Prediction method for maximum seepage distance of shield slurry in saturated sand layer

Abstract

The invention belongs to the technical field of shield slurry support, and relates to a method for predicting the maximum seepage distance of shield slurry in a saturated sand layer, which comprises the following steps: determining slurry parameters and stratum parameters; spatial discretization is carried out on the permeation process of the slurry in the stratum, and the infinitesimal body depth of a permeation area is determined; calculating the height of a sedimentary layer infinitesimal body of the muck on the surface of the stratum; iterative calculation is conducted on the mass concentration of bentonite particles in the slurry penetrating through the sedimentary layer and the retention amount distribution of the bentonite particles in the stratum; and outputting a result of the maximum permeation distance of the slurry by taking whether the permeation distance of the slurry in the stratum exceeds a set threshold value or not and whether the deposition concentration of bentonite particles at a stratum inlet reaches a critical deposition concentration or not as ending standards. According to the method, the maximum permeation distance of the slurry in the saturated sand layer can be rapidly and accurately obtained without a permeation test, the influence of muck mixed into the slurry on the slurry permeation process is considered, and then reliable reference is provided for shield construction parameter adjustment and tunneling stability guarantee.

Description

Technical Field

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

[0002] Based on the principle of mud support, slurry shield is widely used in tunnel excavation in high permeability and high water pressure formations, such as saturated sand formations or highly permeable gravel formations. Slurry shield provides support force to the excavation face by infiltrating pressurized mud into the formation, so the mud penetration process is crucial to the effectiveness of the support force. Since mud penetration will cause the excess pore water pressure in front of the excavation face to increase, the mud pressure cannot act completely on the excavation face, but is converted into a combination of effective support force and excess pore water pressure. Generally speaking, the mud will stop after penetrating a certain distance, and then form a low-permeability filter cake on the excavation face. At this time, the mud pressure can act on the excavation face to the maximum extent; when the mud penetration distance is too large, the mud pressure cannot act on the excavation face in time, and the excavation face is at risk of instability. Accurately predicting the effectiveness of the mud pressure can effectively ensure the stability of the excavation face; in the calculation of the water pressure evolution during the penetration process, it is usually necessary to clarify the maximum penetration distance of the mud in advance.

[0003] In previous studies, there are empirical formulas for calculating the maximum penetration distance of mud. However, the results given by the empirical formulas are dozens of times different from those of the experiments. The reason is that the empirical formula simply regards the penetration of mud in the formation as a continuous fluid, without considering that the bentonite particles in the mud will be retained in the pores of the formation and undergo deep filtration in the porous medium. Therefore, it is still necessary to conduct indoor permeability tests to examine the maximum penetration distance of the mud before actual construction. In addition, most current experiments or theoretical studies assume that the mud is a single bentonite slurry, while the excavated slag in actual construction will enter the mud and water tank, be mixed with the mud, and be transported to the ground for treatment and recycling. Studies have shown that the slag mixed in the mud will accumulate on the surface to form a sedimentary layer during penetration. When the sedimentary layer accumulates too quickly, it will seriously hinder the blocking effect of the bentonite particles on the formation, and the penetration may not stop, resulting in insufficient support force. Therefore, there is currently no method to accurately predict the maximum penetration distance of shield mud in actual construction. Summary of the invention

[0004] In view of the shortcomings existing in the related 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 penetration tests, and consider 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 stable excavation.

[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: S1. Determine mud parameters and formation parameters; 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 surface of the stratum is calculated ; 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; 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; 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 determined 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 deposition concentration is reached, the iterative calculation is stopped and the currently calculated mud penetration distance is The output is the maximum penetration distance of the mud.

[0006] In some of the embodiments, in step S1, the mud parameters include mud pressure, bentonite particle grading 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 grading distribution, original porosity of the sand layer, and density of sand particles.

[0007] In some embodiments, in step S3, the micro-element height of the sedimentary layer of the slag on the surface of the stratum is Calculate according to formula (1); (1); In formula (1), is the mass concentration of the slag 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.

