A construction method for controlling large deformation of soft rock in mining tunnels

Abstract

The present invention discloses a construction method for controlling large deformation of soft rock in a mining-based tunnel, comprising the following steps: first, determining the shape and size of the tunnel; second, excavating the mining-based tunnel and determining the over-excavation construction section to perform over-excavation of the tunnel at fixed intervals; third, backfilling the over-excavated surface of the tunnel with foamed lightweight soil; and fourth, supporting and promptly closing the construction surface after the foamed lightweight soil is backfilled. The present invention changes the properties and structure of the surrounding rock by over-excavating the tunnel and backfilling it with foamed lightweight soil, directly blocking the transmission of high ground stress from a structural perspective, thereby achieving the effect of controlling large deformation of the soft rock, and also exerting a good effect on weak rock masses.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel engineering, and in particular to a construction method for controlling large deformation of soft rock in a mining tunnel. Background Art

[0002] Large deformation of soft rock has always been a research focus in underground engineering. Complex geological conditions (such as those under the influence of fault zones) are even more detrimental to the stability of soft rock tunnels. Soft rock refers to a complex rock mechanical medium that can produce significant plastic deformation under specific environmental conditions. Large deformation of soft rock is a deformation and failure phenomenon of the surrounding rock mass under environmental conditions such as ground stress, engineering disturbance and groundwater activity. Its essence is that the ground stress redistribution caused by excavation of the surrounding rock exceeds the yield strength of the rock mass, causing the rock mass to become plastic, the surrounding rock's self-bearing capacity to be lost or partially lost, the deformation cannot be effectively constrained, and the surrounding rock undergoes plastic deformation and failure, resulting in varying degrees of damage to the surrounding rock support.

[0003] In the existing mining method construction, for the control of large deformation of soft rock, methods such as anchor grouting support, increasing the anchor rod length, and reserving deformation are usually adopted. However, there are still shortcomings. For example, for weak rock masses such as phyllite, carbonaceous shale, metamorphic sandstone, etc., they have the characteristics of native structure in structure, and traditional methods such as shotcrete support are difficult to achieve ideal results. Therefore, the present invention proposes a construction method for controlling large deformation of soft rock in mining method tunnels to solve the problems existing in the existing technology. Summary of the Invention

[0004] In response to the above problems, the purpose of the present invention is to propose a construction method for controlling large deformation of soft rock in mining-based tunnels. This construction method for controlling large deformation of soft rock in mining-based tunnels changes the properties and structure of the surrounding rock by over-excavating the tunnel and backfilling it with foamed lightweight soil, directly blocking the transmission of high ground stress from a structural perspective, thereby achieving the effect of controlling large deformation of soft rock and also having a good effect on weak rock masses.

[0005] To achieve the purpose of the present invention, the present invention is implemented through the following technical solutions: A construction method for controlling large deformation of soft rock in a mining tunnel, comprising the following steps:

[0006] Step 1: First determine the actual engineering conditions based on the tunnel construction area, and then determine the shape of the tunnel;

[0007] Step 2: Tunnel excavation is carried out according to the mining method construction process. The risk of large soft rock deformation is determined based on geological surveys and actual site conditions. Tunnel over-excavation is carried out at fixed intervals in construction sections prone to large soft rock deformation.

[0008] Step 3: Backfill the over-excavated surface with foam lightweight soil to complete the backfill construction of the over-excavated surface;

[0009] Step 4: After backfilling, support should be provided and then concrete should be sprayed in time to seal the construction surface.

[0010] A further improvement is that the tunnel shape determined in step 1 is one of circular and horseshoe-shaped, and then the excavation span of the tunnel is determined according to actual design and use needs, and the over-excavation thickness and over-excavation interval size are determined at the same time.

[0011] Further improvements are as follows: the over-excavation thickness is uniformly selected as 50 cm; when the excavated tunnel is a two-lane tunnel or a train tunnel, the over-excavation interval is twice the excavation span size; when the excavated tunnel is a three-lane tunnel, the over-excavation interval is 1.5 times the excavation span size; when the excavated tunnel is a four-lane tunnel, the over-excavation interval is the excavation span size.

