Dworshak-1998 remedial foundation grouting.pdf

m US Army Corps of Engineers Walla Walla District

Dworshak Dam and Reservoir North Fork Clearwater River, Idaho

1998 Remedial Foundation Grouting

Monoliths 15 Through 19

DWORSHAK DAM AND RESERVOIR

NORTH FORK CLEARWATER RIVER, IDAHO

1998 REMEDIAL FOUNDATION GROUTING

MONOLITHS 15 THROUGH 19

TAB!£ OF CONTENTS

1 . INTRODUCTION

1.1 General

1.2Foundation Geology

1.31995 Grouting Contract

1. 4 Uplift Testing

1. 4 . 1General 1.4.2Test Results

1.5Consultants Review

2. FOUNDATION GROUTING

2 .1 Contract

2. 2 Instrumentation 2.3Cement and Cement Additives

2. 4 Chemical Grout 2.5Grouting Existing Relief Drains

2 . 5 . 1General

2. 5. 2Water Testing 2.5.3Chemical Grouting In Relief Drains 2.5.4Cement Grouting In Relief Drains

2.6Drilling and Grouting the Foundation curtains

2. 6. 1Drilling

2.6.1.1Drilling Upstream Curtain 2.6.1.2Drilling Middle Curtain

2. 6. 2Grouting 2.6.2.1Grouting Upstream Curtain 2.6.2.2Grouting Middle Curtain

2.7Comments on Grouting 2 . 7. 1General 2.7.2Grouting Near Elevation 1222.5

2.8Drilling New Relief Drains 2.9Water Diversion During Grouting

3. REESTABLISHING MONOLITH JOINT UPSTREAM WATERSTOP

3. 1 General ..................... · 3.2Contractors Proposal

3. 3 Contractors Results 3.4Government Directed Waterstop Repair

4. UPLIFT RESPONSE TO FOUNDATION GROUTING AND WATERSTOP

REPAIR

4. 1 General

4. 2 Uplift Response by Individual Monoliths

5. CONCLUSIONS

APPENDICES

A. Table of Information on Grouting Existing Drains

B. Instrumentation Drill Logs

C. Photographs

D. Waterstop Seal Mix Design

II

E. Graphs & Data

PLATES

PLATE NUMBER

LOCATION AND VICINITY MAP

PROJECT ISOMETRIC VIEW

& WATER DIVERSION ROUTE

CONTRACTORS STAGING AREA

& WATER DIVERSION ROUTE

INSTRUMENTATION

PLAN - PIEZOMETER & UPLIFT CELL LOCATIONS

GROUTED AND PLUGGED RELIEF DRAIN HOLE LOCATIONS

NEW RELIEF DRAIN LOCATIONS

GENERAL LOCATIONS OF UPSTREAM GROUT CURTAIN HOLES

MONOLITH 15 & 16 UPSTREAM GROUT CURTAIN

MONOLITH 17 & 18 UPSTREAM GROUT CURTAIN

MONOLITH 19 UPSTREAM GROUT CURTAIN

GENERAL LOCATIONS OF MIDDLE GROUT CURTAIN HOLES

MONOLITH 15 & 16 MIDDLE CURTAIN 20 DEGREE HOLES

MONOLITH 17 & 18 MIDDLE CURTAIN 20 DEGREE HOLES

MONOLITH 19 MIDDLE CURTAIN 20 DEGREE HOLES

MONOLITH 15 & 16 MIDDLE CURTAIN 60 DEGREE HOLES

MONOLITH 17 & 18 MIDDLE CURTAIN 60 DEGREE HOLES

MONOLITH 19 MIDDLE CURTAIN 60 DEGREE HOLES

18 WATERSTOPS AND JOINT DRAINS, PLAN & SECTION

III

1. INTRODUCTION

1.1 General

The flow from foundation relief drains in monoliths 15 through 19 has increased since Dworshak Dam was completed in 1972. In the late 1980's it was reported that noticeable volumes of sand-size rock fragments were being washed out of the relief drains. This indicated that the seepage was causing erosion along bedrock fractures and perhaps within the concrete structure. Due to dam safety concerns for the continuity of the foundation in the left abutment of the dam it was determined that remedial foundation grouting would be performed.

This report covers remedial foundation grouting in monoliths 15 through 19. The foundation grouting included pressure grouting the existing relief drains, drilling and grouting two grout curtains, and drilling new relief drains. The grouting project also included reestablishing the upstream waterstop for monolith joints 14/15, 15/16, 16/17, 17/18, and 35/36. The new waterstops were established by grouting the upstream monolith joint drains.

1.2 Foundation Geology

The Dworshak Dam Foundation Report covers the general geology at the site. The Letter Supplement to DM No. 6 Foundation Seepage, Monoliths 15-18 looks at the geology in the area of the left abutment more specifically. The following is a general overview of the geology using these two sources and the more recent drilling and testing undertaken at Dworshak Dam.

The foundation under the left abutment is a slightly weathered, very hard, slightly to very slightly jointed and fractured granite gneiss. Permeability is very low to moderate and progressively decreases with depth. Recent grout hole and instrumentation coring indicate a very tight contact between the bedrock foundation and the concrete structure. Core drilling also indicates a fairly tight foundation (few open fractures) both upstream and downstream of the relief drains. In general only one or two water making fracture were encountered during the grout hole drilling upstream of the relief drain curtain. Evidence of a tight foundation downstream of the relief drains is the small amount of seepage that exited into the adits and from the downstream toe while relief drains were closed. A borehole camera study of the relief drains indicates many open, water making fractures in the relief drains.

