Mechanical sinking well mud pressure model structure and mud specific gravity regulation method

Abstract

This invention discloses a model structure for the mud pressure inside a mechanically constructed wellbore and a method for controlling the mud specific gravity. The model structure, used to determine the mud specific gravity, includes a model of the underlying confined aquifer and a model of the unconfined aquifer. The model construction process includes: collecting parameters and identifying the formation type; constructing safety evaluation indicators and calculating the minimum effective mud pressure to resist uplift; establishing a safety factor against seepage failure and calculating the effective mud pressure for seepage control; and comprehensively determining the effective mud pressure inside the well. The mud specific gravity control method includes: formulating principles for determining mud specific gravity and clarifying the actual boundary parameters on site; using feasible intervals at each stage to back-calculate the theoretical range of mud density, verifying the compatibility of slag discharge, compressing boundaries, matching slag discharge constraints, and finally combining actual dynamic fine-tuning with slag discharge to achieve mud specific gravity control. This invention enables precise pressure control in stages during the construction process, addressing the progressive instability risks of the underlying confined aquifer ("unloading-confining-seepage") and the risk of seepage instability in the unconfined aquifer.

Description

Technical Field

[0001] This invention relates to the field of safety technology in caisson construction, specifically to the structure of a mud pressure model for mechanical caissons and a method for determining and controlling the mud specific gravity. Background Technology

[0002] With the expansion of underground space development, the demand for shafts, as key channels connecting underground and surface areas, is increasing. With the development of mechanized shaft construction technology, caisson-type shaft boring machines (mechanical caissons) have become core equipment for urban ultra-deep shaft construction due to their advantages such as high mechanization, strong site adaptability, low maintenance costs, and minimal impact on the surrounding environment. This innovative construction method employs non-drainage excavation technology within the shaft, which significantly reduces the cost of the retaining structure and effectively minimizes the impact on the surrounding environment, injecting new vitality into shaft construction.

[0003] In the mechanical caisson excavation without dewatering, the caisson is continuously filled with circulating mud. The circulating mud in the caisson needs to achieve two major functions at the same time: first, to maintain the stability of the milling face through mud pressure and prevent the bottom of the caisson from unloading instability or piping instability; second, to carry out the milled rock and soil debris by means of the fluidity of the mud.

[0004] Therefore, accurate determination and dynamic control of the mud weight during mechanical caisson construction are key to ensuring construction safety and improving slag removal efficiency.

[0005] In existing technologies, caisson design specifications only focus on indicators such as sinking coefficient and buoyancy resistance, and there are no suitable methods for verifying the bottom stability of mechanical caissons and calculating the mud specific gravity. Patent application number 202211354533.0 proposed a "method for determining mud height and density in mechanical caisson construction," but it has key defects: this method equates circular mechanical caissons with planar foundation pits, calculates mud parameters based on the overturning stability of the foundation pit support structure, and ignores the structural characteristics of circular caissons that have no risk of overturning; at the same time, it does not distinguish the hydrological differences between underlying confined water and unconfined strata, and does not take into account the mud concentration restrictions for slag removal requirements, resulting in calculation results that do not match the actual mud action effect and caisson stability requirements, which may lead to problems such as instability of the milling face, slag removal blockage, or insufficient slag carrying capacity.

[0006] Therefore, this application, taking into account the structural characteristics of the caisson, hydrogeological conditions (confined water / unconfined water), and construction functional requirements (surface stabilization and slag removal), proposes a mechanical method for the structure of the mud pressure model inside the caisson and a mud specific gravity control method to solve the technical problems of the progressive instability risk of the underlying confined water layer during the "unloading-confining-permeability" process and the permeability instability of the unconfined water layer, thereby achieving precise pressure control in stages. Summary of the Invention

[0007] The main objective of this invention is to provide a mud pressure model structure and mud specific gravity control method for mechanical caisson construction. Through an integrated system of "stratum-specific modeling → three-stage parameter calculation of underlying confined water + unconfined aquifer anti-seepage parameter calculation → real-time monitoring + multi-dimensional control," it achieves accurate determination and dynamic adaptation of mud specific gravity, ensuring the safety and efficiency of mechanical caisson construction. Ultimately, it addresses the shortcomings of current mechanical caisson mud specific gravity determination and control methods, such as failing to consider the structural characteristics of circular caissons, failing to differentiate between underlying confined and unconfined aquifers, lacking dynamic parameter adjustment for underlying confined aquifers, and failing to consider slag concentration (1.15–1.35 g / cm³). 3 The lack of limits and real-time monitoring loops leads to unscientific mud density control, resulting in milling face instability (such as piping), insufficient or blocked slag discharge, and technical problems that induce well wall displacement, pressurized water surge, and other accidents.

[0008] The present invention solves the above-mentioned technical problems by adopting the following technical solutions:

[0009] A mechanical caisson well drilling mud pressure model structure, used to determine mud specific gravity, includes an underlying confined aquifer model and an unconfined aquifer model. The model construction process includes:

[0010] Step S1. Collect and obtain the foundation parameters of the shaft and the inner diameter of the caisson using existing materials such as the shaft design document. Caisson segment wall thickness Milling surface depth ;

[0011] Step S2. Through geological survey, determine that the area to be excavated using the mechanical method for caisson excavation is an impermeable layer-underlying confined aquifer or unconfined stratum, and obtain geological and hydrological parameters, including: relative density of soil particles. Porosity Cohesion internal friction angle saturation density , natural weight Burial depth of the top plate of the confined aquifer and the groundwater level elevation measured from the surface. , Elevation of confined water level ;

[0012] Step S3. Based on the ultimate bearing capacity theory of sand-based soil, the cohesion resistance of the soil outside the mechanical caisson is introduced to construct a safety evaluation index for the bottom heave of the mechanical caisson. This index is used to calculate the minimum effective mud pressure required to avoid unloading and heave at the bottom of the mechanical caisson. The results are as follows: , This is a safety evaluation index for the bottom heave resistance of mechanically constructed caissons, and its value is generally ≥1.5. This refers to the cohesion resistance term of the soil outside the mechanically constructed caisson, adapted to the constraint effect of circular caisson segment support on the soil. and Both are the bearing capacity coefficient of the foundation, and the friction angle. This information can be found in the Terzaghi coefficient table. Due to ground overloading, The effective pressure of the mud at the bottom of a mechanically constructed caisson, controlled by heave failure. , and For the corresponding The density of the mud and the height of the mud surface;

[0013] Step S4. Construct the safety factor for seepage failure at the bottom of the mechanically caisson. , The safety factor for the bottom of the mechanically caisson to resist seepage damage is generally ≥1.5 (safety threshold). The effective pressure of the mud at the bottom of a mechanically constructed caisson, controlled by seepage damage. , and For the corresponding The mud density and mud level, The critical hydraulic gradient, (Sandy soil) or (Clay soil) To effectively lower the water head, (Confined aquifer) or (Water-filled layer) Let the penetration path length be taken as... ;

[0014] Step S5. Finally, the effective mud pressure inside the caisson is determined by the minimum effective mud pressure required for unloading and heaving at the bottom of the caisson and the safety factor against seepage failure.

