Loading...
HomeMy WebLinkAboutSoils Report for Foundation Design & Perc Test 08.30.2016H-P=INMAR 5020 County Road 154 Glenwood Springs, CO 81601 Phone: (970) 945-7988 Fax: (970) 945-8454 Email: hpkglenwood@kumarusa.com August 30, 2016 Ryan Pratt P.O. Box 1627 Carbondale, Colorado 81623 (Rvan.;-ratt•a probt ild_coni) Office Locations: Parker, Glenwood Springs, and Silverlhome, Colorado Project No.16-7-326 Subject: Subsoil Study for Foundation Design and Percolation Test, Proposed Residence, Lot A, Panorama Reserve Subdivision, 2401 Panorama Drive, Garfield County, Colorado Dear Mr. Pratt: As requested. H-P/Kumar performed a subsoil study and percolation test for foundation and septic disposal designs at the subject site. The study was conducted in accordance with our agreement for geotechnical engineering services to you dated August 15, 2016. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. Proposed Construction: The proposed residence will be a one and two story wood frame structure above a walkout basement with an attached garage and located on the site as shown on Figure 1. Basement and garage floors are proposed to be slab -on -grade. Cut depths are expected to range between about 3 to 15 feet. Foundation loadings for this type of construction are assumed to be relatively light and typical of the proposed type of construction. The septic disposal system is proposed to be located west and downhill of the residence. If building conditions or foundation loadings are significantly different from those described above, we should be notified to re-evaluate the recommendations presented in this report. Site Conditions: The property is vacant and accessed by an existing gravel drive from Panorama Drive. Vegetation in the building area consists of grass and weeds with scattered stands of scrub oak beyond. The site is located on an upland rolling mesa and the ground surface in the building area slopes down to the west at a grade of about 14 percent. There are scattered basalt cobbles and boulders exposed on the ground surface of the lot. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two exploratory pits in the building area and one profile pit in the septic disposal area at the approximate locations shown on Figure 1. The logs of the pits are presented on Figure 2. The -2 - subsoils encountered, below about 6 inches of topsoil, consist of one foot of reddish brown sandy silty clay overlying calcareous sandy silty clayey basalt gravel and cobbles. Results of swell - consolidation testing performed on a relatively undisturbed sample of the sandy silty clay, presented on Figure 4, indicate low compressibility under existing moisture conditions and light loading and high compressibility when wetted and loaded. Results of a gradation analysis performed on a sample of silty clayey sandy gravel (minus 3 inch fraction) obtained from Pit 2 are presented on Figure 5. The laboratory test results are summarized in Table I. No free water was observed in the pits at the time of excavation and the soils were slightly moist to moist. Foundation Recommendations: Considering the subsoil conditions encountered in the exploratory pits and the nature of the proposed construction, we recommend spread footings placed on the undisturbed natural granular soil designed for an allowable soil bearing pressure of 2,000 psf for support of the proposed residence. The matrix soils could compress when wetted under load and result in post -construction foundation settlement on the order of 1 inch. Footings should be a minimum width of 16 inches for continuous walls and 2 feet for columns. The topsoil, reddish clay and loose disturbed soils encountered at the foundation bearing level within the excavation should be removed and the footing bearing level extended down to the undisturbed natural granular soils. Voids created by boulder removal should be backfilled with compacted structural fill or with concrete. We should observe the completed excavation for bearing conditions. Exterior footings should be provided with adequate cover above their bearing elevations for frost protection. Placement of footings at least 42 inches below the exterior grade is typically used in this area. Continuous foundation walls should be reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at Ieast 12 feet. Foundation walls acting as retaining structures should be designed to resist a lateral earth pressure based on an equivalent fluid unit weight of at least 50 pcf for the on-site soil as backtill, excluding organics and rocks larger than about 6 inches. 