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HomeMy WebLinkAboutAPA2348I I I I I I I I I I I I I I I I I I I I ' t I I i . j ?re'Jsred by: I I I I I I ~~IU I ' SUSITNA HYDROELECTRIC PROJECT ACRES SPECIALIST CONSULTANTS PANEL REPORT NOVEMBE~ 18, 198'1 L L_ ___ j _ --ALi~S~<A POVVER AUTHORITY_. __ ___. ~£~~£c~@£@©@ ·-------------- Susitna Joint Venture Document Number ..---------------------, Please Return To DOCUMENT CONTROL ' l I I ! I i I I l l ' .I J 1 I /r I 1 I J I I ?repared by: r-... -, I . .·· 1 lllm! St!S,TNA HYDROELECTRIC PROJECT ACRES SPEC:ALiST CONSULTANTS PANEL me e. ti~J Wo. 1- REiiORT NOVEMBER 18, 1£~&1 • I I I 1 ~ l ASKA POW· E R }\. u-H· OR. 1 ~TY ----------1 __ .,___ __,.._ I .. ill . · , . r\ ! · . 1 . _........ .. -·J I I I I I I I I I I I •• I I I I I I I ALASKA POWER AUTHORITY SUSITNA HYDROELECTRIC PROJECT REPORT ON SPECIALIST CONSULTANT PANEL MEETING NO. 4 NOVEMBER 18, 1981 TABLE OF CONTENTS 1. INTRODUCTION 2. AGENDA 3. LIST OF ATTENDEES 4. MEETING OBJECTIVES AND STUDY STATUS 5a UPDATE ON SEISMIC STUDIES 6. UPDATE ON GEOTECHNICAL FIELD WORK 7. DAM LOWERING-UPDATE ON ECONOMIC STUDIES 8. RELICT CHANNEL TREATMENT 9. WATANA DAM MATERIALS 10. WATANA DAM DESIGN 11. OTHER DAMS 12. PRESENTATION BY J. D. LAWRENCE 13. PRESENTATION BY D. W. LAMB 14. REPORT BY SPECIALIST CONSULTANTS I I I I I I I I .I I I I I I I I I I I ALASKA POWER AUTHORITY SUSITNA HYDROELECTRIC PROJECT SPECIALISTS CONSULTANTS PANEL MEETING NO. 4 BUFFALO, NEW YORK -NOVEMBER 18, 1981 1. INTRODUCTION -----~ P5700.13.30 Acres Specialists Consultants Panel Meeting No. 3 took place October 6-8, 1981 in Buffalo in conjunction with the APA External Review Board Meeting Noe 3. The meeting was attended by Dr. A. Hendron, Dr. L. Syke5 and Mr. M. Copen representing Acres Specialists Consultants Panel. Dr. R. Peck was unable to attend. The current meeting has been convened to review further work undertaken by Acres in the interim period. 2. AGENDA 08:30 -Meeting objectives and study status -J. Lawrence 08:45 -Update on seismic studies -V. Singh 09:15 -Update on geotechni~al field work -s. Thompson 09:45 -Discussion 10:15 -Coffee 10:30 -Dam lowering -update on economic studies -J. Lawrence 11:00 -Relict channel treatment -D. W. Lamb 11:30 -Discussion 12:00 -Lunch (brought in) 13:00 -Relict channel discussion (cont'd) 13:45 -Watana dam materials -D. W. Lamb 14:15 -Discussion 14:45 -Watana dam design -D. W. Lamb 15:15 -Coffee 15:30 -Other dams -D. W. Lamb (saddle/cofferdam designs, construction materials, foundation treatment) 16:15 -Discussion 3. LIST OF ATTENDEES Acres External P~nel Members Dr. R. Peck Dr. A. Hendron (Dr. L. Sykes and Mr. M. Copen were unable to attend) I I I I I I I •• I I I I I I I I I I I 3. LIST OF ATTENDEE~ (Cont'd) Acres Dr. D. H. MacDonald ) J. MacPherson ) Internal Review Panel L. Wolofsky ) A. H. Tawil ) J .. D. Lawrence ) s. N. Thompson ) Participants D. W. Lamb ) v. Singh ) N. Bond/D. Peck -Recorders G. Krishnan (part-time) ) J. Plummer (part-time) ) R. Miller ) Observers L. Duncan ) R • Ibbotson ) 4. MEETING OBJECTIVES AND STUDY STATUS (Speak_er: J. D. Lawrence) After general introductory remarks, the last APA external panel meeting on October 6-8 was briefly summarized. The main points raised by the APA panel were that there are no active faults of any concern at the project site. A magnitude of 6.5 floating earthquake at 5 km from project site should be considered~ Woodward-Clyde 'reported that the location of the 1943 even~ lines up with the extension of the Talkeetna fault and this was a matter to be further resolved. The APA panel were concerned about the excavation slopes associated \'lith the Watana diversion tunnel portals. This problem has been addressed in design. · A hydrothermally altered zone in the Watana powerhouse cavern area was noted and as a result the powerhouse has been moved away from this zone. At Devil Canyon the slopes associated with the spillway excavation gave some concern. These slopes have now been flattened and follow the dip of the bedding plane. To avoid these flat·slopes a tunnel spillway was studied but not considered practical or economic. Because of the relict channel, the APA panel had suggested lowering the main dam height at Watana. Questions were asked about the core material for Watana dam which had been further studied and the results were included in later presentation. The panel also questioned the results of dam stability analyses under seismic conditions, suggested the adoption of an inclined core, and expressed con- cern about permafrost under the saddle dam. I I I I I I I I I I I I •• I I I I ·I I Fixed cone valves were now proposed for spillway discharge of up to 24,000 cfs at Watana and Devil Canyon. These valves have the advantage of not causing nitrogen supersaturation of the water which is harmful to fish. The panel suggested lowering the height of the fuse plug embankments for the emergency spillways and widening the spillway channels. This has been put into effect. 5. UPDATE OF SEISMIC STUDIES (Speaker: V. Singh) 6 • Of the 13 features in the study area, only five have been identified as faults. There is a good degree of confidence that these faults are not active. Woodward-Clyde have proposed an earthquake magnitude of 6 or less for both · sites. More work is being done on the floating earthquake criteria. A meeting was planned on 23 November with Dr. Sykes to discuss this. It is thought that a magnitude of 6.0 at 4 to 5 km distance should be adopted. Dr. Sykes' recent work puts the 1943 event to within 25 km of the Talkeetna thrust extension with an epi centra 1 accuracy of +20 km. Therefore·, in the worst case scenario the event could be as close as 5 km from the Talkeetna thrust fault. So far the Talkeetna thrust has been considered inactive but the question should be asked "what happens if it is active?11 This question is being addressed. Woodward-Clyde are continuing work on analysis of the likeli- hood of an ea~rthquake occurring at the site and reservoir-induced seismi- city. UPDATE ON GEOTECHNICAL FIELD WORK (Speaker: S. Thompson) A brief summary of exploration ~y others since the conception of the pro- ject was presented. Locations of boreholes 9 seismic lines, borrow areas and details of testing carried out for Watana and Devil Canyon site were shown. The main features were identified on an overall geolog1c map. At Watana the main rock types are granodiorite and andesite. Tne andesite is an extrusive material. Where drilled, the contact between the andesite and granodiorite is weathered. This weathered zone has been found to be on the order of several feet of thickness. No evidence for a thick paleosoil zone has been found. A major shear zone, "The Fins", on the north bank has affected the lor.ation of upstream diversion portals. I I I I I I ~ I I I I I I I I I I I I I 7. Boreho'l es 3 and 4 have been dr i 11 ed recently into powerhouse area and have encountered an altered soft zone of rock 5 feet to 10 feet in thickness. Although this is not considered to be a fe·ature that would affect the fea,s- ibility of the underground powerhouse, it has been considered in relocating the powerhouse slightly· upstream. Photographs of typical altered rock, major features and rock jointing were presented. A composite joint plot of several thousand joints was shown and major trends identified. Various sections through the site were discussed and borrow and quarry areas described. The location and nature of the buried channel was described in detail. Further investigations have now shown that for a pool elevation of 2215 feet, the width of the channel is 1600 feet and has a maximum depth of 450 feet. Nine boreholes have been drilled in the area by the Corps of Engineers. The material in the channel consists of sand, gravel, and clays in a complex stratified sequence. At this time it was noted that there is not enough data to analyze flow paths. At Devil. Canyon a brief description of the geology was given and the main features were pointed out. The rock was described as good quality with high RQD's. The rock type is greywacke and argillite. The dip of the bedding being a controlling influence. A series of dikes and associated shears trend approximately north-south across the river. Joint plots were presented together with sections showing major features. The area of open jointing on the south bank explored by BH3 was identified as an area requiring further investigation. DAM LOWERING.