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HomeMy WebLinkAboutAPA4033..t, TK 1425 .88 A23 no.4033 GEDTECHNICAL EVALUATION :THE SUSI'INA HYDIDELECI'RIC PROJEcr. I '-------~~----_._------------- r· ..:..'(f"r c ~~~~..~ESmAI;ICH CORPORATiON ~~~.¥/1JHE ALASKAN THINK TANK ','D<J~TBlGATHEFHNG •ANALYSIS •~RESEARCH •IDEAS S.R~80X 10612 -FAIRBANKS,ALASKA 99701 -PHONE 19071 47!Hl107 TK I Y'J5 I~~ 1123 f)0 I Va 33 GEOTECHNICAL EVALUATION THE SUSITNA HYDROELECTRIC PROJECT Prepared by Lawrence Katkin Dynamic Research Corporation December 10,1979 ARLIS Alaska Resources Library &Information Services Anchorage,~~aska - .. SCOPE OF THE REPORT Originally,this report was to be an evaluation of the Igeotechnicalportions of the three proposed f~asibility studies for the Susitna Hydroelectric Project. Since one of the three studies has already been decided upon by the Alaska Power Authority,the original intent of this report has been somewhat altered. Because all of the proposed feasibility studies have based their procedures and conclusions on previous studies performed or contracted-out by the U.S.Army Corps of Engineers,this author has researched all of the current studies dealing with the Susitna Hydroelectric Project.He has,furthermore,evaluated the conclusions reached by the U.S.Army Corps of Engineers as well as the proposal introduced by Acres American Incorporated, focusing attention on how well they address the potential geologic hazards involved in this project. "'rk!£.j'd5'- \'0,.)25 rif's GEOTECHNICAL OVERVIEW OF THE PROJECT A geotechnical site evaluation of a project of this type is basically concerned with two things: 1)The sUitability of the foundation 2)The existence of a sufficient quantity of suitable construction materials which are to be derived from the earth. Some geotechnical parameters to be considered in the eval- uation of the proposed foundation and reservoirs are: ~. The parameters involved with the construction materials to be derived from the earth are as follows: 1) 2) 3) 4) 5} 6) 1) 2) 3) 4) The seismic activity of the area The seismic stability of the rocks and soils The porosity and permeability of the rocks and soils Potentially hazardous geologic structures Permafrost with thaw-unstable properties Frost-Susceptible soil Determine the existence of necessary quantities Determine the quality of the material Determine .the amou~of processing necessary to produce the quality needed Determine potential probl~ms involved with excavation of materials. .~.: .- - EARTHQUAKE EVALUATION OF THE SITE The proposed sites lie in an area which has been determined to be of considerable seismic activity.In order to accurately calculate the hazards of earthquake potential in this area,a thorough seismic history is necessary. In 1971 the USGS set up a network of seismic stations in southern Alaska which were effective in accurately determining the location and magnitude of the epicenters in the proposed dam sites. The tectonics of the region are too poorly known at this time to make a reliable prediction for the distribution of events which may strongly shake the damsite (Kachadoorian,1975). In addition,the Denali fault,which lies less than 80 km.North of the proposed damsite,is a major strike-slip fault with geologic evidence for a 3 cm.lyear average Holocene slip.This fault could sustain an event of 8.0 magnitude on the Richter Scale (Kachadoorian,1979). The most recent report issued by the U.S.Army Corps of Engineers (Supplemental Feasibility Report,Main Report 1979), quotes a recent United States Geological Survey Report as saying: "Reconnaissance of the proposed Devil's Canyon and Watana Damsites and reservoirs did not uncover evidence of recent or active faulting along any of the known or inferred faults.Their studies did not find any evidence of the Susitna Fault which was previously thought to exist a short dis- tance west of the Watana Damsite;therefore,they were not able to confirm the existence of such a fault." After reading the same USGS Report ("Reconnaissance of the Recent yeology of the Proposed Devil's Canyon and Watana Damsites EARTHQUAKE EVALUATION OF THE SITE (Page 2) Susitna River,Alaska"),I find that the conclusions drawn by the U.S.Army Corps of Engineers are out of context and misleading.