A method for pre-treating hard rock in front of a tunnel

Abstract

The present invention discloses a method for pre-treating hard rock in a tunnel. The pre-treatment time T and the pre-treatment distance L are estimated based on the tunneling machine's advance rate and the rock formation type. A pilot tunnel passage is set between the left and right lines at a distance L from the hard rock. Boreholes are arranged between the pilot tunnels, and a directional drilling rig is used to drill holes into the rock formation starting from the pilot tunnels. After reaching the hard rock formation, drilling is carried out according to the designed hole positions. After the boreholes penetrate the hard rock area, a jet slotting device is used to cut slots in the rock. After slotting is completed, a hydraulic fracturing device is used to fracture the rock. By arranging the boreholes and adjusting the water pressure parameters, the crack propagation depth D is controlled so that the cracks between the boreholes are interconnected, which has obvious advantages in reducing the energy consumption of the tunneling machine, improving the tunneling efficiency, and shortening the tunneling construction period, etc.

Description

Technical Field

[0001] The present invention belongs to the technical field of tunnel excavation, and particularly relates to a method for advanced pretreatment of hard rock in tunnels. Background Technique

[0002] With the rapid development of urban underground traffic construction in China, tunnel construction has become more and more common, and the TBM tunnel construction method has been widely used in the field of urban underground tunnel excavation. Among them, the rock-breaking efficiency of TBM is the key factor restricting its construction economy. The tunnel rock-breaking efficiency depends on the TBM tunneling parameters and the properties of the excavated rock mass. Under the condition of the same tunneling parameters, the tunneling efficiency depends on the properties of the excavated rock mass. The tunneling in hard rock masses seriously affects the tool wear and the mechanical propulsion speed. Therefore, the pretreatment of the excavated rock mass is the key to improving the tunnel tunneling efficiency. The commonly used hard rock treatment methods include explosive blasting method and hydraulic rock splitting method. Among them, the explosive blasting method can significantly improve the tunneling efficiency, but at the same time, it generates large vibrations, noises and a large amount of toxic and harmful gases, so it is not suitable for urban underground construction. The use of the hydraulic rock splitting method can avoid the disadvantages such as pollution and noise generated by presplitting blasting. However, due to its low output (unable to achieve multi-row blasting), low depth (only 1-2 meters can be broken each time), and the TBM construction process can only be carried out after presplitting blasting, the overall tunnel construction progress is restricted.

[0003] For this reason, a method for pre - treating hard rock in advance is proposed. For example, the "Method for Pretreating Ore and Rock" disclosed in Patent No. CN201810890500.5 has good applicability to improving the caving - ability of rocks during the mining of metal mines. However, this method does not clearly define the drilling equipment and drilling process for the guiding boreholes, and only uses some traditional drilling methods such as drill bits, scrapers, saw blades, etc. Moreover, its main purpose is to cause the upper - rock mass of the mine roadway to crack, without considering the problem of secondary treatment of the boreholes. For this reason, a method for pre - splitting treatment of hard rock in tunnels is proposed. A specially - designed drill bit is used to drill into the pre - treatment layer. After the drilling is completed, abrasive water jet slitting is used, and then the hydraulic fracturing method is used to fracture the rock mass within a certain range. By adjusting the water pressure and combining with the layout of the boreholes, the cracks in the rock mass are made to communicate with each other. The formation of the cracks changes the stress distribution around the rock mass, releases the rock stress, thereby effectively reducing the force on the cutters and the system energy consumption during TBM construction, and can significantly improve the tunnel - boring speed, save the construction period, and reduce the tunneling cost. This method uses a specially - designed drill bit. For non - hard - rock areas, a mechanical drill bit is used for drilling (with water jet - assisted slag discharge). When reaching the hard - rock stratum, an abrasive water jet is used to assist the mechanical drill bit in drilling, which can improve the drilling efficiency of the drill bit. The water - jet and abrasive - water - jet channels are automatically switched according to the water - pressure magnitude. At the same time, this method can realize the synchronous progress of tunnel boring and hard - rock pre - treatment. When the hard - rock pre - treatment is completed, the tunnel - boring face can be directly connected, avoiding the reduction of the rock pre - splitting effect caused by the closure of the pre - split cracks. After the tunnel boring is completed, the boreholes in the non - excavated rock mass are classified and backfilled, which maximally ensures the integrity of the non - excavated rock mass of the tunnel, thereby ensuring the safety of the tunnel while accelerating the tunneling efficiency. Summary of the Invention

