Shaft construction method

Abstract: A shaft construction method comprises the depthwise operation of a revolving operating pipe (2) that is revolved within a prescribed range and operated to inject or jet ground hardener from a jetting element provided on the side of the pipe to form a columnar mixed region (71) of soil and hardener in the ground. Such columnar mixed regions are provided side by side to form a continuous wall (72) of shafts.

Description: The present invention relates to a method of constructing a wall. When a scheduled building construction site has poor ground, the ground is generally given an improvement treatment prior to the construction. Such ground treatment usually consists of hardening the soil by permeating it with a hardening agent. One method that has come into extensive use in recent years is the injection mixing method in which air and hardener are forced into the ground under high pressure to form a pile-shaped solid mass. An apparatus for implementing the injection mixing method consists of a high-pressure pump for pumping the cement or the like that constitutes the hardener; a compressor to supply the air; and a machine to operate a double-walled boring pipe the tip of which is provided with a nozzle. The high-pressure pump is usually a plunger-type pump, which is used to pump the hardener from a mixer under very high pressure. The machine mixes the air and hardener and injects it into the ground from the nozzle of the double-walled boring pipe. For this, the boring pipe is inserted into a borehole in the ground, and for the injection process is revolved while being raised up from the bottom part of the hole. A columnar mixed region of soil and hardener is thereby formed in the ground, which the setting of the hardener forms into a pile-shaped solid mass. The injection mixing method is widely employed because it provides good operational efficiency. However, the diameter of the columnar mixed region is dependent on soil condition and pump performance, and in sandy soil or clay the standard effective diameter is limited to 2000 ± 200mm. FR-A-2 116 171 discloses a method having the precharacterising features of claim 1. According to the present invention, there is provided, a wall construction method comprising successive steps of injecting or jetting a ground hardener into the ground by the depthwise operation of rotating jetting means to form a sequence of side by side columnar mixed regions of soil and hardener in the ground to form a continuous wall of piles in the ground, characterised in that, in each of said steps, said jetting means is rotated through only part of a circle so that each of said piles has a fan-shaped cross-section. Adjacent ones of said piles preferably overlap each other. Each of said piles may have a semi-circular cross-section. Said jetting means may be operated around the perimeter of a circle or an ellipse to form said piles on the outer side of the circle or ellipse. Before said steps, said jetting means may be operated underground for forming a pile of a set thickness underneath said piles. The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a drawing showing an overall view of apparatus for use in a method according to the present invention; Figure 2 is a cross-sectional view of a high pressure pump of the apparatus: Figures 3a to 3c are cross-sectional views illustrating steps in an example of a method according to the present invention; Figure 4 is a perspective view showing a wall constructed using an example of a method according to the present invention; and Figure 6 to 8 are drawings illustrating the construction of round or elliptical walls using an example of a method according to the present invention. Figure 1 shows an example of apparatus for use in a method according to the present invention. In Figure 1, reference numeral 1 denotes a machine for raising/lowering and rotating a double-walled boring pipe 2; reference numeral 3 denotes a high-pressure pump for pumping hardener mixed by a mixer 4 and an agitator 5; 6 is a hydraulic unit that drives the high-pressure pump 3; and 7 is a compressor for mixing air in with the hardener pumped by the high-pressure pump 3. A pump (not shown) is used to supply the mixer 4 with water from a water tank 8. The end of the double-walled boring pipe 2 of the machine 1 is provided with a nozzle (not shown) from which hardener pumped by the pump 3 is injected into the ground. The machine 1 is equipped with a drive section for general rotation of the double-walled boring pipe 2 and a drive section for rotating the double-walled boring pipe 2 within a prescribed range, and is provided with a switch-over device for selecting the drive. The drive sections rotate the double-walled boring pipe 2 by means of a rack and pinion arrangement, for example, with the pinion imparting a reciprocating action to the rack. As one example, a projecting portion is provided at each end of the rack to operate a microswitch, for example, and thereby change the direction of rotation of the boring pipe 2. The degree of rotation of the double-walled boring pipe 2 can be controlled by shifting the position of the projecting portions on the rack, thereby changing the position at which the microswitches are operated. An example of the high-pressure pump 3 will now be described with reference to Figure 2. The high-pressure pump 3 is comprises a valve box 10 provided with a valve chamber 9, a plunger box 12 provided with a plunger 11, and a box 13 forming a pressure action chamber 13a disposed between the valve box 10 and the plunger box 12. The valve box 10 has an inlet passage 14 and an outlet passage 15 that communicate with the valve chamber 9 and which are provided with an inlet valve 16 and an outlet valve 17, respectively. The inlet valve 16 and the outlet valve 17 each have a seat 19 having a valve seat formed into a concave, semi-spherical shape and a multiplicity of small holes 18 that extend axially from the concave valve seat ; a valve-piece 20 that has a spherical shape corresponding to the said concave valve seat ; and a valve spring 21 that urges the valve-piece 20 against the seat 19. The holes 18 are for limiting the in-flow of particles that exceed a given size. In the side wall 22 of the valve box 10 is a passage 23 that connects the pressure-action chamber 13a with the interior of the valve chamber 9, and provided at the opening of the passage at the pressure-action chamber 13a end is a screening member 24 constituted of a mesh screen or the like that limits the entry of particles that exceed a given size. The end of the plunger 11, which is maintained within a cylinder 25 in the plunger box 12 via a V-packing 26 so as to project into the pressure action chamber 13a, is reciprocated at high speed by a drive means (not illustrated). A resilient membrane 27 is provided in the pressure-action chamber 13a to divide the pressure-action chamber 13a into a cylinder 25 side A and a valve chamber 9 side B. The cylinder 25 side A of the resilient membrane 27 is filled with an operating medium 28, such as oil. The use of the above apparatus to construct the continuous wall illustrated in Figure 4 will now be described. The double-walled boring pipe 2 of the machine 1 is positioned at the location where the continuous wall is to be constructed and the boring pipe is used to bore a hole to the required depth, using an appropriate pipe rotation and boring rate for the conditions of the ground concerned (Figure 3a). The double-walled boring pipe 2 uses high-pressure jetting from its nozzle to bore the hole, penetrating into the ground 29 under its own weight. Alternatively, the boring pipe 2 may be inserted after the hole has been bored by another means. After the hole has been bored to the required depth, the rotating boring pipe 2 is then withdrawn up the borehole 30 (Figure 3b) while the high-pressure pump 3 is operated to inject hardener from the nozzle. The rate at which the boring pipe 2 is withdrawn up the borehole and the rate at which the pipe is rotated are set in accordance with the nature and softness of the ground concerned. The hardener consists of cement such as Portland cement, for example, as the main constituent and an admixture of a water-reducing agent such as montmorillonite or calcium, suitably combined with a cement based ground improvement agent, with the proportions of the constituent components being changed to suit the ground concerned, and mixed with water. The injection of the hardener breaks up the texture of the soil ground and forms a columnar pile 31 with a fan-shaped cross-section (Figure 3c). A sequence of such piles 31 each having a semicircular cross-section are formed with an overlap between adjacent piles. This results in the formation of a continuous wall 32 of columnar piles 31, as shown in Figure 4. Figure 5 shows a shaft 34 whose wall 34a has a prescribed inside diameter D, constructed by the following method. The double-walled boring pipe 2 is inserted into the ground to a fixed depth and rotated to inject hardener to form a columnar pile 35 having a diameter that is at least D. The pile 35 thus formed has a set thickness 1 at the position that forms the bottom of the shaft 34. Next, with reference to Figure 6, the double-walled boring pipe 2 is operated at evenly spaced positions b1 to b10 around the perimeter of a circle 36 of a diameter D to form fan-shaped columnar piles 37 on the outside of the circle 36 with a partial overlap between adjacent piles 37. Earth and sand, etc., are then removed from an inner portion 38 enclosed by the piles 37 to thereby form shaft 34. Figures 7 and 8 are for illustrating a method of constructing an elliptical shaft 39. In this case, when constructing the bottom 39a of the shaft 39, the double-walled boring pipe 2 is operated twice at points a and a' which are offset relative to each other by a set distance. The double-walled boring pipe 2 is then operated at evenly spaced positions b1 to b10 around the perimeter of an ellipse 40 to form fan-shaped columnar piles 41 around the ellipse 40 with partial overlaps between adjacent piles 41, to thereby form a side wall 39b of the shaft 39. The elliptical shaft 39 is then formed by removing the soil from an inner portion 42 enclosed by the piles 41. In the above described methods, a pump-driven injection mixing method in which the pipe 2 is rotated stepwise by prescribed degrees to construct piles side by side with some overlap, to form a continuous wall. Where the wall is that of a shaft, because the high-pressure pump used has 2.5 or 3 times more output capacity than the pumps used in the prior art, the injection mixing method can be used to construct a columnar pile at the bottom of the shaft in a single step. Moreover, as the size of the radius of the semicircular piles is proportional to the pump output, compared with the prior art, it takes fewer injection operations to construct a shaft, and is therefore more efficient.

