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HomeMy WebLinkAboutSubsoils Study for Foundation Designffi CTLITHOMPSON GEOTECHNICAL ENGINEER¡NG INVESTIGATION REED STORAGE BUILDING 7550 COUNTY ROAD 312 GARFIELD COUNTY, COLORADO Prepared for: JOHN REED 7550 County Road 312 New Castle, CO 81647 CTLIT Project No. GS06770.000-120 July 7, 2A23 (revised July 1 1, 2023) CTllThompson, lnc. Denver, Fort Collins, &lglqd.Q_9pd¡gg, Glenwood Sprinqs, P-Ugþ.!g, Summit County - Colorado Cheyenne, Wyoming and Bozeman, Montana \ $ {e $ N s ffi Table of Contents scoPE,,...., SUMMARY OF CONCLUSIONS SITE CONDITIONS PROPOSED CONSTRUCTION ..,...... GEOLOGIC CONDITIONS AND HAZARDS SUBSURFACE CONDITIONS........,. SITE EARTHWORK.,... Excavations Subexcavation and Structural Fill.....,........ Foundation Wall Backfi11.................. FOUNDATTON ................ SLAB-ON-GRADE CONSTRUCTION .......... BELOW-GRADE CONSTRUCTION SURFACE DRAINAGE CONCRETE CONSTRUCTION OBSERVATIONS GEOTECHNICAL RISK LtMtTATIONS ................ FIGURE 1_VICINITY MAP FIGURE 2 - AERIAL PHOTOGRAPH FIGURE 3 - SUMMARY LOGS OF EXPLORATORY PITS FIGURE 4 - GRADATION TEST RESULTS TABLE I - SUMMARY OF LABORATORY TESTING JOHN REED REED STORAGE BUILDING cTLIT PROJECT NO. GS06770.000-120 REVISED 1 1 2 3 3 3 1 1 ffi SCOPE CTllThompson, lnc. (CTLIT) has completed a geotechnical engineering in- vestigation regarding a new storage building proposed on the Reed property at 7550 County Road 312in Garfield County, Colorado. We conducted this investiga- tion to evaluate subsurface conditions at the site and provide geotechnical engi- neering recommendations for the proposed construction. The scope of our investi- gation was set forth in our Proposal No. GS 23-0036. Our report was prepared from data developed from our field exploration, laboratory testing, engineering analysis, and our experience with similar conditions. This report includes a de- scription of subsurface conditions found in our exploratory pits and provides ge- otechnical engineering recommendations for design and construction of the foun- dation and floor system, and details influenced by the subsoils. A summary of our conclusions is below. SUMMARY OF CONCLUSIONS Our exploratory pits excavated at the site encountered a surficial layer of topsoil underlain by sandy to silty clay with occasional gravel and cobbles to the maximum explored depth of 11 feet. Free groundwater was found in one pit at a depth of 10 feet. 2.The natural clay soils found in our exploratory pit excavations were soft and moist to very moist. Based on our field and laboratory data, and our geotechnical engineering experience, the natural clay soil has potentialfor moderate consolidation when subjected to building and stored equipment loads. Plans show a monolithic slab with turned down edges will support the building. We judge the storage building can be constructed on a monolithic slab with turned down edges sized at low allowable bear- ing pressure placed on the natural clays. Risk of potential slab set- tlement can be mitigated by subexcavation and structuralfill place- ment below the building. 1 3 JOHN REED REED STORAGE BUILDING CTLIT PROJECT NO. GS06770.000120 REVISED Page 1 of 12 SITE COND¡TIONS The Reed property is addressed as 7550 County Road 312 in Garfield County, Colorado. A vicinity map showing the location of the property is included as Figure 1. An aerial photograph of the site is shown on Figure 2. The site is an approximately 18.1-acre parcel northeast of County Road 312. A residence, barn, and a man-made pond are to the east of the planned storage building footprint. Garfield Creek is approximately 150 feet to the building location. Ground surface in the proposed building area generally slopes own e south and southwest at grades visually estimated as less than 5 per- cent. Vegetation in this area is predominantly grasses and sage with tree stands adjacent to the residence and along the banks of an historic creek drainage. A photograph of the site taken during our subsurface investigation is below. '. fr . r.j: s JOHN REED REED