Patent GB-692227-A (GB)
Title: Process for the production and sinking of caissons of any desired form
IPC: E02D23/12
Filed: 1951-02-28
Abstract: 692,227. Caissons sinking etc.; borehole linings. LORENZ, H. Feb. 28,1951 [March 11, 1950; Dec. 22, 1950; Jan. 10, 1951], No. 4932/51. Classes 68(ii) and 85 In a process for the production and sinking of caissons a liquid with thixotropic properties is introduced between the outer wall surfaces of the caisson and the ground and/or above the ceiling of a working chamber forming part of the caisson, the properties of the liquid being such that it does not penetrate into the pores of the ground but by forming a fluid-tight film sets up. a liquid resistance to the earth wall of the caisson which, according to the concentration of the liquid, may be greater than the hydrostatic pressure and thereby secure the cavity wall against collapse and also produce only horizontal readily determinable forces on the walls of the caisson without producing on the walls any vertical components caused by friction, the process being such that the dimensions and reinforcement of the caisson are only such as are necessary to take up the stresses in the sunk and loaded condition. A suitable liquid is a suspension of pure bentonite in water, and to increase the specific gravity finely ground heavy spar may be added. The thixotropic liquid filling the space above the working chamber may decrease in concentration in stages from the soil side to the centre, if necessary to zero, since the columns do not mix with one another. The liquids are preferably introduced through pipe lines and nozzles in or on the top of the unit and fed through delivery tubes during sinking from above or from the working chamber, short partitions being fitted' on the ceiling of the unit to influence the direction of flow of the different liquids. As shown in Fig. 2 the thixotropic liquid 1 is introduced between the caisson jacket 2 and the soil 3 as soon as the curb 7 is below the land surface, and is continuously added so as to fill that space, being prevented from entering the working chamber 5 bv the cutting edge 4 making contact with the soil. The caisson is guided by. a roller guide system 6. When the caisson has reached the required depth the liquid may be recovered by filling the space between the jacket and the soil with concrete. The same method may be used to form foundations under water, the thixotropic liquid remaining in the cavity between the jacket and the soil since its specific gravity is greater than that of the water. The method may be used with open caissons or those having compressed air chambers. The caisson may have no jacket, as in Fig. 10, the working chamber being connected to the outside by a shaft tube 8. The entire space 9 above the caisson is then filled with thixotropic liquid. The caisson is guided and prevented from sudden uenetration by suspension cables secured to bearers over the shaft opening or to containers 10 floating in the liquid. At the required depth first the working chamber and then the space 9 is filled with concrete. Fig. 13 shows a caisson in different stages of an inclined sinking operation, more soil being excavated beneath one cutting edge 11, and the thixotropic liquid filling the space 13 'between the soil and the rearward projections 12 of the caisson and the space 14 between the soil walls. The angle of rotation of the caisson may be increased to 90 degrees or more. Shuttering may be erected on the sunken caisson 15, and a wall 16 of tapering crosssection formed, when the remaining spaces 17, 18 filled with thixotropic liquid may be filled with soil or thin concrete. The wall 16 with the form 19 of the hull of a ship may serve as a quay, the soil on the open side of the wall being dredged away: The space 18 may remain filled with the thixotropic liquid which serves to distribute any load over the whole wall. Excavation may be carried out manually or mechanically, e.g. by automatic flushing devices, and the weight of the thixotropic liquid aids the sinking of the caisson.