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HomeMy WebLinkAboutHARMONY SAFEWAY PAD MARKETPLACE PUD LOT 6 SAFEWAY FUELING STATION - Filed GR-GEOTECHNICAL REPORT/SOILS REPORT -K&A Kumar & Associates, Inc. Geotechnical & Environmental Engineers April 4, 2000 Mr. Dave Galloway Galloway, Romero & Associates 5350 DTC Parkway Englewood, Colorado 80111 1708 E. Lincoln Ave, #3 Fort Collins, CO 80524 970)416-9045 Fax 416-9040 E-Mail: kaftcollinsCaworldnet.att.net www.kumarusa.com Corporate Office — Denver, CO Branch Office — Colorado Springs, CO Subject: Geotechnical Engineering Study, Proposed Safeway Fuel Facility, Lot 6, Safeway Market Place, 1402 E. Harmony Road, Fort Collins, Colorado Project No. 00-3-115 Dear Mr. Galloway: This letter presents the results of a geotechnical engineering study for a proposed Safeway Fuel Facility to be located on Lot 6 of the Safeway Market Place, 1402 E. Harmony Road, Fort Collins, Colorado. The study was conducted for the purpose of developing foundation recommendations and providing criteria for support of floor slabs and recommendations for pavement sections. The project site is generally as shown on Fig. 1. The study was conducted in accordance with the scope of work in our proposal No. P3-00-120 to Galloway, Romero & Associates, dated March 7, 2000. Proposed Construction: We understand the site will be developed as a fueling facility with fuel dispensing islands and a small kiosk covered by an overhead steel canopy. Underground storage tanks and a future 2,600 square foot convenience store are also planned for the facility. Pavement areas will be provided for the parking and combined drive and truck lanes. Floor slabs will be constructed at or near existing grades. Foundation loads are assumed to be light, consistent with the proposed type of construction. Site Conditions: The site is located to the south of the existing Safeway Market Place parking lot. Currently the site is landscaped with grass. The lot is bounded to the east and north by paved Safeway Market Place parking lot access roads and to the south by Harmony Road. A vacant lot is located to the west. The topography of the site is nearly level. Subsurface Conditions: The subsurface conditions at the site were explored by drilling 3 exploratory borings at the approximate locations shown on Fig. 1. Graphic logs of the exploratory borings and a legend and notes are presented on Figs. 2 and 3. The subsurface conditions encountered in the exploratory borings drilled for this study consist of a thin layer of topsoil and 3 to 4 feet of sandy clay fill overlying 12 to 13 feet of slightly sandy to sandy clay. Gravelly, medium to coarse grained sand was encountered at depths of 16 to 17 feet below the ground surface overlying claystone bedrock at depths from 22 to 27 feet. Blow counts in the overburden soils indicate the slightly sandy to sandy clay is stiff to Galloway, Romero & Associates April 4, 2000 Page 2 very stiff and that the slightly silty to silty sand is medium dense to dense. The claystone bedrock classifies as hard to very hard. Groundwater was encountered at depths of 15.5 to 16 feet at the time of drilling and when measured 3 days later. Samples obtained from the exploratory borings were visually classified and selected samples were tested in our laboratory to determine classification properties and swell -consolidation characteristics. Test results are shown adjacent to the boring logs on Fig. 2 and are summarized in Table I. Results of the swell -consolidation tests, presented on Figs. 4 and 5, indicate that samples from the upper 4 feet of overburden consolidated slightly upon constant loading and have moderate swell potential when wetted under a constant load. Test results at 9 feet indicate the natural soils exhibit slight consolidation under a constant load and slight swell potential when wetted. Foundation Recommendations: Considering the subsurface conditions encountered in the exploratory borings and the nature of the construction, we recommend the kiosk and the future convenience store building, be founded on spread footings placed on at least 3 feet of properly compacted structural fill. The most positive method to avoid structural distress, if the soil is subjected to changes in moisture content, is to found the structure on straight shaft piers drilled into the bedrock. However, considering the depth of bedrock and presence of water bearing granular soils above the bedrock, we believe spread footing foundations may be used, provided the risk of movement is accepted by the owner. The following measures should be taken to reduce the risk of movement if foundation soils are subjected to moisture changes. We can provide recommendations for a drilled pier foundation system, if required. The design and construction criteria presented below should be observed for a spread footing foundation