STORAGE BUILDING cTLIT PROJECT NO. G506770.000-120 REVISED Looking east at TP-1 Page 2 of 12 ffi PROPOSED CONSTRUCTION Plans are to construct a one-story, wood-frame storage building with a slab- on-grade floor. Pre-engineered roof trusses and metal roofing are planned. The building footprint will be 28 feet by 48 feet. The storage building will be founded on a monolithic slab with turned down edgòs. Maximum foundation excavation depths of 5 feet are expected. Fill placement below the building is not anticipated. We ex- pect foundation loads of between 1,000 and 2,000 pounds per lineal foot along the building perimeter. We understand that actual construction has not been deter- mined at this writing. We should be provided with "for-construction" building plans when available so we can provide geotechnical/geo-structuralengineering input. GEOLOGIC CONDITIONS AND HAZARDS We reviewed geologic mapping by the Colorado Geological Survey (CGS) for the area of the property titled, "Center Mountain Quadrangle Geologic Map, Garfield County, Colorado", by Carroll, Kirkham, and Stelling, (dated 2014).Wa- satch Formation bedrock underlies the site and is near the ground surface at high- er elevations near the site. Subsurface soils at the site are mapped as colluvium (Qc) and undivided alluvium and colluvium (Qac). The alluvium and colluvium soils on this site are mostly clay and silt deposited by water and gravity derived from bedrock of the Wasatch Formation. No significant geologic hazards were identified that would preclude the planned construction. The soils encountered in our explor- atory pits are consistent with the alluvium and colluvium shown on the mapping. SUBSURFACE CONDITIONS Subsurface conditions were investigated by excavating two exploratory pits (TP-1 and TP-2) on May 17,2023. The pits were excavated at the approximate locations shown on Figure 2. Excavation operations were directed by our repre- JOHN REED REED STORAGE BUILDING cTLlr PROJECT NO. GS06770.000-120 REVISED Page 3 of 12 ffi sentative, who logged subsurface conditions encountered and obtained repre- sentative samples of the soils. Graphic logs of subsurface conditions found in the exploratory pits are included as Figure 3. Our exploratory pits excavated at the site encountered an approximately 6- inch-thick surficial layer of topsoil underlain by I and 10.5 feet of sandy to silty clay with occasional gravel and cobbles. Free groundwater was encountered at a depth of 10 feet in the TP-2 excavation. The pits were backfilled immediately after exca- vation operations were completed Samples of the soils obtained from our pit excavations were returned to our laboratory for pertinent testing. Engineering index testing performed on two sam- ples of the soils indicated liquid limits of 23 and 31 percent and plasticity indices of 6 and 16 percent with 68 and 36 percent silt and clay (passing the No. 200 sieve), respectively. Gradation testing on a sample of soil obtained from TP-1 at a depth of I to 9 feet determined 40 percent gravel, 24 percent sand and 36 percent silt and clay sized particles (passing the No. 200 sieve). A sample of soil tested had a water-soluble sulfate content of 0.09 percent. Gradation test results are shown on Figure 4. Laboratory testing is summarized on Table l. SITE EARTHWORK Excavations Maximum foundation excavation depths of about 5 feet are anticipated. Our subsurface investigation indicates that excavations at the site can be accom- plished using conventional, heavy-duty excavating equipment. Sídes of excavations need to be sloped or retained to meet local, state, and federal safety regulations. The subsoils at the site will likely classify as Type B JOHN REED REED STORAGE BUILDING cTLIT PROJECT NO. GS06770.000.120 REVISED Page 4 of 12 ffi soils based on OSHA standards governing excavations. From a "trench" safety standpoint, temporary slopes deeper than 5 feet that are not retained should be no steeper than 1 to 1 (horizontal to vertical) in Type B soÍls. Contractors are respon- sible for determining the actual OSHA soiltype when excavations