A method for predicting the maximum penetration distance of shield slurry in saturated sand layers

Abstract

The present invention belongs to the technical field of shield slurry support and relates to a method for predicting the maximum penetration distance of shield slurry in a saturated sand layer. The method comprises the following steps: determining slurry parameters and formation parameters; spatially discretizing the slurry's penetration process in the formation to determine the microelement depth of the penetration zone; calculating the microelement height of the sedimentary layer of slag on the formation surface; iteratively calculating the mass concentration of bentonite particles in the slurry after passing through the sedimentary layer and the distribution of the bentonite particle retention in the formation; and outputting the result of the maximum penetration distance of the slurry based on whether the penetration distance of the slurry in the formation exceeds a set threshold and whether the bentonite particle deposition concentration at the formation entrance reaches a critical deposition concentration as termination criteria. The method can quickly and accurately obtain the maximum penetration distance of the slurry in a saturated sand layer without conducting a penetration test, and takes into account the influence of slag mixed in the slurry on the slurry's penetration process, thereby providing a reliable reference for adjusting shield construction parameters and ensuring tunneling stability.

Description

Technical Field

[0001] The invention belongs to the technical field of shield slurry support, and in particular relates to a method for predicting the maximum penetration distance of shield slurry in a saturated sand layer. Background Art

[0002] Leveraging the principle of slurry support, slurry shields are widely used for tunnel excavation in high-permeability, high-water-pressure formations, such as saturated sand or highly permeable gravel formations. Slurry shields provide support to the excavation face by penetrating pressurized slurry into the formation. Therefore, the slurry penetration process is crucial to the effectiveness of this support. Because slurry penetration increases excess pore water pressure ahead of the excavation face, the slurry pressure cannot fully act on the excavation face. Instead, it is converted into a combination of effective support force and excess pore water pressure. Generally speaking, slurry penetration stops after a certain distance, forming a low-permeability filter cake on the excavation face. At this point, the slurry pressure can be maximized. However, if the slurry penetration distance is too great, the slurry pressure cannot be applied to the excavation face in a timely manner, posing a risk of face instability. Accurately predicting the effectiveness of slurry pressure can effectively ensure the stability of the excavation face. Calculating the water pressure evolution during the penetration process typically requires a priori determination of the maximum slurry penetration distance.

[0003] Previous studies have used empirical formulas to calculate the maximum penetration distance of slurry. However, the results obtained by these formulas differ by tens of times from those obtained through experiments. This is because these formulas simply treat the penetration of slurry in the formation as a continuous fluid and fail to consider the potential for bentonite particles in the slurry to become trapped in the pores of the formation and undergo deep filtration within the porous medium. Therefore, laboratory permeability tests are still required to determine the maximum penetration distance of slurry before actual construction. Furthermore, most current experimental and theoretical studies assume that the slurry is a single bentonite slurry. In actual construction, excavated soil enters a slurry silo, where it is mixed with the slurry and transported to the surface for treatment and recycling. Studies have shown that soil mixed with the slurry accumulates on the surface during penetration, forming a sedimentary layer. If this sedimentary layer accumulates too rapidly, it severely hinders the blocking effect of the bentonite particles on the formation, potentially preventing the slurry from stagnating and leading to insufficient support. Consequently, there is currently no method to accurately predict the maximum penetration distance of shield slurry during actual construction. Summary of the Invention

[0004] In response to the shortcomings in the relevant technologies, the present invention provides a method for predicting the maximum penetration distance of shield mud in saturated sand layers, aiming to obtain the maximum penetration distance of mud in saturated sand layers more quickly and accurately without a penetration test, and taking into account the influence of debris mixed in the mud on the mud penetration process, thereby providing a reliable reference for adjusting shield construction parameters and ensuring tunneling stability.

