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Home My WebLink AboutDRB140055 Subsoil Study signed �� ,.'_t.'4_ iui} l i,l !�i I �.�.i �J�c'IlRioi)_�ti� I]Cl�. �.u�if�'�i��U�ti�ll)l�� 1��1�1I11': �`)(��_�')-��-P�)�i� HEPWOR�"H-PAV�JCAK G�OTEChINICAL F.�.-: ��r��.<�a;_:;:�� I� Received TO WN QF VAJ I.�� By Lynne Campbell at 1:40 pm,Mar 1Q 2014 DRB140055 SUBS�IL STUDY FOR FOiJNDATIQN DESYGN P1�qPOSED STOCICN�AR DUPLEX L�T 14, SIGHORI�I SUI3IlIVi�i(3i�i 4096 COLLTMIiINE DRIVE VAIL, COLORADO JOS N�. 113 449A DECEMBER 31, 2013 FREPARED FQR: SC+QTT S. TLTRlrTIPSEED, AIA ATTN. AL�CIA DAVIS P.4. �3�X 33$8 EAGLE, COLORADO $1631 �l�1Cl1i(ll'SS�.�I:i,C.PJ}ll P��ckee iC73-8�}1-711'�) • �C��l��a�l�� S�,o�inys 719-633-55E�Z a �il��z-tliarne �)70-46��-19�9 TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY..........................................................................- 1 - PROPOSED CONSTRUCTION..................................................................................- 1 - SITECONDITIONS...................................................................................................: 2 - GEOLOGICCONDITIONS.........................................................................................- 2 - FIELDEXPLORATION..............................................................................................- 3 - SUBSURFACE CONDITIONS...................................................................................- 4 - FOUNDATION BEARING CONDITIONS.................................................................-4- DESIGN RECOMMENDATIONS............................................................................... 4 - FOLJNDATIONS......................................................................................................-4 - FLOORSLABS .......................................................................................................- 5 - UNDERDRAINSYSTEM........................................................................................- 6 - SURFACEDRAINAGE..........................................................................................: 7 - LIMITATIONS .....................................................................................................:......- 7 - REFERENCES............................................................................................................: 9 - FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURE 4- GRADATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for the proposed Stockmar duplex to be located on Lot 14, Bighorn Subdivision, 4096 Columbine Drive, Vail, 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 Scott S. Tuinipseed, AIA dated December 3, 2014. 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 field exploration and laboratory testing were analyzed to develop recommendations for foundation types, depths and allowable pressures for the proposed building foundation. This report summazizes 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 duplex will be a 2-story structure with a garden level basement. Ground floor will be slab-on-grade. Grading for the structure is assumed to be relatively minor with cut depths of about 4 feet. We assume relatively light foundation loadings, typical of the proposed type of construction. The existing duplex will be razed for the new 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. Job No. 113 449A � C-,�PteCn - 2 - SITE CONDITIONS The lot is occupied by a one and two story duplex located as shown on Figure 1. The ground surface is relatively flat with a gentle slope down to the west across the building site. A small drainage channel crosses the north side of the lot and discharges to Gore Creek which follows the west side of the lot at roughly 5 to 6 feet lower in elevation. The channel is the outlet for a small pond located on Lot 19 across Columbine Drive to the east of the subject site. Vegetation consists of grass, weeds and landscape trees. One to two feet of snow covered the property at the time of our field exploration. GEOLOGIC CONDITIONS Review of the Town of Vail's official geologic hazards maps(Town of Vail, 2000a, 2000b and 2000c) indicates that potential snow aualanche and rockfall hazards are present on and in the vicinity of Lot 14. Potential debris flow or debris avalanche hazards do not impact the lot. Snow Avalanche: The proposed duplex on Lot 14 is located in the lower part the "Possible Avalanche Influence Zone" from the start area located on the valley side to the southwest of the subject site. The snow avalanche hazards zones were defined before construction of the existing residences. The existing residences located to the southwest of Gore Creek will act as snow avalanche retarding structures and will shorten the snow avalanche runout distances and reduce the risk to the proposed development on Lot 14. Considering the above, in our opinion, the proposed duplex on Lot 14 is located