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HomeMy WebLinkAboutWORONZOF TERRACE Soils InvestigationWoRo lzo , oi £S July 5, 1974 279-255! W.O. 16744 1940 POST ROAD UnWin & Scheben 103 East 26~_h Avenue Anchorage, Alaska 99503 Attention: Mr. Earl Korynta Subject: Woronzof Terrace Preliminary Soils Investigation Gentlemen: Transmitted herewith are the results of the subsurface investigation performed on the subject property on July 17, 1974, the results of the laboratory analysis of the underlying soils, and the writers' impression of the site. This report is to be considered preliminary and subject to a more in-depth treatment which will ~ollow, if desired. Under static loads, the site appears to be able to accommodate the development of light residential housing, constrained by a building set back on the order of 40' from tke eziz'Ling bluff line, and the need to avoid or to recompact isolated loose sands. The loose soils are believed to be associated with stretch cracks preceding grabens developed by the last major seismic occurrence (March 27, 1964). The seismic 'stability of the si~e requires additional study. Considerable effort was spent by others after 1964 to analyze the Turnagain area in order to develop corrective features to resist further large scale slope failures due to seismic activity. These actions were not implemented; thus, only the natural features which includes the considerable weight from the past slide debris at the toe of the previous failure is acting to stabilize the general area. In this regard, assuming that the general area has indeed been sufficiently stabilized %o resist large scale land. sliding, there remains the possibility of local instability along the new bluff line. The writer is especially apprehensive due to: 1.. The existence of lean clays at nat~'ral moisture con~ents above i their liquid limits in Test Holes 1 and 3 below 15' MEMBER Unwin and Scheben Page 2, Woronzof Terrace July 5, 1974 2. The existence of 'loose sands at 5.0' in Test Hole 2, indicating a small pre-graben from the 1964 occurrence. The possible existence of soft, sensitive clay at depth as indicated by section B3B, Page 64, Report on Anchorage Area Soil Studies, Alaska for U.S. Army Engineer District. It is prudent, therefore, to examine the local stability of the bluff in more detail, with the probable reco~urtendation being to regrade the bluff to no more than 1 vertical to 5 horizontal, and to recommend that structures built in this area be constructed in accordance to standards substantially more rigorous than are normally associated with the Anchorage.asea, so that in the event of a seismic occurrence similar to 1964, the structure should be able to withstand excessive movement without collapse, thereby emphasizing survivability for the occupants. It should be noted that areas similar to this are being developed in the Anchorage area, often with similar constraints. However, there can be no guarantee that during a major seismic occurrence the area will ~not e~xperience catastrophic instability. ~in ~he interest~of time, this preliminary review has dealt only briefly with the soil conditions expected to most influence the ~.~site. The data is consistent and compatible with the expected trends derived from the referenced study and our experience in ~imilar areas. It is the senior writer's opinion that further definitive analysis and study will not result in a more optimistic opinion with regard to the site's seismic stability. Please advise the writers if further study and its attendent substantial expense is warranted. We trust the foregoing is sufficient for your immediate needs. Please feel free to contact our office, should questions arise or should~additional.effort be required for your upcoming meeting° Ve~ truly yours, ALASKA TESTL/~ , / J. M. Lambe- Approved: H.