Method for improving excavation stability of aeolian sand stratum tunnel

Abstract

The invention discloses a method for improving self-stability of an aeolian sand stratum tunnel after excavation, which comprises the following steps of: performing a water content and cohesive force relation test on aeolian sand in an area, drawing a water content and cohesive force relation curve, and obtaining a water content interval for improving the cohesive force of the sand; testing the water content of the tunnel face; when the water content of the tunnel face is not within the interval, front face water injection holes are drilled in the front face of the tunnel face, and peripheral water injection holes are drilled in the periphery of the tunnel face; peripheral water injection pipes are inserted into the peripheral water injection holes, and front water injection pipes are inserted into the front water injection holes; calculating the maximum water injection rate of each water injection hole, and injecting water through the water injection pipe; and excavating until the water content of the tunnel face reaches the water content interval for guiding construction. The method does not need to inject coagulable material slurry into the stratum to fill and coagulate the stratum fracture, and improves the cohesiveness and shear strength, thereby improving the integrity of the stratum.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel engineering construction, and in particular relates to a method for improving the excavation stability of a tunnel in aeolian sand stratum. Background Art

[0002] The structure of natural wind-blown dry sand is loose, with a single gradation, low cohesion, small internal friction angle, and low shear strength. It is easy to change shape, displace, and flow under the action of external forces. After the tunnel is excavated, the wind-blown sand stratum is in a flowing state, and its stability is extremely difficult to control. In the construction of tunnel engineering in wind-blown sand strata, after excavation, the unsupported wind-blown sand stratum must maintain its own stability without the rapid restraint intervention of external forces, otherwise accidents such as quicksand flow, collapse, sliding, and roof fall will occur.

[0003] In traditional tunnel construction technology, methods such as advanced small guide tubes, pipe-roof grouting, horizontal rotary spraying, etc. are adopted to inject material slurry that can condense sand particles into a whole into the formation, such as cement slurry, cement + water glass slurry, etc., so as to fill and consolidate the formation voids and improve the integrity of the formation; there is also a method of naturally filling the voids by obtaining the optimal water content and the lowest dry density to improve the integrity of the formation, but the technical construction is difficult and has high requirements on technical equipment. Cement and other adhesive fillers have high costs, low construction progress indicators, and great impact on the environment. How to adopt other ideas to solve the problem is an issue that needs to be urgently solved in this field. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for improving the excavation stability of a tunnel in aeolian sand stratum by effectively improving the cohesive force and shear strength, thereby improving the integrity of the stratum, without adding a coagulated material slurry into the stratum.

[0005] The technical solution of the present invention is:

[0006] A method for improving the excavation stability of a tunnel in aeolian sand stratum, comprising the following steps:

[0007] Step 1: Conduct a test on the relationship between moisture content and cohesion of the aeolian sand in the area, and draw a moisture content and cohesion relationship curve based on the Mohr-Coulomb strength theory. The moisture content and cohesion relationship curve is divided into four intervals w1, w2, w3 and w4, and the moisture content interval w1-w3 for improving the cohesion of the sand is obtained;

[0008] Step 2: Determine the moisture content range w2-w4 to guide construction;

[0009] Step 3: Seal the tunnel face with sprayed concrete;

[0010] Step 4: Test the water content of the tunnel face. When the water content of the tunnel face is within the range of w2-w4, excavation is carried out; when the water content of the tunnel face is not within the range of w2-w4, proceed to the next step;

[0011] Step 5: drilling a front water injection hole on the front of the palm face;

[0012] Step 6: drilling peripheral water injection holes around the tunnel face;

[0013] Step 7: inserting a peripheral water injection pipe into the peripheral water injection hole; inserting a front water injection pipe into the front water injection hole;

[0014] Step 8: Calculate the maximum water injection volume of each water injection hole to reach the water content of w3, and inject water through the peripheral water injection pipe and the front water injection pipe. The calculation method of the maximum water injection volume is:

[0015] Step 8.1: Determine the volume of the surrounding rock mass of a single hole:

[0016] V=πR 2 × L,

[0017] Among them, V represents the volume of surrounding rock, L represents the axial length of the injection hole, and R represents the horizontal diffusion radius of the injection hole;

[0018] Step 8.2, calculate the mass of surrounding rock:

[0019] M s =ρ d ×V,

[0020] Among them, M s represents the quality of surrounding rock, ρ d represents the dry density of aeolian sand, and V represents the volume of surrounding rock;