[0008] In some of the embodiments, in step S4, the calculation of the mass concentration of bentonite particles in the mud after passing through the sediment layer comprises the following steps: S41. Calculate the time it takes for mud to pass through a single sediment 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 micro-element of the sedimentary layer; 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 sediment layer; S43. Calculate the particle deposition system of the mud passing through the sedimentary layer micro-element according to formula (5). ; (5); In formula (5), is the effective length of the pore conduit; is the average radius of bentonite particles, and the 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 sedimentary layer 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 , 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 sedimentary layer and enters the formation is calculated according to formula (12): ; (8); (9); (10); (11); (12); In formula (8) to formula (11), is the mass concentration of bentonite particles in the mud passing through the micro-element of the sedimentary layer; 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.

[0009] In some embodiments, in step S5, the calculation of the bentonite particle retention distribution of the mud in the formation includes the following steps: S51. Calculate the time it takes for 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 permeable 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 permeable 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 micro-element 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 zone during the mud infiltration process is calculated as , 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) to formula (20), is the mass concentration of bentonite particles in the mud passing through the micro-element of the infiltration zone.

[0010] In some embodiments, in step S6, the penetration distance of the mud in the formation is Calculate according to formula (21); (twenty one).

[0011] 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), when When the mud permeates in the formation, the current calculated mud permeation distance is The output is the maximum penetration distance of the mud; (twenty two); (twenty three); In formula (23), is the density of bentonite particles.

[0012] In some of the 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.

[0013] Based on the above technical scheme, the prediction method for 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 consider 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

[0014] 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: Figure 1 It is a flow chart of the method for predicting the maximum penetration distance of shield slurry in saturated sand layer of the present invention; Figure 2 It is a 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; Figure 3 A comparison diagram of the calculated value and the test value of the maximum penetration distance of mud according to an embodiment of the present invention; Figure 4 A curve diagram showing the change in mass concentration of bentonite particles in the mud entering the formation calculated according to an embodiment of the present invention; 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

[0015] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0016] 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 orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0017] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0018] refer to Figure 1-Figure 5 As shown, the present invention provides a method for predicting the maximum penetration distance of shield mud in a saturated sand layer, which is used to obtain the maximum penetration distance of the mud in a saturated sand layer. When the shield mud contains slag, the slag will form a sedimentary layer on the surface of the formation during the process of the mud penetrating into the formation, and the mud will first penetrate through the sedimentary layer and then enter the formation.

[0019] 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: 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 mud, mass concentration of slag in mud, etc.; formation parameters include sand layer particle gradation distribution, original porosity of sand layer, density of sand particles, etc.; In this embodiment, the mud pressure is set to 50kPa; the formation is set to a saturated sand formation that meets the actual construction requirements, specifically, the formation is set to sand for sand injection method, with a particle size range of 0.25mm to 0.5mm, a density of sand particles of 2.64g / L, and an original porosity of the formed sand layer of 0.35; the concentration of bentonite particles in the mud is 80g / L, and the mass concentration of the slag in the mud is set to 5 gradients, namely 0, 100g / L, 300g / L, 500g / L, and 700g / L, respectively. The slag is the excavated formation, which is the same as the formation sand, and the apparent viscosity of the mud is 15mPa.s.

[0020] 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 FIG. 1 , after spatial discretization, the mud advances a microelement distance in the formation at each time step.

[0021] 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 surface of the stratum is calculated . 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 sedimentation layer.

[0022] 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.

[0023] 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.

[0024] 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 determined 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 deposition concentration is reached, the iterative calculation is stopped and the currently calculated mud penetration distance is The output is the maximum penetration distance of the mud.

[0025] The above-mentioned illustrative embodiment takes into account the influence of the 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 truly reflects the penetration and filtration mechanism of the shield mud during actual construction. Therefore, 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 the shield construction parameters and ensuring the stability of excavation.

[0026] In some embodiments, in step S3, the mud advances in the formation to a single microelement depth When the micro-element height of the sedimentary layer of the slag on the surface of the stratum is Calculate according to formula (1); (1); In formula (1), is the mass concentration of the slag 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 0.1 mm, when the mass concentration of slag in the mud increases from 0 to 700 g / L, the height of the microelement of the sediment layer Increased from 0 to 0.0143mm.

