Compendium of Case Histories on Repair of Erosion-Damaged Concrete in Hydraulic Structures

Transcription

1 ACI R-94 Compendium of Case Histories on Repair of Erosion-Damaged Concrete in Hydraulic Structures Reported by ACI Committee 210 (Reapproved 1999) Stephen B. Tatro Chairman Patrick J. Creegan James R. Graham Angel E. Herrera Richard A. Kaden James E. McDonald Ernest K. Schrader This report is a companion document to ACI 210R. It contains a series of case histories on hydraulic structures that have been damaged by erosion from various physical mechanical and chemical actions. Many of these structures have been successfully repaired. There were many examples to select from; however, the committee has selected recent, typical projects, with differing repair techniques, to provide a broad range of current experience. These case histories cover only damage to the hydraulic surfaces due to the action of water, waterborne material or chemical attack of concrete from fluids conveyed along the hydraulic passages. In addition to repairs of the damaged concrete, remedial work frequently includes design modifications that are intended to eliminate or minimize the action that produced the damage. This report does not cover repair of concrete damaged by other environmental factors such as freeze-thaw, expansive aggregate, or corroding reinforcement. Keywords: abrasion; abrasion resistance; aeration; cavitation; chemical attack; concrete dams; concrete pipes; corrosion; corrosion resistance; deterioration; erosion; grinding (material removal); high-strength concrete hydraulic structures; maintenance; outlet works; penstocks; pipe linings; pipes (tubes); pittings; polymer concrete; renovating; repairs; sewers; spillways; tolerances (mechanics); wear. CONTENTS Chapter l-introduction, p R-1 Chapter 2-Cavitation-erosion case histories, p R-2 Dworshak Dam Glen Canyon Dam Lower Monumental Dam Lucky Peak Dam Terzaghi Dam Yellowtail Afterbay Dam Yellowtail Dam Keenleyside Dam Chapter 3--erosion case histories, p. 21O.lR-13 Espinosa Irrigation Diversion Dam Kinzua Dam Los Angeles River Channel Nolin Lake Dam Pine River Watershed, Structure No. 41 Pomona Dam Providence-Millville Diversion Structure Red Rock Dam Sheldon Gulch Siphon Chapter 4-Chemical attack-erosion case histories, p R-25 Barceloneta Trunk Sewer Dworshak National Fish Hatchery Los Angeles Sanitary Sewer System and Hyperion Sewage Treatment Facility Pecos Arroyo Watershed, Site 1 Chapter 5-Project reference List, p R-32 CHAPTER 1-INTRODUCTION This compendium of case histories provides information on damage that has occurred to hydraulic structures and the various methods of repair that have been used. ACI Committee 210 has prepared this report to help others experiencing similar problems in existing work. Knowledge gained from these experiences may help ACI Committee Reports, Guides, Standard Practices, and Commentaries are intended for guidance in designing, planning, executing, or inspecting construction and in preparing specifications. References to these documents shall not be made in the Project Documents. If items found in these documents are desired to be part of the Project Documents, they should be phrased in mandatory language and incorporated into the Project Documents. ACI 210.1R-94 became effective Nov Copyright , American Concrete Institute. All rights reserved including rights of reproduction and use in any form or by any means, including the making of copies by any photo process, or by any electronic or mechanical device, printed, written, or oral, or recording for sound or visual reproduction for use in any knowledge or retrieval system or device, unless permission in writing is obtained from tbe copyright proprietors R-1

2 210.1R-2 ACI COMMITTEE REPORT avoid oversights in design and construction of hydraulic structures and provide guidance in the treatment of future problems. Erosion of concrete in hydraulic structures may occur as a result of abrasive action, cavitation, or chemical attack. Damage may develop rapidly after some unusual event such as a flood or it may develop gradually during normal continuous operation or use. In most cases where damage has occurred, simply replacing the eroded concrete will ensure immediate serviceability, but may not ensure long-term performance of the structure. Therefore, repair work usually includes replacing eroded concrete with a more resistant concrete and additional surface treatment, modifying the design or operation of the structure to eliminate the mechanism that produced the damage, or both. A detailed discussion of mechanisms causing erosion in hydraulic structures, and recommendations on maintenance and repair, is contained in ACI 210R. When damage does occur to hydraulic structures, repair work poses some unique problems and is often very costly. Direct access to the damaged area may not be possible, or may be limited by time, or other constraints. In some cases, such as repair to spillway stilling basin floors, expensive bulkheads and dewatering are required. It may not be possible to completely dry the area to be repaired or maintain the most desirable temperature. A great deal of planning and scheduling for repair work are normally required, not only for the repairs and access, but also for control of water releases and reservoir levels. If time permits, extensive investigation usually precedes planning and scheduling to determine the nature and extent of damage. Hydraulic model studies may also be necessary to evaluate possible modifications in the design or operation of the facility. This compendium provides the history on 21 projects with hydraulic erosion damage. They vary in size and cover a variety of problems: 8 with cavitation damage, 9 with abrasion-erosion damage, and 4 with erosion damage from chemical attack. Table 1.1 summarizes the projects. Each repair was slightly different. Each history includes background information on the project or facility, the problem of erosion, the selected solution to the problem, and the performance of the corrective action. Histories also contain references and owner information if further details are needed. CHAPTER 2-CAVITATION-EROSION CASE HISTORIES DWORSHAK DAM North Fork, Clearwater River, Idaho Dworshak Dam, operational in 1973, is a straight-axis concrete gravity dam, 717 ft high, 3287 ft long at the crest, and contains 6,500,000 cubic yards of concrete. In addition to two gated overflow spillways, three regulating outlets, 12 ft wide by 17 ft high, are located in the spillway monoliths. The inlet elevation for each regulating outlet is 250 ft below the maximum reservoir elevation. Each outlet jet is capable of a maximum discharge of 14,000 fij/s. Outlet surfaces are reinforced structural concrete placed concurrently with adjacent lean, large aggregate concrete. Coatings to the outlet surfaces were applied during the original construction. In Outlet 1, the wall and invert surfaces from the tainter gate to a point 50 ft downstream are coated with an epoxy mortar having an average thickness of % in. The same area of Outlet 2 was coated using an epoxy resin, approximately.05 in. in thickness. Outlet 3 was untreated. The outlets were operated intermittently at various gate openings for a period of 4 years between 1971 and 1975, resulting in a cumulative discharge duration of approximately 10 months. The three outlets were not operated symmetrically; outlets 1 and 2 were used primarily. Inspection in 1973 showed minor concrete scaling of the concrete wall surfaces of Outlets 1 and 2. One year later, in 1974, serious erosion had occurred at wall surfaces of both outlets immediately downstream of the wall coatings, 50 ft from the tainter gate. Part of this wall area had eroded to a depth of 22 in., exposing and even removing some No. 9 reinforcing bars. In the wall surfaces downstream of Outlet 1 medium damage, up to 1 in. depth of erosion, also occurred in over 60 square yards of surface, bordered by lighter erosion. Every horizontal lift joint (construction joint) along the path of the jet, showed additional cavitation erosion. Repairs were categorized as three types: Areas with heavy damage, with erosion greater than 2 to 3 in., were delineated by a 3-in. saw cut and the interior concrete excavated to a minimum depth of 15 in. (Fig. 2.1 and 2.2). Reinforcement was reestablished and steel fiber-reinforced concrete (FRC) was used as the replacement material. Areas with medium damage, where the depth of erosion was less than 1 in., were bush-hammered to a depth of % to 1 in. and dry-packed with mortar. The mortar, if left untreated, would easily have failed when subjected to the high velocity discharge. Areas with minor damage, surfaces showing a sandblast texture, were not separately treated prior to polymer impregnation. The entire wall surfaces of Outlet 1 were then treated by polymer impregnation from the downstream edge of the existing epoxy mortar coating to a distance 200 ft downstream.