beyond avalanche impact area and the risk of snow avalanche reaching the proposed duplex is low. If this low risk is not acceptable to the building owners then snow avalanche risk mitigation should be feasible without increasing the potential risks to nearby properties. Rockfall: The proposed duplex on Lot 14 is located in the lower part of a High Severity Rockfall Hazard Zone. The mapped runout limit for the rockfall hazard zone is located 1ob No. 113 449A GeUPtGCh - 3 - along Columbine Drive to the northeast of the proposed duplex on Lot 14. The rockfall hazard zone has not considered the influence of the existing buildings to the southwest of Gore Creek on the rockfall hazard but these buildings should reduce the risk to the proposed duplex on Lot 14. Rock blocks associated with past rockfalls were not observed in the vicinity of the project site but evidence of past rockfall, if present, may have been removed by prior construction grading. Snow cover at the time of our field review in December may have concealed rockfall blocks on-site. Several rockfall blocks are visible within and uphiil (west) of Gore Creek in the project area. Considering the limited number of rockfall blocks in the neighborhood of Lot 14 across Gore Creek, in our opinion, we estimate the rockfall severity to be moderate. If a future rockfall were to hit the proposed duplex or other existing building in the neighborhood, it is likely that it would result in severe damage to the structure and hann to the building occupants. If this moderate rockfall risk is not acceptable to the building owners or government regulatory agencies then additional site specific rockfall study will be needed to evaluate the potential rockfall risk and feasibility of possible mitigation methods to reduce the risk. FIELD EXPLORATION The field exploration for the project was conducted on December 17, 2013. Two exploratory borings were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions. The borings were advanced with 4 inch diameter continuous flight augers powered by a truck-mounted CME-45B drill rig. The borings were logged by a representative of Hepworth-Pawlak Geotechnical, Inc. Samples of the subsoils were taken with a 1'/8 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 Logs of Exploratory Borings, Figure 2. The samples were returned to our laboratory for review by the project engineer and testing. Job No. 113 449A GG(�tGCh - 4 - SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils consist of about one foot of organic silty sand overlying dense, silty sandy gravel with cobbles and boulders to the drilled depth of 5 to 5%z feet. Drilling in the dense granular soils with auger equipment was difficult due to the cobbles and boulders and drilling refusal was encountered in the deposit. Boring 2 was drilled through the existing asphalt paved driveway. 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 1'/z inch fraction) of the coarse granular soils 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 to moist. FOUNDATION BEARING CONDITIONS The natural gravel soils are suitable to support shallow spread footings with moderate bearing capacity and low settlement potential. The planned garden level basement excavation will likely remove debris and old fill from the existing duplex development. Groundwater was not encountered to the drilled depth of about 5 feet but could be encountered at seasonally high water level time of the year. The lower level of the new structure should be protected against potential groundwater level rise. 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. Job No. 113 449A � C�UeteCh - 5 - 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 about 1 inch or less. 2) The footings should haue 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 48 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 a lateral earth pressure corresponding to an equivalent fluid unit weight of at least 50 pcf. 5) The 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 compacted. If water seepage is encountered, the footing areas should be dewatered before concrete placement and we should be contacted for additional consultation. 6) A representative of the geotechnical engineer should observe all footing excauations prior to concrete placement to evaluate bearing conditions. 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 Job No. 113 449A C�CPteCh - 6 - 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 neaz 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 the groundwater level can rise and 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 and garden level 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 least 1.5 feet below lowest adjacent finish (basement floor slab) grade and sloped at a minimum %2 % to outlet above the flood level of Gore Creek. Due to the flood level of Gore Creek, pumping of the underdrain system will likely be required. 