Project Tag: Engineering & Technology

Priest Rapids Dam Spillway Apron and End Sill Underwater Concrete Repair

Unanticipated spill events caused severe erosion to areas of the ogee,stilling basin floor and the end sill at Priest Rapids Dam on the Columbia River. The erosion of the area ranged from 3 inches to more than 3 feet. It affected areas of the ogee,approximately 5 feet below the water line to the stilling basin floor,areas of the floor itself,the leading edge of the end sill,as well as areas along the top and large areas of the vertical face of the end sill. In total,approximately 3,600 square feet of areas was repaired.

Repair areas were delineated by saw cutting and removal of existing material to a minimum of 6 inches of depth throughout the repair area. The entire areas were then pressure washed to remove algae and accumulation. Holes were drilled with rebar dowels set into epoxy,to which rebar mat was affixed. Holes up to 3 feet deep were drilled to anchor rebar along the bottom of the downstream edge of the sill wall. In all,more than 400 holes were drilled to anchor rebar dowels.

Concrete removal was done with a combination of saw cutting (more than 2,000 feet of saw cut was made) and chipping with pneumatic chipping tools. Approximately 12 cubic yards of concrete was removed.

Reusable forms were utilized throughout the project. The rear wall on the end sill was formed to 10 feet high and more than 50 feet in length. Custom-built fill and vent ports had to be fabricated and worked onto modular panels to facilitate underwater concrete pumping.

Specific concrete formulations to allow for underwater installation were developed and tested. All tests yielded a higher performing product than specified. Locations of repair areas required the pumping of concrete over 650 feet. A pump truck was positioned at the end of the power deck. For the farthest pour,over 500 feet of pipe was supported on floats across the stilling basin. Over 300 cubic yards of concrete was placed without a single plug in the pump line.

Canyon Dam Outlet Tower Stem Replacement

Pacific Gas and Electric contracted us for this stem replacement project. We replaced approximately 80 lineal feet of stem,including stem guides and roller assemblies. The existing stem was attached to the vertical slide gate with rivets that were drilled out,enabling re-utilization of the holes to exacting tolerances.

Canyon Dam Outlet Tower in Lake Almanor,CA stands in approximately 85 feet of fresh water at 4,500 feet of elevation. To perform the project,we mobilized a portable barge system,a surface-supplied dive spread with decompression chambers,and a 20-ton hydraulic crane to the lake. The crane was driven onto the barge to assist with removal and replacement of large stem sections.

To remove the existing stem,divers utilized a hydraulic-driven magnetic drill press. The project was performed safely,efficiently,and within budget. Upon completion of the stem replacement,the stem was tested and performed within tolerances.

Underwater Installation of Inlet Gate

Our work was performed in 285 feet of water and at an elevation of 7,300 feet using saturation diving techniques. Tasks included furnishing,installing and grouting in place 47 feet of concrete jacking pipe to form a structural liner in an existing inlet tunnel. An 18-ton stainless steel inlet gate was installed within very tight tolerances. Stainless steel hydraulic lines were fabricated and installed from the crest of the dam to the gate,which included anchoring pipe brackets along the steeply sloped and highly irregular reservoir floor. The existing trash racks were modified along with the installation of new trash rack components to facilitate the installation of the gate valve. Work was completed during a single 50-day saturation diving run.

An innovative system of winches and track allowed the large-diameter sections of steel reinforced pipe to be positioned into place with exact precision. Each pipe segment was advanced through the tunnel using a hydraulic jacking sled designed to mate with the bell end of the pipe segments. A steel jacketed thrust collar located at the downstream end of the liner resists thrust from the closed gate. The thrust collar was installed,grouted in place and then anchored to the existing substrate using rock anchors. Holes for the anchors were core drilled using a hydraulic drill mounted to a circular track system designed to be attached to the interior of the thrust collar,allowing a 360-degree drilling angle. Pre-job engineering enabled complex construction tasks to be performed at depths approaching 300 feet.

