GB703654A - Method of pre-stressing the soil more especially for foundations and preferably in a horizontal direction - Google Patents

Abstract

703,654. Concrete foundations. LORENZ, H. June 12, 1951 [June 17, 1950 ; Aug. 12, 1950], No. 13950/51. Class 20 (2). [Also in Group XXI] In forming a concrete pile or foundation the soil at the point of contact with the concrete is consolidated or pre-stressed at least to the point of maximum earth resistance by means of a consolidating device introduced into the concrete before it has set and then increased in cross-section to cause horizontal displacement of the concrete whereupon after setting of the concrete the device is withdrawn and the cavity so formed filled with concrete. In one form the device comprises a perforated tube 3, Fig. 1, surrounded by a rubber jacket 1, the internal chamber 5 of the tube 3 being placed under air or water pressure to expand the jacket 1. Since the earth resistance increases with depth, the tube and jacket may be sub-divided by partitions 8, Fig. 2, and hoops 7, the top chamber 9 receiving the lowest pressure and the bottom chamber 9 the highest pressure, or alternatively the partitions 8 may be omitted and a single pressure medium supply pipe provided having branches fitted with pressure reducing valves leading directly into the jacket sections. In a further modification the thickness of the rubber jacket 27, Fig. 5, increases in upward direction so that a decreasing extensibility is provided in the upward direction in accordance with the decreasing earth resistance, and in this case a pressure fluid of high specific gravity, e.g. a suspension of bentonite and a supplement of heavy spar, is used. Instead of circular crosssection, the device may have an elongated walllike construction for pre-stressing elongated block foundation elements. The point of maximum earth resistance is ascertained by taking readings of pressure and volume of pressure liquid introduced, the point at which the pressure does not increase with increase in volume being the point of maximum earth resistance. Consolidation may be assisted by vibrating the device and/or by introducing a pulsator into the pressure line.