Sand and gravel pile arrangement structure and method for dissipating excess pore water pressure in soil around tunnels

Abstract

The present invention relates to a gravel pile arrangement structure and method for dissipating excess pore water pressure in the soil around a tunnel. The gravel pile arrangement structure comprises a rectangular gravel pile array arranged on both sides of the tunnel, each side comprising m rows of gravel mixed piles; along the extension direction of the tunnel, the spacing between adjacent gravel mixed piles is S. 纵 Determine it according to the following formula: #imgabs0# where d is the diameter of the sand-gravel pile, n is the well diameter ratio, and determine it according to the following formula: #imgabs1# where t is the time from the arrival of the shield machine to the shield tail being released, U is the consolidation degree of the stratum around the sand-gravel pile, c h is the lateral consolidation coefficient. When m>1, the spacing S between adjacent sand-gravel piles on the same side of the tunnel is perpendicular to the tunnel extension direction. 横 Determine according to the following formula: #imgabs2# where R is the outer diameter of the tunnel. Compared with existing technologies, this invention provides a practical design method for the above-mentioned structure, with a theoretical basis. This solves the problem that existing gravel pile designs lack theoretical basis and fail to achieve the desired effect of dissipating pore water pressure.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel engineering, and relates to a sand and gravel pile arrangement structure and method for dissipating excess pore water pressure in soil around a tunnel. Background Art

[0002] With the sustained and rapid development of my country's economy, infrastructure construction in coastal soft soil areas has been unprecedented in recent years, resulting in significant deformation of rail transit structures. For example, since its opening in 1995, Shanghai Metro Line 1 has experienced significant longitudinal and uneven settlement in most sections of the tunnel, with local maximum settlement exceeding 300 mm. This cumulative settlement stems from changes in pore water pressure and soil stress. Under the disturbance of shield excavation and the long-term cyclic loads of trains, the soil around the tunnel adjusts, compacting and discharging pore water. If such soils are not permeable and drainage is poor, excess pore water pressure will be generated due to the incompressibility of water. This significantly reduces the shear strength of the strata, ultimately leading to cumulative settlement of the strata surrounding tunnels in soft soil areas.

[0003] The soft soil foundation reinforcement around existing tunnels mainly adopts drainage consolidation preloading method, composite foundation method, replacement and dynamic compaction method, etc. Among them, mixing pile (powder injection pile) composite foundation is the most commonly used composite foundation treatment method. However, the above methods are costly and do not solve the problem of excess pore water pressure accumulation in the soil layer.

[0004] Sand piles, on the other hand, have been used in highway subgrades and building foundation treatment. In these cases, the primary purpose of sand pile installation is to increase the bearing capacity of the foundation while also enhancing its resistance to liquefaction through compaction and drainage. The controlling factors in determining the spacing and number of sand piles are the target foundation bearing capacity, target settlement, and compaction density. Actual designs are often based on construction experience, lacking a theoretical basis. This leads to varying degrees of success in dissipating excess pore water pressure in different soil layers.

[0005] The principle of using gravel piles to dissipate excess pore water pressure in the soil around the tunnel is similar to that of sand piles. Compared with sand piles with a single grade, gravel mixed piles composed of gravel and air-dried medium-coarse sand can not only achieve a drainage effect, but also ensure the integrity of the pile body during construction and application. This avoids the long-term influence of the soil squeezing effect on sand piles, which ultimately cannot dissipate pore water pressure and thus lead to structural failure.

[0006] In addition, the cumulative settlement problem of the strata around the tunnel is somewhat different from the above-mentioned foundation treatment problem. It is necessary not only to consider the excavation disturbance during the shield construction period and the influence of train loads during the operation period from the perspective of the disturbance source, but also to match the layout of the gravel piles with the external characteristics of the tunnel. Therefore, it is necessary to provide a structure and design method that uses gravel piles to dissipate the excess pore water pressure in the soil around the tunnel to solve the above-mentioned problems. Summary of the Invention

[0007] The purpose of the present invention is to provide a gravel pile arrangement structure and method for dissipating excess pore water pressure in the soil around the tunnel in order to solve the above technical problems.

