Method for improving self stability of tunnel in aeolian sand stratum

Abstract

The application discloses a method for improving self stability of a tunnel after excavation in a aeolian sand stratum, and comprises the following steps: performing a moisture content and cohesion relationship test on aeolian sand in a region, drawing a moisture content and cohesion relationship curve, obtaining a moisture content interval for improving sand cohesion, and testing moisture content of a tunnel face; when moisture content of the tunnel face is not in the interval, drilling a front water injection hole on the front of the tunnel face and drilling a peripheral water injection hole around the tunnel face; inserting a peripheral water injection pipe into the peripheral water injection hole and inserting a front water injection pipe into the front water injection hole; calculating maximum water injection amount of each water injection hole, injecting water through the water injection pipes, and excavating until the moisture content of the tunnel face reaches the moisture content interval for guiding construction.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of tunnel engineering construction, and particularly relates to a method for improving the self stability of a tunnel in a wind-blown sand stratum. BACKGROUND

[0002] The natural wind-blown dry sand has a loose structure, a single gradation, a small cohesion, a small internal friction angle, and a low shear strength, and is prone to change in shape, displacement and flow under external force. After the tunnel in the wind-blown sand stratum is excavated, the stability is extremely difficult to control. In the tunnel engineering construction in the wind-blown sand stratum, the wind-blown sand stratum without support must maintain its own stability after excavation without external force intervention, otherwise accidents such as sand flow, collapse, landslide and roof fall may occur.

[0003] In the conventional tunnel construction technology, the advanced small pipe, pipe shed grouting and horizontal rotary jet grouting are adopted to fill and consolidate the stratum void by adding the material slurry such as cement slurry and cement+water glass slurry which can condense sand particles into a whole, so as to improve the integrity of the stratum. However, the natural filling of the void by obtaining the optimal water content and the lowest dry density to improve the integrity of the stratum has a high technical construction difficulty, a high requirement for technical equipment, a high cost of cement and other adhesive fillers, a low construction progress index, and a great impact on the environment. How to solve the problem by other ideas is a problem to be solved in the field. SUMMARY

[0004] The present application aims to solve the technical problem of providing a method for improving the self stability of a tunnel in a wind-blown sand stratum without adding the material slurry which can condense sand particles into a whole, so as to effectively improve the cohesion and shear strength and further improve the integrity of the stratum.

[0005] The technical scheme of the present application is as follows:

[0006] A method for improving the self stability of a tunnel in a wind-blown sand stratum, comprising the following steps:

[0007] Step 1: performing a moisture content and cohesion relationship test on the wind-blown sand in the region, drawing a moisture content and cohesion relationship curve according to the Mohr-Coulomb strength theory, the moisture content and cohesion relationship curve being divided into four intervals w1, w2, w3 and w4, and obtaining the moisture content interval w1-w3 for improving the cohesion of the sand;

[0008] Step 2: determining the moisture content interval w2-w4 for guiding the construction;

[0009] Step 3: closing the tunnel face by spraying concrete;

[0010] Step 4: Water content test is performed on the tunnel face, and excavation is performed when the water content of the face is in the interval of w2-w4; when the water content of the face is not in the interval of w2-w4, the next step is performed;

[0011] Step 5: A front water injection hole is drilled on the front of the face;

[0012] Step 6: A peripheral water injection hole is drilled around the face;

[0013] Step 7: A peripheral water injection pipe is inserted into the peripheral water injection hole, and a front water injection pipe is inserted into the front water injection hole;

[0014] Step 8: The maximum water injection amount of each water injection hole to reach w3 water content is calculated, and water injection is performed through the peripheral water injection pipe and the front water injection pipe, and the calculation method of the maximum water injection amount is as follows:

[0015] Step 8.1, determine the volume of the single-hole surrounding rock soil body:

[0016] V=πR 2 ×L,

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

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

[0019] M s =ρ d ×V,

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

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

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

[0023] and the target water content of the surrounding rock be M w3 =w3×M s ,

[0024] wherein 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, and w3 represents the target water content, i.e. the water content w3;

[0025] The required increased water amount is:

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

[0027] wherein, Delta M w represents the required increase in water quality;

[0028] Step 8.4, convert the water amount to volume:

[0029]

[0030] wherein, Delta V w represents the maximum water injection amount, rho w represents the water density;

[0031] Step 9: repeat step 8 until the water content of the working face is in the water content interval in step 2, and then excavate.