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 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 less than 50% passing 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 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 and basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain system. H ffi KUMAR 3 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 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 11/2 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. Free -draining wall backfill should be capped with about 2 feet of the on-site, finer graded soils to reduce surface water infiltration. 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 pavement and walkway areas. A swale will be needed uphill to direct surface runoff around the residence. 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 10 feet from the building. Consideration should be given to the use of xeriscape to limit potential wetting of soils below the building caused by irrigation. Percolation Testing: Percolation tests were conducted on August I8, 2016 to evaluate the feasibility of an infiltration septic disposal system at the site. One profile pit and three percolation holes were dug at the locations shown on Figure 1. The test holes (nominal 12 inch diameter by 12 inch deep) were hand dug at the bottom of shallow backhoe pits and were soaked with water one day prior to testing. The soils exposed in the percolation holes are similar to those exposed in the Profile Pit shown on Figure 2 and consist of about 6 inches of topsoil and one to two feet of reddish brown sandy silty clay overlying calcareous sandy silty clayey basalt gravel and cobbles. The percolation tests were conducted in the underlying granular soil. The percolation test results are presented in Table 2. Based on the subsurface conditions encountered and the percolation test results, the tested area should be suitable for a conventional infiltration septic disposal system. We recommend the infiltration area be oversized due to the relatively slow percolation rate. 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 expressed or implied. The conclusions and recommendations submitted in this report are based upon the data obtained from the exploratory pits excavated at the locations indicated on Figure 1, the proposed type of construction and our experience in the area. Our services do not include H KUMAR -4 - 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 pits 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 at once so 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. If you have any questions or if we may be of further assistance, please let us know. Respectfully Submitted, H-P�K_MAR ouis Eller Reviewed by: Steven L. Pawlak, P.E.! LEG/ksw attachments Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Table 1 — Table 2 — 16x22 r 9 '= T. 7/4 w % c c col.* o 4 �`V f — Locatio �~' xploratory Pits — Logs of Exploratory Pits — Legend and Notes — Swell -Consolidation Test Results -- Gradation Test Results — USDA Gradation Test Results Summary of Laboratory Test Results Percolation Test Results cc: Kurtz and Associates - Brian Kurtz (kurtzengincer ayahoo.com) H- KUMAR N 03°1 o 1 r� 7" E BASIS OF BEARI S 03'17' 20' UT FP?' EASEMENT 10 SERVE LOT B PER RECEPTION No. 772442 J a. 0 CN? 1 d 22 /4," A 3❑ 0 30 6❑ APPROXIMATE SCALE -FEET LOCATION OF EXPLORATORY PITS 2 ra 2 W'iasirrn�wmn�w..•a .yuutadi ran u[-i-oili,sitieaW4.2VA .Ctaa - siot in +•w.ws a s S w w CL. 0 -- 5 PIT 1 EL. 7236' WC=14.6 00=72 PIT 2 EL. 7231' "1+4=76 _ —200=11 PROFILE PIT EL. 72 9' G=49 - 5a=28 — 161=19 C=4 0-1 5 -- 10 10 -- 16-7-326 16--7-326 H-P:KUMAR LOGS OF EXPLORATORY PITS Fig. 2 �a9 LEGEND TOPSOIL; ORGANIC SANDY SILT AND CLAY, FIRM, SLIGHTLY MOIST, DARK BROWN. CLAY (CL); SANDY, SILTY, MEDIUM STIFF, SLIGHTLY MOIST TO MOIST, REDDISH BROWN, POROUS, BASALT GRAVEL AND COBBLES (GM—GC); IN A SANDY SILTY CLAYEY MATRIX, MEDIUM DENSE TO r/ DENSE, SLIGHTLY MOIST, LIGHT BROWN, CALCAREOUS. a HAND DRIVEN LINER SAMPLE. DISTURBED BULK SAMPLE. t PRACTICAL DIGGING REFUSAL. NOTES 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON AUGUST 17, 2016. 