EARTH PRESSURE SYSTEM SHIELD PROCESS

Abstract: This invention relates to an earth pressure system shield process. First of all, an excavation additive consisting of the mixture of an agent for improving fluidity and viscosity of excavated soil and a mud improving main agent is added (1c, P₂) to excavated soil at the time of shield excavation at the working face, inside a mixing chamber (1b) of a shield machine (1) and inside a screw conveyor (3) for discharging soil to sufficiently mix the excavated soil with the improving main agent and a mud improving assistant is then added (5) inside the screw conveyor (3), so that the seal covered by the improving main agent so as not to be dissolved in water is removed chemically by this assistant. In this manner, the excavated soil is improved to quality soil having low fluidity inside the screw conveyor (3) for discharging soil and is discharged. As described above, the improving main agent and the improving assistant are mixed continuously, and at the same time a cut-off plug zone is formed inside the screw conveyor (3₃) for mixing, and a cylinder portion (15) not having a soil and gravel conveyor means is disposed at the rear end of the conveying screw conveyor (3₂) so as to form the cut-off plug, to prevent explosion of the discharged soil, to prevent collapse of the working face and to make the soil discharge work easy.

Description: TECHNICAL FIELD The present invention relates to an earth pressure system shield process for improving the excavated soil utilizing the improved soil and effecting the shield excavation against the earth pressure, particularly to the earth pressure system shield process capable of effecting the shield excavation at the earth to which the high hydraulic pressure applies. BACKGROUND TECHNOLOGY In the conventional earth pressure system shield process, the following problems occurred when an excavation additive is added at the time of shield excavation for giving fluidity and viscosity to the excavated soil. (a) In case where the earth has many underground water and high underground pressure, the excavated soil is being expelled due to high underground pressure together with the pressurized water from the discharge port of a screw conveyor for discharging the excavated soil, thereby disturbing the earth adjacent to a working face of a shield machine which is liable to cause the subsidence or the collapse of the earth. (b) Inasmuch as the excavated soil is difficult to be conveyed by a dump truck and the like outside the shield construction site due to its high fluidity, it was necessary to improve the excavated soil to eliminate the fluidity in the shield construction site. When the excavated soil is being expelled due to high underground pressure, the pressure variation at the working face is restricted to a minimum by providing a rotary valve and the like at the soil discharge port. However, when hydraulic pressure ranging 2 to 3 kg/cm² applies to the earth, the shield excavation cannot be carried out in the earth pressure system shield process but can be carried out in a muddy water pressure system shield process. Accordingly, the system other than the earth system shield process such as the muddy water pressure shield process can be employed. In case of improving the excavated soil having high fluidity, a soft mud improving agent is added to and mixed with the excavated soil in the shield excavation site so as to eliminate the fluidity. A process and apparatus as defined in the preamble part of patent claim 1 and 4, respectively, is disclosed in the document JP-A-61-216 994. Further, the document JP-A 55-165 397 discloses a soil compacted portion, i.e. a cut-off plug zone, provided at the rear portion of a discharge screw conveyor portion for controlling discharge of the excavated soil, so that the amount of soil to be taken in is balanced with the amount of soil to be discharged so as to retain the water pressure and earth pressure at the working face. The length of the cut-off plug zone is regulated or the amount of mud to be discharged is regulated. In this process, merely the amount of soil to be discharged is regulated. It is an object of the present invention to provide the earth pressure shield process capable of solving such drawbacks in that "excavated soil is being expelled due to high underground pressure together with pressurized water of the earth" and "if the excavated soil is not improved, the excavated soil cannot be conveyed outside the shield construction site" and capable of excavating the soil having high hydraulic pressure without resorting to the large scaled and troublesome muddy water pressure system shield process. To achieve the above objects, an earth pressure system shield process comprises