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of struts after excavation is simple; all assures the safety of construction. Earth pressures on Steel piles and strut loads are measured, and the excavation can proceed with a Computer analysis being performed concur-rently.

CAPACITY

JACK THRUST JACK STROKE COUNTER WEIGHT TOTAL WEIGHT CONTACT PRESSURE PILE DIAMETER NORMAL DEPTH WATER PRESSURE

50ton x 2 lOOton

1,500mm 65 - 85ton 100ton

16ton/m (at lOOton) 500 - 1,000$ 0 - 50m - 700kg/cm2

Fig. 2 Pile installation by jetting and jacking instead of driving (courtesy of Kumagai Construction Co.)

Fig. 3 Pneumatic caisson for a blast furnace, Ohgishima Steel mili (courtesy of Shiraishi-Kiso Co.)

Fig. 4 Steel pipę pile caisson under construction (courtesy of Kawasaki Steel Works Co.)

Diaphragm walls are used for excavations, but the constructed walls should be of such a high ąuality that they will perform satis-factorily as permanent structures. The high quality is assured by the use of precast concrete panels as underground walls. After the panels are placed in the trench, com-pressed air is blown, through the pipes which have been installed in the panels, at the bottom of the trench exciting the slurry.

Then two types of cementing agents are poured from the top of the trench, which then jells the mixed slurry. After about three weeks, the compressive strength of the jell reaches 3 to 5 kg/cm². The drilling mud is forced to circulate, minimizing its reąuired quantity.

To excavate the trench for diaphragm wali construction, the "Rotary Cutters" capable of controlling the accuracy automatically are employed. The excavated materials are solidi-fied, if necessary. Construction control is madę possible by tneans of a supersonic wave instrument which measures the width of the trench being excavated. Special connectors link firmly units of diaphragm walls, and also the constructed walls and the inner structure. Fig. 5 shows a method of con-structing high-quality diaphragm walls in this country.

In fabricating Steel frame structures for the underground section, first continuous diaphragm walls are constructed. Then, auger holes are drilled, in which Steel members are installed to reinforce the walls. Thus both the underground and above-ground works can proceed simultaneously. The Setagaya Sub-station of the Tokyo Electric Power Company was constructed in this manner.

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