are made and for maintaining safe excavations. Contractors should identify the soils encountered in excavations and ensure that OSHA standards are met. Free groundwater was found at a depth of 10 feet in our TP-2 excavation. We do not believe excavations to construct the proposed storage building willen- counter a free groundwater table. Subexcavation and Structural Fill Based on our field and laboratory data, and our geotechnical engineering experience in the area, the natural soils at the site have potential for moderate consolidation under building loads. Similar consolidation could occur below heavily loaded floor slabs. We judge the storage building monolithic slab with turned down edges can be supported on the natural soils if floor deflection and cracking are acceptable. Floor deflection and slab cracking can be significantly reduced if the soil below the building footprint is subexcavated and replaced as properly-compacted, structural fill to a depth of at least 3 feet below the bottom of the slab. The subexcavation process should extend at least 1 foot beyond the edges of the building perimeter. The subexcavated soil can be reused as structuralfill, provided it is free of rocks larger than 3 inches in diameter, organic matter, and debris. A positÍve alter- native would be to use imported CDOT Class 6 aggregate base course as struc- tural fill. The structuralfill soil should be moisture-conditioned to within 2 percent of optimum moisture content, placed in loose lifts of I inches thick or less, and com- JOHN REED REED STORAGE BUILDING CTLIT PROJECT NO. GS06770.000-120 REVISED Page 5 of 12 ffi pacted to at least 98 percent of standard Proctor (ASTM D 698) maximum dry density. Moisture content and densíty of structural fill should be checked by a rep- resentative of our firm during placement. Observation of the compaction procedure is necessary. Foundation Wall Backfill Proper placement and compaction of foundation wall backfill soil is im- portant to reduce infiltration of surface water and settlement from consolidation of backfill. This is especially important for backfìll areas that will support exterior con- crete flatwork. The soils excavated from the site can be used as backfill, provided they are free of rocks larger than 4-inches in diameter, organics, and debris. Backfill soil should be placed in loose lifts of approximately 10 inches thick or less, moisture-conditioned, and compacted. The backfill should be compacted to at least 95 percent of standard Proctor (ASTM D 698) maximum dry density. Moisture content and density of the backfill should be checked during placement by a representative of our firm. Observation of the compaction procedure is nec- essary. FOUNDATION The storage building foundation is planned as a monolithic slab with turned down edges. The turned down edges will act as footings and transfer roof and wall loads to the soils. The turned down edges will be subject to significantly greater loads than the adjacent floor slab. The slab design should account for the different load intensity, or a construction joint should be included to allow differential movement. JOHN REED REED STORAGE BUILDING crLlT PROJECT NO. GS06770.000-120 REVTSED Page 6 of 12 ffi We judge the storage building monolithic slab with turned down edges can be supported on the natural soils if floor deflection and cracking are acceptable. Floor deflection and slab cracking can be significantly reduced if the soíl below the building footprint is subexcavated and replaced with structural fill to a depth of at least 3 feet below the bottom of the slab. The subexcavation process should ex- tend at least 1 foot beyond the edges of the building perimeter. Structural fill should be in accordance with the Subexcavation and Structural Fill section. Recommended design and construction criteria for a monolithic slab are be- low. lf plans change and a footing foundation is planned, we should be informed o provide design criteria for a footing foundation. These criteria were developed based on our analysis of field and laboratory