The URL can be used to link to this page

Home My WebLink AboutSoils Report 08.06.2018H-PKUMAR Geotechnical Engineering 1 Engineering Geology Materials Testing 1 Environmental 5020 County Road 154 Glenwood Springs, CO 81601 Phone: (970) 945-7988 Fax: (970) 945-8454 Email: hpkglenwood@kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE AND ADU LOT 3, RIMLEDGE SUBDIVISION 5356 COUNTY ROAD 100 GARFIELD COUNTY, COLORADO PROJECT NO. 18-7-465 AUGUST 6, 2018 PREPARED FOR: DAVID RASMUSSEN DESIGN 826C HIGHWAY 133 CARBONDALE, COLORADO 81623 (david @ vrcabinet.com) TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - PROPOSED CONSTRUCTION - 1 - SITE CONDITIONS - 1 - SUBSIDENCE POTENTIAL - 2 - FIELD EXPLORATION - 2 - SUBSURFACE CONDITIONS - 2 - DESIGN RECOMMENDATIONS - 3 - FOUNDATIONS - 3 - FOUNDATION AND RETAINING WALLS - 4 - FLOOR SLABS - 5 - UNDERDRAIN SYSTEM - 5 - SURFACE DRAINAGE - 6 - LIMITATIONS - 6 - FIGURE 1 - LOCATION OF EXPLORATORY PITS FIGURE 2 - LOGS OF EXPLORATORY PITS FIGURE 3 - GRADATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS H -P- K MAR Project No. 18-7-465 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence and ADU to be located on Lot 3, Rimledge Subdivision, 5356 County Road 100, Garfield County, Colorado. The project site is shown on Figure 1. The purpose of the study was to develop recommendations for the foundation design. The study was conducted in accordance with our agreement for geotechnical engineering services to David Rasmussen Design dated July 16, 2018. A field exploration program consisting of exploratory pits was conducted to obtain information on the subsurface conditions. Samples of the subsoils obtained during the field exploration were tested in the laboratory to determine their classification, and other engineering characteristics. The results of the field exploration and laboratory testing were analyzed to develop recommendations for foundation types, depths and allowable pressures for the proposed building foundation. This report summarizes the data obtained during this study and presents our conclusions, design recommendations and other geotechnical engineering considerations based on the proposed construction and the subsurface conditions encountered. PROPOSED CONSTRUCTION The proposed residence and ADU will both be one story structures with a wood frame storage area attached to the residence. Ground floors will be structural over crawlspace for the residence and ADU and slab -on -grade for the storage area. Grading for the structure is assumed to be relatively minor with cut depths between about 3 to 6 feet. We assume relatively light foundation loadings, typical of the proposed type of construction. If building loadings, location or grading plans change significantly from those described above, we should be notified to re-evaluate the recommendations contained in this report. SITE CONDITIONS The subject site was vacant at the time of our field exploration. The terrain is sloping generally down to the east at grades of around 5 to 10%. Elevation difference across the building area is about 14 feet. Vegetation on the building site consists of pinon pines and sparse grass. H-P-KUIVIAR Project No. 18-7-465 -2 - SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the subject site. These rocks are a sequence of gypsiferous shale, fine-grained sandstone and siltstone with some massive beds of gypsum and limestone. There is a possibility that massive gypsum deposits associated with the Eagle Valley Evaporite underlie portions of the lot. Dissolution of the gypsum under certain conditions can cause sinkholes to develop and can produce areas of localized subsidence. Sinkholes were not observed in the immediate area of the subject lot. No evidence of cavities was encountered in the subsurface materials; however, the exploratory pits were relatively shallow, for foundation design only. Based on our present knowledge of the subsurface conditions at the site, it cannot be said for certain that sinkholes will not develop. The risk of future ground subsidence on Lot 3 throughout the service life of the proposed residence and ADU, in our opinion, is low; however, the owner should be made aware of the potential for sinkhole development. If further investigation of possible cavities in the bedrock below the site is desired, we should be contacted. FIELD EXPLORATION