3 REPAIR OF EROSION DAMAGED HYDRAULIC STRUCTURES R-3 TABLE 1.1- SUMMARY TABLE OF PROJECTS COMPRISING THIS REPORT Project name Dworshak Dam Glen Canyon Dam Lower Monumental Dam Lucky Peak Dam Terzaghi Dam Yellowtail Afterbay Dam Yellowtail Dam Keenleyside Dam Espinosa Irrigation Diversion Dam Kinzua Dam Los Angeles River Channel NoIin Lake Dam Year completed Location Owner Problem Repair type 1974 Gravity dam Idaho Corps of Cavitation Polymer Engineers impregnation 1964 Arch dam Arizona Bureau of Cavitation Aeration Reclamation 1969 Navigation lock washington Corps of Cavitation Engineers Epoxy 1956 Outlet structure Idaho Corps of Cavitation various Engineers 1960 Outlet structure British Columbia B.C. Hydro Cavitation Hydraulic Authority redesign 1966 Montana Bureau of Cavitation Various overlays RecIamation 1966 Montana Bureau of Cavitation Aeration and RecIamation overiays 1968 Outlet structure British Columbia B.C. Hydro Cavitation High-strength I I 1984 Diversion dam New Mexico 1965 Pennsylvania 1940s Channel California 1963 Kentucky Pine River Watershed, Proposed Channel Colorado Structure No. 41 Pomona Dam 1963 Kansas Providence-Millville Diversion Structure Red Rock Dam Sheldon Gulch Siphon Barceloneta Trunk Sewer Dworshak National Fish Hatchery Los Angeles Sanitary Sewer System and Hyperion Sewage Treatment Facility Pecos Arroyo Watershed, Site s Varies 1988 Diversion dam Syphon outlet Pipeline Concrete tanks Sewerage structures Outlet conduit I Utah Iowa Wyoming Puerto Rico Idaho California New Mexico I I Authority I Iconcrete Soil Conservation Steel plate armor Service Corps of Silica fume Engineers concrete Corps of Engineers Corps of Engineers SoiI Conservation Service Siiica fume concrete Hydraulic redesign High-strength concrete Corps of various Engineers Soil Conser- Surface hardener vation Service Corps of Underwater Engineers concrete Soil Conser- Polymer-modified vation Service mortar Puerto Rico Chemical attack PVC lining Aqueduct & Sewer Authority Corps of Chemica l attack Linings Engineers City of Los Chemical attack Shotcrete and Angeles PVC liners Soil Conservation Service Chemical attack HDPE liner and I I hydraulic redesign Reference page 210.1R R R R R R R R R R R R R R R R R R R R R-30 Damage to the epoxy mortar was minimal and located near the outlet gate. This area was repaired with new epoxy. The polymer impregnation process involved drying all the surfaces to a temperature up to 300 F to drive off water and then allowing the surface to cool to 230 F. Monomer was then applied to the surface using a vertical soaking chamber. Excessive monomer was drained and the surface was polymerized by the application of approximately 150 F water. Operation of the outlets from the time of repair in 1975 until 1982 has been minimal averaging 1400 ft3/s per outlet with peak discharges of 3600 ft3/s per outlet. Durations of usage are not known. After 1982 outlet discharges increased, with durations exceeding 50 days. Inspections performed in 1976, the year after the repairs, showed no additional concrete damage except for some minor surface spalling adjacent to a major preexisting crack in an area of dry-packed mortar. The

4 210.1R-4 ACI COMMlTTEE REPORT Fig. 2.1-Dworshak Dam. Detail showing depth of erosion behind reinforcing steel Fig. 2.2-Dworshak Dam. Extent of outlet surface preparation prior to concrete and mortar placements spalled area was patched with epoxy paste, except that the epoxy paste did not bridge the crack this time. Epoxy resin coating repairs applied to Outlet 2 showed some failures, Inspections in 1983 and 1988 showed that epoxy mortar coatings in Outlet 1 continued to perform well. Small areas of damage, typically spalls, are periodically repaired with a paste epoxy. Epoxy resin coatings in Outlet 2 are repaired more frequently but are performing adequately. Surfaces repaired with FRC and mortar and subsequently polymer-impregnated showed negligible damage. Polymer-impregnated parent concrete shows a typical matrix erosion around the coarse aggregate to a depth of 1 /4-in., and lift joints exhibit pitting up to 3 /8-in. deep. Surfaces along lift joints not polymer-impregnated show erosion up to 3 /4-in. in depth and a general surface pitting greater than the companion polymer-impregnated surfaces, DISCUSSION Because of variation in the operation of these outlets, both in flow rate and duration, exact time-rate erosion conclusions are difficult to make. Recent outlet discharge has fluctuated annually from moderate flows to none. In general, surfaces that received replacement materials and were subsequently polymer-impregnated have performed well. Original concrete and new polymer impregnated concrete is showing evidence of deterioration, but at a rate that is less than the unimpregnated surfaces. The

5 REPAIR OF EROSION DAMAGED HYDRAULIC STRUCTURES R-5 best performance was by the original epoxy mortar coating. The epoxy mortar in Outlet 1 continues to display an excellent surface condition, with no cavitation-generated pitting. The epoxy resin coating in Outlet 2 displays good performance. In 1988, outlets were modified by adding aeration deflectors, wedges 27 in. wide by 1.5 in. high, to the sides and bottom of each outlet. These deflectors were designed to increase the aeration of the discharge jet and further reduce the cavitation erosion of the outlet surfaces. Subsequent deterioration of the outlet surfaces has not been observed. The polymer impregnating of the concrete surfaces of the outlets was a very complex system of operations. Success requires continual evaluation of application conditions and flexibility to react to changes in those conditions. Issues relating to safety, cost, and field engineering add significant challenges to a polymer impregnation project. It is doubtful that this process would be attempted today under similar circumstances. It is more likely that the aeration deflectors would be the first remedy considered since they provide a positive solution to the problem without the higher risks of a failure inherent in the polymer impregnation process. Schrader, Ernest K., and Kaden, Richard A, Outlet Repairs at Dworshak Dam, The Military Engineer, The Society of American Military Engineers, Washington, D.C., May-June 1976, pp Murray, Myles A, and Schultheis, Vem F., Polymerization of Concrete Fights Cavitation, Civil Engineering, V. 47, No. 4, American Society of Civil Engineers, New York, April 1977, pp U.S. Army Engineer District, Walla Walla, Polymer Impregnation of Concrete at Dworshak Dam, Walla Walla, WA, July 1976, Reissued April U.S. Army Engineer District, Walla Walla, Periodic Inspection Reports No. 6, 7, and 8, Dworshak Dam and Reservoir, Walla Walla District, Jan CONTACT/OWNER Walla Walla District, Corps of Engineers City-County Airport Walla Walla, WA GLEN CANYON DAM Colorado River, Northeast Arizona Glen Canyon Dam, operational in 1964, is a concrete gravity, arch structure, 710 ft high with a crest length of 1560 ft. The dam is flanked on both sides by high-head tunnel spillways, each including an intake structure with two 40- by 55-ft radial gates. Each tunnel consists of a 41-ft diameter section inclined at 55 percent, a vertical bend (elbow), and 985 ft of near horizontal length followed by a deflector bucket. Water first flowed through the spillways in 1980, 16 years after completion of the dam. In late May 1983, runoff in the upper reaches of the Colorado River was steadily increasing due to snowmelt from an extremely heavy snowpack. On June 2,1983, the left tunnel spillway gates were opened to release 10,000 ft 3 /s. On June 5 the release was increased to 20,000 ft 3 /s. On June 6 officials heard loud rumbling noises coming from the left spillway. Engineers examined the tunnel and found several large holes in the invert of the elbow. This damage was initiated by cavitation, triggered by discontinuities formed by calcite deposits on the tunnel invert at the upstream end of the elbow. In spite of this damage, continued high runoff required increasing the discharge in the left spillway tunnel to 23,000 ft 3 /s. by June 23. Flows in the right spillway tunnel were held at 6000 ft 3 /s. to minimize damage from cavitation. Spillway gates were finally closed July 23, and engineers made a thorough inspection of the tunnels. Extensive damage had occurred in and near the left tunnel elbow (Fig. 23). Immediately downstream from the elbow, a hole (35 ft deep, 134 ft long, and 50 ft wide) had been eroded in the concrete lining and underlying sandstone foundation. Other smaller holes had been eroded in the lining in leapfrog fashion upstream from the elbow. The repair work was accomplished in six phases: 1) removing loose and defective concrete lining and foundation rock; 2) backfilling large cavities in sandstone foundation with concrete; 3) reconstructing tunnel lining; 4) grinding and patching of small defective areas; 5) removing about 500 cubic yards of debris from lower reaches of tunnel and flip bucket; and 6) constructing an aeration device in the lining upstream of the vertical elbow. Sandstone cavities were filled with tremie concrete before the lining was replaced. About 2000 cubic yards of replacement concrete was used. The aeration slot was modeled in the Bureau of Reclamation Hydraulic Laboratory to ensure that its design would provide the performance required. The aeration slot was constructed on the inclined portion of the tunnel approximately 150 ft upstream from the start of the elbow. A small 7-in-high ramp was constructed immediately upstream of the slot. The slot was 4 by 4 ft in cross section and extended around the lower three-fourths of the tunnel circumference (Fig. 2.4). All repairs and the slot were completed in the summer of Because of the moderate runoff in the Colorado River since completion of the tunnel repairs, it has not been