[0004] The object of the present invention is to provide a method for pre - treating hard rock in tunnels in advance, so as to solve the problems of cutter wear, long construction period, and low tunneling efficiency during the process of tunnel boring through hard - rock areas. Through the pre - treatment of hard rock in tunnels in advance, the force on the cutters during tunneling is significantly reduced, thereby reducing the energy consumption of tunnel boring, increasing the tunneling speed, shortening the construction period, and reducing the cost.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for pre - treating hard rock in tunnels in advance includes the following steps:

[0007] (1) Before tunnel construction, geological exploration is carried out on the rock stratum to be traversed, and the thickness h of each rock stratum is determined through advanced geological testing and analysis i and the rock - stratum type C iAnd other rock formation parameters, and determine the advance distance L and the advance treatment time T according to the tunnel excavation speed and the magnitude of the in-situ stress; assume the tunnel excavation speed is 6.2 m / day, the tunnel diameter is d, and the advance pretreatment time T = 3 days, then the advance pretreatment distance is 6.2×3 = 18.6 m (for high in-situ stress areas, the rock burst hazard needs to be considered, and the pretreatment position should be outside 0.5 - 1.5d from the tunnel face); the drilling time t1 + the hydraulic slotting time t2 + the hydraulic fracturing time t3 = the pretreatment time T;

[0008] (2) Adopt the parallel construction method, and the tunnel excavation and the hard rock pretreatment are carried out synchronously. Among them, the drilling starts from the pilot tunnel and drills towards the pretreatment rock formation, and a directional drilling rig is used to control the drilling direction and drill according to the designed hole positions. Three water jet outlets and three abrasive water jet outlets are evenly arranged at the drill bit part, and the included angle between the same type of nozzle outlets is 120°. When drilling in non-hard rocks (such as sandstone, shale, etc.), low-pressure water jets are used to assist in slag discharge, and at this time, the abrasive water jet nozzles with lower pressure are in the closed state; when drilling into the hard rock area, the water pressure is increased, at which time the water jet nozzles are automatically closed, and at the same time, the abrasive jet nozzles are opened, and drilling is carried out with the assistance of the abrasive water jet. The maximum working pressure that the water pump can provide is 150 MPa; using the abrasive water jet to assist drilling can, on the one hand, reduce the force on the drill bit, and on the other hand, improve the drilling efficiency and save the drilling time; after the drilling is completed, the drill is withdrawn to prepare for the next step;

[0009] (3) Cut slots for the drilled holes extending into the pretreatment rock mass by using the abrasive water jet method. The crack position is considered in combination with the tunnel transverse dimension and the jet influence range. To ensure the best pre-splitting effect of the rock, a hydraulic slot is set every 2.4 m, and the slotting depth is 0.5 m;

[0010] (4) After the slotting is completed, hydraulic fracturing is carried out on the pretreatment rock mass. The cracks generated by the hydraulic fracturing will extend along the tunnel excavation direction and the gravity direction according to the direction of the slots. Theoretically, the maximum extension depth of the cracks can reach 20 m. In practice, it only needs the cracks between the drilled holes to penetrate. Combining the drilling layout method, the crack extension depth of the hydraulic fracturing is 5 m (the crack extension surface composed of the gravity direction and the excavation direction); determine the specific pre-splitting crack length according to the thickness of the pretreatment rock formation and the hole spacing. The formula for the rock fracture initiation pressure is:

[0011] P F =3δ h -δ H -P S +δ τ where P F is the fracture initiation pressure, δ h and δ H are the minimum and maximum horizontal principal stresses respectively, P S is the pore pressure, and δ τIt is the tensile strength of rock. During hydraulic fracturing, the generation of cracks and the completion of the fracturing process are judged based on the change in water pressure.

[0012] (5) After the pretreatment is completed, in order to minimize the disturbance of the pretreatment process to the non-excavated rock mass, the borehole between the pilot tunnel and the pretreatment rock layer is grouting backfilled. The grouting pump can be a hydraulic pressure pump. The backfill material is the original rock material and bonding material used during drilling. Different rock types are backfilled separately. This can be achieved by using a pressure-controlled one-way valve combined with a bag. When grouting backfills the borehole, first determine the position of the one-way valve and bag for each rock layer according to the drilling depth corresponding to the different rock layers. i And the corresponding grouting pressure P i .