system. The construction details should be considered when preparing project documents. Footings for the kiosk and convenience store placed on three feet of structural fill underlain by the undisturbed natural soils should be designed for an allowable soil bearing pressure of 3,000 psf. The footings should also be designed for a minimum dead load pressure of 1,000 psf. Wall -on -grade construction is not acceptable to achieve the minimum dead load. Footing pads and grade beams may be required to achieve the above recommended minimum dead load. Footings for the overhead canopy, if founded 5 to 7 feet below the existing grade, may be placed directly on the natural soils without overexcavation and should be designed based on the footing criteria presented. 2. We recommend new fill placed within the building limits should meet the following requirements: Percent Passing No. 200 Sieve Minimum 25 Liquid Limit Maximum 30 Plasticity Index Maximum 10 Kumar & Associates, Inc. Galloway, Romero & Associates April 4, 2000 Page 3 Fill source materials not meeting the above liquid limit and plasticity index criteria may be acceptable provided the minimum percentage passing the No. 200 sieve is satisfied if the swell potential when remolded to 95% of the ASTM D 698 standard Proctor maximum dry density at optimum moisture content under a 200 psf surcharge pressure does not exceed 1 %. Evaluation of potential sources would then require determination of laboratory moisture -density relationships and swell consolidation tests on remolded samples, thereby adding time and cost to evaluate proposed fill materials. The geotechnical engineer should evaluate the suitability of proposed fill materials. Fill should be placed and compacted to at least 95% of the ASTM D 698 standard Proctor maximum dry density within 2 percentage points of the optimum moisture content. 2. Based on experience, we estimate the total movement for footings designed and constructed as discussed in this section will be approximately 1 inch. 3. Exterior footings and footings beneath unheated areas should be provided with adequate soil cover above their bearing elevation for frost protection. Placement of foundations at least 30 inches below the exterior grade is typically used in this area. 4. The lateral resistance of a spread footing placed on properly compacted structural fill material or the natural sandy clay will be a combination of the sliding resistance of the footing on the foundation materials and passive earth pressure against the sides of the footing. Resistance to sliding at the bottoms of the footings can be calculated based on a coefficient of friction of 0.25. Passive pressure against the sides of the footings can be calculated using an equivalent fluid unit weight of 150 pcf. The above values are working values. Compacted fill placed against the sides of the footings to resist lateral loads should be a nonexpansive material. Fill should be placed and compacted to at least 95% of the maximum standard Proctor density (ASTM D 698) at a moisture content near optimum. 5. Continuous foundation walls should be reinforced top and bottom to span an unsupported length of at least 10 feet. 6. A representative of the geotechnical engineer should observe all footing excavations and test fill placement prior to concrete placement. Floor Slabs: Floor slabs present a difficult problem where moderately expansive materials are present near floor slab elevation because sufficient dead load cannot be imposed on them to resist the uplift pressure generated when the materials are wetted and expand. The most positive method to avoid damage as a result of floor slab movement is to construct a structural floor above a well -vented crawl space. The floor would be supported on grade beams and piers the same as the main structure. Based on the moisture -volume change characteristics of the materials encountered, we believe slab -on -ground construction may be used, provided the risk of distress resulting from slab movement is accepted by the owner. The following measures should be taken to reduce the damage which could result from movement should the underslab materials be subjected to moisture changes. Kumar & Associates, Inc. Galloway, Romero & Associates April 4, 2000 Page 4 Floor slab movements can be mitigated by providing a zone of non -expansive, relatively impervious fill directly beneath the slab. This type of fill material would require importation to the site or chemical modification of the on -site soils. We are unable to predict the magnitude of potential floor slab movement without extensive sampling and testing, and even then there is uncertainty in such predictions. Increased thicknesses of nonexpansive fill result in a reduced thickness of expansive soil potentially causing heave, and provide additional confinement to the underlying expansive