[0015] Preferably, in step S4, the safety factor for seepage resistance at the bottom of the mechanically caisson is determined to reflect the effective stress of the soil at the milled face. Alternatively, the following formula can be used for calculation:

[0016]

[0017]

[0018] in, The safety factor for the bottom of the mechanically caisson to resist seepage damage is generally ≥1.5 (safety threshold). For the effective stress of the soil at the milling face, The natural density of the shallow water layer. The water level is saturated with specific gravity. The waterproof layer is naturally heavy. The specific gravity of the confined aquifer is saturated. It is the density of water.

[0019] Preferably, the process for confirming the effective pressure of the drilling mud inside the caisson in the underlying confined aquifer model in step S5 includes:

[0020] Based on the depth of the milled surface Burial depth of the top plate of the confined aquifer Based on location, the underlying confined aquifer is divided into three distinct stages: far from the confined aquifer, close to the confined aquifer, and entering the confined aquifer. If... Then it is determined to be far away from the confined aquifer, if Then it is determined to be close to a confined aquifer, if If so, it is determined to have entered a confined aquifer;

[0021] The effective pressure of this section of mud is calculated using the "inverse safety constraint threshold method" to determine the anti-uplift safety evaluation index. Safety factor against seepage damage As a constraint, when the safety index is equal to the control threshold, the minimum effective mud pressure under the corresponding risk is calculated in reverse.

[0022] In the multi-risk coupling stage, the maximum value of the minimum pressure corresponding to each risk is taken as the control value to ensure construction safety while taking into account economy.

[0023] For areas far from confined aquifers, considering the risk of heave from unloading at the milling face, the effective mud pressure needs to balance the heave failure tendency (i.e., the heave driving force) caused by the unloading of the soil above during excavation at the milling face, in order to ensure the stability of the milling face and minimize the effective mud pressure. The constraints are: ;

[0024] For areas close to confined aquifers, increasing the effective pressure balance of the mud to unload the uplift effect, combined with the partial support force of the confined aquifer, is beneficial. The calculation formula is as follows: , The influence coefficient of confined water is the minimum effective mud pressure. The constraints are: ;

[0025] When entering a confined aquifer, the area below the milled face is subjected to the full pressure of the confined water. The effective mud pressure must simultaneously resist the dual risks of "unloading heave" and "high-head seepage piping." Therefore, a dual-control logic is used to determine the effective mud pressure at this stage. The maximum value of the two constraint calculations is then taken as the effective mud pressure for this section. Thus: , The minimum effective mud pressure required to control the unloading and uplift failure of a confined aquifer. It is the minimum effective mud pressure that controls seepage damage in confined aquifers.

[0026] Preferably, for areas near confined aquifers, the confined aquifer influence coefficient is... The rate decreases linearly with increasing milling depth, as shown by the following calculation formula: , At this time, the effective pressure of the mud increases with... Decrease and increase.

[0027] Preferably, the process for confirming the effective pressure of the drilling mud inside the caisson in the unconfined formation model in step S5 includes:

[0028] For unconfined aquifers, it refers to a situation where there is no underlying confined aquifer below the milling face, and the groundwater level is unconfined (…). The system needs to resist the dual risks of "unloading heave" and "high-head seepage piping". Therefore, a dual-control logic is adopted to determine the effective mud pressure at this stage. The core control objective is to prevent seepage damage (piping / soil flow) in the formation around the milling face and well wall. Unloading heave is a secondary risk. The effective mud pressure is the maximum control value of the two requirements, and the calculation formula is as follows: , The minimum effective mud pressure for controlling unloading and uplift failure in unconfined formations. The minimum effective mud pressure controlled by seepage failure in unconfined formations.

[0029] Preferably, the specific operational procedure for using the model to determine the specific gravity of the mud includes:

[0030] Step L1. Establish principles for determining mud specific gravity: fixed effective mud pressure and bidirectional linkage adjustment—the minimum mud pressure calculated based on different layers and stages. Based on the baseline, with the slag discharge constraint mud specific gravity ∈ [1.15, 1.35] (corresponding to mud unit weight) ∈[11.5, 13.5] kN / m 3 ")" and "well depth adaptation" Within the two designated boundaries of "not exceeding the operating space of the pipe segment", find a reasonable combination of the two, and then make dynamic fine adjustments based on the actual slag discharge.

[0031] Step L2. Determine the actual boundary parameters on site: Based on the measured milling depth of the caisson using the mechanical method on site. Sure feasible range ;

[0032] Step L3. Back-calculate the theoretical range of mud density: based on each stage and The feasible range is used as input to inversely calculate the mud density. The theoretical scope includes: ;

[0033] Step L4. Verify slag discharge compatibility: Convert the theoretical range of the back-calculated mud density into a mud specific gravity range, and compare and verify it with the mud specific gravity constrained by slag discharge within the specified theoretical range of the specified boundary [1.15, 1.35].

[0034] Step L5. Compression Boundary and Matching Slag Discharge Constraints: When the theoretical range exceeds the slag discharge range, then... Within the feasible range, find a way to make the mud heavy Falling into [11.5kN / m 3 13.5kN / m 3 The corresponding boundary requirements for the sub-intervals are to avoid exceeding the slag discharge constraints, specifically according to the following rules:

[0035] like If the value is greater than 13.5, then increase. (reduce ), until ≤13.5, that is ≥ ;

[0036] like If <11.5, then decrease. (improve ), until ≥11.5, that is ≤ ;

[0037] Final feasible combination: Choose any option within this range Reverse calculation Finally, the corresponding mud specific gravity was calculated;

[0038] Step L6 involves dynamic fine-tuning based on actual slag discharge (on-site optimization). After the initial combination is determined, it is necessary to judge whether fine-tuning is needed by monitoring the slag discharge effect. The core principle is that "specific gravity dominates slag discharge capacity, and liquid level height assists in pressure replenishment".

