222 J. E' Mac9iella?i, C.E. — On [Oct. 26. - 



Many of these sites are on Government lands, and the one at Van 

 Wyk's Vley is one of the most extensive and favourable yet brought 

 to the notice of the public. A short description will now be given 

 of the manner in which the works at that place were carried out. 

 The designs were prepared by Mr. John Gr. Gamble, the Hydraulic 

 Engineer to the Colony. The contract for the work was signed on 

 the 28th October, 1882, and the first ground was broken on the 1st 

 December following, the author having been appointed resident 

 engineer. 



Before the contract was given out for tender, trial pits were sunk 

 along the centre line of the bank in order to find, if possible, an 

 impermeable stratum on which to found the puddle core. These 

 were put down by the foreman (R. Taylor) who came out from England 

 to undertake borings. He found on the one side of the kolk or 

 river a stratum of hard rock, varying from 8 feet to 17 feet beloAv 

 the surface of the ground. Close to the east side of the river, no 

 roek could be found, and it was supposed to have been cut off in or 

 near to the other side, this was afterwards, as the work proceeded, 

 found to be correct. Instead of rock, a succession of shales was 

 found, overlaid on the koppies, which formed the abutments of 

 the bank, by beds of a very hard rock, which are much split 

 up but cemented together by deposits of lime. A bore hole was 

 put down on the east side by Taylor to a depth of 50 feet but he 

 did not get through the shale. These shales for a depth of 10 or 

 12 feet were of a very friable and porous nature, and it was found 

 necessary to excavate to a considerable depth to get a good foundation. 

 The contractors (Messrs. Gillet & Perez) then began the work 

 by clearing the ground of all stones, sand and bushes, and by loosening 

 it with picks and ploughs to a depth of 8 inches. On this prepared found- 

 ation the embankment was raised. Simultaneously with the starting of 

 the bank, a trench was excavated, extending the entire length of 

 the bank, and down to the rock where rock could be found. This 

 trench was 8 feet wide at the bottom, the sides having a batter to 

 meet the puddle core of the bank, at the natural surface of the ground. 

 It was then filled in with puddled clay, made as will afterwards be 

 described. The puddle core or wall, placed in the centre of the 

 bank was carried up to within 3 feet of the top, where it reached its 

 minimum width of 4 feet, its sides having a batter of 1 in 5. 



Great difference of opinion exists amongst engineers as to the 

 proper position of puddle in earthen dams. Some advocate the 