~ Under the section entitled "Procedures",the USGS authors state: "Our criteria for designating a fault as active were constrained by the local geology.Much of the area around the Devil's Canyon and Watana Damsites is covered by late Wisconsin glacial sediments." When the USGS authors made the statement that they could not find evidence of active faulting,they were making that statement in regards to the specific technique of ground and aerial observation,and based solely on that technique. Although the potential hazard of earthquakes is somewhat understated by the U.S.Army Corps of Engineers,the Acres American proposal thoroughly addresses those potential hazards. - .. SEISMIC STABILITY OF THE SITE The earthquake stability of the soil and rock in the damsite area is equally as important as the frequency of magnitude of earth- quakes in the region. On March 27,1964,a major earthquake hit Alaska.This tragic event yielded a wealth of information regarding the earth- quake susceptibility of soils. Some of the major damage to the Anchorage area was caused by normally stable soils which liquefied,due to the severity of shocks caused by the earthquake.Many of those soils which were liquefied,caused stable soils above to float. In Homer the vibrations of the earthquake caused large bodies, of sand and gravel to consolidate,thus causing well pipes which were flush with the gr()und,to protrude several feet above the ground. Inhabited places,however,which were located closer to the epicenter,felt little or no effect because of their location upon bedrock. Thus,in order to properly evaluate the damsites,there should be an intensive investigation to determine the location and extent of any soil that is considered earthquake susceptible. 80ils that either settle or liquefy when acted upon by earthquakes are considered earthquake susceptible . The only discussion of earthquake hazards noted by the U.8 ..Army Corps of Engineers is in the report ent i tIed "Earthquake Assessment at the Susitna Project,Alaskan written by E.L. Krinitzky of the U.S.Army Engineering Waterways Experiment Station. This report sufficiently addresses the problems that can be caused by earthquakes,such as the plastic properties of rock understrain,landslide activity along the fault,etc.But no mention is made of liquefaction._ The Acres American proposed study does intend to investigate liquefaction of areas along the transmission line and major access routes.Although their study is limited to those areas, just their mention is enough to note that they are aware of this potential geologic hazard. Note:R.Migliaccio,founder of the R &M Consultants,which is the geotechnical subcontractor for Acres American,is an expert in the field of earthquake susceptibility.Mr.Migliaccio was instrumental in documenting and evaluating the damage which occurred in the 1964 Alaska Earthquake. - GEOLOGIC STRUCTURES The one potentially hazardous geologic structure is the existence of faults. As previously stated,the study area lies in an area of considerable seismic activity.Many of the previous studies of the area have tried to correlate the relationship of seismic activity to the faults. According to Kachadoorian and Moore 1978,E.L.Krinitzkey 1978,it is difficult to correlate the relationship of seismic activity to the faults due to a lack of accurate data. Although there has not been any definite correlation between the local faults and seismic activity,it is important to note that there are a good number of faults.Table 1 on the following page lists the faults in the study area. Another potential problem could arise from the altitude of some of the bedding planes. The right abutment~of the proposed Devil's Canyon Site exhibits bedding planes that strike approximately N70 0 E and dip 600 E.The configuration of the bedding altitude and the canyon alignment may result in the bedding planes corresponding rather closely to the theoretical shearing plane formed by the arch thrust at the abutment (U.S.Army Corps of Engineers,1976). The left abutment of the Devil's Canyon Site exhibits southernly··dipping beds on an overhanging cliff.In some cases southernly dipping beds have resulted in large blocks separating from adjacent bedrock.