[0012] A further improvement is that when the tunnel shape is circular, the cross-section of the over-excavation construction section is an arc with a central angle of 270°, and the bottom arc corresponding to the central angle of 90° is the same as the original tunnel and is not over-excavated.

[0013] A further improvement is that when the tunnel is horseshoe-shaped, the cross-section of the over-excavation construction section is divided into three parts, the upper part is a semicircular arc, the middle part is a rectangle, and the bottom is the invert arch of the original tunnel without over-excavation.

[0014] A further improvement is that when backfilling is performed in step three, lightweight foam soil is quickly poured on the over-excavation surface after each over-excavation portion of the tunnel is completed to quickly complete the sealing of the over-excavation surface.

[0015] A further improvement is that the specific operation of step 4 is to spray concrete on the surface of the foam lightweight soil after backfilling the over-excavation surface, then install the steel mesh and vertical steel arch frame, install anchor rods, and then spray concrete again to complete the closure of the construction surface.

[0016] The beneficial effects of the present invention are as follows: by over-excavating the tunnel and backfilling with foam lightweight soil, the present invention changes the properties and structure of the surrounding rock, directly blocks the transmission of high ground stress from a structural perspective, achieves the effect of controlling large deformation of soft rock, and can also have a good effect on weak rock mass. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flow chart of the construction method of the present invention.

[0018] Figure 2 This is a schematic diagram of the construction dimensions of a circular tunnel in Example 1 of the present invention.

[0019] Figure 3 Schematic diagram of the over-excavation dimensions of a circular tunnel in Example 1 of the present invention.

[0020] Figure 4 Schematic diagram of over-excavation thickness of a circular tunnel in Example 1 of the present invention.

[0021] Figure 5 This is a schematic diagram of the over-excavation interval of a circular tunnel in Example 1 of the present invention.

[0022] Figure 6 This is a schematic diagram of the construction dimensions of a horseshoe-shaped tunnel according to Example 2 of the present invention.

[0023] Figure 7 Schematic diagram of the over-excavation dimensions of a horseshoe-shaped tunnel in Example 2 of the present invention.

[0024] Figure 8 This is a schematic diagram of the over-excavation thickness of a horseshoe-shaped tunnel in Example 2 of the present invention.

[0025] Figure 9 This is a schematic diagram of the over-excavation interval of a horseshoe-shaped tunnel in Example 2 of the present invention. DETAILED DESCRIPTION

[0026] In order to deepen the understanding of the present invention, the present invention will be further described in detail below with reference to the examples. The examples are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0027] The tunnels applicable to the present invention include single-hole double-track tunnels and double-hole single-track tunnels. When used in double-hole tunnels, the over-excavation range of the two holes should be staggered during construction to avoid interference.

[0028] Example 1

[0029] according to Figure 1-Figure 5 As shown, this embodiment provides a construction method for controlling large deformation of soft rock in a mining tunnel. The tunnel shape in this embodiment is a circular tunnel.

[0030] The actual working conditions are determined through geological surveys, and circular tunnels are selected according to engineering design. Figure 2 Shown are the dimensions of a circular tunnel of diameter D, which is one of the most common tunnel shapes in engineering and is representative.

[0031] The tunnel is constructed using the mining method. Based on geological surveys and actual on-site conditions, over-excavation of the tunnel is carried out in construction sections where large deformation of soft rock is likely to occur. Figure 3 The figure shows the overbreak range of a circular tunnel. During the overbreak section, the actual excavation section of the circular tunnel is based on the tunnel center, with an arc of diameter D1 and a central angle of 270°. The bottom arc, corresponding to the lower 90° central angle, is constructed according to the original tunnel dimensions, without overbreak.