-UPDATE ON ECONOMIC STUDIES (Speaker: J. Lawrence) . As general background present 1 ayouts of both Watana and De vi 1 Canyon dams were described. It was noted that the way in \-Jhich the reservoirs will be operated is still being refined. There were three factors to be considered: (1) environmental (2) energy (3) cost A major factor to be considered in the dam lowering study is that if the dam is lowered by more than·5o feet, an emergency spillway cannot be pro- vided. The main spillway would have to be designed to handle the PMF. It was noted that there was concern by the APA panel about the saddle dam st~ ~t:y under seismic loading and the relict channel treatment. The pan< ~ the last meeting suggested lowering the dam to reduce or eliminate these ~· ;blems. Preservation of ideal downstream flow for the fish is not compatible with production of maximum usable energy. Any attempt to com- promise on these coQditions will require the reservoirs to be fluctuated, and this will limi~ their recreational use and could cause problems with caribou crossing the river in winter. I I. I I I I I I I I I I I I I I I li I Two years were considered for the study: (1} 2010 -Watana and Devil Canyon operational (2} 1994 -Watana only operational Four operating conditions were considered: (A) Meeting damand -producing maximum winter energy Summer flow restricted Uniform thermal load (B) Constant thermal/hydro ratio (not now considered) (C) Compromise between (A) and (D) (D) Unrestricted summer flows Reduced usable energy Dam elevations: (1) 2215 feet (2} 2165 feet ·(3). 2115 feet were considered Cases analyzed: Elevation 2215 2165 2115 A X X X B c X X X 0 X It was noted that the flow requirements for fish are all based on flows at Gold Creek. Graphs were shown i 11 ustrat i ng the flows av ai 1 ab 1 e downstream, the amounts of usable hydro energy produced and amounts of thermal energy required to meet total demand (see Section 11). In Case C, 13,000 cfs are·spilled downstream against the 20,000 cfs minimum requirement for fish considerations. Dr. Peck asked what the lowest summer flows were, suggesting that if this were tolerable for one season, maybe it would be tolerated every year. Acres produced flow records to show that the lowest summer flow recorded is 8,900 cfs, whereas Case C gives a flow of 12,000 cfs under average annual flow conditions. In Case 0, not all the energy available is usable. In Case C, based on an approximate rule of thumb in which 1 GWhr = $1 million dollars, the energy lost by lowering the dam 50 feet is equivalent to $220 million dollars. Therefore, if there is a savings less than this amqunt by lowering the dam, then this may be the optimum solution. I I I I I I I I 8. I I I I I I I I I I I . . ... ;: • • . • \ . f •• • _t was noted that predicted energy demand growth curve is based on present conditions and forecasts and does not reflect the possibility that the existence of the Susitna pro~iect could stimulate demand. It was noted that the drawdown of reservoirs will be considerable. Pr·elim- inary estimates arf~ as follows: For Case D: Watana drawdown -172 feet Devil Canyon drawdown -398 feet (for maximum pool elevation 2215 feet) For Case. C: Watana drawdown -202 feet Devil Canyon drawdown -228 feet The possibility of pumped storage from one reservoir to the other was briefly discussed. Acres pointed out that they had considered this earlier and found it impractical. RELICT CHANNEL TREATMENT (Speaker: D. W. Lamb) Slides and sections were presented showing the general layout of the channel. The section of reservoir boundary where bedrock is below 2215 elevation was indicated to be 16,000 feet wide. The channel is 7,000 feet long from Susitna River to Tsusena Creek. Information about the channel is available from seismic lines, borings, some of which extended to rock, and some sampling and testing. It was stressed that the geology of the channe·l is very complicated and a typical borehole log was presented to illustrate this. It was pointed out that there are surface lakes in the area, artesian pressure had been noted in some boreholes, drill water circulation lost and permafrost encountered. It is likely that perched water tables exist in the channel. The channel is 450 feet maximum depth and has a hydraulic gradient of about 10 percent. Dr. Hendron said that he had calculated the gradient to be about 6%. Acres confirmed that their figure of 10% was for the critical thalweg. Four major considerations were listed: (1) Leakage (2) Piping (3) Permafrost (4) Liquefaction From leakage studies so far carried out assuming lo-2 em/sec material~ the average water loss is about 85 cfs varying very little drop within pool elevation. This represents a capital loss of about $40 million. Since the actual gradient in the channe.l is uncertain, there may be concen- trated flows which may cause piping. Possible solutions of an upstream blanket and downstream filter were discussed. Both Dr. Peck and Dr. Hendron a. greed that the upstream b 1 anket should be ruled out. The cost would be excessive, in the region of $500 million~ and the stabi 1 ity of the material on the steep slopes cannot be assured. I I I, I I I I I I I I I I I I I I I I . . ·--. . . . . . . . I . . . ·.. . r ... , . . .. . . . .· ~ .. · .. -; . '. ;' fl . . . . ,;. The positive S€!epage cutoff by slurry \vall and cement grouting at present proposed by Acr·es was discussed. Dr,. Hendron suggested that the slurry \'10. 11 at sha llo'w depth was of doubtful va 1 ue. Dr. Peck suggested that the slurry trench wall be made d~eper, if cheaper than grouting. Acres replied that the depth had been limited by precedent considerations. Dr. Peck noted that the reservoir wi 11 take three years to fi 11 over the depth of the relict channel. If only the minimum treatment in the form of a down- stream fi 1 ter b 1 anket was cart ... i ed out at dam construction stage, then observations could be made and further treatment carried out only if neces- sary. Both members of the panel thought that the channel is unlikely to be a problem if treated in this manner.. They considered that the downstream filter to b~ just as effective a method as the slurry wall and grouted cut- offa The downstream blanket, according to Acres• preliminary design, will be 7 feet thick with a potential cost of $100 million if required to cover the whole of the downstream slopes. Dr. Peck said that if the material in the channel is horizontally strati- fied, then the maximum area of blanket will be required, but then added that a few vertical relief wells might well solve the problem. The effect of thawing of the permafrost is unknown, but increases in leakage could be handled by the filter. J. Lawrence asked the pane 1 if they envisaged r,rob 1 ems with the re 1 i ct channel that could not be dealt with. Dr. Peck thought that the filter could be placed quickly at the toe of the channel, in fact quicker than the dam could be lowered. Dr. Peck said that genera1-fy buried channels in fact turn out to be less of a problem then anticipatad during preliminary design phases of a project.. ' Dr. Hendron could not see liquefaction being a problem except in isolated zones which might lead to settlement of the saddle dam. Jo Lawrence stressed that only 15 feet of water were retained by the dam, and suggested that an allowance for settlement could be built into the dam. Dr. Hendron said that the liquefaction will not be regular and therefore the settle!'rent will lead to cracking. Acres said that only an 1,100-foot length of the saddle dam is normally wetted. . The panel considered that formation of a new channel by settlement due to liquefaction was very remote. Dr. Peck considered a downstream filter to be most effective since the area can be treated where necessary. The upstream blanket solution requires all treatment done in advance of filling the reservoir and considerable surface treatment before placing the b 1 anket. The amount of further investigations required for the re 1 i ct channe 1 was discussed but the panel noted that the need for investigations depended greatly on the method of treatment proposed. Dr. Peck considered the efficiency of cutoff grouting to 400 foot depth to be uncertain. I I I I I I I I I I I I I I I I I I I Dr. MacDonald quoted examples of similar channels with gradients of 1:1~ and 1:20~ The Peace River project with a gradient of 1:20 was mentioned. All these examples have not given any problems. Dr. MacDonald said that a downstream filter will be required in any case. He suggested that observations be taken over a 15-to-20 year period and only do work where required. He felt that the downstream filter was just as positive as a cutoff. It was noted that piezometers located downstream in the channel will indi- cate seepage before effects were noticed at Tsusena Creek. Acres noted that the. source of filter material is located less than one mile away in Tsusena Creek, and this area will not be flooded by the Devil Canyon Reser- voir. The possibility of raising the tailwater level in Tsusena Creek to reduce the hydraulic gradient in the re 1 i ct channel was discussed but was not considered viable. The pane 1 cone 1 uded that ther·e was no. urgent reason for doing anything in advance but stressed the need for continual observations. 