The openness of joints at the relief drains could be due to the flushing of the soft mineral fillings from the joints and fractures in this area. As water flows through fractures into the relief drains erosion is occurring at the drain and proceeding upstream away from the drain. The foundation relief drains are on 5-foot centers. Most of the drains are interconnected through fractures in the foundation. This is evidenced by the increase in flow and the flushing action that occurs when a drain is closed adjacent to an open drain.

1.3 1995 Grouting Contract

A contract to perform foundation grouting was awarded and work started in the Fall of 1995. The contract was awarded to Christensen Boyles Corporation (CBC) of Salt Lake City, UT.

The design called for grout holes on 5-foot centers with primary and secondary holes and 2-stages; 0 to 40-feet and 40 to 130-feet. Two areas were to be grouted as a basic program and two additional areas were optional; to be grouted should the upstream grout curtain not be fully established during the basic grouting program.

CBC started work in early November 1995. The District requested and received permission to maintain the reservoir at elevation 1500 during the grouting contract. The lower reservoir level would assure lower pressures and lower flows in the gallery during the grouting project.

CBC opted to core drill the grout holes with AX-size core bits. Drilling production was good. CBC started grouting on one of the 40-foot grout holes in monolith 16 and the grout almost immediately started flowing out relief drains. The Contract allowed for plugging relief drains with caps or packers during the grouting and CBC was directed to start plugging relief drains. With up to 18 relief drains plugged at the surface grout was still corning through the foundation and out into the gutter on the reli~f drain side of the gallery. Many attempts were made to locate and plug grout leaks into the gallery. Initially the grout mix was 3:1, however, it was thickened to 1:1 in hopes of plugging off some of the fractures through the foundation.

The contract made no provisions for accelerators or filler additives to assist the grout set. We were unable to keep any cement grout in the foundation and finally stopped grouting as the designed method was not working. It was determined that the only way we could hope to establish a grout curtain would be to block the flow through the drains.

The decision was made to grout the relief drains in monolith 15 down through 18 using cement with a filler additive. CBC was directed to acquire a supply of lost circulation materials and several cement accelerators. The Contract was modified to allow for CBC to grout relief drains using a mix of 1:1 cement grout and lost circulation materials. The intention was to grout all relief drains in monolith 15 through 18 and then grout in a curtain oriented upstream as previously specified. CBC took 4-days to gather materials and get ready to resume grouting. During this time the area was experiencing an above normal amount of rain. Reservoir Control was unable to maintain the reservoir at elevation 1500-feet and the reservoir quickly rose to an elevation of 1530-feet. This unforeseen rise in the reservoir was cause for concern for the structural stability of monolith 17.

The concern was that with the reservoir rising, and all relief drains plugged, uplift could increase above design criteria. It was determined that a maximum reservoir head of 1585-feet could be allowed and that additional foundation uplift pressure instruments would be required prior to plugging relief drains. The District Dam Safety Committee was assembled to review the conditions and make a recommendation. The Committee recommended to terminate the contract at the government•s convenience. -The contract was terminated from fear that should there be high spring runoff, it might not be possible to maintain the reservoir below 1585.

1.4 Uplift Testing

1.4.1 General

Following the termination of the 1995 Grouting Contract and prior to developing the scope of work for a new contract, testing was performed to more closely determine the effects of closing off the existing relief drains. Foundation uplift testing was performed to determine what effect closing a portion of the foundation relief drains would have on the foundation and structure with the forebay pool at elevations 1600, 1580, and 1560. The tests were designed to determine if foundation uplift pressures would remain below design criteria with the relief drains closed. A valved mechanical packer was installed and expanded in the concrete below the 6-foot relief drain stand-pipe in every relief drain in Monolith 14 down through Monolith 19.

The foundation pressure was monitored at existing pressure cells located at the concrete/bedrock interface in each monolith. These pressure cells are located SO-feet downstream of the upstream face of the dam. The pressure in the foundation was also monitored at a relief drain pressure gauge located near the center of each monolith. The two instruments formed a foundation pressure profile oriented perpendicular to the dam axis in each monolith. In addition to monitoring pressures in the foundation, visual inspections were made of adit "F",. "G", and the downstream toe. Pressures were monitored on the half hour throughout the test. See Plate 4 for the location of all instrumentation and the downstream adits.

Prior to starting the test the seepage flow from each individual relief drain was measured and an initial pressure reading was taken at each instrument. Following the initial pressure reading all the drains in Monolith 14 were closed.

After 2 hours and no change in foundation pressures the drains in monolith 15 were closed. When all pressures were stable in monolith 15, 1/2 of the drains in monolith 16 were closed (every other drain was closed off) . While closing every other drain the open drains increased in flow and flowed rusty-brown colored water. The flow increase and coloration indicated drain to drain communication and a flushing action occurring within the drainage system. After 2 hours, the remainder of the drains in monolith 16 were closed. The same procedure was followed for the remainder of the drains and a similar test was performed at each of the three pool elevations.

1.4.2 Test Results

Testing indicated the following:

+ Foundation relief drains from Monolith 15 down through Monolith 19 are interconnected with each other through extensive joints and fractures in the foundation and concrete s·tructure.

+ Foundation relief drains are interconnected with the monolith joints through fractures in the foundation and concrete structure.

