A rapid pre-cracking method for subway station entrances and exits in hard rock geology

Abstract

The present invention belongs to the technical field of tunnel construction, and specifically relates to a rapid pre-cracking method suitable for subway station entrances and exits under hard rock geology. A high-energy expansion agent is used for expansion and rock breaking. By designing the high-energy expansion agent dosage and drilling arrangement parameters, large-section segmented construction is carried out in combination with a special filling method. Compared with traditional non-explosive excavation and high-pressure gas expansion rock breaking, the high-energy expansion agent pre-cracking method can make full use of the original cracks in the rock, is suitable for various hard rock geological conditions, and has no sympathetic detonation distance. Whether deep or shallow holes, good pre-cracking effects can be achieved. The construction is flexible and suitable for construction scenarios with diverse cross-sections such as subway station entrances and exits. It can greatly improve work efficiency, and the vibration velocity generated is low, the noise is controllable, and the operation is simple, safe and reliable.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel construction, and in particular relates to a rapid pre-cracking method suitable for entrances and exits of subway stations under hard rock geology. Background Art

[0002] Currently, rapid excavation of subway station entrances and exits in hard rock geology presents challenges due to the diverse cross-sectional variations of these entrances and exits. Furthermore, the proximity of station entrances and exits to the ground makes vibration and noise control particularly important during construction. While various non-explosive excavation solutions exist, including hydraulic breakers, cantilevered tunnel boring machines, and rock-breaking with high-pressure gas expansion, these common non-explosive tunneling techniques each have their limitations.

[0003] For example, the equipment selection of hydraulic breakers is greatly affected by the cross-section and is not suitable for underground excavation construction. It will also generate significant vibration and noise. Cantilever tunnel boring machines are prone to rapid wear of the drill bit in hard rock geology with surrounding rock strength exceeding 80 MPa, thereby reducing construction efficiency and increasing construction costs. The combination of water-abrasive drills and splitting rods not only has low construction efficiency but also poor economy. The non-explosive method of using high-pressure gas for expansion has a phase change reaction process, low energy release efficiency, and high manufacturing and maintenance costs for expansion tubes and related equipment. The operation is difficult and requires the accompaniment of professionals. At the same time, improper operation during the filling and release of high-pressure gas may cause pressure loss or equipment damage.

[0004] Therefore, it is urgent to introduce a new non-blasting excavation method that is low in vibration, high in efficiency, economical, safe and reliable and suitable for urban hard rock areas to meet the needs of construction in environmentally sensitive areas. Summary of the Invention

[0005] In order to address the shortcomings of existing non-blasting excavation, such as poor safety and difficulty in adapting to construction scenarios with diverse cross-sections, a rapid pre-cracking method suitable for subway station entrances and exits in hard rock geology is proposed. By designing the dosage of high-energy expansion agent and drilling layout parameters, the method greatly improves work efficiency, has strong operability, and achieves good pre-cracking effect.

[0006] The present invention is implemented by adopting the following technical solution: a rapid pre-cracking method suitable for subway station entrances and exits under hard rock geology, comprising the following steps:

[0007] Step 1: Conduct a geological survey of the area where the subway station entrances and exits are located to obtain geological survey parameters. Based on the surrounding environment, blasting vibration velocity monitors and sound level meters are deployed in the most susceptible areas for monitoring. The geological survey parameters include rock tensile strength, compressive strength, elastic modulus, and permeability.

[0008] Step 2: Based on the geological survey parameters of the subway station entrance and exit, the high-energy expansion agent dosage and drilling parameters are designed, and a drilling layout diagram is drawn;

[0009] The drilling parameters include the crack-causing hole diameter, hole spacing, and hole depth, which are determined as follows:

[0010] The crack-inducing holes are evenly distributed in a "plum blossom" pattern. The hole spacing ranges from 1.0 to 1.5 m. The number of holes is reasonably arranged according to the cross-sectional dimensions and the hole spacing. The crack-inducing hole diameter is determined by the following method:

[0011] ;in, Refers to tensile stress, which is equivalent to the tensile strength of rock measured by geological survey. Refers to the uniform pressure generated by the high-energy expansion agent. refers to the formation pressure, r refers to the arbitrary radius, a refers to the radius of the high-energy expansion agent coil, and b refers to the diameter of the fracture hole;

[0012] The hole depth is determined by the following method: D = k·R, where D is the hole depth, k is the thickness of the rock to be crushed, and R is an empirical coefficient with a value of 1.2 to 1.5;

[0013] The dosage of high-energy expander is determined by determining the required energy based on the rock compressive strength and the expected fracture volume, and solving the required number of moles in combination with the combustion equation. This leads to the gas volume required to effectively crush the rock, and then the dosage of high-energy expander is determined based on the gas production of the high-energy expander.

