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HomeMy WebLinkAboutPREUSS #4 Blocks 7-9 Soil Investigation October 8, 1971 Air. Gerhard Preuss Eagle River, Alaska Re: Geology and Soil Conditions of Unit 2, Blocks 7 through 9, Preuss Subdivision, Eagle River, Alaska Dear Mr. Preuss: Submitted herewith is our report presenting the findings of a geological and soil investigation of the above-mentioned subdivision. We have enjoyed conducting this .study for you. Please call if you have any questions or comments regarding the report. Yours very truly, BGP:js Attachment ALASKA GEOLOGICAL CONSULTANTS 2227 SPENARD ROAD ANCHORAGE, ALASKA 99503 Telephone: 277-7601 277-7602 GEOLOGY AND SOIL CONDITIONS OF · UNIT 2, BLOCKS 7 THROUGH 9 PREUSS SUBDIVISION REPORT TO GERHARD PREUSS, OWNER-DEVELOPER EAGLE RIVER, ALASKA Prepared by ALASKA GEOLOGICAL CONSULTANTS ANCHORAGE, ALASKA October 1971 INTRODUCTION The Preuss Subdivision is a planned residential development located some two and one-half miles east of the city of Eagle River. The Subdivision has not been programmed for public or group water and sewage utilities necessitating provision for these facilities by each individual lot owner. The purpose of the subject report is co describe soil conditions, topography and ground water characteristics as related to future constrUction of the individual sewer and water systems. INVESTIGATION The subject investigation was confined, to Blocks 7 through 9, Unit 2 of the Subdivision as directed,by the owner-developer, Mr. Gerhard Preuss. The investigation included a review of available geologic information and field reconnaissance of the area. Observation of subsurface geologic conditions was provided by four excavations situated so as to give a sufficient overall view. Lu addition, several road cuts and an adjacSn~../', foundation excavation logged by the engineering'geologist provided supplementary information. The aforementioned test pits excavated for the purpose of this investigation ranged in depth from nine to twelve feet. The test pits were constructed with a backhoe providing an excellent opportunity for observation and sampling of subsurface conditions. ENGINEERING GEOLOGY The area investigated, Blocks 7 through 9, contains a total of thirty single~' family residential lots. These are identical in size, some 120 x 163 feet, with approximately 19,600 square feet total area. The Subdivision is located along the north slope of Eagle River Valley on an easterly extension of Magnificent Mountain. -1- Surficial geologic conditions reflect the movement of glacial ice down Eagle River Valley with the formation of lateral moraines. This is exhibited in the dominant east-~vest trending' terraced or steplike topogTaphy even though some modification occurred througt~ the formation of small steep-sided drumlins and minor erosion of the morainal surface following glacial retreat. The slope of the area~ providing a somewhat continuous southerly drop in elevation of some seventy feet to the exclusion of any kettle topography, should provide excellent drainage characteristics. Some 1/2 to 3/4 of a mile north of the report area at an elevation of 160 feet is an outcrop of the Pre-Cretaceous (?) bedrock formation of the Chugach Mountains. This presents itself in the form of a cliffr like feature being covered by the uppermost extension of the lateral moraine and probably extending' in a U-shaped typical glacial valley manner beneath the report area. Depth of bedrock in the immediate.report area has not been established, however, we understand that several wells in the area, One of thes~ reaching a depth of 245 feet, have not encountered bedrock. SURFICIAL GEOLOGIC CONDITIONS Subsurface geologic conditions observed in the test pits and other adjacent excavations are outlined on the enclosed logs. Generally, these typify lateral morainal deposition with heterogeneous glacial till consisting of silty, sandy gravels with an admixture of cobble and boulder size material. However, in the case of two of the test pits, Nos. 1 and 3, and in the foundation excavation there oocurred lenses of water-sorted medium to fine sand 1½ to 2 feet thick. No correlation could be found between