9. WATANA DAM MATERIAL (Speaker: Do W. Lamb) Grading curves for core materials from Areas D and H were presented and discussed. It was noted that although the materials are ciassified as SM, they are quite we 11 graded. Qr. Peck said that the curve for fvti ca dam core materia 1 falls in the middle of range of curves for Watana material and that Mica was good core material. Acres noted that the surface layer of fine material Area H would be wasted. The modified proctor compaction curves were presented and it was noted that the natural moisture content of the material was 2 percent to 3 percent higher than optimum. Area H core material is 10 miles from the dam, contains extensive perma- frost, and is similar to the deeper materials from Area D. Ten or twelve tests have been done with PI values ranging b~tween 2.5 and 9.2 percent. For Area D at depth, the PI va 1 ue is up to 40 percent, LL up to 65 percent. Samples from twelve auger holes are being tested now giving PI results of 5 percent to 9 percent, but tests are being done with gradation cutoff above 2 inches because of sampling method. Gradation curves for filters were presented and it was noted that 13 per- cent was passing 200 sieve. Acres said that this materia 1 may be worked under water and may 1 ose some of the fines. I I I I I ·I I I I I I I I I I I I I. - I The filters fit into preferred filter envelopes, but the top end is still a little uncertain because of the sampling methods. Dr. Hendron suggested that the filter design incorporate current thought as described in Lowe's paper on Tarbela presented in Mexico. At Devil Canyon there is no till suitable for core material for the embankment dam. The manufacture of core material using bentonite was considered and found to be uneconomic. At present, the plan is to transp~rt material from Area H. There was general discussion about the variability of material from Area 0 and H sources. The curves were displayed overlain and looked very similar. Dr.. Hendron thought the grading curve ·of Area H 1 ooked better than Area D. Dr. Peck was surprised at the increase shown of PI with depth in Area D. Dr. MacDonald asked about the extent of permafrost in borrow areas. In reply Acres said that it was thought that Area D is less frozen than Area H but there was not enough data to be more exact. Dr. Peck could see no compelling reason to use Area H for Watana and con- sidered that it \'/auld be better to use the faster draining materials if, as results show, the natural water content is slightly above optimum. Dr. Peck said that generally lodgement tills are naturally close to optimum moisture content. He did not consider that even 3 percent above optimum would be a problem as long as placing traffic could run over it, even if major rutting did occur. T. Tawil pointed out that the compaction tests were done on material less than 3/4 inch. If less than Noe 4 sieve had been used, the optimum moisture content would have been higher. Also, he felt that the standard Proctor test would have been more suitable and \•IOuld have given an optimum closer to the nature moisture content and closer to the plastic limit of the material. 10. WATANA DAM DESIGN (Speaker: D. W. Lamb) The arrangement of the dam was briefly described. All overburden and weathered rock under the dam is to be removed and under the core and filters excavation to sound rock required. Sketches of grout- ing and drainage layouts were presented and discussed. The advantages of the grouting/drainage galleries were highlighted. The galleries wi11 run the entire length of the dam. They will provide flexibility of working with the embankment being constructed at the same time, permanent inspec- tion, facilities to perform remedial grouting when permafrost completely thaws, access to instrumentation, positive drainage and protection against freezing of drain holes. The question of piping of fines from rock into drain holes was raised. S. Thompson replied that he did not expect any problem with piping. If some piping in shear zones did oc·cur, holes could easily be cleaned or filters provided. . . The latest dam cross section was presented showing the free draining rock fill upstream shell and river gravel downstream shell. I I I. I I I I I I I I I. I I I I I I I Dr .. Peck was concerned about the use of compacted rock fill for the up- stream shell. He would expect such material to settle 3 feet to 4 feet on saturation during filling and this could give rise to a longitudinal crack in the crest of the dam. Acres explained that the present cross section was based on suggestions · from the last panel meeting when Dr. Seed was concerned about the drainage characteristics of the gravel. The pore wat~r pressure buildup under seis- mic loading was a major design factor and clean processed rock fill was chosen for the upstream shell for this reason. The unprocessed gravel for the downstream shell was chosen mainly on a cost basis. Dr. Peck was somewhat sceptical about the method of calculation of pore pressures within the dam. He stressed that there is no experience on rock fill behavior under seismic conditions. Dr. Peck expressed his fears that compaction of rock fill would result in crushing and breakage of the rock leading to an increase in fine material and a decrease in permeability. The analysis of pore pressures at Oroville dam was discussed. Acres said that f·irst analysis had ass·umed rock fill properties equivalent to those for the Oroville dam gravels. Dr. Peck said that assumed permeabilities for rock fill could be.misleading. He commented that the difference between rock fill and gravel were not significant for earthquake design." Dr. Peck was also concerned about the buildup of fines in the rock fill .even after processing. Acres did not think this would be a problem bearing in mind the strength of the rock. Dr. Hendron preferred a gravel material for the upstream shell because under earthquake loading the rock fill tends to be compressible and gravel with high cobble content tends to dilate. Lamb outlined the preliminary dynamic analysis done so far, which was based on properties of fill material from Oroville dam. Dr. Peck questioned the basic material properties.used and was concerned that such an analysis shou1cl f;<Jt control the design of the W~i:ana dam. Dr. Hendron advised doing laboratory tests on gravels to obtain more reli- able properties. Acres explained that this was planned but not in this phase of the work. The analysis of Boruca dam in Costa Rica was discussed. Dr .. Peck advi~ed that this might be helpful. Dr. MacDonald said he would look this up. Dr. Hendron suggested that zones of processed rock within the gravel upstream shell might be a cost effective compromise. Lamb stressed Acres' concern in design for safety against earthquake effects. The geometry of the dam was outlined with 2.25:1 upstream slope and 2:1 downstream slope for purposes of analyses. However, a 2.4:1 upstream slope was.being used for layout studies. There followea much discussion on the relative merits of sloping the core. Tawil pointed out that slightly inclined cores appear to be favored on a number of large dams. This arrangement is believed to give better compressive stresses in the core and less potential for cracking. I I I I I I I I I I I I I I I I I I I Theoretical analysis shows that for a symmetrical core, tensile stresses are produced on the downstream edge. An inclination upstream will prevent this.. Tawil quoted Mica and LG2 as exa.11ples of this. Dr. Peck