The URL can be used to link to this page

Home My WebLink AboutPitkin.EH.273503402001 () (11)H G Wqlfp cfAech HEPWORTH-PAWLAK GEOTECHNICAL Hepword-A'awlak Geotechnical, Inc. 5020 County Road 154 Glenwo(A Springs, Colorado 81601 Phone: 970-945-7988 Fax: 9; 0-945.8454 email_ hpgco@hpgeotech.com SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 1, BUTTERMILK MEADOWS PUD INTERSECTION OF WEST BUTTERMILK ROAD AND BUTTERMILK LANE PITKIN COUNTY, COLORADO JOB NO.115 386A AUGUST 28, 2015 PREPARED FOR: LINDA BEDELL INNER DESIGN, INC. 309K ASPEN BUSINESS CENTER ASPEN, COLORADO 81611 innerdesiun@comeast.net Parker 303-841-7119 ; Colorado Springs 719-633-5562 • Silverthome 970-468-1989 TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY............................................................................- 1 - PROPOSED CONSTRUCTION..................................................................................... 1 - SITECONDITIONS.......................................................................................................- 2- FIELD EXPLORATION.................................................................................................- 2- SUBSURFACE CONDITIONS......................................................................................- 2 DESIGN RECOMMENDATIONS................................................................................. 3- FOUNDATIONS......................................................................................................... 3- FOUNDATION AND RETAINING WALLS............................................................ 4- FLOORSLABS........................................................................................................... 5 UNDERDRAINSYSTEM..........................................................................................- 6- SURFACE DRAINAGE.............................................................................................- 6- PERCOLATIONTESTING........................................................................................... 7- LIMITATIONS................................................................................................................ 7- FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURE 4 - GRADATION TEST RESULTS FIGURE 5 - USDA GRADATION TEST RESULTS FIGURE 6 - GRADATION TEST RESULTS TABLE I - SUMMARY OF LABORATORY TEST RESULTS TABLE 2 - PERCOLATION TEST RESULTS Job No. 115 386A G PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot 1 of the Buttermilk Meadows PUD east of the intersection of West Buttermilk Road and Buttermilk Lane. 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 Linda Bedell of Inner Design, Inc. dated August 14, 2015. 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 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 residence will be a one to two story structure with a partial basement. The attached garage and basement floor will be slab -on -grade. Grading for the structure is assumed to be relatively minor with cut depths between about 4 to 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. Job No. 115 386A -2- SITE CONDITIONS The lot was vacant at the time of our investigation and the ground surface appears mostly natural. There is significant fill for Buttermilk Road to the north. The site is located on a gentle to moderately sloping easterly facing hillside. The elevation difference across the building area is 8 to 10 feet. Scattered boulders were observed on the ground surface and the vegetation on the lot is dominated by sagebrush, scrub oak, grass and weeds. FIELD EXPLORATION The field exploration for the project was conducted on August 19, 2015. Two exploratory borings were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions for the residence. Two additional borings were drilled to characterize the soil conditions at the proposed OWTS location. The borings were advanced with 4 inch diameter continuous flight augers powered by a truck -mounted CME45B drill rig. The borings were logged by a representative of Hepworth-Pawlak Geotechnical, Inc. Samples of the subsoils were taken with 1% inch I.D. spoon sampler and 2 inch California sampler. 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 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 2 feet of topsoil overlying silty, clayey, sand and gravel with cobbles. At a depth of about 6 feet below the ground surface, the soil becomes more Job No 115 386A —�R G&tech sm rocky and less clayey. 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. 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'/s inch fraction) of the coarse granular subsoils are shown on Figures 4 and 6. 