data, as well as our engineering ex- perience. The storage building can be constructed on monolithic slab with turned down edges that is supported by the undisturbed native soil if floor deflection and slab cracking are acceptable. Floor deflection and slab cracking can be significantly reduced by supporting the building on a 3-foot thickness of properly-compacted, structural fill that is in accordance with the Subexcavation and Structural Fill sec- tion. The monolithic slab with turned down edgegcan be designed for a , maximum net allowable soil bearing pressure ofJ0@-æf-Slabs are ade modulus. We recommend a modulus of subgrade reaction of 100 pcf if this de- sign approach is taken. A friction factor of 0.40 can be used to calculate resistance to sliding between concrete footings and the natural soils or structuralfill. 4 3 5 The base of the turned down edge should have a minimum width of 16 inches. The turned down edge should be well-reinforced. We recommend re- inforcement suffícient to span an unsupported distance of at least 12 feet. 1 2 JOHN REED REED STORAGE BUILDING CTLIT PROJECT NO. GS06770.000,1 20 REVTSED PageT of 12 ffi 6.The soils under exterior footings or turned down edges should be protected from freezing. The Garfield County building department should be consulted regarding frost protection requirements. SLAB.ON.GRADE CONSTRUCTION The storage building will be constructed with a slab-on-grade floor. To re- duce the potential for floor deflection and slab cracking, we recommend subexcava- tion of the soils below the floor slab to a depth of 3 feet and replacement with properly-compacted, structuralfill. The structuralfill should be in accordance with recommendations in the Subexcavation and Structural Fill section. Based on our analysis of field and laboratory data, as well as our engineer- ing experience, we recommend the following precautions for slab-on-grade con- struction at this site. The turned down edges will be subject to significantly greater loads than the adjacent floor slab. The slab design should account for the different load intensity, or a construction joint should be included to allow free vertical movement of the slabs. Underslab plumbing should be pressure tested for leaks before the slabs are constructed. Plumbing and utilities which pass through slabs should be isolated from the slabs with sleeves. Exterior concrete flatwork and pavements should be isolated from the building. The exterior slabs should be well-reinforced to function as independent units. Frequent controf joints should be provided, in accordance with Amer- ican Concrete lnstitute (ACl) recommendations, to reduce problems associated with shrinkage and curling. BELOW-GRADE CONSTRUCT¡ON We understand the storage building will not include below-grade areas, such as a basement or crawl space. lf construction plans evolve to include below- JOHN REED REED STORAGE BUILDING crLlT pRoJEcr NO. G506770.000-120 REVISED 1 2 3 4. Page 8 of 12 ffi grade areas, we should be informed so that we can provide recommendations for lateral earth pressures and subsurface drainage systems. SURFACE DRAINAGE Surface drainage is critical to the performance of building foundations, floor slabs, and concrete flatwork. Site grading should be designed and constructed to rapidly convey surface water away from the storage building. Proper surface drainage and irrigation practices can help control the amount of surface water that penetrates below the slab and contributes to settlement. We recommend the fol- lowing precautions. The ground surface surrounding the exterior of the storage building should be sloped to rapidly convey surface water away from the building in all directions. We recommend a constructed slope of at least 12 inches in the first 10 feet (10 percent) in landscaped areas around the building. Backfill around the foundation slab should be moisture-treated and compacted pursuant to recommendations in the Foundation Wall Backfill section. We recommend that the storage building be provided with roof gut- ters and downspouts. The downspouts