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HomeMy WebLinkAboutFile Documents.121 E Hyman Ave.0149.2018 (88).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 Silverthome, Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED CRAWLSPACE ADDITION 121 EAST HYMAN STREET ASPEN, COLORADO PROJECT NO. 18-7-737 JANUARY 30, 2019 PREPARED FOR: MENENDEZ ARCHITECTS ATTN: LUIS MENENDEZ 715 WEST MAIN STREET, UNIT 104 ASPEN, CO 81611 (lam@menenctezarchitects.com) Reviewed by Engineering 03/18/2019 1:39:58 PM "It should be known that this review shall not relieve the applicant of their responsibility to comply with the requirements of the City of Aspen.The review and approval by the City is - offered only to assist the applicants understandingremt ." o the applicableceofpEermit ase RECEIVED requirements."The issuance of a permit based on construction documents and other data shall not prevent the City of Aspen from requiring the correction of errors in the construction 0 2/2 8/2 019 documents and other data. ASPEN BUILDING DEPARTMENT TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - PROPOSED CONSTRUCTION - 1 - SITE CONDITIONS - 2 - 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 - 5 - SLOPE STABLIZATION - 6 - DRYWELL - 6 - LIMITATIONS - 7 - FIGURE 1 - LOCATION OF EXPLORATORY BORING FIGURE 2 - LOG OF EXPLORATORY BORING FIGURE 3 - GRADATION TEST RESULTS RECEIVED H-P KUMAR Project No. 18-9g/2 8/2 019 ASPEN BUILDING DEPARTMENT PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed crawlspace addition to the existing residence located at 121 East Hyman Street, 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 proposal for geotechnical engineering services to Menendez Architects dated December 11, 2018. Hepworth-Pawlak Geotechnical (now H-P/Kumar) previously evaluated the bearing soils at the site for foundation design of the existing building and presented the findings in a report dated January 7, 1999, Job No. 198 777. 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 addition 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 crawlspace addition will be below the northern part of the existing basement and include a drywell below the southern part of the basement. The footprint of the existing building will essentially not change. The existing building is a 2-story structure with a footprint as shown on Figure 1 overlying a basement which encompasses nearly the entire lot. Ground floor of the crawlspace addition will be slab-on-grade. Grading for the structure will be relatively extensive considering the closeness to existing spread footing foundation with a total cut depth of about 17 feet below the ground surface of the lot. Excavation slope stabilization by grouting is tentatively proposed to maintain cut slope stability. We assume relatively light to moderate 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. RECEIVED H-P KUMAR Project No. 18-la 2 8/2 019 ASPEN BUILDING DEPARTMENT - 2 - SITE CONDITIONS The existing residence is a 2-story structure above a full basement and the west unit of a duplex as shown on Figure 1. The lot is essentially covered with building structure(basement level)to within about 5 feet of the property lines. The terrain was nearly flat with a gentle slope down to the northeast. On the south side of the driveway off the alley is asphalt pavement. Landscape vegetation borders the west and north sides of the lot. FIELD EXPLORATION The field exploration for the project was conducted on January 8, 2019. 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 H-P/Kumar. Drilling access closer to the proposed addition area was not possible due to the existing basement level of the structure. Samples of the subsoils were taken with a 1% inch I.D. spoon sampler. The sampler was 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, consist of gravel foundation wall backfill to a depth of about 14 feet overlying relatively dense, slightly silty sand, gravel and cobbles with possible boulders. Drilling in the coarse granular soils with auger equipment was difficult due to the cobbles and possible boulders. The natural granular soils encountered in the boring are consistent with those identified during the previous soils evaluation for the existing structure. Laboratory testing performed