[0039] On the other hand, this invention also discloses a mud specific gravity control method, used to control the mud specific gravity obtained during the construction of the mud pressure model structure in the mechanical caisson well using mud monitoring parameters measured and collected before control. These mud monitoring parameters are divided into core parameters and auxiliary parameters. The core parameters include mud specific gravity, mud level height, slag content at the discharge port, and milling face pressure. The auxiliary parameters include wellbore displacement and wellbore displacement. During the data collection process:

[0040] The mud specific gravity was measured every 15 minutes using a mud specific gravity meter.

[0041] The mud level height is monitored in real time using a level sensor.

[0042] The slag content at the slag discharge port is measured every 30 minutes using a sampling and sieving method.

[0043] The pressure on the milling surface is monitored in real time using a pre-embedded pressure sensor.

[0044] The wellbore displacement was measured once every 1 hour using an inclinometer.

[0045] The groundwater level was measured every 2 hours using a water level gauge.

[0046] The specific control procedures include any of the following:

[0047] (1) Mud specific gravity control strategy:

[0048] 1) If Calculate the value and the difference. If the concentration is ≥0.05, add bentonite (per 10m³). 3 Add 0.5-1.0t of mud or barite powder (per 10m³). 3 Add 0.3–0.6 t of mud, stir for 3–5 minutes, and then retest until… ;

[0049] 2) If Calculate the value and the difference. If the concentration is ≥0.05, add clean water (per 10m³). 3 Add 0.8–1.2 m of mud. 3 After stirring for 5-8 minutes, retest to ensure... Actual measurements show that the slag discharge level is not lower than 1.15 times the lower limit of slag discharge.

[0050] and These are the measured value of mud density and the theoretical calculated value of mud density obtained during the construction of the mud pressure model structure in the mechanical caisson;

[0051] (2) Liquid level control strategy:

[0052] 1) If And the difference If the depth is ≥0.2m, start the mud pump to replenish the mud (the specific gravity of the replenished mud = Grouting rate ≤ 0.5m 3 / min, to avoid a sudden rise in liquid level;

[0053] 2) If And the difference If the depth is ≥0.2m, open the overflow valve to discharge slurry (slurry specific gravity ≤ +0.03), slurry discharge rate ≤0.3m 3 / min, to prevent a sudden drop in pressure on the milling surface;

[0054] and These are the measured effective excavation depth and the theoretically calculated effective excavation depth, respectively, obtained during the construction of the mud pressure model structure inside the mechanical caisson.

[0055] (3) Slag discharge adaptation and control strategy:

[0056] 1) If the slag content in the discharged slag is >15% (risk of pipe blockage), then the concentration should be appropriately reduced. The viscosity decreases by ≤0.05, and CMC is added to increase the mud viscosity (every 10m during the CMC addition process). 3 Add 0.1-0.2 kg of mud).

[0057] 2) If the slag content in the discharged slag is <5% (insufficient slag carrying capacity), then the concentration should be appropriately increased. The increase is ≤0.05, and a dispersant is added to reduce the viscosity of the mud (every 10m during the dispersant addition process). 3 Add 0.05-0.1 kg of mud).

[0058] (4) Emergency control strategies:

[0059] 1) If the pressure on the milling face drops suddenly (the drop is ≥10%), immediately add grout until the pressure is reduced. +0.3m, synchronously increased The pressure increase was set at 0.05–0.10, and milling operations were suspended until the pressure stabilized.

[0060] 2) If signs of piping are detected (sudden increase in mud turbidity, abnormal drop in liquid level), immediately increase the intensity of the operation. The pressure was raised to 1.35-1.40, and the backup mud pump was started to replenish the grout. At the same time, cement-water glass dual-liquid grouting was used to seal the piping channel. Construction was resumed after the signs disappeared.

[0061] 3) If the pressure of the pressurized water rises suddenly, activate the backup well point dewatering system to reduce the pressure until the risk is eliminated.

[0062] As can be seen from the above technical solution, this invention provides a structure for a mechanically caisson well drilling mud pressure model and a method for controlling mud specific gravity. Compared with the prior art, this invention has the following advantages:

[0063] 1. This invention considers the differentiated stress requirements of different strata. By distinguishing between underlying confined aquifers and unconfined strata, and based on the ultimate bearing capacity theory of sand-based soil and introducing the cohesion resistance of the soil outside the mechanical caisson, it constructs safety evaluation indicators for bottom heave and safety factors for seepage failure. It also establishes a well mud pressure calculation model adapted to different strata, which can calculate mud parameters for differentiated stress in different strata. This overcomes the shortcomings of existing technologies that do not distinguish the stress conditions of strata and provides a theoretical calculation basis for determining mud specific gravity.

[0064] 2. This invention divides the underlying confined aquifer into construction stages of being far from, near to, and entering the confined aquifer, and establishes a method for determining the mud specific gravity and liquid level height that dynamically adjusts with the excavation depth. This enables precise pressure control in stages during the construction process, thereby addressing the risks of confined water surge, bottom unloading heave, confined water uplift, and seepage damage. It also takes into account the adaptability requirements of the mud concentration range for slag removal operations.

[0065] 3. This invention targets single unconfined formations and determines the mud specific gravity by integrating anti-permeability damage and unloading balance control conditions. It can simultaneously control permeability and unloading, and ultimately solve the construction hazards of piping and well bottom heave in unconfined formations.

[0066] 4. This invention combines on-site monitoring to form a dynamic control strategy for mud specific gravity, which is adapted to the structural construction characteristics of circular mechanical caisson segment support; it can make up for the shortcomings of existing technologies and the incompatibility between mechanical caisson construction conditions, and finally realize the on-site control of mud pressure in mechanical caisson construction conditions, ensuring construction safety and operational efficiency.