[0013] Furthermore, the directional drilling rig has three inclined water jet channels connected to the central channel of the drill bit on its circumference, the water jet nozzle is located at the front edge of the drill bit, and also includes three abrasive water jet channels connected to the central channel, the abrasive water jet nozzle is located outside the center of the front end of the drill bit, a slidable steel casing is provided in the central channel of the drill bit, the front end of the steel casing is closed, three reserved outlets are provided on the circumference of the steel casing, the length of the steel casing is less than the length of the drill bit, and a spring is provided to seal the front end of the steel casing, the front end of the spring is fixedly connected to the plug in the center of the drill bit, and the abrasive jet nozzle is located outside the drill bit plug.

[0014] The advantages of the present invention are:

[0015] 1. A specially designed drill bit is used. The water pressure can be adjusted according to the rock type during drilling. Low-pressure water jet is used to assist in slag removal in non-hard rock areas, and high-pressure abrasive water jet is used to assist in drilling in hard rock areas, which reduces the force on the drill bit and improves the drilling efficiency;

[0016] 2. The directional drill starts drilling from the pilot tunnel, which ensures that the tunnel excavation process does not affect the drilling of the hole, and the pretreatment of the hard rock does not affect the tunnel excavation construction (i.e. parallel construction method), so that hard rock treatment and tunnel excavation can be carried out simultaneously;

[0017] 3. Pre-treating the hard rock in the tunneling process in advance to produce cracks, thereby releasing the surrounding rock pressure and creating a stress concentration area. When the face is excavated to this position, the force on the tool is significantly reduced, thereby reducing tool wear. At the same time, rock pre-cracking can also greatly improve the efficiency of tunneling, thereby achieving the purpose of reducing energy consumption, shortening construction period and saving costs;

[0018] 4. After the hard rock pretreatment is completed, grouting backfill can be carried out according to the rock type during drilling and combined with bonding materials, which minimizes the disturbance to the non-excavated rock mass;

[0019] 5. Hydraulic fracturing and grouting can use the same pump, which simplifies the equipment and is easy to implement on-site. Brief Description of the Drawings

[0020] Figure 1 It is a schematic structural view of the drill bit in the present invention.

[0021] Figure 2 It is a top view of the overall drilling in the present invention.

[0022] Figure 3 It is a layout diagram of the pilot hole drilling in the present invention.

[0023] Figure 4 It is a side view of the pre-treated hard rock.

[0024] Figure 5 It is a pressure change diagram during the hydraulic fracturing process.

[0025] Figure 6 It is a top view of the hole sealing.

[0026] Figure 7 Schematic diagram of grouting backfill. Detailed Implementation Manner

[0027] Embodiment

[0028] Suppose that in an actual project, the diameter of a single tunnel heading face is d = 12 m, and the average tunneling speed is 6.2 m / day. The left and right lines of the tunnel need to pass through a granite rock stratum with a thickness of 20 m during tunneling. Before tunnel construction, in-situ stress detection is carried out on the rock stratum to be passed through. Specifically, it can refer to the "Standard for Test Methods of Engineering Rock Mass" (GB / T 50266-2013). For high in-situ stress areas, to prevent the occurrence of rock bursts, the pre-treatment position should be more than 0.5 - 1.5d away from the heading face, that is, the advance distance is not less than 1.5×12 = 18 m. Considering the above, the advance distance L = 18.6 m can be initially determined, and the corresponding advance treatment time T = 3 days. A pilot hole channel is set between the left and right lines of the tunnel, and the pilot hole channel connects the left and right lines of the tunnel; especially for rock masses in other in-situ stress areas, the advance distance (0.5 - 1.5d) and advance time T can be appropriately adjusted in combination with the tunneling speed. The specific calculation method is the same as the calculation steps of the above conditions;