[0021] Step 8.3: Determine the difference between the current water content of the surrounding rock and the target water content:

[0022] Assume the current water content of surrounding rock: M w0 =w0×M s ,

[0023] Then the target water content of surrounding rock is: M w3 =w3×M s ,

[0024] Among them, M w0 represents the current water content of the surrounding rock, w0 represents the actual water content of the surrounding rock before tunnel excavation or water injection, M w3 represents the target water content of the surrounding rock, w3 represents the target water content of the surrounding rock, that is, the water content w3;

[0025] The amount of water required is:

[0026] ΔM w =M w3 -M w0 =M s ×(w3-w0),

[0027] Among them, ΔM w Indicates the mass of water required to be added;

[0028] Step 8.4: Convert the required water addition into volume:

[0029]

[0030] Where, ΔV w represents the maximum water injection volume, ρ w Indicates water density;

[0031] Step 9: Repeat step 8 until the water content of the tunnel face is within the water content range in step 2, and then perform excavation.

[0032] Furthermore, the front water injection holes in step 5 are arranged in a plum blossom shape, the spacing between the front water injection holes is 0.5±0.1m, the depth of the front water injection holes is 4±0.5m, and the inclination angle of the front water injection holes is 0.

[0033] Furthermore, the peripheral water injection holes in step 6 are arranged in a circular shape along the circumference of the cave, the spacing between the peripheral water injection holes is 0.4±0.1m, the peripheral water injection holes are 4±0.5m deep, the peripheral water injection holes have an inclination angle of 5°, and the inclination direction is outward along the cave line.

[0034] Furthermore, the front water injection pipe is made of PVC pipe, and the diameter of the front water injection pipe is 40±5mm.

[0035] Furthermore, the peripheral water injection pipe is made of a steel pipe, and the diameter of the peripheral water injection pipe is 40±5 mm.

[0036] Furthermore, a plurality of openings are provided on the front water injection pipe and the peripheral water injection pipe. The openings are arranged at equal intervals along the length direction of the water injection pipe, and the opening interval is 20±5 cm.

[0037] Furthermore, the water injection in step 8 is at room temperature and the water injection pressure is 1.0±0.1Mpa.

[0038] Beneficial effects of the present invention:

[0039] 1. Accurately control the water content and improve the cohesion of the sand body: The present invention obtains the water content range w1-w3 that can significantly improve the cohesion of the aeolian sand layer through the "water content-cohesion relationship test", and then determines the water content range w2-w4 that is more suitable for construction; the water content is accurately controlled according to the range to form a "liquid bridge" or "capillary water film" between the sand particles, thereby increasing the cohesion of the sand body and greatly reducing safety hazards such as quicksand and collapse;

[0040] 2. Water injection in sections and multiple rounds, high construction safety: When the water content of the face does not reach w2, the water content is gradually controlled to w2-w4 through multiple rounds of intermittent water injection (and the water content is tested each time); this "water injection-testing-re-water injection" cycle can effectively avoid the risks of water inrush, roof collapse, mudification, etc. caused by excessive water injection at one time, while ensuring the operability and safety of the construction surface;

[0041] 3. Combining front water injection with peripheral water injection, uniform and comprehensive humidification: The present invention not only sets plum blossom-shaped water injection holes on the front of the tunnel face, but also sets annular water injection holes around the tunnel. Through the coordinated water injection of the front pipe and the peripheral pipe, the water can be more evenly diffused to the tunnel face and various areas of the surrounding rock. Compared with water injection in a single direction only, this "front + peripheral" multi-directional water injection layout is conducive to forming an overall humidification zone around the tunnel, thereby better improving the overall stability of the surrounding rock;

[0042] 4. Use normal temperature water + appropriate water injection pressure to reduce adverse geological impacts: The water injection temperature of the present invention is normal temperature and the pressure is in the range of 1.0±0.1MPa. On the one hand, it can provide sufficient penetration driving force for aeolian sand, and on the other hand, it can reduce the disturbance and formation damage that may be caused by high-pressure or high-temperature water injection; this water injection pressure range takes into account both injection efficiency and formation safety, and is less likely to cause large-scale penetration damage or water gushing risks compared to excessive pressure;