[0067] It should be understood that the descriptions in this section are not intended to identify key or essential features of embodiments of the invention, nor are they intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Of course, implementing any product of the invention does not necessarily require achieving all of the advantages described above simultaneously. Attached Figure Description

[0068] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0069] Figure 1 This is a schematic diagram of the overall operation flow of the method of the present invention;

[0070] Figure 2 This is a schematic cross-sectional view of the mechanical caisson method for the impermeable layer-underlying confined aquifer of the present invention;

[0071] Figure 3 This is a schematic cross-sectional view of the single unwatered stratum mechanical caisson of the present invention. Detailed Implementation

[0072] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0073] For details in the embodiments, please refer to Figures 1 to 3 .

[0074] like Figure 1 As shown in the embodiment of the present invention, the mechanical method for caisson drilling mud pressure model structure is used to determine the mud specific gravity. It includes an underlying confined aquifer model and an unconfined aquifer model. The model construction and application process includes:

[0075] Step S1. Collect and obtain the foundation parameters of the shaft and the inner diameter of the caisson through materials such as the shaft design document. Caisson segment wall thickness Milling surface depth .

[0076] Step S2. Through geological survey, determine that the area to be excavated using the mechanical method for caisson excavation is an impermeable layer-underlying confined aquifer or unconfined stratum, and obtain geological and hydrological parameters, including: relative density of soil particles. Porosity Cohesion internal friction angle saturation density , natural weight Burial depth of the top plate of the confined aquifer and the groundwater level elevation measured from the surface. , Elevation of confined water level .

[0077] Step S3. Based on the ultimate bearing capacity theory of sand-based soil, the cohesion resistance of the soil outside the mechanical caisson is introduced to construct a safety evaluation index for the bottom heave of the mechanical caisson. This index is used to calculate the minimum effective mud pressure required to avoid unloading and heave at the bottom of the mechanical caisson. The results are as follows: , This is a safety evaluation index for the bottom heave resistance of mechanically constructed caissons, and its value is generally ≥1.5. This refers to the cohesion resistance term of the soil outside the mechanically constructed caisson, adapted to the constraint effect of circular caisson segment support on the soil. and Both are the bearing capacity coefficient of the foundation, and the friction angle. This information can be found in the Terzaghi coefficient table. Due to ground overloading, The effective pressure of the mud at the bottom of a mechanically constructed caisson, controlled by heave failure. , and For the corresponding The mud density and mud level.

[0078] Step S4. Construct the safety factor for seepage failure at the bottom of the mechanically caisson. , The safety factor for the bottom of the mechanically caisson to resist seepage damage is generally ≥1.5 (safety threshold). The effective pressure of the mud at the bottom of a mechanically constructed caisson, controlled by seepage damage. , and For the corresponding The mud density and mud level, The critical hydraulic gradient, (Sandy soil) or (Clay soil) To effectively lower the water head, (Confined aquifer) or (Water-filled layer) Let the penetration path length be taken as... .

[0079] The safety factor for seepage resistance at the bottom of the mechanically constructed caisson is determined to reflect the effective stress of the soil at the milled face. Alternatively, the following formula can be used for calculation:

[0080]

[0081]

[0082] in, The safety factor for the bottom of the mechanically caisson to resist seepage damage is generally ≥1.5 (safety threshold). For the effective stress of the soil at the milling face, The natural density of the shallow water layer. The water level is saturated with specific gravity. The waterproof layer is naturally heavy. The specific gravity of the confined aquifer is saturated. It is the density of water.

[0083] Step S5. Finally, the effective mud pressure inside the caisson is determined by the minimum effective mud pressure required for unloading and heaving at the bottom of the caisson and the safety factor against seepage failure.

[0084] in:

[0085] (1) The process for confirming the effective pressure of the drilling mud in the caisson of the underlying confined aquifer model includes:

[0086] Since the underlying confined aquifer refers to a milled face located within an impermeable layer, and a confined aquifer exists below the impermeable layer, the depth of the milled face is used as a basis for determining the location of the confined aquifer. Burial depth of the top plate of the confined aquifer Positional relationship ( The underlying confined aquifer is divided into three sections: far from the confined aquifer, close to the confined aquifer, and entering the confined aquifer. The mud specific gravity must meet the slag concentration limit of 1.15–1.35. If… Then it is determined to be far away from the confined aquifer, if Then it is determined to be close to a confined aquifer, if If so, it is determined to have entered a confined aquifer. The depth for warning of confined water can be 5 to 15 meters, depending on the actual geological conditions.

[0087] It is also necessary to further explain here that the allowable mud specific gravity range for slag discharge is set based on the slag discharge capacity of the milling equipment and the mud circulation characteristics. The upper limit of the mud specific gravity is 1.35 (if it exceeds this, the mud viscosity will be too high and it will easily clog the slag discharge pipeline), and the lower limit is 1.15 (if it is lower, the ability to carry debris will be insufficient and the slag discharge efficiency will decrease).

[0088] Further calculation of the effective pressure of the mud section is carried out using the "safety constraint threshold inverse method". The constraint conditions are the anti-uplift safety evaluation index F≥1.5 and the anti-seepage failure safety factor K≥1.5. When the safety index is equal to the control threshold, the minimum effective pressure of the mud under the corresponding risk is calculated in reverse.

[0089] The definition of F is a safety constraint condition. By limiting the minimum value through constraints, and after algebraically transforming the constraint condition and taking the safety control threshold, the minimum effective mud pressure result can be obtained. In the multi-risk coupling stage, the maximum value of the minimum pressure corresponding to each risk is taken as the control value to ensure construction safety while taking into account economy.

[0090] For example, in geotechnical engineering stability calculations, the approach is to "take the safety factor equal to the standard threshold and back-calculate the minimum support / balance pressure". The calculation result is the lower limit value that meets the stability requirements. The engineering design takes this value as the control benchmark, taking into account both safety and economy.

[0091] (a) For areas far from confined aquifers (where the impact of confined water on the milling face is negligible at this stage), considering the risk of unloading and heaving at the milling face, the effective mud pressure needs to balance the tendency of the milling face to heave and fail due to the unloading of the soil above (i.e., the driving force of heaving), in order to ensure the stability of the milling face and minimize the effective mud pressure. The constraints are: ;

[0092] (b) For areas close to confined aquifers (where the back pressure of the confined water gradually becomes apparent), it is necessary to increase the effective pressure of the mud to balance the unloading and heave effect, combined with part of the back pressure of the confined water. The calculation formula is as follows: , The influence coefficient of confined water is the minimum effective mud pressure. The constraints are: ;

[0093] Among them, for areas close to confined aquifers, the influence coefficient of confined water is... The rate decreases linearly with increasing milling depth, as shown by the following calculation formula: , At this time, the effective pressure of the mud increases with... Decrease and increase.