[0029] Furthermore, holes are arranged according to the tunnel cross-section size and the influence range of hydraulic fracturing. The influence range of hydraulic fracturing is 5 m. To reduce the disturbance of the drilling on the surrounding non-excavated rock mass, the same channel is used for drilling the holes in the same layer between the pilot hole - pre-treated rock stratum, as Figure 3 shown; at the predetermined position, holes are arranged at intervals of 5 m, as Figure 4 shown; drilling is carried out according to the designed position, and the top view of the hole drilling is as Figure 2 shown; the drill bit design is as Figure 1As shown in the figure, the water pressure is adjusted according to the rock stratum type during drilling; low-pressure water is used in non-hard rock areas. At this time, the water pressure is not enough to push the movable steel casing forward, and the low-pressure water flow will spray out from the water jet nozzle 2. When drilling into the hard rock area, the water pressure is increased. At this time, the high-pressure water will push the movable steel sleeve 1 backward, and the reserved outlet 5 of the steel casing will move to the abrasive water jet nozzle 3. At this time, the abrasive water jet outlet is connected to the reserved outlet, and the abrasive water jet channel is automatically opened, and the water jet nozzle 2 will be automatically closed by the movable steel casing 1; after the drilling is completed, the pressure is released, and the drill bit returns to its original state; to extend the service life of the nozzle, the abrasive water jet nozzle is made of cemented carbide material; abrasive water jet slitting is carried out on the drilled hole 12 at the pretreatment position (the slitting forms a closed-loop slitting surface along the gravity and tunneling directions), and the slitting depth is 0.5 m, and slitting is carried out once every 2.4 m in each drilled hole; the pretreatment rock stratum is sealed, and hydraulic fracturing is started. The maximum working pressure of the hydraulic fracturing pump 13 is 150 MPa, and the fracture propagation direction is the same as the slitting direction and extends along the gravity direction and the tunnel longitudinal direction. To save the energy consumption of hydraulic fracturing, it is only necessary to make the fractures penetrate each row of holes, that is, the pre-fracture length is 5 m, and the fracture arrangement is as Figure 2 shown; during operation, the rock fracture initiation pressure is calculated according to the formula P F =3δ h -δ H -P S +δ τ (the meanings of the symbols in the formula are the same as those described above). First, hydraulic fracturing is carried out on the No. 2 drilled hole. When the pump pressure reaches P F , the injection pressure is maintained. When the fracture occurs, the pump pressure will suddenly drop by a certain amount. At this time, it is judged that the fracture has been generated; then the flow rate is increased and the injection pressure is still maintained, and the fracture will expand in the pre-slitted direction (closed-loop slitting surface). When the fracture penetrates another drilled hole, the water pressure will drop again. At this time, it can be judged that the fracture has penetrated the drilled hole, and the hydraulic fracturing of this drilled hole is completed; the schematic diagram of the pump pressure change in each stage of the hydraulic fracturing process is shown in Figure 5 ; further, when the pretreatment is completed, the tunnel excavation face just reaches the initial position of the pretreatment rock face, making the best use of the pretreatment fractures to achieve the purpose of reducing the tool force, accelerating the excavation speed and saving mechanical energy consumption. Further, the above steps are continued for the hard rock that needs to be pretreated subsequently until all the hard rock is processed; further, after all the hard rock is processed, the drilled holes 12 in the pilot tunnel between the tunnels are backfilled. To ensure the integrity of the non-excavated rock mass during tunnel excavation, the backfill material is grouted and backfilled according to the rock combination filling material in the actual drilling process on site, and the grouting pump 13 and the hydraulic fracturing pump are the same one, and only the grouting pressure needs to be adjusted according to the actual needs. Figure 4Taking the rock stratum as an example, when backfilling, the conduit 16 is extended into the grouting position, and two one-way valves 14 (inside the conduit) and the bladder 15 (outside the conduit) are used to seal at the boundary of the rock stratum. The hole sealing direction is: pre-treatment layer → heading face; according to the different depths of the rock stratum, the grouting pressure is different. Combining with the one-way valves, the hole sealing pressures of each rock stratum (in the hole sealing direction) are P1, P2, …, (P1 > P2 > …). When the pressure reaches P1, all the one-way valves open, and the innermost layer of the borehole is grouted and backfilled. After the innermost layer of the borehole is sealed, according to the rock stratum type and position Xi (along the grouting direction, with the outlet position of the grouting pipe as the origin), the grouting raw material is changed accordingly and the grouting pressure is reduced to P2. At this time, one-way valve one automatically closes, and one-way valve two remains open, and the second layer of rock mass borehole is grouted. And so on until the remaining part is filled. The grouting volume Vi of each layer of rock stratum = the cross-sectional area A of the borehole × the stage borehole length Xi (for the first layer of backfilling, the borehole length X* of the part where the borehole turns to the heading face needs to be considered additionally); in this example, P1 is set to 4 MPa and P2 is set to 2 MPa. When backfilling the borehole of the granite layer, first, granite drill cuttings and adhesive materials are injected, and the pump pressure is adjusted to 4 MPa. At this time, the grout can enter the granite layer. When the grouting volume reaches V1 = A×(X1 + X*), the innermost layer of the borehole is backfilled; start to reduce the grouting pressure to 2 MPa. At this time, one-way valve one automatically closes due to the reduction of the grouting pressure, and one-way valve two opens. At this time, the grouting volume V2 = A×(X2 - X1). After the grouting volume is reached, the grouting pressure is reduced again until all the boreholes are backfilled.

