per lineal foot and column loads less than 50 kips. Higher foundation loads will be transmitted by the flex space building. Floor loads for both structure will be light, less than 100 psf. Paved drive and parking areas will be constructed in the vicinity of both buildings. Three to four feet of fill will be required in the office area to develop the final site grades. Small grade changes, involving cuts and fills less than 2 feet, are expected in the flex space area. The purpose of this report is to describe the subsurface conditions encountered in the borings, analyze and evaluate the test data and provide geotechnical recommendations concerning design and construction of foundations and support of floor slabs and pavements. July 25, 1994 W.W. Reynolds 4875 Pearl East Circle, #300 Boulder, Colorado 80301 Attn: Mr. Jerry Lee RE: Subsurface Exploration Report Proposed Chris Wells Development Timberline Road and Bighorn Drive Fort Collins, Colorado EEC Project No. 1942050 Mr. Lee: i EARTH ENGINEERIN( CONSULTANTS, INC. m Enclosed, herewith, are the results of the subsurface exploration you requested for your proposed development south of Bighorn Drive and west of Timberline Road in Fort Collins. In summary, the subsurface soils at the site consist of stiff to soft cohesive soils, underlain by medium dense granular materials. The overburden soils are underlain by weathered claystone bedrock. Groundwater was encountered at a depth of approximately 7 to 9 feet at the time of our exploration. Based on the subsurface materials encountered, it is our opinion light foundation loads could be supported using conventional footings. Drilled piers, driven piles or other deep foundation types should be considered for more heavily loaded foundations. Near surface floor slabs and pavements could be supported directly on the site soils. Geotechnical recommendations concerning design and construction of the foundations and support of floor slabs and pavements are presented in the text of the attached report. We appreciate the opportunity to be of service to you on this project. If you have any questions concerning this report, or if we can be of further service to you in any other way, please do not hesitate to contact us. Very truly yours, Earth Engineering Consultants, Inc. Principal Engineer Curtiss L. Palin, P.E. Principal cc: W.W. Reynolds - Fort Collins, Libby Glass Cityscape, Eldon Ward Vaught -Frye Arch., Frank Vaught 2600 Canton Ct, Suite A Fort Collins, CO 60525 (303) 224-1522 FAX 224-4564