[0094] (c) For entering / passing through a confined aquifer (where the milling face is located within the confined aquifer), the area below the milling face is subjected to the full pressure of the confined water. The effective mud pressure must simultaneously resist the dual risks of "unloading heave" and "high-head seepage piping." Therefore, dual-control logic is used to determine the effective mud pressure at this stage. Thus, the maximum value of the calculation results for the two types of constraints is taken as the effective mud pressure for this section, as follows: , The minimum effective mud pressure required to control the unloading and uplift failure of a confined aquifer. It is the minimum effective mud pressure that controls seepage damage in confined aquifers.

[0095] (2) The process for confirming the effective pressure of the drilling mud inside the caisson in the unconfined formation model includes:

[0096] For unconfined aquifers, it refers to a situation where there is no underlying confined aquifer below the milling face, and the groundwater level is unconfined (…). The system needs to resist the dual risks of "unloading heave" and "high-head seepage piping". Therefore, a dual-control logic is adopted to determine the effective mud pressure at this stage. The core control objective is to prevent seepage damage (piping / soil flow) in the formation around the milling face and well wall. Unloading heave is a secondary risk. The effective mud pressure is the maximum control value of the two requirements, and the calculation formula is as follows: , The minimum effective mud pressure for controlling unloading and uplift failure in unconfined formations. The minimum effective mud pressure controlled by seepage failure in unconfined formations.

[0097] Step S6. The specific operational procedures for determining the specific gravity of the mud in the final model include:

[0098] Step L1. Establish principles for determining mud specific gravity: fixed effective mud pressure and bidirectional linkage adjustment—the minimum mud pressure calculated based on different layers and stages. Based on the baseline, with the slag discharge constraint mud specific gravity ∈ [1.15, 1.35] (corresponding to mud unit weight) ∈[11.5, 13.5] kN / m 3 ")" and "well depth adaptation" Within the two designated boundaries of "not exceeding the operating space of the pipe segment", find a reasonable combination of the two, and then make dynamic fine adjustments based on the actual slag discharge.

[0099] It should be noted here that in the engineering field, 'mud bulk density' and 'mud weight' are essentially equivalent (both units are kN / m³). 3 ), 'specific gravity of mud' is a dimensionless relative value, and the conversion relationship among the three is: specific gravity = density / 10 ( kN / m 3 Throughout this plan, 'heavy weight' is used for calculations and 'specific gravity' is used for material description.

[0100] Step L2. Determine the actual boundary parameters on site: Based on the measured milling depth of the caisson using the mechanical method on site. Sure feasible range ;

[0101] Step L3. Back-calculate the theoretical range of mud density: based on each stage and The feasible range is used as input to inversely calculate the mud density. The theoretical scope includes: ;

[0102] Step L4. Verify slag discharge compatibility: Convert the theoretical range of the back-calculated mud density into a mud specific gravity range, and compare and verify it with the mud specific gravity constrained by slag discharge within the specified theoretical range of the specified boundary [1.15, 1.35].

[0103] Step L5. Compression Boundary and Matching Slag Discharge Constraints: When the theoretical range exceeds the slag discharge range, then... Within the feasible range, prioritize finding the option that allows... Falling into [11.5kN / m 3 13.5kN / m 3 The corresponding boundary requirements for the sub-intervals are to avoid exceeding the slag discharge constraints, specifically according to the following rules:

[0104] like If the value is greater than 13.5, then increase. (reduce ), until ≤13.5, that is ≥ ;

[0105] like If <11.5, then decrease. (improve ), until ≥11.5, that is ≤ ;

[0106] Final feasible combination: Choose any option within this range Reverse calculation Finally, the corresponding mud specific gravity was calculated;

[0107] Step L6 involves dynamic fine-tuning based on actual slag discharge (on-site optimization). After the initial combination is determined, it is necessary to judge whether fine-tuning is needed by monitoring the slag discharge effect. The core principle is that "specific gravity dominates slag discharge capacity, and liquid level height assists in pressure replenishment".

[0108] On the other hand, this invention also discloses a mud specific gravity control method, used to control the mud specific gravity obtained during the construction of the mud pressure model structure in a mechanically caisson well using mud monitoring parameters measured and collected before control. The mud monitoring parameters are divided into core parameters and auxiliary parameters. The core parameters include mud specific gravity, mud level height, slag content at the discharge port, and milling face pressure. The auxiliary parameters include wellbore displacement and wellbore displacement. During the data collection process:

[0109] The mud specific gravity was measured every 15 minutes using a mud specific gravity meter.

[0110] Real-time monitoring of mud level height is achieved using a level sensor.

[0111] The slag content at the slag discharge port was measured every 30 minutes using a sampling and sieving method.

[0112] Real-time monitoring of pressure on the milled surface is achieved using pre-embedded pressure sensors.

[0113] The wellbore displacement was measured every hour using an inclinometer.

[0114] Groundwater level was measured every 2 hours using a water level gauge.

[0115] The slag content at the slag discharge port is monitored using a sampling and sieving method. During the process, a slag discharge status check needs to be performed once. The pressure sensor and flow meter in the slag discharge pipeline are also used to determine the mud's ability to carry debris (a sudden increase in pressure or a decrease in flow indicates that the mud is too thick and needs to be diluted; debris deposition indicates that the mud is too thin and needs to be thickened).

[0116] In addition, when using water level gauges to monitor groundwater levels, a stratum response monitoring system can be deployed as needed: pressure measuring pipes are installed on the outside of the caisson cutting edge to monitor changes in the pressure of confined water / groundwater; high-definition cameras are installed on the milling face to observe whether seepage or bubbling (early signs of seepage failure) occurs.