[0005] The present invention provides a method for predicting the maximum penetration distance of shield slurry in a saturated sand layer, comprising the following steps:

[0006] S1. Determine mud parameters and formation parameters;

[0007] S2. The penetration process of mud in the formation is spatially discretized, and the depth of the microelement of the spatial discretization of the penetration area is recorded as ;

[0008] S3, the depth of a single microelement of mud advancing in the formation When calculating the height of the sedimentary layer microelement of the slag on the surface of the stratum ;

[0009] S4, the depth of a single microelement of mud penetration in the formation , calculate the mass concentration of bentonite particles in the mud after passing through the sediment layer;

[0010] S5, the depth of a single microelement of mud penetration in the formation , calculate the bentonite particle retention distribution of the mud in the formation;

[0011] S6. Calculate the penetration distance of mud in the formation , and judge Whether it exceeds the set threshold If it exceeds, the result of no maximum penetration distance is output; if it does not exceed, it is further judged whether the bentonite particle deposition concentration at the formation entrance reaches the critical deposition concentration; if it does not reach the critical deposition concentration, steps S4 and S5 are repeated for iterative calculation, and the penetration distance of the mud in the formation is calculated. The concentration of bentonite particles at the entrance of the formation is judged; if the critical concentration is reached, the iterative calculation is stopped and the current calculated mud penetration distance is The output is the maximum penetration distance of the mud.

[0012] In some embodiments, in step S1, the mud parameters include mud pressure, bentonite particle gradation distribution, density of bentonite particles, apparent viscosity of the mud, mass concentration of bentonite particles in the mud, and mass concentration of slag in the mud; the formation parameters include sand layer particle gradation distribution, original porosity of the sand layer, and density of sand particles.

[0013] In some embodiments, in step S3, the height of the micro-element of the sediment layer of the slag on the surface of the stratum is Calculate according to formula (1);

[0014] (1);

[0015] In formula (1), is the mass concentration of debris in the mud; is the density of sand particles; is the original porosity of the sedimentary layer, which is the same as the original porosity of the sand layer.

[0016] In some embodiments, in step S4, calculating the mass concentration of bentonite particles in the slurry after passing through the sediment layer includes the following steps:

[0017] S41. Calculate the time it takes for mud to pass through a single sedimentary layer microelement according to formula (2) ; The mud passes through each sedimentary layer microelement, and the time step of its time node is controlled according to formula (3) ;

[0018] (2);

[0019] (3);

[0020] In formula (2), is the spatial node corresponding to the sedimentary layer, ; is the time node, ,and ; is the apparent viscosity of the mud; is the permeability of the sedimentary layer microelement; is the weight of bentonite particles in the mud passing through the sedimentary microelement; is the hydraulic gradient in mud penetration;

[0021] S42. Calculate the pore flow rate of mud through the micro-element of the sediment layer according to formula (4): ;

[0022] (4);

[0023] In formula (4), is the porosity of the microelement of the sedimentary layer;

[0024] S43. Calculate the particle deposition system of the mud through the sedimentary layer micro-element according to formula (5). ;

[0025] (5);

[0026] In formula (5), is the effective length of the porous conduit; is the average radius of bentonite particles, and the gradation distribution of bentonite particles is taken as As a representative value; is the equivalent formation pore radius, calculated according to formula (6); is the aggregation parameter, calculated according to formula (7);

[0027] (6);

[0028] (7);

[0029] In formula (6)-formula (7), It is the radius value less than 50% on the sand layer particle gradation distribution curve; is the formation injectability ratio, ; is the mud pressure; is 1 standard atmosphere; is the relative apparent viscosity of the mud; is the relative density of the sand layer;

[0030] S44. Calculate the retention of bentonite particles in the sediment microelement at each time step according to formula (8): According to formula (9), the amount of bentonite particles deposited in each sedimentary layer microelement during the mud infiltration process is calculated as follows: , and update the porosity of the deposited layer microelement in the next time step according to formula (10) , permeability , according to formula (11), the mass concentration of bentonite particles in the mud passing through the sedimentary layer microelement in the next time step is updated: , severe Finally, the mass concentration of bentonite particles in the mud after the mud passes through the entire sediment layer and enters the formation is calculated according to formula (12): ;

[0031] (8);

[0032] (9);

[0033] (10);

[0034] (11);

[0035] (12);

[0036] In formula (8)-formula (11), is the mass concentration of bentonite particles in the mud passing through the sedimentary layer microelement; is the specific gravity of bentonite particles; is the weight of water; is the original porosity of the sand layer; is the initial mass concentration of bentonite particles in the mud.