Claims

1. A method for pre-treating hard rock in front of a tunnel, characterized in that, It includes the following steps: S1. Conduct geological surveys on the rock formations to be traversed before tunnel construction, and determine the thickness h of each rock formation through advanced geological testing and analysis i , the rock formation type C i , and determine the advance distance L and the advance pre-treatment time T according to the tunnel excavation speed and the magnitude of the in-situ rock stress; S2. Adopt the parallel construction method, with tunnel excavation and hard rock pretreatment carried out simultaneously. Among them, drilling starts from the pilot tunnel and drills towards the pretreated rock formation. A directional drilling rig is used to control the drilling direction, and drilling is carried out according to the designed hole positions. Three water jet nozzles and three abrasive water jet nozzles are evenly arranged at the bit part. The included angle between the outlets of the same type of nozzles is 120°. During drilling, low-pressure water jet is used to assist in slag discharge for non-hard rock, and the water pressure is increased when drilling into the hard rock area. Three inclined water jet nozzles connected to the central channel of the bit are arranged on the circumference of the bit of the directional drilling rig. The water jet nozzles are located at the front edge of the bit. It also includes three abrasive water jet nozzles connected to the central channel. The abrasive water jet nozzles are located outside the center of the front end of the bit. A slidable steel casing is provided in the central channel of the bit. The front end of the steel casing is closed. Three outlets are provided on the circumference of the steel casing. The length of the steel casing is less than the length of the bit, and a spring is provided at the sealed front end of the steel casing. The front end of the spring is fixedly connected to the plug at the center of the bit. The abrasive water jet nozzles are located around the plug of the bit. S3. Cut slots for the drilled holes extending into the pretreated rock formation by using the abrasive water jet method. The crack positions are considered in combination with the transverse dimension of the tunnel and the jet influence range. To ensure the best rock pre-splitting effect, a hydraulic cut slot is set every 2.4 m, and the cut slot depth is 0.5 m. S4. After the slotting is completed, hydraulic fracturing is carried out on the pre-treated rock mass. The fractures generated by hydraulic fracturing extend along the direction of tunnel excavation and the direction of gravity according to the direction of slotting until the fractures between the boreholes are connected. Combining the borehole layout method, the depth of hydraulic fracturing fracture extension is 5m. The specific pre-fracture length is determined according to the thickness of the pre-treated rock layer and the borehole spacing. The formula for the rock fracture initiation pressure is: P F =3δ h -δ H -P S +δ τ , where P F is the fracture initiation pressure, δ h , δ H are the minimum and maximum horizontal principal stresses respectively, P S is the pore pressure, and δ τ is the tensile strength of the rock; during the hydraulic fracturing process, the generation of fractures and the end of the fracturing process are judged according to the change of water pressure; S5. After the pretreatment is completed, in order to minimize the disturbance to the non-excavated rock mass during the pretreatment process, the drilled holes between the pilot tunnel and the pretreated rock formation position are grouted and backfilled.

2. The tunnel hard rock pre-advance pretreatment method according to claim 1, characterized in that: The advanced pretreatment time T = drilling time t1 + hydraulic cut slot time t2 + hydraulic fracturing time t3.

3. The tunnel hard rock pre-advance pretreatment method according to claim 2, characterized in that: During backfilling, the backfill material uses the original rock material during drilling and a bonding material, and is backfilled with a one-way valve combined with a bladder.

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