6 210.1R-6 ACI COMMITTEE REPORT Fig. 2.3-Glen Canyon Dam. Erosion of spillway tunnel invert and sandstone foundation rock downstream of the elbow necessary to use the large spillway tunnels. However, shortly after completion of the work, another high runoff period permitted performance of a field verification test. This test lasted 72 hr with a maximum flow during that time of 50,000 ft 3 /S. The test was conducted in two phases with several interruptions in each for examination of the tunnel Offsets were intentionally left in place to evaluate whether the aeration slot would indeed preclude cavitation and attendant concrete damage. The tunnel repairs and air slot performed as designed. No sign of cavitation damage was evident anywhere in the tunnel. Aeration has decreased the flow capacity of the spillway tunnels by approximately 20 percent of the original flow capacity. Burgi, P.H., and Eckley, M.S., Repairs at Glen Canyon Dam, Concrete International, American Concrete Institute, MI, V. 9, No. 3, Mar. 1986, pp Frizell, K.W., Glen Canyon Dam Spillway Tests Model - Prototype Comparison, Hydraulics and Hydrology in the Small Computer Age, Proceeding of the Specialty Conference, Lake Buena Vista, Florida, Aug , 1985, American Society of Civil Engineers, New York, 1985, pp Frizell, K.W., Spillway Tests at Glen Canyon Dam, U.S. Bureau of Reclamation, Denver, CO, July Pugh, C.A., Modeling Aeration Devices for Glen Canyon Dam, Water for Resource Development, Proceedings of the Conference, Coeur d Alene, Idaho, Aug , 1984, American Society of Cii Engineers, New York, 1984, pp CONTACT U.S. Bureau of Reclamation P.O. Box 25007, Denver Federal Center Denver, CO LOWER MONUMENTAL DAM Snake River, Near Kaloutus, Washington Lower Monumental Dam, operational in 1970, consists of a concrete gravity spillway and dam, earthfii em-

7 210.1R-7 Original tunnel surfac Aeration slot.i8 SECTION A-A Fig. 2.4-Glen Canyon Dam. Diagram of new tunnel spillway air slot bankments, a navigation lock, and a six-unit powerhouse. The 86-ft wide by 675-ft long navigation lock chamber, with a rise of 100 ft, is filled and emptied by two galleries or culverts, landside and riverside of the lock structure. The landside culvert, which supplies five downstream laterals, crosses under the navigation lock to discharge into the river. The riverside culvert supplies and discharges water to the upstream five laterals. Each lateral consists of 10 portal entrances approximately 1.5 ft wide by 3 ft high. Plow velocities in excess of 120 ft/s occur in several of the portals entrances. A tie-in gallery exists between the two main culverts, near the downstream gates, that equalizes the pressure between the two culverts. Inspections as early as 1975 revealed that the ceiling concrete of the landslide culvert was spalled at some monolith joints to depths of 9 in. This may have been initiated by differential movement of adjacent monoliths when the lock chamber was filled and emptied. Damage to the invert, at several locations, was irregular, with erosion a maximum of 18 in. deep at the monolith joint, decreasing to 1 in. at a point 10 ft upstream of the joint. Reinforcing steel was exposed. Other areas of erosion in the invert and on wall surfaces were observed, measuring 2 ft square and 2 in. deep. Later inspections revealed that portal surfaces nearest the culverts of the most downstream laterals were showing signs of concrete erosion (Fig. 2.5). By 1978, the portal walls, ceiling, and invert had eroded as deep as 3 in. over an area of 5 square ft, exposing reinforcing steel. All four corners of the tie-in gallery experienced obvious cavitation damage. The damage varied from minor pitting to exposure and undercutting of the 1 1 /2-in. aggregate. In 1978, the navigation lock system was shut down for two weeks for repairs. The major erosion damage to the landslide culvert was repaired by mechanically anchored steel fiber-reinforced concrete. The smaller areas of damage received a trowel application of a paste epoxy product. Ceiling damage was backfilled with dry-mix shotcrete. Portal and tie-in gallery surfaces received application of a paste epoxy, troweled to a feather edge around the perimeter. The mechanically anchored fiber-reinforced concrete has performed well to date. No additional erosion has been observed. Shotcrete patches to the ceiling adjacent to the joints show continued spalling, but to a lesser extent than prior to repairs. The repairs to the portal surfaces and tie-in gallery surfaces performed poorly. After 1 year of service, approximately 40 percent of the epoxy paste had failed; and after 3 years, nearly 100 percent has failed. Concrete erosion in these areas has subsequently increased to depths of 6 to 8 in. in the tie-in gallery and up to 5 to 6 in. on the two most downstream portal surfaces.