+ The total flow of water into the gallery in monolith 14 through 19 increased as relief drains were closed. The additional water enters the gallery through joint drains and open bore holes into the foundation (these were existing open grout holes drilled under the 1995 Grouting Contract) . Some type of induction is occurring within the joint drains and through the fracturing to account for the increased total flow.

+ With the pool at elevation 1600 and the relief drains closed, uplift pressures in the foundat~on exceed design limits.

+ With the pool at elevation 1580 and 1560, relief drains can be closed without exceeding design uplift. However, uplift pressure relief is taking place through joint drains and open bore holes.

Test results lead to the following conclusions. Should the relief drains be closed o'r grouted to perform foundation grouting, the reservoir should be held below elevation 1560.

Further, given that the relief drains will be grouted closed, the reservoir should be held to no higher then 1530 during the foundation grouting. The additional 30 feet will allow time for the redrilling of some of the foundation drains in the event of an unexpected rise in the reservoir.

Also, the testing verified that the grouting should be extended into monolith 19. Relief drain flows in monolith 19 increased significantly when drains in monolith 18 were closed, indicating a direct connection through the bedrock fractures. Also, seepage from the foundation through the monolith joint relief drains should be addressed in the grouting contract.

1.5 Consultants Review

During the summer of 1996 a Delivery Order was awarded to Dames & Moore, the District's Geotechnical-A/E, to review all pertinent records concerning the foundation grouting of Dworshak Dam. The consultants were to prepare a report and make recommendations on the best method and materials to use in grouting the foundation at Dworshak. Dr. Donald Bruce, an internationally recognized grouting expert, worked with the staff of Dames & Moore in preparing the report. The report was completed on 31 October 1996.

After reviewing District records, interviewing District personnel, and making a site visit the Consultants made the following recommendations:

+ The Grouting Contract should be performance-based to encourage innovative solutions and methods from Contractors.

+ The pool should be held at 1520 or below during the construction window.

+ Control the drain flow from monolith joints 14/15 and 15/16.

+ Any of three grout types will work to stop initial flows:

hot bitumen, chemical, or modified cementitious grout.

+ Recommend using a water reactive hydrophobic polyurethane prepolymer chemical grout to control the high flows in the outer rows in the proposed grouting options.

+ The proposed remedial curtain should range from nearly vertical to upstream in inclination and consist of three rows. The first option proposes drilling three rows the second proposes using the existing relief drains as the most downstream curtain.

+ Drilling should be by rotary or rotary percussion methods. A minimum hole diameter of 3-inches is recommended to allow for the use of nonstandard grouting equipment. Stage length should be 30-feet. Ascending stage grouting is generally feasible, although the upper 30-feet may require special consideration.

2. FOUNDATION GROUTING

-2.1 Contract

A scope of work was determined following the Consultants advise and a Request For Proposals to do the grouting was advertised in the Fall of 1996. Using this contracting method, prospective Contractors submitted a technical proposal and cost bid for completing the specified work.

Then all proposals were evaluated and rated on technical merit and cost using specific criteria. Each proposal was given a point score for technical content and cost, independent of each other. The technical portion of the score weighed 70% while the cost weighed 30% of the total score. The Contractor with the highest total score was awarded the Contract. Five contractors made proposals to do the work. All proposals were independently rated and Layne\Keller LLC had the high score and was awarded the job.

The Government specifications outlined most of the material and method the Contractor would use to accomplish the foundation grouting project. The Contractor's proposal contained the specific details of how the work would be performed. The Government Specifications contained the following requirements:

+ Foundation drilling and grouting will take place between August 15,1997 and December 15,1997.

+ The Contractor will grout the relief drains then drill and grout the upstream curtain then drill and grout the middle curtain.

+ Relief drains and monolith joint drains will be grouted with hydrophilic or hydrophobic urethane chemical grout.

All other grouting will be with cement.

+ Following completion of the grouting, new relief drains will be drilled 100-feet deep on 5-foot centers.

+ All grouting equipment was specified~

+ Standard rotary drilling with minimum AX-size bit was specified.

+ Pressure tests were specified.

+ Standpipes were specified for both grout holes and drain holes.

+ Specific instrumentation and details for monitoring it were specified.

+ The specification required sealing monolith joints within the gallery and reestablishing the entire monolith joint waterstop for monolith joints 14/15 and 15/16. With an option for reestablishing the entire monolith joint water stop at the 16/17, 17/18, 18/19, and 19/20 joint.

2.2 Instrumentation

In order to monitor foundation conditions in monolith 15 through 19 during and after grouting, additional instrumentation was added under the 1997 Contract. All the existing and new instrumentation for monitoring the foundation and structure during and after construction is shown on Plate 4. The drill logs for instrumentation holes are included in Appendix B. The following instrumentation was added under the 1997 contract:

+ Drilled and installed 5 open tube piezometers (P-164, P- 165, P-184, P-185, and P-193) to monitor foundation uplift.

+ Drilled three additional crack relief drains from the drainage and grouting gallery into a mid monolith crack in monolith 19. All crack drainage flow was piped to a flume and monitored.

+ Meters to monitor concrete joint displacement were installed at each monolith joint.

+ An automated flume in monolith 24 monitored the total seepage flow.

The Contractor monitored the new instrumentation and the existing instrumentation in monoliths 14 through 19 during construction. The instrument readings for the entire system were automated and readings were taken hourly and downloaded daily during grouting.