[0014] Step 3: Use a borehole television imager to detect the development of joints and fissures inside the rock mass in the hole to design the filling method of the high-energy expansion agent; when filling the high-energy expansion agent, the expansion agent is arranged in the fissure and joint development section based on the borehole television imaging, and the fracture-inducing hole is set near or in the center of the main fracture.

[0015] Step 4: Perform high-energy expansion agent pre-cracking construction according to the drilling layout and high-energy expansion agent filling method determined in steps 2 and 3, and use a drilling television imager and an acoustic wave detector to evaluate the pre-cracking effect of the high-energy expansion agent.

[0016] Compared with the prior art, the advantages and positive effects of the present invention are:

[0017] This solution uses high-energy expansion agents to expand and break rock. By designing the high-energy expansion agent dosage and drilling layout parameters, combined with a special filling method, large-section segmented construction is carried out. Compared with traditional non-explosive excavation and high-pressure gas expansion rock breaking, high-energy expansion agent pre-cracking can make full use of the original cracks in the rock, is applicable to a variety of hard rock geological conditions, and has no sympathetic detonation distance. Whether deep or shallow holes, it can achieve a good pre-cracking effect. The construction is flexible and suitable for construction scenarios with diverse cross-sections such as subway station entrances and exits. It can greatly improve work efficiency, and the vibration velocity generated is low, the noise is controllable, and the operation is simple, the equipment cost is low, and it is safe and reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of surrounding rock stress distribution under high-energy expansion agent according to an embodiment of the present invention;

[0019] Figure 2 This is a diagram showing the internal structure of a high-energy expander according to an embodiment of the present invention;

[0020] Figure 3 This is a schematic diagram of the drilling arrangement according to an embodiment of the present invention;

[0021] Figure 4 Schematic diagram of the filling of high-energy expansion agent according to an embodiment of the present invention, (a) filling method 1; (b) filling method 2;

[0022] Among them, 1. High-energy expansion agent; 2. Wire connector; 3. Starter; 4. Fuse; 5. Drilling. DETAILED DESCRIPTION

[0023] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described below with reference to the accompanying drawings and embodiments. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can also be implemented in other ways than those described herein. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0024] In one embodiment, a rapid pre-cracking method applicable to subway station entrances and exits in hard rock geology comprises the following steps:

[0025] Step 1: Conduct geological surveys of the areas where subway station entrances and exits are located, and deploy blasting vibration velocity monitors and sound level meters in the most susceptible areas based on the surrounding environment for monitoring.

[0026] When constructing subway station entrances and exits, it is first necessary to conduct a detailed geological survey of the area where the entrances and exits are located in order to understand the geological structure and structural characteristics of the area, measure the physical and mechanical properties of the soil and rock (including tensile strength, compressive strength, elastic modulus, and permeability), and understand the distribution and flow characteristics of groundwater and its impact on station construction.

[0027] In addition, subway stations under existing operating lines and residential buildings that are close to them are generally identified as the most vulnerable areas. Specific measures can be determined based on actual conditions, and vibration velocity monitors and sound level meters are installed in the most vulnerable areas. Vibration velocity and noise monitoring can be used to assist in determining the impact of the high-energy expansion agent pre-cracking process on the surrounding environment and buildings. Once an abnormality is discovered, timely measures can be taken to correct the pre-cracking parameters. For example, in the case of a certain subway, if the vibration velocity during construction exceeds the vibration safety standard (2-3 cm / s) and the allowable standard of a certain subway (the allowable vibration standard for gas pipelines is 0.5 cm / s, and the allowable standard for buildings is 1.0 cm / s), construction will be stopped immediately if an abnormality occurs, and the charge amount will be re-evaluated using the vibration velocity formula. The vibration velocity calculation formula is: V refers to the vibration velocity at a certain measuring point (usually expressed in cm / s), K is an empirical constant that depends on geological conditions and rock properties and is usually determined through experimental data, W is the effective equivalent of the high-energy expander (i.e., weight, expressed in kg), and R is the distance from the pre-cracking point to the measuring point (in meters). In the abnormal section, the charge amount is reduced and the pre-cracking footage is shortened once to meet safety standards.