[0032] Figure 3 The figure also includes the overbreak range of the tunnel, D x The distance of tunnel over-excavation is determined by the size of the tunnel. The larger the size, the larger the over-excavation range. xThe value is selected on the basis of ensuring the anchoring effect of the system anchor rod. The length of the system anchor rod required for tunnels of different sizes is different. At the same time, the surrounding rock grade will also affect the length of the system anchor rod (determined according to the "Highway Tunnel Design Rules"). The specific lengths of system anchor rods for different numbers of lanes are shown in Tables 1 to 3 below.

[0033] Table 1 Reference table of anchor rod lengths for dual-lane tunnel systems

[0034]

[0035] Table 2 Reference table of anchor rod length for three-lane tunnel system

[0036]

[0037]

[0038] Table 3 Reference table of anchor rod length for four-lane tunnel system

[0039]

[0040] For Grade I surrounding rock, the minimum value of Grade II surrounding rock is uniformly taken to ensure stability. For Grade VI surrounding rock, it needs to be determined according to specific conditions. For the rest, the maximum value of the system anchor length is taken to ensure the stability of the surrounding rock.

[0041] Figure 4 The figure shows the tunnel's overcut thickness, which was selected as 50cm. This was chosen for economic and construction convenience, while ensuring effective operation.

[0042] Figure 5 The figure shows the overbreak interval for a tunnel, which is determined by the tunnel size. For two-lane tunnels and railway tunnels, the overbreak interval is twice the tunnel excavation span; for three-lane tunnels, the overbreak interval is 1.5 times the tunnel excavation span; and for four-lane tunnels, the overbreak interval is the tunnel excavation span.

[0043] After over-excavation, foam lightweight soil is used for backfilling. When backfilling the over-excavation surface with foam lightweight soil, excavation and pouring backfill should be carried out in a timely manner to complete the closure of the over-excavation surface of the tunnel as soon as possible.

[0044] After the over-excavation surface is closed, concrete is sprayed on the surface of the foam lightweight soil, steel mesh is installed, steel arch frames are erected, anchor rods are installed, and concrete is sprayed again to complete the closure of the construction surface in a timely manner.

[0045] Then, other normal construction sections will be constructed using conventional mining methods until the tunnel is completed.

[0046] Example 2

[0047] according to Figure 1 and Figure 6-Figure 9As shown, this embodiment provides a construction method for controlling large deformation of soft rock in a mining tunnel. The tunnel shape in this embodiment is a horseshoe-shaped tunnel.

[0048] The actual working conditions are determined through geological survey and the horseshoe-shaped tunnel is selected according to the engineering design. Figure 6 Shown are the dimensions of a four-center horseshoe tunnel with radii R1, R2, and R3, which is one of the most common tunnel shapes in engineering and is representative.

[0049] The tunnel is constructed using the mining method. Based on geological surveys and actual on-site conditions, over-excavation of the tunnel is carried out in construction sections where large deformation of soft rock is likely to occur. Figure 7 The figure shows the overexcavation range of a four-center circular horseshoe tunnel. During the overexcavation construction section, the actual excavation cross-section of the four-center circular horseshoe tunnel is divided into three parts. The upper section is a semicircular arc with a diameter of D1, based on the center of the tunnel's upper semicircle. The middle section is a rectangle with a length of D1 and a height of H, where H is the height from the center of the tunnel's upper semicircle to the top of the invert. The bottom of the overexcavation section is flush with the top of the invert. The bottom invert section is excavated according to the original tunnel dimensions, with no overexcavation. The overexcavation ranges for other multi-center circular horseshoe tunnels refer to the overexcavation ranges for four-center circular horseshoe tunnels.

[0050] Figure 7 The figure also includes the overbreak range of tunnels of different sizes, D x The distance of tunnel over-excavation is determined by the size of the tunnel. The larger the size, the larger the over-excavation range. x The value of is selected on the basis of ensuring the anchoring effect of the system anchor rod. The length of the system anchor rod required for tunnels of different sizes is different. At the same time, the surrounding rock grade will also affect the length of the system anchor rod (determined according to the "Highway Tunnel Design Rules"). The maximum length of the system anchor rod is taken to ensure the stability of the surrounding rock. For details, see Tables 1 to 3 of the embodiment.