[0008] The purpose of the present invention can be achieved by the following technical solutions:

[0009] A gravel pile arrangement structure for dissipating excess pore water pressure in the soil around a tunnel is obtained by the following steps:

[0010] S1: Based on geological survey data, obtain soil parameters of the strata surrounding the tunnel; based on the construction design, obtain tunnel design parameters for the target project; based on the construction schedule, obtain the estimated advancement time of each ring during the shield tunneling process;

[0011] S2: Determine the selected sand-gravel mixed pile material based on the soil parameters of the strata surrounding the tunnel;

[0012] S3: Determine the buried depth of the sand-gravel pile based on the distribution of the strata surrounding the tunnel and the tunnel design parameters of the target project;

[0013] S4: Select the appropriate construction method based on the buried depth of the sand-gravel mixed pile and determine the appropriate pile diameter accordingly;

[0014] S5: Determine the rectangular arrangement of sand-gravel piles in the transverse and longitudinal directions along the tunnel axis based on the distribution of the strata surrounding the tunnel, the tunnel design parameters of the target project, the shield tunneling speed, and the pile diameter.

[0015] Furthermore, step S1 includes the following steps:

[0016] S1-1: Based on geological survey data, obtain the soil parameters of the strata surrounding the tunnel:

[0017] Including the soil compression modulus of the tunnel layer E s Soil permeability coefficient k , and the compression modulus of the soil underlying the tunnel E s * Soil permeability coefficient k * ;

[0018] S1-2: Based on the construction design, obtain the tunnel design parameters of the target project:

[0019] Including tunnel (design) outer diameter R , Tunnel center (design) burial depth D , Length from the cutterhead to the shield tail of the shield machine L 盾构 , length of each ring segment L 管片 ;

[0020] S1-3: According to the construction schedule, obtain the estimated advancement time of each ring during the shield tunneling process t 0 = ( L 管片 / L 总长 )· t 设计 , and calculate the time from the shield machine arriving to the shield tail being out t = ( L 盾构 / L 总长 )· t 设计 ;in, L 总长 is the total tunneling length of the shield machine, t 设计 Design period.

[0021] Furthermore, in step S2, the sand-gravel mixed pile should be made of a mixture of gravel with high strength (particle size 2-30 mm) and air-dried medium-coarse sand with large permeability coefficient (particle size less than 2 mm) as the main material, and the ratio of gravel to medium-coarse sand should be consistent with the soil compression modulus of the tunnel layer. E s Soil permeability coefficient k To match, the higher the compressibility of the formation (the lower the compression modulus) and the weaker the permeability (the lower the permeability coefficient), the more the proportion of coarse gravel should be increased accordingly to improve the ability of sand piles to dissipate excess pore water pressure and the strength of the pile itself and the composite foundation. The specific proportions are:

[0022] when E s <4 MPa or k <10 -9 m / s, the mass ratio of the medium-coarse sand to the gravel is 1:4;

[0023] When 4 MPa ≤ E s≤ 20 MPa, and 10 -9 m / s ≤ k <10 -8 m / s, the mass ratio of medium coarse sand to gravel is 3:7;

[0024] When 4 MPa ≤ E s ≤ 20 MPa, and 10 -8 m / s ≤ k ≤ 10 -6 m / s, the mass ratio of medium coarse sand to gravel is 2:3.

[0025] Furthermore, in step S3, the embedded depth of the sand-gravel mixing pile should match the embedded depth of the tunnel center D , outer diameter R , and the characteristics of the surrounding strata of the tunnel, specifically:

[0026] a) If the underlying layer of the tunnel is a soil layer with a small permeability coefficient k * i.e., k * <10 -9 m / s, the influence of the excess pore water pressure in the surrounding strata during the shield excavation process is mainly concentrated within 0.5 times the outer diameter of the tunnel R range. Therefore, the embedded depth D 桩 of the sand-gravel mixing pile should be greater than the sum of the embedded depth of the tunnel center D and the outer diameter of the tunnel R , that is, D 桩 ≥ D + R;

[0027] b) If the underlying layer of the tunnel is a soil layer with a relatively high permeability, that is, k * ≥ 10 -9 m / s, at this time, the shield excavation and train operation will not cause a sharp increase in the excess pore water pressure of the underlying layer. Even if the depth D 地层 of the tunnel layer is less than the sum of the embedded depth of the tunnel center D and the outer diameter of the tunnel R (D 桩 < D + R), the embedded depth D 桩 of the sand-gravel mixing pile can take the depth D 地层 of this tunnel layer, that is, D 桩 = D 地层 .