2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY, BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE OBTAINED BY INTERPOLATION BETWEEN CONTOURS ON THE SITE PLAN PROVIDED. 4. THE EXPLORATORY PIT 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 PIT LOGS REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXCAVATING. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D 2216); DD = DRY DENSITY (pcf) (ASTM D 2216); +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422); —200 = PERCENTAGE PASSING N0. 200 SIEVE (ASTM D 1140). G = PERCENT GRAVEL PER USDA CLASSIFICATION Sa = PERCENT SAND PER USDA CLASSIFICATION Si = PERCENT SILT PER USDA CLASSIFICATION C = PERCENT CLAY PER USDA CLASSIFICATION. 16-7-326 H-PKUMAR LEGEND AND NOTES Fig. 3 J J 41 VI 0 —10 0 0 U-12 —14 —16 —18 SAMPLE Or: Sandy Silty Clay FROM: Daring 1 0 1' WC = 14.6 %, DD = 72 pcf R... w1 mat* epsh pay to IN, ....vi..1,.,.. Th. loWel egret NW Fa! b. w:F.am h[ 'Armin L....AI.n epfvaM liumor Sne MwdaW. G.rdd.lkn MM arfwm.M acoT A5i4 4.dere. M-.a.e. ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 1.0 APPUEG PRESSURE — KSF l0 100 16-7-326 H - P :t KU MAR SWELL -CONSOLIDATION TEST RESULT Fig. 4 100 90 I0 70 eD 50 a0 70 20 Io CLAY TO SILT SAND FINE MEDIUM (COARSE GRAVEL FINE i COARSE 1 COBBLES 16-7-326 GRAVEL 75 X LIQUID LIMIT SAMPLE OF: Silty Clayey Sandy Craved SAND H -P KUMAR 13 X PLASTICITY INDEX SILT AND CLAY 11 X FROM: Pit 2 0 3.-4' 10 20 30 0 SO 60 70 BD 90 100 Th91e 1111 1/151111 0Dply only To the IOR1p1.1 which ogre %sled. Tho le%lin0 rrp0rt 004n01 h. r.prodund, ..a.p1 In full, wllhau! !h. .r0lfm 00Ar0401 of Kumar A A.4Oc101011. Inc- 51.rr nnolyl!" 1.11145 11 p.rlormed In 0ccord0ncr wllh 4511 [422, A$111 0136 and/or AMC 01140. GRADATION TEST RESULTS Fig. 5 NYDROICTER ANALYSIS SIEVE ANALYSIS 24 40 nu[ 112A0I4G0 HRS 7 HIS IItH 17 Intl e011H 1914111 aulu Tek ISO 1100 12.0. 2Ti110020 WOES 170149_30_ !1i 0t0 10 4.4 3/0' CLEAR 3911411E GrCWIUOO 3/4' 1 I(7' • 5111' E 1 1 11 J 1 1 1 1111 I1 1 11 1111 1 1 111111 1 1 1 111111 D1 .007 .005 .029 .010 .032 .0 DIAMETER 2 .12u OF .020 .502.23 PARTICLES IN 1.10 0.0 2.31 4.75 05 MILLIMETERS 19 30.1 20.2 107 21320 CLAY TO SILT SAND FINE MEDIUM (COARSE GRAVEL FINE i COARSE 1 COBBLES 16-7-326 GRAVEL 75 X LIQUID LIMIT SAMPLE OF: Silty Clayey Sandy Craved SAND H -P KUMAR 13 X PLASTICITY INDEX SILT AND CLAY 11 X FROM: Pit 2 0 3.-4' 10 20 30 0 SO 60 70 BD 90 100 Th91e 1111 1/151111 0Dply only To the IOR1p1.1 which ogre %sled. Tho le%lin0 rrp0rt 004n01 h. r.prodund, ..a.p1 In full, wllhau! !h. .r0lfm 00Ar0401 of Kumar A A.4Oc101011. Inc- 51.rr nnolyl!" 1.11145 11 p.rlormed In 0ccord0ncr wllh 4511 [422, A$111 0136 and/or AMC 01140. GRADATION TEST RESULTS Fig. 5 PERCENT RETAINED HYDROMETER ANALYSIS 24119 7 HR TIME READINGS 1 MIN 0 48 �IN 18 MIN. SOMIN10MiN.4 MIN. #325 10 20 30 40 50 60 70 80 90 100 ,001 .002 005 .009 .019 #140 SIEVE ANALYSIS 1 U 5. STANDARD SERIES 1 CLEAR SQUARE OPENINGS #60 #35 #18 #10 #4 3/ 314 11/2” 3' 5'6' 8' 100 /***/1/41 50 40 90 80 70 60 L .045 106 ,025 .500 100 2.00 DIAMETER OF PARTICLES IN MIWMETERS 4.75 9 5 19,0 37,5 76.2 152 203 CLAY SLT s►vu Y Pl,E f Firci M DLl1 !COMM to mum* SPAU 1 e.M ED UM LARGE COBBLES 16-7-326 GRAVEL 49 % SAND 28 % SILT 19 % CLAY 4 % USDA SOIL TYPE: Very Gravelly Loamy Sand FROM: Profile Pit @ H-PKUMAR USDA GRADATION TEST RESULTS 30 20 10 0 PERCENT PASSING Fig. 6 H -P KUMAR TABLE1 SUMMARY OF LABORATORY TEST RESULTS Project No. 16-7-326 SAMPLE LOCATION NATURAL, MOISTURE CONTENT (%) NATURAL DRY DENSITY (poi) GRADATION PERCENT PASSING NO. 200 SIEVE ATTERBERG LIMITS UNCONFINED COMPRESSIVE STRENGTH (PSF) _ SOIL PIT DEPTH Ift) GRAVEL (%) SAND (%) LIQUID LIMIT (%) PLASTIC INDEX (%) 1 1 14.6 72 Sandy Silty Clay 2 3 to 4 76 13 11 1 Silty CIayey Sandy Gravel Profile Pit 3 to 4 Very Gravelly Loamy Sand 1 HPKUMAR TABLE 2 PERCOLATION TEST RESULTS PROJECT NO. 16-7-326 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 (MIN./INCH) P 1 35 15 Water added Water added 6 5 1 30 6' 5% 3/4 51/2 43/4 % 6 51/4 34 51/4 43/4 1/, 43/4 41/4 1/2 P 2 41 15 Water added Water added 5 2 3 20 5 4 1 4 3 1 5 41/4 3/4 41/4 3'/2 3/4 31/2 2% 34 P 3 39 15 Water added Water added Water added 5 13/4 31/4 20 5 33/4 11/4 5 4 1 4 31/4 34 5 41/4 3/4 41/4 31/2 ,M1 34 Note: Percolation test holes were hand dug in the bottom of backhoe pit and soaked on August 17, 2016. Percolation tests were conducted on August 18, 2016. The average percolation rates were based on the last two readings of each test.