Ground collapse detection system and ground collapse detection method for shield tunneling

Abstract

To provide technology for detecting natural ground collapse more precisely than previous methods, for a shield method to construct a tunnel using a shield machine.SOLUTION: A natural ground collapse detection system is provided with: a measuring device of ground moisture content ratio arranged on a shield machine; and a soil weight management device determining occurrence of ground collapse where there is significant difference between a soil weight in a natural ground state and a discharged soil weight through acquisition of the soil weight in the natural ground state excavated upon assumption there is no collapse in an excavation process excavating a predetermined section with the shield machine and the discharged soil weight actually discharged from the shield machine in the excavation process in a loosened state. The soil weight management device calculates the soil weight of the natural ground in the natural ground state based on the natural ground excavated soil weight excavated upon the assumption there is no occurrence of the collapse in the excavation process and a saturated unit weight of the natural ground calculated based on the ground moisture content ratio measured by the measuring device of the ground moisture content ratio in the excavation process.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a ground collapse detection system and a ground collapse detection method for a shield tunneling method. [Background technology]

[0002] In the shield tunneling method, which uses a shield machine to build tunnels, if the excavation surface collapses as the shield machine excavates, a gap may form between the shield machine's skin plate and the ground, which could lead to situations such as ground subsidence or cave-ins. Therefore, in the shield tunneling method, when a ground collapse is detected, it is important to take immediate action, such as injecting grout into the ground from inside the shield machine, to prevent ground subsidence or cave-ins. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6405198 Summary of the Invention [Problem to be solved by the invention]

[0004] When a ground collapse occurs, an excess amount of excavated soil is discharged, which is greater than the actual amount excavated by the shield machine's cutter head. Therefore, if the amount of soil discharged from the shield machine is significantly greater than the amount of soil actually excavated by the shield machine (ground soil volume), it can be determined that the collapsed soil caused by the ground collapse has been taken into the shield machine.

[0005] However, while the pore spaces of the soil that makes up the natural ground are generally saturated with water, the soil discharged from the shield machine has been loosened by excavation and contains a lot of air in the pore spaces. Therefore, in order to accurately estimate the volume of soil actually excavated by the shield machine (natural ground volume), it is necessary to accurately understand the density of the soil that makes up the natural ground, rather than the volume after excavation.

[0006] There are methods for estimating the density of the soil that makes up the ground from prior boring data, but shield tunnels are generally long in length. Also, boring surveys require effort and cost, so they are usually only conducted at intervals of about one every few hundred meters, making it difficult to accurately determine the density of the soil that makes up the ground based on such boring data.

[0007] The present invention has been made in consideration of the above-mentioned problems, and its purpose is to provide a technology for detecting ground collapses more accurately than conventional methods in shield construction methods, which use shield machines to build tunnels. [Means for solving the problem]

[0008] The present invention employs the following means to solve the above-mentioned problems: That is, the natural ground collapse detection system of the present invention is provided in a shield machine that excavates the natural ground in a shield tunneling method, and includes a natural ground moisture content measuring device that measures the moisture content of the natural ground by emitting neutron rays toward the natural ground, and acquires a natural ground soil weight, which is the weight of soil in a natural ground state that is excavated on the assumption that there will be no collapse in the natural ground during the excavation process when the shield machine excavates a predetermined section, and a discharged soil weight, which is the weight of soil in a loosened state that is actually discharged from the shield machine during the excavation process, and detects the presence of a collapse in the natural ground when there is a significant difference between the natural ground soil weight and the discharged soil weight. and a soil volume management device that determines whether a natural ground collapse has occurred during the excavation process, and the soil volume management device calculates the natural ground soil weight based on the natural ground excavation soil volume, which is the volume of soil in the natural ground that would be excavated assuming that there is no collapse of the natural ground during the excavation process, and the saturated unit volume weight of the natural ground calculated based on the moisture content measured by the natural ground moisture content measuring device during the excavation process.

[0009] Here, the soil volume management device may calculate the natural ground soil weight according to the following formula (1). Mb=Vb×γ sat ···(1) gamma sat is the saturated unit volume weight of the natural ground corresponding to the predetermined section. Vb is the volume of soil excavated in the natural ground, which is the volume of soil in the natural ground that is excavated assuming that there is no collapse of the natural ground during the excavation process of the shield machine through the specified section.

[0010] The soil volume management device may calculate the natural ground excavation volume (Vb) according to the following formula (2). Vb=πr 2 ×Li ···(2) π is the ratio of the circumference of a circle to its circumference. r is the excavation radius when the shield machine excavates the natural ground. Li is the length of the predetermined section.