these lenses and it is assumed that they occur randomly throughout the~S, abdivision. Concerning bearing strength, soils exposed~jn both the test pits and other excavations were observed to be of a compact to'dens~ consistency. This should provide excellent foundation conditions for the proposed residential structures. Because of the fairly high silt content, 'these soils do exhibit a frost-susceptibility in the range of the F-4 category. Consequently, proper foundation placement must be taken into consideration. HYDROLOGY Four wells have recently been completed adjacent to the report area. These have attained depths varying from 96 to 245 feet arid have been test pumped at rates varying from 20 to 35 GPM. Another well is in the process o5 being completed along the southeast corner of Block 9 which has reportedly reached a depth of some 274 feet. At the time of our field investigation no test pumping had yet been a~complished on this last well. Although no substantiated logs are available on She wells, we understand that they have not reached bedrock but were completed in water-bearing stratum of the glacial till material similar to that observed in the test pits. Origin of the ground water is presumed to be the adjacent water shed formed by Magnificent Mountain with bedrock or near bedrock stratum forming the aquifers lower limit. Although no datum is available on the upper limit of the aquifer, observed well depths would indicate that this is somewhat erratic. CONCLUSIONS AND REcoMMENDATIONS Based upon the information derived by us in our investigation of this proposed Subdivision, we conclude the following: A. Bearing capacity of the subsurface soils within the Subdivision are adequate for the proposed building units to be located upon them (residential housing). 23- Bo Frost susceptibility of these soil~ falls within the F-4 category.- The'subsurface soils characteristics in the subject site appear ro be quire uniform throughout with the Unified Cl~assification System comparable to GM (siiW sandy gravel), D. The hydrology or the avai:lability of a,potable water source beneath this Subdivision will proba~bly be adequate based upon the several wells investigated within the near vicinity. Based upon rhes~ above conclusions we propose to make the following recommendations: _&. Placement of foundations to be 3½ to 4 feet below the finish grade. B. Se~va~r~ disposal system should utilize the 225 square feel: per bedroom criteria. ~j-~'-~ We further recommend that at the time excavations are open for foundation accment and se,wage disposal systems that we be contacted to make an inspection to further insure that the subsurface Soil cofiditionS are as determined in our'foundation ~exploration pro · ~-; ~. ~ ........... ~.o ~ : Respectfully submitted, ,j:,~ ~ ~,-e.:.: ~ '~.~ ~ ~ .'-~ ~.'. -~ ' LOG OF TEST BORING ~ : Date Began Oct. 2, 1971 ~= ~, ~ Hole No. Test Pit No. ".' She°, ' Proja~t ~om~ ~'euss Subdivision ' ~ ~ ~ ~ : ............... '- ~ Project No. 71-154 Location Eaffle River Valley GeneraINotes a Location Met~o~ Used T~ ~ Rig, Bactine Field Party Geologist Grey : ~1 Weather - Sampling [ DESCRIPTION ~ Soil type, color, texture, est. particol size ~ ~T ~ ~ ~ ~ampterdrivingnotos, dopthcirculationlo~t, ~ c ~ ~ ~ notes on drilling ease, bite usod~ otc. ~ .a ~ a 8 ~ SAMPLING METHOD, i.e., -- . c Sptitspoon=S.S.I.4 or2.5, Shelbytube=S.~ ~AV~ ~V~. ~ o ~ ~ ~ ~ ~ ~ ~i~ Modifiedsholbytubo=M.S.T, Dia. drillcore= m ~ m--° ~ ~ ~ ~ m ~ ~,~ ~° Pitcherborrol=P.B. ~LK~. l- Residual soil~ reddish brown to ~ay sandy silt ~ ;~. ~, Gravelly silW sand with some cobble size mat~rial~ li~t ~ay "~ - _ 4,~ ~;. ......... ~."x. Fine to medium sand ~ ~ - ,~...... ~.., :[ 7- . ,, Silw sandy ~avel with some cobble size. rounded ~O subrounded 10- Test pit approximately 11 ft. wide tapering inward to 3 1- 5- ~.. ' 0 2227 SPENARD RD. ANCHORAGE~ ALASKA : PHONE* 272-4114 L~,/ LOG OF TEST BORING  Client Gc~h~d ~'euss ~ I ~ Total Depth _ 12 ft. Project Nome ~CUSS Subdivision ~ (~;7L~;~:,7-. _.-::.,..:,2~. ~ Ground Elev. 780 ft. []' Project No. 71-154 Loco¢io~ Eag'le River Valley Generol Nofos ~ Locofion Dio~rom ,~ Method Used Test ~ Rig B&c~oe : Field Party Geolobist ~rey '~ W~af~or · Sampling ~ " DESCRIPTION [ ' ~ ~ ~ Soil type, color, texture, est. partical size, ~0~ ~ ' '~ ~ ~ ~ ~ sampler driving notes, depth circulation Iost~ : % . - E .