(U.S.Army Corps of Engineers,1976). EARTHQUAKE INDUCED BY THE PRESENCE OF THE DAM ITSELF In addition to the naturally occurring earthquake.activity in the region,there is also the hazard that filling a reservoir may trigger a potentially dangerous earthquake (with as large a magnitude as 6.0 on the Richter Scale)in the immediate vicinity of the damsites (Lahr and Kachadoorian,1975). In a recent USGS Report ("Reconnaissance of the Recent Geology of the Proposed Devil's Canyon and Watana Damsites, Susitna River,Alaska lf ),it is highly recommended by authors Kachadoorian and Moore that continuous monitoring by a local network of seismic stations in the region begin well in advance of the filling of the reservoirs.Unless the natural seismic level is established,an important opportunity to study induced seismicity will be lost. Both the U.S.Army Corps of Engineers and Acres American have thoroughly addressed this potential problem. .. .. TABLE 1.*Inferred faults in the general area of the Devil's Canyon and Watana damsites,Susitna River,Alaska Number 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. ..II. 12. 13. 14. 15. 16. Designation Zone of intense shearing Talkeetna Thrust Near Watana Creek Near Portage Creek Chulitna River North of VABM Sheep West of VABM Sheep Susitna Fault Near"Clarence Lake Near'VABM Windus North of VABMs Grebe- Mt.Watana East of VABM Sumarti- dason Watana Creek Along Portage Creek North of Denali Cretaceous to recent shearing Type Thrust Thrust Thrust Thrust Thrust & Vertical Strike Slip Strike Slip Strike Slip High Angle High Angle Thrust Strike Slip Normal Thrust Thrust Complex Remarks Evidence is stratigraphic and petrographic. Evidence is stratigraphic. Evidence is stratigraphic. Evidence is stratigraphic. Evidence is stratigraphic. Right lateral with some vertical displacement. Two faults:left lateral & right lateral. Evidence is topographic lin- eament;inferred to be righl lateral from seismic data. Displacement apparently verl Displacement apparently verl Evidence is apparently.str~ Evidence is questioned. Evidence is stratigraphic. Alternate trace for number l Evidence is apparently stral Evidence partly stratigraph: *Abridged from "Reconnaissance of the Recent Geology of the Proposed Devil's Canyon and Watana Damsites,'Susitna}.R.,Alaska"(Kachadoorian & Moore ~1979). POROSITY AND PERMEABILITY .. A potentially serious hazard for any dam is its failure due to uncontrolled seepage.Porosity (the volume of air space in a rock or soil)and Permeability (which deals with the inter-,;0- connections between these small airspaces)are two engineering properties of soil and rock that cannot be overlooked. In addition,the ponding of water (which could thaw perman- ently frozen soils)could highly affect the permeability of rocks and soils in the area. Since permafrost does exist in the reservoir area of the """, Watana site,these potential hazards should be carefully studied. It has been mentioned that a deeply buried channel striking east-west has been located on the Left Abutment Saddle Dam at the proposed Devil's Canyon Site.This feature has higher perm- eability than the surrounding rocks.It could be necessary to -either seal this channel or else excavate and backfill with non- pervious materials. .. ~- -- - .. PERMAFROST The subject of potential hazards due to permafrost has previously been mentioned in the section dealing with porosity and permeability. It should also be noted that many soils which are permanently frozen are earthquake susceptible when in the thawed state. Permafrost has been a subject of an intensive amount of research.Both the U.S.Army Corps of Engineers and Acres American are well aware of its characteristics and effects. ---------"""',_.