in undersize formers and then to drill out to full size later. (d) Cleaning out, The holes were rammed with steel rods to break out the plaster and cleaned out by compressed air jet. The air blast proved the circuit by forc- ing out water through twenty or so nearby pipes.
Grout pipes were then fixed in the holes and water pumped in at one grout pipe. Other pipes in the area were clipped off when clean water issued from them. The final pipe outlet was raised so that residual heads of 10 ft. for the basement sections, and 20 ft, for the sub-basement, were pumped against. Sodium Sulphosuccinate wetting agent was then pumped through the circuit.
The thorough washing, which removed fines and small quanti- ties of silt which had entered the membrane, and the use of the wetting agent which reduced friction for the subsequent grouting, proved well worth- while.
(e) Caulking. The grout pipes were caulked in by wrapping the pipe in hemp string and using a ham- mer and normal caulking tool.
For the sub-basement the hemp was changed to lead wool on account of the higher pres- sures expected. Re-caulking dur- ing pumping was often neces- sary, but subsequent experience has shown that the trouble would not occur with drilled holes.
(f)
Mixing. The mixers used were of the pan type, of 28 gallons capacity, and operating at 260 r.p.m.
Water was placed first in the mixer, then additives, plus DSP and the cement; after mixing a couple of minutes AM-9 and KFe in water, and AP in water, were added simultaneously from two separate containers. The completed mix was poured through a screen into the trough and pumped.
The proportion of KFe used gave 1 hour and 40 minutes setting time.
The mixing sequence is critic- al and cement, water, and addi- itves must be mixed a good two minutes before the AM-9 ́AP is added. Mixing continued for about one additional minute. (g) Pumps. The pumps used were of the hand operated diaphragm type of 300 g.p.h. capacity, with a maximum pressure of 300 p.s.i. The actual pressures used were 20-100 p.s.i.
It was found that the grout tended to adhere to the pumps and pump valves had to be cleaned, the pump head remov- ed and diaphragm, boss etc. cleaned down every 3-4 hours. Pumps which can be easily dis- mantled are thus a necessity, and spare pumps should be provid- ed to ensure continuity of pump- ing operations.
th) Grouting. Grout was pumped
General view of the site taken in late 1965. Peripheral steel sheet piling was left in place
64
into the porous layer using two or three pumps simultaneously, starting at one end of a section near to the wall. A separate in- jection point was used for each pump.
Pumping was continued until grout of the consistency of that pumped in issued at adjacent pipes, whereupon the pipes were tied off.
Extension pipes to give a 4 ft. residual head were then attach- ed to the next line of holes. When grout issued at this head, pump inlets were moved to the holes immediately behind. The operation was repeated until the end of the section was reached.
The membrane at commence- ment was full of water and the pumped in grout displaced it. Eventually water mixed with grout emerged and this quickly thickened until it was equal in consistency to that pumped in. It was apparent that dilution was minimal due to the cohesion of the grout.
As the grouting of a section neared completion, grøut issued from a few pipes which were previously dry or through which water only had issued. It is considered that a section is not completely grouted until the last few pipes are tied off and the whole area is under pressure. For this reason the longest prac- ticable set should be arranged.
Grout failed to issue through seven pipes, and these were grouted up the next day, five of them without difficulty. With two, which required an apparent- ly excessive quantity of grout, it was afterwards discovered that grout had escaped through joints in subsoil pipes cast into the
concrete.
At the outset unequal friction in the porous layer caused some difficulty in controlling the flow of grout, which did not issue uni- formly from all the pipes in the area being grouted. The difficul- ty was overcome by increasing the pump pressure, after the free flowing pipes had been tied off. Pump gauge pressures had to be built up to 100 p.s.i. on such occasions, but suddenly fell, when grout commenced to issue through the previously dry or deficiently flowing pipes.
To ensure maximum control. each grouting operation should be confined to a bay of not greater than 50 ft. in each direc- tion, using two pumps. This would involve the prior division of the porous layer by water- proof boundaries between adja- cent bays.
Walls
The basement walls were not gen- erally grouted. Leaky joints in the steel sheet piles were sealed by weld- Continued on next page
Far East Architect & Builder July, 1967