Construction method for sinking sinking well by regulating water level in cabin under low permeability soil layer

Abstract

The application discloses a construction method for regulating the water level in a cabin to sink a sinking well in a low-permeability soil layer, and comprises the following steps: step one, the pre-sinking of a large sinking well on land is drainage sinking, in the pre-drainage sinking, water pumping tests are conducted through the set dewatering wells, the permeability coefficient is determined in combination with geological exploration data, and the water level elevation that can be maintained when the water level in the sinking well hole is increased or decreased is preliminarily calculated and analyzed. In the non-drainage sinking stage of the super large sinking well, the construction method of realizing single-stage large-height heightening sinking is realized by controlling the buoyancy. The application can increase the single-stage heightening height of the sinking well, effectively solve the problem that the sinking well state is not easy to be controlled under the condition of large heightening, and reduce the sinking well heightening sinking combination times. In addition, the self-weight of the sinking well under the condition of large heightening promotes the subsequent sinking speed of the sinking well to be faster. The safe and efficient heightening sinking construction effect is achieved, and the construction cost is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of sinking well construction. More particularly, the present application relates to a construction method for sinking well height connection and sinking in low-permeability soil layer. BACKGROUND

[0002] In the current domestic and foreign sinking well foundation construction cases, there is no mature research on the sinking well construction technology in deep silt soil layer. With the rapid development of bridge construction technology in China, the application range of sinking well has gradually expanded from the previous sandy soil layer to the most complex silt soil layer, which puts forward higher demands on sinking well construction technology. Compared with other structures, the whole construction process of sinking well, from height connection to sinking and to the completion of bottom sealing, is in a state of instability, and the factors affecting the instability are very complex, including the size, weight, structural characteristics of the structure itself, the topography and geomorphology of the external environment, the engineering geological conditions, the construction method, the construction sequence, and the control means. The above factors ultimately affect the construction results and determine whether the sinking well can be successfully sunk to the predetermined position. The sinking well height connection and sinking combination and the excavation and sinking method are the key points to ensure the rapid and stable sinking of the sinking well.

[0003] The sinking well height connection and sinking combination of large sinking well is mainly limited by the bearing capacity of the foundation, and it is necessary to ensure that the sinking well meets the stability requirements during height connection. Therefore, the single height connection height of the previous sinking well is not large, and the total number of height connection and sinking is relatively large, which increases the number of process conversions. How to reduce the number of height connection and sinking combination as much as possible while ensuring the controllable state of the sinking well is crucial to improve the construction efficiency of the sinking well. With the increase of the sinking depth of the sinking well, the resistance ratio of the sinking well gradually increases, and it is necessary to start from the end resistance, side resistance and buoyancy to speed up the sinking and posture control of the sinking well. In terms of end resistance, the weakening magnitude is limited and is constrained by the posture of the sinking well. In terms of side resistance, the construction cost is generally high, the safety risk is large, and the traditional air curtain and other sinking measures are not suitable for cohesive soil. In terms of buoyancy, silt soil is a typical representative of soft soil, which has the engineering property of small permeability, so that the water level in the sinking well cabin can be maintained at a certain elevation to maintain the stability of the soil body, and then the purpose of controlling the buoyancy by controlling the water level in the cabin can be achieved, and the difficulty of controlling the water level in the cabin is small. SUMMARY

[0004] The purpose of the present application is to provide a method for realizing the effect of increasing the height of a single interface of a large-scale caisson in a land area under low-permeability soil conditions in non-draining interface sinking construction by regulating the water level in the cabin to control the buoyancy, so as to achieve the effect of increasing the height of a single interface of the caisson in a controllable state and reducing the buoyancy to assist sinking, thereby efficiently completing the non-draining interface sinking construction of the subsequent caisson. The method can increase the height of a single interface of the caisson, reduce the number of interface sinking combinations, overcome the uncontrollable problem of the caisson in a large interface state, and make the subsequent sinking speed of the caisson faster due to the large weight of the caisson in the large interface state. The interface sinking construction can be safely and efficiently completed, and the construction cost is reduced.

