Precise Control Method for Micro Deformation of Deep Foundation Pit

Abstract

The present invention discloses a precise control method for micro-deformation of deep foundation pits, which includes: constructing the first concrete support between the retaining structures of the foundation pit; successively constructing the subsequent concrete supports between the retaining structures of the foundation pit as the soil of the foundation pit is excavated. An active servo control device is installed between each concrete support of the subsequent concrete supports and the retaining structure of the foundation pit. Grouting reinforcement is carried out on the unexcavated soil in the pit under both ends of each concrete support of the subsequent concrete supports. According to formula (1), the micro-deformation generated by the retaining structure of the foundation pit during the excavation process of the foundation pit is precisely controlled through the collaborative control method of the active compensation of the servo support force applied by the active servo control device and the passive compensation of the grouting reinforcement of the soil in the pit. The present invention can accurately control the micro-deformation generated during the excavation process of the foundation pit, effectively guarantee the safety of the foundation pit construction, and has the effect of dynamic intelligent regulation of the micro-deformation of the foundation pit.

Description

Technical Field

[0001] The present invention relates to the technical field of foundation pit construction, and particularly relates to a precise control method for micro-deformation of deep foundation pits. Background Art

[0002] During the excavation of deep foundation pits, the control of micro-deformation of foundation pits is the key and difficult point of construction projects. In traditional technologies, the passive earth pressure compensation is insufficient, relying on the initial strength of the soil in the pit, and it is impossible to dynamically compensate for the deformation of the foundation pit retaining structure, resulting in lateral displacement of the foundation pit retaining structure and excessive bottom heave of the pit (>5 mm), threatening the safety of surrounding sensitive facilities, low efficiency of the support system, rough grouting process, single material function, and lagging risk control. Summary of the Invention

[0003] The purpose of the present invention is to provide a precise control method for micro-deformation of deep foundation pits to solve the problem of poor precision in controlling micro-deformation of foundation pits.

[0004] To solve the above technical problems, the present invention provides a precise control method for micro-deformation of deep foundation pits, including:

[0005] Construct the first concrete support between the foundation pit retaining structures;

[0006] Construct the subsequent concrete supports between the foundation pit retaining structures in sequence as the soil in the foundation pit is excavated. Install active servo control devices between each concrete support of the subsequent concrete supports and the foundation pit retaining structures. Grout and reinforce the soil in the unexcavated pit under both ends of each concrete support of the subsequent concrete supports. According to formula (1), precisely control the micro-deformation generated by the foundation pit retaining structure during the excavation of the foundation pit through the active compensation of the servo support force applied by the active servo control device and the passive compensation of grouting and reinforcement of the soil in the pit;

[0007] (1);

[0008] In formula (1), ΔD is the micro-deformation amount of the foundation pit, k is the soil compression coefficient, ΔV is the grouting volume expansion amount, S 0 is the area of the grouting influence zone, β is the servo support force sensitivity coefficient of the active servo control device, ΔF is the real-time adjustment amount of the servo support force of the active servo control device, F 0 is the initial servo support force of the active servo control device.

[0009] Further, for the precise control method of micro-deformation of deep foundation pits provided by the present invention, during the grouting test stage at the construction site, record the micro-deformation amount of the foundation pit in formula (1) ΔD and the relationship with the grouting volume expansion amount ΔV , and calculate the soil compression coefficient through a linear regression function k .

[0010] Further, for the precise control method of micro-deformation of deep foundation pits provided by the present invention, during the activation stage of the active servo control device, make the grouting volume expansion amount ΔV = 0, record the real-time adjustment amount ΔF of the servo support force of the active servo control device and the corresponding relationship with the micro-deformation amount ΔD , and calculate the servo support force sensitivity coefficient according to formula (2) β；

[0011] (2);

[0012] In formula (2), β is the servo support force sensitivity coefficient of the active servo control device, ΔD is the micro-deformation amount of the foundation pit, F 0 is the initial servo support force of the active servo control device, ΔF is the real-time adjustment amount of the servo support force of the active servo control device.