[0028] Step 2: Based on the geological survey parameters of the subway station entrance and exit, the high-energy expansion agent dosage and drilling parameters are designed, and a drilling layout diagram is drawn;

[0029] (1) The dosage of high energy expander is determined by the following method:

[0030] The working principle of a high-energy expander is that upon ignition, the expander rapidly generates high-pressure gas that wedges into the rock's primary fractures, generating shear stress within the rock, causing the fractures to expand. As the high-pressure gas forms the gas wedge, the pressure continues to rise. Once the set pressure is reached, the agent transitions from combustion to detonation, further developing the fractures and fracturing the rock blocks trapped between the fractures in a network-like manner.

[0031] In this embodiment, Figure 2 As shown, the high-energy expansion agent adopts D type, and the size of the high-energy expansion agent is 30mm×300mm. The following formula is used to calculate the amount of gas required for effective rock pre-cracking. The ideal gas equation is used to calculate the amount of gas to ensure that the required gas can effectively release energy at a specific pressure and temperature. The calculation formula is:

[0032] ;

[0033] Where P is the gas pressure (Pa), V is the gas volume (m 3 ), n is the number of moles of gas (mol), R is the ideal gas constant (8.314 J / (mol·K)), and T is the gas temperature (K);

[0034] The rock compressive strength σ(Pa) and the expected fracture volume V1(m 3 ) Calculate the required energy E:

[0035] ;

[0036] Substitute the energy E into the combustion equation to find the number of moles n:

[0037] ;

[0038] The above formula can be used to derive the formula for the gas volume required to effectively crush rocks: In addition, the test of high-energy expansion agent showed that the average gas production per kg was about 600L, and the dosage of high-energy expansion agent could be determined.

[0039] The mass of each section of high-energy expansion agent is 0.3 kg. In this embodiment, it is preferred to fill 7 / 8 sections into a single hole, that is, the mass of the single hole filling is 2.1 / 2.4 kg.

[0040] (2) Drilling parameters include the crack hole diameter, hole depth and hole spacing, which are determined as follows:

[0041] The diameter of the cracking hole is based on the stress component expression of a ring or cylinder under uniform pressure in elastic mechanics. The high-energy expansion agent pre-cracking rock mainly overcomes the tensile stress inside the rock by generating gas expansion. Therefore, the tensile stress expression is used, and the calculation formula is:

[0042] ;

[0043] in, Refers to the tensile stress calculation equivalent to the tensile strength of the rock measured by geological survey in the early stage. It refers to the uniform pressure generated by the high-energy expansion agent. refers to the formation pressure, r refers to the arbitrary radius, a refers to the radius of the high-energy expansion agent coil, and b refers to the diameter of the crack hole. Figure 1 ; Generally, the diameter of the fissure hole ranges from 35 to 60 mm, and in this embodiment, 42 mm is preferred;

[0044] The design value of the hole depth is determined by the thickness of the rock to be crushed and an empirical coefficient. The calculation formula is D=k·R, where D is the hole depth, k is the thickness of the rock to be crushed, and R is an empirical coefficient determined according to factors such as geological conditions, usually ranging from 1.2 to 1.5.

[0045] The design values ​​of the hole spacing and hole number are determined mainly based on the mechanical properties of the rock and the influence range of the high-energy expansion agent. The crack-causing holes are evenly distributed in the common "plum blossom" spacing arrangement, such as Figure 3As shown, the range of the hole spacing L is 1.0~1.5m. The specific arrangement of the hole spacing needs to be appropriately adjusted in combination with other factors. The number of holes is reasonably arranged according to the cross-sectional size and the hole spacing. Figure 3 As shown, in this embodiment, the distance between holes #1, #2, and #3 and the upper edge of the step is 4.0 m; the distance between holes #1 and #6 and the side edge is 4.0 m; the hole depth is 5 m; and the diameter of the crack-inducing hole is 42 mm.