[0011] The soil volume management device calculates the saturated unit volume weight (γ sat ) may be calculated. gamma sat =(1+w / 100) / (1 / γs+w / 100 / γw) ···(3) where w is the water content of the ground measured by the water content measuring device during the excavation process of the shield machine through the specified section, γw is the unit volume weight of water, and γs is the unit volume weight of soil particles.

[0012] The present invention may also be a ground collapse detection method executed by an earth volume management device of the above-mentioned ground collapse detection system. That is, in the ground collapse detection method according to the present invention, the earth volume management device may calculate a ground state soil weight, which is the weight of the soil in the ground state, based on the ground excavation volume, which is the volume of soil in the ground state that would be excavated on the assumption that no collapse occurs in the ground during the excavation process when the shield machine advances a predetermined section, and the saturated unit volume weight of the ground calculated on the basis of the moisture content measured by the ground moisture content measuring device during the excavation process, and may determine that a collapse has occurred in the ground when there is a significant difference between the ground state soil weight and the discharged soil weight, which is the weight of soil in a loosened state that was actually discharged from the shield machine during the excavation process. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a technique for detecting ground collapse with higher accuracy than conventional techniques in a shield tunneling method in which a shield machine is used to construct a tunnel. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram illustrating a shield machine according to an embodiment. [Figure 2] FIG. 2 is a diagram illustrating an excavated soil discharge device and a ground moisture content measuring device of the shield machine according to the embodiment. [Figure 3] FIG. 3 is a diagram showing a schematic configuration of a natural ground collapse detection system according to the embodiment. [Figure 4] FIG. 4 is a diagram showing an installation mode of the natural ground moisture content measuring device according to the embodiment. [Figure 5] FIG. 5 is a block diagram showing an example of the configuration of the soil volume management device according to the embodiment. [Figure 6] FIG. 6 is a diagram showing a flow of natural ground collapse detection processing according to the embodiment. [Figure 7] FIG. 7 is a diagram illustrating an installation mode of a natural ground moisture content measuring device according to a modified embodiment. [Figure 8] FIG. 8 is a diagram illustrating an installation mode of a natural ground moisture content measuring device according to another modified example of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0016] <Embodiment> FIG. 1 is a diagram illustrating a shield machine 1 according to an embodiment. The shield machine 1 rotates a disk-shaped cutter head 3 mounted on the front of the machine body 2 to excavate a tunnel face (not shown) while advancing forward. Reference numeral 4 denotes a skin plate that constitutes the machine body 2. Inside the machine body 2, an erector (not shown) for assembling the segments and a shield jack (not shown) for propelling the machine body 2 are installed. The erectors and shield jacks of the shield machine used in the shield tunneling method are well known, so a detailed description thereof will be omitted here.

[0017] 2 is a diagram illustrating an excavated soil discharge device 10, a ground moisture content measuring device 20, and the like installed in the shield machine 1 according to the embodiment. Here, reference numeral 6 denotes a partition wall that separates the rear of the chamber 5 at the front of the machine body 2 so that a chamber 5 is formed between the machine body 2 and the cutter head 3. The excavated soil discharge device 10 includes a screw conveyor 11, a belt conveyor 12, and the like for discharging the excavated soil taken into the chamber 5.

[0018] Reference numeral 30 denotes the natural ground. The shield machine 1 advances while cutting the natural ground 30 using the rotating cutter head 3 during excavation. The cutter head 3 has an opening (not shown) for introducing excavated soil (including earth, sand, gravel, rock fragments, etc.) into the chamber 5. The screw conveyor 11 is installed with its front end protruding into the chamber 5 from the bottom of the partition wall 6. The screw conveyor 11 transports excavated soil taken into the chamber 5 from the outside (the front side of the cutter head 3) through the bottom of the chamber 5 and discharges the excavated soil onto the belt conveyor 12. The belt conveyor 12 is laid along the tunnel axis inside the shield tunnel T constructed by assembling the segments 7, and transports the excavated soil (shown as S in Figure 2) received from the screw conveyor 11. Reference numeral 8 in Figure 2 denotes a vertical shaft at the launch base from which the shield machine 1 departs. Reference numeral 9 denotes a soil pit (sometimes called a "soil dumping site") for storing the excavated soil S. The excavated soil discharged from the shield machine 1 is transported to the earth and sand pit 9 via a belt conveyor 12. Of course, instead of the belt conveyor 12, the excavated soil may be transported to the earth and sand pit 9 using a pressure pump or the like. The shield tunnel T has a ring-shaped tunnel wall constructed by assembling segments 7 in the circumferential direction.

