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HomeMy WebLinkAboutFile Documents.219 N Monarch St.0179.2017 (6).ARBKH -PKU MAR 5020 County Road 164 '� Glenwood Springs, CO 81601 GeotechMcal 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 FERER RESIDENCE 219 NORTH MONARCH STREET ASPEN, COLORADO PROJECT NO. 17-7-317 APRIL 21, 2017 PREPARED FOR: ALIUS DESIGN CORPS ATTN: MICHAEL EDINGER michael@aliusdc.com TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY ...................................... PROPOSED CONSTRUCTION................................................................................................. DESIGN I - SITECONDITIONS................................................................................................................... 1 - FIELDEXPLORATION............................................................................................................. 2 - -SUBSURFACE SUBSURFACE CONDITIONS..-'------........................................................................_..------- 2 - -FOUNDATION FOUNDATION BEARING CONDITIONS............................................................................... - 3 - DESIGN RECOMMENDATIONS............................................................................................. FIGURE 3 - FOUNDATIONS....................................................................................................................- 3 - FOUNDATION AND RETAINING WALLS........................................................................ 4 - FLOORSLABS....................................................................................................................... 5 - UNDERDRAINSYSTEM.....................................---------....................................... 6 - SURFACE DRAINAGE......................................................................................................... 6 - -LIMIDRYWELL.............................................................................................................................. 7 - LIMITATIONS TATIONS........................................................................................................................... 7 - - FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURE 4 - GRADATION TEST RESULTS TABLE I - SUMMARY OF LABORATORY TEST RESULTS TABLE 2 - PERCOLATION TEST RESULTS Project No. 17-7-317 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for the proposed Ferer residence to be located at 219 North Monarch Street, Aspen, Colorado. The project site is shown on Figure I. 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 Alius dated January 41h, 2017. A field exploration program consisting of exploratory borings 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 Geld 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 existing residence and garage structures on the property will be razed for construction of the new residence. The proposed residence will be a 1 and 2 -story stmeture with a one level basement. Ground floor will be slab -on -grade. Grading for the structure is assumed to be relatively minor with cul depths between about 4 to 12 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 proposed development area is currently occupied by a two-story residence and a single -story detached garage which will be razed prior to construction the proposed residence. The site lies at an elevation of around 7,900 feet and slopes gently down to the west. The vegetation on the site Protect No. 17-7-317 -2 - consists of a grass lawn with numerous trees in the front along Hallam and Monarch Streets and in the backyard. FIELD EXPLORATION The field exploration for the project was conducted on April 19i', 2017. Two exploratory borings were drilled at the locations shown on Figure I to evaluate the subsurface conditions. The borings were advanced with 4 -inch diameter continuous Bight augers powered by a truck- mounted CME -45B drill rig. The backyard was fenced and not accessible to the drill rig. The borings were logged by a representative of H-P/Kumar. Samples of the subsoils were taken with a P/ -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 testis 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 Logs of Exploratory Borings, 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 I to 1'h feet of topsoil overlying dense, slightly silty sand, gravel and cobble soils. Drilling in the coarse granular soils with auger equipment was difficult due to the cobbles and probable boulders and drilling refusal was encountered in the deposit. Laboratory testing performed on samples obtained from the borings included natural moisture content and gradation analyses. Results of gradation analyses performed on small diameter drive samples (minus Ilk inch fraction) of the coarse granular subsoils are shown on Figure 4. The laboratory testing is summarized in Table 1. No free water was encountered in the borings at the time of drilling and the subsoils were slightly moist. Project No. 17.7-317 -3 - FOUNDATION BEARING CONDITIONS The underlying natural granular soils are adequate for support of spread footing foundations. Existing fill from past site development will likely be encountered in the building site. The man - placed fill and debris should be removed from beneath proposed building areas down to the natural granular soils. 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 chemical grouting, micro piles and soil nails should be feasible at the site from a geoteclmical viewpoint. A shoring contractor should provide design drawings to support the proposed excavation slopes as needed. Other City requirements may also be applicable. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory borings 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 should be designed for an allowable bearing pressure of 3,000 psf. Based on experience, we expect settlement of footings designed and contracted as discussed in this section will be about I 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 meas should be provided with adequate soil cover above their bearing elevation for frost protection. Placement Project No. 17-7-317 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 10 feet. Foundation walls acting as retaining structures should also he designed to resist lateral earth pressures as discussed in the "Foundation and Retaining Walls" section of this report. 