the steps of adding an excavation additive consisiting of the mixture of an agent for improving fluidity and viscosity of an excavated soil and a mud improving main agent to the excavated soil at the time of shield excavation at the working face, inside a mixing chamber of a shield machine and inside a soil conveying screw conveyor to sufficiently mix the excavated soil with the improving main agent, then adding a mud improving assistant inside the soil discharge screw conveyor so that the excavated soil is improved to a high quality soil inside the soil conveying screw conveyor and conveyed. As a result, the soil can be mixed with the excavation additive and improved sufficiently even if the shield machine having small diameter is employed. The improved high quality soil is continuously conveyed toward the rear end of a conveying screw conveyor by a screw provided with the conveying screw conveyor and a mixing screw conveyor and filled under high pressure in the rear end of the conveying screw conveyor. A cut-off plug zone is formed by a cylinder portion having no soil and gravel conveyor means disposed at the rear end of the conveying screw conveyor. As a result, the earth pressure system shield process according to the present invention enables the shield construction at the earth to which high hydraulic pressure is applied. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1(a) is a cross sectional view of a shield machine employing the earth pressure system shield process according to an embodiment of the present invention, Fig. 1(b) is a view explaining Fig. 1(a), Fig. 2 is a view explaining another embodiment and Fig. 3 is a block diagram showing a control procedure of measurement. BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described in detail with reference to the drawings. Referring to Figs. 1(a) and 1(b), 1 is a shield machine, 2 is a cutter head provided at the front portion of the shield machine for discharging an agent for improving fluidity and viscosity, a so-called excavation additive composed of bentonite, clay, water and the like and cutting and excavating the soil by the rotation thereof, 1b is a mixing chamber for introducing the excavated soil thereinto and mixing the excavated soil with the excavation additive introduced thereinto from an excavation additive introduction tube to thereby fluidify the resultant mixture plastically. The excavation additive is manufactured outside a shield pit. The excavation additive is conveyed inside the shield pit by a pump P1 and a conveying pipe 4 and passes an excavation additive introduction pipe 1c communicating with the conveying pipe 4 and introduced into the earth by the cutter head 2 and thereafter mixed with the excavated soil in the mixing chamber 1b. The mud improving main agent in the form of slurry is conveyed through the conveying pipe 4 and mixed with the excavated soil depending on the excavation speed of the shield machine 1, i.e. the amount of the excavated soil and the nature of the excavated soil. The resultant mixture is introduced into the working face and mixed with the excavated soil in the mixing chamber 1b so that the mud improving main agent is uniformly dispersed into the excavated soil. The mud improving main agent can be mixed with the excavation additive at the excavation additive mud manufacturing plant located outside the shield pit or mixed with water at the back of the shield machine 1 and formed as the slurry and introduced into the excavation introduction pipe 1c through an introduction pump P2. In case where the mud improving main agent is introduced into the working face, the mud improving main agent is introduced through the excavation additive introduction pipe 1c or through an exclusive introduction pipe provided in the shield machine 1 independently from the introduction pipe 1c. The introduction pump P2 detects the excavation speed of the shield machine 1 and adjusts the amount of the mud improving main agent to be supplied therefrom and has a regulator, not shown, capable of introducing at the proper ratio to the excavated soil. The mud improving main agent comprises a chemical for improving the soil by introducing into and mixing with the mud e.g. a coagulant composed of a natural vegetable chemical such as "ERFRESH" (Japanese Trade Mark Registration No. 2,304,178 owned by one of the assignees of the present application) as a main ingredient. The surface of the mud improving main agent is sealed so as not to be disolved in water. As set forth above, the excavated soil is mixed with the excavation additive in the mixing chamber 1b and formed as the mud having high fluidity and viscosity. The mud is drawn rearward by the soil discharge screw conveyor 3. The soil discharge screw