[0005] The technical solution adopted by the present application to solve the technical problem is: a construction method for regulating the water level in the cabin to sink a caisson in a low-permeability soil layer, which is mainly composed of the following steps:

[0006] Step one: The pre-sinking of a large-scale caisson in a land area is all draining sinking, and the water level that can be maintained in the well hole of the caisson is calculated and analyzed;

[0007] Step two: The subsequent sinking is non-draining sinking, and in this stage, the interface height of the caisson is determined by comprehensively considering the pre-consolidation effect; the interface sinking coefficient and the required buoyancy increase of the caisson in the interface state are calculated;

[0008] Step three: A mechanical model is established to calculate and analyze the limiting amount of the reduction of the water level of the caisson, so as to ensure that the stability of the foundation pit, the interface stability coefficient, and the safety of the structure stress meet the requirements; the non-draining sinking of the caisson in the previous stage is completed, and the bottom is finished according to the attitude and base stress ratio method; the water level in the cabin is gradually reduced by stage, the reduced buoyancy is converted to the end resistance and side resistance, and the settlement amount is observed and compared after the water level in the cabin is reduced to the predetermined value; the calculation and analysis are corrected; after the caisson is stably settled, the water level in the cabin is refilled to an appropriate height;

[0009] Step four: A mechanical model is established to calculate and analyze the limiting amount of the increase of the water level of the caisson, so as to ensure that the interface stability coefficient and the safety of the structure stress meet the requirements; the interface sinking of the caisson is constructed, and the water injection test is carried out in the cabin to ensure that the water level can be maintained at the predetermined high water level in the cabin;

[0010] Step five: Before the last section of the interface, the settlement data of the caisson are monitored according to the calculation and analysis of the pre-settlement, the water level in the cabin is gradually reduced by stage, and the reduced buoyancy is further converted to the end resistance and side resistance for the preparation of the last section of the interface;

[0011] Step six: After the water level in the cabin is reduced to the predetermined value, the settlement amount is observed and compared, and the calculation and analysis are corrected; after the settlement is stable, the water level in the cabin is refilled to the highest position, and the last section of concrete is poured in a partitioned manner;

[0012] Step seven: the large height of the caisson is completed, and the process is converted into the sinking construction of the caisson.

[0013] Preferably, in step six, during the partition pouring, according to the attitude data, the principle of pouring the well wall and the peripheral partition wall first and then pouring the remaining partition wall in the middle is followed to complete the final section of concrete pouring.

[0014] Preferably, in step one, during the early-stage drainage sinking, the water pumping test is performed through the setting of the dewatering well, the permeability coefficient is determined by combining the soil physics parameter test, and the water level that can be maintained in the caisson hole is calculated and analyzed by using the MODFLOW numerical simulation software.

[0015] Preferably, in step two, whether the soil taking equipment meets the use requirements in the large height state should be comprehensively analyzed.

[0016] Preferably, in step seven, the caisson pot bottom is gradually converted from a small pot bottom to a large pot bottom sinking state; and the water level in the cabin is adjusted to not less than 2m of the ground level.

[0017] The present application at least includes the following beneficial effects: the present application is the first time to sink a large caisson in a deep silt and silt clay layer, and the large caisson can be safely and controllably sunk in a large height state; the weight of the caisson is increased, the overall sinking speed of the caisson is accelerated; the single height of the caisson is increased, the sinking times of the caisson are reduced, the process conversion time is reduced, the construction efficiency is greatly improved, and the construction cost is reduced.

[0018] Other advantages, objects and features of the present application will be partly embodied by the following description, and partly understood by those skilled in the art through research and practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a plan view of the caisson;

[0020] Figure 2 is an elevation view of the caisson;

[0021] Figure 3 is a schematic view of the cabin after the step six of slow and staged dewatering;

[0022] Figure 4 is a schematic view of the cabin after the step six of rapid and staged water recharging to not less than 2m of the ground level;

[0023] Figure 5 is a schematic view of the cabin after the step seven of water injection experiment after the completion of the four sections of the height;

[0024] Figure 6 is a schematic view of the cabin after the step eight of slow and staged dewatering;

[0025] Figure 7 is a schematic diagram of rapidly refilling the water level in the chamber to the highest position in step eight;

[0026] Figure 8 is a partition pouring direction diagram;

[0027] Figure 9 is a caisson pot bottom initial state diagram;

[0028] Figure 10 is a caisson pot bottom large pot bottom sinking state diagram;

[0029] Figure 11 is a deep silt stratum diagram;

[0030] Figure 12 is a different depth of soil layer properties. DETAILED DESCRIPTION

[0031] The present application will be described in detail below with reference to the drawings. Those skilled in the art will be able to implement the present application based on these descriptions. Before the present application is described in detail with reference to the drawings, it should be specifically pointed out that the technical solutions and technical features provided in each part of the present application, including the following description, can be combined with each other without conflict.

[0032] In addition, the embodiments of the present application involved in the following description are generally only a part of the embodiments of the present application, not all the embodiments. Therefore, based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should be within the scope of protection of the present application.

[0033] The caisson high connection sinking is usually measured by the high connection sinking coefficient as an important index of high connection sinking combination, and the formula is as follows:

[0034]

[0035] In the formula:

[0036] G—caisson self weight;

[0037] F—caisson buoyancy;

[0038] R1—caisson end resistance;

[0039] R2—caisson side resistance.