8 210.1R-8 ACI COMMITTEE REPORT CONTACT/OWNER Walla Walla District, Corps of Engineers City-County Airport Walla Walla, WA LUCKY PEAK DAM Boise River, Near Boise, Idaho DISCUSSION Recent inspections have shown that the rate of erosion has decreased. The accumulated erosion of concrete from certain surfaces is significant; however, subsequent erosion is almost negligible. Consequently, repair schedules are not critical. Paste epoxy was applied to the concrete surfaces transitioning to feather edges along the perimeter of the patches. Cavitation eroded the concrete adjacent to the feather edges as weil as eroding the thin epoxy edges (Fig. 2.5). These new voids undermined the new, thicker epoxy, and at some point caused another failure of the leading edge. As the leading edge void increased in size, the failure progressed until little epoxy was left in the repaired area. After erosion of the epoxy patch material, no further concrete erosion has occurred. It appears that the eroded configuration of the surface is hydraulically stable. Patch-type repair procedures are not sufficient for this structure because erosion is initiated at the edge of the new patch. Eventual repairs will replace larger areas of the concrete flow surfaces and will include substantial anchoring of new materials. U.S. Army Engineer District, Walla Walla, Periodic Inspection Report No. 6, Lower Monumental Lock and Dam, Walla Walla, WA, Jan U.S. Army Engineer District, Walla Walla, Periodic Inspection Report No. 7, Lower Monumental Lock and Dam, Walla Walla, WA, Jan U.S. Army Engineer District, Walla Walla, Periodic Inspection Report No. 8, Lower Monumental Lock and Dam, Walla Walla, WA, Jan Lucky Peak Dam, operational in 1955, is 340 ft high with a crest length of 2340 ft. The dam is an earth and rockfill structure with a silt core, graded filters, and rock shells. The ungated spillway is a 6000-ft-long ogee weir discharging into an unlined channel. The outlet works consists of a 23-ft-diameter steel conduit that delivers water to a manifold structure with six outlets. Each outlet is controlled by a 5.25-ft by 10-ft slide gate. Individual flip lips were constructed downstream from each slide gate. Downstream of the flip lips is the plunge pool, excavated into the basalt rock, with bottom areal dimensions of 150 by 150 ft. The outlet alignment and design were determined by hydraulic modeling. The sir outlets operated under a maximum head of 228 ft with a design discharge of 30,500 ft 3 /S and a maximum discharge velocity ranging between 88 ft/s and 124 ft/s. The steel manifold gates have a long history of cavitation erosion problems. The original bronze gate seals were seriously damaged by cavitation after initial use. Flow rates across the manifold gate frames in excess of 150 ft/s for many days were common. The gate seals were replaced with new seals made of stainless steel and aluminum-bronze. The cast-steel gate frames required continual repair of cavitated areas. In 1975 alone, over 2000 pounds of stainless steel welding rod was manually welded into the eroded areas and ground smooth. Neat cement grout was pumped behind the gate frames to reestablish full bearing of the gate frames with the concrete structure. The concrete invert and side piers, which separate each of the six flip lips suffered extensive erosion soon after the start of operations in 1955 (Fig. 2.6). 3 /4-in.-thick steel plates were anchored to the piers and invert areas just downstream of the manifold gates. These steel wall plates became severely pitted, as did the downstream concrete flip lip invert surfaces. In 1968, the damaged plates were again repaired by filling the eroded areas with stainless steel welding, and grouting behind the plates Deteriorated concrete on the flip lips was removed and additional steel plates were installed over those areas. This also failed and repairs commenced again. Deep areas of cavitation damage in the invert and piers were filled with concrete. New 1 /2-in.-thick plates were installed. These were stiffened with steel beams, welded on 5-ft centers in each direction. Deep anchor

9 REPAIR OF EROSlON DAMAGED HYDRAULIC STRUCTURES 210.1R-9 bars were welded to the plate material to hold them in place. Again, the voids under the plates were grouted. But during the next two years, these repairs also failed. In 1974, it was recommended that the outlet be restudied hydraulically. That year, remaining plate material was removed. Cavities were found penetrating the invert and through the piers and into the adjacent outlet invert. These voids were crudely filled with FRC in a field expedient manner. Much of this FRC was placed in standing water with little quality control, while adjacent bays were discharging. The side piers were redesigned and replaced to provide vents that would introduce air to the underside of the jet just downstream of the gates. This modification was intended to prevent additional invert erosion. However, major modifications to the gates and gate frames were necessary if cavitation erosion was to be eliminated These modifications were not made since future powerhouse construction would reduce and nearly eliminate the need to use the outlet, reserving the structure for emergency and special operations use only. Steel lining on the piers was strengthened and replaced. Stiffened steel plates, 1 1 /4-in. thick, were installed on the piers and invert. Mortar backfill was pumped behind the invert plates and new concrete placed between pier plates. After one year of above average usage on bays 3 and 4, cavitation was again observed. The side piers just downstream of the gates showed areas of 1 to 2 square ft that had eroded through the steel plate and into the concrete about 6 in. No erosion of the invert plates or the field expedient FRC occurred. Use of these bays has almost stopped since the new powerhouse became operational. DISCUSSION The introduction of air beneath the jet appears to have cushioned the effects of cavitation on the flip lip invert. However, pier walls continue to erode at an extraordinary rate. The cause lies with the design of the gates and gate frame. It is evident that satisfactory performance of the structure can never be achieved until the gates and frames are redesigned and reconstructed to eliminate the conditions that cause cavitation. U.S. Army Engineer District, Walla Walla, Lucky Peak Lake, Idaho, Design Memorandum 12, Flip Bucket Modifications, Supplement No. 1, Outlet Works, Slide Gate Repair and Modification, Walla Walla, WA, July U.S. Army Engineer District, Walla Walla, Periodic Inspection Report No. 6, Lucky Peak Lake, Walla Walla, WA, Jan U.S. Army Engineer District, Walla Walla, Periodic Fig. 2.6-Lucky Peak Dam. Cavitation erosion of flip lip surface Inspection Report No. 7, Lucky Peak Lake, Walla Walla, WA, Jan CONTACT/OWNER Walla Walla District, Corps of Engineers City-County Airport Walla Walla, WA TERZAGHI DAM Bridge River Near Lillooet, British Columbia, Canada Terzaghi Dam, operational in 1960, is 197 ft high with a crest length of 1200 ft. The earth and rockfill embankment consisting of an upstream impervious fill, clay blanket, sheet pile cutoff, and multiline grout curtain, is founded on sands and gravels infilling a deep river channel. The dam impounds Bridge River flow to form the Carpenter Lake reservoir, from which water is drawn through two tunnels to Bridge River generating stations 1 and 2, located at Shalalth, B.C., on Seton Lake. Terzaghi Dam discharge facilities are composed of a surface spillway consisting of a 345 ft long free overflow section; and a gated section with two 25 ft wide by 35 ft high gates. Two rectangular low level outlets (LLO), each

10 210.1R-10 ACI COMMITTEE REPORT Fig. 2.7-Terzaghi Dam. Downstream detail of constrictor ring 8 ft wide by 16 ft high are subject to a maximum heat of 169 ft. These outlets were constructed in the top half of the concrete plug in the 32 ft, horseshoe-shaped diversion tunnel. The LLOs were operated in 1963 for about 23 days to draw down Carpenter Lake to permit low-level embankment repairs. Severe cavitation erosion of the concrete wall and ceiling surfaces downstream of bulkhead gate slots was observed in the north LLO after the water release. Dam safety investigations in 1985 identified that the LLOs were required to permit emergency drawdown of Carpenter Lake for dam inspection and repair, and to provide additional discharge capacity during large floods. The repair consisted of three main categories of work - repair of damage, improvement to reduce cavitation potential, and refurbishing gates and equipment. Repair of cavitation damage in the north LLO included repair of the walls, crown, and gate slots. Improvements to reduce cavitation potential included 1) installing 9-in. deep rectangular constrictor frames (Fig. 2.7) immediately downstream of the operating gates to increase pressures in the previously cavitated area, 2) backfilling old bulkhead gate slots and streamlining the existing LLO invert entrances, and 3) installing piezometers in the north LLO to provide information on flow characteristics of the streamlined LLO during discharge testing. Refurbishing gates and equipment included 1) replacing leaking gate seals on closure gates; 2) sandblasting and repainting gates, guides, head covers, and air shafts, 3) cleaning gate lifting rods and replacing bonnet packings; 4) replacing ballast concrete in north LLO gates and installing ballast cover plates on all gates; and 5) refurbishing hydraulic lifting mechanisms of gates. Repair concrete was designed to fully bond with existing concrete. Surface preparation included; saw cutting around the perimeter of the damage, chipping to expose rebar, and installation of grouted dowels. Latexmodified concrete was used for all repair work, with steel fiber reinforcement for the cavitation-damaged areas. A total of 26 cubic yards of 3000 psi ready-mixed concrete was placed by pumping. Maximum aggregate sizes of 3 /8-in. and 3 /4-in. were used for general repair and invert entrance backfill, respectively. The constrictor frames were made from 1 /2-in. and 3 /4-in. steel plate. They were installed in the LLOs by means of the following: 1) bolting the constrictor frame to the existing concrete with a double row of l-in. diameter adhesive anchors at 12-in. spacing 2) keying the constrictor infill concrete into the existing concrete; 3) welding the constrictor frame to the existing gate metalwork in the walls and soffit; and 4) embedding the constrictor sill shear bar into the existing concrete invert (Fig. 2.7). A test with a full reservoir and a peak discharge of 7000 ft 3 /S, with both gates opened 7 ft, verified that the constrictor frames and concrete repairs, downstream of the closure gates, performed as designed No cavitation erosion of the wall and ceiling surfaces was observed. DISCUSSION Piezometer readings confirmed that the constrictor frames in the LLOs helped maintain pressures above atmospheric, indicating that cavitation should not be a problem in the future. B.C. Hydro, Terzaghi Dam, Low Level Outlet Repairs-Memorandum on Construction, Report No. EP6, Vancouver, B.C., Dec B.C. Hydro, Terzaghi Dam, Low Level Outlet Tests, Report No. H1902, Vancouver, B.C., Mar

