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HomeMy WebLinkAboutSubsoil Study for Foundation Design 07.31.2008HEPWORTH - PAWLAK GEOTECHNICAL [:le[.rvo¡th-l)arvlak ( ìerrteclurical, Inc 5tl]0 (ìrunrv Ro¡rl Ii4 ( ìlcttrvotxl Springs, ( ìrkr':rtlt: lJ I (rtlI l)l ì( )rìc: ()7(l-()4 5 -7()¿ìiì Irrìx : r)7tr-()45-S4 54 eruuil: l4.getúÐlrpgct rtcch.ctxu H $ü4,iluNffiffi O =+-7.= t'-- u-c., .O (fF3 = -,, a.i gv t.r--;ô., '=Ò17 v.z5l) l- c ',1-<E SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 5, MONUMENT CREEK VILLAGE, SECTION ONE 577 PONDEROSA CIRCLE BATTLEMENT MESA, COLORADO JOB NO. 108 391A JULY 31, 2008 PREPARED FOR: CIMARRON LAND & HOMES,LLC ATTN: BILL WILDE 73 SIPPRELLE DRM, SUITE E-3 BATTLEMENT MESA, COLORADO 8163s i'arkcr 3tll-¡ì41-7I l9 o ()olorurkr Springs Ilt).6\)-5567 . Silvertllrure 970-4(18-l9t'ì9 TABLE OT'CONTENTS PURPOSE AND SCOPE OF STUDY PROPOSED CONSTRUCTION SITE CONDITIONS. FIELD EXPLORATION SUBSURFACE CONDITIONS DESIGN RECOMMENDATIONS ............... FOI.'NDATIONS FLOOR SLABS. SURFACE DRAINAGE .............. LIMITATIONS.... FIGURE I - LOCATION OF EXPLORATORY BORING FIGURE 2 - LOG OF EXPLORATORY BORING \ FIGURE 3 - LEGEND AND NOTES FIGURE 4 - SV/ELL-CONSOLIDATION TEST RESULTS 1 I 2- 2- 2- C) =o> ı= ¿- a- =>.N: o(d ã:o ^ .= .c =ôl> .ì :+:i ¡r '-- .9 rPo 9> .:! u¡.o <Ë J 3 4 5 5 PURPOSE AI\D SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot 5, Monument Creek Village, Section One,577 Ponderosa Circle, Battlement Mesa, Colorado. The project site is shown on Fþre 1. The purpose ofthe studywas to develop recommendations for the foundation design. The study was conducted in accordance with our proposal for geotechnical engineering services to Cimarron Land & Homes, LLC dated July 3, 2008. An exploratory boring was drilled on the lot to obtain information on the general 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 t¡res, depths and allowable pressures for the proposed building foundation. This report summarizes the\ata obtained during this study and presents our conclusions, design recommendations and other geotechnical engineering considerations based on the proposed construction and the subsurface condit ions encount ered. PROPOSED CONSTRUCTION The proposed residence will be a tri-level wood frame structure with an attached garage. Ground floor will be structural over a crawlspace for the living area and slab-on-grade in the garage. Grading for the structure is assumed to be relatively minor with cut depths between about 3 to 5 feet. We assume relatively light foundation loadings, typical ofthe proposed tlpe of construction. If building loadings, location or grading plaus change sþificantly from those described above, we should be notified to re-evaluate the recommendations contained in this report. C) =.e7 7-1=-ı .! l5 U Od 7 zt, a .IY'h o cvd^ =Õì¿ al ':Ô¿ //-?uY> .:.!) ¿¡..a)<ã JobNo. 108 39lA cÆtecrr -2- SITE CONDITIONS The site was vacant at the time of our field exploration. There could be some minor filI on the lot from overlot grading as part ofthe subdivision development. The ground surface slopes moderately down to the west. Vegetation consists of grass and weeds. FIELD EXPLORATION The field exploration for the project was conducted on húy 22,2008. 