[0019] Next, a description will be given of a ground collapse detection system 100 according to an embodiment. Fig. 3 is a diagram showing a schematic configuration of the ground collapse detection system 100 according to an embodiment. The ground collapse detection system 100 includes a ground moisture content measuring device 20 and a soil volume management device 40, and is a system for detecting collapse of the ground 30 being excavated by a shield machine 1.

[0020] As shown in Fig. 2, the ground moisture content measuring device 20 is installed, for example, at the front and upper part of the machine body 2. Fig. 4 is a diagram showing an installation mode of the ground moisture content measuring device 20 according to the embodiment. The ground moisture content measuring device 20 is, for example, a scattering type RI (radioisotope) measuring device, and mainly has a radiation source 21 that emits (emits) neutron rays toward the ground 30, and a detector 22 that detects neutron rays that have entered the ground 30 and scattered. This type of RI measuring device is well known, so a detailed explanation will be omitted. However, the moisture content of the ground 30 can be measured by counting the neutron rays that have entered the ground 30 from the radiation source 21, collided with hydrogen atoms in the ground 30, turned into thermal neutron rays, and scattered by the detector 22. As an example, the radiation source 21 of the ground moisture content measuring device 20 may be californium-252 ( 252 Cf) can be used as the detector 22. 3 He) neutron counter can be used.

[0021] The front part of the machine body 2 where the ground moisture content measuring device 20 is disposed may be, for example, immediately behind the chamber 5. Furthermore, the upper part of the machine body 2 refers to the part located on the ground G side, based on the posture of the shield machine 1 when excavating through rock. For example, when the radiation source 21 emits neutron beams toward the ground 30, the ground moisture content measuring device 20 may be disposed on the upper part of the machine body 2 so that the neutron beams are emitted in a substantially vertically upward direction. Furthermore, the ground collapse detection system 100 may include multiple ground moisture content measuring devices 20. In this case, the multiple ground moisture content measuring devices 20 may be disposed at intervals around the circumferential direction of the machine body 2. For example, the radiation source 21 may be disposed at a position where the neutron beams are emitted in a substantially vertically upward direction, and at positions approximately 30° apart on the left and right of the position around the circumferential direction of the machine body 2. However, the positions where the ground moisture content measuring devices 20 are installed on the machine body 2 are not particularly limited, and the above-described positions are merely examples. That is, the natural ground moisture content measuring device 20 does not have to be provided at the front of the machine body 2, nor does it have to be provided at the top.

[0022] Reference numeral 31 in FIG. 4 denotes a gap (clearance) formed between the natural ground 30 and the outer peripheral surface of the skin plate 4. The gap 31 is formed by over-excavating the natural ground 30 using the cutter head 3. In the example shown in FIG. 4, the natural ground moisture content measuring device 20 is disposed inside the thin-walled portion 4A of the skin plate 4. The thin-walled portion 4A is a portion of the skin plate 4 where the member thickness is formed thinner than other portions. In this embodiment, the moisture content of the natural ground 30 is measured across the skin plate 4 and the gap 31. Therefore, by disposing the natural ground moisture content measuring device 20 inside the thin-walled portion 4A, a decrease in the moisture content measurement accuracy is suppressed. In the example shown in FIG. 4, the thin-walled portion 4A is formed by excavating the inner surface of the skin plate 4 more deeply than other portions. In addition, in the example shown in FIG. 4, the radiation source 21 and the detector 22 of the natural ground moisture content measuring device 20 are configured to be in close contact with the inner surface of the skin plate 4 (thin-walled portion 4A). Note that the above-described manner in which the ground moisture content measuring device 20 is installed inside the thin-walled portion 4A of the skin plate 4 is one example, and the ground moisture content measuring device 20 may also be installed inside the skin plate 4 in a manner in which the skin plate 4 does not have a thin-walled portion 4A.

[0023] Next, the earth volume management device 40 will be described. The earth volume management device 40 can be configured, for example, by a general-purpose computer. Fig. 5 is a block diagram showing an example configuration of the earth volume management device 40 according to the embodiment. The earth volume management device 40 includes a communication I / F 41, a storage device 42, a display device 43, a processor 44, an input / output device 45, a communication bus 46, etc.

[0024] The communication I / F 41 is, for example, a wired or wireless network card, and transmits and receives information to and from other computers via a network. Specifically, the communication I / F 41 receives measurement information on the moisture content of the natural ground 30 from the natural ground moisture content measuring instrument 20.