[0117] The final control process includes any of the following:

[0118] (1) Mud specific gravity control strategy:

[0119] 1) If Calculate the value and the difference. If the concentration is ≥0.05, add bentonite (per 10m³). 3 Add 0.5-1.0t of mud or barite powder (per 10m³). 3 Add 0.3–0.6 t of mud, stir for 3–5 minutes, and then retest until… The purpose of adding bentonite here is to increase viscosity, and the purpose of adding barite powder is to increase weight.

[0120] 2) If Calculate the value and the difference. If the concentration is ≥0.05, add clean water (per 10m³). 3 Add 0.8–1.2 m of mud. 3 After stirring for 5-8 minutes, retest to ensure... Actual measurements show that the slag discharge level is not lower than 1.15 times the lower limit of slag discharge.

[0121] and These are the measured values ​​of mud density and the theoretical calculated values ​​of mud density obtained during the construction of the mud pressure model structure in the mechanical caisson;

[0122] (2) Liquid level control strategy:

[0123] 1) If And the difference If the depth is ≥0.2m, start the mud pump to replenish the mud (the specific gravity of the replenished mud = Grouting rate ≤ 0.5m 3 / min, to avoid a sudden rise in liquid level;

[0124] 2) If And the difference If the depth is ≥0.2m, open the overflow valve to discharge slurry (slurry specific gravity ≤ +0.03), slurry discharge rate ≤0.3m 3 / min, to prevent a sudden drop in pressure on the milling surface;

[0125] and These are the measured effective excavation depth and the theoretically calculated effective excavation depth, respectively, obtained during the construction of the mud pressure model structure inside the mechanical caisson.

[0126] (3) Slag discharge adaptation and control strategy:

[0127] 1) If the slag content in the discharged slag is >15% (risk of pipe blockage), then the concentration should be appropriately reduced. The viscosity decreases by ≤0.05, and CMC is added to increase the mud viscosity (every 10m during the CMC addition process). 3 Add 0.1-0.2 kg of mud).

[0128] 2) If the slag content in the discharged slag is <5% (insufficient slag carrying capacity), then the concentration should be appropriately increased. The increase is ≤0.05, and a dispersant is added to reduce the viscosity of the mud (every 10m during the dispersant addition process). 3 Add 0.05-0.1 kg of mud).

[0129] (4) Emergency control strategies:

[0130] 1) If the pressure on the milling face drops suddenly (the drop is ≥10%), immediately add grout until the pressure is reduced. +0.3m, synchronously increased The pressure increase was set at 0.05–0.10, and milling operations were suspended until the pressure stabilized.

[0131] 2) If signs of piping are detected (sudden increase in mud turbidity, abnormal drop in liquid level), immediately increase the intensity of the operation. The pressure was raised to 1.35-1.40, and the backup mud pump was started to replenish the grout. At the same time, cement-water glass dual-liquid grouting was used to seal the piping channel. Construction was resumed after the signs disappeared.

[0132] 3) If the pressure of the pressurized water rises suddenly, activate the backup well point dewatering system to reduce the pressure until the risk is eliminated.

[0133] In summary, this scheme distinguishes between underlying confined aquifer and unconfined strata, incorporates the cohesive resistance of the soil outside the caisson based on the sand-based ultimate bearing capacity theory, and constructs safety evaluation indicators for bottom heave resistance and safety factors for seepage failure resistance, establishing differentiated calculation models for in-well mud pressure. It can dynamically adjust mud specific gravity and mud level height at different excavation stages for confined aquifer strata, and determine mud specific gravity for unconfined strata by integrating seepage failure resistance and unloading balance requirements. Furthermore, it provides a practical dynamic control strategy for mud specific gravity based on the construction characteristics of circular mechanical caisson structures. Ultimately, it overcomes the shortcomings of traditional technologies that fail to differentiate between strata conditions and lack sufficient pressure control precision, solving risks such as bottom heave due to unloading, confined water rise, and seepage piping failure during caisson construction. It also considers the mud concentration requirements for slag removal, achieving precise pressure control in stages and ensuring the safety and operational efficiency of mechanical caisson construction.

[0134] Furthermore, the present invention also discloses the mechanical caisson construction operation based on the precise determination and dynamic adaptation of mud specific gravity, employing different tunneling strategies in the impermeable layer and in the unconfined strata.

[0135] During the excavation of the aquitard, such as Figure 2 The shaft shown is excavated from the surface downwards, with pre-assembled segmental supports at the top. The tunneling machine (TBM) is located at the bottom of the shaft, with steel cutting edge rings around its perimeter to cut into the strata. The TBM extends its cutting arm, and the cutting head at the front breaks up the rock and soil. High-pressure water is sprayed from the flushing branch pipe to disperse the excavated soil. The slurry pump discharges the mixed mud to the surface through the main mud return pipeline, maintaining a certain mud level inside the shaft to balance the ground pressure. The key to this tunneling is that the excavation section is located in an impermeable aquitard, beneath which lies a confined aquifer; therefore, the excavation depth must be strictly controlled. No more than the thickness of the waterproof layer To prevent the confined water from surging due to penetration of the impermeable layer, the height difference between the mud level in the well and the surface is determined by the elevation of the underlying confined water level. express.

[0136] During the excavation of unconfined strata, such as Figure 3 As shown, the vertical shaft is excavated downwards from the surface, and also includes segment support, the tunneling machine main unit, steel cutting edge foot rings, cutting arm, flushing pipeline, and mud return system. However, because the stratum is a highly permeable unconfined aquifer with the groundwater level close to the surface, a high-pressure water cutter head is used at the front end of the cutting arm to assist in rock breaking, and a bottom locking head is used to stabilize the excavation face. Since the aquifer is connected to the groundwater, the core of this working condition is the water head pressure generated by the mud level in the shaft. It balances external groundwater pressure and prevents water inrush, quicksand, and well wall collapse.

[0137] For example, in one embodiment, taking a shield tunnel receiving shaft project as an example, the caisson construction is carried out using the circular segment support mechanical method, and the inner diameter of the caisson is... Precast segment wall thickness Design final milling depth The site consists of an impermeable layer and an underlying confined aquifer. The first layer of silty clay (impermeable layer) is 18m thick, which is the depth of the top of the confined aquifer. The second layer of silt below is a confined aquifer, 12m thick. Overloading occurred during ground construction. .

[0138] The stratigraphic and hydrological parameters measured here are: natural unit weight of the aquitard. Cohesion internal friction angle , , ; saturated specific gravity of confined aquifer , , , , Confined water level elevation , .