did not agree that inclined cores '~'!ere selected for these r1:asons and explained that the location of the core at Mica was for reasons other than stress distribution in the core. The location of the core of Infer- nillo dam was also discussed. Dr. Hendron said that during shaking by an earthquake the she 11 s wi 11 tend to settle more than the core. With a central core, the shells will not tend to settle away from the core which could lead to cracking ~r the core. A multiple plot of dam shapes constructed worldwide was tabled. In conclusion it was generally agreed that symmetr,ical core is the most suitable arrangement for Watana dam. The det ai 1 at the dam crest was presented and discussed. Dr: Pe·ck said that even if a crack opened up 6 inches wide the whole length of the dam, this would not be a major problem. Lamb said that post-construction settlement of 1 percent for static and 0.5 percent (5 feet) for earthquake conditions, had been allowed. Dr. Peck thought that 1 percent was probably too much for the gravel fill downstream and not enough for the rockfill upstream. It was noted that it had been suggested that the settlement of rock fill . would be very small, in ~he order of 0.1 percent. Dr. Peck did not tnink · that this was an appropriate figure to use. Dr. Hendron suggested that a 25-foot to 50-foot wide zone be constructed next to the coarse filter in layers with half the normal thickness to pro- vide a well compacted transition zone. A brief description of the dynamic analysis of the dam section was present- ed. Lamb stated that at the previous panel meeting Dr. Seed was not happy about the size of the finite element mesh used for the analysis. Acres was intending to rerun the analysis using a smal~er mesh. The properties used were discussed and Dr. Peck stressed that whenever possible a range of properties should be uscJ in analysis. Both Dr. Peck and Dr. Hendron agreed that finding background ·information on this type of material was very difficult. The material properties used in the dynamic analysis, the earthquake 25 cycle history,, accelerations and shear stresses in the dam were displayed" The panel generally concluded that there was a need to firm up on material properties and geometry and then do further dynamic analysis. I I I I I I I I I . I I I I I I I I I I 11. OTHER DAMS (Speaker: D. We Lamb) Devil Canyon Saddle Dam It is proposed to use the same cross section as at Watana. All overburden will be removed. The core material is not available locally and will be imported from Area H. Dr. Hendron suggested that a concr~te-faced rockfill dam be considered at this location. Acres said that this had been considered but thought that there might be a concrete aggregate freeze-thaw problem with the thin con- crete slab. The possibility of using rollcrete was also discussed but Acres said this should be rejected because it was susceptible to freeze- thaw damage. It was pointed out that the grouting/drainage gallery would be extended from the main dam under the whole length of the saddle dam. In response to Dr. Hendron, Acres stated that no evidence of permafrost had been found. Cofferdams The cofferdam ·sections were reviewed. Dr. Peck questioned the proximity of the cofferdam to the main dam excavation. Acres replied that the final excavation for the toe of the dam could be done at. low river flow and the cofferdam reduced temporarily if found to be necessary. The program for construction of the slurry wall cutoff was discussed .. Acres explained that they had ruled out a sheet pi 1 e cutoff because of boulders. Dr. Peck was not happy about the proposed grouted cutoff at Devil Canyon. cofferdam and the slurry cutoff at the Watana upstream cofferdam.. He sug- gested the use of upstream impervious blankets and provision of extra dewatering in place of grouting. Lamb noted that an upstream blanket was not possible at Devil Canyon cofferdam because of the geometrical arrange- ment. The schedule of construction of the Watana cofferdam slurry wall was discussed. The closure in September would be followed by construction of the slurry trench. The embankment would not be placed during winter months. The cofferdam is required to full height by May 1. The slurry wall is to a maximum depth of 80 feet. Emergency Spillway It was exp!ained that there will be water against the fuse plug frequently but the plug is required to fail only at PMF. Dr. Peck was concerned that the plug might be frozen when PMF occurs. Acres said that PMF always occurs in summer months. I I. I I I I I I I I I I I I I I I I I Fog Lakes Relict Channel This is a similar channel to the relict cha~nel near the main dam but recent investigations show a maximum hydraulic gradient of 0.3 percent with expected flows of less than 4 cfs. Acres said this is not now considered a problem. The rest of the vJatana reservoir is surrounded by a 20-mi 1 e band of mountains. At De vi 1 Canyon the reservoir is surrounded totally ·bY rock. Concluding Remarks Dr. Hendron asked what Acres was going to do about the dam lowering at Watana. Acres said they were carrying out studies to determine the optimum pool 1 evel. Dr. Peck was not happy about the Watana saddle dam, even 10 feet high, and did not think that the slurry wall and grouted cutoff of the relict channel could be justified. He thought that the height of the main dam should be fixed on overall economic grounds. · Dr. Hendron said that Acres should make sure that if a saddle dam was required, then sufficient costs should be allowed for the preculiarities of the foundation. He also suggested that it might be possible to build the dam up to lower elevation with a wide crest and increase the height later if desired. J. Lawrence did not think this would be acceptable to FERC for granting the license. The panel recommended that the reservoir level be adjusted to eliminate the need for a saddle dam·. The PMF water 1 eve 1 wou 1 d then be fixed by the lowest ground level in the relict channel area with suitable freeboard allowance. · Dr. Peck quoted the example of the James Bay project \'Jhere the rock foundation was very irregular and was expensive to prepare. Acres should make sure they have sufficient cost for foundation preparation. NB/rmr P db A//J ~. ?(/ repare y: -------~'~r~ 117~\~--~~~~,~~--·---------­~~ I I I I I I· ~ •. I '·• I I I I I I 'I ,. I I I I 12. PRESENTATION BY J. D. LAWRENCE ( . I . . . . . I .DAM ELEVATlON . , ]l<ADE. -OFFS..! . · • ENYIT()NME.,NTAL • E,N~GY •CO'f>T ' . ~A ~~T" rl'~''lr·.t=oA· ~~ )n~'~ · ~f\f _.. ... I ~Jf'I~!V\..-·~ , Ur'"~~ • ., 1'z•n=e-er wrrrz ··sr z'PF'"k?etr~-"~iS£( ..... # • ~At> t>L.F.. l:>~Vf . • P~'\J\A~-y'SEePAGe, • L\~UC~Ac..:rtoN I( I I I f ·" ·-~ • . . l I c . . . . . . . . . El'/ViRONMENl.AL~ . · · · · · ·. · TRADE -OFF~ · . •RESERYOiff LE,VEL . · FLUCTUATIONS • MULTI-~6VEI.... JlfrAK---- (WATER · QUAUTY I . • DOWNSTREAM Fl!J~/ VARlATIONS ·. · . . . . . . . ~ . ' "' _ENERGY'·~ PRODUC&[\QN_ I ·~'lEAR .20\0(WA:TAAA/DCV\L.cAN.) ... ' .. " ·YEAR · l 9 9··4 (WA.T ANA . A LoN s) • 1 ,• K.e:J5E:RVO\R· ~ER..A-T\ON ! · : "' . .. .. @.. -~AAX1~1U~~·· W~NTER ~5Y . .:.l)· !i\.eo· r.s..A _ _,....u..~cMA). 1.~"'-.. ~ . N ,, .,w~ .·• rf~--..-.. ., -~ ~.,_....~ f ·SUMMER F!..Ov'VS -~e~fRtC~~·~ .. .• .· . . . . . . . . . . . . f.r"·N~-rA.·t..,.,-.. 'r.J.':'--T\O. '-~ .. yf")r.~· ~ ... .,.,. • ~·'~· ~~ y '\ J ~\~-:.._., .•• ~ 11+eKM,~~. (!~1\T!A.,~. . . 1 · "c-c~rv'~-~r.A1;4'C·.)~) ~ .._ /"\.. .--" ,.__ . .,p..\ ~ _. . ' ~ • I '4 . © .. UNf<E6TR\CfE.D SUM·M·ER.. FLOWS --R6t>UCEJ:) Utf>ABLE, ENE~GY . IZE'OE.R.VOI'2. ELEVA TlON~: l. '2 2.\6 (o-R\GdNAL-) . ~-2 ,-~5 3, ~\ \6 I . . . . . • I . { . I . . CAS£5 ANAL-YSED .. . . W, S. ElhVATt ON . OfUATION CAIE, --==--~~~· ' . . ' ·:·_ '®· @ . © @; . ~(S . . .)( .. 2115 . •' .. I I I I I -AVG!~. M,ONTt-ll~ Y · · EN1.E.RGY GENSRATlON ' 1 ,,..,.... __ __,..,-==~--=----~---...., .I I I ,. ,....._-. 2o I 0 J)6MAIW J) -' ,, ' ' ' ' ' '~·-..~--~ ..... , ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ... ,-' ' ' ' ' ·' ' ' ' ' ' -~ ' ' ' ,'' ''·'' ,, '' ' ' S~ITNA Gt.WE-RATION , ', ', ', '. · ' CAse. t1C\"\. '-' , ' ',, ~, ' " ''''' ,,_ ,, '' .. ' '''' '' ,, ' ' ' . ' ' ' ' ,_ ' ' . " ' ' ', ", ' ' ' ' ·, ' " ', ' ' .. • ' ' ' ' ' ' ' l ' '· ' ~-' ~ ' ' ' ' ,._~--~..z----,..... ,. -7.. \. / / /. / , . _/., /I'" / / / / / / ~---:r~· j '- . • , / ; Tl-\ E.