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HomeMy WebLinkAboutFile Documents.267 Roaring Fork Dr.0289.2018.ARBK H-P KU MAR 5020 County Road 154 '`. Glenwood Springs,CO 81601 Geotechnical Engineering I Engineering Geology Phone:(970)945-7988 Materials Testing I Environmental Fax: (970)945-8454 Email: hpkglenwood@kumarusa.com Office Locations: Parker,Glenwood Springs,and Summit County,Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED ADDITION LOT 2, BLOCK 2, KNOLLWOOD SUBDIVISION 267 ROARING FORK DRIVE ASPEN, COLORADO PROJECT NO. 17-7-173 MARCH 14,2017 PREPARED FOR: HEATHER KROEGER 16 FORDYCE LANE ST. LOUIS, MISSOURI 63124 (heatherkroegera y ahoo.com) RECEIVED 12/12/2018 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 - 3 - DESIGN RECOMMENDATIONS - 3 - FOUNDATIONS - 3 _ FOUNDATION AND RETAINING WALLS -4 - FLOOR SLABS - 5 - UNDERDRAIN SYSTEM - 6 - DRYWELL - 6 - SURFACE DRAINAGE - 7 - LIMITATIONS - 7 - FIGURE 1 - LOCATION OF EXPLORATORY BORING FIGURE 2 - LOG OF EXPLORATORY BORING FIGURE 3 - GRADATION TEST RESULTS TABLE 1 - PERCOLATION TEST RESULTS RECEIVED 12/12/2018 H-Pk KUMAR Project No. 17-7-173 ASPEN BUILDING DEPARTMENT PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed addition to the residence located on Lot 2, Block 2, Knollwood Subdivision, 267 Roaring Fork Drive, 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 Heather Kroeger, dated February 15, 2017. A field exploration program consisting of an exploratory boring 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 construction consists of an addition attached to the existing residence shown on Figure 1. The addition will be 2-story wood frame construction partly cut into the hillside and daylight on the downhill, west side. Ground floors will be slab-on-grade. Grading for the addition will involve cut depths up to about 10 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 property is occupied with a 2-story residence with a walkout lower level on the west side and attached garage on the north end. The west part of the property is moderately sloping down to the southwest from the house to Roaring Fork Drive. The eastern part of the property is REC EIVED 12/12/2018 H-Pt KUMAR Project No. 17-7-173 ASPEN BUILDING DEPARTMENT - � - moderately steep sloping down to the west. Vegetation consists of scattered aspen trees. About 2 feet of snow covered the property at the time of our field exploration. FIELD EXPLORATION The field exploration for the project was conducted on February 28, 2017. One exploratory boring was drilled at the approximate location shown on Figure 1 to evaluate the subsurface conditions. Drill rig access was limited to the driveway due to the sloping terrain and snow cover. 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 H-P/Kumar. Samples of the subsoils were taken with 1%-inch and 2-inch 1.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, below the asphalt pavement and about 2 feet of fill material and topsoil, consist of relatively dense, silty sand and gravel with cobbles and probable boulders to the boring depth of 16 feet. Drilling in the coarse granular soils with auger equipment was difficult due to the cobbles and probable boulders and practical auger refusal was encountered in the deposit. 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 I!i-inch size fraction) of the natural granular soils are presented in Figure 3. No free water was encountered in the boring at the time of drilling and the subsoils were slightly moist to moist. RECEIVED 12/12/2018 H-P KUMAR Project No. 17-7-173 ASPEN BUILDING DEPARTMENT - 3 - FOUNDATION BEARING CONDITIONS The natural granular soils encountered below the fill material and topsoil are adequate for support of spread footing foundations. The man-placed fill and topsoil should be completely removed from beneath proposed building areas. The proposed addition is will be cut into the hillside and the excavation is expected to extend down below the fill material but the extent of existing fill should be further evaluated at the time of excavation. The City of Aspen requires an engineered excavation stabilization plan if proposed foundations are within 15 feet of a neighboring structure or public travel way. The plan is not required if excavations are less than 5 feet below existing grades or further than 15 feet from travel ways and less than 15 feet deep. Slope bracing through use of a variety of systems such as micro-piles and soil nailing should be feasible at the site. A shoring contractor with experience in the area should provide design drawings to support the proposed excavation slopes where needed. Other City requirements may also be applicable. