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Home My WebLink AboutFile Documents.211 W Hopkins Ave.0078-2021-BRES (13) I( Kumar&Associates,Inc.° Geotechnical and Materials Engineers 5020 County Road 154 and Environmental Scientists Glenwood Springs,CO 81601 phone:(970)945-7988 fax:(970)945-8454 email:kaglenwood@kumarusa.com An Employee Owned Company www.kumarusa.com Office Locations: Denver(HQ),Parker,Colorado Springs,Fort Collins,Glenwood Springs,and Summit County,Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RENOVATION AND BASEMENT ADDITION 211 WEST HOPKINS AVENUE ASPEN, COLORADO PROJECT NO. 21-7-156 MARCH 4, 2021 PREPARED FOR: MATTHEW JOBLON 3003 EAST 3"AVENUE, SUITE 201 DENVER, COLORADO 80206 (matW,bmcinv.com) RECEIVED 05/21/2021 ASPEN BUILDING DEPARTMENT TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - PROPOSED CONSTRUCTION - 1 - SITE CONDITIONS - 1 - FIELD EXPLORATION - 2 - SUBSURFACE CONDITIONS - 2 - FOUNDATION BEARING CONDITIONS - 2 - DESIGN RECOMMENDATIONS - 3 - FOUNDATIONS - 3 - FOUNDATION AND RETAINING WALLS - 3 - FLOOR SLABS - 4 - UNDERDRAIN SYSTEM - 5 - PERCOLATION TEST - 5 - SURFACE DRAINAGE - 6 - LIMITATIONS - 6 - FIGURE 1 - LOCATION OF EXPLORATORY BORING FIGURE 2 - LOG OF EXPLORATORY BORING FIGURE 3 - GRADATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS TABLE 2 -PERCOLATION TEST RESULTS RECEIVED 05/21/2021 Kumar&Associates,Inc.° Project No.21-7-156 ASPEN BUILDING DEPARTMENT PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for the proposed renovation and basement addition to the existing residence located at 211 West Hopkins Avenue, Aspen, 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 Matthew Joblon dated January 26, 2021. An exploratory boring was drilled 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 construction includes a single story residence over a full depth basement detached from the existing historic residence. A full depth basement addition will also be constructed below the historic residence. An attached two car garage will be constructed as part of the detached addition. Ground floors will be slab-on-grade. Grading for the structure is assumed to include cut depth up to about 12 feet. We assume relatively light foundation loading, 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 is developed with a single-story historic residence. The ground surface is relatively flat with some cut and fill from the previous development. Vegetation consists of landscaped lawn grass and trees. There was approximately 16 to 18 inches of snow cover present at the time of our exploration. RECEIVED 05/21/2021 Kumar&Associates,Inc.® Project No.21-7-156 ASPEN BUILDING DEPARTMENT -2 - FIELD EXPLORATION The field exploration for the project was conducted on February 9, 2021. One exploratory boring was drilled at the location shown on Figure 1 to evaluate the subsurface conditions. The boring was advanced with 4-inch diameter continuous flight augers powered by a truck-mounted CME-45B drill rig. The boring was logged by a representative of Kumar&Associates, Inc. Samples of the subsoils were taken with 13/8 inch and 2-inch I.D. spoon samplers. The samplers were driven into the subsoils at various depths with blows from a 140 pound hammer falling 30 inches. This test is similar to the standard penetration test described by ASTM Method D-1586. The penetration resistance values are an indication of the relative density or consistency of the subsoils. Depths at which the samples were taken and the penetration resistance values are shown on the Log of Exploratory Boring, Figure 2. The samples were returned to our laboratory for review by the project engineer and testing. SUBSURFACE CONDITIONS A graphic log of the subsurface conditions