~M.A L G E.N ER.A' Tl ON / / --; / / / /CAse.. ® "' / , // / / J / / / / ~ F M A. M J J·A S • MONTHS ,, I . I • i . AYGE~ MQtlJJ~,t-1 · · . ENERG.~ GENSRAT\ON . .. .. ' !. • • • . . , II . ··- ~ . . \0 2oto J)6M~J) 9 ~ ~ . ' 1 ' ... " ' ~, ' ' ' ' ' ~ ~5 04 0 (\ .... ~ 1 ' I ......., .MONTHS I I I I I I I I I I I I . I I •• I I I I .,.. ~ -AYGE ... MONT~l LY . . ENERGY GENSRATlON --11~======~~~~---------------------- lO ' ~ ' ' ' . ' ' ' . ' ' . ,. ' '. ' ' • I # • • . . ~ . . . . AVGE_ MONiHLY FLow · AT GOLD CR££K . . . . . . • . -. . . . . . . . -. . . . . . ' . " • . ' (f;) . ~~'C~A~E ......... I . . ........ ',\ . : . ......... , ... • .. : .......... . . . .l ..... ·--o •• . ~ ......... . t . .... -... ;-.-.. ····-• ,••. ···-:.::~ . . .... 7······ .. -.... -... ' WA.TAN~ s -ALONE. . ~TAAQ&T ® ' a f' . i O a-H , J) • J 1 F 1 M • A 1 M 1 J T J 1 A a ~ t i'10NTH~ \ I I I 20 ... UlJ5 \.1. .. 0 0 0 o~ I 0.· AVGE. MONTHL/ FLOW: AT QOLD CRE.E..K . . J . . I ,.. "" • • . l . ~--• • -• • .. • 0 • • • !-••··-· . CASE.@ . ---6 ·---. • • • • . . '. ·-' ......... . ....... f->-• .... ..,-........... • • I rs I I I -"' { ______ , ..... _. I : '"~AN~ I 1.--·-" A:J-oMe.. ~iAAGET ® -- I I • I l ' I ' ' -• I () If t> .J F M A ·M J. J AS ;f\1\ o N-r H 5 I I ·I . J I· · 2o- .l I· -:J ~IS"· I o I o 0 I ~~to- /\ J I •• I I I I ' . AVGE. MONTHL{ FLoW . AT Q OLD CRE.E.. K . . . . . r/"• ' . • l -CASE cC}--., . . ~ . ~··--.. -. ..,._____.,.., . · cAs£ ® r - ~~-~~/jr I _._ ... -· . ~--~ I e .____ · • · · ·~ t I -~~ .... ~ •• ••-•J r---· ......... ...._ r--· .... ..l"'. •• ..... : ........-.... • . t ...• 7·-· ··-···· : . .._.. . \. ...... ~ w~~H~ · ~o~s.. I:::\ . . ~ 1'ARGET \BI ..... o • If • J) • ,J • r ' M ' A. ' M • J. • J. ' A • s . MO.NIH5 . . . I •. I . • I __ ...;.,..__ _____ _____;_,_ _____ _ I --. . . . . . I O~~~tON · . GWh . ·. · ti5-ER 'fr~~ E~~J~· . I I I I I .I I I I fV./ATANA' . ~1.8 ~2~0 2977 (M.A.X._l>/b) .0 (Jlf4) (2*) (ltto) · 1) CV\ L CAN. . (Mt\)(. I>}D) \'OtAL . __ ss:::;, "" . . ~'$\0 -a279 ~~b : (Jet) {41) . . (\~9) ''2s. · '~ ~2oa ~6tS ~280 2917 (110) (!~4) . (~'11:4) . ~2 9b ~?Job '3r;..e7 . (lt) (.Col) (4l) . "509 "sab (:,2"4 WATANA 3557 ..... ....... (M A:'J.. ~/J>) { \1-o) t>EV\L CAN. ~Ub -- (MAX. b/1>) · (~si) . . .. . ~OTAL --'<'62!f -.... :. ·~ • .. ~589 MeN ~Hl-)' fl_oNS) ·~~----------~-------~~ . . 1 · UELT COH~1RUCT\ON 1 · -. cos1·s . -· · . I ( 4 Mtt..LlCN~-\98~) .. ? - WATANA TeAN~M'N. · fOTAL DEY\ L CArJ'/oN ~A~SM~f't . ~01AL . ·.2216 21~5 2ll5. . . . . . . 5/o 72 ·.. ~.?OS ~ 9~3 .. . . . ., . .• 374 ·. ·. 374 ~7+ 4 04c; 8fo 79: 3 3 37 J . J . } . \,534-. \J534 \)534 9'3 ~a 93 \,'=>27 ';"27 '·"27 I ·I I I I I I I I I I I I I I I I I I 13. PRESENTATION BY D. W. LAMB ----· - - ... -----•• ----- ----'f ... ..... _"""":'_ .. ____ .,. _ ....... ,.. -·~-_, ....... -................. -.....,_,. ---·--___ ,...,_..__ .. _ ~----q-...,._. _ .... "!'···-·-'":--~- ~· . : •.::' '" :~ -· .. ~--·-----._~ .... ,.,...,.--.. :· \ a .., • • ~ {I .... "'~r, ..... .... ... .... ~ "' ..... ----... 0 I I I •• I I· ·I I I I I I I I I I I I I PROBLE'1S 1, LEAKAGE 2. PIPING 3 • . PERMAFROST . 3. · ILJQUEFAC1]0t~ WATAt~A DAn RELICT CHANNEL • .. . I •• I I I I I I I I •• I I I I I I I I I WATANA DA!1 RELICT CHAt~tiEL . SOLUTIONS 1. SLURRY WAll-GROUTED.CUT-OFF 2. MOHITOR SEEPAGE THROUGH CUT-OFF 3. DAM CROSS SECT10~ 4. ? • <REJECTED: -UPSTREA~ IMPERVIOUS BLANKET -DOWNSTREAM FILTER BLANKET> l ' I I I- I I I I I I •• ~. I I I I I I I I POOL 2235' <~lAX FLOOD) POOL 2215' <MAX FLOOD> POOL 2160~ <AVE POOl) WATANA RELICT CHANNEL ESTiMATED COST/BENEFIT K (CM/SEC) -- 10-4 86 CFS 0.86 . . 83 .83 .. 75 0.75 .0083 .0075 ANNUAl lOSS $1.7-Z MILLION $20K $ 200 CAPITAL LOSS $34-39 MILLION $0.4 MILLIO~ $4000 <CAPITAL VALUE OF WATER - : $450K/CFSl <ANNUAL VALUE OF HATER --: $22. 4KICFS) _ .. ,....-..,_. I I I I I I I I I I I I I I I I I I I WA~ANA RELICT CHANNEL EST;MATt:O Q..l!.ANT:T!ES COMPARISON MARCri 81 EST MAX POOL 2225 OPER POOL 2205 MAX CHANNEL DEPTH 450 ft MAX CUTOFF DEPTH. 430 ft (below max pool) AVG CUTOFF DEPTH ' 240 ft CUTOFF LENGTH 7500 ft SLURRY LENGTH (in total) (7500 ft} SF CUTOFF -SLURRY .75 msf ' SF -GROUT OA9 msf # GROUT HOLES 1830 LF HOLES -DRILLED 507000 -GROUTED 324000 VOLUME -GROUTED 1.2 mcy -SLURRY CU;"QFF 0.05 mcy EST TONS CEME~T 38000 EST TO~S BENTONITE 26400 EST C'l SAND 150000 EST COST -SLURRY 11 mtlltan -GROUTING 34 m, 111-on TOTAL 45 mt11Jon NOV 81 EST 2235 ft 2215 ft 410 ft 390 ft .131 ft 14275 (7500 ft) 0.525 msf 1 ·38 msf 4705 980000 677000 2 52 mcy 0.05 mcy 400000 4170 630000 15 mtll1on 105 million 120 m1ll1on RESULTA~T UNIT COSTS -SLURRY CiB CUTOFF -$"35/SF USABLE, $29/SF TOTAl -GROUT CUTOFF -$76/SF USABLE ... I -- I I I I I I I I I I I I I I I I I I - WATANA RELICT CHANNEl ESTIMATEU-QUANTITIES COMPARI30N MARCH 81 EST: MAX POOL 2225 OPER POOL 2205 MAX CHANNEL DEPTH 450 ft MAX tUTOFF DEPTH .. 430 ft (be ltlw max pool} AVG CUTOFF DEPTH 240ft CUTOFF LENGTH 7500 ft SLURRY LENGTH (in total} (7500 ft} SF CUTOFF -SLURRY .. 75 msf SF -GROUT 0.9 msf I GROUT HOLES 1830 lF HOLES -DRILLED 50700(): -GROUTED. 324000 VOLUME -GROUTED 1.2 mcy -SLURRY CUTOFF 0.05 mcy EST TONS CEMENT 38000 EST TONS BENTONITE 26400 EST CY SAND 150000 ... EST COST -SLURRY 11 million -GROUTING 34 million TOTAL· 45 million . NOV 81 EST 2235 ft 2215 ft 410 ft 390 ft 131 ft 14275 {7500 ft) 0.525 msf 1.38 msf 4705 980000 677000 2.52 mcy 0.05 mcy 400000 4170 630000 15 million 105 mill i_on 120 million RESULTANT UNIT COSTS -SLURRY C/8 CUTOFF -$35/SF USABLE, $29/SF TOTAL -GROUT CUTOFF -$76/SF USABLE DR-18 :r,. ... ___ ,., WP.TANA RELICT CHANNEL TREATMENT POSSIBILITIES UPSTREPr CLAY BLANKET: TASK.~ CLEAR & GRUB Sr.OOTH SURFACE 850 ACRES JQ; FOOT CLAY BlANKET 2 FOOl FLNE FILTER CMIN) (1~3 SQ MILES) ~ 2 FOOT COARSE FILTER cr.IN) RIPP~P SURFACE \) COST: (ROUGH ESTIMATE) . $509 MILLION PLUS CONTINGENCY _]1, _______ .: _____ ._ _____ ~_-.a ___ _. ______________ ........ _____ _. .... _~----~~---------.... -·-.------~- DOWNSTREAf·1 TOE FII!..TER/DRAIN: 460 ACRES (0.7 SQUARE Ml LES) TASK: CtEAR & GRI!B SV.OOTH SURFACE 7 FOOT FILTER COST: (ROUGH; ESTiMATE) $105 MILLION ----.::..a----------------.---------------·-------... ---.--------------... ..a~-~ ..... --,_. . . .• . . . . . . . . . . . . . . .. REL1£li CHANNEl TREATMENT ' 1. FURTHER INVESTJ6A1~0t~ ~ REPRESEN~ATJVE SAMPtES -IN-SITU~ PERMEAB!l!..Lli~ TESTS Itt UNFROZE:f GROUND -TEST TRENCHES AT CHANNEl!. OUTLEl -IDENTIFY SOILS WHICH MAY llQUEFV· -EXTENm OF PERMAFROST -PIEZOMETER AND THERMISTER INSTAlLATIONt 2. DESIGNi -CUT-OFF V DOWNSTREAH·BLANKET. -PARTIAl!. CUT-OFF PLUS DIS BLANKET -DAM LOCATIION AWAY FROM SHALLOW DEPOSITS WHlCH MAY LIQUEFY -ASSESS· RDSK OF u/s AND D/S LIQUEFACTION -ASSESS SETTlEMENT ALLOWANCE FOR DAM TO COUNTER EFFECTS OF THAWING· PERMAFROST 3. CONSTRUCTION' 4. RESERVOIR FILLING AND OPERATION -MONITOR THAWING· PERMAFROST -MONITOR· PfEZOMETERS . -MONITOR CHANNEL OUTlET FOR SEEPAGE -REMEDIAL WORK AS NECESSARY ... ... ..... --"' "' • .. "11 "' -· ' • ... -· ., ·~· • • ..... --· --.... ..-..... --.. "'·-.... ... ,., ... , ___ ...... , __ ,,._ --.. _ - Js-~o()' . --· ---iiliiiiooioti.-''' .......... -. ~"Jol • l ... T ... l f r I • I Boo . . I I I I I i l · I r I ! . I I I •• I I I I .s-oo I Per G-ruzl • /GOO t .. W ~ .. :to.... n f.Aw, R e. I a c:. -t. C h 4t...hn ll/ . ..l I 0 . .': I Ve.r-6 u;. ~1 ·CXA..'Jje.r-~t.-IOn Lot>/\'"' s,uiA \SOO 1000 - WATANA • RELICT CHANNEL PROFILE SADDLE DA!·: UISTINli EDGE OF RIVER ·ro TSUSEHA CREEK • 93CX)' OPERATING POOL • 62DU' !-+ ~32•w sl2°£ SECTION A-A •tHE FINS• to T~US~HA CREEK DIRECT LlNE, SHORiEST OlSTAHCE ON UPSTREAM fLANK OF DAM SITE PLUTON t ' SL 81·3 t f SlBl-16 ·t SW-3 t ~-A SL60-2 22\S txtSTlHG EDGE OF RIVER to lSUSEHA CR££K • \2,000' OP£1\AllHG POOL TO TSUSf.HA CREEK • 7, 100' • • SECTiON B-B SECTlOH OM APPftOXlAATE THALWEG, LOCATION ABOUT 4000' UPSTREAM OF UPSTREAM COFFERDAI·: . RELICT CHANNEl PlOFlLES ,,,..._ ___ .... ~ .. ,, ...... __ ---~- \ ' I WATANA RELICT CHANNEL TREATMENT POSSIBILITIES • c SLURRY WALL & GROUT CURTAIN: 2.8 MSF OF SECTION 1.9 MSF OF CUTOFF SLURR't WALL : CEMEN.T/BENTONITE <15% CEMENT) 5250 l.F, 3' THICK~ 100' DEEP 525000 SF a $17/SF = $9, MILLloN ., ~~-----~.-.--------------~ ... ------..--.. ---------ea. __________ ..._.._.._ ... _._. ____ .__~ GROUT CURTAIN: ROTP.RY HOLES DRILLED P.T lO' iNTERVALS . 3 ROW~ TO 250' OF HEAD~ 5 TO 400' .· ROUGH COSli: DRllLLMG FLUID PLANT <LS> · 14075 LF -198 AVG Q aB 1 -13S'AVG CURTAIN 960000Lf DRILLING 3600 HOLES TO 250 1 OF HEAD 1025 II OVER II II II ·2.8 MSF DRILLED SECTIOK 1. 