[0046] Step 3: Use a borehole television imager to detect the development of joints and fissures in the rock mass in the hole, so as to design the filling method of the high-energy expansion agent;

[0047] In this embodiment, the high-energy expansion agent filling method is based on borehole TV imaging. The expansion agent is placed in the section with developed fracture joints, and crack-inducing holes are set near or in the middle of the main fractures. This can better utilize the advantages of the fractures and achieve a more effective crushing effect. Try to avoid setting the explosive holes in the solid parts of the solid rock, but should be close to the fractures to use the fractures for crack propagation. Therefore, this construction section has derived two filling methods ( Figure 4 ), where loading method 1 involves combining high-energy expansive agents in pairs, with empty tubes between adjacent pairs. Starters are installed on the first, third, and sixth high-energy expansive agents, respectively, with no starter installed on the last pair. Loading method 2 involves using empty tubes immediately adjacent to the sealing cement section, with a single high-energy expansive agent installed in the last section. High-energy expansive agents are then combined in pairs in the middle section, with empty tubes between adjacent pairs. Starters are installed on the first, third, and sixth high-energy expansive agents, respectively. Using air-spaced charge can effectively improve pre-splitting quality and reduce expansive agent usage. Compared to traditional continuous charge, air-spaced charge can effectively reduce the dispersion of small gravel and dust during pre-splitting, providing a more efficient, environmentally friendly, and controllable solution for the pre-splitting process. The specific loading method used in other areas should also consider the development of fissures and joints within the hole. The purpose is to make the gas flow more effectively in the original cracks and expand the cracks. The hole is sealed at 1.7m. In this embodiment, 8 expansion agents, 3 starters, and 3 30*300mm empty tubes are installed in holes 1, 3, 4, and 7; 7 expansion agents, 3 starters, and 3 30*300mm empty tubes are installed in holes 2, 5, 6, and 8.

[0048] Then, the hole is sealed and the footing is connected. The sealing process is to mix high-strength quick-setting cement and water in proportion. After the mixture is evenly mixed, it is put into the drill hole and compacted with a ramming rod. The specific method is flexible according to the actual situation. After the hole is sealed, wait for more than 30 minutes to allow the sealing material to fully solidify. The footing connection adopts parallel connection inside the hole and series connection outside the hole. The triggering operation uses the FD200 coal mine capacitor detonator, connected to the busbar, to start ignition.

[0049] Step 4: Carry out high-energy expansion agent pre-cracking construction at the subway station entrance and exit according to the high-energy expansion agent pre-cracking parameters and construction diagram. Before starting ignition, confirm that all personnel have evacuated outside the warning area; use a borehole television imager and an acoustic wave detector to evaluate the pre-cracking effect of the high-energy expansion agent;

[0050] To evaluate the pre-splitting effect, a multifunctional borehole imaging analyzer is used to detect the pre-splitting effect within the borehole, monitoring and capturing the borehole conditions in real time. An acoustic wave detector is used to assess the integrity and physical properties of the pre-splitting rock mass. The propagation velocity of acoustic waves in the rock mass is closely related to the mechanical properties and fracture state of the rock. By detecting the wave velocity, the development characteristics of the rock mass fractures can be determined: the more fractures in the rock mass, the lower the wave velocity, and vice versa. After pre-splitting is completed, an excavator is used for processing and slag removal.

[0051] While the weakening mechanisms of high-energy expansion agent pre-cracking and explosive fracturing are similar—both achieve their effects through the combined action of shock waves, stress waves, and explosive gases—blasting releases energy extremely rapidly, and the accompanying shock waves propagate rapidly, resulting in vibrations that are typically high-frequency and intense. In contrast, high-energy expansion agents pre-generate high-pressure gas upon application, driving the propagation of pre-existing fractures around the borehole. This process helps reduce the detonation energy consumption caused by the crushing shock and weakens the inhibitory effect of ground stress on stress wave propagation, reducing the rate of stress wave decay. Consequently, high-energy expansion agents can slow the rate of energy release, reduce vibration intensity, and enhance the pre-cracking effect.