~R. Lee~ P.E. JML/pf -h 'D ¢18 33 SLIDE AREA SHOWING ,50RiNg Ai"d"¢ TRENCH LOCAl I0~'~.¢ 'Z 0 .Z,-T7~_~ ,Al/ h!OZZV, dZ/77~ Test Hole 1 Elevation: 71' - 72' Depth in Feet From To 0.0! 0.5~ 0.5~ 4.0' 4.0' 7.5' 7.5' 18.0'~ 18.0'~ 21.5' Bottom of Test Hole: Frost Line: Free Water. Level: Sample 1 2 3 4 Remarks: Depth S.0'~6.5' 10.0'-ll.S' 15.0'-16.5' 20.0'-21.5' 1. 2. 3. 4. TABLE A W.O. #16744 Date: June 17, 1974 Soil Description Brown organic overburden NFS, reddish brown sand, damp, ~edium density, SP/SM NFS, grey fine sand, damp, medium density, SP/SM F-4, grey clayey silt layered with coarse silt, damp to wet, medium to stiff consistency, Pl+, Lw+, CL/ML F-4, grey clayey }ilt, wet, medium consistency, Pi+, Lw+, CL 21.5' None Observed None Observed Type of Dry Blows/6" M%_ Sample S_trength Group 8/12/1~ 7.1 SP N A 5/4/6 20.1 SP L B 315/5/ 30.7' SP Z B 2/3/5 31.9 SP H C D~te of test, June 17, 1974 Group refers to similar material, this study only Type of Sample, SP - Standard Penetration Dry strength, N = None, L = Low, M = Medium, H = High Test Hole 2 Hlevation: 71'5 Depth in Feet From TO 0.0' 2.5' 2.5' 5.5' 5~5' 18.0' 18.0' 21.5' Bottom of Test Hole: Frost Line: Free Water Level: Sample lA lB 2 $ 4 TABLE A Soil Description W.O. #16744 Date: June 17, 1974 F-4, reddish brown sandy silt, damp,-medium density, SM/ML NFS, reddish brown fine sand, damp, medium density, SP/SM F-4, grey clayey silt layered coarse and fine silt, damp to wet, stiff, CL/ML F-4, grey clayey silt, wet, medium consistency, Pi+, Lw-, CL 21.5' None Observed None Observed Type of Dry Depth Blows/6" M% Sample Strengt~ Group 5.0'-6.0' 5/2 10.6 SP N D 5.5'-6.5' 4 19.8 SP H E 10.0'-11.5' 5/6/8 17.9 SP M B 15.0'-16.5' 5/5/8 25.9 SP H B 20.0'-21.5' 2/5/5 28.6 SP H C Other ML Remarks: 1. Date of test: June 17, 1974 2. Group refers to similar material, this study only 5. Dry strangth, N = None, L = Low, M = Medium, H = High 4. Type of Sample, SP = Standard Penetration T~st Hole 3 Elevation: 71' - 72' Depth in Feet From To 0.0' 2.5' 2.5' 4.0' 4.0' 9.0' 9.0' 13.0'! 13.0'~ 18.0'± 18.0'± 21.5· Bottom of Test Hole: Frost Line: Free Water Level: TABLE A W.O. #16744 Date: June 17, 1974 Soil Description NFS, grey sand, damp, medium density% SP NFS, reddish brown sand, damp, medium density, SP/SM NFS, grey sand, damp, medium density, SP/SM F-4, grey coarse silt w/layers of clayey silt, damp, stiff, NP, ML F-4, grey clayey silt w/layers of coarse silt, damp to wet, stiff, CL F-4, grey clayey silt, wet, medium consistency, Pi+, Lw+,. CL 21.5' None Observed None Observed Sample Depth 1 5.0'-6.5' 8/14/21 2 lO.0'-ll.S' 5/4/7 3 15.0'-1~.5' 3/4/6 4 20.0'-21.5' 2/5/4 Remarks: 1. 2. $. 4, Dry Blows/6" Strength Group Date of test: M% 5.5 26.0 26f7 33.2 June 17, 1974 N A M-H F H G H C Type of Sample SP SP SP SP Group refers to similar material, this study only Dry strength, N = None, L = Low, M = Medi-um, H = H~gk Type of Sample, SP = Standard Penetration Test Hole 4 Elevation: 69' - 70' Depth in Feet From To 0.0' 0.3' 0.3' 2.5~ 2.5~ 4.0' 4.0' 11.5' 11.5' 13/5'± 13.5'! 21.5' Bottom of Hole: --Frost Line: Free Water Level: sample Depth 1 5.