[0037] In some embodiments, in step S5, the calculation of the bentonite particle retention distribution of the slurry in the formation includes the following steps:

[0038] S51. Calculate the time it takes for the mud to penetrate a single microelement in the formation according to formula (13): The mud passes through each microelement, and the time step of its time node is controlled according to formula (14). ;

[0039] (13);

[0040] (14);

[0041] In formula (13), is the spatial node corresponding to the infiltration area, ,and ; is the permeability of the microelement in the permeation zone; is the weight of bentonite particles in the mud passing through the micro-element of the infiltration zone;

[0042] S52. Calculate the pore flow rate of mud through the micro-element in the permeable area according to formula (15): ;

[0043] (15);

[0044] In formula (15), is the porosity of the microelement in the infiltration zone;

[0045] S53. Calculate the particle deposition system of mud passing through the micro-element of the permeable zone according to formula (16). ;

[0046] (16);

[0047] S54. Calculate the retention of bentonite particles in the microelement of the permeable zone at each time step according to formula (17): According to formula (18), the amount of bentonite particles deposited in each microelement of the infiltration area during the mud infiltration process is calculated as follows: , and update the porosity of the microelement in the next time step according to formula (19) , permeability , according to formula (20), the mass concentration of bentonite particles in the mud passing through the micro-element of the infiltration zone in the next time step is updated: , severe ;

[0048] (17);

[0049] (18);

[0050] (19);

[0051] (20);

[0052] In formula (17)-formula (20), is the mass concentration of bentonite particles in the mud passing through the micro-element of the infiltration zone.

[0053] In some embodiments, in step S6, the penetration distance of the mud in the formation is Calculate according to formula (21);

[0054] (twenty one).

[0055] In some embodiments, in step S6, the bentonite particle deposition concentration at the formation inlet is According to formula (22), the critical sedimentation concentration at the formation entrance is Calculate according to formula (23); when When the mud stops penetrating into the formation, the currently calculated mud penetration distance The output is the maximum penetration distance of the mud;

[0056] (twenty two);

[0057] (twenty three);

[0058] In formula (23), is the density of bentonite particles.

[0059] In some embodiments, in step S6, the results output during the iterative calculation also include changes in formation porosity and permeability with mud penetration distance, distribution of bentonite particle retention in the formation, and distribution of bentonite particle retention in the slag.

[0060] Based on the above technical solution, the method for predicting the maximum penetration distance of shield mud in saturated sand layers in the embodiment of the present invention can obtain the maximum penetration distance of mud in saturated sand layers more quickly and accurately without a penetration test, and take into account the influence of slag mixed in the mud during actual shield construction on the mud penetration process, thereby providing a reliable reference for adjusting shield construction parameters and ensuring excavation stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0062] Figure 1 Flow chart of the method for predicting the maximum penetration distance of shield slurry in saturated sand layer of the present invention;

[0063] Figure 2 Schematic diagram of the slurry penetration process in the method for predicting the maximum penetration distance of shield slurry in a saturated sand layer of the present invention;

[0064] Figure 3 A comparison chart of the calculated value and the experimental value of the maximum penetration distance of mud according to an embodiment of the present invention;

[0065] Figure 4 A curve diagram showing the change in mass concentration of bentonite particles in the mud entering the formation calculated according to one embodiment of the present invention;

[0066] Figure 5 This is a curve diagram of the change in bentonite particle deposition concentration at the formation entrance calculated according to one embodiment of the present invention. DETAILED DESCRIPTION

[0067] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0068] In the description of the present invention, it should be understood that the terms "center", "lateral", "longitudinal", "up", "down", "top", "bottom", "inside", "outside", "left", "right", "front", "back", "vertical", "horizontal", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0069] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood broadly. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to direct connections, indirect connections through an intermediary, or internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0070] refer to Figure 1-Figure 5 As shown, the present invention provides a method for predicting the maximum penetration distance of shield slurry in a saturated sand layer, which is used to obtain the maximum penetration distance of the slurry in a saturated sand layer. When the shield slurry contains debris, the debris will form a sedimentary layer on the surface of the formation during the process of the slurry penetrating into the formation. The slurry will first penetrate the sedimentary layer and then enter the formation.