Richmond Beach Outfall Repair

We provided all project management,diving services and topside support for this location as part of an overall three-outfall repair project. Work done at Richmond Beach involved the moving of approximately 50 cubic yards of sediment that had accumulated around the existing diffuser flange. Once the flanges were exposed,the bolts were cut off using a Broco underwater cutting rod. The original steel diffusers were raised to the surface and new HDPE diffusers were installed.

The work was done in 150 feet of water,with divers using surface-supplied air.

Carkeek Outfall Repairs

We provided project management,diving and topside services as required to perform work on all three outfalls of this contract. The work on the Carkeek outfall was performed in approximately 200 feet of water. The work was carried out from a flat-deck barge that had been outfitted to perform deep-diving operations. The barge was moored on location with a four-point anchor system,allowing the barge to be positioned directly over the work at any point along the diffuser section alignment.

The project required the removal and replacement of all 11 of the existing steel diffusers. The four bolts per flange were burned off using a Broco underwater cutting rod. Once the existing diffusers were removed,we noticed that the interior of the pipe had filled approximately half-full with sediment. This material was removed with an air lift. The nozzle was inserted into the end diffuser,and once the surrounding materials were removed,the remaining sediment in the pipe was jetted to the air lift using a pressure washer to move the materials. When the pipe was clear of the sediment,the new diffusers were installed using stainless steel hardware,connecting the new diffuser flange to the existing outfall flange.

Due to the depth of the work,divers used a mixed gas,Heliox (86% helium,14% oxygen). This combination allowed the divers to stay on the bottom longer while also negating the effects of nitrogen at increased pressure. The divers entered and exited the water via a dive stage. The stage is used to control the diver descent and ascent and allow the dive supervisor to control the the diver’s decompression stops. Once the diver had fulfilled his in-water decompression commitment,they were raised to the surface and put into the deck decompression chamber to complete their decompression.

Hood Canal Bridge Replacement

We were contracted by Kiewit to provide diving and ROV services to route the 3-inch galvanized steel anchor wires through the new concrete anchor blocks that support the new east half of the bridge. The anchors are located in 60 to 380 feet of water. The new anchor wire was pulled through an anchor and connected to the bridge where the proper tension was achieved. Each leg of the two wires that attach to the anchor block has a tensile strength of over 1 million pounds. The anchors themselves weigh over 2 million pounds each. The project required the placement and connection of 20 anchors to secure the bridge in place.

Our divers connected the new anchor lines to the messenger lines that were in place and observed that the new wire,as it was pulled through,did not kink or get bound up. On the deeper anchors,the Cougar XT ROV was used. This vehicle,equipped with two five-function manipulators,was able to make the required connections and had enough power to stay on station during all but the heaviest currents.

The Dalles Bay 8/9 Spillwall

We were contracted by Kiewit to provide diving services to assist with the installation of a wall between Bays 8 and 9 of The Dalles Dam on the Columbia River. The wall is intended to redirect the salmonids that are migrating downstream and increase their survival rate.

The wall is 10 feet wide and over 800 feet long,the last 150 feet of which is at an angle to direct the water flow into a deeper portion of the river. It is constructed of precast concrete segments that were installed in the spillway and onto a leveling slab built on the river bottom. The segments were set in place and leveled using jacking rods. Once level and in place,the next segment was brought in and the process repeated. After several of them were in place,divers tied the segments together with rebar dowels. Forms were then installed on the joints between and around the bottoms. Concrete was then tremied into the segments. This process was repeated across the stilling basin.

Where the wall extends beyond the stilling basin,a 15-foot-wide leveling slab was installed. The river bottom was cleaned of loose debris. An area that ran across the path of the wall was excavated,because the underlying rock was fractured and non-competent. Form work was lowered from the surface and fit to the bottom contour. Rebar doweling was drilled and epoxied into the river bottom where needed. Rebar mats were installed inside the form work. Concrete was again tremied in place.

The wall has been carried over onto the leveling slab in the same manner as on the stilling basin.

New York Water Supply

Phase 1

We were contracted by Roundout Constructors to perform detailed inspection and measurements of an existing horizontal drift and submarine door,removal of existing plumbing components,remove and replace a 24-inch gate valve encased in concrete. The work was performed in an access shaft of the Delaware Aqueduct system,owned and operated by New York City’s Department of Environmental Protection. The drift and valve are located in approximately 685 feet of water,at the bottom of an 13-foot diameter shaft,north of New York City.