[0043] 5. Spraying concrete to seal the tunnel face and reduce water loss: The present invention sprays concrete to seal the tunnel face before water injection (or in the early stage of water injection), which can significantly reduce water volatilization and lateral loss and improve water injection efficiency; at the same time, it can also provide initial support on the tunnel face surface to reduce sand and soil falling and collapse; this measure is coordinated with the water injection process, taking into account both water retention and support safety;

[0044] 6. Reasonable layout of injection holes and design of puncture holes in the injection pipes improve the uniformity of water injection: the front injection holes are in a plum blossom shape, and the circumferential spacing of the peripheral injection holes is controlled in a smaller range (0.4m to 0.5m), which can better cover the tunnel face and the surrounding aeolian sand bodies; puncture holes (20±5cm) are opened on the injection pipes at equal intervals, and water can penetrate in layers at different depths, greatly improving the uniformity of water injection and penetration efficiency;

[0045] 7. Calculate the maximum water injection volume for a single hole to avoid excessive water injection: The present invention calculates the amount of water required for a single hole to reach a water content of w3 through a clear volume-mass balance formula (dry density, water content difference, water injection loss coefficient, etc.), so that water injection has a basis to rely on;

[0046] 8. The overall process is simple and easy to operate, and has strong operability: the present invention does not require high-temperature water, chemical slurry or special equipment, and can be implemented only by relying on common water injection pipes, water injection pumps, and water content detection methods; it has low requirements for construction units and high safety, and is easy to promote and apply on a large scale in aeolian sand formations;

[0047] In summary, the present invention fully utilizes the relationship between moisture content and cohesion through a series of steps of "first closing the heading face - testing moisture content - multi-point water injection - cyclic testing", while improving the stability of the sand layer, taking into account both construction safety and construction efficiency; the process mode of joint water injection from the front and the periphery and the scientific calculation of the maximum water injection volume of a single hole make the humidification of the surrounding rock more uniform and controllable; and the combination of shotcrete sealing of the heading face and normal temperature and high-pressure water injection further reduces the risk of moisture loss and loosening of the surrounding rock; in short, the present invention can significantly improve the self-stability and construction safety of tunnels in aeolian sand strata during excavation, and has good engineering application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a schematic diagram of the process steps of a method for improving the excavation stability of a tunnel in aeolian sand stratum according to the present invention.

[0049] Figure 2 The present invention discloses a curve diagram showing the relationship between moisture content of aeolian sand and cohesion in a method for improving the excavation stability of a tunnel in aeolian sand stratum. DETAILED DESCRIPTION

[0050] like Figure 1-2 As shown, a method for improving the excavation stability of a tunnel in aeolian sand stratum comprises the following steps:

[0051] Step 1: Conduct a test on the relationship between moisture content and cohesion of the aeolian sand in the area, and draw a moisture content and cohesion relationship curve based on the Mohr-Coulomb strength theory. The moisture content and cohesion relationship curve is divided into four intervals w1, w2, w3 and w4 ( Figure 2Point w1 represents the dry state of aeolian sand. At this time, the aeolian sand is dry and loose, and its cohesion is approximately zero. In this state, the aeolian sand has no self-stabilizing ability, and it cannot form a hole by excavation without external force constraints). The moisture content interval w1-w3 that improves the cohesion of sand is obtained (from point w1 to point w3, as the water content in the aeolian sand increases, the water film on the surface of the particles will produce a certain cohesion, reaching the maximum value at point w3. The influence of moisture content on aeolian sand mainly has the following points: first, the non-lubricating adsorption effect of water on the surface of minerals such as quartz, which is caused by the viscosity of water, secondly, the suction caused by capillary stress, and thirdly, the water bonding effect of the common binding water film between particles, combined with Water is different from free water. It has certain viscosity, elasticity and shear resistance. When the water content is low, the water bonding effect generated by the common bound water film is very strong, thereby increasing the cohesive force. After reaching w3, the thickness of the bound water film increases with the increase of water content. Since the inner and outer layers of the thick bound water film have different properties, the viscosity of water decreases with the increase of the distance from the surface of the soil particles, the lubrication effect of water between particles gradually increases, and the non-lubricating adsorption effect decreases. At the same time, the capillary effect decreases and even disappears with the increase of water content. Therefore, the relative movement between particles becomes easy. When the saturated state is reached, the role of water completely becomes lubrication, and the movement of sand particles becomes the easiest).