materials, thereby resulting in less movement potential. Whether placing nonexpansive fill beneath the floor slab to provide a reasonably low potential for floor slab movement is less costly than a structural floor should be evaluated prior to selecting the final floor system. We recommend the existing expansive soils be subexcavated to a depth of at least 3 feet below the bottom of the floor slab elevations. New fill placed within the excavation should meet the fill requirements as defined in the foundation recommendations. Fill should be placed and compacted to at least 95% of the ASTM D 698 standard Proctor maximum dry density within 2 percentage points of the optimum moisture content. The natural soil encountered during this study will be expansive when placed in a compacted condition. Consequently, it should not be used as fill beneath floor slabs. The natural soil can be used for fill near the bottom of fills outside building areas. 1. Floor slabs should be separated from all bearing walls and columns with expansion joints which allow unrestrained vertical movement. 2. Interior nonbearing partitions resting on floor slabs should be provided with slip joints at the tops so that, if the slabs move, the movement cannot be transmitted to the upper structure. This detail is also important for wallboards, stairways and door frames. Slip joints which will allow at least 2 inches of vertical movement are recommended. 3. Floor slab control joints should be used to reduce damage due to shrinkage cracking. Joint spacing is dependent on slab thickness, concrete aggregate size, and slump, and should be consistent with recognized guidelines such as those of the Portland Cement Association (PCA) or American Concrete Institute (ACI)• The joint spacing and slab reinforcement should be established by the designer based on experience and the intended slab use. 4. If moisture -sensitive floor coverings will be used, mitigation of moisture penetration into the slabs, such as by use of a vapor barrier, may be required. If an impervious vapor barrier membrane is used, special precautions will be required to prevent differential curing problems which could cause the slabs to warp. A minimum 2-inch sand layer between the concrete and the vapor barrier is sometimes used for this purpose. 5. All plumbing lines should be tested before operation. Where plumbing lines enter through the floor, a positive bond break should be provided. Flexible connections should be provided for slab -bearing mechanical equipment. Kumar & Associates, Inc. Galloway, Romero & Associates April 4, 2000 Page 5 The precautions and recommendations itemized above will not prevent the movement of floor slabs if the underlying expansive materials are subjected to alternate wetting and drying cycles. However, the precautions should reduce the damage if such movement occurs. Surface Drainage: The following drainage precautions should be observed during construction and maintained at all times after the facility has been completed. 1. Excessive wetting or drying of the foundation excavations and underslab areas should be avoided during construction. 2. Exterior backfill should be adjusted to near optimum moisture and compacted to at least 95% of the maximum standard Proctor density (ASTM D 698) in pavement areas and to at least 90% of the maximum standard Proctor density in landscape areas. 3. The ground surface surrounding the exterior of the building should be sloped to drain away from the foundation in all directions. We recommend a minimum slope of 6 inches in the first 10 feet in unpaved areas and a minimum slope of 3 inches in the first 10 feet in paved areas. 4. Roof downspouts and drains should discharge well beyond the limits of all backfill. 5. Landscaping which requires typical irrigation and lawn sprinkler heads should be located at least 10 feet from foundation walls. 6. Plastic membranes should not be used to cover the ground surface adjacent to foundation walls. A pervious geotextile may be used to inhibit weed growth. Underaround Storage Tanks Construction: The installation of the underground storage tanks at the fueling facility should be in accordance with the tank manufacturers specifications. The installer should be made aware that groundwater could occur within the anticipated depth of installation and should be accounted for in the design. Dewatering of the excavation may be required to allow for installation. If groundwater is encountered in the excavation, dewatering should be performed from a sump excavated at least 3 feet below the base of the excavation. A moist unit weight of 125 pcf may be used for backfill consisting of the on -site soils. The buoyant unit weight of the backfill should be used below the groundwater table. Pavement Thickness Design: A pavement section is a layered system designed to distribute concentrated traffic