Claims: A wall construction method comprising successive steps of injecting or jetting a ground hardener into the ground by the depthwise operation of rotating jetting means (2) to form a sequence of side by side columnar mixed regions (31) of soil and hardener in the ground to form a continuous wall (32 or 34a or 39b) of piles (31 or 37 or 41) in the ground, characterised in that in each of said steps, said jetting means is rotated through only part of a circle so that each of said piles (31 or 37 or 41) has a fan-shaped cross-section. A method according to claim 1, characterised in that adjacent ones of said piles (31 or 37 or 41) overlap each other. A method according to claim 1 or 2, characterised in that each of said piles (31 or 37 or 41) has a semi-circular cross-section. A method according to any preceding claim, characterised in that said jetting means (2) is operated around the perimeter of a circle (36) or an ellipse (40) to form said piles (37 or 41) on the outer side of the circle (36) or ellipse (40). A method according to any preceding claim, wherein, before said steps, said jetting means (2) is operated underground for forming an underground pile (35 or 39a) of a set thickness underneath said piles (37 or 41).

Inventors: KOIWA YOSHINOBU, KOIWA, YOSHINOBU
Applicants: FUJIMORI SHUICHI, KELBIN CO LTD, KOIWA YOSHINOBU, LITTLE ROCK LTD, FUJIMORI, SHUICHI, KABUSHIKI KAISHA LITTLE ROCK, KELBIN CO., LTD., KOIWA, YOSHINOBU
Application year: 1989
Main classification: E02D5
IPC codes: E02D5, E02D3