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory boring and the nature of the proposed construction, we recommend the building 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 or a limited depth of structural fill 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 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. PlacemRent rEl Y ED 12/12/2018 H-P KUMAR Project No. 17-7-173 ASPEN BUILDING DEPARTMENT -4 - 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 12 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) The existing fill soils, topsoil, debris and any loose or 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. Structural fill placed to re-establish design bearing level should be limited to 2 feet in depth and should consist of a relatively well graded granular soil approved by the geotechnical engineer and compacted to at least 100%of standard Proctor density at near optimum moisture content. The fill should extend laterally out from the footing edges a distance at least equal to the depth of fill below the footing. 6) A representative of the geotechnical engineer should observe all footing excavations and test compaction of structural fill 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 or imported granular materials. Cantilevered retaining structures which are separate from the building 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 or imported granular materials. The backfill should not contain debris, topsoil or oversized (plus about 6 inch) rock. RECEIVED 12/12/2018 H-P a KUMAR Project No. 17-7-173ASPEN BUILDING DEPARTMENT - 5 - 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. BackfilI 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 over compact 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. Increasing compaction to at least 98%of standard Proctor density could be used to help limit the 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 relatively well graded granular soil compacted to at least 95% of the maximum standard Proctor density at a moisture content near optimum. FLOOR SLABS The natural granular soils encountered below the existing fill are suitable to support lightly loaded slab-on-grade construction. To reduce the effects of some differential movement, floor ilg slabs should be separated from all bearing walls and columns with expansion joints whichpCEIVED 12/12/2018 H-P4 KUMAR Project No. 17-7-173 ASPEN BUILDING DEPARTMENT - 6 - 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 debris, topsoil and rock larger than about 6 inches. 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, drywell or sump and pump. 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 1!4 feet deep. DRYWELL Drywells and bio-swales are often used in the Aspen area for site water runoff detention and disposal. The natural granular soils encountered below the fill soils and topsoil are typically relatively 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 1, indicate an infiltration rate of about 2 minutes per inch. Bedrock and groundwater levels are genera ECEIVED 12/12/2018 H-P'KUMAR Project No. 17-7-173 ASPEN BUILDING DEPARTMENT _ 7 _ known to be relatively deep compared to the proposed lower floor level and not affect drywell or bio-swale design. If a drywell is used, it should have solid casing down to at least 2 feet below basement floor level with perforations below that level. SURFACE DRAINAGE The following drainage precautions should be observed during construction and maintained at all times after the building 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 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 covered with filter fabric and capped with at least 2 feet of 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 geotechnicaI engineering principles and practices in this area at the time of this study. 