encountered at the site is shown on Figure 2. The subsoils consist of about 12 feet of medium dense, gravelly sand fill overlying dense, slightly silty to silty sand and gravel with cobbles and possible boulders down to the maximum drilled depth of 21 feet. Laboratory testing performed on samples obtained from the boring included natural moisture content and gradation analyses. Results of gradation analyses performed on small diameter drive samples (minus 11/2-inch fraction) of the coarse granular subsoils are shown on Figure 3. The laboratory testing is summarized in Table 1. No free water was encountered in the boring at the time of drilling and the subsoils were slightly moist to moist. FOUNDATION BEARING CONDITIONS The natural granular soils encountered in the boring are adequate for support of spread footing foundations. Man-placed fill and debris from previous site development should be completely removed from beneath proposed foundation areas. At the planned basement level excavation depth, we expect existing fill and debris from prior site development and clay soils (if present) will be removed but we should observe the foundation excavation for bearing conditions. RECEIVED 05/21/2021 Kumar&Associates,Inc.® Project No.21-7-156 ASPEN BUILDING DEPARTMENT - 3 - DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory boring and the nature of the proposed construction, we recommend new building foundations be supported 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 3,000 psf. Based on experience, we expect settlement of footings designed and constructed as discussed in this section will be minor, about '/2 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 42 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 10 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) Existing fill, debris from previous site development and loose or disturbed soils should be removed and the footing bearing level extended down to the relatively dense natural granular soils. Disturbed granular soils in footing area should then be moistened and compacted. 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 con t r. Y of the on-site granular soils. Cantilevered retaining structures which are separate from thRE ,.# 05/21/2021 Kumar&Associates,Inc.° Project No.21-7-156 ASPEN BUILDING DEPARTMENT -4 - building (if any) 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. Backfill should not contain organics, debris and rock larger than about 6 inches. 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 in landscape areas. Backfill placed 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 be a relatively well graded granular material and could be compacted to at least 98% standard Proctor density to help limit settlement potential. 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 0.50. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 400 pcf. The 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 granular soils, exclusive of topsoil and debris from previous construction, are suitable to support lightly loaded slab-on-grade construction. To reduce the effects of soRE 1 E IVE D 05/21/2021 Kumar&Associates,Inc.° Project No.21-7-156 ASPEN BUILDING DEPARTMENT - 5 - 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 the area that local perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can 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 excavation and at least 1 foot below lowest adjacent finish grade and sloped at a minimum 1%to a suitable gravity outlet or drywell. 