Pre-support cushion structure parameter determination method and system, and construction method

Abstract

This invention relates to the field of support systems. To achieve quantitative design of pre-supported buffer structures, it provides a method, system, and construction method for determining the parameters of pre-supported buffer structures. First, a target for blasting energy attenuation is preset based on the critical failure stress of the surrounding rock. Then, based on the one-dimensional stress wave propagation theory and the multi-layer medium transmission coefficient formula, the material and geometric parameters of the elastic buffer layer and the pre-supported concrete layer are calculated. This achieves quantitative design of the pre-supported buffer structure, making the vibration reduction effect predictable, controllable, and optimizable. Based on the design parameters, an integrated construction process of "static pre-excavation—elastic layer laying—concrete layer pouring—drilling and blasting excavation" is implemented, placing the initial support (concrete layer) before drilling and blasting excavation, effectively improving the support effect.

Description

Technical Field

[0001] This invention relates to the field of support, specifically a method, system, and construction method for determining parameters of a pre-supported buffer structure. Background Technology

[0002] Due to its wide geological adaptability and low cost, the drill-and-blast method remains the dominant construction method for hard rock tunnel excavation and is widely used in railway tunnels, highway tunnels, hydraulic tunnels and mine roadways.

[0003] However, the inherent drawbacks of the drill-and-blast method are also very prominent: the shock waves and vibrations generated by blasting operations will inevitably disturb the surrounding rock of the tunnel, leading to damage to the surrounding rock, expansion of the loose zone, damage to the support structure, and even inducing disasters such as rock bursts and collapses.

[0004] Currently, the vibration reduction measures commonly used in engineering practice mainly include the following categories:

[0005] (1) Pre-splitting blasting

[0006] A row of closely spaced blast holes is detonated along the tunnel's design outline to create a pre-crack, which blocks the propagation of stress waves generated by the main blasting zone to the retained rock mass. This method can reduce vibration by 20%-50%, but it has the following problems: the pre-crack blasting itself is also a blasting operation, which will generate new disturbances; the formation quality of the pre-crack is greatly affected by geological conditions; for deeply buried high-stress areas, the pre-crack may become a stress concentration point, inducing rockburst.

[0007] (2) Vibration damping holes

[0008] One or more rows of unloaded holes are drilled between the blasting zone and the retained rock mass, utilizing the hole interface to reflect and scatter the blasting stress waves. This method is structurally simple, but its vibration reduction effect is limited (usually 10%-30%), and the increased number of holes increases construction costs and time.

[0009] (3) Segmented delayed blasting

[0010] By precisely controlling the detonation sequence and time interval of each borehole, the amount of explosive charge in a single stage can be kept within a small range, reducing the peak value of blasting vibration. This is currently the most widely used vibration reduction technology, but its effectiveness is limited by factors such as the reliability of the detonation network and the accuracy of the detonators, and it cannot fundamentally eliminate the generation of stress waves.

[0011] (4) Blasting after advance support

[0012] After implementing reinforcement measures such as advanced pipe roofing and advanced small-diameter pipe grouting in front of the tunnel face, blasting is carried out. This method can improve the self-stabilizing capacity of the surrounding rock, but the support operation itself is time-consuming (often several hours to several days), and it cannot solve the direct impact of blasting vibration on the surrounding rock of the excavated section.

[0013] (5) Vibration-damping blasting of flexible cushion layer

[0014] A flexible pad (such as air, water, or plastic pipe) is placed between the blast hole and the explosive to reduce the efficiency of energy transfer from the explosion to the rock mass through impedance mismatch.

[0015] For vibration damping blasting using flexible cushion layers, the following problems exist:

[0016] (1) Only the local vibration reduction at the borehole scale is considered, without considering the overall buffer structure of the tunnel face;

[0017] (2) There is a lack of systematic parameter design methods, and the parameters of flexible pads (thickness, material) are usually selected based on experience;

[0018] (3) The critical failure stress of the surrounding rock was not taken as the design target, and the vibration reduction effect was out of sync with the requirements of surrounding rock protection;

[0019] (4) Initial support is still lagging behind blasting, and the surrounding rock is in an unsupported state during the blasting process;

[0020] (5) The energy transmitted to the rock mass in the blasting area is reduced, resulting in a waste of blasting energy. Summary of the Invention

[0021] To achieve quantitative design of pre-supported buffer structures, this invention provides a method, system, and construction method for determining the parameters of pre-supported buffer structures.