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-458 drill rig. The boring was logged by.a representative o f Hepworth-Pawlak Geotechnical, Inc. Samples ofthe subsoils were taken withl% inch and 2 in$ I.D. spoon samplers. The , samplers were driven into the subsoils at various d€pths 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 ofthe 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 ofthe subsurface conditions encountered at the site is shown on Figure 2. The subsoils consist of about tÁ foot of topsoil and l0% feet of stiffto very stif{, sandy clay and silt overlying relatively densen basalt gravel, cobbles and possible boulders in a sandy silt and clay matrix to the drilled depth of 15 feet. Drilling in the bæalt rock soils with auger equipment was difficult due to the size and hardness ofthe basalt rock and drilling refusal was encountered in the deposit. O = 7.=ı-+=J.u-c !osi -. .=YØ ıâ =.1 -f= ct Í7 8.. ç,= v,QØ;+ã= JobNo. l0839lA eåStecn 3 Laboratory testing performed on samples obtained from the boring included natural moisture content and density. Results of swell-consolidation testing performed on a relatively undisturbed drive sample of silt, presented on Figure 4, indicate low compressibility under conditions of loading and wetting. No free water was encountered in the boring at the time of drilling and the subsoils were slightly moist. DESIGN RECOMMENDATIONS FOTINDATIONS Considering the subsurface conditions encountered in the exploratoryborirrg and the nature of the proposed mnstruction, we recommend the building be founded with spread footings bearing on the natural subsoils. \ The design and construction criteria presented below should be observed for a spread footing foundation system. l) Footings placed on the undisturbed natural subsoils should be designed for an allowable bearing pressure o[500 p$ Based on experience, we expect settlement of footings designed and constructed as discussed in this section will be about 1 inch or less. There could be some additional movement of footings ifthe bearing soils become wet. 2) The footings should haveaminimumwidthof l8 inches forcontinuous 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 leÍ!S..3éjlgþs below exterior grade is t¡lpically 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 () = ,= d* I:- 4)¿c f.{ * .t 0d 7zool Ò i ar >7_ 9r¿'!> 5fr 1: t, -i) 4E JobNo. 108 3914 c$tecll -4- designed to resist a lateral earth pressure coffesponding to an equivalent fluid unit weight of at least 55 pcf Resistance to sliding at the bottoms of the footings can be calculated based on a coefficient of friction of 0.35. Passive pressure of compacted backfill against the sides ofthe footings can be calculated using an equivalent fluid unit weight of 300 pcf A perimeter under drain should not be needed for the proposed shallow crawlspace provided that good surface drainage is maintained around the house as desgibed below. The topsoil and any loose or disturbed soils should be removed and the footing bearing level extended down to the natural soils. The exposed soils in footing area should then be moistened and compacted. A re'presentative ofthe geotechnical engineer should observe.all footing excavations prior to concrete placement to evaluate bearing änditions. FLOOR SLABS The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab- on-grade construction. The clay and silt soils have variable settlement potential which could result in some slab movement if the bearing soils become wetted. 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 slab use. A minimum 4 inch layer of sand and gravel, such as road base, should be placed beneath interior slabs-on-grade for subgrade support. This material should consist ofminus 2 inch aggregate with at least 50%o rda¡ned on the No. 4 sieve and less than 12o/o 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 ofthe on-site soils or suitable imported granular fill devoid ofvegetatior¡ topsoil and oversized rock. O = -= r'_- D. l'.1 "t od = ^,, ^ .:Yt ô = cì , at :+ð., '=a .=' tJú.,c) .a. 