The field exploration for the project was conducted on July 18, 2018. Three exploratory pits were excavated at the locations shown on Figure 1 to evaluate the subsurface conditions. The pits were dug with a Caterpillar 313 trackhoe. The pits were logged by a representative of H-P/Kumar Samples of the subsoils were taken with relatively undisturbed and disturbed sampling methods. Depths at which the samples were taken are shown on the Logs of Exploratory Pits, Figure 2. The samples were returned to our laboratory for review by the project engineer and testing. SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils consist of about 11 to 3 feet of topsoil overlying dense silty sand and gravel with cobbles and boulders. Digging in the dense granular soils with the backhoe was difficult due to the cobbles and boulders and refusal to digging was encountered in the deposit. H-P�KUMAR Project No. 18-7-465 -3 - Laboratory testing performed on samples obtained from the pits included natural moisture content and gradation analyses. Results of gradation analyses performed on small diameter drive samples (minus 3 inch fraction) of the coarse granular subsoils are shown on Figure 3. No free water was encountered in the pits at the time of excavation and they were backfilled subsequent to sampling. The subsoils were slightly moist. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory pits and the nature of the proposed construction, we recommend the buildings be founded with spread footings bearing on the natural granular soils. The design and construction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on the undisturbed natural granular soils should be designed for an allowable bearing pressure of 2,000 psf. Based on experience, we expect settlement of footings designed and constructed as discussed in this section will be about 1 inch or less. 2) The footings should have a minimum width of 16 inches for continuous walls and 2 feet for isolated pads. 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 36 inches below exterior grade is typically used in this area. 4) Continuous foundation walls should be reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 14 feet. Foundation walls acting as retaining structures should also be designed to resist lateral earth pressures as discussed in the "Foundation and Retaining Walls" section of this report. 5) Topsoil and any loose disturbed soils should be removed and the footing bearing level extended down to the relatively dense natural granular soils. The exposed soils in footing area should then be moistened and compacted. H-P�KUMAR Project No. 18-7-465 -4- 6) A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. FOUNDATION AND RETAINING WALLS Foundation walls and retaining structures which are laterally supported and can be expected to undergo only a slight amount of deflection should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 50 pcf for backfill consisting of the on-site granular soils. Cantilevered retaining structures which are separate from the residence and ADU and can be expected to deflect sufficiently to mobilize the full active earth pressure condition should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 40 pcf for backfill consisting of the on-site granular soils. All foundation and retaining structures should be designed for appropriate hydrostatic and surcharge pressures such as adjacent footings, traffic, construction materials and equipment. The pressures recommended above assume drained conditions behind the walls and a horizontal backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain should be provided to prevent hydrostatic pressure buildup behind walls. Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum standard Proctor density at a moisture content near optimum. Backfill in pavement and walkway areas should be compacted to at least 95% of the maximum standard Proctor density. Care should be taken not to overcompact the backfill or use large equipment near the wall, since this could cause excessive lateral pressure on the wall. Some settlement of deep foundation wall backfill should be expected, even if the material is placed correctly, and could result in distress to facilities constructed on the backfill. Backfill should not contain organics, debris or rock larger than about 6 inches. The lateral resistance of foundation or retaining wall footings will be a combination of the sliding resistance of the footing on the foundation materials and passive earth pressure against the side of the footing. Resistance to sliding at the bottoms of the footings can be calculated based on a coefficient of friction of 0.45. