The third Hydro was Seymour. The site had five vertical double runnerFrancis units, they were replaced by five Horizontal Kaplan turbines, as the result the capacity was uprated from 3.15 MW to 5.7 MW.

The site is situated on the Trent River approximately 170 km north east of Toronto, Ontario, Canada. It’s one of 17 generation station built along the Trent-Severn Waterway between 1899 and the 1920s. The power house building is an imposing 3 story masonry structure typical
of the period architecture. The generating station consists of an intake structure integral with regulatory dam, a 300 m long power canal, a 5 unit powerhouse and a short tailrace channel to the Trent River. The preservation of the existing architecture of the powerhousesuperstructure and the need to maintain the general arraignment ofthe GS brought the principal engineering challenge of the project.

We got very big water seepage into the power house at Sidney and as the result had to use very expensive chemical grouting to fix it. The intermediate walls of the powerhouse at Seymour were also very badly cracked. I decided to remove all walls between turbine bays and to create a single turbine pit containing all five turbines. That concept allowed contractor to complete all demolition in the initial phase of the project and once demolition was completed contractor could work on all units without any restriction. As the result it was saving of two month on the schedule. The original substructure was designed as a rigid space frame consisting of intermediate concterete walls built monolithically with the intake and draft tube water passages , together with two concrete slab diaphragm one on the trust deck floor level and the other at generator floor level. In order to accommodate the new units up to 85% of the

existing substructure had to be removed. This included most of the intermediate walls and most of the intake and draft tube concrete, as well as much of both floors. Unfortunately this idea of removing all intermediate walls was very unusual and I had to work very hard to convince the management of the company that this idea will work. Fortunately for me we had a very
smart geotechnical Engineer on the project –Tim Orpwood, he was a maverick like me and under his supervision an extensive system of temporary supports and underpinning was developed. What also helped-I had drawings of Ogdensburg site where a very similar
transverse section of the power house was used for a new powerhouse. I was involved in the design as well as construction of Ogdensburg site upstate New York in 1987. In order to eliminate the possibility of failure, the demolition and rock excavation sequence was engineered together with specials shoring and electronic monitoring system. To preserve and minimize any possible damage to the superstructure masonry walls blasting was not allowed. Concrete was demolished by hoe ramming and saw cutting, including massive blocks of 10 m high by 6m wide and by 1.2 m thick that were removed in stages from each of the four intermediate walls and the end walls. The lateral stability of the powerhouse was restored by the installation of a new diaphragm system consisting of new reinforced crane girder beams running along the length of the powerhouse with steel trust beams connecting them at each intermediate wall location.

At the foundation level the upstream portion was secured to the sound rock by using a special system of rock dowels and the downstream portion of the remaining walls was secured to the rock through a steel HSS needle beam and mini-pile system. The needle beams were connected from both sides of the walls to 150 mm diameter steel HSS mini -piles filled with concrete that were inserted into drill holes up to 6m in the bedrock then pressure grouted.

Instrumentation was installed in the powerhouse for monitoring movement of the superstructure and substructure during demolition, foundation excavation and initial concreting. Survey targets were attached to the masonry of the upstream outside face of the powerhouse for monitoring vertical deflection by conventional leveling techniques. Electro levels were used to monitor for lifting of the piers in the upstream/downstream directions. The purpose of the electro levels was to detect any changes in the geometry of the powerhouse substructure, providing early warning of any tendency toward a “domino” collapse of the powerhouse. Fortunately no substantial deflection was detected during construction.

MY TRIP TO SEYMOUR GENERATION STATION
BY Timmie G. Orpwood

On Tuesday June 14 /1994 my friend Lev and I visited the Seymour Generation Station . It is in Campbellford Ontario. It was a sunny day and the weather was nice and warm. When we arrived Mr. Nauss, he is the construction project administrator, asked us to look at several part of the construction project. First we looked at bay number five. There is a place on the thrust deck where my friend Lev and I drew a steel to hold up the walls during construction and Mr. Nauss explained that someone had put a big steel pipe and concrete in the middle of this place and Mr. Nauss said it was an excited penstock. The contractor was excited but I didn’t see why he thought the pipe was. My friend Lev picked another piece of steel to cover a hole in the wall above the penstock so that we could put in the steel beam that the contractor had made. Everybody thought that this was a good idea and the contractor said he would do it without delay. Next we looked at the floor in the ice run bay. It does not have the same shape as the construction drawings showed. It is higher at the front of the station. It has been patched. It is 500 mm lower in the middle of the station. Lev and I had to move three rock anchors because of this difference. We will lower them 500mm. There will be no other changes.  The contractor had dug a hole in front of the station. They call this place up stream but there is no stream now. We looked at the hole. Right beside the station building you could see the bedrock but it was dirtying and wet. Mr. Nauss told the contractor that he had to clean this place so he could see the rock better. We will have to come to the Seymour Generation Station again to see this. Above the bed rock, there is a clay and broken rock. We were told that the contractor had made this three to one. (3-2-1 blast- off!!!).

We locked at cracks in the block wall of the station building. The contractor had put back the loose mortar between the bricks but he had not fixed the cracks that were through the bricks. I remembered seeing these cracks when I visited the power station before. I made steel straps on the drawings to hold the walls together. Mr. Nauss wanted to know if he should use glue too. I said no the steel straps would be enough. One of the contractor’s people asked me to look at some holes he was drilling. This man is a sub-contractor but he was working on the concrete floor over the ice run. I don’t know where he parked his sub? The sub-contractor told me he was moving his drill holes to miss the steel floor beams. This was a good idea and I agreed he was smart to do it this way. He told me he would like me to visit him again and see how he stretches the steel he glues into the holes. I told him to telephone and I would be happy to come to visit again. I saw a lot of interesting things on my trip to the Seymour Generation Station and I hope that I can visit it again soon. Me and Lev said good-bye to Mr. Nauss and we came back to Toronto at the end of the day.