[0028] As a preferred technical solution, to ensure the construction quality of the sand-gravel mixing pile, the embedded depth of the sand-gravel pile should not be greater than 20 m .

[0029] Furthermore, in step S4, the sand-gravel mixed pile should first be constructed using a pile construction method such as the vibratory pipe sinking method or the vibroflotation method, depending on the length of the sand-gravel mixed pile and the construction environment requirements. The deeper the sand-gravel mixed pile, the more difficult it is to vibrate and compact it to form strength. Therefore, the pile construction method should be selected based on both its compaction capacity and cost. Based on engineering experience, the specific method selection criteria are:

[0030] a) When the buried depth of sand-gravel pile is D 桩 When the pile depth is less than 15 m, the vibrating pipe sinking method should be used to produce sand-gravel mixed piles;

[0031] b) When the buried depth of sand-gravel pile is D 桩 When the pile depth is ≥ 15 m, the vibratory method should be used to produce sand-gravel mixed piles;

[0032] After that, the diameter of the sand-gravel mixed pile is determined according to the pile forming method. d , specifically:

[0033] a) When using the vibration pipe sinking pile method, that is, D 桩 When the diameter of the sand-gravel mixed pile is less than 15 m, d Should meet the following requirements: 300 mm ≤ d <800 mm;

[0034] b) When using the vibro-impact method, D 桩 ≥ 15 m, the diameter of the sand-gravel mixed pile d Should meet the following requirements: 800 mm ≤ d ≤1200 mm.

[0035] Furthermore, in step S5, the sand-gravel mixed piles are first arranged in a square pattern on both sides of the tunnel, and the number of pile rows on one side is m , lateral spacing between adjacent sand-gravel mixed piles S 横 (perpendicular to the tunnel extension direction), longitudinal spacing between adjacent sand-gravel piles S 纵 (along the tunnel extension direction), should be based on the pile diameter of the sand and gravel mixed pile d 2. Consolidation degree of the stratum around the sand-gravel pile (the layer where the tunnel is located) U , Time from shield machine arrival to shield tail escape t , soil compression modulus of the tunnel layer E s and soil permeability coefficient k The specific determination process is as follows:

[0036] For the longitudinal spacing of adjacent sand-gravel mixed piles S 纵, due to the use of square pile layout,

[0037]

[0038] In the formula, the coefficient 1.128 is the effective influence range when the piles are arranged in a square shape. d is the diameter of the sand-gravel mixed pile, n is the well diameter ratio;

[0039] Number of pile rows on one side m , should be determined according to the following formula:

[0040] ;

[0041] when m = 1, the gravel pile is located 0.25R from the tunnel edge to ensure the gravel pile's ability to dissipate excess pore water pressure; where R is the outer diameter of the tunnel;

[0042] when m >1, in order to make the horizontal arrangement of the sand-gravel mixed piles uniform within the range of excess pore water pressure, the actual horizontal spacing between adjacent sand-gravel mixed piles is S 横 ’ It should be corrected according to the following formula:

[0043] ,

[0044] At this time, the innermost sand-gravel mixed pile should be located 0.5 S 横 ’ .

[0045] Furthermore, for the well diameter ratio n , the method to obtain it is as follows

[0046] Consolidation degree of the ground around the sand-gravel pile (the layer where the tunnel is located) U , and the time factor T h , considering the well diameter ratio n Affected parameters F n The relationship between can be expressed as:

[0047]

[0048] in, T h Combined soil permeability and excess pore water pressure dissipation time (time from shield machine arrival to shield tail exit) t ), which can be expressed as:

[0049]

[0050] Where, d e The effective influence range of the gravel pile can be d Build relationships, i.e. d e =n·d , n is the well diameter ratio, the above formula can be converted to:

[0051]

[0052] c h is the lateral consolidation coefficient, which can be expressed as:

[0053]

[0054] in k is the permeability coefficient of the stratum where the tunnel is located; E s is the compression modulus of the layer where the tunnel is located; γ w is the weight of water;

[0055] Well diameter ratio n Affected parameters F n , expressed as:

[0056]

[0057] Arrange the above formula and use the intermediate function G Connecting both sides of the equal sign, we get:

[0058]

[0059] Since G( n ) is a transcendental function and cannot be derived from G( n ) value to calculate the well diameter ratio n , so we can first use the numerical method to draw the function graph, that is, first draw the G( n ) function graph, and then the surrounding strata of the sand-gravel mixed pile U , gravel pile diameter d , the time from the arrival of the shield machine to the shield tail being released t , lateral consolidation coefficient c h Substituting into the right side of the equation, we get the intermediate function G( n ) function value, and then check G( n ) function graph, the well diameter ratio can be obtained n results.

