ENG-1960 — Page 35

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REVIEW

would be so great as to be unacceptable. The Governor in Council then decided to limit investigations to the Shek Pik site only.

The consultants submitted a report in November 1956 which brought to light a new and alarming problem. Gravel and boulders across the centre of the valley went down to a depth of 40 feet, below which there was decomposed granite to a maximum depth of 97 feet. Ground level was only about 15 feet above sea level for the length of 1,000 feet across the valley on the line of the proposed dam and the site itself was about half a mile from the shore. The problem was to prevent salt water from seeping in, during the excavation and construction of the foundations, and the contents of the reservoir from percolating out under the dam and undermining it. The normal type of concrete dam embedded on solid rock foundations was impracticable, or at least prohibi- tively expensive, and to the layman it seemed at first sight that the project was impossible. The consultants, however, foresaw a likely solution and recommended a recently developed system of foundation stabilization in which a mixture of water, cement and a special type of clay is pumped into the porous strata under considerable pressure. This process is known as 'grouting', and avoids the heavy excavation necessary in conventional dam foundations. They proposed as a first step to put down a 'box' of concrete piles and to grout the enclosed area so as to test the effectiveness of the method and hence the feasibility of building a dam. They would place this 'box' in the ultimate line of the dam so that if the experiment proved successful the work would not be wasted. The consultants went on to report that if this experiment were successful, an impounding reservoir containing 4,125 million gallons could be constructed in the Shek Pik valley with a maintainable yield of 21 million gallons a day. In January 1957 Government approved construction of the Shek Pik reservoir in principle, and in due course negotiated a contract with Soil Mechanics Ltd, in conjunction with the French firm Soletanche who agreed to undertake the specialist grouting test. The test might take a year or eighteen months and Government was anxious not to lose this valuable time. They therefore commis- sioned Messrs Binnie, Deacon & Gourley in May 1957 to begin work on the design of the dam and other essential equipment such as pumping machinery. This bold decision was something