4 II GROUTED , 0.55 r.CY GROUT 8lL CEMENT GROUI 8LL CLAY GROUT $48 MILLION • 1 $48 MILLION 54 11 2 2 $104· $61 _,..._._...., _____ .._,_, __ .,.. ___ .... .-_________ _,_. ____ ... ~._----·~-----------------~----~--------..... ._.-ao-:-.-. . ~---~-----~~-~---~~-~~~---~-~-~~~-~---~~---~----~-~-----~--~~--~- TOTAL ESTIMATED CUTOFF. 113 70 -- ,- a , - 0 • ........... " 10 -- llrfiMI{liU~l III'AIIUt ~lliUIIU lnllCM n.u IWith llO -· lAlli QflllJ- SI'OI!IISilllfAG: ID Elm n~' !!4'111 • 7 nm Fll( FILtn 11~11 11111f milS{ flllr.l llllll lll'Q'$11fA(l UlllllllJ tml• - 4,J AIU.JM N. ft. ISO ran "'"" """' loa Jon ,..., IIIII ..,, .... IIINH. to. I IU<ISIICIII II£ fllllllfillllt VQ -· Us(, nua a Ull$ l.l IIHUica 14o q. VQAU<I Sl1mll!iiSIJa 1 llllf flllil 1.5 ... u ..... - uur . .um r.::;t, 1115 ~ua t"L/aa. q.J t 7 ---.. -·-It. • -,. ... •4•. {J 0 6 --... _., ........... _....... .. --· _...,.,_ llolll&o\ Inlet CI!ICl TII'Allal fllUIIIUIIU - --·---~ ----~ SU.tliiU. a UCll1 Qallll• I,' "" • .....,., I,JIAh.I.JaM. ... l WID IIIU1 UIOI18Ialtillt list""'~"'' ~ "· )• lwtc:ll. J(G• ... . S2SOI:U Sl • 111111 • ., ..... _ Yall OliiAII: lrOTAif IIOlU OllllQ AI II' 1410:11.11( 1 -.. 10 zso· • ..,. ... s tt WI)• ·~If. l!t .... 0.1. • US' • .,., (»&TAll tEaXO l1 atuuu. , --- - -·~-- -~ - - .. -.. ;-· -. ... -"''.. ,_.. ... ~ -....... ·.-------.._,.,.._....._-._ .. _.,... -· -···,.--~ ..... _ ....... ~--... --... . ·-"' ,._' ~/------------------------------------------------~~-----------------~·----------------------~ ee.d ..._ WJCK8 CA~IN& ~Toea tETEAMlNIO LAT1!R I I WATANA SAODLEDAM CSOSS-:-SECTION w •. NCfT1!: INSThLL Wt:K DAA.INS UP TO GRD. EL.. Z220 . .co FE!. iii -- ----- C) --I .. -I ~L61·'J s lJ s I .,. !tJ 2ZOO A t I " E 2~oD R • 1860 • l~f> I~DD -- --.. -0 C) I ... .I . -r-t SLfii·J{_, sw-3 On1·A SLBO·Z. ' I I & • t . .V:JQ..cJ-1 I ID"O •• ------~I -'----- -.... ---,. . .,_ .. ., . '""" ~ ' ....... -·---·---· . SLS~-1 ... c . 1\ E E t ---.. ---·-- C) SUSITNIJ .. ;,~:n . -... . RllfrR ' DR -eo I : I l l • SW-;3 ~-11 £•2. '1800 /(,00 ---0 D{l·l& I SL~ ---·--0 TSVS"I~A Ckfll( . . . --·--t-t-----·- • --, .. - . -----------------,--.C) o· o mszrxsz;z rc--T7 /$"(?0()' j . I I I I " .. ..... . ........ -· .. I . I f • • ' ( w~_;tt>-h "-.. Re.lac.-t Ch«...tHI)~t It>,·: 1 Ve.r-t.Jc. a..l Exa..~je.r~.:i:wn Look•n 1 s,,-ch 11 /11/8 I .... ~ vnc.he~tt~d 'f~&f; /e. ---- . l ... ,. ... ' ... ::r~ -··:..:: .. _ ··dJ (Y .s~ . .,. .roo. . .;AKS .. - --- ' . ·~ -~·· , . -, .. ......._, ... . . -- • . .. ,I ~~ ... _,.,.. . •· • , .... .,.,.,...,.. .. • ~. ~.lfi4 ~~by lha ~-~~ ; ........ "e 'I! A•'• ...... U' £&C. ... • ' . • I \ • Y.)' . -" ,. ... · .,.. ...... •. :. ,, • .. • •: lao=_ I . .. ·-- ···J .. • ~& • ..----... , ' . . . . . 2l ---- ' J I l ll ' ' •• lU • ,: -· •• -~-. -!!f! J9, ----- FOn tAKES $~D1JLE SEISMIC LINE. r.PRtFERREO LOC~TIOM I . • • . ~ ~~~\.._'I) ii~V~ h4•~'t.ht Dttl.a..·•l).'t.,_ -tl• -to •\', tit•.-11 to/A 1 I ,t .. t <\ t-' <t-l"'1''N'l '-'"'l~··h'•al•~·.t ~..,.,.,.t;lr ~·•• ••' ~ ,., ! 1'• ~,,..., 'U \.tfc :,J..~~ ,. 1 t• ,..,JO ..... ~ )lt}~ t·"~ • \'A•• •• c t• •• t ~ v•;.,•'J c. ··•· &.••• •· t•• ... !~/~3/61 i\.CQ ?510t).,~~4.05.05 - \ I ---------------........ -· -------·---·-.. ---------_ ...... _,_ __ ---.. ---.-· .. -~-... . -~ --.. ---.--· ~- ,----------..-- ,. v . .. .. --. -. ... .. D:6f!l . -. . --.. -. . :' ' ·fr ·-- ~~ I ' I ·HaM 6aff, .· ,. -.. . - - -·-- -~~ I ~ f(Ct.lf . I 6~ ·eui:fild~ --r . 44~Y''Ist' . ' Sl'kut~ ;fs. REr;f!· I . I • .-..~ It t I . . -·-. . l ,. . . . . -··--··--... - .;/. -·------··--- 11··-·------... l i l ' ' 0 0 • : . I ! -. ···----------·--_, -------------·-·---------·--1 . • ... -·--------..... ---.. .-~-~P--------~ -.. ---... .. . . --. --. ---· -.. . . . -···-· -------·-..... ----------------· ·-·· oJ 1 I ---. ~--.. ··---... -----· --------------"'-' 1 I ----·' .. -----··----------·· : . . . ----------------·---··--------__ ., ________ :-~1 ..... --· ..... _ ....-...... __ .. --------.·--.---.. ~~--... ·-------. ·-·-· ----- ---.. - ·-... ~~r-.. ~~=~i \ ... _____ ., 'tid Ole .. ~r 1:CN1I - nta.••,.I'C>f ZDa ~T>ON Mtt4 -...c:T c.--. Tl'leo.'!WC~f - .. --\ \ \ \ - ' -, --=-~~1- ~n..a~ -..e'ftXIC •• ~ "nn11e>tta -.. -------- -- ..... i·-· ,, I I I I I I I I 'I I I I I I I I I I EXCAVATION SUSITNA HYDROELECTRIC PROJECT WATANA DAl'1 MAIN DPu~ OVERBURDEN -AVERAGE 20 FEET DEPTH OVER ALL FOUNDATION AREA. WEATHERED ROCK UNDER CORE AND FILTERS -40' DEPTH. WEATHERED ROCK UNDER SHELLS -10 ~ DEPTH •. MAXIMUM SLOPES -1H:2V BELOW 1800' ELEVATION lH:lV ABOVE 1800' ELEVATION CONSOLIDATJO~ GROUTING 10' X 10' GRID OF HOLES 30' DEEP OVER AREA OF CORE AND FILTERS. .. I. I I I I I I I I I I I I I I I I I I . SUSITNA HYDROELECTRIC PROJECT WATANA DAfv1 CURTAIN GROUTING DOUBLE ROW CURTAIN -VERTICAL. · 350' MAXIMUM DEPTH CAT MAXiMUM HEAD)~ 0 50' MINIMUM DEPTH IN ABUTMENTS. HOLE SPACING PRIMARY 40' . SECONDARY TERTIARY SPLIT SPACING TO GIVE QUATERNARY FINAL SPACING 5'. GALLERIES FULL LENGTH OF DAM~ APPROXIMATE SIZE 10' X 10'. DRAINAGE 50' DEEPER THAN GROUT CURTAIN. HOLE SPACING 10'. DRILLED-FROM GROUT GALLERIES. FULL LENGl'H OF DAM., EXTENDING 600' INTO LEFT ABUTI·iENT. CONNECTING TO INTAKE AND SPILLWAY STRUCTURES ·RIGHT ABUTMENT, HOLES INCLINED DOWNSTREM1 15° FROM VERTICAL~ (. I •• I I I I I I I I I I I I I I I I • I 0 > w a: 0 z .~ c:: 0 u. l· Calculations SUBJECT: .S V S r "T t..JA t;,e-vu-Crl~Vc>U (. ~ c>t.li"' h R A 1 P-J t:c.E C A{.. l,.P:,.t':f ... ' 0 JOB NUMBER ______ ...,. F1LE NUMBER ______ _ SHEET ____ OF ___ _ BY OATE __ _ APP DATe -1-• i i I ! ' I ht~,u.:u.~ ~ '"'()\..~ -------------(----18- _..,. _______ ... • Z9So ,/ Roett Fta.L \ \ \ 'WATAJJA bAM Se.c.TIOIJ Aouc Ptc..t. . SltEa.a. Geov'TuJI A-ub t. Rll-• u Ae s CALLettv. rt . Df~t~alC.E C.V~'tAIU ' ' ------------------ .. ,.. .. . ,,_ ...... , 10 . -. .. ... , .. --.. I .. coBBLES ' GRAVEL L COARSE I FINE ~ '"'.. . .. U.S. STANDARD SIEVE SIZE -t--+-+---f·----4 rl . _ I ; I I _ 1l ; 1 ; r · .. 1if-f-t-+-f-__ -_.-~----~H-IH--I--'J.-..I·-~----~ I I ; I II I ~ I J. ·~ 0.1 GRAIN SIZE AN MILLIMETERS ,.._ ~· ~~ ... ---SAND .. . .... ~--COARSE I MEDIUM I FINE 0.01 . SILT OR CLAY .. .. . .. 0-.001 UNIFIED SOIL CLASS IFICATJO U SYSTEM URAL MOISTURE CONTENT RANGED FROM 6 TO 19% -AVERAGE OF 12% COf·1POSITE CURVES FOR H-1 THRU H-8 -· .. 100 90 80 70 1- :1: CD w 60 • ,.. tD a: Ill eo z -.... 1--z 40 1&1 0 a: w 30 Q. to 10 0 .. ~ ..... ··- .. ·. - ._ ... __ ... . 200 100 ~----_., ·-· COBBLE a ....... -........ ...... .. .. ......... ----··~· ... U.S. STANDARD SIEVE SIZE 21N liN 3/41N I/2.1N N04 NO 10 NO 20 N040N0.60 NO.IOO NO 200 . . . . . . . . """ ' 'I ~ ~ v ~,-It ""> ~~ T I ! ~ ~ ~~ ....... 1'< ~ tl Iii ~ "' ~ ~ ~ I I I I I 1..,; I II ;<6~ ~~~ I; ~ ~ ~ ~ I l I I t ~ I I ; I 1<: ~~ I ~ ~ ~ Vh r' I I I I~ I ~ ·~ -~~ I 1 I ; v~ I '/ ~ ~ ~h If~ ~ ~ T . I I li.J ill ll I I I I ~< r /: ~ ~ II" '? -~ ~ I I I I / ~ I il ~· I~ I ; ''(' tl ~ ~ ~ -~ v I! ~ ~~~ I l: i '~/ ~ j ~ I I 1 I I v ~ Vh fl :1 I ~ ~ ~ I I I. ~~ ~ I ~ ; I ~ ~~ ll,l ~ , ~ r{~ ~ ~ I . Uti ~ ~ ; -I : ~ ~~ ~~ v ~ t/ v-v_ ~~~ I ll 'v I l ' I ~~ ~~ ~ ~ v. ~~ Vh~ "' '/ I ~ '(<~~ I'~ I ~ ~ ~~ ~~~ ~ . t ~LJ' ~~ ~\1 ., % ~ ~~~ ~t}. I / I i~ I I ' , ~ ~ N v:: ~~ - :< I. I i '< I . I ..... ~ I' ~ ~ ~~ ~ I I rl I . ~ ~ 'l tfi~ j --. I I i I I I I I I '< ~~ A II . I I ~ ~ I I I -I J I I ~ ~ I I I I ~ I I I ; t L J -- I I I :: . : 1 ! i_ . .L 10 an 0.1 0.01 GRAIN SIZE IN YILLIMET£RS ~ -·-. ----... '"'· . , __ ____ ... _ .. _ GRAVEL -. • ·~ II' .~ --SAND -----SILT OR CLAY COARSE I FINE COARSE I MEDIUM·~ 1 ... FINE - . . " ·- 0.001 UNIFIED SOIL CLASStflCATION SYSTEM ATURAL MOISTURE CONTENT RANGED FROM 6 TO 16% • AVERAGE OF 11% . ··-: _fDPl_.m t-A_C_R_ES_AM_E_R_IC_AN_I_N_C_O~~RA ~E .lAi_l_f!l BUffALO. 1 HEW YORK COMPOSITE CURVES FOR D-5 THRU 0-9 GRADATION A I 145 t . , 1401 I I . . . 35.5 . I 135f j . 130 ;7 \ i 128.7 I -t/' I .z~ . . I I 125 . . • ! I . l ' 120 2 4 l I . . ! l i " l i I I . ! I ' . i . I . . .... ---~ : v 7.5% . ~ /I . ! I • ' I I 95% MAX OF y DENS ITY -,. - I I l i i s a WATER CONTENT (~) AREA D COMPOSITE MINUS 3/4 INOi . . . . I . I 1\ . l • I i \ . t \ - 10 .1\: ~ I t 10 . . I ; . . '\ 12 . ' l ' # . I I ' . I --~----~----~----------------~------~-------------------/· tHc-of:+r:il J rv-oc{cV' .t/ fh " ~~ .1'. 145 . 14 0.7 140 135 . 133.7 -~ n "TT - . 130 . 125 120 I ' . : ~ . I ' ! • ' • • ~ l ; . ( ' i \/ . . 