[0013] Further, for the precise control method of micro-deformation of deep foundation pits provided by the present invention, the method for grouting and strengthening the unexcavated soil mass in the pit includes:[[]]

[0014] Drill holes in the unexcavated soil mass under the two ends of each concrete support of the subsequent concrete supports on the inner side of the foundation pit enclosure structure to form multiple rows of grouting holes, and determine the grouting hole depth according to formula (3);

[0015] D = 1.2L p + d (3);

[0016] In formula (3), D is the grouting hole depth, L p is the excavation depth of the soil mass in the foundation pit, d is the allowable value of the deformation of the foundation pit enclosure structure;

[0017] Calculate the grouting density according to formula (4);

[0018] (4);

[0019] In formula (4), D(x,y) is the grouting density, which is the number of grouting holes per unit area, and P p (x,y) is the value of the passive earth pressure after grouting, and k(x,y) is the permeability coefficient;

[0020] By inserting grouting pipes into each grouting hole and winding geotextiles around the periphery of the grouting pipes;

[0021] The soil in the pit is grouted through the grouting pipes wound with geotextiles according to the predetermined slurry mixing ratio of three kinds of slurries: cement slurry, water glass mixture and slurry containing an expansive agent.

[0022] Furthermore, for the precise control method of micro-deformation of deep foundation pits provided by the present invention, the spacing between grouting holes is adjusted according to formula (5) to adjust the grouting density;

[0023] (5);

[0024] In formula (5), S is the spacing between grouting holes, α is an empirical coefficient, R is the effective diffusion radius of a single grouting hole, D(x,y) is the grouting density, and it is the number of grouting holes per unit area of the grouting area.

[0025] Furthermore, for the precise control method of micro-deformation of deep foundation pits provided by the present invention, it is determined that the diffusion range after the grouting holes are filled with grout can cover the grouting area according to the constraint formula (6);

[0026] S 2 ≤ R 2 (6);

[0027] In formula (6), S is the spacing between grouting holes, and R is the effective diffusion radius of a single grouting hole.

[0028] Furthermore, for the precise control method of micro-deformation of deep foundation pits provided by the present invention, the grouting volume expansion amount is calculated according to formula (7);

[0029] (7);

[0030] In formula (7), ΔV 1 is the actual expansion amount of the grouting volume, where ΔV = ΔV 1 , is the efficiency coefficient, ΔV 0 is the theoretical expansion amount of the grouting volume, V 0 is the grouting volume before expansion, R exp is the grouting volume expansion rate, and Q1 is the injection flow rate of cement slurry per unit time, with the unit of m 3 / s, Q2 is the injection flow rate of the sodium silicate mixture per unit time, with the unit of m 3 / s, Q3 is the injection flow rate of the expansive agent slurry per unit time, with the unit of m 3 / s, t is the total grouting time, k 1 、 k 2 are material characteristic coefficients, and γ is the volume ratio of the expansive agent.

[0031] Furthermore, for the precise control method of deep foundation pit micro-deformation provided by the present invention, the grouting volume expansion rate is determined according to formula (8);

[0032] (8);

[0033] In formula (8), R exp is the expansion rate, k 1 、 k 2 are material characteristic coefficients, and γ is the volume ratio of the expansive agent.

[0034] Furthermore, for the precise control method of deep foundation pit micro-deformation provided by the present invention, during the grouting curing period, the servo support force applied by the active servo control device is maintained at 50 - 70% of its designed axial force value; by real-time monitoring the displacement of the foundation pit retaining structure and the axial force value of the servo support force of the active servo control device, the axial force value of the servo support force of the active servo control device and the parameters of passive grouting compensation are dynamically adjusted to precisely control the micro-deformation amount generated by the foundation pit retaining structure during the foundation pit excavation process.