loads to the subgrade. Performance of the pavement structure is directly related to the physical properties of the subgrade soils and traffic loadings. Soil subgrade strength is represented by a resilient modulus, MR, for flexible pavements which can be empirically correlated to classification data. Pavement design procedures are based on strength properties of the subgrade and pavement materials assuming stable, uniform conditions. Certain soils, such as those encountered on this site, are expansive and require precautions be taken to provide for adequate pavement performance. Expansive soils are problematic only if a source of water is present. If those soils are wetted, the resulting movements can be large and erratic. Therefore, pavement Kumar & Associates, Inc. Galloway, Romero & Associates April 4, 2000 Page 6 design procedures address expansive soils only by assuming they will not become wetted. Proper surface and subsurface drainage is essential for adequate performance of pavement on these soils. Subgrade Materials: Based on the results of the field and laboratory studies, a sample of the subgrade materials at the site classifies as A-6 with a group index of 9 in accordance with the American Association of State Highway and Transportation Officials (AASHTO) classification. Results of these tests are shown on Table I. For design purposes, a R-value of 5 was estimated, corresponding to a resilient modulus of 4,000. Since anticipated traffic loading information was not available at the time of report preparation, an equivalent 18-kip daily load application (EDLA) of 5 was assumed for parking areas and an EDLA of 10 was assumed for combined drive and truck lanes. Pavement Section: Pavement thickness sections were determined by using the 1993 AASHTO pavement design procedure. The DARWinT" Pavement Design and Analysis System computer program was used in the analysis. Based on this procedure, we recommend that automobile parking areas constructed with 6 inches of full -depth asphalt, and drives and/or fire lanes should be constructed with 7 inches of full -depth asphalt. Our experience indicates full -depth asphalt sections generally perform better on expansive subgrades than combined asphalt/aggregate base course sections. The use of aggregate base course provides a pervious layer above a relatively impervious subgrade. The base course can transmit water causing changes in moisture content within the subgrade materials. Variations in the subgrade moisture content can be erratic and result in erratic volume changes which cause premature deterioration of the pavement. In addition, the thinner asphalt surface of a combined section can more easily allow water to penetrate through cracks and migrate through the aggregate base course. High moisture contents in the subgrade or base course will result in loss of strength. Truck loading dock areas and other areas where truck turning movements are concentrated should be paved with 6 inches of portland cement concrete. The concrete pavement should contain sawed or formed joints to 1 /4 of the depth of the slab at a maximum distance of 15 feet on center. Subgrade Preparation: Prior to placing the pavement section, the entire subgrade area should be scarified to a depth of 8 inches, adjusted to a moisture content near optimum and compacted to 95% of the maximum standard Proctor density (ASTM D 698). The pavement subgrade should be proofrolled with a heavily loaded pneumatic -tired vehicle. Pavement design procedures assume a stable subgrade. Areas which deform excessively under heavy wheel loads are not stable and should be removed and replaced to achieve a stable subgrade prior to paving. Drainage: The collection and diversion of surface drainage away from paved areas is extremely important to the satisfactory performance of pavement. Drainage design should provide for the removal of water from paved areas and prevent the wetting of the subgrade soils. Kumar & Associates, Inc. Galloway, Romero & Associates April 4, 2000 Page 7 Limitations: This study has been conducted in accordance with generally accepted geotechnical engineering practices in this area for use by the client for design purposes. The conclusions and recommendations submitted in this report are based upon the data obtained from the exploratory borings drilled at the locations indicated on Fig. 1, and the proposed type of construction. The nature and extent of subsurface variations across the site may not become evident until excavation is performed. If during construction, fill, soil, rock or water conditions appear to be different from those described herein, this office should be advised at once so reevaluation of the recommendations may be made. We recommend on -site observation of excavations and foundation bearing strata by a representative of the geotechnical engineer. Swelling soils occur