2 ' I :/ 1 I . ! --, : t? 1 ' .JS% 0i I · 3.6~ I i : ' j ! i . i i I ! • I ' ' . I 4 .. .., '""" .......... _ ___......,.__, ____ ..,......:-.-.-"""" .. "... . .. ~ \ . ! l • t . . i I . ! i I I l I . ·~ It . vs. 9~ I / -. . I . I I \: . ! ' . . ~X: D~ y, DEN~ ITY -I ---.. i 1\ . ! I ! 9>.7% t\ ~ . I . • ; l \' . i j . \ . I . I ' I . ' ,. 6 a 12 WATER CONTENT (%) AREA H Cot-1POSITE MINUS 3/4 INCH . •, .. .. AH-H2 PEAT SANDY SILT WITH ~RACE GRAVEL SANDY SILT WITH SOME CLAY AND GRAVEL SILTY CLAY WITH SOME SAND AND GRAVEl:. 40.7 FT. AreG-H .; 0 0 0 J I I AH-Dll ~~· PEAT ~;=; r SILT ....-~""'!i'l SILTY SAND WITH SOME GRAVEL I 10 1 t SILTY SAND~ WITH SOME CLAY. GRAVEL. AN~_SAND ! , CLAYEY SILT/ SllTY ClAY WITH· SOME SAND AND GRAVEL . ; ' 54.8 FT. --------~------------------------------------ /. TyfL~~( a.~Jo'Y ~ D c· .. 0 .. -... 0 -~ .. ., ___ .. ____ .., --.... ---·--·· .. SIEVE SiZE IN INCHES < .. _ ... ........ -... __ .GRAVEL COBBLES CO~RS£. I FIN£ ---· . ---0 --C) ·-... -.. --...... ---· ,....._ --.. U.S. StANDARD SIEVI~ SIZE . ··--· ·-. . -..... -. .. . . SAND . COARSE I I MEDIUM FINE 80Rit!G no. SAMPLE HO. O£PTH CURVE SYMBOL ClASSiflCATtON 1\ I - SILT OR CLAY .. ·•-• UNIFIED SOll. a..ASSIFDllCtJ SYSTEM ACRES AMERICAN INCORPOAAtE - --- 100 "" 90 10 .. 70 F .. :t IS -60 w f--....... • ,.. ID a: DO . 1&1 z -... fZ 40 IIJ u 1: w &L ao to .,. -.. . . . ~ 10 . . -~ -·--~- 0 ·-·· - 200 100 -· COBBLES .. -· ., - 21N. I [ L I -. I L. . ·-· - -.. - C=:> -.. - 0 .. ---.. C) --· ---~ .. -.... -·--·---·-.. --. ------... -~···--.. --......... U.S. STANDARD SIEVE SIZE IIN.3/41N.I/21H. N0.4 HO.IO N0.20 NOAONQ60NruOONn200 l'f' r! I I -I! I ~ il •· ! I I I I I I I I 85X I I I ~ I ~:--. I I I ... I l r I' J I I 1 "' .. w ~ ·~ l 1~-..... I ; II .... ~ I ; ,j h. J I I f I I l I . I r-.~ I II .. .. f I I .... tj I I I -.. I ~ I I ._--w•• I I ""' I' I I ~ I ,f 1 "' t-· ~ II I f ~. l I I I J -I II l I I ~ L. I ll II I II i I I ~J 45% 2 f-f-I ,: J I I I ll't'. I I I ~ .. . -~~ I ; J I I [\ ~ I "' ' .L II I I L ' "' t i. .. .. I I I ' ~ I I I I -I J "" I I I .. -· I I I J ' . l ; I ~ ' I J I " .. -· II I ; l I i I 1 I -.. . I I I . I ~ . ·I i I I .. I I J ~ I --i. f -.~i,. ' .... "1... 10 l.O 0.1 o.u& GRAIN SIZE m MtLLlMETERS __ ... ··-·--..----· ' • - ('j6AVEL .. ... . .. .... .. . ._. s= --. SAND ~ .. ___ ·-....... ---SlLT OR CLAY --.. . --·• . .. . .. . . . ~~ i'-~ 0.001 --UNIFeEO SOil • CLASSIFICATION COARS,E_ J() fiNE . COARSE I MEDIUM FINE -. '"0 "<'•"P ~ --· SYST£M '>.~ ~ ~ ...... _ " -··· ~"""----~ ~ '----· -•. . ~ -~· [ii] G=2 .. 7l AChES AMERICAN INCORPORATED BUff'ALO, HEY# YORK COMPOSITE CURVES FOR AREA D ......... -....-·· . --~>· -· .. --GRADATION ANALYSIS CURVES flLE! bAtE: IFtG., .•. -. -- .I\ ' 1. 'II ,__,... --- - - --- - - - - - --- - - - - <> . U.S. STANDARD SIEVE SIZE . I\ 21N. IIH.3/41N.I/21N. N0.4 NO.IO N0.20 N0.40H0.60 NO.IOO N0.200 iOO JJ \ ; tl t I )q, ~~ , I I I :J i 10 ~~ I I I I ' • I ~ ·~ I I I ,J 10 l 1 . ~ I I 1 I l t\ ' I "" ' t : ' ~72l . I I I I -. 10 I I . I I I I """ I I l I J I ~ I !C .. r-·~ 1--· ~ ~ I I I I I CD . I I -60 w II !--I' I I 1 • 1'-I I .. --)-if I 'l I m I ~ ~ li -A: 00 --. I I' I I w I N z t -·' I '"' ... . I l I i 1 38% ti I I i I 40 II I . : I A ~:-. )~ t:-J + -I u - II: __ ..I II I I : ..... !'. .... r.... --"' ~0 I ........... -. II -----,.= ~--' -: I I '" 20 ---I -··--,.,__,,. .. --. : -.l r . I I I ,'~ II I I -0 ··-... --r I I 1-I I I t'-. " I "' ,. I I r-. . . 10 !i ·-·· I I I I I li if - 1 : I I I I 0 ~ -.__.. 1 .. i II ' , 200 JOO 10 1.0 0.1 0.01 0.001 GRAIN SiZE IN MilLIMETERS . . . _. ..... . -.. UNIFIED SOIL ' -·-·4·-r· - coaeLEs GRAVEL ·-. I ----·~'-~-...... SAND . .. . SILT OR CLAY CLASSIFICATION -COARSE I :fiNE_ CQ~-~~E ·~ MEDIUft! __ .. f.~~E . . ,,._,. -··-... . -.... ,.,._ .. ,. ............. -SYSTEM ~---· ·---........ ·-----_ .... -~ ... ...... , ... •· .. . .. .... .... -·-. ... _ ...... -. " G=-2o72 • ACR£S AM~RICAN QNCORPORATED . B~ff~~O r· tiEW __ XORK ··- COMPOSITE CURVES FOR AREA H "·-~~ ....... ·--··''"" .... _ .. ------..- GRADATION -ANALYSIS CURVES Flf..E: DATE: _I FIG. ""' . --------~-0 --0 ---C) ----- .. , "'-·liP' __ .,_. .. -- IOO 21N IIH.3 141N.i/21N. H0.4 HO.IO N0.20 N0.40N0.60 NO.IOO N0.200 l~W/j~~f~~;)~ I I I '~~ ~~~~ ! F % G. w 60 • COOBLES _ .. ..-~._., .. _....,._, ..... _ .... .__ .GRAVEL _ ...... ,~ -.. -·-!AND __ COAASE ...... J F I HE ... ~ ... COARSE f_.ME~IUN I FINE o.ot . . . SILT OR CLAY ~ ~· - _ __ .... o.oa. UNIFfED SOIL CLASSIFICATION SYSTEM r;;;l _ ACA_~~-·~M~~~C~N INCORPORATED llltlt 0UFf'ALO HtW YORK . .. ~-··---· r-I ' f • -----------~--------- DYNAMIC SHEAR STRESS <KSF) . .. .. ... . .. .. ~ -.. "-~ ~ . -..,.., .... --.,, .... c 60 -,.1~1111111'111!11111111!1 50 - qo -~, 111 n 1111111 m1 11111!11111111111111 m 1111111111111111111 mmuunumm111111•! : i 111 "" n ,tu1 , ',, ,,.•.! • I, • II~ Ill II' II ~· i: I!!! ~ '' unnnn 30 -I 28 -a -i: li II AVAILABLE DYNAMIC SHEAR STRESS l u li II .. !! !I jj nu1111 111111 uau: ;un ;urlllllitll! II IIlli ~•:' i It r= I! !I llll~~~llll mtm 'ii r; """"""'" 1111111111111111111 li llllllllllillillilillllllllllll:lti!!UU:HJ:IIIH ~ !!~/~~ IMIII ;mf! ,i :l li ,j ,i !l r; llllllllllllllllllll.llllllllll IIIII 1111111: 111111! :I 1: ,,. !!I .. !! r:! ii I i: II ill !I ;; ii ii II I! ~ J! '!l_ HORIZONTAL Sl.ICE B-B •• I I )I I I :I ;I II f • tzo• HEIGHT OF DAM <FT> 140' 160' 11o• / MAX ACCELERATIOn 0.0 .10 .ZO .JO .40 • .5il lt ', t i r LJ ... 3921 .4070 .3421 .3068 .ZS03 .2638 .Z371 .4360 ACCELERATIOn VS DEPTH AT CENTER OF DAM ------------------ ( \ 0 0. 0.5 - BASE 0. 3 ~ ~:~ ·~· ~~I l~ I~ ~·~·~·~· -0 I 5 .I f .. rj*FP"j I -i j rnpz ·, I . t .~. 'T ...... ,--,· I I I I I I ' 0 12. 2!1 36 48 tO ·rIME <sEc. > DESIGN E~RTHQUAKE TIME HISTORY I~ .... , -·7 I i i I I I I l i • 72 84 9E .. .-.. .. .,.. .. ~ ........ SO I 11, PROPEB.Till CORE rrATERHAI!. FILTER MAT:ERIAL ROC!{ f·1ATER IAL DESIGNrE/\RTHQUAKE G/Su 2500 - - A) MAGNITUDE 8.5 RICHTER Kz - 100 180 . ~ .. DAMP I NCi/SHEAR·- TYPE CURVE CLAY SAND SAtiD B) LOCATION' 40 KILOMETERS BELOW SITE (BEfiiOFF ZONE) c) ~1AXIMUM ACCELERATION OF .436a o) DURATIOi11 OF STRONG MOTION ·-45 SEC. E) SIGNIFICAlNT NUMBER OF CYCLES -25 ----~--~--~------~--------~ I j I . --;':'" ... ~; .. " ...... -..... ., .... ,. -:'"' .. • • • ~. ;:;, ;. ··,..·:.. • • ..t;. .I ·~ . ,. .'.. • ... • • ... .. .. ~ " -. ~. ..... -.;;--. ....;..~-. .... .... . ., . .. . ~ .. , ... ... .. ... .. . t• •• .. -: ) ~ ·-~ ,. .. I I SAE -1\f ANALYSES. . I €S.:~p IV) WERE DONE TO DETERMINE THE INITIAL STRESSES IN; THE DAM THE STATIC ANALYSES USING THE LINEAR ELASTIC Fir~ITE ELEMENT PROGR.~t·1 I DURING NORMAIL OPERATING CONDITIONS. YOUNG'S MODULUS WAS DETERMHIED FROM THE FOl~Ol~ING RELATION·SHIP: II •• I I E = KPA (~)~ l!A WHERE: E = YOUNG'S MODUULUS PA = ATMOSPHERIE PRESSURE CJ3 = CONFINING PRESSURE K;~Nt = CONSTANTS ·1 THE IN-IT:lAl VALUES OF THE PARAMETERS K AND N AND THE POISSON'S HATIO I (~)FOR THE VARIOUS DAM MATERIALS USED IN THE PROGRAM ARE AS FOLLOWS: I CORE MATERIAL il FILTER MATERIAL I I I I I I ROCKFILL MATERIAL .L 300 2000 2000 _lL 0.2 0.2 0.3 1 0.333 0.299 0.263 / ----------------~--. ,JfQRIZONTAL SLICE A-A HORIZONTAL SLICE B-B "' .. --..,_ .. '"' .... .. - LOCATION OF HORIZONTAL SLICES ·--·--.............. ~ .. ~-..... ~. --... __ I .• ---18--------·--Ill·-:-- ---------------------------------------------------------------------~~----------------------- n.s• n.s' FILTER fiAMlC ea.o 1.0 1.0 '-coRrl"\. fl"INI! PlL.TI!R QREST PETAL. FIGI..f\E 002 ---------·----------- 2&0() 22.0{) 210l:l 2.0C.)Q soo eoo noo IG»>Q 1500 l400 LO J-LO rl'tOCK ... w..J 1.ss ~ CO-'RBI. a-tl-TBR FIN!£ F'lt.-.T!A- CRe&T Oe"TAU .. ~EI! FJGUI'll! NO.2. MAN DAM SECTION AT MAXIMUM HEIGHT ~NO.I I I I I I I I I I I I I I I I I I . I I . WATANA DA, DESIGN FOUNDATION -STRIP WEATHERED ROCK & OVERBURDEN OVER WHOLE fOUNDATIOM -EXCAVATE TO SOUND ROCK UNDER CORE -CONSOLIDATION GROUTING/SlUSH GROUTING -GROUT CURTAJr• -DRAINAGE "OILES -DOWiiSTREAM DI-SCHARGE -UNDER DAM TUNNEl S¥STEM -INSTRUMENTATlO~ & MOniTORING I' --- ,--··~~ 0'«-... \ CL.oc.URE b \ 1:.~ er1<JIDI~ 6-t:.D~h.SE , ... T'O FINE.. ------··--- ----.. _..., -· -··-.. ·-~-·--.. ··--__ .. ______ -........ _. -·---... ·-. '---- ELIS'SO u-..---.-~URRY WAl..L. To Roc.K ---- ROCk OR GRAVEL till .. ~­c) - ·-.. ·---~-. -· ------ CLOSURE DAR ---------------~. t\\Xltllt OEPfH 70ft. TYPICAL UPSTREAM cOffERDAM CROSS SECTiott . SCALE 1••40' .. - --.... -·---· ... ... . ... ..... ·--- -COARSE filTER .. .. EXCAVATION I I - -----· ..