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 350 pcf. The H-PKUMAR Project No. 18-7-465 -5 - coefficient of friction and passive pressure values recommended above assume ultimate soil strength. Suitable factors of safety should be included in the design to limit the strain which will occur at the ultimate strength, particularly in the case of passive resistance. Fill placed against the sides of the footings to resist lateral loads should be a granular material compacted to at least 95% of the maximum standard Proctor density at a moisture content near optimum. FLOOR SLABS The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab -on -grade construction. To reduce the effects of some differential movement, floor slabs should be separated from all bearing walls and columns with expansion joints which allow unrestrained vertical movement. Floor slab control joints should be used to reduce damage due to shrinkage cracking. The requirements for joint spacing and slab reinforcement should be established by the designer based on experience and the intended slab use. A minimum 4 inch layer of free - draining gravel should be placed beneath basement level slabs to facilitate drainage. This material should consist of minus 2 inch aggregate with at least 50% retained on the No. 4 sieve and less than 2% passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 95% of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of the on- site granular soils devoid of vegetation, topsoil and oversized rock. UNDERDRAIN SYSTEM Although free water was not encountered during our exploration, it has been our experience in mountainous areas that local perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can also create a perched condition. We recommend below -grade construction, such as retaining walls, crawlspace and basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain system. The drains should consist of drainpipe placed in the bottom of the wall backfill surrounded above the invert level with free -draining granular material. The drain should be placed at each level of H -P- KUMAR Project No. 18-7-465 -6 - excavation and at least 1 foot below lowest adjacent finish grade and sloped at a minimum 1% to a suitable gravity outlet. Free -draining granular material used in the underdrain system should contain less than 2% passing the No. 200 sieve, less than 50% passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at least 11 feet deep. SURFACE DRAINAGE The following drainage precautions should be observed during construction and maintained at all times after the residence and ADU have been completed: 1) Inundation 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 in pavement and slab 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 12 inches in the first 10 feet in unpaved areas and a minimum slope of 3 inches in the first 10 feet in paved areas. Free -draining wall backfill should be capped with about 2 feet of the on-site soils to reduce surface water infiltration. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. LIMITATIONS This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this area at this time. We make no warranty either express or implied. The conclusions and recommendations submitted in this report are based upon the data obtained from the exploratory pits excavated at the locations indicated on Figure 1, the proposed type of construction and our experience in the area. Our services do not include determining the presence, prevention or possibility of mold or other biological contaminants (MOBC) developing in the future. If the client is concerned about MOBC, then a professional in this special field of practice should be consulted. Our findings include interpolation and extrapolation of the H-P�KUMAR Project No. 18-7-465 -7 - subsurface conditions identified at the exploratory pits and variations in the subsurface conditions may not become evident until excavation is performed. If conditions encountered during construction appear different from those described in this report, we should be