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 maacimum size of 2 inches. The drain gravel backfill should be at least 1%z feet deep. The under slab lob No. l 13 449A GecPtECh - � - gravel should be connected to the perimeter foundation drain with interior lateral drains placed at about 15 feet center to center. SURFACE DRAINAGE The following drainage precautions should be observed during conshuction and maintained at all times after the duplex 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 standazd 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 azeas and a minimum slope of 3 inches in the first 10 feet in paved azeas. Free-draining wall backfill should be 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 wananty either express or implied. The conciusions 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. Job No. 1 l3 449A G�cPtGCh - 8 - 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 explorato�y borings and variations in the subsurface conditions may not become evident until excavation is perfonned. If conditions encountered during construction appear different from those described in this report, we should be notified so that re-eval_nation 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 inodifications 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, HEPWORTH - PAWLAIC GEO ICAL, INC. ��N+`.r`'Pq. f.;�•.��ej� •• � , o , *: 15222 :x' Steven L. Pawlak, P.E. ;..��3// ��: Reviewed by: i1'l9:�;'oNa��;:,Pp� jf OF.�04 0 ��r'�`"-�.�,+... Daniel E. Hardin, P.E. SLP/ksw cc: Samelson Development— Les Samelson (le�� - '� i _;:i;i) Job No. I 13 449A C��h _ 9 _ REFERENCES Town of Vail, 2000a, Official Avalanche Hazard Map, Town of Vail: Prepared by the Town of Vail, Vail, Colorado (Adopted by the Town Council on October 17, 2000). Town of Vail, 2000b, Official Debris Flow Hazard Map, Town of Vail: Prepared by the Town of Vail, Vail, Colorado (Adopted by the Town Council on October 17, 2000). Town of Vail, 2000q O�cial Rockfall Hazard Map, Town of Yail: Prepared by the Town of Vail, Vail, Colorado (Adopted by the Town Council on October 17, 2000). Job No. ]13 449A C�CPt2Ch � APPROXIMATE SCALE (''��''�C=tcF� 1" = 30' � � � � � 83g8 �� \ � � 1 � —`pQ � � � I � � —�_ �� ' - - - - � i 8402_ �� - - - - - - - � \ � —�� 100 YEAR FLOOD LINE�^ � � _ �\ � � i \\ \` �� \ 8404 � I ,� � � � EXISTING � � / �' � BORING 1 � � DUPLEX / � / 8406 �� • / � 8402 � / l� �/� 8408� �� UNITB UNITA � / � / / fi � � � � � � 8410� \ �� / � / /� � I \ �� //� /� 8404 � I\ � � � �li�i i / i \� GARAGES �� / /i�/ � � � ,/ �i�i � � I � - - \ %/ /`/ �/ /� 8406 1 � � LOT 14 � � � LOT 15 1 / � BORING 2 � � I � / / � (FIRE STATION) / � � I � � � o \ �� \ \� �-� / j � —� �� / J � � _ � \ \ � 8408 �410 COLUMBINE DRIVE 113 449A � C78p1�@Ch LOCATION OF EXPLORATORY BORINGS Figure 1 He worth—Pawlak Gaotechnical BORING 1 BORING 2 ELEV.= 8405' ELEV.= 8408' 0 p 44/12 50/5 � b: WC=6.5 �° +4=29 m �•. ��: -200=21 � ii 98/10 �� 36/12 °� 5 �� .•�,� � � WC=4.1 •Q: 5 a +4=43 '� °� � '200=12 � � O �� 10 Note: Explanation of symbols is shown on Figure 3. H 113 449A �7Q h LOGS OF EXPLORATORY BORINGS Figure 2 He worth—Pawlak Geotechnical LEGEND: � ASPHALT PAVEMENT; Boring 2, about 3 inches thick. � SAND (SM); silty, with gravel, slightly organic, firm, moist, dark brown. o•: GRAVEL, COBBLES AND BOULDERS (GM); silty, sandy, dense, moist, brown, subangular to subrounded rock. ■ Drive sample; standard penetration test (SP�, 1 3/8 inch I.D. split spoon sample,ASTM D-1586. r 34/12 Drive sample blow count; indicates that 34 blows of a 140 pound hammer falling 30 inches were required to drive the SPT sampler 12 inches. � Practical drilling refusal. Where shown above bottom of log, indicates that multiple attempts were made to advance the boring. NOTES: 1. Exploratory borings were drilled on December 17, 2013 with 4-inch diameter continuous flight power auger. 2. Locations of exploratory borings were measured approximately by pacing from features shown on the site plan provided. 3. Elevations of exploratory borings were obtained by interpolation between contours shown 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 beiween materials shown on the exploratory boring logs represent the approximate boundaries between material types and transitions may be gradual. 6. No free water was encountered in the borings at the time of drilling. Fluctuation in water level may occur with time. 7. Laboratory Testing Results: WC = Water Content (%) +4 = Percent retained on the No. 4 sieve -200 = Percent passing No. 200 sieve 113 449A �'�,Ch LEGEND AND NOTES Figure 3 He worth—Pawlak Geotechnical Q � � ¢ � (� � v � p u � C/1 0 O � � .-�i o y o m � ti � v� C7 �' �' � � o � z � � — � c� zzz �n O a ' Z � N ] O U N Z � �' x 1- w J' VI 1' Q � 2,: a W � a ? V K � � z t~/1 w = W m F- U �— w � H K ¢ o � � � d � a J Y � J `� � O � w m Z Z j � g w � w N � Q m � � o � cv Q. 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