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 11/2 feet deep. PERCOLATION TEST Drywells and bio-swales are often used in the Aspen area for site runoff detention and disposal. The natural granular soils encountered are typically free draining and should be suitable for surface water treatment and disposal as needed. The results of percolation testing performed in Boring 1, presented in Table 2, indicate an infiltration rate of about 6 minutes per inch(inverted units equivalent rate of 10 inches per hour). The bedrock and groundwater level are generally known to be relatively deep in this area and should not affect drywell or bio-swale designs. If a drywell is used, it should have solid casing down to at least basement level and perforation pipe below that level. RECEIVED 05/21/2021 Kumar&Associates,Inc.° Project No.21-7-156 ASPEN BUILDING DEPARTMENT - 6 - SURFACE DRAINAGE The following drainage precautions should be observed during construction and maintained at all times after the basement level has 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 6 inches in the first 10 feet in unpaved areas and a minimum slope of 2'/2 inches in the first 10 feet in paved areas. Free-draining wall backfill should be covered with filter fabric and capped with about 2 feet of the on-site finer graded soils to reduce surface water infiltration. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 5) Landscaping which requires regular heavy irrigation should be located at least 5 feet from foundation walls. 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 boring drilled at the location 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 subsurface conditions identified at the exploratory boring 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 evoR E IVE ID 05/21/2021 Kumar&Associates,Inc.° Project No.21-7-156 ASPEN BUILDING DEPARTMENT - 7 - 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, Kumar & Associates, Inc. Pgt#445"- James H. Parsons, E.I. Reviewed by: _•��.��,1,, O-*pQ•REGjs ." 70 :n 15222 ' Steven L. Pawla P.E. f • e•e •� - SLP/kac SS%pNA•EN�= Cc: Rowland &Broug Rowland (johngrowlandbroughton.com) RECEIVED 05/21/2021 Kumar&Associates,Inc.® Project No.21-7-156 ASPEN BUILDING DEPARTMENT \7893 WEST Itopk„, \ CURB 12714' YPC 3 LSy 24312 BENCHMARK=7893.0.1 W 10718'' 0717' 977 LOT E LOT F I 12"/8'"4~r 2./8' 30 /18_ — 8"/9 __7593 � 8p1- ------/ 879' G9./8 YPC BORING 1 LOT G LS/24312 • / i 3'..�L--.� \ N 79'8.57 W y+e, , \24'/17' 458.57 FF 893.7 \ LOT H I o 2'//13'W/i i / / SINGLE FAMILY / / / I RESIDENCE // Q 5.0' • f l/I / SETBACK 1713' /10 Otise / I / i , Cl_ „ / WOOD j .. / >A , DECK ^' .� 11 / l I CITY OF ASPEN / / GPSfl 3 SETBACK --J 16.3' / / 12713' 15 / / / / / 10710' 12'/12 \ 9711'/})-- YPC \ LS#24312 4712'\ / TOP OF POST Cam SEITBACK 12e \ 5, -------= }12"/16 Y 876'/ / 8 V N75.0g,/I, a \5 60.00' - YPC ciOn S LS#24312 A,r_ S , OF POST � y 9 G 20.00'GCE\S R.O.A 53 G G S \0 S s w i 2 `o i E 1 10 0 10 20 ,T14. APPROXIMATE SCALE—FEET RECEIVED I H L I � 0 /F21/2021 21 -7-156 Kumar & Associates I LOCATION OF EXPLORATORY BORING 1g. 1 Y% - ASPCPti BUILDING DEPARTMENT BORING 1 LEGEND EL. 7893' p TOPSOIL; SILTY SAND WITH GRAVEL AND ORGANICS, FIRM, MOIST, DARK BROWN. ♦ 44/12 X FILL: CLAYEY GRAVEL AND SANDY CLAY, MEDIUM DENSE TO DENSE, MOIST, DARK BROWN. 17/12 WC=15.8 5 —200=66 O SAND AND GRAVEL (SM—GM); SILTY, COBBLES, DENSE, MOIST, • GRAY—BROWN, ROUNDED ROCK. 56/12 WC=5.3 +4=40 � DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE. —200=20 10 DRIVE SAMPLE, 1 3/8—INCH I.D. SPLIT SPOON STANDARD w— 41/12 PENETRATION TEST. 44 12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 44 BLOWS OF _— _ / A 140—POUND HAMMER FALLING 30 INCHES WERE REQUIRED 43/12 TO DRIVE THE SAMPLER 12 INCHES. o WC=3.1 15 -0•:;.t +4=45 —200=8 NOTES 1. THE EXPLORATORY BORING WAS DRILLED ON FEBRUARY 9, 2021 WITH A 4—INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER. 20r. 2. THE LOCATION OF THE EXPLORATORY BORING WAS MEASURED yi38/12 APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 3. THE ELEVATION OF THE EXPLORATORY BORING WAS OBTAINED BY INTERPOLATION BETWEEN CONTOURS ON THE SITE PLAN PROVIDED. 