should discharge well beyond the limits of all backfill. Splash blocks and/or extensions should be provided at all downspouts so water discharges onto the ground be- yond the backfill. We generally recommend against burial of down- spout discharge pipes. Landscaping should be carefully designed and maintained to mini- mize irrigation. Plants placed close to foundation walls should be lim- ited to those with low moisture requirements. lrrigated grass should not be located within 5 feet of the foundation. Sprinklers should not discharge within 5 feet of foundatíons. Plastic sheeting should not be placed beneath landscaped areas adjacent to foundation walls or grade beams. Geotextile fabric will inhibit weed growth yet still allow natural evaporation to occur. 1 2 3 4 JOHN REED REED STORAGE BUILDING cTLIT PROJECT NO. G506770.000¡ 20 REVTSED Page 9 of 12 ffi CONCRETE Concrete in contact with soil can be subject to sulfate attack. One sample of the soil from our exploratory pits that was tested contained 0.09 percent water sol- uble sulfates (see Table l). For this level of sulfate concentration, ACI 332-08, "Code Requirements for Residential Concrete", indicates there are no special ce- ment requirements for sulfate resistance in concrete that is in contact with the subsoils. ln our experience, superficial damage may occur to the exposed surfaces of highly permeable concrete, even when sulfate levels are relatively low. To control this risk and to resist freeze-thaw deterioration, the water-to-cementitious materials ratio should not exceed 0.50 for concrete in contact with soils that are likely to stay moist due to surface drainage or high-water tables. Concrete should have a total air content of 6 percent +l- 1.5 percent. CONSTRUCTION OBSERVATIONS We recommend that CTLIT be retained to provide construction observation and materials testing services for the project. This would allow us the opportunity to verify whether soil conditions are consistent with those found during this investi- gation. lf others perform these observations, they must accept responsibility to judge whether the recommendations in this report remain appropriate. lt is also beneficialto projects, from economic and practical standpoints, when there is con- tinuity between engineering consultation and the constructíon obseruation and ma- terials testing phases. JOHN REED REED STORAGE BUILDING cTLIT PROJECT NO. G506770.000-120 REVTSED Page 10 of 12 ffi GEOTECHNICAL RISK The concept of risk is an important aspect of any geotechnical evaluation. The primary reason for this is that the analytical methods used to develop ge- otechnical recommendations do not comprise an exact science. We never have complete knowledge of subsurface conditions. Our analysis must be tempered with engineering judgment and experience. Therefore, the recommendations pre- sented in any geotechnical evaluation should not be considered risk-free. We can- not provide a guarantee that the interaction between the soils and the proposed structure will lead to performance as desired or intended. Our recommendations represent our judgment of those measures that are necessary to increase the chances that the structure will perform satisfactorily. lt is critical that all recom- mendations in this report are followed. LIMITATIONS This report was prepared for the exclusive use of the client. The infor- mation, conclusions, and recommendations presented herein are based upon consideration of many factors including, but not limited to, the type of structures proposed, the geologic setting, and the subsurface conditions encountered. The conclusions and recommendations contained in the report are not valid for use by others. Standards of practice continuously change in geotechnical engineering. The recommendations provided in this report are appropriate for about three years. lf the proposed storage building is not constructed within three years, we should be contacted to determine if we should update this report. Our exploratory pits provide a reasonable characterization of subsurface condítions at the