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. 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. I ) Footings placed on the undisturbed natural granular soils should be designed for an allowable bearing pressure of 2,000 psf. Based on experience, we expect settlement of footings designed and constructed as discussed in this section will be about l 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. Job No. 115 396A -4- 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 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) All existing fill, 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 soils. Cantilevered retaining structures which are separate from the residence 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 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 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 !oh No. 115 386A -5- 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 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. 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 375 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 Iateral 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, are suitable to support Iightly 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 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 Job No. i l5 396A C9 W-2 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 local area that perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can also 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 %n to a suitable gravity outlet. 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'/z feet deep. SURFACE DRAINAGE Positive surface drainage is an important aspect of the project to prevent wetting of the bearing materials. 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. Job No. 115 386A -7- 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 capped with about 2 feet of the on - site soils to reduce surface water infiltration. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. PERCOLATION TESTING Percolation tests were conducted on August 21, 2015 to evaluate the feasibility of an infiltration septic disposal system at the site. Two profile borings and three percolation holes were drilled at locations as shown on Fig. 1. The test holes were drilled with 6 inch diameter auger and were soaked with water one day prior to testing. The soils encountered in the percolation holes are similar to those encountered in the Profile Borings shown on Fig. 2 and consist of very gravelly loamy sand. The percolation test results are presented in Table II. Based on the subsurface conditions encountered and the percolation test results, the tested area should be suitable for a conventional infiltration septic disposal system. A civil engineer should design the infiltration septic disposal system. 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 borings drilled at the locations Job No, 115 386A G&bech 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. 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, HEPWORTH - PAWLAK GEOTECHNICAL, INC. C-"-< C �� Tom C. Brunner Reviewed by: Daniel E. Hardin, P. E. TCB/ksw �p Q o -L'�� Q 24443 z" 431 ONAL'E Job No. 115 386A 8070 \ APPROXIMATE SCALE �o \ 11l = 60' �o \ l ` \ BORING 2 `� \ • I \ 1 i I � 1 P3 • / / PROFILE A / BORING 2 r \ PROFILE I�BORING 1 1 0 P 1 \ \ LOT 1 11 I Fy \ \ \ \ I L lop 8050 a°6° 4 V 115 386A CeaMeK:M LOCATION OF EXPLORATORY BORINGS Figure 1 He worth—Pawlak Geotachnicd BORING 1 BORING 2 PROFILE BORING 1 PROFILE BORING 2 ELEV.= 8049' ELEV. 8046' ELEV.= 8044 ELEV.= 8037' 0 0 WC 62 16112 d 13112 10112 DD 98 9/12 WC4!=4 5 a 51112 -200 51 +4=38 -200 g 16 5 ••� �•• WC 58 5 6112 WC 6.5 50/12 +4--20 7/12 DD-95 -200 41 -200 34 • ; 50/0 �• LL q +• ;. a)' LL c. 10 .. 0 9018 67112 WC 6 8 10 a� O •4' 5010 +4 15 -200 47 15 15 Note: Explanation of symbols is shown on Figure 3. 115 386A GgRech I LOGS OF EXPLORATORY BORINGS Figure 2 HEPWOATN-PAWLAK GEo7ECNNICAL LEGEND: MTOPSOIL; sandy, silty clay, moist, brown, organic. SAND (SC); gravelly, silty, clayey, with cobbles, loose to medium dense, slightly moist, brown. e. SAND AND GRAVEL (SC -GC); silty, clayey, with cobbles, slightly moist, dark brown. oR GRAVEL (GP -GM); slightly sandy, very silty, with cobbles and possib'e boulders,very dense, slightly moist, brown Relatively undisturbed drive sample; 2-inch I.D. California liner sample. Drive sample; standard penetration test (SPT), 1 318 inch I.D split spoon sample, ASTM 0-1586. 