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

[0033] Further, the peripheral water injection holes in step 6 are arranged in a ring shape along the hole, the spacing between the peripheral water injection holes is 0.4±0.1m, the depth of the peripheral water injection hole is 4±0.5m, the inclination angle of the peripheral water injection hole is 5°, and the inclination direction is outward along the hole line.

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

[0035] Further, the material of the peripheral water injection pipe is steel pipe, and the diameter of the peripheral water injection pipe is 40±5mm.

[0036] Further, a plurality of openings are formed 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±5cm.

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

[0038] The beneficial effects of the application are:

[0039] 1. Accurate control of moisture content, improve the cohesion of sand body: the invention obtains the moisture content interval w1-w3 which can significantly improve the cohesion of aeolian sand layer through the "moisture content-cohesion relationship test", and further determines the more suitable moisture content interval w2-w4; according to the interval, the moisture content is accurately controlled, the "liquid bridge" or "capillary water film" effect is formed between sand particles, the cohesion of sand body is increased, and the safety hidden danger such as quicksand and collapse is greatly reduced;

[0040] 2. Interval, multiple rounds of water injection, high safety in construction: when the moisture content of the working face does not reach w2, through multiple rounds of intermittent water injection (and detecting the moisture content each time), the moisture content is gradually controlled to w2-w4; this "water injection-detection-water injection again" cycle can effectively avoid the risks of water inrush, roof fall and mudification caused by excessive one-time water injection, while ensuring the operability and safety of the construction surface;

[0041] 3. Combination of front water injection and peripheral water injection, uniform and comprehensive humidification: the invention not only sets up the water injection hole in the form of plum blossom on the front of the working face, but also sets up the annular water injection hole around the periphery of the hole, through the coordinated water injection of the front pipe and the peripheral pipe, the water can be more evenly spread to each area of the working face and surrounding rock; compared with water injection in only one direction, this "front+peripheral" multidirectional 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 of normal temperature water + appropriate water injection pressure to reduce the influence of adverse geology: the water injection temperature of the invention is normal temperature, and the pressure is in the interval of 1.0±0.1MPa, on the one hand, it can provide enough penetration driving force for aeolian sand, on the other hand, it can reduce the disturbance and stratum damage that may be caused by high pressure or high temperature water injection; this water injection pressure range takes into account the injection efficiency and stratum safety, compared with excessively high pressure, it is not easy to cause large-scale penetration damage or water gushing risk;

[0043] 5. Spray concrete to seal the working face to reduce water loss: the invention sprays concrete to seal the working face before (or at the initial stage of) water injection, which can significantly reduce water evaporation and lateral loss, and improve water injection efficiency; at the same time, it can also provide initial support on the surface of the working face, reducing the falling and collapse of sand; this measure cooperates with the water injection process, taking into account water retention and support safety;

[0044] 6. Reasonable layout of water injection hole and design of water injection pipe piercing hole to improve water injection uniformity: the plum blossom-shaped front water injection hole and the ring-shaped peripheral water injection hole have a small range of spacing control (0.4m-0.5m order of magnitude), which can better cover the working face and the surrounding aeolian sand body; the piercing holes (20±5cm) are arranged at equal intervals on the water injection pipe, water can penetrate at different depths, greatly improving the water injection uniformity and penetration efficiency;

[0045] 7. Single-hole calculation of maximum water injection amount to avoid excessive water injection: The required water amount of the single-hole to reach the water content w3 is calculated by the clear volume-mass balance formula (dry density, water content difference, water injection loss coefficient, etc.), so that the water injection has a basis;

[0046] 8. The whole process is simple and easy to operate, and has strong operability: The present application 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 means; the construction unit has low requirements and high safety, and is convenient for large-scale popularization and application in aeolian sand stratum;

[0047] In summary, the present application fully utilizes the relationship between water content and cohesion through a series of steps of "first closing the working face-detecting water content-multipoint water injection-cyclic detection", improves the stability of sand layer while considering construction safety and construction efficiency; The process mode of front and peripheral joint water injection and scientific calculation of single-hole maximum water injection amount make the moisture of surrounding rock more uniform and controllable; The combination of shotcrete closing the working face and normal temperature high pressure water injection also further reduces the risk of water loss and surrounding rock loosening; In summary, the present application can significantly improve the self-stability and construction safety of aeolian sand stratum tunnel in the excavation process, and has good engineering application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 is a flow step schematic diagram of a method for improving the self-stability of aeolian sand stratum tunnel of the present application.

