Material testing method for friction-reducing materials used in construction methods for underground structures

Abstract

To provide a material testing device of a friction reducing material used for an execution method of an underground structure, and a material testing method, capable of specifying a property of material which receives compression force in a vertical direction of the friction reducing material used for an execution method of an underground structure capable of executing it without causing troubles when excavating and constructing an underground structure of a great width in a transverse direction in the underground of a railway, road, and the like, and is simply sheared when a box body is advanced.SOLUTION: A material testing device is composed of a pedestal 26 on which a test specimen 25 is placed, and an upper board 27 that opposes to the pedestal 26 and sandwiches the test specimen 25. The upper board 27 has a rod 28, and is driven to vertically move and rotate by the rod. A torque meter that becomes a load meter is installed in an upper part of the rod 28, thereby measuring a direct load Q and torque T.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a material testing method for friction-reducing materials used in underground structure construction methods that enable construction of large-width underground structures by excavating them transversely beneath the ground below railways, roads, etc. without interfering with traffic above. [Background technology]

[0002] Excavating a large underground structure transversely beneath a railway, road, or other structure requires protective work to support the traffic above. One way to do this is to install a pipe roof, which consists of horizontally aligned steel pipes, but an alternative to the pipe roof is the box roof method, as described in Patent Document 1 below. [Patent Document 1] Patent No. 2789523

[0003] As shown in Figure 7, this involves constructing a departure shaft 3 and an arrival shaft 4 by driving steel sheet piles 2 beside an overhead transportation 1 such as a railway, and installing a press-in machine 5 inside the departure shaft 3 to press a box-shaped roof cylinder 6 into the arrival shaft 4, thereby forming a roof as a protective work.

[0004] The box-shaped roof cylinder 6 is a box-shaped cylinder made of steel pipe with a substantially square cross section, and has a flat friction cutter plate (hereinafter referred to as FC plate) 7 mounted on the top surface (see Figure 10).

[0005] Such a box-shaped roof cylinder 6 is made by pressing in unit cylinders one by one, and as shown in Figure 14, joint flanges 6c are formed at the ends, and these joint flanges 6c are fastened together with bolts and nuts 19 to add one piece at a time in the longitudinal direction, and the required length from the departure shaft 3 to the arrival shaft 4 is buried, and then the second, third, etc. are buried in sequence in parallel with the first buried one. In the figure, 17 is a box punch for fastening with bolts and nuts 19.

[0006] The press-fitting machine 5 has a push-out mechanism for the box-shaped roof cylindrical body 6 using a jack or the like.

[0007] The arrangement of the box-shaped roof cylinders 6 can be appropriately selected according to the underground structure to be installed later, such as a gate-shaped arrangement as shown in FIG. 13, a straight-line type, a box-shaped arrangement, etc. (not shown).

[0008] Next, as shown in Figure 8, a reaction wall 8 and an underground structure 9 consisting of a concrete box are set inside the starting shaft 3, a propulsion jack 10 is installed between the reaction wall 8 and the underground structure 9, a cutting edge 11 is installed at the tip of the underground structure 9, and a small jack 12 is interposed between the tip of the underground structure 9 and the box-shaped roof cylinder 6.

[0009] In the figure, 13 is a support material for the box-shaped roof cylinder 6, 14 is a stopper member for the friction cutter plate 7, and these are provided on the departure shaft 3 side, while a stand (receiving base) 15 is provided on the arrival shaft 4 side.

[0010] The small jacks 12 are extended, and the underground structure 9 acts as a reaction force to push forward the box roof cylinders 6 one by one while leaving the friction cutter plates 7 behind. Once all of the box roof cylinders 6 have advanced, the small jacks 12 are retracted and the propulsion jacks 10 are extended to excavate the underground structure 9. In the figure, 16 denotes a strut that is interposed between the propulsion jacks 10 and the underground structure 9.

[0011] In this way, the advancement of the box-shaped roof cylinder 6 and the advancement of the underground structure 9 are alternately repeated until one unit piece of the box-shaped roof cylinder 6 has completely emerged into the arrival shaft 4 as shown in Figure 12, and then the fastening of the bolts and nuts 19 between the joint flanges 6c is released, the cylinder is separated lengthwise, and the pieces are removed one by one.