[0071] refer to Figure 1-Figure 5 As shown, a method for predicting the maximum penetration distance of shield slurry in a saturated sand layer of the present invention comprises the following steps:

[0072] S1. Determine mud parameters and formation parameters; specifically, mud parameters include mud pressure, bentonite particle gradation distribution, bentonite particle density, mud apparent viscosity, mass concentration of bentonite particles in the mud, mass concentration of slag in the mud, etc.; formation parameters include sand layer particle gradation distribution, original porosity of the sand layer, density of sand particles, etc.;

[0073] In this embodiment, the mud pressure is set to 50 kPa; the formation is set to a saturated sand formation in accordance with actual construction. Specifically, the formation is set to sand for sand injection method, with a particle size range of 0.25 mm to 0.5 mm, a density of sand particles of 2.64 g / L, and an original porosity of the formed sand layer of 0.35; the concentration of bentonite particles in the mud is 80 g / L, and the mass concentration of the slag in the mud is set to 5 gradients, namely 0, 100 g / L, 300 g / L, 500 g / L, and 700 g / L. The slag is the excavated formation, which is the same as the formation sand. The apparent viscosity of the mud is 15 mPa.s.

[0074] S2. The penetration process of mud in the formation is spatially discretized, and the depth of the microelement of the spatial discretization of the penetration area is recorded as . refer to Figure 2 As shown in Figure 2, after spatial discretization, the mud advances a distance of a microelement in the formation at each time step.

[0075] S3, the depth of a single microelement of mud advancing in the formation When calculating the height of the sedimentary layer microelement of the slag on the surface of the stratum . refer to Figure 2 As shown in the figure, when the mud advances one microelement depth in the formation When the slurry is used, the debris in the mud will accumulate on the surface of the formation. High sedimentary layer.

[0076] S4, the depth of a single microelement of mud penetration in the formation , calculate the mass concentration of bentonite particles in the mud after passing through the sediment layer.

[0077] S5, the depth of a single microelement of mud penetration in the formation , calculate the bentonite particle retention distribution of the mud in the formation.

[0078] S6. Calculate the penetration distance of mud in the formation , and judge Whether it exceeds the set threshold If it exceeds, the result of no maximum penetration distance is output; if it does not exceed, it is further judged whether the bentonite particle deposition concentration at the formation entrance reaches the critical deposition concentration; if it does not reach the critical deposition concentration, steps S4 and S5 are repeated for iterative calculation, and the penetration distance of the mud in the formation is calculated. The concentration of bentonite particles at the entrance of the formation is judged; if the critical concentration is reached, the iterative calculation is stopped and the current calculated mud penetration distance is The output is the maximum penetration distance of the mud.

[0079] The above-mentioned illustrative embodiment takes into account the influence of debris mixed in the mud during actual shield construction on the mud penetration process, breaking through the cognitive limitations of previous experiments or theoretical studies that did not pay attention to the debris mixed in the mud during actual construction, and more realistically reflects the penetration and filtration mechanism of the shield mud during actual construction. As a result, the maximum penetration distance of the shield mud in the saturated sand layer or the situation where there is no maximum penetration distance can be quickly and accurately obtained without a penetration test, thereby providing a reliable reference for adjusting shield construction parameters and ensuring tunneling stability.

[0080] In some embodiments, in step S3, the mud advances in the formation to a depth of a single microelement When the height of the sedimentary layer microelement of the slag on the surface of the stratum is Calculate according to formula (1);

[0081] (1);

[0082] In formula (1), is the mass concentration of debris in the mud; is the density of sand particles; is the original porosity of the sedimentary layer, which is the same as the original porosity of the sand layer. Assuming it is 0.1mm, when the mass concentration of slag in the mud increases from 0 to 700g / L, the height of the microelement of the sediment layer Increased from 0 to 0.0143mm.

[0083] The above exemplary embodiment refines the height of the microelement of the sediment layer on the surface of the stratum. Calculation method of the micro-element height of the sedimentary layer of slag on the surface of the stratum With the concentration of slag in the mud varies depending on the situation.

[0084] In some embodiments, in step S4, the mud penetrates into the formation to a depth of a single microelement. , the calculation of the mass concentration of bentonite particles in the mud after passing through the sediment layer includes the following steps:

[0085] S41. Calculate the time it takes for mud to pass through a single sedimentary layer microelement according to formula (2) ; The mud passes through each sedimentary layer microelement, and the time step of its time node is controlled according to formula (3) ;

[0086] (2);

[0087] (3);

[0088] In formula (2), is the spatial node corresponding to the sedimentary layer, ; is the time node, ,and ; is the apparent viscosity of the mud, which is assumed to remain unchanged during the mud penetration process; is the permeability of the sedimentary layer microelement; is the weight of bentonite particles in the mud passing through the sedimentary microelement; is the hydraulic gradient in mud penetration, which is an arbitrary constant value.