• ' . .• . . :· :t. \' . . . \ .!. f .· - -·-- ( -'--..... 0 -... ~ --.. ....... ---·---~-·-----·· -__ , __ •. *"'--..... -... . ' -· -·---......... -~ -~... • ... -'"' .. .. _ ~rAAL. OP!AATI~ L.!.Vf!l.. !L.. 14!6 DEYl~OANXQN_BAOOlE DAM MAXMUM HEIGt;tt SECTIQI\J 0 TOP OF ROCJc:. . - I I I I ' I I I I I I 1 I I I I I I I 14 .. REPORT BY SPECIALIST CONSULTANTS I I I 1: I I I I I I 'I ~ I I •• I I Mr. John Lawrence Project Manager Acres American Inc. 900 Liberty Bank ~~uildin~ Buffalo NY 94202 Subject: Susitna Project 18 November 1981 Specialist Consultants ~anel Meeting No. 4 November 18, 1981 Dear Mr. Lawrence: INTRODUCTION On this date, Profs. Hendron and Peck met in Buffalo to · discuss certain geotechnical features of the project. Brief- ing a~d discussions followed the attached agendao This letter was drafted in the Acres American office at the end of the meeting and was finalized by the undersigned shortly thereafter • WATANA CORE MATERIALS The well graded materials from borrow area D are suitable for use in the core of Watana Dam; current thought regarding filter requirements for well graded materials should be taken I .... into account in the design of the filters (John Lowe III, 4th ' I I I I I ,, I 1: I I I I I, I I I I I I -2- Naber Carrillo Lecture, 1979)& ~he well graded materials from borrow area H are also suitable and have some plasticity which possibly makes them slightly more desirable when considering design against piping. However, the clayey materials may be . more compressible than the materials from area D; also, they may exi~t at water contents too high to be placed at the de- sired densJ.ties and there will .oe little possibility of drying them during the construction seasono In summary, both mater- ials are acceptable on the basis of present information. More information is necessary on insitu water contents and de- sired densities in the dam before the final selection can be made properlyo WATANA DAM SHELL MATERIALS We feel that the dam would perform better statically if river gravel and cobbles were used for the upstream shell, because rock fill dams over about 500 ft high usually develop longitudinal cracks upon first filling due to additional break- age at sharp contacts on saturatione Zones of processed gra- vel could.be provided to eliminate the fines and assure higher permeabilities if excess pore pressures are thought to be a problem during earthquakes. It is possible that too low an I I I ~- 1 I I I I I I I I I I I I I I I, -3- assumed stiffness for the compacted river gravels may bt~ a· cause for the high pore pressures computed in dynamic analyses. Stiffness values for these materials could be approximated by back calculation from the observed settlement of Portage Mountain Dam in which both processed and pit-run compacted gravels were used. WATANA CORE GEOMETRY Although static analyses may indicate that a more favor- able stress distribution is achieved if the core is sloped upstream (on the assumption that the core is more compressi~ ble than the shells), we feel that a central core is prefer- able under earthauake conditions because the shells will ... probably shake down more than the core. Thus the downdrag on tl1e core will tend to produce higher vertical stresses in the core and so reduce the probability of cracking. WATANA RELICT VALLEY Control of seepage through this buried valley is required for safety; the cost of the lost water is of little import because the seepage loss merely offsets the requirement for a minimum downstream flow. Three alternatives have been consid- ered; I I '• I I I J I I ·I I •• I I ,. I I I I I I -4- 1) An upstream blanket over the entire inflow area. This would be costly and, in fact, impractical because of the . limitation on its extent imposed by the entrance to the di- version works~ 2) A cutoff across the pervious channel. This would be extremely costly and probably ineffec~ive. For practical rea- sons it would hardly be possible to construct a slurry wall deeper than 200 ft. Attempts to create a grouted alluvial cut- tl off between the bottom of the wall and bedrock would have small chance for success in view of the likelihood of encountering permafrost and in view of the great variation of permeability likely to exist. If such a cutoff were to be provided, it would be necessary to moni.tor points of possible emergence of ,;; seepage downstream in the Talkee~~a valley and, in all proba- bility, to protect part of the area by filter blankets. In our judgment no further consideration should be given to the cutoff alternative. 3) Preven·tion of piping or backward erosion by providing suitable filters in the zone of seepage emergence in the Tal--- ~~etna valley. This can be done, as the need is demonstrated, in the following steps: I I I I I' I I I I I t I I I I I I I I -s- a) Establish the location and regime of springs that presently exist in the area of possible emergence, and install and observe piezomet~rs at suitable locations prior to reservoir filling. b) If discharges appear or increase during reservoir filling (or thereafter as perrna~rost zones melt), or if piezometric levels so in.dicate,' cover the emergence areas with filter drains. If se~-page em<.~rges high above the .A- Talkeetna valley bottom, conside't'ation can be given to .directing the seepage into lower strata by means of fil- ter wells and providing filter ~Lotection for the lower strata. We consider this alternative to be the most oositive . . control measure. It will, in addition, be the least costly. Similar treatment would be necessary to a lesser extent even if one of the other alternatives were adopted. The procedure requires a period of surveillance, adequately funded, for sev-,. eral years until conaitions stabilize, including the melting of permafrost until thermal equilibrium developso It also requires maintaining the ability at site to execute the mea- sures that may be found necessary. It should be noted, how- ever, that the requirements of surveillance and capability of I ·I I I ,, I I ·I I I I I- I I I I I I I -6- remedial work would exist in any event, in view of the remote- ness and rigorous climatic conditions at the sitee SADDLE DIKE AT WATANA RELICT VAI.I.EY In view of our preference to eliminate the cutoff in the valley, the design of the saddle dike would not be premised on the incorporation of the cutoff in its foundation. · The rela- tively low head across the dike would permit conventional seepage Ct.'lntrola However, consideration must be given to th.e possible existence and thawing of permafrost zones in the foundation after the reservoir has risen and to the influence of liquefiable zones. Exploration is presently inadequate to determine if such zones exist. If the maximum reservoir level would be no higher than the natural saddle, these considera- tions would become insignificant. We believe the proposed studies of reservoir elevation will be useful to determine if there is an optimum level at which most of the project bene- fits may be retained while the problems of the dike can be substantially reduced. I I I I I I I I I I I I I I I I I I I -7- WATANA UPSTREAM COFFERDAM We are concerned about the space limitation that may re- quire steepening the downstream slope of this cofferdam if the bedrock in the river should be lower than anticipated where the main-dam excavation would occur adj a.tcent to the cofferdam. We also have concern that constructing the proposed cutoff to rock beneath the cofferdam may involve delays due to its depth and to obstructions in the alluvium. We suggest that the cofferdam design be studied further. PERFORMANCE OF CONCRETE DAMS We beiieve it would be pertinent to review the experience in~arctic climates of concrete darns, including the long-time history of several dams in Norway. (For example, Heggstad and Myran, Investigations on 132 Norwegian Concrete Darns, 9th Con- ~ gress Large Dams, Q34, R28, Istanbul 1967; Berdal and Kiel, Skogfoss Hydroelectric Power Station, Norway/USSR; Civil Engi- neering Works, Proce Inst. CE, Vol. 30, pp. 271-290, Feb. 1965, discussion Vol. 33, pp. 481-491, March 1966$) This in- formation would be pertinent to several features of the pro- ject, including possible cotJ.sideration of ac concrete-faced rockfill dike at the side channel to' the left of the Devil Can- yon site. I I -a- I Yours sincerelyg I I I I RBP/ajj "I I I I . I I I I lr I I I