2.3 Cement and Cement Additives

The cement used for grouting was standard Portland Type II Cement. The water cement ratio used for grouting varied from 3:1 to .8:1 with the majority at 1:1. The Contractor also added a high range water reducing admixture (HAWRA) to all the cement grout as specified. This material is designed to permit the use of a higher cement content while retaining low fluidity.

The Contractor used two types of accelerators in an attempt to create a fast-set cement grout. The two types used were Sodium Silicate and Master Builders Delvocrete Activator S-

51. Both types of accelerators were introduced into the cement grout in the header at the collar of the hole. If the grout take was small (under 3-gpm) the accelerators tended to set up in the manifold where it combined W'ith the cement or in the grout hole rather then out in the fracture.

If the grout take w~s high such as in holes that intersected monolith joints or fractures leading directly into monolith joints, the accelerators had little or no effect in stopping or even slowing the high take.

In an attempt to control flows in holes that communicated with monolith joints the Contractor used lost circulation materials (Shredded cellophane) . The lost circulation material helped to form a bridge in fractures or joints under high flow conditions. Shredded cellophane was added to the grout(1:1 or .8:1 grout mix) in the gallery transfer tub in very small quantities (generally 1 to 3 hand-fulls per tub) .

2.4 Chemical Grout

The Contractor's technical proposal outlined elaborate testing of the chemical grout prior to grouting. The testing was to incorporate similar pressures and temperatures as would be experienced at the project site.

The Contractor videoed the chemical grout testing and the Government viewed the videos. The Contractor tested two grouts: Stratathane 530/531 and Mtn. Grout ISP. The Stratathane 530/531 grout would not set under cold temperature/high pressure conditions or flow conditions.

However, at least in one instance the grout did set when aggressively agitated. The Mtn. Grout ISP set almost instantly and in several cases broke the Plexiglas testing apparatus due to excessive expansion.

The Contractor started the project using Stratathane ST 530/531 a water-reactive, semi rigid, solvent free, MDI based, hydrophobic, polyurethane prepolymer for relief drain grouting (as specified). However, due to the suppliers restock policy the Contractor requested for an approved equal. The Contractor requested to use DeNeef Hydro Active

Cut and the Government approved the request. The Hydro Active Cut is very similar to the Stratathane product. The Contractor used drum heaters in the gallery to warm the chemical grout prior to injection. The grout was injected through a short mixing tube/packer.

The Contractor used both Stratathane ST 530/531 and DeNeef Hydro Active Cut in their attempts to grout relief drains.

The Contractor tried several different types of grout in the monolith joint drains in their attempts to reestablish the waterstops. The primary grout used was DeNeef Flex LV. The other grout the Contractor u~ed was Mtn. Grout ISP. The Mtn.

Grout set to a rather rigid Styrofoam type material and so was not ideal for a waterstop material. The Mtn. Grout was used in the bedrock portion of the joint drain holes in hopes of stopping or slowing the flow from the foundation into the joint. The DeNeef product would not set due to the flow in the joint.

2.5 Grouting Existing Relief Drains

2.5.1 General

The Contractor proposed to chemically grout the relief drains using the following procedure: First clean the drains then install the MPSP (Multi-Port Sleevepipe Packer) into each drain. After installation of the MPSP, each stage would be water tested and then chemically grouted.

Cleaning The drain holes were cleaned using a rotating reaming tool with carbide cutters then washed and flushed with water and air. During cleaning, material from silt to gravel size was flushed from the relief drains. The highest flowing drains contained the most material. A calcite fracture filling material washed out of some drains.

MPSP Installation After cleaning the drains the Contractor installed the MPSP•s. The MPSP system used by the Contractor is a 2-inch PVC pipe with sleeved ports and a bottom cap. The sleeved ports are holes in the PVC covered with a rubber strap designed to allow one way ·flow from inside the pipe to outside. 20-inch long packer bags surround the sleeved pipe on approximate 16-foot centers. The sleeved ports are on approximate 8-foot centers. The packer bags are a porous cloth bag strapped around the pipe straddling a sleeved port.

Most MPSP•s were installed with a cap on the downhole ~nd.

However, if the drain had appreciable flow the Contractor removed the cap to facilitate installation. Once the MPSP was in place, a double packer was lowered down the hole to inflate the cloth bags with a cement/bentonite grout mixture. If the MPSP is installed correctly and operating properly there should be no flow at the surface of the drain once the MPSP is installed and the packers are inflated.

The inflated cloth bag packer should prohibit flow through the annulus and the oneway sleeved ports should stop flow into and through the sleeve pipe. After installation of the MPSP•s, most drains flowed from both the annulus and through the MPSP pipe, indicating the MPSP 1 S were not operating properly. The Contractor•s solution to this problem was to plug the annulus at the surface on those holes that made water from the annulus; and to insert a packer in the MPSP in those holes making water through the pipe.

There were problems with the construction and installation of the MPSP 1 s. It appeared that the cloth packer bags were leaking in the high flow. Also, the contractor had trouble locating the sleeved ports with the double packer. While there is a specific quantity of grout that is required to fill the packer within the hole, the Contractor consistently pumped more then this quantity while trying to fill packer bags. This indicated either grout was being pumped into leaking bags or into sleeves that did not lead into bags.

The MPSP•s installed in non-flowing drains appeared to function properly.

2.5.2 Water Testing

Following installation of the MPSP•s the Contractor attempted to water test the holes. The Contractor made a total of 322 water tests on 60 relief drains. Of the 60 drains water tested, 15 showed a water take. The Contractor had a great deal of difficulty locating the ports with the straddle packer to perform a water test. Due to the overall unreliability of water testing using a double packer through the sleeved ports this method was discontinued and the remainder of the holes were water tested using a single packer in the MPSP at the surface.