~ ~ ~ ~ notes on drilling ease, bits used, etc. i ~ o c o o ~ o O ~ SAMPLING METHOD~ I.e.~ ~ ~ ~ ~ ~ ~ .~ * c ~ ~ ~ Splitspoon=S.S.I.4 orS.5~ Shelbytube=S.~ % ~ ~ = > ~ ~ ~ % Modified shelby tube=M.S.~ Dia. drill core = ~ ~ ~ ~ ~ ~ ~ D.D.C., Chipsomple=C.S.,Grobsomple=G.S., ~L~ ~ ~ G~ave]]v ~8[d~m~ so~[ mosdv sflW sa~d to sandy si]t~ b~ow~sh / . o o ~ ~ Pitcher barrel = ~'" O-- to ~Tay .. ~-~, .~ - -- -- 421~ /. / I Glacial. till, silW sand~ gravels to sond7 silt7'~ravels with admixture / Of cobble and boulder size material ~ light ~ray to dark ~ay in color. ~-I_:__ ~Z%4'11 I / ~,~,,oobb~¢~. snbroundedtosuban~laT compsct to dense -'--- - , 'F ,. ...... ,,2 /./ Bottom of test p,~  Test alt agoroximatelv 1.2 f~, deept 13'ft. longt slopin~ inward to 4 ft. ~- ~ Random ~ab~gample from 3 to 5 fr. taken alon~ wall of test o 2227 SPENARD RD. ANCHORAGE~ ALASKA ~ _~ : PHONE~ 272-41J4 LOG OF TEST BORING Date Began Oct. 2, 1971 Date Completed Oct. 2r 1971 Client q]erhard lh'euss Drill Co. Project Name Pl~etlss Stlbc]~Vi~[Qn Project No. 71-154 Location Test Pit Method Used Field Party Weather Sampling Eagle ~vez Valley Rig BacMtoe Goolo~i~f. Grey rain DESCRIPTION Soil typo, color, texture, est. portical size, sampler driving notos~ depth circulation loot, notes on drilling ease, bits used~ etc. SAMPLING METHOD~ Split spoon =S.S. 1.4 or Modified shelby tube=M.S.T.~ Dia. drill core D.D.C., Chip semple=C.S, Grab scruple Pitcher barrel = P.B. Hole No Test Pit No. Sheet ] of ' Total Depth ] 0 ft. Ground Elev... 830 ft. General Notes & Location Die,Item soil~ reddish brown in color Glacial till consisting of sandy silty gravels with admix[nrc of and boulders, dark gray in color and minor clay Gravels suban~ular to subround¢~ {ome boulders to.2 - 3{ It, Bottom of test pit Trench 10 ft. deep approximately 9 ft. lon~ du~ with backhoe 2227 SPENARD RD. ANCHORAGE~ ALASKA - ~ PHONE~ 272-4114 Date Se¢on ©ct:. 2, 1971 : ~'~c~._~27.~.~ lC Halo ~o. Test Pit No. 4 ; ' - ~ Shoot Pro/oct &'omo ~'euss Subdivision ' -. '~ ............. :¢--~.'~ ~ Project No.~Locotion ~agPe River Valley General Nofo~ Method Used Test ~ Rig Backhoe Field Party Geolo'gist Grey Sampling DESCRIPTION ~ ~oil t~po, cotoG toxturo, o~t, porticol uizo~ % - ~ c -~ ~ ~ ~ ~ notes on drilling ease, ~its used, otc. BL~ 2d = [c : ~ '~ ~ ~ ac ~° SAMPLING METHOD, i.e., I o ~ ~ c E c ~ c Splltspoon=S.S. 1.4 or2.5, Shelby tuborS.~ . o o ~ ~:~, .~'- ~ ~ ~ ~ .~ Modified shelby Iubo=M.S.T~ Dia. drill core= ~. ~ ~ ~ ~ ~ ~ D.D.C.~ Chip somple=C.S, Grob scruple =G.S. 0-_///. Residual soil, reddish bro~ with roots, sandy silt I I~ ' Glacial till wi~ silW ~andy gTavelr some cobble & boulder size [Z- ~" ? material and some minor clay matr~ --- Gravels subrounded re suban~lar 4-~ ~" Trench 11 fr. dce~ and a~proximatc]y 12 fr, wide s]opina inward ' 3 ft. at bot~om l { - - ~ Material compact to dense 10_ ~,.,,/ Last 1~ ft. space re contain more coarse sand size material 11- . , . ] RaCom of trench 3- 8- 2227 SPENARD RD. ANCHORAGE, ALASKA _i ~'r ' ' ;: PHONE* 272-4114 Road Cut No. Road Cut No. Road Cut No. 0 -J.' OBSERVATIONS ON ROAD CUTS AND FOUNDATION EXCAVATIONS THROUGHOUT PROPOSED SUBDIVISION i (occurs on top of steep north-south trending ridge) Organics ' Residual soft Sandy gravels 2 (appears to be small drumlin trending south-southeast) Residual soil, red-brown · Silty sandy gravels with some cobbie size Silty sandy gravels, gravels small size, more sand 3 Residual soil, red -brown Glacial till silty sandy gravel Road Cut No. 4 0 - i' Residual soil,' red to brown, sandy silts 1' - 7' Sandy gravels to gravelly sands House - Foundation Cut No. 1 0 -1' Residual soil, redish brown Silty sandy gravels with some cobbles Medium to fine sand lenses nearly horizontal 1'- 3' thick, dips to east moderately underlain by silty sandy gra,/els DTI00i331 6 /0 PlA T/~PPROV,41 SURVEYOR5 CERT/FICAT~ (~ ......... -':'"- DTI001332 LEGEWD: NOTE: PLAT OF PREUSS SU~D UNIT ~ m.~=o.~s~w...,~, s....~(o~..~) tm'. ~,~,~,~.,~ **~ ),~. ~ ~,'/,~, ,..~ A &UBD. OF TRACT &'2, UNIT NOS