[0025] The storage device 42 is a main storage device such as RAM or ROM, and an auxiliary storage device such as HDD, SSD, or flash memory. The main storage device caches programs and data read by the processor and reserves a working area for the processor. The auxiliary storage device stores programs and other data executed by the processor.

[0026] The display device 43 is, for example, a liquid crystal monitor, and receives a predetermined video signal and displays an image.

[0027] The processor 44 is an arithmetic processing device such as a CPU, and performs each process according to this embodiment by executing a program. Specifically, the processor 44 functions as a ground state soil weight acquisition unit 47, a discharged soil weight acquisition unit 48, and a determination unit 49, and performs the ground collapse detection process described later. As will be described in detail later, in the ground collapse detection process, the ground state soil weight acquisition unit 47 The discharged soil weight Md is acquired during the excavation process in which the field machine 1 excavates a predetermined section from a certain point. The discharged soil weight acquisition unit 48 acquires the discharged soil weight Md during the excavation process. The determination unit 49 compares the ground state soil weight Mb with the discharged soil weight Md, and determines whether or not a collapse has occurred in the ground 30 based on the result.

[0028] The input / output device 45 is, for example, an input device such as a keyboard, a mouse, or a touch panel, or an output device such as a printer.

[0029] The above-mentioned components are connected via a communication bus 46. The soil volume management device 40 may include some of the above-mentioned components, or may include other components in addition to those described above.

[0030] <Ground collapse detection processing> The soil volume management device 40 performs a ground collapse detection process, which will be described below. The ground collapse detection process is realized, for example, by the processor 44 executing a program stored in the storage device 42. Figure 6 is a diagram showing the flow of the ground collapse detection process according to the embodiment.

[0031] In the natural ground collapse detection process, the natural ground state soil weight acquisition unit 41 of the soil volume management device 40 acquires the natural ground state soil weight Mb, which is the weight of soil in the natural ground state that would be excavated if it were assumed that there would be no collapse in the natural ground 30 during the excavation process in which the shield machine 1 excavates a predetermined section (hereinafter referred to as the "inspection section") from a certain point (step S01). Here, the length of the inspection section (hereinafter referred to as the "inspection section length") Li is a predetermined length along the excavation direction of the shield machine 1, and may be, for example, a length equivalent to one ring of the tunnel wall constructed in a ring shape by assembling segments 7 circumferentially (for example, about 2 m).

[0032] The natural ground soil weight acquisition unit 47 acquires the natural ground soil weight Mb corresponding to the inspection section length Li each time the shield machine 1 excavates the inspection section length Li from a certain point, in other words, each time it constructs one ring of segment 7. The natural ground soil weight Mb is a theoretical value of the weight of soil in the natural ground that is excavated when the shield machine 1 excavates the inspection section from a certain point, assuming that there is no collapse of the natural ground 30, and is calculated by the following formula (1).

[0033] Mb=Vb×γ sat ···(1) where γ sat is the saturated unit volume weight of the natural ground 30 corresponding to the inspection section. The saturated unit volume weight of the natural ground 30 is the unit volume weight of the natural ground 30 when all the gaps between the soil particles are filled with water, that is, when the saturation level is 100%. Here, Vb is the volume of soil in the natural ground state (hereinafter referred to as "natural ground excavation volume") that is excavated assuming that there is no collapse of the natural ground 30 during the excavation process of the shield machine 1 through the inspection section.

[0034] The volume of excavated natural ground Vb is calculated, for example, by the following formula (2). Vb=πr 2 ×Li ···(2) Here, π is the ratio of the circumference of a circle to its circumference. r is the excavation radius when the shield machine 1 excavates the natural ground 30. The radius of the cutter head 3 of the shield machine 1 may be used as the value of the excavation radius r. Li is the inspection section length (the length of the specified section) described above.

[0035] Next, the saturated unit volume weight γ of the natural ground 30 sat The calculation method of saturated unit volume weight γ sat is calculated by the following formula (3):

[0036] gamma sat =(1+w / 100) / (1 / γs+w / 100 / γw) ···(3) Here, w is the water content of the natural ground 30 (hereinafter referred to as "natural ground water content"). The ground moisture content w is the moisture content of the ground 30 measured by the ground moisture content measuring device 20 during the excavation process in which the shield machine 1 excavates the inspection section. γw is the unit volume weight of water. The unit volume weight of water γw can be substituted as a known and unchanging value. γs is the unit volume weight of soil particles. The unit volume weight of soil particles γs can be obtained based on the results of soil tests performed in advance using boring surveys.