2.5.3 Chemical Grouting In Relief Drains

The Contractor attempted to inject chemical grout through the MPSP in several relief drain holes. The Contractor pumped the chemical grout through a high pressure hose with a single packer on the end. The idea was to set the packer above the lowest sleeved port, pump grout, then move the packer up to above the next sleeve port and repeat the procedure. With the exception of RD 17-I, chemical grouting either met with immediate refusal and pushed the packer up out of the hole, or chemical grout returned to the surface through the annulus of the drain hole. The grout did not appear to set. RD 17-I was the exception. The Contractor pumped 143-gallons of chemical grout into relief drain RD 17-I with only minor leakage at the surface. Later while drilling a new relief drain in this area a piece of core was recovered containing chemical grout in a joint. Table 1 in Appendix A shows the quantity of chemical grout pumped into individual drains.

2.5.4 Cement Grouting In Relief Drains

Due to the failure of the MPSP installation and the inability to attain a reliable set with chemical grout the Contractor followed a suggestion by the Government and proposed grouting the remainder of the relief drains with cement. A packer was set in the top of the MPSP in each of the remaining holes and cement grout was pumped in under pressure. Table 1 in Appendix A, shows the quantity of cement pumped into each relief drain. Most of the relief drains containing MPSP•s went to refusal instantly and wouldn•t except grout under pressure. While many of these relief drains made water prior to installing the MPSP, after installing the MPSP they would not take water or cement grout. The MPSP•s in these drains were backfilled with cement grout. Plate 5 shows the relief drains that were backfilled and the tables in Appendix A show the method and material used to backfill or pressure grout them. It appears that the existence of the MPSP•s in the relief drains hindered establishing a continuous grout curtain along the alignment of the existing relief drains. With a few exceptions these drains do appear to be effectively plugged at the surface.

2.6 Drilling and Grouting the Foundation Curtains

2.6.1 Drilling

The Contractor used air driven LY 65 screw feed drills with AW core barrels to drill the grout holes. Compressed air was supplied from air compressors set up on the left abutment just downstream of the dam. The AW core barrels drilled a hole 1.812 in diameter. Black steel standpipes (nipples) were set at the surface for each grout hole. The standpipes were set by drilling a hole to a depth of 3-feet with a electric core drill then grouting a 4-foot length of pipe into this hole leaving a 1-foot stickup. The standpipes were oriented to the angles shown in the specifications during installation. The drills were then mounted to the standpipes to drill the grout holes.

See Plate 7 and 11 for the location, orientation, and depth of each grout hole.

2.6.1.1 Drilling Upstream Curtain

Construction of the upstream curtain started after the existing relief drains were grouted and plugged. The holes were drilled on approximate 5-foot centers to l30-feet deep.

Plate 7 shows the location and orientation of the grout holes drilled for the upstream curtain. The Contractor drilled a total of 10,506-feet in establishing the upstream curtain.

2.6.1.2 Drilling Middle Curtain

Construction of the middle curtain started after the upstream curtain was approximately 3/4 finished. The 20 degree holes in the middle curtain were drilled and grouted first, then the 60 degree holes were drilled and grouted.

Plate 11 shows the location and orientation of the grout holes drilled for the middle curtain. The Contractor drilled a total of 10,000-feet in establishing the.middle curtain.

2.6.2 Grouting

Grout was mixed in a batch plant located on the left abutment downstream of the dam. After mixing, the grout was blown through a 1 1/2-inch line down into the gallery into one of three 17-cubic-foot holding tanks (transfer tubs).

From the holding tank the grout was pumped into the hole using a Mono pump. Pressure was monitored with a pressure gauge and regulated through a bypass. The grout also passed through a flow meter that gave gallons per minute flow and total flow in gallons. When pumping reached refusal a valve at the top of the hole was closed to hold the pressure on the grout until it set.

The specifications suggested stage up grouting, however, the Contractor proposed a modified stage down grouting technique. The Contractors accepted plan was to drill the initial holes to a depth of 40-feet and water test two 20 foot zones then grout the two zones as necessary. The hole would then be drilled to the final depth. In general, all curtain grout holes were 130-feet deep. The only grout holes that varied from this depth were the ones drilled from the stair landings. The final depth of all holes are shown on plates 7 and 1l.

The Contractor tried several different staging techniques during the grouting. In general, if during the water test a stage took more then 1.5-cubic feet of water in 5-minutes the stage was grouted. However, the details of the final procedure used by the Contractor is as follows:

a) The hole was drilled to the final depth of 130-feet unless a high water flow is encountered during the drilling. If high flow was encountered drilling was stopped and the hole water tested and grouted.

b) Once the hole was at 130-feet a water test from 60 to 130-feet was performed. If the water test showed a take of greater than 1.5-cubic feet in 5-minutes this zone was grouted using a packer set at 60-feet. After the grout set (minimum of 24-hours) the zone between 0 and 60-feet was water tested. If this zone showed a take greater than 1.5-cubic feet in 5-minutes then this zone was grouted with a packer set at the surface.

c) If during the water test betweeri 60 to 130-feet the hole didn't take greater than 1.5-cubic feet in 5-minutes the hole was water tested again with a packer set at the surface. Then, if the hole takes greater than 1.5 cubic feet in 5-minutes the zone from 0 to 130-feet was grouted with a packer set at the surface.

d) If the hole took less then 1.5 cubic feet in 5-minutes during the water tests the hole was backfilled with cement using a tremie.