11 REPAIR OF EROSION DAMAGED HYDRAULIC STRUCTURES 210.1R-11 CONTACT/OWNER British Columbia Hydro Hydrotechnical Department, HED 6911 Southpoint Drive Burnaby, British Columbia, Canada V3N 4X8 YELLOWTAIL AFTERBAY DAM Bighorn River, Montana Yellowtail Afterbay Dam, operational in 1966, is a 33-ft-high concrete gravity diversion type structure, 300 ft long, located about 1 mile downstream from Yellowtail Dam. In 1967 following a heavy winter/spring snowpack in the upstream drainage basin, flood flows passed through both Yellowtail Dam and the Afterbay Dam. Divers examined the Afterbay Dam sluiceway and stilling basin after the flood flows had passed. They found cavitation damage on the dentates (baffle blocks) and adjacent floor and wall areas in the spillway stilling basin. Although the cavitation damage was moderate, repairs were necessary to lessen the likelihood that future cavitation damage would occur. Damage to the dentates and floor in the sluiceway was caused by abrasion. The relatively low sill at the downstream end of the sluiceway was permitting downstream gravel and sand to be drawn into the stilling area, where a ball mill-type action ground away the concrete surfaces. In the stilling basin downstream of the reverse ogee section, cavitation severely eroded the sides of the dentates and the adjacent floor areas. A similar condition developed in the sluiceway except that it was caused by abrasion erosion. Since the damage from the two causes occurred essentially side by side, the situation graphically illustrated the dissimilar types of erosion resulting from cavitation and abrasion. Following the flood, low flows at the dam could be maintained for only one month. That situation required that all repairs be completed quickly and concurrently. In addition to repairing damaged areas, the downstream sill in the sluiceway was raised about 3 ft to stop river gravels from being drawn into the sluiceway. Repairs were completed using a combination of bonded concrete, epoxy-bonded concrete and epoxy-bonded epoxy mortar, depending upon thickness of the repair. Epoxy used in this repair was a polysulfide-type material. After repaired materials had been placed and cured, they were ground to provide a smooth, cavitation-resistant surface. The dam has now been in service about 23 years since the repairs were made. With the exception of a minor number of spalls, the performance of the repairs has been excellent. Graham, J.R., Spillway Stilling Basin Repair Using Bonded Concrete and Epoxy Mortar, Proceedings, Irrigation and Drainage Specialty Conference, Lincoln, NE, Oct. 1971, pp Graham, J.R., and Rutenbeck, T.E., Repair of Cavitation Damaged Concrete, a Discussion of Bureau of Reclamation Techniques and Experiences, Proceedings, International Conference on Wear of Materials, St. Louis, MO, April 1977, pp CONTACT Bureau of Reclamation P.O. Box 25007, Denver Federal Center Denver, CO YELLOWTAIL DAM Bighorn River, Montana The dam, operational in 1966, is a concrete arch structure 525 ft high with a crest length of 1480 ft. Normal flow through the dam occurs in two 84-in. outlet pipes and through the turbines of the powerhouse. Flows exceeding the capacity of these facilities are routed through a high-head spillway located in the left abutment. At this spillway, water enters through a radial-gated intake structure, then passes into an inclined section of tunnel varying in diameter from 40.5 ft at the upper end to 32 ft at the beginning of the vertical elbow. Thereafter, flow follows the 32-ft-diameter tunnel through the elbow and 1200 ft of near horizontal tunnel, exiting into a combination stilling basin-flip bucket, then into the river. During the spring of 1967, heavy rains in the watershed area of the Bighorn River resulted in high inflows into Bighorn Lake behind Yellowtail Dam. A total of 650,000 acre-ft of flood waters was released through the spillway over a period of 30 days. Maximum flow was 18,000 ft 3 /S. During the 1967 spill, severe damage occurred to the concrete tunnel lining and underlying rock in the elbow, as well as upstream and downstream. After the flows into the river had subsided sufficiently for a temporary shutdown of the tunnel, divers made an examination. Major damage was found in the near-horizontal section of the tunnel lining and in the elbow. Failure occurred along the tunnel invert in a leapfrog fashion, typical of cavitation damage. The largest cavity was about 100 ft long, 20 ft wide and 6 to 8 ft deep. After the tunnel was dewatered, it was found that a small concrete patch placed during construction had failed. therebv causing the dis-

12 210.1R-12 ACI COMMlTTEE REPORT continuity in the flow that triggered the cavitation. The tunnel liner was repaired using several systems depending on the size and depth of the damage. Areas where the damage extended through the lining into the foundation rock were repaired with high quality replacement concrete. Major areas of damage where the erosion did not penetrate through the concrete lining were repaired with bonded concrete. Shallow-damaged concrete was repaired with epoxy-bonded concrete and epoxy-bonded epoxy mortar. Surfaces were ground where necessary to bring tolerances into conformance with specifications requirements. Finally, tunnel surfaces below spring line were painted with an epoxy-phenolic paint, to help seal the surface and bond any aggregate particles that may have been loosened In order to avoid recurring damage, an aeration device was model tested in the laboratory and then constructed in the tunnel a few ft upstream of the point of curvature of the vertical elbow. This aeration slot measured 3 ft wide and 3 ft deep and extended around the lower three quarters of the tunnel circumference. It was designed to entrain air in the flow for all discharges up to 92,000 ft 3 /S, without the slot filling with water. A 27-in-long ramp was constructed upstream of the slot which raised the upstream face of the slot 3 in. at the tunnel invert. Under most flow conditions the bottom of the jet was forced away from the tunnel floor surface. The jet remained free for a considerable distance downstream, all the while drawing air into the jet from the aeration slot. Aeration has reduced the discharge capacity by approximately 20 percent. It has now been 23 years since the tunnel was repaired and the aeration slot installed, but flows in the river have never been sufficient to require use of the spillway. However, a controlled prototype test with flows to 16,000 ft 3 /s was conducted in 1969 and As a result of this test, less than one percent of the concrete repairs failed and no cavitation damage was observed, even in areas downstream from discontinuities. To ensure that the tunnel will always be ready for the next flow, there is a regular maintenance program to repair ice damage and remove calcium carbonate buildups. Borden, R.C., et al., Documentation of Operation, Damage, Repair, and Testing of Yellowtail Dam Spillway, Report No. REC-ERC-71-23, Bureau of Reclamation, Denver, CO, May Colgate, D., and Legas, J., Aeration Mitigates Cavitation in Spillway Tunnel, Meeting Preprint 1635, National Water Resources Engineering Meeting, Jan , 1972, Atlanta, GA, American Society of Civil Engineers, New York, NY, 29 pp. CONTACT U.S. Bureau of Reclamation Denver Office, Code D-3700 P.O. Box 25007, Denver Federal Center Denver, CO KEENLEYSIDE DAM Columbia River, near Castlegar, B.C., Canada The dam, operational in 1968, consists of an earthfill embankment 1400 ft long and about 171 ft high and a concrete gravity section about 1180 ft long and 190 ft high. The concrete section contains four 55 ft wide sluiceways, eight 20 by 24 ft high low level ports, and a navigation lock. The sluiceway downstream of the gate slot has an ogee section designed very conservatively for 65 percent of the design head. Upstream of the gate sill the profile is a fairly broad three-radius compound curve. Accordingly, no negative pressures should occur anywhere on the crest under free discharge operation. Cavitation damage has occurred on the sluiceway crest near the gate slots on all four bays. The damage extended from inside the upstream portion of the gate slot to a point about 4 ft downstream, extending at an angle of about 30 degrees to the direction of flow (Fig. 2.8). All attempts to repair the eroded concrete with epoxy mixtures and steel fiber-reinforced concrete (FRC) in 1973, 1975, and 1977 were unsuccessful. Continued cavitation soon pitted the repaired areas which later progressed to development of major voids. By 1980 approximately 80 percent of the previous repair had eroded. During a high water inspection in 1986, sluiceway No. 2 was flow tested for 4 hr at gate openings of 4, 8, 12 and 16 ft and full opening. Characteristic noises of cavitation bubble collapse could be heard intermittently at all gate settings. The highest rate of cavitation activity was observed to be with gate openings from 4 to 12 ft. The deepest erosion usually occurred just outside the gate slot with depths ranging from about 8 to 14 in. Downstream of the badly eroded area, the concrete at the invert was observed to be roughened for another 2 ft. The maximum width of the eroded area varied from 18 to 24 in. The cavitation erosion at the foot of the gate slot damaged not only the concrete invert but also the lower part of the steel liner within the gate slot and an area of the wall immediately downstream of the liner. The 1986 study concluded that the severe concrete erosion at and just downstream of the gate slots was due to 1) cavitation caused by vortices originating in the upstream corners of the gate slots at small, part-gate operation; and 2) lack of rounding and lack of offset of downstream edge of gate slot.