~'-6.5' 2A t0.0'-11.5' 2B 11.5'-12.0' 5 15.0'-16.5' 4 20.0'-21.5' TABLE A W.O. #16744 Date: June 17, 1974 Scil Description F-l, brown silty sandy gravel, damp, medium density, GM F-4, brown silt, damp, stiff, ML F-2, grey silty_ sand, damp, medium density, SM NFS, grey medium to coarse sand, damp, medium density, SP/SW F-4, grey sandy coarse silt, wet, stiff, SM F-4, grey clayey silt w/layers of coarse silt, wet, stiff, CL/ML 21.5' None Observed None Observed Type o£ Dry Blows/6" M% Sample Strength Group 9.14/23 6.0 SP N A 13/14/13 15.5 SP N H 19.1 SP M-L I 4/5/7 20.3 SP H B 4/7/6 24.2 SP M-L B Remarks: 1. Date of test} June 17, 1974 2. Group refers to similar material, this study only $. Dry strength, N = None, L = Low, M = Medium, H = High 4. Type of Sample, SP = Standard Penetration % 'i, ~o o ~ i~> ,m o o o~ o° 0 'D 0 0 0 ALASKA TESTLAB CONSULTATION ,~ TESTING ~ EXPLORATION ~ CHEMICAL ~ MATERIALS 0 INSPECTION SOIL CLASSIFICATION CHART 50% GRAVEL '%. 0 ~0 20 ;5o 4o 50 6o 7o 8o 90 Ioo GRAVEL (+~4SCREEN) % BY_~ WEI_~HT NONFROST SUSCEPTIBLE SOILS ARE INORGANIC SOILS CONTAINING LESS THAN 5% FINER THAN O.O?.mm, GROUPS OF FROST-SUSCEFTIBLE SOILS= FI GRAVELLY SOILS CONTAINING BETWEEN 3 AND ~'0% FINER THAN O.02rnm. F2" SANDY SOILS CONTAINING BETWEEN ;5 AND 15°/o FINER THAN O.02mm. F5 (3. GRAVELLY SOILS CONTAINING MORE THAN 20% FINER THAN O.02rnm. AND SANDY SOILS (EXCEPT ~ SILTY~ SANDS) CONTAINING MORE THAN 15°/o FINER THAN O.02mm. b, CLAYS WITH PLASTICITY INDEXES OF MORE THAN 12., EXCEPT VARVEO CLAYS. F4 a. ALL SILTS INCLUDING SANDY SILTS. b. FINE SILTY SANDS CONTAINING MORE THAN [5% FINER THAN O,O~'mr~.' c. LEAN CLAYS WITH PLASTICITY INDEXES OF LESS THAN d. VARVED CLAYS. ALASKA TESTLAB CONSULTATION @ TESTING ~ EXPLORATION ~ CHEMICAL ~) MATERIALS {~ INSPECTION ' i 5oil The soil descriptions shown on the logs are the best estimate of the soil characteristics at 'the time of field examinationl Such examinations do not achieve the precision of laboratory tests for the various properties. 1. The relative type of soil and the frost classification are shown on 'the sheet, "Soil Classification Chart." ~ , 2. Other criteria: Density - PL - · Peat Boulder - greater than 8" Cobble - approximately 3" to 8" Blow Count - blows/6" of 140-1b. weight falling 30"; 2" split spoon. (The standard penetration is'blows/12".) estimated by the rate of drilling type of soil, blow count, and moisture range. Plasti'C Limit, moisture content being approximated as above (+) or below (-) plastic limit (PL) or liquid limit (Lw) as appropriate. Lw - Liquid Limit, see PL Dilatency - is the ability of water to migrate to the surface upon vibration or jolting of a sample, an aid in determining 'whether a soil is predominately a clay or silt. Well graded - uniformity coefficient greater than 7 Poorly graded - uniformity coefficient less than 7 (Uniform particles, gap graded) Organic Content - estimated by volume, not particularly precise. Clayey Soils - a field method now being used as an aid to identifi- cation of these soils as a combinat'ion ball drop, and rolled thread test in which a 2" diameter ball of the Sand-Silt-Clay fraction is dropped 2' until a 1" thick pat develops. The diameter of a thread at crumbling rolled from the resultant pat determines whether clay or silt predominates. Dry Strength - a small sample of the soil is formed into a cube and air dried, and crushed between the fingers. High dry strength indicates clays and low silts~ Water Table - the apparent water table at the time of observation. Often the actual water table may be higher unless the hole is allowed to remain open or is converted to an observation well. Capillary Fringe - change from moist to very damP, or saturated soil, usually indicates that water table is close. - Fibrous material of macroscopic and microscopic fragments of d~cayed vegetable matter; very compressible, unsuit- able for foundation or embankment. Color light brown to black. Ao The upper layer, surface soil or topsoil, containing humus and/or organic debris, not satisfactory for foundations.