5) All existing fill, debris, topsoil 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. 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. All foundation and retaining structures should be designed for appropriate hydrostatic and surcharge pressures such as adjacent Footings, traffic, construction materials and equipment. The pressure recommended above assumes 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 H-PiKUMAR Project No. 17-7-317 -5 - 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% standard Proctor density and use of a relatively well graded sand and gravel soil can be provided to limit the settlement potential. We recommend granular soils for backfilling foundation walls and retaining structures because their use results in lower lateral earth pressures and they will improve subsurface drainage. Subsurface drainage recommendations are discussed in more detail in the "Underdrain System" section of this report. 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 bused on a coefficient of friction of 0.5. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 400 pef. 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 soils, exclusive of topsoil, am 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 expansionjoinls 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. Proiect No. 17-7317 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 rill 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 Gee -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 I % 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 I'/z feet deep. SURFACE DRAINAGE The following drainage precautions should be observed during construction and maintained at all times after the residence 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 3 inches in the first 10 feet in paved areas. Free -draining wall backfill should be Project No. 17.7-317 -7 - covered with filter fabric and capped with at least 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. DRYWELL We understand that a drywell or bio-swale may be used for site runoff detention and disposal. The Natural Resources Conservation Service has identified four hydrologic soil groups (HSG) in the Aspen area and the site is located in Type B soil having a moderate infiltration rate. Results of a percolation test performed at Boring 1 in the natural sand and gravel soils are presented in Table 2 and indicate an infiltration rate of about I minute per inch. The groundwater level and bedrock are generally known to be relatively deep in this area and should not affect drywell or bio-swale performance. LIMITATIONS This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this area at the time of the 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 borings drilled 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 subsurface conditions identified at the exploratory borings 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. P um(No. 17-7-317 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, P- KUMAR (1-) Steven L. Pawlak, P.E. Reviewed by: e- D Lt Daniel E. Hardin, P.E. r44 SLP/kac �'OF H-PEKUMAR Project No. 17-7-317 F.HALLAM STREET Y� ----------------------- BORING 1 7 Z: - ---------- ----------- - BORING 2 w -o I PROPOSED k k u RESIDENCE It _j 7Z BLOCK 72 ALLEY -------------- ------- ----------- - 10 0 10 20 APPROXIMATE SCALE -FEET 17-7-317 H-P:,WUFvlAR LOCATION OF EXPLORATORY BORING 1 BORING 2 EL. 7895.5' EL. 7896' 0 31/12 WC=1.7 40/12 +4=42 -200=6 5 76/12 72/12 +4=4 -200=B -200=6 10 50/2 15 20 DI 17-7-317 1 H-Pz-XtJ AR I LOGS OF EXPLORATORY BORINGS I Fig. 2 LEGEND ®TOPSOIL; ORGANIC SANDY SILT AND CLAY, FIRM, MOIST, DARK BROWN. SAND, GRAVEL AND COBBLES (GM-GP); SLIGHTLY SILTY, BOULDERS, DENSE. SLIGHTLY MOIST, s BROWN, ROUNDED ROCK. DRIVE SAMPLE; STANDARD PENETRATION TEST (SPT), 1 3/8 INCH I.D. SPLIT SPOON SAMPLE, ASTM D-1586. 40/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 40 BLOWS OF A 140-POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SPT SAMPLER 12 INCHES. t PRACTICAL AUGER REFUSAL. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON APRIL 19, 2017 WITH A 4-INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER. 2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE OBTAINED BY INTERPOLATION BETWEEN CONTOURS ON THE SITE PLAN PROVIDED. 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. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS 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)- 17-7-317 H-PEWUMAR I LEGEND AND NOTES Fig. 3 NTYRONCRX .VIK15R 4EVE INLLY315 M nvmde va. nua.no foNf NY SpIY¢ OPNAO ,w Jie .MJI^� Y_I I J 19. 1 14 Ir If'_' e w �s ad .. m I .wz .wz ao. aR .Ai+ OIAMETEN OF PANIIClES IN aNILWETEB54m is O a+ su R1N w CUT TO SILT EINE S MEOIUN CWDSC —WCOMSE COBBLES FINE MAL 40 X SATED 46 X SILT AND CLAY 6 X UDBID UNIT PIASTIOW INDEX SALIM OF. 511D101, Sill, San end CwRI no.: Bonn, 1 O S. XNRYYL+LR Y14RI3 SILVL .VYlYy3 M INMKC Y.F inxp.p af4s aau iw R mC.q e. nm + x.i m� u rvii 1 1 I _ 1 m F .o m I 1 — m I 1 I:IJ- ma .wa .w. e^ 'Oa+ DIAMETER OF PMTICLES IN aMILLIMETERS CUT TO SILT FINE SA NEOIDN COARSE G. FINE ----VECOMSE LOBBIES DMVEL 42 X SAINT 52 X SILT AND CUT 6 X IIOND NUN I ASTOW INOEX SANPLL OF. AIDM1XF 911, Son and Gravel FROM: B ,I,q i O 3 5- Tnw NN vwN ao» M N N. ` Few ".°Im��wr"ixI- -=—dl Nwx:ymml .LiM11lofYl. STY CnF .na/.. Xs*a owo. '� 17-7-317 H-P:KUMAR GRADATION TEST RESULTS Fig. 4 V) J W w w a a � c=i a a >w F V] Vnl O N _T L _T d w?x W zwz paw n i£f >ON U N x UW ~ Igoe N J n W m � OF W a � rW wzow UN�y7j �p l'J W Q�N naz D 2 _ Q v 0 N a J w C O W G a m (v n V 7 A Q -JNN QoW 2 � JwF K n'JW F � F p _ 450 2f,U z x 0 n C v a W N U O w J ff n z N � iLl m — — — H-R�KUMAR TABLE 2 PERCOLATION TEST RESULTS PROJECT NO. 17-7.317 HOLE NO. HOLE DEPTH (INCHES) LENGTH OF INTERVAL (MIN) WATER DEPTH AT START OF INTERVAL (INCHES) WATER DEPTH AT END OF INTERVAL (INCHES) DROP IN WATER LEVEL (INCHES) AVERAGE PERCOLATION RATE (MINJINCH) 8.1 116 2 32 221/1 9'/i 0.2 0.5 0.6 0.8 0.8 0.8 0.7 22% 18'A 4 18'% 15 314 15 12'h 2'k 12'b 10 2'h 10 7'h 21% TA 4% 3 Note: The percolation test was conducted in the completed 4 -inch diameter borehole on April 18, 2017.