on samples obtained from the boring included natural moisture content and gradation analyses. Results of gradation analyses performed on a sample(minus 1%2-inch fraction) of the coarse granular subsoils are shown on Figure 3. RECEIVED H-P KUMAR Project No. 18-O /2 8/2 019 ASPEN BUILDING DEPARTMENT - 3 - 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 below the foundation wall backfill are adequate for support of spread footing foundations. Man-placed fill and debris from previous site development should be completely removed from beneath the proposed addition area. The addition as planned is slab-on-grade and structural fill can be used to backfill below slab areas and as foundation wall backfill after rock larger than about 3 inches and debris have been removed. The excavation slopes will need to be stabilized such as with grouting to maintain stability and to not undermine the existing foundations or laid back to a stable grade consistent with OSHA requirements for confined excavations. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory boring and the nature of the proposed construction,we recommend the building addition 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 4,000 psf. Based on experience, we expect settlement of footings designed and constructed as discussed in this section will be relatively 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 (if any) 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 to anomalies such as byassumingan unsupported length of at least 10 feet. CEIVED pP � H-P KUMAR Project No. 18-9A 2 8/2 019 ASPEN BUILDING DEPARTMENT -4 - 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) All existing fill and debris from previous site development, 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 as needed. 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 45 pcf for backfill consisting of the on-site granular soils. Cantilevered retaining structures which are separate from the residence(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. All foundation and retaining structures should be designed for appropriate hydrostatic and surcharge pressures such as adjacent footings, construction materials and equipment. The excavation cut slope stabilization should consider potential surcharge from existing foundations near the addition including the drywell. 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 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 E IVE 0 H-P=KUMAR Project No. 18-9 2 8/2 O 19 ASPEN BUILDING DEPARTMENT - 5 - backfill should be expected, even if the material is placed correctly, and could result in distress to facilities constructed on the backfill. 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 are suitable to support lightly loaded slab-on-grade floors. To reduce the effects of some differential movement, non-structural 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 crawlspace 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 RECEIVED H P KUMAR Project No. 18-94 2 8/2 019 ASPEN BUILDING DEPARTMENT - 6 - 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 drywell outlet 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%2 feet deep. SLOPE STABLIZATION The City of Aspen requires an engineered excavation slope stabilization plan if proposed foundations are within 15 feet of neighboring structures or public travel ways. The plan is not required if excavations are less than 5 feet below the existing grade or further than 15 feet from travel ways and less than 15 feet deep. The proposed building addition area is below the existing basement and slope bracing could be required depending on the addition location, size and excavation depth. Excavation slope bracing through use of a variety of systems such as grouting, micro-piles and soil nails should be feasible at the site. A shoring contractor should provide design drawings to support the proposed excavation slopes where needed. Other City requirements may also be applicable. DRYWELL 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 and subsurface water treatment and disposal as needed. We understand percolation testing has been performed by others and the resulting infiltration rate indicated the drywell is feasible for water disposal. The bedrock is generally