[0139] (I) Constructing safety evaluation indicators

[0140] (1) Safety evaluation index for bottom hole heave Based on Terzaghi's ultimate bearing capacity theory, the cohesion resistance of the soil outside the caisson is introduced to control the threshold. , , Time lookup table , .

[0141] (2) Safety factor for bottom hole seepage failure The critical hydraulic gradient method was used to construct the threshold. , penetration path length , .

[0142] (ii) Calculation of effective mud pressure in stages

[0143] (1) Stage 1: Away from the confined aquifer ( , )

[0144] Substituting into the formula, we get The soil itself has sufficient resistance to uplift, and the effective pressure of the mud is controlled according to the lower limit of slag discharge.

[0145] (2) Stage Two: Approaching the confined aquifer ( , )

[0146] Confined water influence coefficient Pressurized water jacking force The minimum effective mud pressure in stage two was calculated. .

[0147] (3) Stage Three: Entering the confined aquifer ( , )

[0148] Anti-uplift control pressure is negative, and the risk of unloading is negligible; anti-seepage control: effective head. Critical hydraulic gradient Effective severe The calculated anti-permeability control pressure Ultimately, the maximum value of both controls is taken. .

[0149] (III) Determining the specific gravity of the mud and the height of the liquid level under the constraint of slag discharge

[0150] With the allowable specific gravity range of slag discharge [1.15, 1.35] as a rigid constraint, the linkage matching parameters are as follows: for stage one, the specific gravity is 1.15, corresponding to a liquid level height of 3.0m; for stage two, the specific gravity is 1.20, corresponding to a liquid level height of 5.1m; and for stage three, the specific gravity is 1.28, corresponding to a liquid level height of 14.4m, all of which meet the requirements of the working space inside the well.

[0151] (iv) On-site dynamic control and construction effect

[0152] Data is collected on-site at a frequency of 15-minute specific gravity testing, real-time liquid level monitoring, and 30-minute slag discharge screening. The specific gravity is finely adjusted within ±0.03 based on the slag discharge status on a daily basis, and the liquid level is simultaneously linked to maintain stable working face pressure.

[0153] Throughout the construction process, parameter control was stable, the milling face was stable, slag removal was smooth, the caisson was accurately sunk to the design elevation, and the quality of the completed caisson met the requirements for shield tunneling acceptance.

[0154] In another embodiment provided in this application, a computer program product containing instructions is also provided, which, when run on a computer, causes the computer to construct a mud pressure model structure inside any of the mechanical caissons in the above embodiments and to execute the corresponding mud specific gravity control method.

[0155] It is understood that the system provided in the embodiments of the present invention corresponds to the method provided in the embodiments of the present invention, and the explanation, examples and beneficial effects of the relevant content can be referred to the corresponding parts of the above methods.

[0156] In the above embodiments, implementation can be achieved entirely or partially through software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented entirely or partially in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of this application are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired or wireless means. The computer-readable storage medium can be any available medium accessible to a computer or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium, an optical medium, or a semiconductor medium, etc.

[0157] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0158] Furthermore, it should be noted that if any directional indication (such as up, down, left, right, front, back, etc.) is involved in the embodiments of the present invention, the directional indication is only used to explain the relative positional relationship and movement of each component in a specific posture. If the specific posture changes, the directional indication will also change accordingly.

[0159] Furthermore, those skilled in the art should understand that in the actual use of the embodiments of this application, there may be preset thresholds used as the basis for judging the corresponding technical solutions. These thresholds are conventional technical means commonly used in the field to implement functions such as state judgment, condition recognition, and control logic switching. The specific values, setting basis, value selection methods, determination methods, and adjustment rules of the thresholds involved in this technical solution are all conventional technical choices that can be reasonably determined by those skilled in the art based on conventional technical factors such as actual application scenarios, system working states, characteristics of the detection object, hardware performance parameters, and functional requirements, through conventional experiments, calibrations, and debugging. The specific setting and adjustment of the aforementioned thresholds will not cause this technical solution to be unimplementable as a whole, nor will it affect the realization of the core concept and the achievement of the technical effects of this technical solution.

[0160] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Additionally, the meaning of "and / or" throughout the text includes three parallel solutions. Taking "A and / or B" as an example, it includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, in the embodiments of this invention, "multiple" refers to two or more. Moreover, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

Claims

1. A mechanical method for caisson construction, characterized in that: The method for determining mud specific gravity includes models of underlying confined aquifers and unconfined strata. The construction process of these models includes: Step S1. Collect the foundation parameters of the vertical shaft, including the inner diameter of the caisson. Caisson segment wall thickness Milling surface depth ; Step S2. Through geological survey, determine that the area to be excavated using the mechanical method for caisson excavation is an impermeable layer-underlying confined aquifer or unconfined stratum, and obtain geological and hydrological parameters, including: relative density of soil particles. Porosity Cohesion internal friction angle saturation density , natural weight Burial depth of the top plate of the confined aquifer And the groundwater level elevation measured from the surface. , Elevation of confined water level ; Step S3. Based on the ultimate bearing capacity theory of sand-based soil, the cohesion resistance of the soil outside the mechanical caisson is introduced to construct a safety evaluation index for the bottom heave of the mechanical caisson. This index is used to calculate the minimum effective mud pressure required to avoid unloading and heave at the bottom of the mechanical caisson. The results are as follows: , This refers to the cohesion resistance term of the soil outside the mechanically constructed caisson. and All are foundation bearing capacity coefficients. Due to ground overloading, The effective pressure of the mud at the bottom of a mechanically constructed caisson, controlled by heave failure. , and For the corresponding The density of the mud and the height of the mud surface; Step S4. Construct the safety factor for seepage failure at the bottom of the mechanically caisson. , The effective pressure of the mud at the bottom of a mechanically constructed caisson, controlled by seepage damage. , and For the corresponding The mud density and mud level, The critical hydraulic gradient, To effectively lower the water head, This represents the length of the penetration path. Step S5. Finally, the effective mud pressure inside the caisson is determined by the minimum effective mud pressure required for unloading and heaving at the bottom of the caisson and the safety factor against seepage failure.