10112 Drive sample blow count; indicates that 10 blows of a 140 pound hammer falling 30 inches were required to drive the California or SPT sampler 12 inches TPractical drilling refusal. NOTES 1. Exploratory borings were drilled on August 19 2015 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 obta ned by -nterpolat'on between contours shown on the site plan provided 4. The exploratory bor.ng locations and e'evat:ons 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 transitions may be gradua'.. 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 (%) DID = Dry Density (pcf) f4 - Percent retained on the No 4 sieve -200 - Percent passing No. 200 sieve 115 386A LEGEND AND NOTES I Figure 3 HEPWORTH-PAWLAK GE0T=H?Y1CAL rrr rr� �� rrr� rr� e� rrr� rrrr� rrr � rrr� rrr� rrrr r r. rrrr rrrrrr rr�rrn.r� rrr� rrr� ri a � rrrrl rrrr� rrr i rrrrl rrrrl rrr s r� �� rrrrl rrrr� rr� i rrrrl r� r� � r� rrrrl rrrr� iA i rrrrl rrrrl rf i r� �- rr� rrrrl rrrrl rrr� r� �� rrrr� rr� rrrrl rrrrl rrrrl rI irk �- rr� rrrrl rrrrt r� � � � rrri♦ rr� i rrrrl rrrrl � i r� �- rr� rrrrl rrrrt rrrrl � � r� ii rrr� rr� rrrrl r� rrrrl f � r� �-rr�rrrrlrrr✓rrrrl �� rr� rr� rrrrl rrrrl rrrr[ r� �— rrr irrr r� rr� nw�r� A- rr� i rrrrl rrrrl rrrrl r� �- rr� � r� rri rrrrf r� �-�� .wis � s_ rr� rrr� ri r rrr� rrr� rrr� r�rrr r� iw� ri r �� rr� i..�� r�� •� i_ ri r rrr� rrr� rrr� � rrr. � rrr,s ri r rrrr. rr� r,� � �� rrr� � ri r rwr��rrr— rir r—�w��►��irr rrr� rrr� rrr� rr �r� rrr� ii ri r rr_ rr� r�� rrr� � ri r rrr� rrr� rrr� ��rr� rr� rw� ri r r— w��sr�rrr�rrr�rir rrr� rrr� rr�, rr r�r rrr� ii ri r r_ w�� rrr� rrr� rrr�ri r rrr� rrr� �� r.er� rr� w.ww� ri r rrr� rr� �� r� rs rrr� ri r ��rrrrrr_ r�r rr� ��rr_r rrr� r�� rrr� �r � rri n� ri r ��^��rrrr =. rrr� rrr� rrr� rrrAs rrr� ri r � rr�� rrr� � r� rrr� rrr� r� r �s rrr� rrr�r rr rr.�Rrrr� ri r -�^��rr_r ri r ri i.n r� rrrrl � ri r ri r�� rrrrl ii ri � ri �� rri'ri r i• � r� rrrrl r� � r ri � r� rrrrl rrrr[ ri r rrr rrrr � ri r ri � r� rrrrl rrr� ri r � r� rr• rrrrl i� ri r ri rrr� rrr� rrrrrri r ri �rrr rr� ■.iw� ri r ri � r� rrr� rrr�ri r ri ter— rr�rirri �� rrr� rr�rr ri r rn.nr rr rr. rrw� rrr� ri r ri � r� rrr� rrrrt ri rn r.� rr� w�i rrr� ri r ri � r� rrr� rrrr ri w ri � r� rrr� rrr� � r ri r�� rrr� rrr� ^� r ri �wrrt� rrr� rrr� ri r ri �r�rri�ii�r� �r� rrw� rrr� ri r � rrr�r r�r_ rr� w� rri � r� rri rrr� ria si � r� rri rr�� ri a s_ rrr� rri rrr� ri � ire rr��rr �� ri a ri � r� i rrrrl ri r rr� ram sity 1�� ri r ri r�� rrrrl ri r ri � r� rtr� 1�Iwi ri r ri � r� rrrrl rrrrl� � r� �.��. rrrr� ri r�rr , ��. ��.r_.. ��,. rrrri � rrr ra �r��a■ � � err rr. isi i!i iai � � Ali��ri ��a��ar.�r— rrr�r�� i..w��ri � r� err✓ �i si riiai ■..�w�ar��r�ri r��r��r��iai ��a�i.r � i• � ��ri r_�r— �^�i..r.i�ri r��►- riiai r� it r�i�i s i r��i-�� -.��ri ri illr•r iw i•i-r�ri � � � rrrrrrrr� r�i.-fir ri i•iri � i♦ � � iii ��rrrr��itr�r� i�ri iri ��iirrr��i�,�Ai��ri ��i�r�ri r�s�-�r-��iri ri �i�r� ��ir•rr�rw�w�ws��ri ��i-�Wrrrip.lw��iri ri riirr� ��i�r-i•�►--�lri ��i�rrr�ri� �r�r•rrrr�wi�iri �i�i ��i�r�i•-.�-rrr�ri��i�i ��i-��-I�-�ri rr�rrr�wr� i� �rrr��rrirr�ri i♦�iri rrr� r� i rrrr� rr� � � � err �r.r.r� r� �R � ri i r i i•��r�i•��5-rrr�ri�i�r��i ��-r��i�r��iri rrirr r� � �w ��rr � � � i r� rrrr� rrrrrr��riiri rrr� � � rrrr �� w i �� i��rrrr�rr��irr�A�i r� rrrr a r� � ^� sew ww� � �. i.� rrr•� r� � � � � rrr� rrrr� ^ram s � ri i r i � � ir_ � i r i �rrrri��r�r�r��^w��riiri rrr�rr�i�rirrrr �w��rrr��r��ri rr� ��ww��ri rr_ iAi riir� ��w�ri��i��r��r��.rwrriri r��i�i.�' �wnw� � � � ��wn.nw��ri�irr� rr�. � rrr� � � � errs �� i r i r��a�r�r—��r�r��r��riri�ir� r•��a��rr��ri�r�iri � � i r� ��r�•�ri��rrr.r�t�w��iri r� �r wr_r nn.r•r r� � ri � i� rrr r �� rrr rrr_.��a��rr�r�^i ^�rrrr r�r��-�---r_ r_rr i��r�w��r�rrrri��r�r�riiwi �rw�siri ��i��rrrr�w��iri ��'-�5��-�i•-�i�i ��Ir��s��i�ri i��/�i_�ri��rrrrr�rii�iAiri i•��i�i �� S-�5��i�riiri ��w�-�i��-��i�i rrr� �i-�Sr�r� i�rsi�i a co m lli O z m 0 13 (3 co z J J V1 U � z Cl) = W U LU w 0 Lea a-j0 'J CO m a U. ' 0 o a a UJ :3 _ V) �. w co cts cts O x —'' E IX c ca >, ,� m C� co cis v] v] va o� u' W O paW a ZOO �U U g� O a W F J F U � N 7 VN Lu CLM ZO a < I M M f G 0 a o C9 J a woZ a w z a W H w e N N o0 GO a o z0 �o �o to Z20 d W to N Ln N C U 0 0 HEPWORTH-PAWLAK GEOTECHNICAL, INC. TABLE 2 PERCOLATION TEST RESULTS JOB NO. 115 386A 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) P1 24 15 6 5 % % - f 30 5 % 4% '/2 4% 4% '/2 4% 3% % 3% 3 1/4 % 3'/. 2 % '/2 P2 22 15 Add Water 6 4'/4 1 % 30 4% 3% 1 5 % 4% 1/2 4% 4 '/A '/2 4'/, 3% % 3% 3 "/a % P3 18 15 Add Water 6 4% 1 "A 30 4% 4 % 4 3'/, % 5'/4 4% % 4% 4 '/4 % 4% 3% % Note: Percolation tests were conducted on August 21, 2015. The average percolation rates were based on the last three readings of each test.