conveyor 3 comprises a first conveying screw conveyor 3₁ arranged linearly by way of a shutter 14, a second conveying screw conveyor 3₂ and a mixing screw conveyor 3₃ disposed over the second conveying screw conveyor 3₂ and the shutter 14 disposed between the first and the second conveying screw conveyors 3₁ and 3₂ for communicating therewith. The first conveying screw conveyor 3₁ is housed in a cylindrical case 3a having a tip end portion opened into the shield chamber 1b while a hole for communicating with the mud improving assistant agent introduction pipe 5 is defined at the rear portion of a separating wall 1a over the case 3a. The mud improving assistant agent has a function to chemically remove the seal covered by the mud improving main agent. The mud improving assistant agent is introduced into the soil discharge screw conveyor 3 from the mud improving assistant agent introduction pipe 5 and added to the mud in the proper proportion to the conveying amount of the mud so that the mud improving assistant agent is mixed with the mud in the screw conveyor 3, thereby rendering the mud to have no fluidity. The mixing of the mud improving assistant agent with the mud can be made by the first conveying screw conveyor 3₁ alone where no second conveying screw conveyor 3₂ is installed. If the soil discharge screw conveyor is composed of a ribbon screw conveyor, the position of the introduction port can be changed appropriately as shown in Fig. 2 so that the mixing ratio can be regulated. If the screw conveyor is composed of a screw conveyor having a shaft attached thereto, the mixing can be made by providing a mixing assistant screw. The shutter 14 comprises a closing cylinder 14b provided at both sides thereof and a shutter plate 14a which is vertically closable by the closing cylinder 14b. When the shutter plate 14a is closed, the soil conveyed by the first conveying screw conveyor 3₁ is blocked by the shutter plate 14a and introduced downward into the mixing screw conveyor 3₃. The mixing screw conveyor 3₃ facilitates the solidification by mixing the excavated soft mud having high fluidity but not sufficiently solidified by the first conveying screw conveyor 3₁ with the soil improving agent and forms a cut-off plug zone by compressing the soil. The mixing screw conveyor 3₃ is rotatably driven by a drive motor 8 provided at the rear end of the case 3b through a reduction gear 9 to thereby form the cut-off plug zone inside the case 3b by the operation, described later. The soil mixed sufficiently with the soil improving agent by the mixing screw conveyor 3₃ and solidified thereby is fed into the case 3c of the second conveying screw conveyor 3₂. The second conveying screw conveyor 3₂ is rotatably driven by a drive motor 10 provided at the rear end portion of the case 3c through a reduction gear 11 so that the solidified soil is conveyed in the rearward direction of the case 3c. The mixing of the soil with the soil improving agent and the conveyance of the resultant mixture are successively made by the first conveying screw conveyor 3₁, the mixing screw conveyor 3₃ and the second conveying screw conveyor 3₂ so that the improved soil is successively compressed and filled in the rear portion 16 of the second conveying screw conveyor 3₂, thereby forming the cut-off plug zone for resisting the hydraulic pressure influencing the working face. To form the cut-off plug zone, a cylinder portion 15 having no soil and gravel conveyor means, is provided at the rear end portion of the second conveying screw conveyor 3₂ so that the excavated soil is discharged from the end portion of the cylinder portion 15. A shutter 12 is provided at the rear end of the case 3c and comprises a closing cylinder 12b and a shutter plate 12a which is vertically closable by the closing cylinder 12b. A hopper 13 protrudes from a rear side of the shutter 12. The soil conveyed by the second conveying screw conveyor 3₂ drops on the conveying vehicle such as a truck and a belt conveyor for discharging the soil by way of the hopper 13 when the shutter 12 is open. The cylinder portion 15 resists the conveyance of the soil and has a function to compress and fill the improved soil into the rear portion 16 of the second conveying screw conveyor 3₂ with assuraance. The resistance of the cylinder portion 15 against the conveyance of the soil can be regulated by regulating the length of the cylinder portion 15 or gradually reducing the cross-sectional area of the cylinder portion 15 toward the rear portion thereof. Inasmuch as the cut-off plug zone is formed, the soil improved by the excavation additive is recovered in density at the state before the excavation additive is mixed with the soil so that the cylinder portion 15 can resist the