2.6.2.1 Grouting Upstream Curtain

The orientation of the holes drilled to establish the upstream curtain are shown on Plate 7. The Contractor designated primary grout holes on 20-foot centers, secondary on 20-foot centers and tertiary on 10-foot centers resulting in a curtain with grout holes spaced every 5-feet. All holes were drilled regardless of grout take in adjacent holes. Additional grout holes were added in the stairwell landings as shown on plate 7. A total of 1,908 sacks of cement were used in grouting the upstream curtain. For an average of 0.18-sacks/foot of drilled hole. However, this quantity of grout is the total pumped, which includes backfilling holes not pressure grouted, grout loss from leakage through the monolith joints, and leakage through holes into the gallery. The foundation may have retained only about two thirds of the grout pumped. See plates 8

'through 10 for the individual grout takes in the upstream curtain grout holes.

2.6.2.2 Grouting Middle Curtain

The orientation of the holes drilled to establish the middle curtain are shown on Plate 11. The middle curtain row consisted of intersecting 20 and 60-degree holes. The 60-degree holes were drilled and grouted first, with primaries spaced every 20-feet and secondaries every 20-feet. Then the 20-degree holes were drilled and grouted using the same spacing. The resulting middle curtain has grout holes on approximate 5-foot centers. All holes were drilled regardless of grout take in adjacent holes. A total of 328 sacks of cement were used in grouting the middle curtain.

This quantify of grout includes backfilling holes not pressure grouted and grout loss from leakage through the monolith joints. The average grout take was 0.03-sacks/foot of drilled hole. Of the 77 holes drilled for the middle curtain only 19 took grout. The foundation for the middle curtain was tight and so took very little grout. See plates 12 through 17 for the individual grout takes in middle curtain grout holes.

2.7 Comments on Grouting

2.7.1 General

In general grout takes were small. Holes that show a relatively large take were likely communicating with a monolith joint and the grout was traveling to the downstream face of the dam within the monolith joint. Accelerators, added to the cement had little effect on set time in fractures with a high flow. Lost circulation material was more effective than accelerators in slowing high flows.

Many grout holes seeped after they were grouted, tremied, and patched at the surface. Weeping in completed grout holes increased as the pool came up. Holes that were identified as weeping prior to completion of construction were cleaned to 6-feet, a mechanical packer set between 4 and 5-feet in the hole, and the hole above the packer grouted to the surface. Approximately 18 additional weeping grout holes have been identified since the reservoir pool reached elevation 1600. These weeping holes appear to be the result of inadequate surface seals in the completed grout holes.

2.7.2 Grouting Near Elevation 1222.5

Attempts to grout the foundation near the stair landing at elevation 1222.5 required extensive surface and stairwell drain sealing. While attempting to grout foundation grout holes, grout entered into the stairwell drain system at some location under the landings. Repeated efforts to grout these zones from grout holes failed. The final solution was to bolt a 4-inch valve on the drain outlet at the 1222 elevation and on the drain inlet at elevation 1247. Once these valves were installed, sand was poured in the upper intake and the outlet valve was closed. Then the drain was pressure grouted from the inlet valve using cement. This grouting sealed off the drain system and the foundation leaks into the system. The Contractor was then able to proceed with the foundation grouting in this area. Surface piping was later installed to reestablish a drainage channel over the stair landings.

2.8 Drilling New Relief Drains

As the middle grout curtain was completed new relief drains were drilled. Standpipes were set in 5-inch diameter holes to a depth of 3-feet. The standpipes were 3.5-inch diameter by 4-feet long galvanized pipe, and were threaded for a cap on the outlet. The new drains are approximately 3-inch in diameter (NGS or NX size core barrel) and drilled on approximate 5-foot centers to a depth of 100-feet in monoliths 15 through 19. See Plate 6 for the locations of the new relief drains.

2.9 Water Diversion During Grouting

The method to capture waste water from drilling and grouting operations was specified in the Contract. Plates 2 and 3 show the water diversion route from the gallery in the left abutment. All water from the Drainage and Grouting Gallery in the left abutment was diverted down the gallery into the monolith 24 upstream/downstream drainage gallery which empties into the Skeleton Bay sump. Two sand bag retention dams were erected in the skeleton bay to provide for settling cement and drill cuttings. The Contractor pumped water from the Skeleton Bay up and over to the Diversion Tunnel. Water in the Diversion Tunnel seeps through random fill back into the river or through a 24-inch cmp overflow intake which drains into random fill near the outlet of the tunnel and into the river. The Contractor tested for turbidity in the river during every shift. No grout entered the river except for a few occurrences of grout coming out the monolith joints into the left groin and emptying into the Stilling Basin. The amount of grout that entered the river via this route was small due to settling that occurred prior to flowing through the outlet into the Stilling Basin.

3. REESTABLISHING MONOLITH JOINT UPSTREAM

WATERS TOP

3.1 General

Prior to grouting, excessive water was coming into the gallery through the monolith joint drains. The flow was highest through the joint drains at monolith 14/15 and 15/16, however, the joint drains at 16/17, 17/18, and 18/19 also made water. Water also entered the gallery through the monolith joint where it intersected the gallery. Water was entering the joint through both the foundation and reservoir pool. Failed waterstops were allowing water to travel downstream through the structure along the monolith joint.