[0052] Step 2: Determine the water content interval w2-w4 for guiding construction (the cohesion in this interval is at a high level. If the interval is too small, the cohesion will increase too much, making construction control difficult; if the interval is too large, the cohesion will increase too little. Selecting a suitable water content interval according to actual conditions can significantly improve efficiency. At this time, excavation construction can be carried out without adding condensable material slurry to the stratum to fill and condense the stratum cracks, which can effectively improve the cohesion and shear strength, thereby improving the integrity of the stratum);

[0053] Step 3: Seal the tunnel face with sprayed concrete;

[0054] Step 4: Test the water content of the tunnel face. When the water content of the tunnel face is within the range of w2-w4, excavation is carried out; when the water content of the tunnel face is not within the range of w2-w4, proceed to the next step;

[0055] Step 5: drilling a front water injection hole on the front of the palm face;

[0056] Step 6: drilling peripheral water injection holes around the tunnel face;

[0057] Step 7: inserting a peripheral water injection pipe into the peripheral water injection hole; inserting a front water injection pipe into the front water injection hole;

[0058] Step 8: Calculate the maximum water injection volume of each water injection hole to reach the water content of w3, and inject water through the peripheral water injection pipe and the front water injection pipe. The calculation method of the maximum water injection volume is:

[0059] Step 8.1: Determine the volume of the surrounding rock mass of a single hole:

[0060] V=πR 2 × L,

[0061] Among them, V represents the volume of surrounding rock, L represents the axial length of the injection hole, and R represents the horizontal diffusion radius of the injection hole;

[0062] Step 8.2, calculate the mass of surrounding rock:

[0063] M s =ρ d ×V,

[0064] Among them, M s represents the quality of surrounding rock, ρ d represents the dry density of aeolian sand, and V represents the volume of surrounding rock;

[0065] Step 8.3: Determine the difference between the current water content of the surrounding rock and the target water content:

[0066] Assume the current water content of surrounding rock: M w0 =w0×M s ,

[0067] Then the target water content of surrounding rock is: M w3 =w3×M s ,

[0068] Among them, M w0 represents the current water content of the surrounding rock, w0 represents the actual water content of the surrounding rock before tunnel excavation or water injection, M w3 represents the target water content of the surrounding rock, w3 represents the target water content of the surrounding rock, that is, the water content w3;

[0069] The amount of water required is:

[0070] ΔM w =M w3 -M w0 =M s ×(w3-w0),

[0071] Among them, ΔM w Indicates the mass of water required to be added;

[0072] Step 8.4: Convert the required water addition into volume:

[0073]

[0074] Where, ΔVw represents the maximum water injection volume, ρ w Indicates water density;

[0075] Step 9: Repeat step 8 until the water content of the tunnel face is within the water content range in step 2, and then perform excavation.

[0076] Preferably, the front water injection holes in step 5 are arranged in a plum blossom shape, the spacing between the front water injection holes is 0.5±0.1m, the depth of the front water injection holes is 4±0.5m, and the inclination angle of the front water injection holes is 0.

[0077] Preferably, the peripheral water injection holes in step 6 are arranged in a ring shape along the circumference of the cave, the spacing between the peripheral water injection holes is 0.4±0.1m, the peripheral water injection holes are 4±0.5m deep, the peripheral water injection holes have an inclination angle of 5°, and the inclination direction is outward along the cave line.

[0078] Preferably, the front water injection pipe is made of PVC pipe (the head is processed into a cone by hot melt), and the diameter of the front water injection pipe is 40±5mm (when installing the PVC pipe water injection pipe, if the advancement resistance is large, a rotary electric drill can be used to sweep the hole and continue to lower the pipe; if the resistance is still large and the pipe cannot be lowered to the specified hole depth, it can be replaced with a hard plastic pipe as the water injection pipe, and a pneumatic rock drill and other equipment can be used to slowly push the water injection pipe into the hole).

[0079] Preferably, the peripheral water injection pipe is made of steel pipe (the pipe head is processed into a cone using hot pressing equipment), and the diameter of the peripheral water injection pipe is 40±5mm (when installing the steel pipe as the water injection pipe, use equipment such as a pneumatic rock drill to slowly push the water injection pipe into the hole).

[0080] Preferably, a plurality of openings are provided on the front water injection pipe and the peripheral water injection pipe, and the openings are arranged at equal intervals along the length direction of the water injection pipe, and the opening interval is 20±5 cm.

[0081] It should be noted that the surrounding steel water injection pipes do not need to be removed, and they have the same effect as traditional advance small ducts; the front PVC water injection pipes are set in the planned excavation area, which is easy to remove during excavation.