The purpose of the project was to inspect and verify the condition of the drift and submarine door,remove several pieces of plumbing and replace a valve to allow de-watering of the system.

Prior to start of the project on-site,all aspects of the project had to be performed in a full-scale mock-up,to demonstrate the methodology and constructibility of the tasks. Full-size mock-ups were designed and built addressing the salient points of the project. Highly specialized tooling had to be designed and work plans drawn up simply to get to the work location. All the tools,equipment and personnel had to come and go via an 13-foot diameter shaft. To complicate matters,the top of the shaft was enclosed by a concrete structure with doors on opposing sides,10-feet wide by 15-feet high,that limited access. We designed and built all of the mock-ups,specialized tooling and equipment in our Seattle office. The mock-up demonstrations were carried out at a local shipyard in shallow water. Access to the shaft and drift required the specialized design of components and rigging to move tooling into place. A track system was designed to allow for adjustment in both the X and Y axis,allowing for a consistent,repeatable point to be moved in and out of the drift. A fast-scanning sonar head was mounted to a purpose built cart,combined with some tactile measurements,we were able to achieve measurement of the 70 feet long drift to within +/- 1/8”. The track system and cart were also designed to accommodate the core drill base which allowed for sample cores to be taken at any radial location along the drift.

Sections of the existing 24-inch manganese bronze piping: elbow,tee and needle valve were removed. Piping was cut using a remotely operated rotary mill. Approximately 25,000 pounds of piping was removed. A 24-inch gate valve,encased in concrete to above the valve bonnet was completely exposed using a combination of hydraulic splitting and ultra high pressure water blasting to remove approximately 7 cubic yards of concrete. 1 ¾” holes were cored over 6-feet deep to accept the hydraulic splitters. A detailed plan of the hole spacing and splitting sequence was planned and performed on a mock-up of the valve and concrete encasement in our yard in Seattle to ensure that there would be no stress on the active valve during the concrete removal. This was critical,because the allowable work periods would not have let us return to the project until late fall of 2009. The valve was exposed and removed,and we then completed installation of the new hydraulically operated valve.

Working at 685 feet of water required the use of saturation diving. The complete system was moved into the building that housed the shaft. Every component had to be moved through a 10-foot wide door. This system was set up to accommodate 6 divers. The system is equipped with re-breathers,enabling the reuse of the helium component of the breathing gas mixtures.

Phase 2

In preparation for the upcoming bypass tunnel installation Global Diving & Salvage,Inc. was further contracted to install a mechanical plug to isolate the dewatering shaft from the Delaware Aqueduct in upstate New York. At the bottom of the shaft is a horizontal drift that was used for access during the original construction. The drift has a bronze hemispherical submarine door to isolate the aqueduct from the shaft. Depending on the demand,this door can see up to 1,100 feet of head pressure.

To install the pumps and plumbing required to support the bypass operation the shaft will need to be dewatered. To provide an added safety measure,saturation divers installed a mechanical plug approximately 50 feet into the drift.

The plug weights over 23,000 pounds,is five feet wide by seven feet tall and approximately four feet thick. It has a mechanical seal as well as two grout actuated seals to seal the perimeter. To withstand the over two million pounds of force the plug may see a series of struts were mechanically anchored into the drift walls around the perimeter of the bulkhead.

Highly specialized tooling and fixtures were developed for this project in order to assist the diver in the installation of the plug and its components. Divers were transported to and from the work site by an eight foot diameter diving bell. Given a shaft diameter of only thirteen feet,all materials and tools had to be lowered prior to the bell being launched and had to be retrieved after the bell was recovered.

A detailed rigging plan was developed to allow for the loads to be lowered in the center of the shaft then pulled over to the side wall to allow room for the bell. A track system was installed along the floor of the drift to allow the divers to move the equipment and materials to the plug location.

A remote operated hydraulic crane was also designed and fabricated by Global specifically for this project. The crane,operated from the surface,assisted the diver in handling and installing the various pieces of the plug,some of which weighted up to 500 pounds.