[0060] As a preferred technical solution, the longitudinal spacing between adjacent sand-gravel mixed piles isS 纵 , should not be larger than the diameter of the sand-gravel mixed pile d 4.5 times of S 纵 ≤ 4.5 d .

[0061] As a preferred technical solution, the above-mentioned sand and gravel mixed piles are constructed in the early stage of tunnel excavation. After the shield tunneling is completed, the system is retained as a permanent channel for dissipating the excess pore water pressure generated during the train operation phase.

[0062] Compared with the prior art, the present invention has the following characteristics:

[0063] 1) The structure of the present invention targets the soft soil layer surrounding the tunnel. Before shield construction, an excess pore water pressure dissipation channel is set up through sand and gravel mixed piles. This controls and reduces the excess pore water pressure accumulated due to excavation disturbance during shield construction, preventing and controlling uneven settlement of the soft soil layer at the source, thereby reducing the deformation of the rail transit structure during the shield construction period.

[0064] 2) After construction is completed, the structure of the present invention will serve as a permanent excess pore water pressure dissipation channel, effectively alleviating the accumulation of excess pore water pressure in the ground surrounding the tunnel caused by vehicle dynamic loads during the operation phase, thereby avoiding the problem of uneven ground settlement during the operation phase;

[0065] 3) The present invention relates to a structure that utilizes gravel piles to dissipate excess pore water pressure in the soil surrounding the tunnel. The gravel pile structure forms a composite foundation with the soft soil layer surrounding the tunnel, thereby enhancing the bearing capacity of the strata surrounding the tunnel and effectively preventing foundation settlement and deformation of the rail transit structure.

[0066] 4) The present invention provides a practical design method for the above-mentioned structure, which has a theoretical basis and solves the problem that the existing sand pile (sand and gravel pile) design process lacks a theoretical basis and the pore water pressure dissipation effect cannot achieve the expected effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 Schematic diagram of a sand and gravel pile arrangement structure capable of dissipating excess pore water pressure in soil surrounding a tunnel according to an embodiment;

[0068] Figure 2 Schematic diagram of a flow chart of a method for arranging gravel piles capable of dissipating excess pore water pressure in soil surrounding a tunnel according to an embodiment;

[0069] Figure 3 This is a schematic diagram of the design structure of the buried depth and diameter of the sand-gravel mixed pile;

[0070] Figure 4 G( n ) Function curve graph;

[0071] Figure 5 Schematic diagram of a tunnel axial cross-section of a gravel pile arrangement structure capable of dissipating excess pore water pressure in the soil surrounding the tunnel according to an embodiment;

[0072] Figure 6 Schematic diagram of a radial cross section of a tunnel of a gravel pile arrangement structure capable of dissipating excess pore water pressure in soil surrounding the tunnel according to an embodiment;

[0073] Description of the marks in the figure:

[0074] 1-sand-gravel mixed pile, 2-tunnel, 3-tunnel layer, 4-tunnel underlying layer, 5-extent of excess pore water pressure;

[0075] R -Tunnel outer diameter, D -Tunnel center burial depth, D 桩 -Burial depth of sand-gravel mixed pile, S 横 '-actual horizontal arrangement spacing of sand-gravel mixed piles, m-number of sand-gravel mixed piles on one side. DETAILED DESCRIPTION