13 REPAIR OF EROSION DAMAGED HYDRAULIC STRUCTURES 210.1R-13 Initially, it was recommended that 1) eroded areas should be filled with concrete and armored with steel plates, and; 2) field tests should be conducted to identify cavitation zones. Later, the recommendation was changed to backfill cavitated areas with aggregate, high strength (6000 psi) concrete. The bond between the backfill and the original sluiceway concretes was enhanced by epoxy bonding agent. The top surface of the new patch and the surrounding original concrete were coated with an acrylic latex selected through an extensive laboratory screening process.the work was carried out in the summer of In order to test the effectiveness of the repairs, during the following year it was decided to operate the sluice gates mostly in the worst range. A year later, the repaired and coated surfaces began to show signs of pitting. The performance of the repair still did not appear satisfactory. It became obvious that besides repairing the eroded areas other initiatives were needed to alleviate recurrence of the problem. DISCUSSION Based on the observations of the effect of gate opening on cavitation, it was decided to limit gate operation to that outside of the destructive range. Gate operating orders were rewritten to require passing over the rough zones as quickly as possible without any sustained operation in those zones. B.C. Hydro, Hydroelectric Engineering Division, Hugh Keenleyside Dam, Cavitation Damage on Spillway, Report No. H1922, Vancouver, B.C., Mar B.C. Hydro, Hydroelectric Engineering Division, Keenleyside Dam, Comprehensive Inspection and Review 1986, Report No. H1894, Vancouver, B.C., May B.C. Hydro, Hydroelectric Engineering Division, Hugh Keenleyside Dam, Cavitation Damage on Spillway, Field Investigation of Cavitation Noise and Proposed Gate Operating Schedules, Report No. 2305, Vancouver, B.C., June CONTACT/OWNER British Columbia Hydro Structural Department HED6911 Southpoint Drive Bumaby, British Columbia, Canada V3N4X8 CHAPTER 3-ABRASION-EROSION CASE HISTORIES ESPINOSA IRRIGATION DIVERSION DAM EspBnola, New Mexico, on the Santa Cruz River Fig. 2.8-Keenleyside Dam. Cavitation erosion of concrete invert and adjacent damage to steel liner. Maximum depth approximately 9 in. The diversion dam is a reinforced concrete structure that is capable of diverting up to 13 f& in the Espinosa Ditch for irrigation purposes. A 50-ft-long reinforced rectangular concrete channel, sediment trap, and sluice gate structures were constructed between the headgate and the ditch heading. A sidewall weir notch is provided in the rectangular ditch lining to allow emergency discharge of flood flows back to the river. A 24-in.-round sluice gate at the right side of the dam was placed at the slab invert elevation, to sluice sand and cobbles through the dam and to prevent these materials from entering the irrigation ditch head gate. The dam is tied back into the riverbanks on either side with small earthen dikes that protect the surrounding land against flood flows of 1000 ft3/s or less. Debris plugged the sluice gate, preventing the diversion of the bedload from the irrigation ditch. The structure experienced severe erosion damage to the apron and

14 ACI COMMITTEE REPORT Fig. 3.1-Espinosa Irrigation Diversion Dam. Erosion damage to the floor blocks Fig. 3.2-Espinosa Irrigation Diversion Dam. Steel plate protection added to floor blocks and endsill floor blocks (Fig. 3.1) due to impact and abrasion by the bedload. The bedload consists of gravels and boulders ranging up to 24 in. in diameter. The concrete in the apron in the impact area was abraded to a depth of 6 in. Except for very low flows and flows diverted for irrigation, the bedload is carried over the weir. Repairs were made by extensive structural modifications. These modifications included the following (Fig. 3.2): 1) removing and replacing the top layer of reinforcement in the apron; 2) removing and replacing the top 6 in. of concrete; 3) protecting the apron with a?&n.

15 REPAIR OF EROSION DAMAGED HYDRAULIC STRUCTURES 210.1R-15 steel plate; and 4) replacing the 24-in-round sluice gate with a 36-in. square sluice gate. The structure has been operating satisfactorily since rehabilitation in DISCUSSION Five alternatives were evaluated for the placement of the diversion dam back into service. The ones not selected as the solution are as follows: 1. Install a reinforced concrete lining inside the walls and apron of the existing structure. 2. Protect the apron with a 1 /2-in. steel plate. 3. Remove the entire apron of the structure and replace it with one that is adequately reinforced. Add the liner inside the structure. 4. Remove the entire structure and replace it with a new one. U.S. Department of Agriculture, Espinosa Diversion Dam, Report of Investigation of Structural Failure, Soil Conservation Service, Albuquerque, NM, Nov U.S. Department of Agriculture, Espinosa Diversion Dam, Design Engineer s Report," USDA, Soil Conservation Service, Albuquerque, NM, Sept CONTACT/OWNER State Conservation Engineer U.S. Department of Agriculture Soil Conservation Service 517 Gold Avenue, SW, Room 3301 Albuquerque, NM Because of the proximity of a pumped-storage powerplant on the left abutment and problems from spray, especially during the winter months, the right side sluices were used most of the time. Use of these sluices caused eddy currents that carried debris into the stilling basin. The end sill was below streambed level and contributed to the deposition of debris in the basin. Divers reported erosion damage to the basin floor as early as Also, piles of rock, gravel, and other debris in the basin were reported. About 50 cubic yards of gravel and rock, ranging up to 8 in. in diameter, were removed from the basin in erosion damage reached a depth of 3.5 ft in some areas before initial repairs were made in 1973 and These repairs were made with steel fiber-reinforced concrete. Approximately 1400 cubic yards of fiber concrete was required to overlay the basin floor. From the toe of the dam to a point near the baffles, the overlay was placed to an elevation 1 ft higher than the original floor. In April 1975, divers reported several areas of abrasion-erosion damage in the fiber concrete. Maximum depths ranged from 5 to 17 in. Approximately 45 cubic yards of debris were removed from the stilling basin. Additional erosion was reported in May 1975, and another 60 cubic yards of debris were removed from the basin. At this point, symmetrical operation of the lower sluices was initiated to minimize eddy currents downstream of the dam. After this change, the amount of debris removed each year from the basin was drastically reduced and the rate of abrasion declined. However, nearly 10 years after the repair, the erosion damage had progressed to the same degree that existed prior to the repair. KINZUA DAM Allegheny River, Warren County, Pennsylvania Kinzua Dam became operational in The stilling basin consists of a horizontal apron, 160 ft long and 204 ft wide. It contains nine 7-ft-high by l0-ft-wide baffles, located 56 ft upstream from the end sill. The verticalfaced end sill is 10 ft high and 6 ft wide. The basin slab was constructed of concrete with a 28-day compressive strength of 3000 psi. The outlet works consists of two high-level and six low-level sluices. A maximum conservation flow of about 3600 ft3/s is supplied by the high-level sluices. The lowlevel sluices with flared exists containing tetrahedral deflectors are located 26 ft above the stilling basin slab. Bank-full capacity, 25,000 ft3/s, can be discharged through these sluices at reservoir elevation The maximum 24,800-ft3/s record discharge was discharged through the sluices in The maximum velocity at the sluice exit was 88 ft/s. A materials investigation was initiated prior to the second repair, to evaluate the abrasion-erosion resistance of potential repair materials. Test results indicated that the erosion resistance of conventional concrete containing a locally available limestone aggregate was not acceptable (Fig. 3.3). However, concrete containing this same aggregate with the addition of silica fume and a highrange, water-reducing admixture exhibited high compressive strengths (approximately 14,000 psi at 28 days age) and very good resistance to abrasion erosion. Therefore, approximately 2000 cubic yards of silica-fume concrete were used in a 12-in. minimum thickness overlay when the stilling basin was repaired in 1983 (Fig. 3.4). Construction of a debris trap immediately downstream of the stilling basin end sill was also included in the repair contract. Hydraulic model studies showed that such a trap would be beneficial in preventing downstream debris from entering the stilling basin. The trap was 25 ft long with a 10-ft-high end sill that spanned the entire width of the basin.