hydraulic pressure influencing the working face with the shearing resistance possessed by the soil and the blades of the screw conveyor. If the shearing resistance is insufficient, a fibrous shearing resistance reinforcing member can be added in the soil. Fig. 3 is a block diagram showing a measuring control procedure in which supplied to a controller 30 are input signals from a shield jack stroke detector 21, a shield jack speed detector 22, a screw conveyor rpm detector 23, a screw conveyor torque detector 24, a discharge soil flowing speed detector 25, a discharge soil density detector 26, an excavation additive addition amount measuring device 27, an improving main agent addition amount measuring device 28 and an improving assistant agent addition amount measuring device 29. The controller 30 supplies data into or receives the data from a memory 31 so that the addition amounts of the improving main agent 32 and the improving assistant agent 33 are determined. The addition of the improving main agent is controlled in interlocking relation with the shield jack speed while the addition of the improving assistant agent is controlled in interlocking relation with the rpm of the screw or the measured discharged amount of the soil. The addition amounts of the mud improving main agent and the mud improving assistant agent are regulated by measuring and deciding whether the improvement of the excavated mud and the formation of the cut-off plug zone are respectively made or not in the soil discharge screw conveyors while the discharge amount of the soil from the soil discharge screw conveyors are measured, thereby deciding as to whether an excessive excavation made at the working face disturbs the earth at the periphery of the working face. Accordingly, it is possible to effect the determined mixture of the soil and the excavation additive and the improvement of the soil by the shield machine having the small diameter without adding the specific mixer thereto since the mud and the mud improving main agent are sufficiently mixed in the cutter chamber and the seal of the improving main agent is removed by the mud improving assistant agent in the soil discharge screw conveyor. INDUSTRIAL UTILIZATION According to the present invention, an excavation additive consisiting of the mixture of the agent for improving fluidity and viscosity of excavated soil and the mud improving main agent is added to the excavated soil at the time of shield excavation at the working face, inside the mixing chamber of the shield machine and inside the discharge screw conveyor, thereby sufficiently mixing the excavated soil with the improving main agent. Thereafter, the seal covering the improving main agent is removed chemically by the mud improving assistant added to the mud in the soil discharge screw conveyor. Inasmuch as the excavated soil is improved into a high quality soil having low fluidity inside the soil discharge screw conveyor, it is possible to effect the sufficient mixture of the soil and the excavation additive and the improvement of the soil by the shield machine having the small diameter without providing the specific mixer. Furthermore, according to the present invention, the improving main agent and the improving assistant are mixed with each other continuously, and at the same time the cut-off plug zone is formed inside the discharge screw conveyor for resisting the hydraulic pressure influencing the shielded front portion, thereby preventing the explosion of the discharged soil, to prevent collapse of the working face and to make the soil discharge work easy. Furthermore, it is possible to recover the soil improved by one improved agent in density at the state before the excavation additive is added to the soil by providing the cylinder portion having no soil and gravel conveyor means at the rear end portion of the soil screw conveyor. The cut-off plug is formed by the improved soil at the rear half portion of the conveying screw conveyor for resisting the hydraulic pressure influencing the working face so that the shearing resistance possesed by the soil and the blade of the screw conveyors can sufficiently resist the hydraulic pressure influencing the working face, thereby preventing the explosion of the discharged soil. Accordingly, according to the present invention, it is not necessary to employ the mud pressure system shield process at the time of excavation of the soil having the high hydraulic pressure. Furthermore, there are excellent advantages that it is possible to prevent the collapse of the working face and the disturbance of the earth at the periphery of the working face at the time of excavation of the soil by the earth pressure system shield process and to discharge the soil with ease.