[0052] The above description is merely a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any person skilled in the art may utilize the technical contents disclosed above to change or modify them into equivalent embodiments with equivalent changes for application in other fields. However, any simple modification, equivalent change, and modification of the above embodiments made in accordance with the technical essence of the present invention without departing from the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A rapid pre-cracking method suitable for subway station entrances and exits under hard rock geology, characterized in that: The following steps are involved: Step 1: Conduct a geological survey of the area where the subway station entrances and exits are located to obtain geological survey parameters. Based on the surrounding environment, blasting vibration velocity monitors and sound level meters are deployed in the most susceptible areas for monitoring. The geological survey parameters include rock tensile strength, compressive strength, elastic modulus, and permeability. Step 2: Based on the geological survey parameters of the subway station entrance and exit, the high-energy expansion agent dosage and drilling parameters are designed, and a drilling layout diagram is drawn; The drilling parameters include the crack-causing hole diameter, hole spacing, and hole depth, which are determined as follows: The crack-inducing holes are evenly distributed in a "plum blossom" pattern. The hole spacing ranges from 1.0 to 1.5 m. The number of holes is reasonably arranged based on the cross-sectional dimensions and the hole spacing. The crack-inducing hole diameter is determined by the following method: ;in, Refers to tensile stress, which is equivalent to the tensile strength of rock measured by geological survey. Refers to the uniform pressure generated by the high-energy expansion agent. refers to the formation pressure, r refers to the arbitrary radius, a refers to the radius of the high-energy expansion agent coil, and b refers to the diameter of the fracture hole; The hole depth is determined by the following method: D = k·R, where D is the hole depth, k is the thickness of the rock to be crushed, and R is an empirical coefficient with a value of 1.2 to 1.5; The dosage of high-energy expander is determined by determining the required energy based on the rock compressive strength and the expected fracture volume, and solving the required number of moles in combination with the combustion equation. This leads to the gas volume required to effectively crush the rock, and then the dosage of high-energy expander is determined based on the gas production of the high-energy expander. Step 3: Use a borehole television imager to detect the development of joints and fissures in the rock mass in the hole to design the filling method of the high-energy expansion agent; Step 4: Perform high-energy expansion agent pre-cracking construction according to the drilling layout and high-energy expansion agent filling method determined in steps 2 and 3, and use a drilling television imager and an acoustic wave detector to evaluate the pre-cracking effect of the high-energy expansion agent.

2. The rapid pre-splitting method for subway station entrances and exits in hard rock geology according to claim 1 is characterized in that: In step 3, when the high-energy expansion agent is filled, the expansion agent is arranged in the fracture and joint development section according to the borehole television imaging, and the fracture-inducing hole is set near the main fracture or in the middle of it.

3. The rapid pre-splitting method for subway station entrances and exits in hard rock geology according to claim 1 is characterized in that: In step 3, there are two ways to fill the high-energy expansion agent: One of the filling methods is: the high-energy expansion agents are grouped in pairs, with empty tubes between the high-energy expansion agents in adjacent pairs, and the starters are evenly set on the high-energy expansion agents in the pairs, and the last group is not set with a starter; Another filling method is: the tube next to the sealing cement section is empty, and the last one is filled with a high-energy expansion agent. The middle part uses high-energy expansion agents in pairs. The empty tubes are between the adjacent pairs of high-energy expansion agents, and the starters are evenly set on the high-energy expansion agents in pairs.

4. The rapid pre-splitting method for subway station entrances and exits in hard rock geology according to claim 1 is characterized in that: In step 1, the blasting vibration velocity monitor and the sound level meter are used for monitoring. If any abnormality is found, the construction is stopped immediately and the charge amount is re-evaluated using the vibration velocity formula: The vibration velocity calculation formula is: , V refers to the vibration velocity at a certain measuring point, K is an empirical constant, W is the effective equivalent of the high-energy expansion agent, and R is the distance from the pre-cracking point to the measuring point. In the abnormal section, the charge amount is reduced and the pre-cracking footage is shortened once to meet the safety standard.

5. The rapid pre-splitting method for subway station entrances and exits in hard rock geology according to claim 1 is characterized in that: In step 4, the pre-cracking effect is evaluated by using a multifunctional borehole imaging analyzer to detect the pre-cracking effect of the cracks in the hole and perform real-time monitoring and photography of the hole conditions; and an acoustic wave detector is used to evaluate the integrity and physical properties of the rock mass after pre-cracking.

6. The rapid pre-splitting method for subway station entrances and exits in hard rock geology according to claim 1 is characterized in that: In step 2, the diameter of the crack hole ranges from 35 mm to 60 mm.

7. The rapid pre-splitting method for subway station entrances and exits in hard rock geology according to claim 1 is characterized in that: The high-energy expansion agent is of D type, and the size of the high-energy expansion agent is 30mm×300mm.

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