'ã s) 6) JobNo. l0839lA cåFte*' -5- SURFACE DRAINAGE The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: 1) Inundation ofthe 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 95o/o of tIrc 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 ofthe 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. 4) Roofdownspouts and drains should dischafue well beyond the limits of all backfill. 5) Irrigation sprinkler heads and landscaping which requires regular heavy irrigation, such as sod, 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 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 ofpractice should be consulted. Our findings include extrapolation ofthe subsurface conditions identified at (J = =ta J.- D.c ñ-c'-O 2cn a.I c > at - _1]' c'lf. >7 v.>.:l Eú..() ¡t: JobNo. 108 3914 cå5tecr¡ -6- 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 ofthe 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 construstion to review and monitor the implementation of our recommendations, and to veri$i 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 ofthe geoteclinical engineer. Respectfully Submitted, {.) = =-= ]E ::- D¿ =>,N*.U Ud = ^..ô .=-Ò > at -;'3d, ';9 9o'v> .::' ')û .r-) ¡!: HEP\ryORTH - PAWLAK GEOTECHNICAL, INC. Jordy Z. Adamsoq Jr., Reviewed by: þ-*fc Daniel E. Hardiq P.E. JZAlksw cc Lindauer Dunn, Inc. JobNo. 108 39lA e$teclr APPROXIMATE SCALE 1u: 20' LOT 4 4) o ()-ı ; =,E =¿ -.o C': 5J) ='ı, o U ôl (-l =s(.ìtoZ () PONDEROSA CIRCLE u N o 5 =I Ir LOT 6 LOTs BLOCK9 J BENCH MARK: GROUNDAT PFOPERTY CORNER; ELEV, = 100.0', ASSUMEÞ. LOT 29 108 391A LOCAÏION OF EXPLORATORY BORING Figure 1 GARAGE PROPOSED RESIDENCE BORING 1 o LOT 17 BORING 1 ELEV.: 105.2' a ı'o CSE a N Lo -c o ç(g ¡- = =of È 4) .?J 110 110 105 105 261't2 100 111',t2 WC:6.7 DD=103 100 c)o)lJ- Ico (d (l) tr¡411',t2 c)o LL Ico (d ot9595 2014 90 90 85 85 NOTE: Explanation of symbols is shown on F¡gure 3. = 108 391A eäShgcrr H EPwoRIat-PATvLAK GEolEcHNrcar. LOG OF EXPLORATORY BORING Figure 2 c.) Ð d 9r) = o O u . LEGEND: TOPSOIL; sandy silty clay, organics, roots, firm, slightly moist, brown. o-r) t- Ðc6N o = - c3 v t Ðc)l) CLAY AND SILT (CL-ML); sandy, stitf to very stiff, slightly moist, light brown, calcareous ffi BASALT GRAVEL AND COBBLES (GC-GM); in a sandy silt and clay matrix, possible boulders, dense, slightly moist, grayish brown. F I Relatively undisturbed drive sample; 2-inch l.D. California liner sample Drive sample; standard penetration test (SPI, 1 3/8 inch l.D. split spoon sample, ASTM-1586. ^^ ,¿ ^ Drive sample blow count; indicates that 26 blows of a 140 pound hammer falling 30 inches were ¿ot t¿ required to drive the California or SPT sampler 12 inches. T Practical drilling refusal NOTES: \ 1. The exploratory boring was drilled on July 22,2008 with a ¿þinch diameter continuous flight power auger. 2. The exploratory boring location was measured approximately by taping from features shown on the site plan provided. 3. The exploratory boring elevation was measured by instrument level and refers to the Bench Mark shown on Figure 1 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 materialtypes and transitions may be gradual. 6. No free water was encountered in the boring at the time of drilling. Fluctuation in water level may occur with time. 7. Laboratory Testing Results: WC = Water Content (þ DD = Dry Density (pcf) 108 391A eäFtecrrFlsoworth-Porld Gcotcchnlool LEGEND AND NOTES Figure 3 50a O nc .9alto o- Eo C) 0 u ()-ñT Dc N L 4) -Õ C - = -Ë,= -Ðuç 5J'ã 4. 1 2 10 APPLIED PRESSUBE - ksf Moisture Content : 6.7 Dry Density = 103 Sample of: Saldy Silt From: Boring 1 at 4 Feet percent pcf ( , No movement .upon wetting 0,1 1.0 100 Figure 4SWELL-CONSOLI DATION TEST RESU LTS108 391A O = -Õt åt = -f Õl;c Z. c)