on this site. Such soils are stable at their natural moisture content but will undergo high volume changes with changes in moisture content. The recommendations presented in this report are based on current theories and experience of our engineers on the behavior of swelling soil in this area. The owner should be aware that there is a risk in constructing a building in an expansive soil area. Following the recommendations given by a geotechnical engineer, careful construction practice and prudent maintenance by the owner can, however, decrease the risk of foundation movement due to expansive soils. Sincerely, KUMAR & ASSOCIATES, INC. Reviewed By: By Keith E. Mattecheck, E.I.T. KEM/bhc Enclosures Kieth B. Fiebig, P.E. 00', uno' R E iii',, i c. KI i F 803 Kumar & Associates, Inc. SAFEWAY MARKET PLACE 1402 E. HARMONY RD. BM TO CONCRETE J/BASE ON LIGHT£ ASSUMED _ELEIl. = 10 — — r —, I I KIOSK ' CANOPY BORING _-- ill C o E) . u FUTURE i BORING 12 LUNDERGROUND C" STORE STORAGE TANKS BORING a• 2,600 SF N ,®o I A A L---____ -- I I 1-1 U C HARMONY ROAD COLORADO HIGHWAY 68 SCALE —FEET II 0 0 — 3 — i 1 S i Kumar & Associates I LOCATION OF EXPLORATORY BORINGS I Fig. 1 1 BORING 1 EL.=98.0 100 20/12 WC=11.0 DD=1 13.0 LL=34 95 PI=18 22/12 WC=17.3 DD=108.9 200=40 90 22/12 85 o — 80 a wJ W 13/12 15/12 BORING 2 EL.=97.5 25/ 12 19/12 WC=14.6 DD=1 13.5 200=71 15/12 10/12 3 18/12 51 /9 50/0 BORING 3 EL.=97.5 100 19/12 WC=11.6 DD=1 17.7 4=3 200=61 95 LL=35 PI=20 A-6 (9) 16/12 90 12/12 85 10/12 M rm a 80 z 22/12 M 75 50/6 70 65 60 9 00-3-115 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 LEGEND TOPSOIL FILL GRAVELLY, SANDY CLAY, MEDIUM PLACTIC, MOIST, BOWN. SANDY CLAY TO CLAYEY SAND (CL—SC), STIFF TO VERY STIFF, MOIST TO VERY MOIST, TAN TO BROWN, OCCATIONALLY CALCAREOUS. SAND (SP), SLIGHTLY SILTY TO SILTY, GRAVELLY, POORLY GRADED, MEDIUM TO COARSE GRAINED, MEDIUM DENSE, WET, TAN TO BROWN. CLAYSTONE BEDROCK, WITH INTERBEDDED SANDSTONE LENSES, HARD TO VERY HARD, MOIST, TAN TO OLIVE. hDRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE. i DISTURBED BULK SAMPLE. i 20/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 20 BLOWS OF A 140—POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES. DEPTH TO WATER LEVEL AND NUMBER OF DAYS AFTER DRILLING MEASUREMENT WAS MADE. DEPTH AT WHICH BORING CAVED. NOTES 1 . THE EXPLORATORY BORINGS WERE DRILLED ON MARCH 13, 2000 WITH A 4—INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER. 2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY TAPING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE MEASURED BY HAND LEVEL AND REFER TO THE BENCHMARK ON FIG. 1. 4. THE EXPLORATORY BORING LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED. 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUND —WATER LEVELS SHOWN ON THE LOGS WERE MEASURED AT THE TIME AND UNDER CONDITIONS INDICATED. FLUCTUATIONS IN THE WATER LEVEL MAY OCCUR WITH TIME. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT %); DD = DRY DENSITY (pcf); 4 = PERCENTAGE RETAINED ON NO. 4 SIEVE; 200 = PERCENTAGE PASSING NO. 200 SIEVE; LL = LIQUID LIMIT (%); PI = PLASTICITY INDEX (X); A-6 (9) = AASHTO CLASSIFICATION (GROUP INDEX) 00-3-115 Kumar & Associates LEGEND & NOTES I Fig. 3 I 3 2 X J 1J W 3 Vi 1 O Z O Q J O Z O U 2 3 4 0.1 t0 APPLIED PRESSURE — KSF 10 100 3 r. 2 X v JJW 3 N 1 O Z O t= a J 0 n Z O U —2 3 4 0.1 t0 APPLIED PRESSURE — KSF 10 100 00-3-115 Kumar & Associates SWELL —CONSOLIDATION TEST RESULTS Fig. 4 MOISTURE CONTENT = 17.3 PERCENT DRY DENSITY = 117.7 PCF SAMPLE OF: Very Clayey Sand FROM: Boring 1 O 4 feet EXPANSION UNDER CONSTANT PRESSURE UPON WETTING. MOISTURE CONTENT = 14.6 PERCENT DRY DENSITY = 113.5 PCF SAMPLE OF: Sandy Clay FROM: Boring 2 O 4 feet EXPANSION UNDER CONSTANT PRESSURE UPON WETTING. Thr,e tr,t rr,ula aPMf to Sht ,ugln t.,a.at rr. tr,tYip report shoo not b. npraducrd raapt h IuU ,khaut thr rrtttm approval oP Kunar 1, In,odate,, Inc. SreLL Canfolkathn trrthp prKarwrd h a¢ordarice r1M STK D-243. I 3 2 x J 1J W 3 in 1 O Z O a o 1 J O n Z O 2 3 4 01 to APPLIED PRESSURE — KSF 10 7DO 3 x JJ Li 3 to I 0 Z O Q J O Z O 2 3 4 0.1 to APPLIED PRESSURE — KSF 10 100 00-3-115 Kumar & Associates SWELL —CONSOLIDATION TEST RESULTS Fig. 5 MOISTURE CONTENT = 1 1.6 PERCENT ' DRY DENSITY = 117.7 PCF SAMPLE OF: Fill: Sandy Clay FROM: Boring 3 O 1 feet EXPANSION UNDER CONSTANT PRESSURE UPON WETTING. MOISTURE CONTENT = 15.7 PERCENT DRY DENSITY = 114.5 PCF SAMPLE OF: Sandy Clay FROM: Boring 2 O 9' LL c CQ G LO } O J_ 'a U CO ai oOLO O J U w Z LL c O w U O w o d LL Q LL wn. U M @O m U U m c C0 f9 m coUm U U co O cA LO J 0 OLL i to 0 LL Z O F- QCLX O) LL O c Z QQU) Q J U H cn U X 00 O F Oc Z J Q C7 0_ m w m w f- d° V M M Q J J Z Z o w U Nw O F.. W Q Z0_ CL Z O Q o O M V) Q J 0 Q co J Q E- O In O m Z a Cl) O M 4 N LLB Q Z 0 r J w H O LL! ._ O M CO Z Lf r Q O O Z U Z J w J 0 0 CL F- Q U 0 cn O Z N N M O m