[0040] The above formula K=1 indicates that the caisson tends to be in limit equilibrium. In the case of a certain self weight, by controlling the resistance (buoyancy, end resistance and side resistance), the effect of controlling the state of the caisson can be achieved. For example, Figures 11-12As shown, for the silt, its permeability is poor, and the water level in the cabin can be increased or decreased to achieve the effect of buoyancy control, so as to achieve the goal of controlling the state of the sinking well.

[0041] Embodiment 1

[0042] As Figures 1-2 shown, taking a certain sinking well construction as an example (the size of the sinking well is 70x63x67.5m, vertically divided into 13 segments, and the geology is mainly silt and silt clay, with small permeability), the sinking well is first drained and sunk, and then sunk without drainage from the second to the fourth time, and the third time is connected with 5 segments.

[0043] Step one: In the early stage of drainage sinking, water pumping test is carried out through the set dewatering well, the permeability coefficient is determined combined with soil physics parameter experiment, and MODFLOW numerical simulation software is used for calculation and analysis to determine the water level that can be maintained when the water level in the sinking well hole is increased or decreased.

[0044] Step two: Calculate the sinking coefficient of connecting 5 segments and the required floating force lifting amount.

[0045] a. Sinking coefficient

[0046] k st =(G k -F fw,k ) / F fk =(G+G′-F w ) / (R1+R2)

[0047] In the formula: G is the total self-weight of the poured sinking well; G' is the construction load; F w is the buoyancy; R1 is the limit end resistance of the blade foot and the bottom surface of the partition wall; R2 is the limit friction of the sinking well.

[0048] b. Connection stability coefficient

[0049] k=G k / (F fk +F fw,k )=(G+G') / (R1+R2+F fw,k )

[0050] In the formula: G is the total self-weight of the poured sinking well; G' is the construction load; F w is the buoyancy; R1 is the limit end resistance of the blade foot and the bottom surface of the partition wall; R2 is the limit friction of the sinking well.

[0051] According to the sinking formula, the corresponding buoyancy when the sinking well reaches the critical sinking state is deduced, and then the water level in the sinking well is obtained. It is found that the required lifting buoyancy is calculated to correspond to the water level in the cabin, which meets the calculation conditions of water level maintenance.

[0052] Table 1

[0053]

[0054] Step three: Because the height of the caisson is large (the height exposed to the ground), the air suction machine working water head is calculated to determine whether the suction equipment can operate normally.

[0055] Step four: The caisson sinking simulation calculation is carried out by using the MIDAS FEA finite element software, and the construction stage analysis method is used to simulate and analyze each control condition in the caisson sinking process. In the model, the concrete structure is simulated by using three-dimensional solid elements, and the steel shell structure is simulated by using plate elements. In the calculation, the reinforced structure inside the steel shell and the reinforced structure inside the concrete are not considered, and their influence on the structure is ignored.

[0056] a. Earth pressure: During the sinking construction process of the caisson, the earth outside the caisson tends to flow into the pit, so the active earth pressure is calculated.

[0057] b. Water pressure: The water uplift force acting on the caisson is applied by changing the unit weight of the part of the caisson below the water level to the floating unit weight.

[0058] The caisson stress of each control condition meets the requirements.

[0059] Step five: In the second undrained sinking final sinking stage, the pot bottom is completed. The influence of the dewatering in the cabin on the safety of the foundation pit and the surrounding buildings (mainly the settlement calculation of the surrounding buildings and the foundation pit base uplift calculation) is evaluated, and the depth of the dewatering in the cabin is determined.

[0060] Step six: As shown in Figure 3 , the settlement monitoring points are arranged around the caisson, and the dewatering in the cabin is carried out in stages and slowly according to the calculated drawdown. The actual drawdown is evaluated according to the settlement data, earth pressure data, attitude data and sinking rate.

[0061] By pumping water to reduce the buoyancy, the reduced buoyancy is converted to the end resistance and side resistance; after the water level in the cabin is lowered to the limit, the settlement amount is observed and compared, and the calculation analysis is corrected. As shown in Figure 4 , after the caisson is stably settled, the water level in the cabin is quickly raised to not less than 2m above the ground level.

[0062] Step seven: As shown in Figure 5 , the fourth section of the height connection is completed, and the water injection experiment in the cabin is carried out to ensure that the water level at the predetermined high water level in the cabin can be maintained.