2. The mechanical method caisson well mud pressure model structure as described in claim 1, characterized in that, In step S4, the safety factor for the bottom seepage resistance of the mechanically caisson well is calculated using the following formula: in, The safety factor for the bottom of the mechanically caisson to resist seepage damage. For the effective stress of the soil at the milling face, The natural density of the shallow water layer. The water level is saturated with specific gravity. The waterproof layer is naturally heavy. The specific gravity of the confined aquifer is saturated. It is the density of water.

3. The mechanical method caisson well mud pressure model structure as described in claim 1, characterized in that, The process for confirming the effective pressure of the drilling mud inside the caisson in the underlying confined aquifer model in step S5 includes: Based on the depth of the milled surface Burial depth of the top plate of the confined aquifer Based on their location, the underlying confined aquifer is divided into different stages. Then it is determined to be far away from the confined aquifer, if Then it is determined to be close to a confined aquifer, if If so, it is determined to have entered a confined aquifer; Calculate the effective pressure of this section of mud, specifically based on the anti-uplift safety evaluation index. Safety factor against seepage damage As a constraint, when the safety index is equal to the control threshold, the minimum effective mud pressure under the corresponding risk is calculated in reverse. For areas far from confined aquifers, the minimum effective mud pressure The constraints are: ; For areas close to confined aquifers, the minimum effective mud pressure The constraints are: For areas near confined aquifers, increase the backing force of the confined water. The calculation formula is as follows: , Given the influence coefficient of confined water, the effective pressure of the mud in this section is calculated as follows: ; For entering the confined aquifer, a dual-control logic is used to determine the effective mud pressure at this stage. Therefore, the effective mud pressure for this section is calculated as follows: , The minimum effective mud pressure required to control the unloading and uplift failure of a confined aquifer. It is the minimum effective mud pressure that controls seepage damage in confined aquifers.

4. The mechanical method caisson well mud pressure model structure as described in claim 3, characterized in that, For areas near confined aquifers, the confined aquifer influence coefficient The rate decreases linearly with increasing milling depth, as shown by the following calculation formula: .

5. The mechanical method caisson well mud pressure model structure as described in claim 3, characterized in that, The process for confirming the effective pressure of the drilling mud inside the caisson in the unconfined formation model in step S5 includes: For unconfined formations, the effective mud pressure at this stage is determined using dual-control logic, and the calculation formula is as follows: , The minimum effective mud pressure for controlling unloading and uplift failure in unconfined formations. The minimum effective mud pressure controlled by seepage failure in unconfined formations.

6. The mechanical method caisson well mud pressure model structure as described in claim 1, characterized in that, The specific operational procedures for determining the specific gravity of mud using the model include: Minimum mud pressure calculated for different stages Based on the benchmark, within the specified boundaries, the actual milling depth of the caisson is determined using on-site mechanical methods. Sure feasible range ; by each stage and The feasible range is used as input to inversely calculate the mud density. Theoretical scope; The theoretical range of the back-calculated mud density is transformed into the mud specific gravity range, and the mud specific gravity constrained by slag discharge is compared and verified within the specified theoretical range of the specified boundary. When the theoretical range exceeds the slag discharge range, then... Within the feasible range, find a way to make the mud heavy To avoid exceeding the slag discharge constraint, the interval must fall within the corresponding boundary requirement sub-interval, specifically according to the following rules: like If the value is greater than 13.5, then increase. until ≤13.5, that is ≥ ; like If <11.5, then decrease. until ≥11.5, that is ≤ ; Final feasible combination: Choose any option within this range Reverse calculation Finally, the corresponding mud specific gravity was calculated.

7. A method for adjusting the specific gravity of mud, characterized in that, The mud specific gravity obtained during the construction of the mechanical caisson mud pressure model structure as described in claim 6 is adjusted using mud monitoring parameters collected from actual measurements before adjustment. The specific adjustment process includes: 1) If Calculated value, and If the concentration is ≥0.05, add bentonite or barite powder, stir, and retest until the concentration reaches ≥0.

05. ; 2) If Calculated value, and If the concentration is ≥0.05, add water, stir, and retest to ensure accuracy. Actual measurements show that the slag discharge level is not lower than the lower limit. and These are the measured value of mud density and the theoretical calculated value of mud density obtained during the construction of the mud pressure model structure in the mechanical caisson.

8. A method for adjusting the specific gravity of mud, characterized in that, The mud specific gravity obtained during the construction of the mechanical caisson mud pressure model structure as described in claim 6 is adjusted using mud monitoring parameters collected from actual measurements before adjustment. The specific adjustment process includes: 1) If And the difference If the depth is ≥0.2m, start the mud pump to replenish the mud. 2) If And the difference If the depth is ≥0.2m, open the overflow valve to discharge the slurry; and These are the measured effective excavation depth and the theoretically calculated effective excavation depth, respectively, obtained during the construction of the mud pressure model structure inside the mechanical caisson.

9. A method for adjusting the specific gravity of mud, characterized in that, The mud specific gravity obtained during the construction of the mechanical caisson mud pressure model structure as described in claim 6 is adjusted using mud monitoring parameters collected from actual measurements before adjustment. The specific adjustment process includes: 1) If the slag content in the discharged slag is >15%, then reduce the amount of slag. The viscosity was reduced by ≤0.05, and CMC was added to increase the viscosity of the mud. 2) If the slag content in the discharged slag is <5%, then increase the... The increase is ≤0.05, and a dispersant is added to reduce the viscosity of the mud.

10. A method for adjusting the specific gravity of mud, characterized in that, The mud specific gravity obtained during the construction of the mechanical caisson mud pressure model structure as described in claim 6 is adjusted using mud monitoring parameters collected from actual measurements before adjustment. The specific adjustment process includes: 1) If the pressure drop at the milled surface is ≥10%, immediately add grout until the pressure drops to the required level. +0.3m, synchronously increased The pressure increase was set at 0.05–0.10, and milling operations were suspended until the pressure stabilized. 2) If signs of piping are detected, immediately increase the intensity of the operation. The pressure was raised to 1.35-1.40, and the backup mud pump was started to replenish the grout. At the same time, cement-water glass dual-liquid grouting was used to seal the piping channel. Construction was resumed after the signs disappeared. 3) If the pressure of the pressurized water rises suddenly, activate the backup well point dewatering system to reduce the pressure until the risk is eliminated.

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