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 professioRlecEIVED 12/12/2018 H-Pk KUMAR Project No. 17-7-173 ASPEN BUILDING DEPARTMENT - 8 - this special field of practice should be consulted. Our findings include 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 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, H-P- KUMAR ` � •p4`'` • i ' II, 5223 Steven L. Pawlak, .E SvolI 0.1 1 ;Reviewed by: • .gClT" + s if bdi... ....(k ,.„47:,.-.„,...11.3, ;,•,' .. IL ji ...i.;,..0!E.,°_,-;`-. Daniel E. Hardin, P.E. SLP/kac Cc: Alius Michael Edinger(michael a,aliusdc.com) RECEIVED 12/12/2018 H-PkKUMAR Project No. 17-7-173ASPEN BUILDING DEPARTMENT WESTVIEW DRIVE , • / • i 1 .,/ �' , I // \' ; Xc\\ (I / \,, ; \.'\ \ 1 // �,; \\ 1 , \ \ ` �.• 1 ,I / / \ • / ,/`.,, `\ �\\,• •i I , 1 I / 2, /� 1 ) \\ 't l I / , , , , I i / i `� \ \ I 1 1 I� \ r` / ; / \s) /' ,e / 1 1 I \ /// Zr \/ ` BORI G 1/, k,V% , 1 i i� \ II � / / 1 ) i I I 1 / / 1 4. •\ / / / - ; \ ; ;, ;1 1 — — — ✓ / Th\ 1 )/ ! I ti S - - - ♦ r \ V 1li I 267 ROARING /' ' I 1 f \ `� \ II � d 1 FORK DRIVE j + r i �'•�`_ -`-.. `, 1 ASPEN, CO ' /! i i 1 j , . j o I ' 1 / / / 1. J !f / .moo ^ -- ! I �, /1.-�,/ / / -69_ `�_ , , i / , ' , is , n f I\---Vily, % ... •.. ...43001 I I I\I I I I I I I 1 I 1;0 %, 1 I I I f s, / r (Ady is i, , le/ I, / if ( c , i i / s ,I f/ / / /cf.. I / f, 1 I ISS'IN, 11; L \ ‘,..// ,"17::,\:1/(,,:::\ IgE . s, N %,, \\\,,,(\1,1‘,i\i,1%:,t,,,(: 7',%':..\:: ::„, , 1a.•.\:\.N:,\ç , _ \ 1 .‘I,-.s..:....:-\-:::.:N:",..,..:II s:‘•:I..:1..-ita.I .• 2, `. ` `•• .`- J 15 0 15 30 ,N N `••• iSCALE—FEET ``N ,I , A çEIVED 4s17--7-173 H-PI<UMAR LOCATION OF EXPLORATORY BORING Fig. 12/12/2018 ASPEN BUILDING DEPARTMENT BORING 1 LEGEND EL. 8102' (4) — ASPHALT, THICKNESS IN INCHES SHOWN IN PARENTHESES TO 8105 LEFT OF THE LOG. FILL: SILTY SAND AND GRAVEL, FIRM, MOIST, BROWN. TOPSOIL, ORGANIC SANDY SILT AND CLAY, STIFF, MOIST, DARK 8100 , ,0 BROWN. 17/12 ZS+ fasw F^ 7 SAND AND GRAVEL (SM-GM), SILTY, COBBLES, PROBABLE w BOULDERS, DENSE, MOIST, BROWN. 50/2 1 - 0 8095 ! DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE. w w- DRIVE SAMPLE, 1 3/8-INCH I.D. SPLIT SPOON STANDARD 28/6, 50/4 PENETRATION TEST. 17/12ORIVE SAMPLE BLOW COUNT. INDICATES THAT 17 BLOWS OF 8090 A 140-POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES. 0 t REFUSAL TO DRILLING. 35/6, 50/2 NOTES - 8085 COMBINED 1. THE EXPLORATORY BORING WAS DRILLED ON FEBRUARY 28, 2017 WITH A 4-INCH DIAMETER CONTINUOUS FLIGHT POWER WC=4.3 AUGER. +4=23 -200=20 2. THE LOCATION OF THE EXPLORATORY BORING WAS MEASURED 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. 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 0 2216); +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422); -20D = PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140). 17-7-173 H-P-t KUMAR LOG OF EXPLORATORY BORING 1FLIf�1 /2 018 ASPEN BUILDING DEPARTMENT HYDROMETER ANALYSIS SIEVE ANALYSIS } Vat RGDWOS U.S.STYllullo URIC! I GUAR MARE DRNIR03 20 PM 7 NU we IPLYI 1,7 MIN YIll—HultL.1f 4UtN.__IM a/ ' 40 /Saa0/ i1a /!� M 3 3 . 1/3' 1_I:3_ ' I'C — — — _— --- —I— —I -- — Imo_ NO ID Pr: ��� ... ......mot _ 30 1 a --- —fir— t0 R a -©Mp �EM -E Cr ���CM t ___=____-.______ ..1- m iimilimi...._:____________=_,___ .• __ --,_mn I_ L1711- — ZI.1 11—T — 100 .001 .002 .00e .009 .013 .037 .073 .130 .300 I .000 1.19 I 2.30 e.73 9.9 19 39.1 70.2 127 300 I DIAMETER OF PARTICLES IN MILLIMETERS ma I CLAY TO SILT SAND GRAVEL COBBLES FINE MEDIUM COARSE FINE I COARSE GRAVEL 23 X SAND 57 X SILT AND CLAY 20 X LIQUID LIMIT PLASTICITY INDEX SAMPLE OF. Silty Sand with Gravid FROM: Boring I 0 10' & 15' (Combined) The,• 1nt re1u It op ply only to P. •amplle, which rem tested.be reproduced, The except In full tooling report •holl l, without the wrttbn ,,^ approval of Komar A Assocloles. Inc ,� Si.,. analysis Jesting Is •rtormed In 8.L occordance witn ASI 0422, ASTY C136 and/or ASTM EC. EIVED �g 17-7-173 H--P-�KUMAR GRADATION TEST RESULTS 1%. 3 '' 12/12/2018 ASPEN BUILDING DEPARTMENT H-PKUMAR TABLE 1 PERCOLATION TEST RESULTS PROJECT NO. 17-7-173 HOLE NO. HOLE LENGTH OF WATER WATER DROP IN AVERAGE DEPTH INTERVAL DEPTH AT DEPTH AT WATER PERCOLATION (INCHES) (MIN) START OF END OF LEVEL RATE INTERVAL INTERVAL (INCHES) (MIN./INCH) (INCHES) (INCHES) - J B-1 108 2 39 37'/z 11/2 1.3 37'/z 36% 1% 1.7 36'/4 351/4 1 2 35'/4 341/4 1 2 341/4 331/4 1 2 331/4 321 1 2 32% 311/4 1 2 Note: The percolation test was conducted in the completed 4-inch diameter borehole on February 20, 2017. RECEIVED 12/12/2018 ASPEN BUILDING DEPARTMENT