USE, CONSTKUCTION, AND COST OF SERVICE RESERVOIRS. 155 



crete being laid on a twelve or eighteen inch bed of puddle clay, 

 which under the feet of the workmen was worked up into a nice 

 soft condition, so much so that the concrete sank into it, and 

 where the puddle left off and the concrete began it was hard to 

 say, indeed the whole floor appeared to be a mixture of puddle 

 and concrete. Water tight possibly, but not quite what was 

 desired. 



The brickwork if properly laid and grouted will be absolutely 

 watertight, where then, comes in the necessity for puddle? If 

 any water does soak through the brickwork and concrete backing 

 it would be better to let it go than to attempt to retain it in the 

 wall with puddle. 



I may here mention a precaution that is necessary to take in 

 the event of anything like a spring or soakage being found in the 

 bottom of the excavation for a Reservoir, a dry stone French drain 

 should be laid connecting the soakage with the outlet or scour pipe 

 trench to let off any water, it may also be in some cases desirable 

 to have one or two French drains leading from the outlet trench 

 across the bottom of the Reservoir bed to let off any water that 

 may soak from the surrounding strata down behind the abutments, 

 as it is quite possible to get an hydraulic pressure under the floor 

 tending to raise it up. 



During the construction of one of the largest of the before 

 mentioned Reservoirs about one hundred superficial feet of the 

 floor was found to have lifted in a curved form about two inches 

 at the centre to nothing round the edges ; the cause, a spring 

 underneath, was at once suspected, and upon punching a hole 

 through the brickwork a quantity of water escaped and the floor 

 dropped to its original level. Examination showed that the water 

 must have found a way up through the concrete but was success- 

 fully stopped by the brickwork and rendering, but the pressure 

 was sufficient to part the brickwork from the concrete and lift it. 

 To effect a remedy, a groove was cut in the floor, a small pipe 

 laid in underneath and connected with the outlet drain, this gave 

 the spring a vent, the floor was made good again, and no further 

 trouble was experienced. 