[0035] Furthermore, for the precise control method of deep foundation pit micro-deformation provided by the present invention, when grouting and reinforcing the unexcavated soil mass in the pit in each subsequent concrete support, the grouting depth is determined according to formula (3);

[0036] When there is a next concrete support below the current subsequent concrete support, the grouting depth of both ends of the current subsequent concrete support into the unexcavated soil mass in the pit is determined according to formula (3);

[0037] When the current subsequent concrete support is the last subsequent concrete support, the grouting depth of both ends of the current subsequent concrete support into the unexcavated soil mass in the pit is at least 2 meters below the pit bottom.

[0038] Compared with the prior art, the beneficial effects of the precise control method of deep foundation pit micro-deformation provided by the present invention are as follows:

[0039] Precisely control the micro-deformation generated by the foundation pit retaining structure during the foundation pit excavation through the collaborative control method of the active compensation of the servo support force applied by the active servo control device according to formula (1) and the passive compensation of the grouting reinforcement of the soil in the pit, so as to accurately control the micro-deformation generated during the foundation pit excavation, effectively ensure the safety of the foundation pit construction, achieve the effect of dynamic intelligent regulation of the micro-deformation of the foundation pit, and avoid the problem of poor accuracy of the control of the micro-deformation of the foundation pit caused by the independent control of the active compensation and the passive compensation of the foundation pit deformation respectively.

[0040] By maintaining the servo support force during the grouting process through the collaborative control method of formula (1), it is possible to enhance the accuracy, effectiveness and injection volume of the passive compensation of the micro-deformation of the foundation pit by grouting and reinforcing the soil in the pit, avoid the increase in cost and waste of materials caused by excessive grouting, and avoid the problem of poor reinforcement effect caused by insufficient reinforcement of the soil in the pit due to too little grouting volume. Specific implementation mode

[0041] The embodiment of the present invention provides a method for precisely controlling the micro-deformation of a deep foundation pit, including:

[0042] Step 100, construct the first concrete support between the foundation pit retaining structures. The foundation pit retaining structure can be a diaphragm wall or a row of piles. The cross-sectional size of the first concrete support is determined according to the designed axial force value, and the typical value of the cross-sectional size of the first concrete support is 800mm×1000mm. The first concrete support is cured to the designed strength (≥C30, curing time ≥ 7 days). After constructing the first concrete support, excavate the soil in the foundation pit to the design elevation of the second support.

[0043] Step 200, successively construct the subsequent concrete supports between the foundation pit retaining structures as the soil in the foundation pit is excavated. Install an active servo control device between each concrete support of the subsequent concrete supports and the foundation pit retaining structure, and grout and reinforce the unexcavated soil in the pit under both ends of each concrete support of the subsequent concrete supports. Precisely control the micro-deformation generated by the foundation pit retaining structure during the foundation pit excavation through the collaborative control method of the active compensation of the servo support force applied by the active servo control device according to formula (1) and the passive compensation of the grouting reinforcement of the soil in the pit;

[0044] (1);

[0045] In formula (1), ΔD is the micro-deformation amount of the foundation pit, k is the soil compression coefficient, ΔV is the grouting volume expansion amount, S 0 is the area of the grouting influence zone, β is the servo support force sensitivity coefficient of the active servo control device,ΔF is the real-time adjustment amount of the servo support force of the active servo control device, with the unit of kN. F 0 is the initial servo support force of the active servo control device, with the unit of kN.

[0046] Among them, the cross-sectional dimensions and design strengths of the subsequent concrete supports can be set with reference to the first concrete support. The active servo control device includes a servo oil cylinder, whose rated axial force value can be 2000 - 5000 kN, and pressure sensors such as strain gauges, with an induction accuracy of ±0.5% FS. Interfaces can be embedded at the ends of the concrete supports to ensure the stability of the active servo control device installed on the subsequent concrete supports.