[0051] Figure 8 The figure shows the tunnel's overcut thickness, which was selected as 50cm. This was chosen for economic and construction convenience, while ensuring effective operation.

[0052] Figure 9 The figure shows the overbreak interval for a tunnel, which is determined by the tunnel size. For two-lane tunnels and railway tunnels, the overbreak interval is twice the tunnel excavation span; for three-lane tunnels, the overbreak interval is 1.5 times the tunnel excavation span; and for four-lane tunnels, the overbreak interval is the tunnel excavation span.

[0053] After over-excavation, foam lightweight soil is used for backfilling. When backfilling the over-excavation surface with foam lightweight soil, excavation and pouring backfill should be carried out in a timely manner to complete the closure of the over-excavation surface of the tunnel as soon as possible.

[0054] After the over-excavation surface is closed, concrete is sprayed on the surface of the foam lightweight soil, steel mesh is installed, steel arch frames are erected, anchor rods are installed, and concrete is sprayed again to complete the closure of the construction surface in a timely manner.

[0055] Then, other normal construction sections will be constructed using conventional mining methods until the tunnel is completed.

[0056] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various improvements and modifications may be proposed without departing from the principles of the present invention, and such improvements and modifications should be considered within the scope of protection of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A construction method for controlling large deformation of soft rock in a mining tunnel, characterized in that: The following steps are involved: Step 1: First determine the actual engineering conditions based on the tunnel construction area, and then determine the shape of the tunnel; The tunnel shape is determined to be either circular or horseshoe-shaped. The tunnel excavation span is then determined based on actual design and use requirements. The over-excavation thickness and over-excavation interval are also determined. The over-excavation thickness is uniformly set to 50 cm. When the tunnel shape is circular, the cross section of the over-excavation construction section is an arc with a central angle of 270°, and the bottom arc corresponding to the central angle of 90° is the same as that of the original tunnel and does not over-excavate; When the tunnel is horseshoe-shaped, the cross section of the over-excavation construction section is divided into three parts, the upper part is a semicircular arc, the middle part is a rectangle, and the bottom part is the invert arch of the original tunnel without over-excavation; When the tunnel over-excavation distance is in Grade I surrounding rock, the minimum value of Grade II surrounding rock is used to ensure stability. When it is in Grade VI surrounding rock, the value needs to be determined according to the specific situation. For other cases, the maximum length of the system anchor bolt is used to ensure the stability of the surrounding rock. Step 2: Tunnel excavation is carried out according to the mining method construction process. The risk of large soft rock deformation is determined based on geological surveys and actual site conditions. Tunnel over-excavation is carried out at fixed intervals in construction sections prone to large soft rock deformation. Step 3: Backfill the over-excavated surface with foam lightweight soil to complete the backfill construction of the over-excavated surface; Step 4: After backfilling, support should be provided and then concrete should be sprayed in time to seal the construction surface.

2. A construction method for controlling large deformation of soft rock in a mining tunnel according to claim 1, characterized in that: When the excavated tunnel is a two-lane tunnel or a train tunnel, the over-excavation interval is twice the excavation span size. When the excavated tunnel is a three-lane tunnel, the over-excavation interval is 1.5 times the excavation span size. When the excavated tunnel is a four-lane tunnel, the over-excavation interval is the excavation span size.

3. The construction method for controlling large deformation of soft rock in a mining tunnel according to claim 1, characterized in that: When backfilling is performed in step 3, lightweight foam soil is quickly poured on the over-excavation surface after each over-excavation portion of the tunnel is completed, so as to quickly complete the sealing of the over-excavation surface.

4. The construction method for controlling large deformation of soft rock in a mining tunnel according to claim 1, characterized in that: The specific operation of step 4 is to backfill the over-excavation surface, spray concrete on the surface of the foam lightweight soil, then install the steel mesh and vertical steel arch frame, install anchor rods, and then spray concrete again to complete the closure of the construction surface.

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