known to be relatively deep in this area and groundwater level was not encountered to the boring depth of 20 feet. The drywell should have solid casing down to at least footing bearing grade of the lowest level (new crawlspace) and perforation below that level. In our opinion, the proposed drywell located near proposed or existing foundations will not adversely impact bearing condition of the natural granular soils. We should observe the soils encountered in the drywell excavation for possible variations iE C'EIVED subsurface conditions and the need for modifications to the foundation or drywell construc on. H-P KUMAR Project No. 18-P5i 2 8/2 019 ASPEN BUILDING DEPARTMENT - 7 - 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 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 Steven L. Pawlak, P.E. Reviewed by: Daniel E. Hardin, P.E. 24443 2. SLP/kac �' oli-3tf(`Z.��? Cc: Kollar Engineeri �: e erniekollar(a gmail.com) RECEIVED Hansen Construction ' ke(justin@hansenhomecare.com) H-P KUMAR oject No. 18-9-?34 2 8/2 019 ASPEN BUILDING DEPARTMENT F,i EA,' HYMAN HUE •\ 1 p oo ' OE CO tVI . r 5 ',I I a .� t;t 5.1 p, Ea i 8 hm Rolls., „„•.~.•.✓ 1.0/ ; r a IT i,Z`iii .aa . u u °" — — 1. ,1. it� e ltu t �, �,� ito 01 a r _.; / • nnr�Yl�i._ k, , �1mP l■■ra■lJfil Ili• 1 \\ I •t Sri millI11•,P'III en.a. , igi gig oil.114WilltiIin:_i;�•a!! \ + i 0 iii �im i r �'I'I iiI a � �" ��`. 121 EAST 4 vti:„ 7 ti. HYMAN AVE. ~�`\ ►l.• ,g ��6 i:7 �, a � InnId�`` gg '© ."j, o 1 9l k !f'trl r '� ' 4 . r,Il�x 1. lal 11 0 c I : ! .- it I •n PERK alb ." w.+ a V.,,-1 ,! I,1 .1 i t-11 i''`,,, ,, 1 r.i 1.1 ILI[lfll.-' - - tI _I �i a ,� J ~ • 1I[1IyIlII�1�,�iItIII ,1)4, -� .. 1 I �s Fr! I X `�,ALEY BLOCK 89 w„ —• ' • t a e A i s 1 tI 10 0 10 20 ; APPROXIMATE SCALE—FEET ¢i 18-7-737 - H—P-KUMAR LOCATION OF EXPLORATORY BORINGwtivED o2/2872019 ASPEN BUILDING DEPARTMENT BORING 1 LEGEND EL. 7911' 0 (3),— (3) ASPHALT, THICKNESS IN INCHES SHOWN IN PARENTHESES (5)raw, TO LEFT OF THE LOG. -1 (5) t 'Y AGGREGATE BASE COURSE, THICKNESS IN INCHES SHOWN IN 4/12 • PARENTHESES TO LEFT OF THE LOG. FILL: SCREENED GRAVEL BACKFILL, SCATTERED DEBRIS, 5 50/5 SLIGHTLY SILTY, LOOSE. METAL PIECE ENCOUNTERED AT 5' DRIVE SAMPLE. GRAVEL DENSE, MOIST, BROWN,BROUNDED ROCK. SLIGHTLY SILTY, 10 • DRIVE SAMPLE, 1 3/8-INCH I.D. SPLIT SPOON STANDARD a ♦ PENETRATION TEST. nw I DISTURBED BULK SAMPLE. IL A /12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 4 BLOWS OF 15 A 140-POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES. DEPTH AT WHICH BORING CAVED. WC=2.9 +4=54 20 -200=7 NOTES 1. THE EXPLORATORY BORING WAS DRILLED ON JANUARY 8, 2019 WITH A 4-INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER. 2. THE LOCATION OF THE EXPLORATORY BORING WAS MEASURED APPROXIMATELY BY TAPING 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 D 2216); +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422); -200 = PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140). i a6 f 18-7-737 H-P~KUMAR LOG OF EXPLORATORY BORING RErEIVED 02/28/2019 ASPEN BUILDING DEPARTMENT HYDROMETER ANALYSIS SIEVE ANALYSIS TIME READINGS U.S. STANDARD SERIES CLEAR SQUARE OPENINGS 24 NRS 7 NRS 100 45 INN J5 YIN WHIN 19vIN 4MIN 110N 4200 1t00 ISO A10#0 e 6 IT A .4 3/j' 3 4" 1 2" 3 ',' 0'O I — t 90 - 1__ 1 — T --_ Al1 - 10 — — _ — _ — I - I — A NO - L- 1 l 20 — _—_ - 1 1 _ 70 ( 30 I I-- - I I ieD _-1 ___I____ I ' 40 g 50 — _ I _ I So M .4- 1 T1 49 I 1 60 t I--- 30 _ 70 20 _ _ I T - 1.i 60 10 ~ 90 0 I I fir I I— 1 1 1 1 1 1 1 1 I 111 1 1 1 1 I 1 1 r I I I UI I 1 1 1 1 1 1 1 1 1 100 .001. .002 .005 .009 .019 .037 .075 .150 .300 I .600 1.19 12.36 4.75 9.5 19 36.1 76.2 127 200 .425 2.0 I DIAMETER OF PARTICLES IN MILLIMETERS 152 CLAY TO SILT SAND GRAVEL COBBLES FINE MEDIUM COARSE FINE COARSE GRAVEL 54 % SAND 39 % SILT AND CLAY 7 Yo LIQUID LIMIT PLASTICITY INDEX SAMPLE OF: Slightly Silty Sandy Gravel FROM: Boring 1 0 18'-20' 4 c, i Y EThese teat results apply only to the samples which were tested. The testing report shall not be reproduced. 8 except In full, without the written 5g approval of Kumar& Associates, Inc. 7 0 Sieve analysis tostIng is performed In D accordance wIth ASTM D422, ASTM C136 >g and/or ASTM D1140. $Er0EIVE t; 18-7-737 H- tiKUVAR GRADATION TEST RESULTS g .02/26/2019 ASPEN BUILDING DEPARTMENT