[0076] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0077] Example

[0078] Tunnel 2 is planned to be built in a soft soil area. The stratum structure in this area is as follows: Figure 1 As shown in the figure, from top to bottom, there are plain fill, clayey silt, silty clay and silty clay. The shield tunnel passes through the stratum, that is, the layer 3 where the tunnel is located is a silty clay layer, which has high compressibility ( E s =2.3 MPa) and poor permeability (permeability coefficient k= 3.6×10 -8 m / s), and the tunnel underlying layer 4 is also a silty clay layer with poor mechanical properties ( E s * =3.39 MPa, k * = 7.3×10 -8m / s). At the beginning of shield construction, considering the disturbance of the above-mentioned strata by shield excavation, and the poor permeability of this type of soil, it is very easy to accumulate excess pore water pressure and cause cumulative settlement of the strata around the tunnel. Therefore, through this method, a sand and gravel pile arrangement structure that can dissipate the excess pore water pressure in the soil around the tunnel is designed to ensure the safety of the track structure during the shield construction process and later operation. The specific design steps can be found in the attached Figure 2 , including the following processes:

[0079] Step 1:

[0080] (1-1) Obtain soil parameters of the strata surrounding the tunnel based on geological survey data:

[0081] The strata where the tunnel is located are plain fill (0.8 m), clayey silt (3.0 m), silty clay (12.6 m) and silty clay (18 m) from top to bottom. Layer 3 where the tunnel is located is a silty clay layer, and the corresponding soil parameters are ( E s =2.3MPa, k= 3.6×10 -8 m / s); the underlying layer 4 of the tunnel is a silty clay layer, and the corresponding soil parameters are ( E s * =3.39 MPa, k * = 7.3×10 -10 m / s);

[0082] (1-2) Based on the construction design, obtain the tunnel design parameters of the target project:

[0083] like Figure 3 As shown, the designed outer diameter of the proposed tunnel 2 is R The center depth of the tunnel is 6.2 m, and the center depth of the tunnel is within the range of 12~15.5 m. D The length from the cutter head to the shield tail of the shield machine is 12 m. L 盾构 9 m, the length of each ring segment L 管片 1.2 m;

[0084] (1-3) According to the construction schedule, the estimated advancement time of each ring during the shield tunneling process is obtained:

[0085] According to the construction schedule, the left line of the proposed tunnel has a total of 1,181 rings, and is expected to be completed in 200 days. The estimated advancement time for each ring of the target project can be obtained. t 0 ≈14631.7 s, and the time from the shield machine reaching the shield tail to the escape can be obtainedt= 109740 s;

[0086] Step 2: Determine the selected sand-gravel mixed pile material based on the soil parameters of the strata surrounding the tunnel:

[0087] The gravel mixed pile 1 should be made of gravel with high strength and air-dried medium-coarse sand with large permeability coefficient as the main material. At the same time, according to the parameters of the silt clay layer obtained in step 1 ( E s =2.3 MPa<4 MPa, k= 3.6×10 -8 m / s), it can be seen that 20% (by mass) of medium-coarse sand (particle size less than 2 mm) and 80% of gravel (particle size within the range of 2-30 mm) should be used;

[0088] Step 3: Determine the buried depth of the sand-gravel pile based on the distribution of the strata around the tunnel and the tunnel design parameters of the target project:

[0089] As attached Figure 3 As shown, since the tunnel underlying layer 4 is a silty clay layer with a small permeability coefficient ( k * = 7.3×10 -10 m / s), at this time, the influence range of the shield excavation process on the surrounding strata is mainly concentrated in the 0.5 times outer diameter outside the tunnel. R Within the range (3.1 m), the buried depth of sand-gravel mixed pile 1 is D 桩 Should be greater than the tunnel center burial depth D and tunnel outer diameter R The sum of D 桩 ≥D+R=18.2 m. At the same time, in order to ensure the construction quality of sand-gravel mixed piles, the buried depth of sand-gravel piles is D 桩 Not more than 20 m, so the gravel pile burial depth D 桩 =18.5 m;

[0090] Step 4: Select the appropriate construction method based on the buried depth of the sand-gravel mixed pile and determine the appropriate pile diameter accordingly:

[0091] According to the buried depth of gravel pile D 桩 =18.5 m>15 m, it can be seen that the vibratory method is required to pile. At this time, the pile diameter d It is better to be within the range of 800~1200 mm, so the diameter of the gravel pile is d =800 mm;

[0092] Step 5: Determine the horizontal and vertical layout of the sand-gravel piles along the tunnel axis based on the distribution of the strata surrounding the tunnel, the tunnel design parameters of the target project, the shield tunneling speed, and the pile diameter:

[0093] (5-1) First, arrange the sand-gravel piles in a square shape around the tunnel. Combine the consolidation degree of the stratum around the sand piles (layer 3 where the tunnel is located) U , time factor T h and time t The relationship between the well diameter ratio and the wellbore ratio n is obtained as follows:

[0094] Degree of consolidation U It can be expressed as follows:

[0095]

[0096] Where, T h is the time factor, F n To consider the well diameter ratio n Influencing parameters;

[0097] Time factor T h and time t The relationship can be expressed as:

[0098]

[0099] Where, d e The effective influence range of the gravel pile is the diameter of the mixed gravel pile. d Build relationships, i.e. d e =n·d , n is the well diameter ratio; t It is the time from the arrival of the shield machine to the shield tail being pulled out, which can be understood as ensuring that the ground disturbance during the shield advancement process does not accumulate excess pore water pressure; c h is the lateral consolidation coefficient, and is:

[0100]

[0101] Where, k is the soil permeability coefficient of layer 3 where the tunnel is located; E s is the soil compression modulus of layer 3 where the tunnel is located; γ w The weight of water.

[0102] Well diameter ratio n Affected parameters F n , which can also be expressed as:

[0103]

[0104] Arrange the above formula and use the intermediate function G Connecting both sides of the equal sign, we get:

[0105]

[0106] (5-2) Since G( n ) is a transcendental function and the well diameter ratio cannot be calculated from G n Therefore, in this embodiment, the numerical method can be used to draw G( n ) Function graph (such as Figure 4 As shown), and then take the degree of consolidation in the calculation process U =80% (according to existing engineering data, the influence of residual excess pore water pressure can be ignored when the consolidation degree reaches 80%), and substitute the diameter of the gravel pile d =800 mm, estimated advancement time for each ring of the target project t 0 ≈14631.7 s, lateral consolidation coefficient c h =8.45×10 -6 On the right side of the equation, we get the intermediate function G( n ) function value, and finally check the attached Figure 4 The well diameter ratio can be obtained n As a result, the well diameter ratio corresponding to this embodiment is n = 3.42;

[0107] (5-3) Sand-gravel piles 1 are arranged in a square shape around tunnel 2, as shown in the attached Figure 5 As shown, the horizontal and vertical spacing S 横 、S 纵 Ratio to well diameter n The relationship is:

[0108]

[0109] Where: The coefficient 1.128 is the effective influence range when the piles are arranged in a square shape. d is the diameter of the sand-gravel mixed pile, n is the well diameter ratio. In addition, the longitudinal pile spacing S of the gravel pile 纵 Not larger than the diameter of the gravel pile d 4.5 times of S 纵 ≤4.5d=3.6 m, empirical calculation meets the requirements.

[0110] (5-4) As attached Figure 6 As shown, there are 1 row of sand and gravel mixed piles perpendicular to the axis direction along both sides of the tunnel (2). m It should be determined according to the following formula:

[0111]

[0112] Since m>1, the actual horizontal spacing of the sand-gravel mixed piles is S 横 'Should be corrected to:

[0113]

[0114] In summary, for this project, two rows of sand-gravel piles should be laid on both sides of the proposed tunnel to dissipate the excess pore water pressure in the surrounding soil. The lateral spacing of the sand-gravel piles should be S 横 ' is 1.55 m, the longitudinal spacing S 纵 The diameter of the gravel pile is 2.4 m. d The diameter is 800 mm and the length is 18.5 m. It should be made of a mixture of 20% (by mass) medium-coarse sand (particle size less than 2 mm) and 80% gravel (particle size within the range of 2 to 30 mm), and the vibratory method should be used to form the pile.

[0115] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A gravel pile arrangement structure for dissipating excess pore water pressure in the soil around a tunnel, characterized in that: The gravel pile arrangement structure comprises a gravel pile array arranged in a rectangular pattern on both sides of a tunnel (2), each side comprising m rows of gravel mixed piles (1); Along the extension direction of the tunnel (2), the spacing between adjacent sand-gravel mixed piles (1) is S 纵 Determine according to the following formula Where d is the pile diameter of the sand-gravel pile (1), n ​​is the well diameter ratio, and is determined according to the following formula: Where d is the diameter of the sand-gravel pile (1), t is the time from the arrival of the shield machine to the exit of the shield tail, U is the consolidation degree of the stratum around the sand-gravel pile (1), and c is the average value of the stratum around the sand-gravel pile (1). h is the lateral consolidation coefficient and is determined according to the following formula Where k is the soil permeability coefficient of the tunnel layer (3); E s is the soil compression modulus of the tunnel layer (3); γ w is the weight of water; When m>1, the distance S between adjacent sand-gravel mixed piles (1) located on the same side of the tunnel (2) perpendicular to the extension direction of the tunnel (2) is 横 Determine according to the following formula Where R is the outer diameter of tunnel (2).