[0022] The technical solution adopted by the present invention to solve the above problems is:

[0023] On one hand, the present invention provides a method for determining the parameters of a pre-supported buffer structure, comprising:

[0024] Step 1: Determine the design input parameters, including the surrounding rock density. Longitudinal wave velocity of surrounding rock Tensile strength of surrounding rock Allowable peak stress of surrounding rock and the original peak blasting stress ;

[0025] Step 2, according to Calculate the target energy decay rate;

[0026] Step 3: Determine the material combination for the pre-supported buffer structure;

[0027] Step 4: Calculate the transmittance coefficient and energy transmittance. ;

[0028] Step 5, if If the thickness is sufficient, then determine the thickness of the pre-support buffer structure material; otherwise, adjust the pre-support buffer structure material until the requirements are met. .

[0029] Furthermore, the pre-supported buffer structure material combination consists of an elastic layer and a concrete layer.

[0030] Furthermore, in step 4, the transmission coefficient when the wave enters medium j from medium i. , , These are the wave impedances corresponding to media i and j, respectively;

[0031] Energy transmittance , The transmission coefficient is the wave's velocity as it travels from the rock mass to be excavated into the elastic layer. Let be the transmission coefficient of the wave as it travels from the elastic layer into the concrete layer. is the transmission coefficient when a wave enters the surrounding rock from the concrete layer.

[0032] Furthermore, in step 5, the specific thickness of the pre-supported buffer structure material is determined as follows:

[0033] Elastic layer thickness , This is the dominant frequency wavelength of the blast stress wave in the elastic layer;

[0034] Concrete layer thickness and P is the surrounding rock pressure, and R is the tunnel radius. This is the design value for the compressive strength of concrete.

[0035] Furthermore, the elastic layer is made of polyurethane foam, rubber pads, or closed-cell foam boards.

[0036] Furthermore, k is a preset coefficient.

[0037] Furthermore, the value of k ranges from 0.3 to 0.5.

[0038] On the other hand, the present invention provides a system for determining the parameters of a pre-supported buffer structure, comprising:

[0039] The input parameter determination unit is used to determine the design input parameters, including the surrounding rock density. Longitudinal wave velocity of surrounding rock Tensile strength of surrounding rock Allowable peak stress of surrounding rock and the original peak blasting stress ;

[0040] The target energy decay rate calculation unit, based on Calculate the target energy decay rate;

[0041] Pre-support buffer structure material combination unit, used to determine the pre-support buffer structure material combination;

[0042] The energy transmittance calculation unit is used to calculate the transmittance coefficient and energy transmittance. ;

[0043] Thickness determination element, if If the thickness of the pre-support buffer structure material is sufficient, then determine the thickness of the pre-support buffer structure material; otherwise, adjust the pre-support buffer structure material until the requirements are met. .

[0044] The present invention also provides a construction method, comprising:

[0045] Step a: Determine the thickness of the pre-support buffer structure material using the pre-support buffer structure parameter determination method;

[0046] Step b: Static pre-excavation to form a free face;

[0047] Step c: Set up a pre-supported buffer structure;

[0048] Step d: Excavation using the drill and blast method.

[0049] Further, step c includes: laying an elastic buffer layer and pouring a concrete layer.

[0050] The advantages of this invention compared to existing technologies are as follows: First, it presets the blasting energy attenuation target based on the critical failure stress of the surrounding rock; then, based on the one-dimensional stress wave propagation theory and the multi-layer medium transmission coefficient formula, it back-calculates and determines the material and geometric parameters of the elastic buffer layer and the pre-supported concrete layer; this achieves quantitative design of the pre-supported buffer structure, making the vibration reduction effect predictable, controllable, and optimizable. Based on the design parameters, it implements an integrated construction process of "static pre-excavation—elastic layer laying—concrete layer pouring—drilling and blasting excavation," placing the initial support (concrete layer) before drilling and blasting excavation, effectively improving the support effect. Attached Figure Description

[0051] Figure 1 The flowchart below shows the method for determining the parameters of the pre-supported buffer structure corresponding to the embodiment.

[0052] Figure 2 This is a cross-sectional view of the pre-supported buffer structure;

[0053] Attached diagram labels: 1 represents the rock mass to be excavated, 2 represents the elastic layer, 3 represents the concrete layer, and 4 represents the surrounding rock. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0055] like Figure 1 As shown, the method for determining the parameters of the pre-supported buffer structure includes:

[0056] Step 1: Determine the design input parameters, including the surrounding rock density. Longitudinal wave velocity of surrounding rock Tensile strength of surrounding rock Allowable peak stress of surrounding rock and the original peak blasting stress Among them, the density of the surrounding rock The longitudinal wave velocity of the surrounding rock can be obtained through indoor tests or field tests. The tensile strength of the surrounding rock was obtained through acoustic wave testing. The allowable peak stress of the surrounding rock was obtained through a Brazilian splitting test. Pick 0.3-0.5 times the original peak blasting stress Estimated based on blasting parameters.

[0057] Step 2, according to Calculate the target energy decay rate.