[0012] Then, when the tip of the underground structure 9 reaches the arrival shaft 4, the cutting edge 11 and the like are removed and backfill grouting is carried out as appropriate to complete the construction.

[0013] The underground structure 9 may be constructed by successively lowering precast concrete boxes into the starting shaft 3 and connecting them together, or by pouring concrete inside the starting shaft 3 to extend the required length.

[0014] In addition, with regard to the method of propelling the underground structure 9, a reaction wall and a center-hole type traction jack can be provided on the side of the arrival shaft 4, and the underground structure 9 can be pulled in from the side of the arrival shaft 4 by using this traction jack to pull a traction member made of PC steel wire whose one end is fixed to the underground structure 9.

[0015] In the construction of underground structures using the box roof method described above, the construction is carried out while the commercial railway line remains running directly above the site. Therefore, a box roof is installed in the ground beneath the tracks to provide temporary protection, and then a concrete box (box culvert) is pushed in to construct the under-track crossing structure.

[0016] However, in recent years, as the cross section of the box has become larger in under-track crossing construction methods, the box thrust and traction forces have increased, and large frictional forces are generated at the interface between the box and the ground, so it is necessary to ensure thrust using multiple jacks.

[0017] In particular, in the construction method of replacing a box roof installed in a crossing section with a box body, when re-pushing a box roof that has been installed in the crossing section for a long time (pushing the box body), frictional resistance caused by the consolidation of the surrounding ground requires an unexpected amount of thrust, which can have an impact (vibration and noise) on the surrounding ground when cutting the edge or pushing / towing the box body.

[0018] The inventors have previously proposed and filed a patent application for a construction method for underground structures and a friction-reducing material to be used therein, which can reduce the pushing and pulling force when cutting edges and the impact on the surrounding ground when the box is pushed and pulled by effectively reducing the friction between the box roof and the friction cutter (FC) plate, or between the box periphery and the FC plate, that occurs when the box is pushed and pulled during construction of under-rail crossing structures.

[0019] As shown in Figure 2, this is a friction reduction material 20 consisting of a ball or roller made of hard iron or the like and covered with a covering material that can be sheared, placed between a box-shaped roof cylinder 6 and a friction cutter plate 7.

[0020] The friction reduction material 20 is a sphere 21 made of hard iron or the like, covered with mortar 22 as a shear-breakable covering material, and as shown in Figure 3, the mortar 22 is shaped into a hexahedral block with a height, width, and depth that match the diameter of the sphere 21.

[0021] Although one sphere 21 is shown in the drawing, the friction reducing material 20 may be configured as a block in which a plurality of spheres 21 are covered with mortar 22. The friction reducing material 20 has a prismatic shape.

[0022] When molding the friction reducing material 20, the spheres 21 are placed in a mold, and then the mold is filled with mortar 22, which is then removed from the mold after hardening.

[0023] The block-shaped friction reducing material 20 is disposed between the friction cutter plate 7 and the box-shaped roof cylinder 6 with a gap therebetween.

[0024] As shown in FIG. 4, instead of the balls 21, rollers 23 made of steel rods can be used as rigid members.

[0025] In this case, the mortar 22 may be in the shape of a hexahedron having a height, width, and depth that match the diameter of the roller 23, or the roller 23 may be made long and covered with mortar 22 to form a long rod-like shape.

[0026] The friction reducing materials 20 in the form of long rods are placed at intervals across the box-shaped roof cylinders 6 arranged side by side, and are sandwiched between friction cutter plates 7.

[0027] In this way, during the construction of under-rail crossing structures, the friction between the box roof and the friction cutter (FC) plate, or the friction between the box periphery and the FC plate, which occurs when the box is pushed and pulled, can be effectively reduced, thereby reducing the pushing and pulling force when cutting the edge and the impact on the surrounding ground when the box is pushed and pulled.

[0028] If only spheres or rollers are placed at the interface between the FC plate and the box roof, the interfacial friction between the ground and the box body can be reduced to almost zero, but the behavior of the box body during construction becomes extremely unstable due to the influence of train loads and ground pressure.However, the spheres or rollers roll over the fragments of covering material that can be shear-fractured, encountering resistance, thereby preventing the construction from becoming unstable.