site. Variations in subsurface conditions not indicated by the pits will occur. We should be provided with architectural plans, as they are further de- veloped, so we can provide geotechnical/geo-structural engineering input. JOHN REED REED STORAGE BUILDING CTLIT PROJECT NO. GS06770.000-120 REVTSED Page 11 of 12 ffi This investigation was conducted in a manner consistent with that level of care and skill ordinarily exercised by geotechnical engineers currently practicing under similar conditions in the locality of this project. No warranty, express or im- plied, is made. lf we can be of fudher service in discussing the contents of this re- port, please call. CTLITHoMPSON, INC Revíewed by ß"-,f?- fan R. Bang, P.E. Principal E imech linq @ctlthompson. com JOHN REED REED STORAGE BU¡LDING crLlT pRoJEcr No. GS06770.000-'120 REVTSED R rbone, Division Manager Page 12 of 12 ffi 0 t.000 2.000trFtrFtr-I NOTE: SQALE: 1'- !,000' JOHN REED 7650 COUNTY ROAD 312 SATELLITE IMAGE FROM MAXAR (CoPYRTGHT 2023) Vicinity MapcTUT PROJECT NO. GSO6770.OOO-120 FIG. 1 LEGEN D: TP_1 APPROXIMATE LOCATION OFI EXPLORATORY PIT APPROXIMATE LOCATION OF PROPERTY BOUNDARY ffi 0 50 100 NOTE: SCÁLE: l'- 100' JOHN REED 75ıO CC'UNTYRC'.AD3I2 SATELLITE IMAGE FROM GOOGLE EARTH (DATED oCTOBER 13, 2022) Aerial PhotographoTUT PROJECT NO. GSO6770.OOO-120 FIG. 2 TP-1 TOPSOIL, CIáY, SANDY. SILTY, ORGANICS, WET, DARK BROWN, CI.AY, SILTY TO SANDY, GRAVEL, COBBLES. VERY MOTST TO WET, SOFT, DARK BROWN. (CL, CL-ML, GC) BULK SAMPLE FROM EXCAVATED SOILS. WATER LEVEL MEASURED AT TIME OF EXCAVATION EXPLORATORY PITS WERE EXCAVATED WITH A TRACKHOE ON MAY 17,2023. EXPLORATORY PITS WERE BACKFILLED IMMEDIATELY AFTER EXCAVATION OPERATIONS WERE COMPTETED. 2. THESE LOGS ARE SUBJECT TO THE EXPLANATIONS, LIMITATIONS. AND CONCLUSIONS IN THIS REPORT. TP.2 ffi F UJult! IÍF o_ IJJo 00 55 l- Llj LrJlr tFû UJo 10 15 LEGEND: JOHN REED 7550 COUNTY ROAD 312 Summary Logs of FìIE'rratóry FIG.3 g NOTES: 1. 10 15 F g CTLIT PROJECT NO. GS06770.000-120 ffi GRAVELSANDS GLAY (PLAST|C) TO StLT (NON-PLASTTC) FINE MEDIUM COARSE FINE coARsË COBBLES SIEVE ANALYSISHYDROMETERANALYSIS .--t-- __-t ---, ---1- ---t- -t--- _--t.-_-__t_-__t_-__ -_-_t------t--* -j=:: .-t7- ---t-_t-____t___ -._t_-- =_.--*t---- -l-/ __---t-- -----,-_,t-- _t__t_ -----J- _-t_ _-t_ _- 0 l0 20 30 40 50 60 70 00 90 9706.t) Í60 F-z 850 É.t¡lÊ40 o IUz Þ uJü t-z IJJo É. UJÀ 127 ZOO 152 90 80 '100 s.52 19.1 36.1 76.2.001 0.002 .005 .009 .01s .037 .o74 .149 100 DIAMETER OF PARTICLE IN MILLIMETERS TIME READINGS 60 MrN. 19 MlN. 4 MlN. I MrN. '200 U.S, STANDARD SERIES '100 '50'40 '30 '18 '10'8 CLEAR SAUARE OPENINGS 3/8' 314" 1%" 3" 5'8" 8' 30 20 10 u .297 .590 1.19 2.0 2.38 4.78 0.42 25 HR. 7 HR. 45 MtN. r5 MtN. Somple of GRAVEL, cLAyEy (cc)From TP-1 AT 2-3 FEET Somple of From JOHN REED 7550 COUNTY ROAD 312 PROJECT NO. GS06770.000-120 GRAVEL SILT & CLAY PLASTICITY INDEX GRAVEL SILT & CLAY PLASTICITY INDEX SAND LIQUID LIMIT 24% o/o % 4O o/o is v" o/o SAND o/o LIOUID LIMIT o/o Yo % Gradation Test Results SANDS GRAVEL COBBLEScLAY (PLASTTC) TO SrLT (NON-PI-ASTTC) FINE MEDIUM COARSE FINE COARSE -t-_ I___ì__ ---_--t---,_,,,.- -_t-- 4_._t.__-_ --- t--- -'---- -t-_*- ----- --t---"-.-l------ 10 20 30 40 50 60 7g 80 90 100 127 200 152 90 80 otoz6Ø Í60 t-z 850 Uodo 30 20 10 0 .001 0.002 .005 .009 .019 .037 9.52 t9,1 36.1 76.2 loo TIME READINGS 60 MtN. 19 MtN. 4 MlN. 1 MlN. '200 U,S. STANDARD SERIES '100 .50'40 '30 t16 '10'8 CLEAR SOUARE OPENINGS 3/8' 3t4' 1yi', 3', 5'6" .074 .149 .297 .590 1.19 2.O 2.38 4,76 o.42 OIAMETER OF PARTICLE IN MILLIMETERS 25 HR. 7 HR. 45 MlN. 15 MtN. FIG.4 TABLE I SUMMARY OF LABORATORY TESTING PROJECT NO. cS06770-120 ffi DESCRIPTION CLAY, SANDY (CL) GRAVEL, CLAYEY (GC) CLAY, SILTY, SANDY (CL.ML) CLAY, SILTY, SANDY (CL-ML) PASSING NO.200 SIEVE (%j 36 68 50 PERCENT SAND (o/o\ 24 PERCENT GRAVEL ("/") 40 SOLUBLE SULFATES (o/o) 0.09 ATTERBERG LIMITS PLASTICITY INDEX (o/o\ 16 6 LIQUID LIMIT (o/o) 31 23 DRY DENSITY (PCF) MOISTURE CONÏENT (o/o\ 21.0 10.2 21.6 28.6 DEPTH (FEET) 2-3 8-9 4-5 10-11 EXPLORATORY PIT TP.1 TP-1 TP-2 1P-2 Page 1 of 1