25 4. THE EXPLORATORY BORING LOCATION AND ELEVATION SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED. 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOG REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORING AT THE TIME OF DRILLING. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D 2216); +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 6913); —200 = PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140). riF s En 1 rl 61 21 -7-156 Kumar &Associates LOG OF EXPLORATORY BORING 0 51/2o21 ASPEN BUILDING DEPARTMENT HYDROMETER ANALYSIS SIEVE ANALYSIS TIME READINGS U.S. STANDARD SERIES CLEAR SQUARE OPENINGS 24 HRS 7 HRS io, 45 MIN 15 MIN 6OMIN 19MIN 4MIN 1MIN #200 #100 #50#40#30 #16 #10#8 #4 3/8" 3/4" 1 1 2" 3" 5"6" 8"0 90 10 80 - 20 70 30 60 - 40 G 50 50 ' a 40 60 30 70 20 80 10 90 0 I I I I I I I I 11 I I 111 II 1 I 1 11 I I I I II 1 I I I I I I I I I I I I I II II 100 .001 .002 .005 .009 .019 .037 .075 .150 .300 I .600 1.18 2.36 4.75 9.5 19 38.1 76.2 127 200 .425 2.0 152 I DIAMETER OF PARTICLES IN MILLIMETERS CLAY TO SILT SAND GRAVEL COBBLES FINE MEDIUM COARSE FINE COARSE GRAVEL 40 % SAND 40 % SILT AND CLAY 20 % LIQUID LIMIT PLASTICITY INDEX SAMPLE OF: Clayey Gravel and Sand (Fill) FROM: Boring 1 0 7' HYDROMETER ANALYSIS SIEVE ANALYSIS TIME READINGS U.S. STANDARD SERIES CLEAR SQUARE OPENINGS 24 HRS 7 HRS 1D0 45 MIN 15 MIN 60MIN 19MIN 4MIN 1MIN #2 0 #100 50#40 30 16 #10#8 #4 3/8" 3/4" 1 1 2" 3" 5"6" 8"O 90 10 80 20 70 30 60 - 40 50 - 50 rc u 40 60 ' 30 70 20 80 10 90 v 1 13 0 I I 1 1 1 1 I I I 1 1 1 1 1 1 I I 1 1 1 11 I I I I I I III I I I I I I III 100 .001 .002 .005 .009 .019 .037 .075 .150 .300 .600 1.18 12.36 4.75 9.5 19 38.1 76.2 127 200 <71 .425 2.0 152 DIAMETER OF PARTICLES IN MILLIMETERS SAND GRAVEL CLAY TO SILT COBBLES FINE MEDIUM COARSE FINE COARSE E GRAVEL 45 % SAND 47 % SILT AND CLAY 8 % LIQUID LIMIT PLASTICITY INDEX These test results apply only to the e SAMPLE OF: Slightly Silty Gravel and Sand FROM: Boring 1 0 15' samples which were tested. The testing report shall not be reproduced, E„ except In full, without the written g2 approval of Kumar & Associates, Inc. e L Sieve ant analysis testingis 9 r3. h __in accordance with A M D691 f m Ii ASTM C136 and/or STM D1140 E,i" o 21 -7-156 Kumar & Associates GRADATION TEST RESULTS _> 0 5/E1i2021 ASPEN BUILDING DEPARTMENT I( i Kumar&Associates,Inc.° Gumar&Aland Materials Engineers and Environmental Scientists TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Project No.21-7-156 SAMPLE LOCATION NATURAL NATURAL GRADATION ATTERBERG LIMITS UNCONFINED MOISTURE DRY GRAVEL SAND PERCENT PLASTIC COMPRESSIVE BORING DEPTH CONTENT DENSITY (%) (%) PASSING 200 S EVE LIQUID LIMIT INDEX STRENGTH SOIL TYPE (ft) (%) (pcf) (%) (%) (psf) 1 4 15.8 66 Gravelly Sandy Clay (Fill) 7 5.3 40 40 20 Clayey Gravel and Sand (Fill) 15 3.1 45 47 8 Slightly Silty Gravel and Sand RECEIVED 05/21/2021 ASPEN BUILDING DEPARTMENT Ic+AKumar&Associates,Inc.° Gumar&Aland Materials Engineers and Environmental Scientists TABLE 2 PERCOLATION TEST RESULTS PROJECT NO.21-7-156 HOLE NO. HOLE DEPTH LENGTH OF WATER DEPTH WATER DEPTH DROP IN AVERAGE (INCHES) INTERVAL AT START OF AT END OF WATER LEVEL PERCOLATION (MIN) INTERVAL INTERVAL (INCHES) RATE (INCHES) (INCHES) (MIN./INCH) 50 48 2 1.5 48 47 1 3 47 46 1 3 B-1 124 3 46 45 1 3 45 44 1 3 44 431/2 6 43'/2 43 1/2 6 43 421/2 1/2 6 Note: The percolation test was conducted in the completed 4-inch diameter borehole on February 9, 2021. RECEIVED 05/21/2021 ASPEN BUILDING DEPARTMENT