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HomeMy WebLinkAboutB12-0385 OBSERVATION OF EXCAVATION Hepworth-Pawlak Geotechnical, Inc. L e� 1 fm h 5020 Counev Road 154 `�� \I \Itec 1 Glenwood 97 Springs, Colorado 31601 Phone: 970-945.7988 HEPWORTH - PAWLAK GEOTECHNICAL Fax: 970-945,8454 email: hpgeo©hpgeotech.com October 17, 2012 DW Dantas Construction, LLC Attn: Dave Dantas P.O. Box 2322 Avon, Colorado 81620 davena,dwdantas.com Job No. 112 097A Subject: Observation of Excavation, Proposed Duplex (East Unit), 2801 Snowberry Drive, Lot 9, Vail Intermountain, Vail, Colorado Dear Dave: As requested, a representative of Hepworth-Pawlak Geotechnical, Inc. observed the excavation at the subject site on October 5, 9 and 11 , 2012 to evaluate the soils exposed for foundation support. The findings of our observations and recommendations for the foundation design are presented in this report. We previously conducted a subsoil study for design of foundations at the site and presented our findings in a report dated June 11 , 2012, Job No. 112 097A. The proposed residence will be similar to that assumed in our previous report. The lower levels will step down the hillside to provide bearing of spread footings on the natural soils. At the time of our initial visit to the site, the building excavation had recently begun and we discussed extending the bearing level down through existing fill and topsoil to predominantly granular soils. When observed on October 9, the excavation was mostly complete except for the west end and had been cut in multiple levels up to roughly 17 feet below adjacent ground surface with roughly 5 to 8 between levels. When observed on October 11 , the west end had been completed and cut in 3 levels stepped down the hillside. The soils exposed in the bottom of the excavation consisted of silty clayey sandy gravel with cobbles and scattered boulders. The results of a gradation analysis performed on a sample of the gravel (minus 3 inch fraction) obtained from the site are presented on Figure 1 . Free water was typically not encountered in the excavation and the soils were moist. A small amount of seepage was encountered in the middle level of the western excavation area and it was recommended to install a subdrain to collect the seepage and keep the excavation dry. The subdrain can be connected to the foundation drain that will be needed at each bench level of the excavation. The gravel soils exposed at the excavation bottom are consistent with those previously encountered on the site and suitable for support of spread footings designed for the Parker 303 -841 . 7119 Colorado Springs 719-633 .5562 Silverthorne 970-468- 1989 DW Dantas Construction, LLC October 17, 2012 Page 2 recommended allowable bearing pressure of 2,000 psf. Loose disturbed soils should be removed in the footing areas to expose the undisturbed natural soils. The water seepage into the excavation should be collected and diverted away from the footing areas and any softened soils and mud removed before concrete placement. The bearing soils should be protected from frost and concrete should not be placed on frozen soils. Careful attention should be given to exterior foundation wall backfill placement and compaction due to potential for settlement and distress of surface facilities. Frost heave of the bearing soils could also be a problem due to the groundwater seepage and onset of winter and heating of the lower level and crawlspaces could be needed. We should observe the excavation of the western duplex unit for bearing conditions at the time of construction. Other recommendations presented in our previous report which are applicable should also be observed. The recommendations submitted in this letter are based on our observation of the soils exposed within the foundation excavation and the previous (limited) subsurface exploration at the site. Variations in the subsurface conditions below the excavation could increase the risk of foundation movement. We should be advised of any variations encountered in the excavation conditions for possible changes to recommendations contained in this letter. 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. If you have any questions or need further assistance, please call our office. Sincerely, HEPWORTH — PAWLAK GEOTECHNICAL, INC. Steven L. Pawlak, P. *S t 55222 .� SLP/ksw see apAti ••••� qlf OF Attachment: Figure 1 — Gra est Results Job No. 112 097A C-�teCh HYDROMETER ANALYSIS SIEVE ANALYSIS TIME READINGS U.S. STANDARD SERIES CLEAR SQUARE OPENINGS 24 HR 7HR 45 MIN. 15MIN. "IN. 1910K 4MIN. 1MIN. #200 #100 #50 #30 #18 #8 #4 w 31P 112' T S 6' Y 0 100 0 90 - -- - zo � 30 70 0 40 ( Z 50 Z w ... — - __ ._ --_ w aso ::: -- — - -- --- -- -I— : - w cc 30 90 7. A01 .002 .005 ,009 .019 W .074 .150 .300 M 1.18 2.38 4.75 9.512.5 19.0 37.5 ]8.2 1152 210 DIAMETER OF PARTICLES IN MILLIMETERS CLAY TO SILT SAN° caAOEL FINE MEDIUM COMBE FINE C(NaCF CpEW ce Gravel 47 % Sand 27 % Silt and Clay 26 % Sample of: Silty Clayey Sandy Gravel From: Bottom of Excavation, West End (10-11 -12) H 112097A C_- ?