[0049] Figure 2 is a water content and cohesion relationship curve diagram of a method for improving the self-stability of aeolian sand stratum tunnel of the present application. DETAILED DESCRIPTION

[0050] As shown in Figures 1-2 , a method for improving the self-stability of aeolian sand stratum tunnel, comprising the following steps:

[0051] Step 1: Perform water content and cohesion relationship test on the aeolian sand in the area, and draw a water content and cohesion relationship curve according to the Mohr-Coulomb strength theory, wherein the water content and cohesion relationship curve is divided into four intervals w1, w2, w3 and w4 Figure 2The point w1 represents the dry state of the aeolian sand, at this time the aeolian sand is dry and loose, and the cohesion is approximately zero, the aeolian sand has no self-stability, and cannot form a hole without external force constraint, the moisture content interval w1-w3 (from the point w1 to the point w3, with the increase of the moisture content in the aeolian sand, the water film on the surface of the particles will produce a certain cohesion, and the maximum value is reached at the point w3, the influence of the moisture content on the aeolian sand mainly includes 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, second, the suction caused by the capillary stress, and third, the water glue connection effect of the common combined water film between particles, the combined water is different from the free water, and has a certain viscosity, elasticity and shear resistance, when the moisture content is low, the water glue connection effect of the common combined water film is strong, thereby increasing the cohesion; when reaching w3, with the increase of the moisture content, the thickness of the combined water film increases, because the inner layer and the outer layer of the thick combined water film have different properties, the viscosity of water decreases with the increase of the distance from the surface of the soil particles, the lubricating effect of water between particles gradually increases, the non-lubricating adsorption effect decreases, at the same time, the capillary action decreases with the increase of the moisture content and disappears, therefore, the relative movement between particles becomes easy, when reaching the saturation state, the effect of water is completely lubricating, and the movement of the sand particles becomes the easiest);

[0052] Step 2: determining the moisture content interval w2-w4 for guiding construction (the cohesion is high in this interval, if the interval is too small, the cohesion is too high, and the construction control is difficult; if the interval is too large, the cohesion is too low; according to the actual situation, a suitable moisture content interval is selected, which can obviously improve the efficiency, at this time, the excavation is carried out, without the need of adding the coagulation material slurry to fill and coagulate the stratum fissure, the cohesion and the shear strength can be effectively improved, thereby improving the integrity of the stratum);

[0053] Step 3: closing the tunnel face by spraying concrete;

[0054] Step 4: testing the moisture content of the tunnel face, when the moisture content of the tunnel face is in the interval w2-w4, the excavation is carried out; when the moisture content of the tunnel face is not in the interval w2-w4, the next step is carried out;

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

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

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

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

[0059] Step 8.1, determine the volume of the single-hole surrounding rock soil:

[0060] V = πR 2 ×L,

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

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

[0063] M s = ρ d ×V,

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

[0065] Step 8.3, determine the difference between the current moisture content of the surrounding rock and the target moisture content:

[0066] Let the current moisture content of the surrounding rock be M w0 = w0×M s ,

[0067] The target moisture content of the surrounding rock is M w3 = w3×M s ,

[0068] Wherein, M w0 represents the current moisture content of the surrounding rock, w0 represents the actual moisture content of the surrounding rock before tunnel excavation or water injection, M w3 represents the target moisture content of the surrounding rock, and w3 represents the target moisture content, i.e. the moisture content w3.

[0069] The required increased water amount is:

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

[0071] Wherein, ΔM w represents the required increased water mass;

[0072] Step 8.4, convert the required increased water amount into volume:

[0073]

[0074] Wherein, ΔVw represents the maximum water injection amount, p w represents the water density;

[0075] Step 9: repeat step 8 until the water content of the working face is in the water content interval in step 2, and then excavate.

[0076] Preferably, the front water injection holes in step 5 are arranged in a quincunx 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 hole, the spacing between the peripheral water injection holes is 0.4±0.1m, the depth of the peripheral water injection holes is 4±0.5m, the inclination angle of the peripheral water injection holes is 5°, and the inclination direction is outward along the hole line.

[0078] Preferably, the material of the front water injection pipe is a PVC pipe (the head is processed into a conical shape by hot melting), and the diameter of the front water injection pipe is 40±5mm (when installing the PVC pipe as the water injection pipe, if the pushing resistance is large, a rotary electric drill machine 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, a hard plastic pipe can be used as the water injection pipe, and a pneumatic rock drill and other equipment are used to slowly push the water injection pipe into the hole).