-----.,.",...;------------ MATERIALS Recent investigations by the U.S.Army Corps of Engineers have indicated that the gravel necessary to build the earthfill dam at the proposed Watana Damsite does not exist in sufficient quantities for the construction of the dam. The Watana Dam design has been altered accordingly by changing the gravel shell to a rock shell and by widening the semipervious core. Table 2-:lists the types and quantities of materials necessary to construct the proposed Watana and Devil's Canyon Dams. Although it is reasonable to substitute crushed rock for gravel fill,a question arises as to whether the designers plan to use processed rock to replace the aggregate'in the concrete,if -sufficient quantities of gravel are not to be found.• This is an important question as regards the quality and cost of the proposed project and one which will eventually have to be addressed. ~.' 1Ifii'!.. .~ Type of Material Concrete Requirements Impervious Core Semipervious Core Filtle Filters Coarse Filters Pervious Rock Shell Riprap TABLE 2 * Devil's Canyon Dam (cu/yds) 2,600,000 Watana Dam (cu/yds) 2,000,000 7,373,000 6,077,000 5,621,000 2,201,000 36,297,000 223,000 .. *Data supplied by the U.S.Army Corps of Engineers,1979 CONCLUSIONS This report has illustrated that the proposed Susitna Hydro- electric Project poses several geotechnical problems as to its feasibility.Most of the problems should be answered by the study to be performed by Acres American Incorporated. However,with the amount of data which has been collected to date,it seems difficult to say whether the project is or is not feasible.A more logical assessment of the situation could be made upon gathering and compiling more extensive data. - REFERENCES CITED 1.Anon.,1976,Southcentral Railbelt Area,Alaska U.S.Army Corps of Engineers.Part 1 2.Anon.,1978,Southcentral Rai1belt Area,Alaska U.S.Army Corps of Engineers.Appendix,Part 1: Supplemental Feasibility Report. 3.Anon.,1979,Southcentral Railbe1t Area,Alaska U.S.Army Corps of Engineers.Supplemental Feasibil~ty Report,Main Report. 4.Kachadoorian and Moore,1979,"Reconnaissance of the Recent Geology of the Proposed Devil's Canyon and Watana Damsites,Susitna River,Alaska','. 5.Katchadoorian,Reuben,1974,Geology of the Devil's Canyon damsite,Alaska,U.S.Geological Survey Open-file Report 74-40,17 p. 6.Lahr,John C.and Kachadoorian,Reuben,1975,"Preliminary .geologic and seismic evaluation of the proposed Devil's Canyon and Watana Reservoir areas,Susitna River,Alaska: Informal report to the U.S.Army Corps of Engineers. 7.Krinitzky,E.L.,1978,"Earthquake Assessment at the Susitna . Project,Alaska (U.S.Army Waterways Experiment Station, Vicksburg,Mississippi) Anon.,1979,"Susitna Hydroelectric Project:Plan of Study", Acres American Incorporated. 8.Krinitzky and Chang,1977,"Specifiying Peak Motions for Design Earthquakes,State-of-the-Art for Assessing Earth- quake Hazards in the United States,MP S-73-l,Report 7, Waterways Experiment Station,Vicksburg,Mississippi,34 p ..... ,...."...... 9"". ---,-------~--,---------------------------_._-- ~, - "'" DVNAMIC RESEARCH CORPORATION THE ALASKAN THINK TANK DATA GATHERING •ANALYSIS.RESEARCH •IDEAS S.R.BOX 10612 -FAIRBANKS,ALASKA 99701 -PHONE (907)479·8107 PRELIMIARY EVALUATION OF THE GEOTECHNICAL PORTIONS OF THE SUSITNA HYDROELECTRIC PROJECT PROPOSALS PREPARED FOR THE.LEGISLATIVE AFFAIRS AGENCY OF THE STATE OF ALASKA SCOPE AND PURPOSE OF THIS REPORT THIS REPORT HAS BEEN PREPARED AS "AN AID FOR THE EVALUATION OF THREE PROPOSALS FOR THE ENGINEERING AND FEASIBILITY OF THE SUSITNA HYDROELECTRIC PROJECT. THE SCOPE OF THIS EVALUATION HAS BEEN LIMITED