[0047] The precise control method for micro-deformation of deep foundation pits provided by the embodiments of the present invention precisely controls the micro-deformation generated in the foundation pit enclosure structure during the foundation pit excavation process through the collaborative control method of the active compensation of the servo support force applied by the active servo control device according to formula (1) and the passive compensation of soil grouting reinforcement in the pit, thereby precisely controlling the micro-deformation generated during the foundation pit excavation process, effectively ensuring the safety of foundation pit construction, and achieving the effect of dynamic intelligent regulation of the micro-deformation of the foundation pit, that is, while actively compensating through the servo support force applied by the active servo control device, tracking the collaborative control method of the grouting construction of the passive compensation of soil grouting reinforcement in the pit, achieving the effect of dynamic intelligent regulation of the micro-deformation of the foundation pit, and avoiding the problem of poor accuracy in controlling the micro-deformation of the foundation pit caused by the independent control of the active compensation and the passive compensation for the foundation pit deformation.

[0048] The precise control method for micro-deformation of deep foundation pits provided by the embodiments of the present invention can maintain the servo support force during the grouting process through the collaborative control method of formula (1), which can enhance the precision, effectiveness, and injection volume of the passive compensation for the micro-deformation of the soil in the pit by grouting and reinforcing the soil in the pit, avoid the increase in cost and waste of materials caused by excessive grouting, and avoid the problem of poor reinforcement effect due to insufficient reinforcement of the soil in the pit caused by too little grouting volume.

[0049] To determine the soil compression coefficient in formula (1), the precise control method for micro-deformation of deep foundation pits provided by the embodiments of the present invention records the micro-deformation amount of the foundation pit in formula (1) ΔD and the grouting volume expansion amount ΔV during the on-site grouting test stage, and calculates the soil compression coefficient k through a linear regression function.

[0050] To determine the servo support force sensitivity coefficient in formula (1), the precise control method for micro-deformation of deep foundation pits provided by the embodiments of the present invention enables the grouting volume expansion amount ΔV= 0, record the real-time adjustment amount of the servo support force of the active servo control device ΔF and the micro-deformation amount ΔD corresponding relationship, calculate the servo support force sensitivity coefficient according to formula (2) β；

[0051] (2);

[0052] In formula (2), β is the servo support force sensitivity coefficient of the active servo control device, ΔD is the micro-deformation amount of the foundation pit, F 0 is the initial servo support force of the active servo control device, ΔF is the real-time adjustment amount of the servo support force of the active servo control device. Among them, formula (2) is derived from formula (1) when ΔV = 0.

[0053] In order to ensure the precise control effect of the grouting reinforcement of the soil mass in the foundation pit, for the deep foundation pit micro-deformation precise control method provided by the embodiments of the present invention, in step 200, the method for grouting and reinforcing the unexcavated soil mass in the foundation pit includes:

[0054] Step 201, drill holes in the unexcavated soil mass under both ends of each concrete support of the subsequent concrete supports on the inner side of the foundation pit enclosure structure to form multiple rows of grouting holes, and determine the grouting hole depth according to formula (3);

[0055] D = 1.2L p + d (3);

[0056] In formula (3), D is the grouting hole depth, L p is the excavation depth of the soil mass in the foundation pit, d is the allowable value of the deformation of the foundation pit enclosure structure. Through formula (3), it can ensure that the slurry covers the weak area of the soil mass in the foundation pit. Among them, multiple rows of grouting holes in the unexcavated soil mass under both ends of each concrete support of the subsequent concrete supports can be arranged at the collar of the foundation pit enclosure structure. Among them, multiple rows of grouting holes include but are not limited to two rows.