[0029] In addition, the friction reducing material can be formed into a block by covering it with a shear-breakable covering material, and can be stably installed between the box roof and the friction cutter plate without the spheres or rollers rolling out.

[0030] Furthermore, the FC plate and box roof do not displace in the vertical direction due to the use of rigid iron balls or rollers, so vertical displacement of the track and road can also be suppressed.

[0031] Mortar is an ideal covering material that will undergo shear failure due to forced displacement caused by friction, and is therefore suitable in terms of formability and cost. Summary of the Invention [Problem to be solved by the invention]

[0032] The action and effect of the friction reducing material 20 are as described above. When the friction reducing material 20 is installed, it can withstand earth pressure due to the strength of the base material, mortar 22, but when the box is advanced, the base material undergoes shear failure, which has the effect of reducing frictional resistance. At this time, it is subjected to a compressive force from the vertical direction, and undergoes simple shear when the box is advanced. There is no existing method for identifying the properties of this material.

[0033] There is no way to investigate the material properties of the friction reducing material 20 under the stress state at the time of installation, because there are no tests for simple shear mode of rock.

[0034] The object of the present invention is to eliminate the disadvantages of the above-mentioned conventional examples and to provide a material testing method for friction-reducing materials used in construction methods for underground structures that can be used in construction methods for underground structures that can be constructed without interfering with overhead traffic when excavating large-width underground structures in a transverse direction below the ground for railways, roads, etc., and that can identify the material properties of the friction-reducing materials that are subjected to a compressive force in the vertical direction and are subjected to simple shear when the box is advanced. [Means for solving the problem]

[0035] In order to achieve the above object, the present invention provides: A friction-reducing material made by covering a sphere of hard iron or other material with mortar as a shear-breakable coating. The test consists of a base plate on which the test specimen is placed and an upper plate facing the base plate, sandwiching the specimen in between. The upper plate has a rod that moves up and down and rotates with the rod. A material testing device with a load meter and torque meter attached to the top of the rod is used, and a rectangular prism test specimen is placed symmetrically on the base plate. The test specimen is sandwiched between the base plate and the upper plate and compressed. While sandwiched, a circumferential displacement is applied to the upper plate to transmit a shear force, and the direct load Q and torque T are measured.

[0036] According to the present invention, the test specimen can be sheared under a stress state that corresponds to the construction conditions, and by measuring the direct load Q and torque T, the friction coefficient and material properties of the friction-reducing material can be obtained from the ratio of the measured shear stress to the direct stress.

[0037] Furthermore, the present invention can obtain deformation and strength characteristics in simple shear mode, and can adjust the failure mode by increasing or decreasing the normal stress.

[0038] The present invention can acquire not only the material properties of friction-reducing materials, but also the mechanical properties of hard materials such as rocks in simple shear mode. [Effects of the Invention]

[0039] As described above, the material testing method for friction-reducing materials used in the construction method of underground structures of the present invention can identify the material properties of friction-reducing materials used in the construction method of underground structures, which can be used to excavate and construct large-width underground structures in the transverse direction below the ground such as railways and roads without interfering with traffic above, such as being subjected to compressive force in the vertical direction and being subjected to simple shear when the box is advanced. [Brief explanation of the drawings]

[0040] [Figure 1] 1 is an explanatory diagram showing one embodiment of a material testing device for a friction reducing material used in the construction method for an underground structure of the present invention. FIG. [Figure 2] This is a side view of a construction method for underground structures using friction-reducing materials. [Figure 3] FIG. 2 is a perspective view showing an example of a friction reducing material. [Figure 4] FIG. 2 is a perspective view showing another example of the friction reducing material of the present invention. [Figure 5] This is an explanatory diagram showing the change in the construction method from when the friction-reducing material is installed to when the box is advanced. [Figure 6] 10 is a graph showing the relationship between jack thrust and thrust amount. [Figure 7] This is a side view showing the first step of the construction method for underground structures using the box roof construction method. [Figure 8] This is a side view showing the second step of the construction method for underground structures using the box roof construction method. [Figure 9] This is a side view showing the third step of the construction method for underground structures using the box roof construction method. [Figure 10] FIG. 1 is a partial perspective view showing an example of a cylindrical body for a box-shaped roof. DETAILED DESCRIPTION OF THE INVENTION

[0041] The present invention will be described in detail below with reference to the drawings. Used in material testing methods1 is an explanatory diagram showing one embodiment of a material testing device, in which 25 is a test specimen made of a friction reducing material 20, which has been described above.