[0037] The soil volume management device 40 stores the parameters used in equations (1) to (3), such as the excavation radius (radius of the cutter head 3) r, the inspection section length Li, the unit volume weight of water γw, the unit volume weight of soil particles γs, and the natural ground moisture content w, in the storage device 42. The natural ground condition soil weight acquisition unit 47 then substitutes these values ​​into equations (1) to (3) to calculate the natural ground condition soil weight Mb. Note that the excavation radius r, the inspection section length Li, and the unit volume weight of water γw may be values ​​previously stored in the storage device 42, or, if an input operation by an operator via the input / output device 45 is received, values ​​input by the operator may be used. The storage device 42 also stores the unit volume weight γs of soil particles obtained based on the results of previous surveys at multiple boring positions. The storage device 42 may automatically select a value based on the survey results of the boring position closest to the current position of the shield machine 1 and use that value for the above calculation.

[0038] The natural ground weight Mb is calculated using the natural ground moisture content w newly acquired during the excavation process in which the shield machine 1 excavates the inspection section. The number of data points for the natural ground moisture content w acquired using the natural ground moisture content measuring instrument 20 during the excavation process in which the shield machine 1 excavates the inspection section is not particularly limited, but the average value of data acquired multiple times using the natural ground moisture content measuring instrument 20 in one inspection section may be used as the natural ground moisture content w. The measurement data by the natural ground moisture content measuring instrument 20 is passed to the soil volume management device 40 via the communication I / F 41 and can be stored in the storage device 42.

[0039] Next, the discharged soil weight acquisition unit 48 of the soil volume management device 40 acquires the discharged soil weight Md, which is the weight of the loosened soil actually discharged from the shield machine 1 during the excavation process when the shield machine 1 advances through the inspection section (step S02). As described above, the shield machine 1 excavates while taking in the excavated soil from the opening of the cutter head 3 into the chamber 5. The excavated soil is then discharged (carried out) from the rear of the shield machine 1 using a transport mechanism such as the screw conveyor 11 or the belt conveyor 12. In this step, the weight of the excavated soil associated with the inspection section that is actually taken into the chamber 5 from the opening of the cutter head 3 during the excavation process when the shield machine 1 advances through the inspection section and discharged from the machine body 2 in a loosened state is acquired as the discharged soil weight Md. Note that in this step, the discharged soil weight Md is acquired as the weight including the pore water between the soil particles.

[0040] When obtaining the discharged soil weight Md, there are no particular limitations on the specific measuring device or method, as long as it is possible to measure the total weight of the excavated soil taken into the chamber 5 during the excavation process in which the shield machine 1 excavates the inspection section. For example, a belt conveyor 12 with a weighing function may be used, and the weight of the excavated soil corresponding to the inspection section may be measured while the excavated soil is being transported by the belt conveyor 12. Furthermore, the weight of the excavated soil after it has been transported to the soil pit 9 via the belt conveyor 12 may be measured by a separate measuring device.

[0041] Furthermore, instead of directly measuring the weight of the excavated soil actually discharged from the shield machine 1 as described above, the volume of the excavated soil may be measured and converted into weight based on the measurement result and the unit volume weight of the excavated soil to obtain the discharged soil weight Md. Furthermore, for example, cross-sectional shape measurement technology using a line laser light and a digital camera may be used to continuously measure the volume of the excavated soil transported by the belt conveyor 12 in a non-contact manner. Furthermore, the unit volume weight of the excavated soil may be determined by conducting soil tests on samples taken from the excavated soil. The obtained discharged soil weight Md is stored in the memory device 42 of the soil volume management device 40.

[0042] After the soil volume management device 40 acquires the ground condition soil weight Mb and discharged soil weight Md corresponding to the inspection section as described above, the determination unit 49 compares the ground condition soil weight Mb with the discharged soil weight Md and determines whether or not a collapse has occurred in the ground 30 based on the comparison result (step S03). Note that in this embodiment, the order of the above-mentioned steps S01 and S02 is not particularly limited.

[0043] Specifically, the determination unit 49 of the soil volume management device 40 reads out the natural ground soil weight Mb and the discharged soil weight Md from the storage device 42 and compares them. Here, if no collapse occurs in the natural ground 30 during the excavation process in which the shield machine 1 excavates the inspection section, there should be no significant difference between the weight of the excavated soil formed by cutting the natural ground 30 with the cutter head 3 and the weight of the excavated soil taken into the chamber 5 (inside the machine) from the opening of the cutter head 3 (the weight of the discharged soil discharged from the shield machine 1 on the belt conveyor 12). This is because, although the volume of the soil increases after it has been loosened compared to when it was in the natural ground, there is basically no change in the weight of the soil before and after it has been loosened.