[0057] Step 202, calculate the grouting density according to formula (4);

[0058] (4);

[0059] In formula (4), D(x,y) is the grouting density, that is, the number of grouting holes per unit area, P p(x,y) is the value of passive earth pressure after grouting, and k(x,y) is the permeability coefficient. The strength of the soil mass grouted in the pit is ensured by the grouting density. To ensure the strength of the soil mass in the pit, the larger the value of D(x,y), the more necessary it is to increase the number of grouting holes arranged. Among them, D(x,y) is the planar layout relationship of the number of grouting holes per unit area, that is, the grouting density. It can be seen from formula (4) that the number of grouting holes per unit area is affected by the passive earth pressure and the permeability coefficient. The larger the grouting density, the smaller the spacing between grouting holes.

[0060] The spacing between grouting holes can be adjusted according to formula (5) to adjust the grouting density, that is, to adjust the number of grouting holes per unit area;

[0061] (5);

[0062] In formula (5), S is the spacing between grouting holes, α is an empirical coefficient, R is the effective diffusion radius of a single grouting hole, and D(x,y) is the grouting density, that is, the number of grouting holes per unit area in the grouting area.

[0063] To ensure that the diffusion radius of the grouting holes is completely covered and improve the grouting effect, the diffusion range of the grouting holes after injecting the grout can cover the grouting area according to the constraint formula (6);

[0064] S 2 ≤ R 2 (6);

[0065] In formula (6), S is the spacing between grouting holes, and R is the effective diffusion radius of a single grouting hole.

[0066] Step 203: Insert a grouting pipe into each grouting hole and wind geotextile around the periphery of the grouting pipe to prevent the grouting pipe from being blocked and affecting grouting. The grouting pipe can be a steel perforated pipe with a diameter of Φ42mm.

[0067] Step 204: Grout the soil mass in the pit according to the predetermined slurry mix ratio of three slurries, namely cement slurry, water glass mixture and slurry containing expansive agent, through the grouting pipe wrapped with geotextile. The predetermined slurry mix ratio of the three slurries can be calculated by a large grouting reinforcement model based on the soil reinforcement detection data in the pit. The large grouting reinforcement model is an engineering analysis system constructed based on fluid mechanics, elastoplastic mechanics and numerical simulation technology, which is used to optimize the grouting reinforcement process parameters and predict the formation response. The injected cement slurry (water-cement ratio 0.6 - 0.8) is used to fill the pores of the soil mass in the pit, and the injected water glass mixture (dosage 3 - 5%) is used to control the initial setting time of the slurry ≤ 30 min; the injected slurry containing expansive agent (dosage 8 - 12%) is used to generate an expansion rate of 3 - 5%. Grouting pressure control: initial pressure 0.5 MPa, final pressure ≤ 1.5 MPa; after grouting, seal the hole and the curing time ≥ 48 hours.

[0068] To calculate the grouting volume expansion amount in formula (1), the precise control method for micro-deformation of deep foundation pits provided by the embodiments of the present invention calculates the grouting volume expansion amount according to formula (7);

[0069] (7);

[0070] In formula (7), ΔV 1 is the actual grouting volume expansion amount, where ΔV = ΔV 1 , is the efficiency coefficient, ΔV 0 is the theoretical grouting volume expansion amount, V 0 is the grouting volume before expansion, R exp is the grouting volume expansion rate, Q1 is the injection flow rate of cement slurry per unit time, with the unit of m 3 / s, Q2 is the injection flow rate of water glass mixture per unit time, with the unit of m 3 / s, Q3 is the injection flow rate of slurry containing expansive agent per unit time, with the unit of m 3 / s, t is the total grouting time, determined by the setting time of the water glass mixture, k 1 , k 2 are the material characteristic coefficients, and γ is the volume ratio of the expansive agent.

[0071] The actual grouting volume expansion amount ΔV 1 calculated by formula (7) ΔV, so as to control the influence of the passive compensation of grouting in the pit on the micro-deformation of the foundation pit through the grouting volume expansion in formula (1). ΔV The influence of the passive compensation of in-pit grouting on the micro-deformation of the foundation pit can be controlled.