TO THE GEOTECHNICAL <!!!!II"PORTIONS OF THE THREE PROPOSALS. IT SHOULD BE NGTED THAT THE EVALUATION HEREIN CONTAINED IS A PRELIMIARY EVALUATION PREPARED AS AID TO THE AGENCY AT THE ALASKA POWER AUTHORITY HEARINGS IN ANCHORAGE TO HELD SEPT.27TH &28TH. THE PURPOSE OF THE EVALUATION IS TO ISOLATE WEAK POINTS IN THE PROPOSALS,NOTE THESE WEAK POINTS,AND PREPARE QUESTIONS FOR THE HEARINGS THAT WILL EITHER ILLUSTRATE A PROBLEM,OR ALLOW THE CONTRACTORS OF THE PROPOSALS A CHANCEIIBETTER CLARIFY THEIR POSTION ON THE RECORD. "Ttl - IJ$il!It., DIHECTED TO: BACKROUND: QUESTION: QUESTION 1 THE ALASKA POWER AUTHORITY THERE LIES IN EACH PROPOSALS AN INHERENT CONFLICT OF INTEREST BETWEEN THE CONTRACTOR AND HIMSELF.FOR IF AT POINT DURING THE STUDY THE CONTRATOR WERE TO CONCLUDE THAT THIS PROJECT WERE NOT FEASIBLE THE CONTRACTOR WOULD LOGICALLY CEASE THE STUDY.THIS PREMATURE TERMINATION OF THE STUDY COULD COST THE CONTRACTOR AS MUCH AS FIFTEEN MILLION DOLLARS IN GROSS INCOME. WHAT INCENTIVES AND SAFEGUARDS ARE INCORPORATED IN THE PRESENT CONTRACTUAL STRUCTURE TO INSURE THAT THE CONTRACTOR WILL NOT OVERLOOK ANY ITEMS THAT MAY RESULT IN EXCESS COST TO THE STATE,OR OVERLOOKING ANY ITEMS THAT MAY LEAD TO THE CONSTRUCTION OF A PROJECT THAT MAY TURN OUT TO BE 'HAZARDOUS? ---,~~--".""-------_.-.-------",,,,,,,------------------ DIRECTED TO: BACKROUND: QUESTION 2 EICO THE OTHER TWO CONTRACTORS (ACRES &HARZA )BOTH SEEM TO BE SPENDING SUBSTANTIALLY MORE ON THE GEOPHYSICAL PORTION OF THE PROJECT. ACRES HARZA EICO GEOTECHNICAL EXPLOR. SEISMIC STUDIES DRILLING PROGRAM 3,620,500 2,167,000 1,174,000 984,000 (UNDET.)979,000 2,590,000 562.000 1,000,000 QUESTION:~YOUR SEISMIC STUDIES ~SO BARE,ESPECIALLY .SINCE YOU NO'!i THE $300,000 of the $562,000 IS TOWARD INSTRUMENTS? - QUESTION 3 DIRECTED TO:ALL CONTRACTORS BACKROUND: QUE:STION: IT HAS BEEN NOTED BY DR.OSTERKAMP A SPECIALIST IN PERMAFROST AND ICE PHYSICS AT THE UNIVERSITY OF ALASKA GEOPHYSICAL INSTITUTE J THAT THE PRODUCTION OF A THERMAL MODEL OF THE ENTIRE DAM SITE AND RESERVIOR IS ESSENTIAL TO THE PLANNING OF THE SUSITNA HYDROELECTRIC PROJECT. CONSIDERING THE IMPORTANTS OF HAVING A THERMAL MODEL OF THE DAM SITE J WHAT WAS YOUR REASONING FOR OMITTING -THIS TASK FROM YOUR PROPOSALS. ----;---------------------,------- \Jc ;!j11, DIRECTED TO: BACKROUND: QUESTION: QUESTION 4 ALL CONTRACTORS SINCE IT IS BELIEVED THAT A DRILLING PROGRAM IS THE BACKBONE OF A GOOD GEOTECHNICAL STUDY,COULD THE CONTRACTORS BE A LITTLE MORE SPECIFIC IN REGARDS TO THEIR DRILLING PROGRAMS. APPROXIMATELY HOW MANY HOLES DO YOU EXPECT TO DRILL? APPROXIMATELY WHAT AREAS WILL YOU BE CONCENTRATING YOUR PROGRAM ON.APPROXIAMTELY HOW DEEP WILL YOUR HOLES BE. ALTHOUGH THESE ???ARE VERY SPECIFIC AND FAIRLY TECHNICAL !'>" FOR THIS PARTICULAR TIME YOUR COST ESTIMTES ON YOUR DRILLING PROGRAM HAD TO BE BASED ON SOMETHING. i!I\ISOFORTHERECORDC~YOU GIVE US SOME SPECIFICS ON YOUR DRILLING PROGRAM? DVNAMIC RESEARCH CORPORATION THE ALASKAN THINK TANK DATA GATHERING •ANALYSIS.RESEARCH.IDEAS S.R.BOX 10612 -FAIRBANKS,ALASKA 99701 -PHONE (907)479-8107 MEMORANDUM TO: FR0M: Representative Brian Rogers House Committee on Aternatives To Susitna Larry Katkin Geotechnical Consultant The Acres American In.Propsal - SUBJ: ** * ***'***** * * * - '-- I have briefly reviewed the Acres American proposal for any defects in the geotechnical portion of the proposal. The proposal covers such a vast number of areas that each area or portion is presented in a very general manner.It is therefore difficult to unfold·any tech- nical defects that are of a specific nature. The only noteable defect I see in this proposal is the omission of any procedure investigating the permeabilty of rocks in the ponding areas.Acres failed to mention permeabilty as a potential hazard in their list of potential hazards presented at the APA hearing in Anch. Although the proposal ~s general the geotechnical port- ions illustrate procedures sufficent to produce a fair- ly accurate study.