Claims: An earth pressure system shield process which comprises excavating underground soil from the working face of an underground tunnel excavation, discharging a mud comprised of excavated soil and water into a mixing chamber and then feeding the mud through a soil discharge screw conveyor to a location spaced from said working face and said mixing chamber, wherein a mud improving agent is used to establish viscosity properties of the mud, characterized by feeding into the region of said working face an excavation additive comprising an agent improving the fluidity and viscosity of the excavated soil and a mud-improving main agent effective to coagulate the soil, said mud-improving main agent that is fed into said region being coated with a water-insoluble coating so that it is not effective to coagulate the soil in said region, said excavation additive being uniformly dispersed in said mud in said region, in said mixing chamber and in said soil discharge screw conveyor to form a mud having high fluidity and viscosity, then adding to and mixing with the mud that is being moved through said soil discharge conveyor a mud-improving assistant agent effective to chemically remove the water-insoluble coating on said mud-improving main agent, whereby said mud-improving main agent then becomes effective to coagulate the excavated soil to convert same into a high quality coagulated soil, in particular a high quality soil having a decreased fluidity. A process as claimed in claim 1, characterized in that said mud-improving main agent and said mud-improving assistant agent are mixed inside the soil discharge screw conveyor and a cut-off plug zone is formed to maintain the hydraulic pressure acting on the working face of the underground tunnel excavation. A process as claimed in claim 1 or 2, characterized in that a cylinder portion, free of conveyor means, is disposed at the rear end of the soil discharge screw conveyor so as to form a cut-off plug and enable the excavation at the working face to be performed under a high hydraulic pressure. An earth pressure system shield apparatus for excavating underground soil from the working face of an underground tunnel excavation, comprising a soil discharge screw conveyor for feeding a mud comprised of excavated soil and water which had been discharged into a mixing chamber to a location spaced from said working face and said mixing chamber, wherein a mud improving agent is used to establish viscosity properties of the mud, characterized in that said soil discharge screw conveyor (3) is divided into first and second discharge screw conveyors (3₁, 3₂), wherein said first discharge screw conveyor (3₁) removes fluidity from viscous and fluid excavated soil containing uniformly dispersed excavation additive comprising at least a mud-improving main agent effective to coagulate the soil, but coated with a water-insoluble coating to prevent its effectiveness, by adding a mud-improving assistant agent effective to chemically remove the water-insoluble coating on said mud-improving main agent, thereby improving said excavated soil and said second discharge screw conveyor (3₂) compacts said improved excavated soil and discharges said compacted improved excavated soil. The apparatus as claimed in claim 4, characterized in that said first and second discharge screw conveyors (3₁, 3₂) have respectively rotary driving sources which are turned in opposite directions, namely, one of which is turned normally and the other one is turned reversely, for disturbing said mud to be discharged at the dividing boundary of said first and second discharge screw conveyors (3₁, 3₂), so as to assist the mixture of said mud-improving assistant agent. The apparatus as claimed in claim 4, characterized in that said second discharge screw conveyor (3₂) includes a cut-off plug zone formed of a cylindrical space (15) which is structured by extending an end portion (16) of said second discharge screw conveyor (3₂) and a shutter (12) and a discharge gate and wherein said discharge soil is compacted and discharged from said discharge gate. The apparatus as claimed in claim 6, characterized in that a third discharge screw conveyor (3₃) as a part of said discharge screw conveyor (3) is provided, wherein said first discharge screw conveyor (3₁) is disposed at said mixing chamber (1b), said second discharge screw conveyor (3₂) is disposed at the portion extending from said first discharge screw conveyor (3₁) and said third discharge screw conveyor (3₃) is disposed over a shutter (14) which is positioned at the portion where said first and second discharge screw conveyors are halved and positioned intermediate therebetween so as to form a bypass discharge path from said first discharge screw conveyor to said second discharge screw conveyor so as to assist the mixture of the mud-improving assistant agent at said third discharge screw conveyor (3₃).

Inventors: KOBAYASHI RYOJI, TANAKA HIROSHI, KOBAYASHI, RYOJI, TANAKA, HIROSHI, KOBAYASHI, Ryoji, c/o K.K. Komatsu Seisakusho
Applicants: KOMATSU MFG CO LTD, KONOIKE GUMI KK, KABUSHIKI KAISHA KOMATSU SEISAKUSHO, KABUSHIKI KAISHA KONOIKE GUMI
Application year: 1990
Main classification: E21D9
IPC codes: E21D9