[0072] The grouting volume expansion rate can be determined according to formula (8);

[0073] (8);

[0074] In formula (8), R exp is the expansion rate, k 1 , k 2 are material characteristic coefficients, and γ is the volume ratio of the expansion agent.

[0075] Furthermore, in the deep foundation pit micro-deformation precise control method provided by the embodiments of the present invention, during the grouting maintenance period, the servo support force applied by the active servo control device is maintained at 50-70% of its designed axial force value; the displacement of the foundation pit retaining structure can be monitored in real time by a total station, and the axial force value of the servo support force of the active servo control device can be monitored by a strain gauge. According to formula (1), the axial force value of the servo support force of the active servo control device and the parameters of passive grouting compensation are dynamically adjusted to precisely control the micro-deformation amount generated by the foundation pit retaining structure during the foundation pit excavation process.

[0076] In order to ensure the precise control of passive compensation, in the deep foundation pit micro-deformation precise control method provided by the embodiments of the present invention, when grouting and reinforcing the unexcavated in-pit soil in each subsequent concrete support, the grouting depth is determined according to formula (3);

[0077] When there is a next concrete support below the current subsequent concrete support, the grouting depth at both ends of the current subsequent concrete support into the unexcavated in-pit soil is determined according to formula (3);

[0078] When the current subsequent concrete support is the last subsequent concrete support, the grouting depth at both ends of the current subsequent concrete support into the unexcavated in-pit soil is at least 2 meters below the pit bottom. Among them, the grouting depth at least 2 meters below the pit bottom of the last subsequent concrete support can prevent the micro-deformation of the foundation pit retaining structure caused by the pit bottom heave.

[0079] The present invention is not limited to the above specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present invention fall within the scope of protection of the present invention. Those skilled in the art can make other modifications and changes to the present invention. Thus, if these modifications and changes of the present invention are within the scope of the claims of the present invention, the present invention also intends to include these modifications and changes.

Claims

1. A precise control method for micro-deformation of deep foundation pits, characterized in that Including: Construct the first concrete support between the foundation pit retaining structures; Construct the subsequent concrete supports between the foundation pit retaining structures successively as the soil in the foundation pit is excavated. Install active servo control devices between each concrete support of the subsequent concrete supports and the foundation pit retaining structures. Grout and reinforce the unexcavated soil in the pit under the two ends of each concrete support of the subsequent concrete supports. Accurately control the micro-deformation of the foundation pit retaining structures generated during the foundation pit excavation process through the collaborative control method of the active compensation of the servo support force applied by the active servo control device according to formula (1) and the passive compensation of the grouting and reinforcement of the soil in the pit. （1）； In formula (1), ΔD is the micro-deformation amount of the foundation pit, k is the soil compression coefficient, ΔV is the volume expansion amount of grouting, S 0 is the area of the grouting influence zone, β is the servo support force sensitivity coefficient of the active servo control device, ΔF is the real-time adjustment amount of the servo support force of the active servo control device, F 0 is the initial servo support force of the active servo control device; During the grouting test stage at the construction site, record the micro-deformation of the foundation pit in formula (1) ΔD and the grouting volume expansion ΔV relationship, and calculate the soil compression coefficient through the linear regression function k； During the activation stage of the active servo control device, the grouting volume expansion ΔV = 0, and record the real-time adjustment amount of the servo support force of the active servo control device ΔF and the micro-deformation amount ΔD corresponding relationship, and calculate the servo support force sensitivity coefficient according to formula (2) β； （2）； In formula (2), β is the servo support force sensitivity coefficient of the active servo control device, ΔD is the micro deformation amount of the foundation pit, F 0 is the initial servo support force of the active servo control device, ΔF is the real-time adjustment amount of the servo support force of the active servo control device.