[0044] On the other hand, if a collapse occurs in the ground 30 while the shield machine 1 is excavating the inspection section, more soil will be taken into the chamber 5 (inside the machine) than the amount of soil that the shield machine 1 actually cuts into the ground 30 with the cutter head 3. In other words, if a collapse of the ground 30 occurs, an excess amount of soil will be taken into the shield machine 1 and discharged compared to what was originally planned. As a result, the discharged soil weight Md will be significantly greater than the ground state soil weight Mb.

[0045] Therefore, the determination unit 49 of the soil volume management device 40 determines that a collapse of the natural ground 30 has occurred when the discharged soil weight Md is significantly greater than the natural ground weight Mb. As a specific determination method, for example, it may be determined that a collapse of the natural ground 30 has occurred in the inspection section when the value (Md - Mb) obtained by subtracting the natural ground weight Mb from the discharged soil weight Md is greater than a threshold value Tv1. Alternatively, it may be determined that a collapse of the natural ground 30 has occurred in the inspection section when the value (Md / Mb) obtained by dividing the discharged soil weight Md by the natural ground weight Mb is greater than a threshold value Tv2. Moreover, these determination methods may be used in combination to determine whether a collapse of the natural ground 30 has occurred.

[0046] Furthermore, the determination unit 49 of the soil volume management device 40 causes the display device 43 to display the determination result as to whether or not a collapse has occurred in the ground 30 (step S04). A worker can understand whether or not a collapse has occurred in the ground 30 based on the determination result displayed on the display device 43. Then, if a collapse of the ground 30 is detected, measures such as injecting grout into the ground 30 from inside the shield machine 1 are immediately taken.

[0047] Furthermore, in this embodiment, the above-mentioned ground collapse detection process is repeatedly performed each time the shield machine 1 excavates the inspection section length Li (for example, each time one ring of segment 7 is constructed), thereby making it possible to detect whether a collapse has occurred in the ground 30 throughout the construction section of the tunnel.

[0048] As described above, according to the ground collapse detection system 100 of this embodiment, when the shield machine 1 excavates, the presence or absence of a collapse of the ground 30 can be easily detected based on whether there is a significant difference between the theoretical ground state soil weight Mb that should be excavated assuming that there is no collapse in the ground 30, and the loosened soil weight Md that is actually discharged from the shield machine 1.

[0049] In particular, in this embodiment, the natural ground moisture content w is measured by the natural ground moisture content measuring device 20 for each inspection section, and the saturated unit volume weight γ of the natural ground 30 is calculated based on the measured natural ground moisture content w. sat and the theoretical volume of excavated soil V that should be excavated assuming that there is no collapse in the ground 30. The natural ground soil weight Mb is calculated based on b. Here, if the intake of excess soil due to the collapse of the natural ground 30 is not taken into consideration, the natural ground excavation soil volume Vb (volume) is determined from the excavation radius (radius of the cutter head 3) and the inspection section length Li, so calculation errors are unlikely to occur. On the other hand, the saturated unit volume weight γ of the natural ground 30 sat is a factor that is likely to fluctuate in the excavation direction of the shield machine 1. However, in this embodiment, the natural ground moisture content w is measured for each inspection section using the natural ground moisture content measuring device 20 as described above, and therefore the saturated unit volume weight γ of the natural ground 30 that reflects the moisture content state for each inspection section can be calculated. sat can be obtained with high accuracy. As a result, it becomes possible to accurately detect the collapse of the natural ground 30. Furthermore, according to the natural ground collapse detection system 100, the presence or absence of collapse of the natural ground 30 is directly detected by comparing the natural ground state soil weight Mb with the discharged soil weight Md, so it is possible to detect the presence or absence of collapse of the natural ground 30 by simply installing at least one natural ground moisture content measuring device 20 on the shield machine 1, and it is not necessarily necessary to install multiple natural ground moisture content measuring devices 20 at intervals around the circumferential direction of the machine body 2.

[0050] Next, a modification of the above-described embodiment will be described.

[0051] <Variation 1> Here, a modified method for calculating the natural ground soil weight Mb will be described. In this modified method, the natural ground soil weight Mb may be calculated by the following formula (1') instead of the above formula (1).

[0052] Mb=Vb×γ sat +Ma ···(1´) Ma is the weight of the additive material (hereinafter referred to as "additive material weight") added to the natural ground during the excavation process in which the shield machine 1 excavates the inspection section.