notified so that re-evaluation of the recommendations may be made. This report has been prepared for the exclusive use by our client for design purposes. We are not responsible for technical interpretations by others of our information. As the project evolves, we should provide continued consultation and field services during construction to review and monitor the implementation of our recommendations, and to verify that the recommendations have been appropriately interpreted. Significant design changes may require additional analysis or modifications to the recommendations presented herein. We recommend on-site observation of excavations and foundation bearing strata and testing of structural fill by a representative of the geotechnical engineer. Respectfully Submitted, �I-P1 KUMAR Prio/k/ez James H. Parsons, E.I. Reviewed by: Daniel E. Hardin, JHP/kac Project No. 18-7-465 M ME 30 0 30 60 APPROXIMATE SCALE—FEET ,r5 • \ \ \ \\ \. —7-- PIT i • itPJfeUr 18-7-465 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1 0 5 10 LEGEND PIT 1 EL. 6744' 7� WC=10.1 +4=33 -200=19 LL=44 PI=18 0 0 O PIT 2 EL. 6751' 0 0 / PIT 3 EL. 6758' 0 0 WC=5.2 rr +4=73 -200=7 TOPSOIL; CLAY, SANDY, SCATTERED GRAVEL, STIFF, SLIGHTLY MOIST, BROWN. 0 5 10 SAND AND GRAVEL (GM); SILTY, COBBLES, SMALL BOULDERS, DENSE, SLIGHTLY MOIST, TAN. HAND DRIVEN LINER SAMPLE. DISTURBED BULK SAMPLE. I PRACTICAL REFUSAL TO BACKHOE DIGGING. NOTES 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A TRACKHOE ON JULY 18, 2018. 2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE OBTAINED BY INTERPOLATION BETWEEN CONTOURS ON THE SITE PLAN PROVIDED. 4. THE EXPLORATORY PIT 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 PIT LOGS REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF DIGGING. PITS WERE BACKFILLED SUBSEQUENT TO SAMPLING. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D 2216); +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422); -200 = PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140); LL = LIQUID LIMIT (ASTM D 4318); PI = PLASTICITY INDEX (ASTM D 4318). 18-7-465 H -P- KUMAR LOGS OF EXPLORATORY PITS Fig. 2 HYDROMETER ANALYSIS SIEVE ANALYSIS 100 TIME READINGS 24 HRS 7 HRS 45 MIN 15 MIN 60MIN 19MIN 4MIN IMIN U.S. 200 gl00__� STANDARD SERIES p4o 130 X16 III? 18 CLEAR SOUARE OPENINGS 4 3 6' 3 4' 1 1 2' 5'6' 8'0 901 _ — _ 1 I _. _ 70 -- I 1 1 1 ■■ 1 20 60 — —J- 1 1 1 50 1 I I I el k W I IW 50 i 40 - , t -----n 30 -. _- ... I I 1 60 I _ -- - _ 70 = 20 .. — = == I 90 _ -. Bin 99_99 10 j I 0 I _I I I I I 11 1_41 1 1 III 1 I [L u I 1 1 I J 1 I_-1 L 90 .001 .002 .005 .009 .019 .037 .075 DIAMETER .150 .300 I .600 1. 8 2.36 4.75 9 5 19 .425 2.0 OF PARTICLES IN MILLIMETERS 38.1 _LI1 76.2 1_1_1_1 127 152 100 200 CLAY TO SILT SAND GRAVEL FINE MEDIUM COARSE FINE COARSE COBBLES GRAVEL 33 % LIQUID LIMIT 44 SAMPLE OF: Silty Sand and Gravel SAND 48 % SILT AND CLAY 19 % PLASTICITY INDEX 18 FROM: Pit 1 0 2'-3' HYDROMETER ANALYSIS SIEVE ANALYSIS 100 90 TIME READINGS 24 HRS 7 HRS 45 MIN 15 MIN 60MIN 19MIN 41.1IN IMIN 1200 U.S. 1100 STANDARD 50 1.10,13A____/ SERIES 6 /1048 -- /4 3/8 CLEAR 5/4' SOUARE 1 OPENINGS j/2 _,._ 5'6" l 1 8% — 0 80 --- T--10 1 1 70 1 I 1 1 1 20 t r — —1 — 30 —_. — a60 1— 40 ,, 50 -- 1 40 I 1 - -- 1 >< 30 1 I 60 20 1 1 1 1 1 70 10 t 1 80 0 1 I. 1 1 1 I I I 1 I I I I 1 1 J L_LJ_LI t _ ____1_ I t_[ 1_LI I__- [ 90 - .001 .002 .005 .009 .019 .037 .075 .150 DIAMETER 1 I"i T1-1 .300 I .600 1.18 2.36 4.75 9 5 19 38.1 76.2 127 .425 2.0 152 OF PARTICLES IN MILLIMETERS 100 200 CLAY TO SILT SAND GRAVEL FINE MEDIUM COARSE FINE COARSE COBBLES GRAVEL 73 % SAND SAMPLE OF: Slightly Silty Sand and Grovel 20 % SILT AND CLAY 7 % FROM: Pit 3 0 4.5'-5.5' These fest results apply only to the samples which were tested. The testing report shall not be reproduced, except In full, without the written approval o1 Kumar k Associates, Inc. Sieve analysis testing Is performed In accordance with ASTM 0422, ASTM C136 and/or ASTM D1140. 18-7-465 H-PvKUMAR GRADATION TEST RESULTS Fig. 3 Project No. 18-7-465 U) H J u)CY W ix u) W 2i_ } fx MO W CC J O 0 mm H J u - O Th >._i < a 2 D Silty Sand and Gravel Slightly Silty Sand and Grave GRADATION ATTERBERG LIMITS PERCENT GRAVEL SAND PASSING LIQUID PLASTIC (%) (%) NO. 200 LIMIT INDEX SIEVE 44 18 48 19 o ci NATURAL DRY DENSITY (pct) NATURAL MOISTURE CONTENT (%) tri SAMPLE LOCATION PIT DEPTH (ft) 11 2 41-51/2