2. The precise control method for micro-deformation of deep foundation pits according to claim 1, characterized in that, The method for grouting and reinforcing the unexcavated soil in the pit includes: Drill holes in the unexcavated soil in the pit under the two ends of each concrete support of the subsequent concrete supports on the inner side of the foundation pit retaining structures to form multiple rows of grouting holes, and determine the grouting hole depth according to formula (3); D = 1.2L p + d （3）； In formula (3), D is the grouting hole depth, L p is the excavation depth of the soil mass in the foundation pit, d is the allowable value of the deformation of the foundation pit retaining structure; Calculate the grouting density according to formula (4); （4）； In Equation (4), D(x, y) is the grouting density, which is the number of grouting holes per unit area, and P p (x, y) is the value of the passive earth pressure after grouting, and k(x, y) is the permeability coefficient; Insert grouting pipes into each grouting hole, and wind geotextiles around the periphery of the grouting pipes; Grout the soil in the pit through the grouting pipes wound with geotextiles according to the predetermined slurry mix ratio of three slurries: cement slurry, water glass mixture and slurry containing expansion agent.

3. The precise control method for micro-deformation of deep foundation pits according to claim 2, characterized in that Adjust the grouting density by adjusting the spacing between grouting holes according to formula (5); （5）； In formula (5), S is the spacing between grouting holes, α is the empirical coefficient, R is the effective diffusion radius of a single grouting hole, D(x,y) is the grouting density, and the number of grouting holes per unit area of the grouting area.

4. The precise control method for micro-deformation of deep foundation pits according to claim 3, characterized in that, Determine that the diffusion range of the grouting holes after grouting can cover the grouting area according to constraint formula (6); S 2 ≤ R 2 (6); In formula (6), S is the spacing between grouting holes, and R is the effective diffusion radius of a single grouting hole.

5. The precise control method for micro-deformation of deep foundation pits according to claim 1, characterized in that, Calculate the grouting volume expansion amount according to formula (7); （7）； In formula (7), ΔV 1 is the actual expansion volume of the grouting volume, where ΔV=ΔV 1 , is the efficiency coefficient, ΔV 0 is the theoretical expansion volume of the grouting volume, V 0 is the grouting volume before expansion, R exp is the grouting volume expansion rate, Q1 is the injection flow rate of the cement slurry per unit time, with the unit of m 3 / s, Q2 is the injection flow rate of the sodium silicate mixture per unit time, with the unit of m 3 / s, Q3 is the injection flow rate of the expansion agent slurry per unit time, with the unit of m 3 / s, t is the total grouting time, k 1 、 k 2 are the material characteristic coefficients, and γ is the volume ratio of the expansion agent.

6. The precise control method for micro-deformation of deep foundation pits according to claim 5, characterized in that Determine the grouting volume expansion rate according to formula (8); （8）； In formula (8), R exp is the expansion rate, k 1 , k 2 are the material characteristic coefficients, and γ is the volume ratio of the expansion agent.

7. The precise control method for micro-deformation of deep foundation pits according to claim 1, characterized in that During the grouting curing period, keep the servo support force applied by the active servo control device at 50 - 70% of its designed axial force value; Dynamically adjust the axial force value of the servo support force of the active servo control device and the parameters of the passive grouting compensation by real-time monitoring the displacement of the foundation pit retaining structures and the axial force value of the servo support force of the active servo control device to accurately control the micro-deformation amount of the foundation pit retaining structures generated during the foundation pit excavation process.

8. The precise control method for micro-deformation of deep foundation pits according to claim 2, characterized in that When grouting and reinforcing the unexcavated soil in the pit in the subsequent concrete supports, determine the grouting depth according to formula (3); When there is a next concrete support under the current subsequent concrete support, determine the grouting depth of the two ends of the current subsequent concrete support into the unexcavated soil in the pit according to formula (3); When the current subsequent concrete support is the last subsequent concrete support, the grouting depth of the two ends of the current subsequent concrete support into the unexcavated soil in the pit is at least 2 meters below the pit bottom.

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