[Ptech HNICAL GRADATION TEST RESULTS FIGURE 71 HEPWORTH-PAWLAK GEOTEC Hepworth-Pawlak Geo[echnical, Inc. 4 5020 County Road 154 ■ tech Glenwood Springs, Colorado 8I601 Phone: 970-945-79SS IICI'WORTII - PAWLAK GCOTCCIINICAL Fax: 970-945-8454 email hpgeo@l,pgeorech.com October 17, 2012 DW Dantas Construction, LLC Attn: Dave Dantas P.O. Box 2322 Avon, Colorado 81620 _d_ave?,,dwdantas com Job No. 112 097A Subject: Observation of Excavation, Proposed Duplex (East Unit), 2801 Snowberry Drive, Lot 9, Vail Intermountain, Vail, Colorado Dear Dave: As requested, a representative of Hepworth-Pawlak Geotechnical, Inc. observed the excavation at the subject site on October 5, 9 and 11 , 2012 to evaluate the soils exposed for foundation support. The findings of our observations and recommendations for the foundation design are presented in this report. We previously conducted a subsoil study for design of foundations at the site and presented our findings in a report dated June 11 , 2012, Job No. 112 097A. The proposed residence will be similar to that assumed in our previous report. The lower levels will step down the hillside to provide bearing of spread footings on the natural soils. At the time of our initial visit to the site, the building excavation had recently begun and we discussed extending the bearing level down through existing fill and topsoil to predominantly granular soils. When observed on October 9, the excavation was mostly complete except for the west end and had been cut in multiple levels up to roughly 17 feet below adjacent ground surface with roughly 5 to 8 between levels. When observed on October 11 , the west end had been completed and cut in 3 levels stepped down the hillside. The soils exposed in the bottom of the excavation consisted of silty clayey sandy gravel with cobbles and scattered boulders. The results of a gradation analysis performed on a sample of the gravel (minus 3 inch fraction) obtained from the site are presented on Figure 1 . Free water was typically not encountered in the excavation and the soils were moist. A small amount of seepage was encountered in the middle level of the western excavation area and it was recommended to install a subdrain to collect the seepage and keep the excavation dry. The subdrain can be connected to the foundation drain that will be needed at each bench level of the excavation. The gravel soils exposed at the excavation bottom are consistent with those previously encountered on the site and suitable for support of spread footings designed for the Parker 303 -841 - 7119 Colorado Springs 719-633 -5562 Silverthorne 970-468- 1989 DW Dantas Construction, LLC October 17, 2012 Page 2 recommended allowable bearing pressure of 2,000 psf. Loose disturbed soils should be removed in the footing areas to expose the undisturbed natural soils. The water seepage into the excavation should be collected and diverted away from the footing areas and any softened soils and mud removed before concrete placement. The bearing soils should be protected from frost and concrete should not be placed on frozen soils. Careful attention should be given to exterior foundation wall backfill placement and compaction due to potential for settlement and distress of surface facilities. Frost heave of the bearing soils could also be a problem due to the groundwater seepage and onset of winter and heating of the lower level and crawlspaces could be needed. We should observe the excavation of the western duplex unit for bearing conditions at the time of construction. Other recommendations presented in our previous report which are applicable should also be observed. The recommendations submitted in this letter are based on our observation of the soils exposed within the foundation excavation and the previous (limited) subsurface exploration at the site. Variations in the subsurface conditions below the excavation could increase the risk of foundation movement. We should be advised of any variations encountered in the excavation conditions for possible changes to recommendations contained in this letter. 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. If you have any questions or need further assistance, please call our office. Sincerely, HEPWORTH — PAWLAK GEOTECHNICAL, INC. L P-4.ly N • Steven L. Pawlak, P. 15222 SLP/ksw ,pl�� yQ�POO Attachment: Figure 1 — Gra F CO st Results Job No. 112 o9 /A tiiPP Gl tech HYDROMETER ANALYSIS SIEVE ANALYSIS TIME READINGS U.S. STANDARD SERIES 24 HR. 7HR CLEAR SQUARE OPENINGS 45MIN. iSMIN. WMIN. 19MIN. 4MIN. 1MIN. 8200 •100 M50 on N16 Y8 44 3/8' y4' 11? 3 k k k 0 IDD _— __ __.. _.- - - 0 40 Z -- _ — I — 60 Z -- — __._ — .. - -- ---- a so a so � 70 100 .001 .002 .005 ,OC9 .019 A37 .074 .150 3W ,80p 0 118 236 4.75 9.5125 19.0 3].5 76.2 12]1 � DIAMETER OF PARTICLES IN MILLIMETERS CLAY TO SILT SAND GRNV FI E COEELEB OAR6E Gravel 47 % Sand 27 % Silt and Clay 26 % Sample of: Silty Clayey Sandy Gravel From: Bottom Of Excavation, West End (10-11 -12) 112 097A Pt�r1 GRADATION TEST RESULTS HEPWORTH�PAWLAK GEOTECHNICAL FIGURE 1