[0089] S42. Calculate the pore flow rate of mud through the micro-element of the sediment layer according to formula (4): ;

[0090] (4);

[0091] In formula (4), is the porosity of the microelement of the sedimentary layer.

[0092] S43. Calculate the particle deposition system of the mud through the sedimentary layer micro-element according to formula (5). ;

[0093] (5);

[0094] In formula (5), is the effective length of the pore channel (assuming a cylindrical shape); is the average radius of bentonite particles (i.e., filter particles), and the gradation distribution of bentonite particles is taken as As a representative value, It is the radius value less than 85% on the bentonite particle gradation distribution curve; is the equivalent formation pore radius, calculated according to formula (6); is the aggregation parameter, calculated according to formula (7);

[0095] (6);

[0096] (7);

[0097] In formula (6)-formula (7), It is the radius value less than 50% on the sand layer particle gradation distribution curve; is the formation injectability ratio, , It is the radius value less than 10% on the sand layer particle gradation distribution curve. It is the radius value less than 95% on the bentonite particle gradation distribution curve; is the mud pressure; is 1 standard atmosphere; is the relative apparent viscosity of the mud, that is, the apparent viscosity of the mud Apparent viscosity than water; is the relative density of the sand layer, which is 90% in this embodiment.

[0098] S44. Calculate the retention of bentonite particles in the sediment microelement at each time step according to formula (8): , expressed as the retention amount at the center of the microelement, the amount of bentonite particles deposited in each microelement of the sediment layer during the mud infiltration process is calculated according to formula (9): ;refer to Figure 2 As shown in the figure, it is assumed that no bentonite particles are filtered when a new sediment layer is formed, and the spatial node count of the sediment layer microelement is from bottom to top. The porosity of the sediment layer microelement in the next time step is updated according to formula (10): , permeability , according to formula (11), the mass concentration of bentonite particles in the mud passing through the sedimentary layer microelement in the next time step is updated: , severe ; Finally, after the mud passes through the entire sediment layer, it will pass through the first sediment layer ( The mass concentration of bentonite particles in the mud after it passes through the entire sedimentary layer and enters the formation is calculated according to formula (12): ;

[0099] (8);

[0100] (9);

[0101] (10);

[0102] (11);

[0103] (12);

[0104] In formula (8)-formula (11), is the mass concentration of bentonite particles in the mud passing through the sedimentary layer microelement; is the specific gravity of bentonite particles; is the weight of water; is the original porosity of the sand layer; is the initial mass concentration of bentonite particles in the mud.

[0105] The above-mentioned exemplary embodiment takes into account the influence of the debris mixed in the mud on the mud penetration process, and refines the calculation method of the mass concentration of bentonite particles in the mud after the mud passes through the sedimentary layer formed by the debris, thereby providing more accurate input conditions for the penetration process of the mud into the formation.

[0106] In some embodiments, in step S5, the mud penetrates into the formation to a depth of a single microelement. , calculate the distribution of bentonite particle retention in the slurry in the formation. The overall calculation process is similar to equations (2) to (11) in step S4, but the mass concentration of bentonite particles in the slurry after passing through the sediment layer is used. As the input value of the mass concentration of bentonite particles in the mud entering the formation, the height of the sedimentary layer microelement Replaced by the depth of the microelement in the penetration zone To distinguish it from the infiltration process of mud in the sedimentary layer, the spatial node symbol of mud infiltration in the stratum is changed from Change to The penetration direction of mud is opposite to the accumulation direction of sedimentary layer, and the spatial nodes of mud in the formation are counted from top to bottom.

[0107] Specifically, the calculation of the bentonite particle retention distribution of the slurry in the formation includes the following steps:

[0108] S51. Calculate the time it takes for the mud to penetrate a single microelement in the formation according to formula (13): ; The mud passes through each microelement of the permeable area, and the time step of its time node is controlled according to formula (14) ;

[0109] (13);

[0110] (14);

[0111] In formula (13), is the spatial node corresponding to the infiltration area, ,and ; is the permeability of the microelement in the permeation zone; It is the density of bentonite particles in the mud passing through the micro-element of the infiltration zone.

