JP7759614B2 - Material testing method for friction-reducing materials used in construction methods for underground structures - Google Patents

Description

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

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 arranged steel pipes, but an alternative to the pipe roof is the box roof method, as described in Patent Document 1 below.
Patent No. 2789523

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

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

This 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. These joint flanges 6c are fastened together with bolts and nuts 19, adding one piece at a time in the longitudinal direction and burying the required length from the departure shaft 3 to the arrival shaft 4. The second, third, etc. pieces are then buried in sequence alongside the first piece thus buried, lining them up in parallel. In the figure, reference numeral 17 denotes a box cutter for fastening with bolts and nuts 19.

The press-fitting machine 5 has a push-out mechanism using a jack or the like to push out the box-shaped roof cylinder 6.

The arrangement of the box-shaped roof cylinders 6 can be selected appropriately to suit the underground structure to be installed later, such as a gate-shaped arrangement as shown in Figure 13, a straight-line arrangement, or a box-shaped arrangement (not shown).

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.

In the figure, reference numeral 13 denotes a support member for the box-shaped roof cylinder 6, and reference numeral 14 denotes a retaining member for the friction cutter plate 7; these are provided on the departure shaft 3 side, while a platform (receiving stand) 15 is provided on the arrival shaft 4 side.

The small jack 12 is extended, and the underground structure 9 acts as a reaction force to push forward the box roof cylinders 6 one by one, leaving the friction cutter plate 7 behind. Once all the box roof cylinders 6 have advanced, the small jack 12 is retracted and the propulsion jack 10 is extended to excavate the underground structure 9. In the figure, 16 indicates a strut that is interposed between the propulsion jack 10 and the underground structure 9.

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 of the box-shaped roof cylinder 6 has completely emerged into the arrival shaft 4 as shown in Figure 12. Then, the bolts and nuts 19 fastening the joint flanges 6c together are released, the structure is separated lengthwise, and the pieces are removed one by one.

Then, when the tip of the underground structure 9 reaches the arrival shaft 4, the cutting edge 11 and other parts are removed and backfill grouting is performed as appropriate to complete the construction.

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

In addition, the underground structure 9 can be advanced by providing a reaction wall and a center-hole type traction jack on the arrival shaft 4 side, and using this traction jack to pull a traction member made of PC steel wire, one end of which is fixed to the underground structure 9, so that the underground structure 9 can be pulled in from the arrival shaft 4 side.

When constructing underground structures using the box roof method described above, the construction is carried out while the commercial railway line remains in operation 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 advanced to construct the under-track crossing structure.

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

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

The inventors previously proposed and filed a patent application for a construction method for underground structures and a friction-reducing material for use therein, which effectively reduces the friction between the box roof and friction cutter (FC) plates, or between the box periphery and the FC plates, that occurs when the box is pushed and pulled during construction of under-rail crossing structures. This reduces the pushing and pulling force during edge cutting and the impact on the surrounding ground when the box is pushed and pulled.

As shown in Figure 2, this consists of a friction-reducing material 20, consisting of a rigid iron or other sphere or roller covered with a shear-breakable coating material, placed between the box-shaped roof cylinder 6 and the friction cutter plate 7.

The friction-reducing material 20 is made by covering a sphere 21 made of rigid iron or the like with mortar 22 as a shear-breakable coating material. As shown in Figure 3, the mortar 22 forms a hexahedral block shape with a height, width, and depth that match the diameter of the sphere 21.

Although the illustration shows a single sphere 21, the friction-reducing material 20 may also be configured as a block of multiple spheres 21 covered with mortar 22. The friction-reducing material 20 has a rectangular column shape.

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.

These block-shaped friction-reducing materials 20 are placed at intervals between the friction cutter plate 7 and the box-shaped roof cylinder 6.

As shown in Figure 4, instead of the spheres 21, rigid steel rod rollers 23 can also be used.

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

Long rod-shaped friction-reducing materials 20 are placed at intervals across the horizontally arranged box-shaped roof cylinders 6 and are sandwiched between friction cutter plates 7.

In this way, 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, it is possible to reduce the pushing and pulling force during edge cutting and the impact on the surrounding ground when the box is pushed and pulled.

If only spheres or rollers are installed 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. However, due to the influence of train loads and ground pressure, the behavior of the box body during construction becomes extremely unstable. However, the spheres or rollers roll against resistance over fragments of shear-fracturable covering material, preventing the construction from becoming unstable.

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

Furthermore, the FC plate and box-shaped roof do not displace vertically due to the use of rigid iron or other spheres or rollers, so vertical displacement of the track and road can also be suppressed.

Mortar is an ideal covering material that will undergo shear failure due to forced displacement caused by friction, and is therefore ideal in terms of formability and cost.

The action and effect of the friction-reducing material 20 are as described above. When installed, the friction-reducing material 20 can withstand earth pressure due to the strength of its base material, the mortar 22, but when the box is advanced, the base material undergoes shear failure, 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 are no existing methods for identifying the properties of this material.