The uplift tests indicated that if foundation relief drains were closed the flow through monolith joints would increase.

Most large fractures in the foundation were interconnected with the monolith joints. Reestablishing the monolith joint waterstop and sealing leaks from the foundation into the joint were critical to establishing a grout curtain in the foundation of these monoliths. New waterstops were established by grouting the upstream joint drain at monolith joint 14/15, 15/16, 16/17, 17/18, and 35/36. The upstream monolith joint drains for monolith 18/19 and 19/20 were not grouted because there was only minor leakage along these joints. Also, these joints are located under the Spillway and inaccessible from the roadway deck. The procedure for grouting the upstream joint drain required access to the top of the drain. The waterstop repair at monolith 35/36 was performed under a modification to the Contract to take -advantage of the Contractor being on site, but was not critical to the foundation grouting.

3.2 Contractors Proposal

The Contractor followed the specifications and formed a plan to reestablish the monolith joint waterstops. The following steps outline the Contractors proposal:

+ Reestablish waterstops prior to any foundation grouting.

+ View the joint drains with a downhole camera. *

+ Clean the holes if necessary.

+ Set a packer in the 8-inch monolith joint drain outlet into the gallery. *

+ Set a drill up on the upstream joint drain on the top of the dam. Drill down through the drain elbow through the concrete and 10-feet down into bedrock.

+ Install a PVC MPSP into the upstream joint drain down into bedrock.

+ Seal downstream monolith joint drain with a removable steel MPSP.

+ Grout with a pot-packer through the MPSP using a flexible hydrophobic MDI based, solvent free, water reactive prepolymer chemical grout. *

+ Locally seal the monolith joint in the gallery by driving wedges and installing absorbent pads soaked in chemical grout and by drilling holes into the joint and pumping chemical grout.

+ Set a mechanical packer in the joint drain where it enters the gallery. *

+ Reestablish drainage through the downstream joint drain upon completion of all grouting. *

* Denotes items specified by the Government as part of reestablishing the waterstops.

3.3 Contractors Results

The Contractor's efforts to stop water movement into the gallery at the monolith joint and monolith joint drain were effective. The Contractor set a packer in the joint drain leading into the gallery (as specified) which stopped or slowed the flow through the joint drain into the gallery.

Flow through the joint where it intersects the gallery was stopped by locally grouting the joint near the surface with chemical grout. With these outlets closed, the water in the joint rerouted and came out the monolith joint on the downstream face.

The Contractor made several attempts to reestablish a waterstop by chemically grouting the upstream joint drain prior to starting foundation grouting. The Contractor attempted to seal the downstream monolith joint drain with a removable MPSP to stop the flow through the joint and create a static condition. The MPSP was a 2-inch steel sleeve pipe with injection ports on 5-foot centers. The pipe was enveloped in a woven geotextile bag. The idea was to inflate the bag with bentonite through the injection ports.

The installation of these MPSP's did not appear to have any effect on the flow through the joint. In attempts to establish a upstream waterstop the Contractor pumped chemical grout through the MPSP in the upstream monolith joint drain. The Contractor first attempted grouting with DeNeef Flex LV. The grout would not set and flowed through the joint and came out downstream. They then proposed using Mountain grout ISP (see section 2.4.4.2) in the foundation portion of this hole. The Contractor pumped 140-gallons of Mtn. Grout into the foundation below the elbow. The grout did not show up downstream or upstream and a noticeable slowing of the flow through the joint occurred at the downstream face. The packer was grouted in during the process and lost.

Further attempts to reestablish the waterstop by grouting with chemical grout failed and the Contractor ceased operations in regard to establishing a waterstop prior to proceeding with foundation grouting. The Contractor, at the insistence of the Government, resumed attempts to reestablish the waterstop near the time of completion of the foundation grouting. The Government felt it critical to slow the water movement through the monolith joints prior to completing the grouting of the foundation. The Contractor drilled out the MPSP in the upstream joint drain at monolith 14/15 and reinstalled a new MPSP and again attempted chemical grouting with the Mtn. Grout ISP, varying the amount of chemical grout and accelerator. The grout still would not set in the joint and flowed out the downstream face indicating the grout would not set under these flow conditions. The MPSP the Contractor installed in the downstream joint drain was ineffective in stemming the flow through the joint.

3.4 Government Directed Waterstop Repair

The Contractor was unable to slow the flow in the downstream monolith joint drains with the use of MPSP's with a bentonite filled sack. Without this control on the flow the chemical grout would not set in the upstream joint drains and was washed downstream along the joint. The Government then directed the work to reestablish a waterstop in the upstream joint drain. The Government directed the Contractor to remove all MPSP's from the upstream and downstream joint drains. The downstream joint drain was then extended by drilling down through the-elbow and concrete and 10-feet into bedrock (same as the upstream joint drain) . The downstream joint drains were then tremie filled with a thick bentonite/sawdust slurry. This slurry stopped flow through the joint. The upstream joint drains were then tremied full of a sand/cement grout mix. The mix was designed to have a lower finial set strength than the concrete in the dam. This would allow for a drill to follow the original hole, should the material need to be removed and replaced later. Once the sand/cement set, the downstream joint drain was then cleaned out and the bottom of the hole up to the elbow was tremied full of sand/ cement grout. See Appendix D for the mix used for the bentonite/sawdust slurry and sand/Gement mix. The Contractor then reopened the joint drains into the gallery.

Only a small amount of water is now flowing through the joint drains.