[0112] S52. Calculate the pore flow rate of mud through the micro-element in the permeable area according to formula (15): ;

[0113] (15);

[0114] In formula (15), is the porosity of the microelement in the infiltration zone.

[0115] S53. Calculate the particle deposition system of mud passing through the micro-element of the permeable zone according to formula (16). ;

[0116] (16).

[0117] S54. Calculate the retention of bentonite particles in the microelement of the permeable zone at each time step according to formula (17): , expressed as the retention at the center of the microelement, the amount of bentonite particles deposited in each microelement in the infiltration area during the mud infiltration process is calculated according to formula (18): , and update the porosity of the microelement in the next time step according to formula (19) , permeability , according to formula (20), the mass concentration of bentonite particles in the mud passing through the micro-element of the infiltration zone in the next time step is updated: , severe ;

[0118] (17);

[0119] (18);

[0120] (19);

[0121] (20);

[0122] In formula (17)-formula (20), is the mass concentration of bentonite particles in the mud passing through the micro-element of the infiltration zone.

[0123] The above exemplary embodiment refines the calculation method of the bentonite particle retention distribution in the mud and the bentonite particle deposition amount in each microelement of the permeability zone as the mud penetrates into the formation, thereby providing a basis for calculating the bentonite particle deposition concentration at the subsequent formation entrance.

[0124] In some embodiments, in step S6, the penetration distance of the mud in the formation is Calculate according to formula (21);

[0125] (twenty one).

[0126] In this embodiment, the threshold value of the mud penetration distance in the formation is set to 30 cm; when the calculated mud penetration distance exceeds 30 cm, a result of no maximum penetration distance will be output, that is, the mud penetration will not stop, which means that the mud's support force on the excavation surface is insufficient, and the relevant parameters of the shield construction need to be pre-adjusted; when the calculated mud penetration distance does not exceed 30 cm, it is necessary to further judge the bentonite particle deposition concentration at the formation entrance.

[0127] In some embodiments, in step S6, the bentonite particle deposition concentration at the formation inlet is According to formula (22), the critical sedimentation concentration at the formation entrance is According to formula (23), based on the above setting conditions, the critical sedimentation concentration at the formation entrance in this embodiment is is 1466kg / m3; when When , repeat steps S4 and S5 to perform iterative calculations and calculate the penetration distance of the mud in the formation. and the bentonite particle deposition concentration at the formation entrance judge the situation; when When the mud stops penetrating into the formation, the iterative calculation stops and the current calculated mud penetration distance is The output is the maximum penetration distance of the mud;

[0128] (twenty two);

[0129] (twenty three);

[0130] In formula (23), is the density of bentonite particles.

[0131] Further explanation: Based on the above setting conditions, the mass concentration of slag in the mud The mass concentration of bentonite particles in the mud entering the formation under different gradients Mud penetration distance The change curve of Figure 4As shown, the concentration of bentonite particles at the formation entrance is Mud penetration distance The change curve of Figure 5 As shown; Figure 4 and Figure 5 It explains that when the mass concentration of slag in the mud is too high, the mud has no maximum penetration distance, that is, the internal mechanism of continuous penetration of mud; when the mud does not contain slag, the mass concentration of bentonite in the mud entering the formation remains unchanged, and the bentonite deposition concentration at the formation entrance increases approximately linearly until it reaches the critical deposition concentration and penetration stops; when the mud contains slag, the mass concentration of bentonite particles in the mud entering the formation decreases with increasing penetration distance. If the mass concentration of slag in the mud is too high, such as 700 g / L, the mass concentration of bentonite particles entering the formation approaches 0 during the penetration process, which makes it difficult to reach the critical deposition concentration at the formation entrance, and penetration will not stop, so there is no maximum penetration distance; that is, when the mass concentration of slag in the mud is too high, the mud will have no maximum penetration distance in the saturated sand layer.