[0053] In the shield tunneling method, excavation may be performed while injecting additives from within the machine body 2 toward the natural ground 30 (face). Various types of additives are available, including mineral-based, polymer-based, and foam-based additives. When additives are injected toward the natural ground 30 (face) while the shield machine 1 is excavating, the additives are taken into the chamber 5 together with the excavated soil, and are then finally transported together with the excavated soil by the belt conveyor 12. In such cases, it is preferable to calculate the natural ground soil weight Mb taking into account the additive weight Ma. This makes it possible to compare the discharged soil weight Md with the natural ground soil weight Mb taking into account the additive weight Ma, thereby enabling more accurate detection of the collapse of the natural ground 30.

[0054] <Variation 2> Next, a description will be given of a modified example of the natural ground moisture content measuring instrument 20 installed in the shield machine 1. Fig. 7 is a diagram illustrating the installation mode of the natural ground moisture content measuring instrument 20 according to a modified example of the embodiment. The upper part of Fig. 7 shows the natural ground moisture content measuring instrument 20 installed inside the thin-walled portion 4A, and the lower part shows the natural ground moisture content measuring instrument 20 removed.

[0055] 7 denotes a sleeve pipe that surrounds the natural ground moisture content measuring device 20. As described above, the mode in which the natural ground moisture content measuring device 20 is disposed inside the thin-walled portion 4A of the skin plate 4 is effective from the viewpoint of improving the measurement accuracy of the natural ground moisture content w, but there are cases in which the shield machine 1 excavates while the outer surface of the skin plate 4 is in contact with the natural ground 30, which may cause the thickness of the skin plate 4 to gradually become thinner.

[0056] Therefore, in this modified example, the thickness of the thin-walled portion 4A of the skin plate 4 is measured as needed, for example, by an ultrasonic thickness gauge. Then, when the thickness of the thin-walled portion 4A falls below a predetermined thickness, the ground moisture content measuring device 20 installed inside the thin-walled portion 4A is removed, and a water stop valve 24 and a cover member 26 are attached to the sleeve pipe 23, as shown in the lower part of Figure 7. This prevents groundwater and the like from entering the machine body 2 even if a hole opens in the thin-walled portion 4A. In this modified example, the ground moisture content measuring devices 20 may be installed in advance at multiple locations on the machine body 2, and when the ground moisture content measuring device 20 is removed as described above, another ground moisture content measuring device 20 may be used to measure the ground moisture content w thereafter. Furthermore, when a single ground moisture content measuring device 20 is installed on the machine body 2, the removed ground moisture content measuring device 20 may be reinstalled in another location. In this case, by providing the thin-walled portions 4A and the sleeve pipes 23 in advance at multiple locations on the skin plate 4, it becomes easy to relocate the ground moisture content measuring device 20.

[0057] <Variation 3> Fig. 8 is a diagram illustrating an installation mode of a natural ground moisture content measuring instrument 20 according to another modified example of the embodiment. In the mode shown in Fig. 8, an opening 4B is provided in the skin plate 4 at a location where the natural ground moisture content measuring instrument 20 is to be installed, and a bottomed sleeve pipe 25 is installed to seal the opening 4B. The bottomed sleeve pipe 25 includes a plate-shaped bottom portion 25A that closes the opening 4B and a cylindrical side portion 25B that stands upright from the bottom portion 25A. The natural ground moisture content measuring instrument 20 is fixed inside the bottomed sleeve pipe 25, and the radiation source 21 and the detector 22 are configured to be in close contact with the inner surface of the bottom portion 25A.

[0058] The bottomed sleeve pipe 25 can be inserted and removed within a predetermined range relative to the skin plate 4 in the insertion and removal direction indicated by the arrow in the figure. The upper part of Fig. 8 shows the state when the shield machine 1 is excavating. The lower part of Fig. 8 shows the state when the ground moisture content w is measured by the ground moisture content measuring device 20. As shown in the upper part of Fig. 8, when the shield machine 1 is excavating, the bottomed sleeve pipe 25 is maintained so that it does not protrude from the outer surface of the skin plate 4 (the position of the bottomed sleeve pipe 25 at this time is also referred to as the "retracted position"). This prevents the bottomed sleeve pipe 25 from coming into contact with the ground 30 when the shield machine 1 is excavating.