16 210.1R-16 ACI COMMlTTEE REPORT I I I I 0A -STEEL FIBER REINFORCED CONCRETE REMOVED FROM THE KINZUA DAM STILL- ING BASIN B -CONVENTIONAL CONCRETE, PENN- SYLVANIA LIMESTONE AGGREGATE, 5710 PSI (39 MPa) 0C -CONVENTIONAL CONCRETE, LOS AN- GELES AGGREGATE, 7470 PSI (52 MPa). 0D -SILICA-FUME CONCRETE, LOS AN- GELES AGGREGATE, 11,500 PSI (79 MPa) 0E -SILICA-FUME CONCRETE, PENNSYL- VANIA LIMESTONE AGGREGATE, 13,850 PSI (95 MPa) 2.0 I I - OL TEST TIME, HR Fig 3.3-Kinzua Dam. -erosion performance of 5 materials tested using the underwater abrasion-erosion test method In August 1984, after periods of discharge through the upper and lower sluices, abrasion-erosion along some cracks and joints was reported by divers. The maximum depth of erosion was about % in. The divers also discovered two pieces of steel plating that had been embedded in the concrete around the intake of one of the lower sluices. Because of concern about further damage to the intake, the use of this sluice in discharging flows was discontinued. This nonsymmetrical operation of the structure resulted in the development of eddy currents. The next inspection, in late August 1984, found approximately 100 cubic yards of debris in the basin. In September 1984, a total of about 500 cubic yards of debris was removed from the basin, the debris trap, and the area immediately downstream of the trap. The rock debris in the basin ranged from sand sized particles to over 12 in. in diameter. Despite these adverse conditions, the silica-fume concrete continued to exhibit excellent resistance to abrasion. Erosion along some joints appeared to be wider but remained approximately 1 /2-in. deep. Sluice repairs were completed in late 1984, and symmetrical operation of the structure was resumed A diver inspection in May 1985 indicated that the condition of the stilling basin was essentially unchanged from the preceding inspection. A diver inspection approximately 3 1 /2 yr after the repair indicated that the maximum depth of erosion, located along joints and cracks, was about 1 in. Fenwick, W.B., Kinzua Dam, Allegheny River, Pennsylvania and New York; Hydraulic Model Investigation, Technical Report HL-89-17, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS, Aug Holland, T.C., -Erosion Evaluation of Concrete Mixtures for Stilling Basin Repairs, Kinzua Dam, Pennsylvania, Miscellaneous Paper SL-83-16, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS, Sept Holland, T.C., -Erosion Evaluation of Concrete Mixtures for Stilling Basin Repairs, Kinzua Dam,

17 REPAIR OF EROSION DAMAGED HYDRAULIC STRUCTURES 210.1R-17 Fig. 3.4-Kinzua Dam. Typical silica-fume concrete placement operation for a stilling basin slab Pennsylvania," Miscellaneous Paper SL-86-14, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS, Sept Holland, T.C.; Krysa, A; Luther, M.D.; and Liu, T.C., Use of Silica-Fume Concrete to Repair -Erosion Damage in the Kinzua Dam Stilling Basin, Fly Ash, Silica Fume, SIag, and Natural Pozzolans in Concrete, SP-91, V. 2, American Concrete Institute, Detroit, MI, 1986, pp McDonald, J.E., Maintenance and Preservation of Concrete Structures, Report 2, Repair of Erosion- Damaged Structures, Technical Report No. G78-4, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS, April CONTACT/OWNER U.S. Army Engineer District Pittsburgh William S. Moorhead Federal Building 1000 Liberty Avenue Pittsburgh, PA LOS ANGELES RIVER CHANNEL Los Angeles River, California The Los Angeles River Channel is an improved structural channel that drains a watershed of 753 square miles. The majority of the channel was constructed in the 1940s. In the invert of the concrete-lined main channel is a reinforced concrete low-flow channel, This low-flow channel is approximately 12 miles long and was originally constructed with an invert thickness of 12 in. Water velocities in that channel range from 20 to 30 ft/s. Over the years abrasion erosion has occurred to varying degrees along the low-flow channel, In some reaches, erosion had progressed completely through the concrete by the early 1980s. This erosion was the result of a combination of abrasion by waterborne sediment and debris passing over the concrete, and chemical attack. Prior to repair, laboratory studies were conducted to evaluate the abrasion-erosion resistance of concretes containing locally available aggregates. Typically, these aggregates exhibit a relatively high abrasion loss tested according to ASTM C 131, using the Los Angeles machine. Results of the laboratory tests indicated that concrete with a high cement content, a silica fume content of 15 percent by mass of portland cement, and a low water-cement ratio would provide excellent abrasionerosion resistance, even when produced with aggregates that might be marginal in durability. Beginning in 1983, the existing concrete in the approximately Yknile reach of most severe damage was removed and replaced with reinforced, silica-fume concrete (Fig. 35). The thickness of the replacement concrete was

18 210.1R-18 ACI COMMITTEE REPORT Fig. 3.5-Los Angeles River Channel. Concrete for a full depth replacement was placed with a conveyor and finished with a specially shaped vibratory screed 12 in. Subsequent rehabilitation of the remaining channel during 1984 and 1985 was accomplished by either fulldepth slab replacement or an overlay on the existing concrete. Full-depth repairs consisted of a new, reinforced base slab of conventional concrete and 6-in. overlay of silica-fume concrete. Overlays on the existing concrete were 4- to 6-in-thick sections of silica-fume concrete. Various mixture proportions were used with compressive strengths ranging from 8000 to 10,500 psi. Approximately 27,500 cubic yards of silica-fume concrete were required to complete the rehabilitation. The unit costs for the silica-fume concrete decreased with time as bidders became more familiar with the material. The unit cost for the 1985 project was $154/cubic yard, which was slightly less than twice the unit cost of conventional concrete. Scour gauges were installed to monitor long-term wear of the silica-fume concrete. Because of the nature of the mechanism causing abrasion-erosion, an evaluation of performance will require an extended period of time. However, the abrasion resistance of the silica-fume concrete, according to the laboratory tests, should be two to four times better than the conventional concrete previously used Visual inspections of the channel surfaces indicate little or no erosion of the concrete has occurred in the 8 years following repair. Holland, T.C., -Erosion Evaluation of Concrete Mixtures for Repair of Low-Flow Channel, Los Angeles River, Miscellaneous Paper SL-86-12, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS, Sept Holland, T.C., and Gutschow, R.A., Erosion Resistance with Silica-Fume Concrete, Concrete International, V. 9, No. 3, Detroit, MI, March 1987, pp CONTACT/OWNER U.S. Army Engineer District, Los Angeles 300 North Los Angeles Street Los Angeles, CA NOLIN LAKE DAM Nolin River, Edmonson County, Kentucky Nolin Lake Dam became operational in The stilling basin is 40 ft wide, 174 ft long with a 7-ft-high end sill and 35-ft-high sidewalls. The basin contains a parabolic section with an 8.4-ft drop in elevation from the outlet tunnel invert to the horizontal floor slab. The design discharge is 12,000 ft3/s with an average velocity of 61 ft/s entering the basin. The structure was built of reinforced concrete with a design compressive strength of 3000 psi. The conduit and stilling basin at Nolin were dewatered for inspection in 1974, following approximately 11 years of operation. Erosion was reported in the lower portion of the parabolic section, the stilling basin floor, the lower