[0082] Preferably, the water injection in step 8 is at room temperature and the water injection pressure is 1.0±0.1Mpa.

[0083] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for improving the excavation stability of a tunnel in aeolian sand stratum, characterized in that: The following steps are involved: Step 1: Conduct a test on the relationship between moisture content and cohesion of the aeolian sand in the area, and draw a moisture content and cohesion relationship curve based on the Mohr-Coulomb strength theory. The moisture content and cohesion relationship curve is divided into four intervals w1, w2, w3 and w4, and the moisture content interval w1-w3 for improving the cohesion of the sand is obtained; Step 2: Determine the moisture content range w2-w4 to guide construction; Step 3: Seal the tunnel face with sprayed concrete; Step 4: Test the water content of the tunnel face. When the water content of the tunnel face is within the range of w2-w4, excavation is carried out; when the water content of the tunnel face is not within the range of w2-w4, proceed to the next step; Step 5: drilling a front water injection hole on the front of the palm face; Step 6: drilling peripheral water injection holes around the tunnel face; Step 7: inserting a peripheral water injection pipe into the peripheral water injection hole; inserting a front water injection pipe into the front water injection hole; Step 8: Calculate the maximum water injection volume of each water injection hole to reach the water content of w3, and inject water through the peripheral water injection pipe and the front water injection pipe. The calculation method of the maximum water injection volume is: Step 8.1: Determine the volume of the surrounding rock mass of a single hole: V=πR 2 ×L, Among them, V represents the volume of surrounding rock, L represents the axial length of the injection hole, and R represents the horizontal diffusion radius of the injection hole; Step 8.2, calculate the mass of surrounding rock: M s =ρ d ×V, Among them, M s represents the quality of surrounding rock, ρ d represents the dry density of aeolian sand, and V represents the volume of surrounding rock; Step 8.3: Determine the difference between the current water content of the surrounding rock and the target water content: Assume the current water content of surrounding rock: M w0 =w0×M s , Then the target water content of surrounding rock is: M w3 =w3×M s , Among them, M w0 represents the current water content of the surrounding rock, w0 represents the actual water content of the surrounding rock before tunnel excavation or water injection, M w3 represents the target water content of the surrounding rock, w3 represents the target water content of the surrounding rock, that is, the water content w3; The amount of water required is: ΔM w =M w3 -M w0 =M s ×(w3-w0), Among them, ΔM w Indicates the mass of water required to be added; Step 8.4: Convert the required water addition into volume: Where, ΔV w represents the maximum water injection volume, ρ w Indicates water density; Step 9: Repeat step 8 until the water content of the tunnel face is within the water content range in step 2, and then perform excavation.

2. The method for improving the excavation stability of a tunnel in aeolian sand stratum according to claim 1, characterized in that: The front water injection holes in step 5 are arranged in a plum blossom shape, the spacing between the front water injection holes is 0.5±0.1m, the front water injection holes are 4±0.5m deep, and the inclination angle of the front water injection holes is 0.

3. The method for improving the excavation stability of a tunnel in aeolian sand stratum according to claim 1, characterized in that: The peripheral water injection holes in step 6 are arranged in a ring shape along the circumference of the cave, the spacing between the peripheral water injection holes is 0.4±0.1m, the peripheral water injection holes are 4±0.5m deep, the peripheral water injection holes have an inclination angle of 5°, and the inclination direction is outward along the cave line.

4. The method for improving the excavation stability of a tunnel in aeolian sand stratum according to claim 1, characterized in that: The front water injection pipe is made of PVC pipe, and the diameter of the front water injection pipe is 40±5mm.

5. The method for improving the excavation stability of a tunnel in aeolian sand stratum according to claim 1, characterized in that: The peripheral water injection pipe is made of a steel pipe, and the diameter of the peripheral water injection pipe is 40±5 mm.

6. The method for improving the excavation stability of a tunnel in aeolian sand stratum according to claim 1, characterized in that: A plurality of openings are provided on the front water injection pipe and the peripheral water injection pipe. The openings are arranged at equal intervals along the length direction of the water injection pipe, and the opening interval is 20±5 cm.

7. The method for improving the excavation stability of a tunnel in aeolian sand stratum according to claim 1, characterized in that: The water injection in step 8 is at room temperature and the water injection pressure is 1.0±0.1Mpa.

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