There is no way to investigate the material properties of the friction-reducing material 20 under the stress conditions at the time of installation. This is because there are no tests for simple shear mode of rock.

The object of the present invention is to overcome the disadvantages of the above-mentioned conventional examples and to provide a material testing method for friction-reducing materials used in underground structure construction methods that allows for the construction of large-width underground structures in the transverse direction beneath railways, roads, etc. without interfering with traffic above. The method also allows for the identification of material properties, such as the ability to receive a compressive force in the vertical direction and undergo simple shear when the box is advanced.

In order to achieve the above-mentioned object, the present invention comprises a base plate on which a test specimen of a friction-reducing material, which is made of spheres 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 attached to the top of the rod is used, in which rectangular prism test specimens are placed symmetrically on the base plate, the test specimen is sandwiched and compressed between the base plate and the upper plate, and while sandwiched, a circumferential displacement is given to the upper plate to transmit a shear force, and the direct load Q and torque T are measured.

According to the present invention, the test specimen can be sheared under a stress state appropriate 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.

In addition, 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.

In addition to the material properties of friction-reducing materials, this invention can also obtain the mechanical properties of hard materials such as rock in simple shear mode.

As described above, the material testing method for friction-reducing materials used in the construction method for underground structures of the present invention can identify the material properties of friction-reducing materials used in the construction method for underground structures, which can be used to excavate large underground structures in the transverse direction beneath railways, roads, etc. without interfering with traffic above. These materials are subjected to a compressive force in the vertical direction and are subject to simple shear when the box is advanced.

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. This is a side view of a construction method for underground structures using friction-reducing materials. FIG. 2 is a perspective view showing an example of a friction reducing material. FIG. 2 is a perspective view showing another example of the friction reducing material of the present invention. 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. 10 is a graph showing the relationship between jack thrust and thrust amount. This is a side view showing the first step of the construction method for an underground structure using the box roof construction method. A side view showing the second step of the construction method for underground structures using the box roof construction method. A side view showing the third step of the construction method for underground structures using the box roof construction method. FIG. 2 is a partial perspective view showing an example of a box-shaped roof cylinder.

The present invention will be described in detail below with reference to the drawings. Fig. 1 is an explanatory diagram showing one embodiment of a material testing device used in a material testing method for friction-reducing materials used in an underground structure construction method of the present invention. In the drawing, reference numeral 25 denotes a test specimen made of a friction-reducing material 20, which has been described above.

The material testing device consists of a base plate 26 on which the test specimen 25 is placed, and an upper plate 27 that faces the base plate 26 and serves as a lid that sandwiches the test specimen 25. While the base plate 26 and upper plate 27 are shown as being disk-shaped, they are not limited to this.

The upper platen 27 has an upward-facing rod 28 in the center, which drives it to move up and down and rotate.

In addition, although not shown, a load meter and torque meter are installed on the top of the rod 28 to measure the direct load Q and torque T.

Anti-slip grooves 29 are formed at the same position on the inner surfaces of the base plate 26 and upper plate 27, which face each other. The grooves 29 are approximately 2 mm wide and are arranged radially toward the center.

To conduct a material test on the friction-reducing material 20, rectangular prism-shaped test specimens 25 are placed symmetrically on the base plate 26. In the illustration, four test specimens 25 are placed radially symmetrically around the axis.

The number of test 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 test specimen, there will be no test specimen 25 on the opposite side to support the upper plate 27, so increasing the axial stress will cause bending to act on the upper plate 27 and rod 28.

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

It is desirable to place the specimen 25 on the groove 29. Torque is applied in the circumferential direction, so if the groove 29 is not present, the specimen may slip and shearing may not be possible.

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

The test specimen 25 is sandwiched between the base plate 26 and upper plate 27 and compressed. 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; the base plate 26 is fixed.

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.

In addition, 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.

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

1...Upper access 2...Steel sheet pile 3...Departure shaft 4...Arrival shaft 5...Press-in machine 6...Box roof cylinder 6c...Joint flange 7...Friction cutter plate 8...Reaction wall 9...Underground structure 10...Pushing jack 11...Cutting edge 12...Small jack 13...Support material 14...Stopping member 15...Receiving base 16...Strut 17...Box punch 19...Bolt, nut 20...Friction reduction material 21...Sphere 22...Mortar 23...Roller 25...Test specimen 26...Base plate 27...Upper plate 28...Rod 29...Groove

Claims (1)

A material testing method for friction-reducing materials used in the construction of underground structures, characterized in that it comprises a base plate on which a test specimen of a friction-reducing material is placed, which is a sphere of hard iron or the like covered with mortar as a shear-fracturable covering material, 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 attached to the top of the rod, in which rectangular prism test specimens are placed symmetrically on the base plate, the test specimen is sandwiched and compressed between the base plate and the upper plate, and 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.