[0027] The above exemplary embodiment refines the micro-element height of the sedimentary layer of the slag 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 type.

[0028] 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: S41. Calculate the time it takes for mud to pass through a single sediment 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, 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 micro-element of the sedimentary layer; is the hydraulic gradient in mud penetration, which is an arbitrary constant value.

[0029] 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.

[0030] S43. Calculate the particle deposition system of the mud passing through the sedimentary layer micro-element according to formula (5). ; (5); 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 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); (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, , It is the radius value less than 10% on the sand layer particle grading 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.

[0031] S44. Calculate the retention of bentonite particles in the sedimentary layer microelement at each time step according to formula (8): , expressed as the retention 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, assuming that no bentonite particles are filtered when a new sediment layer is formed, the spatial node count of the sediment layer microelement is from bottom to top, and 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 sedimentary layer, it will pass through the first sedimentary layer ( The mass concentration of bentonite particles in the mud after the mud passes through the entire sedimentary layer and enters the formation is calculated according to formula (12): ; (8); (9); (10); (11); (12); In formula (8) to formula (11), is the mass concentration of bentonite particles in the mud passing through the micro-element of the sedimentary layer; 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.

[0032] The above exemplary embodiment takes into account the influence of the slag 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 slag, thereby being able to provide more accurate input conditions for the penetration process of the mud into the formation.

[0033] 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 micro-element height of the sediment layer needs to be 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.

[0034] Specifically, the calculation of bentonite particle retention distribution of mud in the formation includes the following steps: S51. Calculate the time it takes for mud to penetrate a single microelement in the formation according to formula (13): ; The mud passes through each microelement of the permeable zone, 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 permeable zone; It is the density of bentonite particles in the mud passing through the micro-element of the infiltration zone.

[0035] 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 permeable zone.

[0036] S53. Calculate the particle deposition system of mud passing through the micro-element of the permeable zone according to formula (16). ; (16).

[0037] S54. Calculate the retention of bentonite particles in the micro-element 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 ; (17); (18); (19); (20); In formula (17) to formula (20), is the mass concentration of bentonite particles in the mud passing through the micro-element of the infiltration zone.

[0038] The above exemplary embodiments refine the calculation method of the bentonite particle retention distribution in the mud and the bentonite particle deposition amount in each microelement of the permeable zone when the mud penetrates into the formation, thereby providing a calculation basis for the bentonite particle deposition concentration at the subsequent formation entrance.

[0039] In some embodiments, in step S6, the penetration distance of the mud in the formation is Calculate according to formula (21); (twenty one).

[0040] 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, the 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.

[0041] 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 the penetration distance of the mud in the formation is and the bentonite particle deposition concentration at the formation entrance judge the situation; When , it means that the mud penetration in the formation stops, the iterative calculation stops, and the current calculated mud penetration distance is The output is the maximum penetration distance of the mud; (twenty two); (twenty three); In formula (23), is the density of bentonite particles.

[0042] 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 4 As shown, the concentration of bentonite particles at the inlet of the formation 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 the 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 the 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 700g / 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 the penetration will not stop, so there is no maximum penetration distance; that is to say, 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.

[0043] Furthermore, the mass concentration of slag in the slurry The calculated maximum penetration distance of mud under different gradients is shown in Table 1, and compared with the maximum penetration distance of mud obtained by experiment. Figure 3 For intuitive display (the specific process of the maximum penetration distance test of mud can be found at 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 mass concentration of the slag in the mud. When the mass concentration of slag in the mud When the mass 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 it reaches 700g / L, both the calculated and tested results output no maximum penetration distance; the difference between the calculated value and the test value shows that the prediction method still has certain shortcomings. However, in engineering practice, people expect the mud to have a shorter penetration distance. Therefore, the maximum penetration distance of the mud calculated by this prediction method can provide a relatively conservative result for construction, which is more conducive to the reliability and stability of excavation.