[0058] According to the theory of one-dimensional elastic waves, the energy density of a stress wave is proportional to the square of the stress amplitude. Let the energy density of the original blast stress wave be... The energy density transmitted into the surrounding rock is Then we have: ,in, This represents the peak stress transmitted into the surrounding rock.

[0059] According to the allowable peak stress of the surrounding rock The required target energy transmittance value can be calculated: .

[0060] Step 3: Determine the material combination for the pre-supported buffer structure.

[0061] In this embodiment, the pre-support buffer structure material combination adopts an elastic layer and a concrete layer, combined with the surrounding rock to form a four-layer composite structure of "surrounding rock - concrete layer - elastic layer - rock mass to be excavated", such as Figure 2 As shown, the stress wave propagates outward from the rock mass 1 to be excavated, passes through the elastic layer 2 and the concrete layer 3 in sequence, and finally penetrates into the surrounding rock 4.

[0062] Step 4: Calculate the transmittance coefficient and energy transmittance. .

[0063] According to the theory of one-dimensional stress wave perpendicular incidence, the transmission coefficient (stress amplitude ratio) when the wave enters medium j from medium i is: , , These are the wave impedances corresponding to media i and j, respectively. , For the density of the medium, Let be the speed at which the wave propagates in the medium.

[0064] The elastic material should be selected with low wave impedance to generate strong reflection at the rock-elastic layer interface. Typical parameter range:

[0065]

[0066] Concrete layer: Wave impedance is between that of elastic materials and surrounding rock, typical value: , , .

[0067] Surrounding rock: Wave impedance was obtained through field testing, typical granite: , , .

[0068] For multilayer media, when the thickness of each layer is large enough that the multiple reflection effect is negligible, the total transmission coefficient (stress amplitude ratio) is the product of the transmission coefficients of each interface. In this embodiment, The corresponding energy transmittance is: .

[0069] The energy transmittance formula can be used to establish a quantitative relationship between material parameters and vibration reduction effect.

[0070] Step 5, if If the thickness of the pre-support buffer structure material is determined, then the thickness of the pre-support buffer structure material is determined; otherwise, the thickness of the pre-support buffer structure material is adjusted.

[0071] like If so, select an elastic material with lower impedance and recalculate until the requirements are met.

[0072] like Then determine the thickness of the pre-supported buffer structure material:

[0073] When the elastic layer thickness is small, stress waves will be reflected multiple times within the layer, affecting the overall transmission coefficient. To simplify the design, this invention proposes a thickness design criterion:

[0074] Take the elastic layer thickness ,in The wavelength of the blast stress wave in the elastic layer is given by f, where f is the dominant frequency of the stress wave (obtainable through blasting tests, typically 500-2000 Hz). The wave speed.

[0075] This criterion ensures that: stress waves propagate for a sufficiently long time within the elastic layer, and the phases of multiple reflected waves are randomized; the total transmission coefficient is approximately equal to the product of the transmission coefficients of each interface, simplifying design calculations; and at the same time, it meets the requirements for construction feasibility.

[0076] The thickness of the concrete layer is determined according to the bearing capacity requirements of the initial support structure: and (P is the surrounding rock pressure, which can be estimated through in-situ stress testing or empirical formulas), and R is the tunnel radius. This is the design value for the compressive strength of concrete.

[0077] Correspondingly, the present invention also provides a pre-supported buffer structure parameter determination system, comprising:

[0078] The input parameter determination unit is used to determine the design input parameters, including the surrounding rock density. Longitudinal wave velocity of surrounding rock Tensile strength of surrounding rock Allowable peak stress of surrounding rock and the original peak blasting stress ;

[0079] The target energy decay rate calculation unit, based on Calculate the target energy decay rate;

[0080] Pre-support buffer structure material combination unit, used to determine the pre-support buffer structure material combination;

[0081] The energy transmittance calculation unit is used to calculate the transmittance coefficient and energy transmittance. ;

[0082] Thickness determination element, if If the thickness of the pre-support buffer structure material is sufficient, then determine the thickness of the pre-support buffer structure material; otherwise, adjust the pre-support buffer structure material until the requirements are met. .

[0083] The construction method of the present invention will be explained in detail below with reference to a design example.

[0084] Assumptions for the design example:

[0085] Surrounding rock: granite, , , , The peak stress is allowed to be 40% of the tensile strength. .

[0086] Calculate the target energy decay rate: .

[0087] Selected material combination:

[0088] Initial selection of polyurethane foam: , , , , .

[0089] Calculate the transmission coefficient: , , ,

[0090] .

[0091] Verification: It meets the design requirements.

[0092] Determine the thickness of the elastic layer: Take f = 1000Hz. λ=0.2m, take =0.1m.

[0093] Determine the thickness of the concrete layer: according to structural requirements. ,Require , unit m.