[0132] Furthermore, the mass concentration of slag in the mud The calculated maximum mud penetration distance under different gradients is shown in Table 1, and compared with the maximum mud penetration distance obtained by the test. Figure 3 For intuitive display (the specific process of the maximum penetration distance test of mud can be found in the website doi.org / 10.1063 / 5.0236681); Figure 3 As shown in Table 1, the calculated value of the maximum penetration distance of the mud is close to the experimental value and the calculated value is always slightly larger than the experimental value. The difference between the two increases with the concentration of the slag in the mud. When the concentration of slag in the slurry increases When the concentration of slag in the slurry reaches 500g / L, the maximum difference between the calculated value and the test value is about 1.51cm. When the concentration reaches 700 g / L, both the calculated and tested results show no maximum penetration distance. The difference between the calculated and tested values indicates that this prediction method still has certain shortcomings. However, in engineering practice, people prefer a shorter mud penetration distance. Therefore, the maximum mud penetration distance calculated by this prediction method can provide a relatively conservative result for construction, which is more conducive to the reliability and stability of tunneling.

[0133] Table 1 Comparison of calculated and experimental values of maximum penetration distance of mud at different concentration gradients of soil in mud

[0134]

[0135] In some embodiments, in step S6, the output result of the iterative calculation also includes the formation porosity and penetration rate Mud penetration distance Changes in bentonite particle retention in the formation Distribution of bentonite particles in slag soil This exemplary embodiment can obtain parameters that are difficult to directly detect through indoor permeability tests, and thus can more comprehensively and detailedly understand the permeation and filtration mechanism of shield slurry in saturated sand layers during actual construction.

[0136] Through the description of multiple embodiments of the method for predicting the maximum penetration distance of shield slurry in saturated sand layers of the present invention, it can be seen that the present invention has at least one or more of the following advantages:

[0137] 1) This invention focuses on the impact of debris mixed in the slurry during actual shield construction on the slurry penetration process, breaking through the limitations of previous experiments or theoretical studies that have not paid attention to the cognition of debris mixed in the slurry during actual construction. It can more realistically reflect the penetration and filtration mechanism of shield slurry during actual construction;

[0138] 2) The present invention can quickly and accurately obtain the maximum penetration distance of shield slurry in saturated sand layers, or the absence of a maximum penetration distance, without conducting a penetration test, thereby providing a reliable reference for adjusting shield construction parameters and ensuring stable excavation.

[0139] Finally, it should be noted that the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0140] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the same. Although the present invention has been described in detail with reference to preferred embodiments, persons of ordinary skill in the art should understand that the specific implementation methods of the present invention may still be modified or some technical features may be replaced by equivalents without departing from the spirit of the technical solutions of the present invention, and all of these should be included in the scope of the technical solutions for which protection is sought.