[0059] On the other hand, when measuring the ground moisture content w using the ground moisture measuring device 20, as shown in the lower part of FIG. 8 , the bottomed sleeve pipe 25 is slid relative to the skin plate 4 so that the bottomed sleeve pipe 25 protrudes from the outer surface of the skin plate 4 (the position of the bottomed sleeve pipe 25 at this time is also referred to as the “protruding position”). For example, when switching the bottomed sleeve pipe 25 from the retracted position to the protruding position, the bottomed sleeve pipe 25 may be pushed outward so that the bottom 25A contacts the ground 30. In this way, by switching the bottomed sleeve pipe 25 from the retracted position to the protruding position and measuring the ground moisture content w with the bottom 25A abutting against the ground 30, the measurement accuracy can be improved. Note that in this modification, the ground moisture content w is measured using the ground moisture measuring device 20 while the shield machine 1 is stopped. For example, the ground moisture content w may be measured after one ring of segments has been excavated, when the segments are being assembled by the erector or when the inner shell is being replaced.

[0060] In this modification, the sliding movement of the bottomed sleeve pipe 25 can be performed using the driving source of a hydraulic jack, but the driving source is not particularly limited. Furthermore, the portions of the bottomed sleeve pipe 25 that slide along the edge of the opening 4B in the skin plate 4, such as the side surface of the bottom 25A and the outer peripheral surface of the side portion 25B, may be provided with sealing members (packing, etc.) to prevent infiltration of groundwater or other water from the outside.

[0061] Although the embodiments of the present invention have been described above, the aspects and modified aspects disclosed in the embodiments can be combined as much as possible. [Explanation of symbols]

[0062] 1. Shield machine 2. Aircraft 3. Cutter head 4. Skin plate 5. Chamber 10. Excavated soil discharge device 20. Ground moisture content measuring instrument 21...ray source 22. Detector 30. Ground 40...Earth volume management device 100. Ground collapse detection system

Claims

1. a ground moisture content measuring device that is installed in a shield machine that excavates the ground in a shield tunneling method and measures the moisture content of the ground by emitting neutron beams toward the ground; a soil volume management device that acquires the natural ground soil weight, which is the weight of soil in the natural ground state that would be excavated assuming that there is no collapse of the natural ground during the excavation process when the shield machine excavates a specified section, and the discharged soil weight, which is the weight of soil in a loosened state that is actually discharged from the shield machine during the excavation process, and determines that a collapse has occurred in the natural ground if there is a significant difference between the natural ground soil weight and the discharged soil weight; Equipped with The soil volume management device calculates the natural ground soil weight based on the natural ground excavation volume, which is the volume of soil in the natural ground that is excavated assuming that there is no collapse of the natural ground during the excavation process, and the saturated unit volume weight of the natural ground calculated based on the moisture content of the natural ground measured by the natural ground moisture content measuring device during the excavation process. Ground collapse detection system.

2. The ground collapse detection system according to claim 1 , wherein the soil volume management device calculates the ground state soil weight according to the following formula (1): Mb=Vb×γ ｓａｔ ・・・(1) gamma ｓａｔ is the saturated unit volume weight of the natural ground corresponding to the predetermined section. Vb is the volume of soil excavated in the natural ground, which is the volume of soil in the natural ground that is excavated assuming that there is no collapse of the natural ground during the excavation process of the shield machine in the specified section.

3. The ground collapse detection system according to claim 2 , wherein the soil volume management device calculates the ground excavation soil volume (Vb) according to the following formula (2): V=πr ２ ×L・・・(2) π is the ratio of the circumference of a circle to its circumference. r is the excavation radius when the shield machine excavates the natural ground. Li is the length of the predetermined section.

4. The soil volume management device calculates the saturated unit volume weight (γ ｓａｔ The system for detecting a natural ground collapse according to claim 2 or 3, wherein the system calculates the natural ground collapse amount. c ｓａｔ =(1+w / 100) / (1 / γs+w / 100 / γw) ・・・(3) where w is the water content of the ground measured by the water content measuring device during the excavation process of the shield machine through the specified section, γw is the unit volume weight of water, and γs is the unit volume weight of soil particles.

5. A ground collapse detection method executed by an earth volume management device of the ground collapse detection system according to any one of claims 1 to 4, comprising: The soil volume management device is Calculate the natural ground soil weight, which is the weight of the soil in the natural ground, based on the natural ground excavation volume, which is the volume of soil in the natural ground that will be excavated assuming that there will be no collapse of the natural ground during the excavation process when the shield machine excavates a predetermined section, and the saturated unit volume weight of the natural ground calculated based on the moisture content measured by the natural ground moisture content measuring device during the excavation process; If there is a significant difference between the weight of the soil in the natural ground and the weight of the discharged soil, which is the weight of the loosened soil actually discharged from the shield machine during the excavation process, it is determined that a collapse has occurred in the natural ground. A method for detecting ground collapse.

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