19 REPAIR OF EROSION DAMAGED HYDRAULIC STRUCTURES 210.1R-19 part of the baffles, and along the top of the end sill. The most severe erosion was in the area between the wall baffles and the end sill, where holes 2 to 3 ft deep had been eroded into the stilling basin floor along the sidewalls. The stilling basin was dewatered and repaired in Conventional concrete designed for 5000 psi compressive strength was used to restore the basin slab to an elevation 9 in. above the original grade. A hydraulic model study of the existing basin was not conducted, but the structure was modified in an attempt to reduce the amount of debris entering the basin. New work included raising the end sill 12 in., adding end walls at the end of the stilling basin, and paving a 50-ft-long channel section. A diver inspection in 1976 indicated approximately 4 tons of rock was in the stilling basin. The rock, piled up to 15 in. deep, ranged up to 12 in. in diameter. Also, l8-in.-deep rock piles were found on the slab downstream from the stilling basin. Erosion, up to 8 in. deep, was reported for concrete surfaces that were sufficiently clear of debris to be inspected. In August 1977, approximately 1 to 1 1 /2 tons of large, limestone rock all with angular edges, was reported in the stilling basin. No small or rounded rock was found. Since the basin had been cleaned during the previous inspection, this rock was thought to have been thrown into the basin by visitors. When the stilling basin was dewatered for inspection in October 1977, no rock or debris was found inside the basin. Apparently, the large amount of rock discovered in the August inspection had been flushed from the basin during the lake drawdown, when the discharge reached a maximum of 7340 ft3/s. Significant erosion damage was reported when the stilling basin was dewatered for inspection in The most severe erosion was located behind the wall baffles, similar to that prior to repair in Each scour hole contained well-rounded debris ranging from marble size to approximately 12-in. diameter. Temporary repairs included removal of debris from the scour holes and filling them with conventional concrete. Also, the half baffles attached to each wall of the stilling basin were removed. A hydraulic model of the stilling basin was constructed to investigate potential modifications to the basin to minimize chances of debris entering the basin and causing subsequent erosion damage to the concrete. Results of this study were incorporated into a permanent repair in Modifications included rebuilding the parabolic section in the shape of a whale s back, overlaying the basin floor, adding a sloping face to the end sill, raising the basin walls 2 ft, paving an additional 100 ft of the retreat channel, slush grouting all derrick stone in the retreat channel, and adding new slush-grouted riprap beside the basin. The condition of the concrete was described as good with no significant defects when the basin was dewatered for inspection in August The maximum discharge to that point had been 5050 ft3/s for a period of 13 days. McDonald, J.E., Maintenance and Preservation of Concrete Structures, Report 2, Repair of Erosion- Damaged Structures, Technical Report No. C-784, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS, April McDonald, J.E., and Liu, T.C., Repair of - Erosion Damage to Stilling Basins, Concrete International, V. 9, No. 3, American Concrete Institute, Detroit, MI, March 1987, pp CONTACT/OWNER U.S. Army Engineer District, Louisville P.O. Box 59 Louisville, KY PINE RIVER WATERSHED, STRUCTURE NO. 41 La Plata and Archuleta Counties, Colorado Structure No. 41 is a high velocity reinforced concrete chute spillway with a St. Anthony Falls (SAF) stilling basin. The SAF stilling basin is a design developed by the Agricultural Research Service at the St. Anthony Falls Hydraulic Laboratory of the University of Minnesota. The design includes chute and floor blocks with an end sill sized by hydraulic modeling for maximum energy dissipation. The floor of the basin in Structure No. 41 is depressed about 4.6 ft below the downstream channel grade. The design wall thickness is 8 in. and the design floor thickness is 9 in. The reinforcement is a single mat of steel centered in the floor and walls. From 1974 to 1984 the structure had displayed significant erosion of the concrete. The most severe erosion had occurred at the lower end of the SAF stilling basin. The stilling blocks, end sill, and reinforcement was completely deteriorated. The reinforcing steel was exposed in the floor, sidewalls (Fig. 3.6), and wingwalls from immediately upstream of the end sill downstream through the structure. The exposed reinforcement showed considerable wear. Erosion in the floor of the chute was limited to about % in. This erosion appeared constant throughout the length of the chute. During a 1984 investigation, it was concluded that the damage exhibited the characteristics of erosion and abrasion damage by the ball mill effect, as described on pages 14 and 15 of Chapter 1 of the Bureau of Reclamation Concrete Manual. The major damage to the structure is attributed to gravel and larger sized material being introduced into the stilling basin from the outlet channel

20 210.1 R-20 ACI COMMITTEE REPORT Fig. 3.6-Pine River Watershed, Structure No. 41. Erosion of sidewall, exposing reinforcing steel slope protection rock. The SAF outlet channel was designed and constructed with a 3 to 1 adverse grade from the top of the end sill to the canal invert elevation, approximately 4 ft above the end sill. It has a bottom width of 10 ft with 2 to 1 side slopes. The entire section is lined with loose rock riprap. The rock is rounded to subrounded and is easily dislodged. Much of the rock on the adverse slope appears to have been displaced and the slope eroded, so that it is considerably steeper than originally constructed. Hydraulic transport of the smaller rock into the basin appears to be the method of debris introduction. The investigating team made the following recommendations: 1. Study the hydraulics of the outlet and design an outlet basin to fit most favorably with those predicted by model studies. Minimize use of rock riprap but, if needed, grout to prevent movement. 2. Replace concrete end sill, floor blocks, and chute blocks using high-strength concrete. The effect on hydraulic performance will need to be studied. A model study was conducted in 1984 to determine the design for a preshaped, riprapped energy dissipation pool. The design was recommended for the repair and rehabilitation of the structure and was also considered appropriate information for use in the design of similar pools. No permanent work has been completed on the repair of the structure to date. Options for repair are being considered at this time. Bureau of Reclamation, Concrete Manual, 8th Edition, U.S. Department of the Interior, Rice, C.E., and Blaisdell, F.W., Energy Dissipation Pool for a SAF Stilling Basin, Applied Engineering in Agriculture, V. 3, No. 1, USDA-ARS, Stillwater, Oklahoma, 1987, pp CONTACT/OWNER State Conservation Engineer U.S. Department of Agriculture, Soil Conservation Service Sixth Avenue Central, 655 Parfet Street, Room E200C Lakewood, CO POMONA DAM Hundred Ten Mile Creek, Vassar, KS The stilling basin at Pomona Dam, operational in 1963, is 35 ft wide and 80 ft long. The reinforced concrete transition and horizontal basin floor have a design discharge velocity of 58 ft/s. Two staggered rows of baffles, 3 ft wide and 5 ft high, are spaced at 7 ft on centers. A two-step, vertical-faced end sill is 4 ft high. Fill concrete was placed the width of the basin for a distance of 20 ft downstream from the end sill. The initial dewatering of the basin in February 1968 revealed erosion damage at the downstream end of the transition slab and on the upstream one-third of the basin slab. This erosion, caused by the abrasive action of