[0042] The material testing apparatus comprises a base plate 26 on which a specimen 25 is placed, and an upper plate 27 as a cover that faces the base plate 26 and sandwiches the specimen 25. The base plate 26 and the upper plate 27 are shown in the figure as being disk-shaped, but are not limited to this.

[0043] The upper platen 27 has an upward rod 28 at its center, and is driven by this rod 28 to move up and down and rotate.

[0044] Although not shown, a load meter and a torque meter are installed on the top of the rod 28 to measure the direct load Q and torque T.

[0045] Anti-slip grooves 29 were formed at the same positions on the inner surfaces of the base plate 26 and the upper plate 27. The grooves 29 were about 2 mm wide and were formed to radiate toward the center.

[0046] To conduct a material test on the friction reducing material 20, rectangular columnar specimens 25 are placed symmetrically on a base plate 26. In the drawing, four specimens 25 are placed radially symmetrically about an axis.

[0047] The number of specimens 25 to be installed is not limited to four, but the reason for installing them symmetrically is simply to prevent instability. For example, if there is only one specimen, there is no specimen 25 on the opposite side to support the upper plate 27, so if the axial stress is increased, bending will act on the upper plate 27 and rods 28.

[0048] When bending is applied to the rod 28, friction occurs in the rod 28, and part of the load acts on the device rather than on the specimen 25, making it impossible to obtain accurate strength and deformation characteristics.

[0049] It is desirable to place the specimen 25 on the groove 29. Since torque is applied in the circumferential direction, if there is no groove 29, the specimen may slip and shearing may not be possible.

[0050] The base plate 26 and the upper plate 27 serve to transmit compressive and shear forces to the specimen 25 through the rigid plates.

[0051] The test piece 25 is sandwiched between the base plate 26 and the upper plate 27 and compressed, and while sandwiched, the upper plate 27 is displaced in the circumferential direction to transmit shear force, and the direct load Q and torque T are measured. Only the upper plate 27 is movable, and the base plate 26 is fixed.

[0052] By measuring the direct load Q and torque T, the direct stress σ = Q / (nLW) (n is the number of specimens) and shear stress τ = F / (nLW) = T / {(nLW)(d+1 / 2)} can be calculated according to the soil cover.

[0053] Furthermore, by measuring the rotation angle θ and vertical displacement △H at the top of the rod 28, it is possible to measure the shear strain θ and the normal strain ε = △H / H, and it is also possible to calculate the shear modulus G = τ / γ and Young's modulus E = ff / ε. The friction constant of the friction-reducing material can be calculated as τ / σ using the peak stress.

[0054] The material testing device can also be applied to rock materials for which simple shear mode mechanical testing methods have not yet been established. [Explanation of symbols]

[0055] 1…Upper traffic 2…Steel sheet pile 3...Departure shaft 4...Arrival shaft 5...Press-fitting machine 6...Box roof cylinder 6c...Joint flange 7...Friction cutter plate 8…Reaction wall 9…Underground structure 10...Propulsion jack 11...Cutting edge 12...Small jack 13...Support material 14: Stop member 15: Receiving base 16...Strut 17...Unboxed 19...Bolts and nuts 20...Friction reducing material 21...Sphere 22...Mortar 23...Collo 25...Test piece 26...Base plate 27...Upper plate 28...Rod 29...Groove

Claims

[Claim 1] A material testing method for friction-reducing materials used in construction methods for underground structures, comprising a base plate on which a test specimen of friction-reducing material, which is a sphere of hard iron or the like covered with mortar as a shear-breakable covering material, is placed, and an upper plate facing the base plate and sandwiching the test specimen therebetween, the upper plate having a rod which moves up and down and rotates by the rod, and a material testing device having a load meter and a torque meter installed on the top of the rod, in which rectangular prism test specimens are placed symmetrically on the base plate, the test specimens are sandwiched and compressed between the base plate and the upper plate, a circumferential displacement is applied to the upper plate while sandwiched, thereby transmitting a shear force, and the direct load Q and torque T are measured.

Images