[0094] Construction Implementation:

[0095] 1. Static pre-excavation

[0096] At the tunnel face, along the designed excavation outline, a series of holes (80-120mm in diameter, 15-25cm between holes) are drilled using a water-cooled drilling rig to create a continuous cutting surface. Subsequently, a hydraulic rock splitter is used to break up and remove the cut rock blocks piece by piece. The annular space is 15-20cm wide and has a depth equivalent to one blasting cycle advance (1.5-2.5m).

[0097] 2. Laying of elastic buffer layer

[0098] A polyurethane foam spraying device is used to evenly spray the foam onto the inner rock surface of the tunnel face, forming a continuous elastic layer with a thickness of 10cm. During spraying, it is essential to ensure complete coverage without any omissions, creating a continuous and sealed isolation surface.

[0099] 3. Pouring of pre-supported concrete layer

[0100] A single layer of steel mesh (8-12mm in diameter, 15-20cm spacing) is laid in the annular space between the elastic buffer layer and the tunnel surrounding rock. C30 concrete is pumped and poured from the bottom up to form a 20cm thick concrete layer. Grouting pipes (20-32mm in diameter, 2-3m spacing) are pre-installed during pouring for later backfilling grouting.

[0101] 4. Drill and blast excavation

[0102] After the concrete layer reaches more than 70% of its design strength, conventional drilling and blasting operations are carried out on the rock mass in the middle of the working face under the protection of the composite buffer structure, and the slag is removed after blasting.

Claims

1. A method for determining parameters of a pre-supporting buffer structure, characterized in that, include: Step 1, determining design input parameters, including surrounding rock density , surrounding rock longitudinal wave velocity , surrounding rock tensile strength , surrounding rock allowable peak stress , and original blasting peak stress ; Step 2, according to calculating a target energy decay rate; Step 3: Determine the material combination for the pre-supported buffer structure; Step 4, Calculate the transmission coefficient and energy transmissivity ; Step 5, if If the thickness is sufficient, then determine the thickness of the pre-support buffer structure material; otherwise, adjust the pre-support buffer structure material until the requirements are met. .

2. The method for determining the parameters of a pre-supported buffer structure according to claim 1, characterized in that, The pre-supported buffer structure consists of an elastic layer and a concrete layer.

3. The method for determining the parameters of a pre-supported buffer structure according to claim 2, characterized in that, In step 4, the transmission coefficient when the wave enters medium j from medium i. , , These are the wave impedances corresponding to media i and j, respectively; Energy transmittance , The transmission coefficient is the wave's velocity as it travels from the rock mass to be excavated into the elastic layer. Let be the transmission coefficient of the wave as it travels from the elastic layer into the concrete layer. is the transmission coefficient when a wave enters the surrounding rock from the concrete layer.

4. The method for determining the parameters of a pre-supported buffer structure according to claim 2, characterized in that, In step 5, the specific thickness of the pre-supported buffer structure material is determined as follows: Elastic layer thickness , This is the dominant frequency wavelength of the blast stress wave in the elastic layer; Concrete layer thickness and P is the surrounding rock pressure, and R is the tunnel radius. This is the design value for the compressive strength of concrete.

5. The method for determining the parameters of a pre-supported buffer structure according to claim 2, characterized in that, The elastic layer is made of polyurethane foam, rubber pad, or closed-cell foam board.

6. The method for determining the parameters of a pre-supported buffer structure according to claim 1, characterized in that, k is a preset coefficient.

7. The method for determining the parameters of a pre-supported buffer structure according to claim 6, characterized in that, The value of k ranges from 0.3 to 0.

5.

8. A system for determining the parameters of a pre-supported buffer structure, characterized in that, include: The input parameter determination unit is used to determine the design input parameters, including the surrounding rock density. Longitudinal wave velocity of surrounding rock Tensile strength of surrounding rock Allowable peak stress of surrounding rock and the original peak blasting stress ; The target energy decay rate calculation unit, based on Calculate the target energy decay rate; Pre-support buffer structure material combination unit, used to determine the pre-support buffer structure material combination; The energy transmittance calculation unit is used to calculate the transmittance coefficient and energy transmittance. ; Thickness determination element, if If the thickness of the pre-support buffer structure material is sufficient, then determine the thickness of the pre-support buffer structure material; otherwise, adjust the pre-support buffer structure material until the requirements are met. .

9. Construction method, characterized in that, include: Step a: Determine the thickness of the pre-support buffer structure material using the pre-support buffer structure parameter determination method described in claim 1; Step b: Static pre-excavation to form a free face; Step c: Set up a pre-supported buffer structure; Step d: Excavation using the drill and blast method.

10. The construction method according to claim 9, characterized in that, Step c includes: laying the elastic buffer layer and pouring the concrete layer.

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