[0044] Table 1 Comparison of calculated and experimental values ​​of maximum penetration distance of mud at different gradients of soil mass concentration in mud

[0045] In some embodiments, in step S6, the output results of the iterative calculation also include formation porosity and penetration Mud penetration distance The change of bentonite particles in the formation Distribution of bentonite particles in the slag This exemplary embodiment can obtain parameters that are difficult to directly detect in 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.

[0046] Through the description of multiple embodiments of the method for predicting the maximum penetration distance of shield slurry in saturated sand layer of the present invention, it can be seen that the present invention has at least one or more of the following advantages: 1) The present invention focuses on the influence of the slag mixed in the mud during actual shield construction on the mud penetration process, breaking through the cognitive limitation that previous experiments or theoretical studies did not pay attention to the slag mixed in the mud during actual construction, and can more realistically reflect the penetration and filtration mechanism of the shield mud during actual construction; 2) The present invention can quickly and accurately obtain the maximum penetration distance of shield slurry in saturated sand layers or the situation where there is no maximum penetration distance without a penetration test, thereby providing a reliable reference for adjusting shield construction parameters and ensuring stable excavation.

[0047] 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.

[0048] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or some technical features can be replaced by equivalents without departing from the spirit of the technical solution of the present invention, which should be included in the scope of the technical solution for protection of the present invention.

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; 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 surface of the stratum is calculated ; 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; 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; 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 determined 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 deposition concentration is reached, the iterative calculation is stopped and the currently 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 S1, the mud parameters include mud pressure, bentonite particle grading distribution, density of bentonite particles, apparent viscosity of mud, mass concentration of bentonite particles in mud, and mass concentration of slag in mud; the formation parameters include sand layer particle grading distribution, original porosity of sand layer, and density of sand particles.

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 S3, the micro-element height of the sedimentary layer of the slag on the surface of the stratum Calculate according to formula (1); （1）； In formula (1), is the mass concentration of the slag 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.

4. The method for predicting the maximum penetration distance of shield slurry in saturated sand layer according to claim 3 is characterized in that: In step S4, the calculation of the mass concentration of bentonite particles in the mud after passing through the sediment layer includes the following steps: S41. Calculate the time it takes for mud to pass through a single sediment 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 micro-element of the sedimentary layer; 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 sediment layer; S43. Calculate the particle deposition system of the mud passing through the sedimentary layer micro-element according to formula (5). ; （5）； In formula (5), is the effective length of the pore conduit; is the average radius of bentonite particles, and the 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 sedimentary layer 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 , 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 sedimentary layer and enters the formation is calculated according to formula (12): ; （8）； （9）； （10）； （11）； （12）； In formula (8) to formula (11), is the mass concentration of bentonite particles in the mud passing through the micro-element of the sedimentary layer; 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.

5. The method for predicting the maximum penetration distance of shield slurry in saturated sand layer according to claim 4, characterized in that: In step S5, the calculation of the bentonite particle retention distribution of the mud in the formation includes the following steps: S51. Calculate the time it takes for 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 permeable 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 permeable 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 micro-element 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 zone during the mud infiltration process is calculated as , 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) to formula (20), is the mass concentration of bentonite particles in the mud passing through the micro-element of the infiltration zone.

6. The method for predicting the maximum penetration distance of shield slurry in saturated sand layer according to claim 5, characterized in that: In step S6, the penetration distance of the mud in the formation Calculate according to formula (21); （21）。 7. The method for predicting the maximum penetration distance of shield slurry in saturated sand layer according to claim 6, 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 According to formula (23), when When the mud permeates in the formation, the current calculated mud permeation distance is The output is the maximum penetration distance of the mud; （22）； （23）； In formula (23), is the density of bentonite particles.

8. The method for predicting the maximum penetration distance of shield slurry in saturated sand layer according to claim 7, characterized in that: In step S6, the results outputted during the iterative calculation also include the changes in formation porosity and permeability with mud penetration distance, the distribution of bentonite particle retention in the formation, and the distribution of bentonite particle retention in the slag.

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