2. The gravel pile arrangement structure for dissipating excess pore water pressure in the soil around a tunnel according to claim 1, characterized in that: The sand-gravel mixed pile (1) comprises medium-coarse sand with a particle size of less than 2 mm and gravel with a particle size of 2-30 mm; When E s <4MPa or k<10 -9 m / s, the mass ratio of the medium-coarse sand to the gravel is 1:4; When 4MPa≤E s ≤20MPa, and 10 -9 m / s≤k<10 -8 m / s, the mass ratio of the medium-coarse sand to the gravel is 3:7; When 4MPa≤E s ≤20MPa, and 10 -8 m / s≤k≤10 -6 m / s, the mass ratio of the medium-coarse sand to the gravel is 2:

3.

3. The gravel pile arrangement structure for dissipating excess pore water pressure in the soil around a tunnel according to claim 1, characterized in that: The permeability coefficient of the soil in the tunnel underlying layer (4) is denoted as k * The buried depth of the sand-gravel mixed pile (1) is recorded as D 桩 ; When k * <10 -9 m / s, D 桩 ≥D+R; Where D is the depth of the center of tunnel (2); When k * ≥10 -9 m / s, D 桩 =D 地层 ; where D 地层 is the depth of the layer (3) where the tunnel is located.

4. The gravel pile arrangement structure for dissipating excess pore water pressure in the soil around a tunnel according to claim 3, characterized in that: D 桩 ≤20m。 5. The gravel pile arrangement structure for dissipating excess pore water pressure in the soil around a tunnel according to claim 4, characterized in that: When D 桩 When the pile depth is less than 15m, a sand-gravel mixed pile (1) is produced by using a vibrating pipe sinking pile method; When D 桩 When the depth is ≥15m, the sand-gravel mixed pile (1) is made by vibratory flushing method.

6. The gravel pile arrangement structure for dissipating excess pore water pressure in the soil around a tunnel according to claim 5, characterized in that: When D 桩 When the distance is less than 15m, 300mm≤d<800mm; When D 桩 When ≥15m, 800mm≤d≤1200mm.

7. The gravel pile arrangement structure for dissipating excess pore water pressure in the soil around a tunnel according to claim 6, characterized in that: S 纵 ≤4.5d.

8. The gravel pile arrangement structure for dissipating excess pore water pressure in the soil around a tunnel according to claim 1, characterized in that: The number of columns m of the sand-gravel mixed pile (1) is determined according to the following formula:

9. The gravel pile arrangement structure for dissipating excess pore water pressure in the soil around a tunnel according to claim 1, characterized in that: When m=1, the distance between the sand-gravel mixed pile (1) and the edge of the tunnel (2) is 0.25R, where R is the outer diameter of the tunnel (2).

10. A method for arranging a gravel pile structure for dissipating excess pore water pressure in soil surrounding a tunnel according to any one of claims 1 to 9, characterized in that: The arrangement method comprises the following steps: S1: Based on geological survey data, obtain soil parameters of the strata surrounding the tunnel; based on the construction design, obtain tunnel design parameters for the target project; based on the construction schedule, obtain the estimated advancement time of each ring during the shield tunneling process; S2: Determine the selected sand-gravel mixed pile material based on the soil parameters of the strata surrounding the tunnel; S3: Determine the buried depth of the sand-gravel pile based on the distribution of the strata surrounding the tunnel and the tunnel design parameters of the target project; S4: Select the appropriate construction method based on the buried depth of the sand-gravel mixed pile and determine the appropriate pile diameter accordingly; S5: Determine the horizontal and vertical layout of sand-gravel piles along the tunnel axis based on the distribution of the strata surrounding the tunnel, the tunnel design parameters of the target project, the shield tunneling speed, and the pile diameter.

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