In conjunction with this work the Contractor was directed to core a NX hole along the 15/16 and 16/17 joint. These holes were drilled from the gallery oriented downstream and up 20 degrees from vertical. The holes were drilled to just beyond the concrete bedrock contact. Upon completion of drilling these holes they were to be pressure grouted using cement grout with lost circulation materials. The idea was to form a downstream water stop along the joint to help contain grout movement along the monolith joints. The_holes were drilled prior to tremie grouting the upstream joint drain. The coring on monolith joint 16/17 stayed on joint for 6-feet then off to 27-feet (6 to 27-feet, hole may run next to joint, however, no evidence of joint in core), on edge of joint from 27 to 28-feet, bedrock at 35-feet and total depth at 39-feet. The hole was then grouted. The initial take was 7 to 10 gpm with no back pressure.

Grouting was stopped as grout take would not slow. Waited overnight, then grouted next mourning using 2:1 then 1:1 then .8:1 mix with lost circulation material. The total take was 163 gal at 40 psi. The coring on monolith joint 15/16 stayed on the joint for 8-feet and hit bedrock at 30-feet, for a total depth of 34-feet. The hole was water tested and would not take water. Due to an oversight this hole was not grouted. With the reservoir pool up to elevation 1600 this hole now makes up to 50 gpm.

Joint drains were reestablished using the downstream joint drain. On joints 14/15, 16/17, and 17/18 new drain outlets were drilled from the gallery to intersect the joint drain at a higher elevation as shown on Plate 18. PVC pipe was added to these drains to direct the flow into the upstream gutter.

4. UPLIFT RESPONSE TO FOUNDATION GROUTING AND

WATERSTOP REPAIR

4.1 General

The uplift and flow in the left abutment was monitored very closely prior, during, and after construction to determine the effectiveness of the new grout curtain. Appendix E contains the graphs showing uplift pressure at different locations in monoliths 15 through 19. Uplift is shown in relation to time and pool elevation. In general the graphs indicate a sharp increase in uplift pressures when the monolith joint drains were closed, followed by a sharp decrease in pressure when the relief drains were pressure grouted. Uplift pressures continued to decline as the foundation grouting was completed.

4.2 Uplift Response by Individual Monoliths

The uplift response in individual monoliths is described in the following paragraphs:

Monolith 14 -Prior to foundation grouting no uplift pressure had been recorded at uplift cell P-143 in monolith 14 (see Plate 4, and graphs in Appendix E). When the relief drains were closed during the testing in 1996, P-143 showed no pressure response. During the grouting in 1997, P-143 responded with a sharp increase in pressure when the flow into the gallery from the 14/15 monolith joint drain was shut-off. The pressure head rose from 1378-ft to 1455-ft .

. The pool was at elevation 1560. The pressure head remained approximately steady at this elevated head for approximately 5-weeks. The pressure head dropped off from 1456-feet to

1389-feet in response to grouting the relief drains in monolith 15. The pool was lowered to 1500-feet during this time. The pressure then slowly dropped during the next 3-weeks back to 1363, coinciding with the upstream curtain grouting. Following completion of the grouting the pool was raised back up to 1600. The uplift cell in monolith 14 showed no response, as shown on the graph in Appendix E.

Monoljtb 15 - Uplift pressure has been slight and sporadic in the past at the uplift cell P-153 in Monolith 15 (see Plate 4, and graphs in Appendix E). When the relief drains were closed during the testing in 1996, P-153 responded with a maximum pressure of 18-PSI or a head elevation of 1315, well below the maximum design uplift. During the grouting in 1997, P-153 responded with a sharp increase in pressure when the flow into the gallery from the 14/15 monolith joint drain was shut-off. The pressure head rose from 1382-ft to 1502-ft. The pool was at elevation 1560. The pressure head dropped slightly but remained approximately steady at this elevated head until the relief drains in monolith 15 were pressure grouted, then the head dropped from 1480 to 1409.

The reservoir pool level dropped to 1500. -The uplift head continued to drop to 1313 as the foundation curtain was constructed. Following completion of the grouting when the pool was raised back up to 1600 this uplift cell showed a slow pressure increase following the pool raise as shown on the graph in Appendix E.

Monoljth J6 -Uplift pressure has been slight and followed the pool raises in the past at the uplift cell P-163 in Monolith 16 (see Plate 4 and graphs in Appendix E) . The head varied between approximately 1260-ft and 1280-ft showing a response to pool elevation changes. When the relief drains were closed during the testing in 1996, P-163 responded to a maximum pressure of 107-PSI or a head elevation of 1478. Which is above the maximum design uplift at the 1600 pool. During the grouting in 1997, P-163 rose from 1263-ft to 1435-ft over a two week period while the joint flow was packered off into the gallery and the contractor was attempting to grout the U/S monolith joints.

The pressure remained elevated at approximately. 1435-ft for 2-weeks then slowly dropped during the next month back to 1263 coinciding with the existing relief drain grouting and upstream curtain grouting. Following completion of the grouting when the pool was raised back up to 1600 this uplift cell showed a slow pressure increase following the pool up as shown on the graph in Appendix E.

Two additional uplift piezometers were installed in monolith 16 under the 1997 Grouting Contract (P164 and P165) . The uplift cells are located in the center of monolith 16 and downstream as follows:

P163 80-ft D/S from U/S face P164 100-ft D/S from U/S face

P165 150-ft D/8 from U/8 face

These three piezometers, while separated downstream, all react approximately the same.