[0079] Preferably, the material of the peripheral water injection pipe is a steel pipe (the head is processed into a conical shape by hot pressing), and the diameter of the peripheral water injection pipe is 40±5mm (when installing the steel pipe as the water injection pipe, a pneumatic rock drill and other equipment are used 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, the openings are arranged at equal intervals along the length direction of the water injection pipe, and the interval of the openings is 20±5cm.

[0081] It should be noted that the peripheral steel water injection pipe does not need to be removed, and it has the same effect as the traditional advanced small guide pipe; the front PVC water injection pipe is arranged in the area to be excavated, which is convenient for 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 examples are only used to illustrate the technical solutions of the present application and not to limit it. Although the present application 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 application can be modified or replaced by equivalents without departing from the purpose and scope of the present application, and they should be covered in the scope of the claims of the present application.

Claims

1. A method for improving the stability of a tunnel during excavation in a dune sand formation, characterized in that, The method comprises the following steps: Step 1: Conducting a moisture content and cohesion relationship test on the aeolian sand in the region, drawing a moisture content and cohesion relationship curve according to the Mohr-Coulomb strength theory, the moisture content and cohesion relationship curve being divided into four intervals w1, w2, w3 and w4, and obtaining the moisture content intervals w1-w3 for improving the cohesion of the sand; Step 2: Determining the moisture content intervals w2-w4 for guiding the construction; Step 3: Conducting a shotcrete closure on the tunnel face; Step 4: Conducting a moisture content test on the tunnel face, and when the moisture content of the tunnel face is in the interval w2-w4, excavating; when the moisture content of the tunnel face is not in the interval w2-w4, proceeding to the next step; Step 5: Drilling a front water injection hole on the front face of the tunnel face; Step 6: Drilling a peripheral water injection hole around the tunnel face; Step 7: Inserting a peripheral water injection pipe into the peripheral water injection hole and a front water injection pipe into the front water injection hole; Step 8: Calculating the maximum water injection amount of each water injection hole to reach the moisture content w3, and conducting water injection through the peripheral water injection pipe and the front water injection pipe, the calculation method of the maximum water injection amount being as follows: Step 8.1: Determining the volume of the single-hole surrounding rock soil body: ， wherein, V represents the volume of the surrounding rock, L represents the axial length of the water injection hole, R represents the horizontal diffusion radius of the water injection hole; Step 8.2: Calculating the mass of the surrounding rock: ， wherein, represents the quality of the surrounding rock, represents the dry density of the aeolian sand, V represents the volume of the surrounding rock; Step 8.3: Determining the difference between the current moisture content and the target moisture content of the surrounding rock: Surrounding rock current water content: , Then the target water content of the surrounding rock is: , wherein, represents the current water content of the surrounding rock, represents the actual water content of the surrounding rock before tunnel excavation or before water injection, represents the target water content of the surrounding rock, represents the target water content of the surrounding rock, i.e. the water content w3; The required increased water amount is: ， wherein, represents the mass of water required to be added; Step 8.4: Converting the required increased water amount into volume: ， wherein, represents the maximum water injection rate, represents the water density; Step 9: Repeating step 8 until the moisture content of the tunnel face is in the moisture content interval in step 2, and then excavating; A plurality of openings are formed on the front water injection pipe and the peripheral water injection pipe, the openings being arranged at equal intervals along the length direction of the water injection pipe, and the interval of the openings being 20±5 cm.

2. The method for improving the self-stability of tunnel excavation in a sand dune deposit according to claim 1, characterized in that, The front water injection holes in step 5 are arranged in a quincunx shape, the interval between the front water injection holes being 0.5±0.1 m, the depth of the front water injection holes being 4±0.5 m, and the inclination angle of the front water injection holes being 0.

3. The method for improving the self-stability of tunnel excavation in a sand dune deposit according to claim 1, characterized in that, The peripheral water injection holes in step 6 are arranged in a ring shape around the hole, the interval between the peripheral water injection holes being 0.4±0.1 m, the depth of the peripheral water injection holes being 4±0.5 m, the inclination angle of the peripheral water injection holes being 5°, and the inclination direction being outward along the hole line.

4. The method for improving the self-stability of tunnel excavation in a sand dune deposit according to claim 1, characterized in that, The material of the front water injection pipe is PVC pipe, and the diameter of the front water injection pipe is 40±5 mm.

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

6. The method for improving the self-stability of tunnel excavation in a dune sand stratum according to claim 1, characterized in that, The water injection in step 8 is at normal temperature, and the water injection pressure is 1.0±0.1 MPa.

Images