Claims

1. A method for predicting the maximum penetration distance of shield slurry in saturated sand layer, characterized in that: The following steps are involved: S1. Determine mud parameters and formation parameters; the mud parameters include mud pressure, bentonite particle gradation distribution, bentonite particle density, mud apparent viscosity, mass concentration of bentonite particles in the mud, and mass concentration of slag in the mud; the formation parameters include sand layer particle gradation distribution, original porosity of the sand layer, and density of sand particles; S2. The penetration process of mud in the formation is spatially discretized, and the depth of the microelement of the spatial discretization of the penetration area is recorded as ; S3, the depth of a single microelement of mud advancing in the formation When the height of the sedimentary layer microelement of the slag on the stratum surface is calculated according to formula (1): ; （1）； In formula (1), is the mass concentration of debris in the mud; is the density of sand particles; is the original porosity of the sedimentary layer, which is the same as the original porosity of the sand layer; S4, the depth of a single microelement of mud penetration in the formation , calculate the mass concentration of bentonite particles in the mud after passing through the sediment layer, which includes the following steps: S41. Calculate the time it takes for mud to pass through a single sedimentary layer microelement according to formula (2) ; The mud passes through each sedimentary layer microelement, and the time step of its time node is controlled according to formula (3) ; （2）； （3）； In formula (2), is the spatial node corresponding to the sedimentary layer, ; is the time node, ,and ; is the apparent viscosity of the mud; is the permeability of the sedimentary layer microelement; is the weight of bentonite particles in the mud passing through the sedimentary microelement; is the hydraulic gradient in mud penetration; S42. Calculate the pore flow rate of mud through the micro-element of the sediment layer according to formula (4): ; （4）； In formula (4), is the porosity of the microelement of the sedimentary layer; S43. Calculate the particle deposition system of the mud through the sedimentary layer micro-element according to formula (5). ; （5）； In formula (5), is the effective length of the porous conduit; is the average radius of bentonite particles, and the gradation distribution of bentonite particles is taken as As a representative value; is the equivalent formation pore radius, calculated according to formula (6); is the aggregation parameter, calculated according to formula (7); （6）； （7）； In formula (6)-formula (7), It is the radius value less than 50% on the sand layer particle gradation distribution curve; is the formation injectability ratio, ; is the mud pressure; is 1 standard atmosphere; is the relative apparent viscosity of the mud; is the relative density of the sand layer; S44. Calculate the retention of bentonite particles in the sediment microelement at each time step according to formula (8): According to formula (9), the amount of bentonite particles deposited in each sedimentary layer microelement during the mud infiltration process is calculated as follows: , and update the porosity of the deposited layer microelement in the next time step according to formula (10) , permeability , according to formula (11), the mass concentration of bentonite particles in the mud passing through the sedimentary layer microelement in the next time step is updated: , severe Finally, the mass concentration of bentonite particles in the mud after the mud passes through the entire sediment layer and enters the formation is calculated according to formula (12): ; （8）； （9）； （10）； （11）； （12）； In formula (8)-formula (11), is the mass concentration of bentonite particles in the mud passing through the sedimentary microelement; is the specific gravity of bentonite particles; is the weight of water; is the original porosity of the sand layer; is the initial mass concentration of bentonite particles in the mud; S5, the depth of a single microelement of mud penetration in the formation , calculating the bentonite particle retention distribution of the mud in the formation, which includes the following steps: S51. Calculate the time it takes for the mud to penetrate a single microelement in the formation according to formula (13): The mud passes through each microelement, and the time step of its time node is controlled according to formula (14). ; （13）； （14）； In formula (13), is the spatial node corresponding to the infiltration area, ,and ; is the permeability of the microelement in the permeation zone; is the weight of bentonite particles in the mud passing through the micro-element of the infiltration zone; S52. Calculate the pore flow rate of mud through the micro-element in the permeable area according to formula (15): ; （15）； In formula (15), is the porosity of the microelement in the infiltration zone; S53. Calculate the particle deposition system of mud passing through the micro-element of the permeable zone according to formula (16). ; （16）； S54. Calculate the retention of bentonite particles in the microelement of the permeable zone at each time step according to formula (17): According to formula (18), the amount of bentonite particles deposited in each microelement of the infiltration area during the mud infiltration process is calculated as follows: , and update the porosity of the microelement in the next time step according to formula (19) , permeability , according to formula (20), the mass concentration of bentonite particles in the mud passing through the micro-element of the infiltration zone in the next time step is updated: , severe ; （17）； （18）； （19）； （20）； In formula (17)-formula (20), is the mass concentration of bentonite particles in the mud passing through the micro-element of the infiltration zone; S6. Calculate the penetration distance of mud in the formation , and judge Whether it exceeds the set threshold If it exceeds, the result of no maximum penetration distance is output; if it does not exceed, it is further judged whether the bentonite particle deposition concentration at the formation entrance reaches the critical deposition concentration; if it does not reach the critical deposition concentration, steps S4 and S5 are repeated for iterative calculation, and the penetration distance of the mud in the formation is calculated. The concentration of bentonite particles at the entrance of the formation is judged; if the critical concentration is reached, the iterative calculation is stopped and the current calculated mud penetration distance is The output is the maximum penetration distance of the mud.

2. The method for predicting the maximum penetration distance of shield slurry in saturated sand layer according to claim 1, characterized in that: In step S6, the penetration distance of the mud in the formation Calculate according to formula (21); （21）。 3. The method for predicting the maximum penetration distance of shield slurry in saturated sand layer according to claim 2, characterized in that: In step S6, the bentonite particle deposition concentration at the formation inlet is According to formula (22), the critical sedimentation concentration at the formation entrance is Calculate according to formula (23); when When the mud stops penetrating into the formation, the currently calculated mud penetration distance The output is the maximum penetration distance of the mud; （22）； （23）； In formula (23), is the density of bentonite particles.

4. The method for predicting the maximum penetration distance of shield slurry in saturated sand layer according to claim 3, characterized in that: In step S6, the results output during the iterative calculation also include changes in formation porosity and permeability with mud penetration distance, distribution of bentonite particle retention in the formation, and distribution of bentonite particle retention in the slag.

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