[0063] Step eight: Before the fifth section of the height connection, the calculation is corrected according to the comparison and analysis of the actual settlement of the first four sections of the height connection and the calculation analysis data. As shown in Figure 6 , the dewatering in the cabin is carried out in stages and slowly, the actual drawdown is evaluated according to the settlement data, earth pressure data, attitude data and sinking rate, and the reduced buoyancy is further converted to the end resistance and side resistance to prepare for the last section of the height connection.

[0064] After the water level in the inner chamber is reduced to a predetermined value, the contrast settlement is observed and the calculation analysis is corrected. Figure 7 As shown in the figure, after the settlement is stable, the water level in the inner chamber is quickly raised to the highest position.

[0065] As shown in the figure, the last section of concrete is symmetrically poured in different zones. According to the attitude data, the pouring sequence of the fifth section of the caisson is adjusted. Figure 8

[0066] Step nine: the fifth section of the caisson is connected and the process is converted to the sinking construction of the caisson. As shown in the figure, the caisson pot bottom is gradually converted from a small pot bottom to a large pot bottom sinking state; at the same time, the water level in the inner chamber is adjusted to not less than 2m above the ground level. Figures 9-10

[0067] Based on the above situation, a large-scale land caisson large-height connection construction method in deep silt stratum is invented. The method is characterized in that in the sinking construction of the caisson without drainage height connection, the conversion of the self-weight of the caisson, the side resistance and the end resistance is realized by controlling the buoyancy, the single height connection of the traditional large-scale caisson is not more than 3 sections (about 15m), which is improved to 5 sections (about 25m), the sinking combination times of the caisson height connection are reduced in the case of ensuring the controllability of the caisson, and the construction efficiency of the caisson is improved.

[0068] Although the embodiments of the present application have been disclosed as above, it is not limited to the application listed in the specification and the embodiments, and it can be fully applied to various fields suitable for the present application, and other modifications can be easily realized by those skilled in the art, therefore, the present application is not limited to specific details and the embodiments shown and described herein, without departing from the general concept defined by the claims and the equivalent scope.​​

Claims

1. A construction method for sinking a caisson with in-cabin water level regulation and height increase sinking in a low-permeability soil layer, characterized in that, It comprises the following steps: Step one: the large caisson sinking in the early stage adopts drainage sinking, and the water level that can be maintained when the water level in the caisson hole is increased or decreased is calculated and analyzed; Step two: the subsequent sinking adopts non-drainage sinking, and the height of the caisson is determined in this stage; the sinking coefficient of the caisson and the required buoyancy lifting amount in the height connection state are calculated; Step three: the limiting amount of the caisson lowering water level is calculated and analyzed to ensure that the stability of the foundation pit, the stability coefficient of the height connection, and the safety of the structure stress meet the requirements; the caisson is finally sunk in the non-drainage sinking stage, the bottom of the caisson is modified according to the attitude and the base stress ratio method, the water level in the cabin is slowly lowered in stages according to the calculated minimum water level and the caisson attitude observation, the reduced buoyancy is converted to the end resistance and side resistance by pumping water to reduce the buoyancy; after the water level in the cabin is lowered to the predetermined value, the settlement amount is observed and compared, and the calculation and analysis are corrected; after the caisson is stabilized, the water level in the cabin is refilled to an appropriate height; Step four: the limiting amount of the caisson raising water level is calculated and analyzed to ensure that the stability coefficient of the height connection and the safety of the structure stress meet the requirements; the caisson height connection construction is carried out, and the water injection test is carried out in the cabin to ensure that the water level can be maintained at the predetermined high water level in the cabin; Step five: before the last section of the height connection, the settlement data of the caisson is calculated and analyzed according to the previous settlement, the water in the cabin is slowly lowered in stages, and the reduced buoyancy is further converted to the end resistance and side resistance to prepare for the last section of the height connection; Step six: after the water level in the cabin is lowered to the predetermined value, the settlement amount is observed and compared, and the calculation and analysis are corrected; after the settlement is stabilized, the water level in the cabin is refilled to the highest position, and the last section of concrete is poured in zones; Step seven: the large height connection of the caisson is completed, and the process is converted to the sinking construction of the caisson.

2. The method according to claim 1, wherein the water level in the caisson is adjusted by the water level in the chamber. In step six, when pouring in zones, the attitude data is used as the principle to pour the remaining middle partition wall after pouring the well wall and the surrounding partition wall, and the last section of concrete is poured.

3. The method according to claim 1, wherein the method is characterized by: In step one, during the early stage of drainage sinking, the water pumping test is carried out by setting the dewatering well, the permeability coefficient is determined by combining the physical parameter test of the soil body, and the water level that can be maintained when the water level in the caisson hole is increased or decreased is calculated and analyzed.

4. The method according to claim 1, wherein the method is characterized by: In step two, the use demand of the soil taking equipment in the large height connection state should be comprehensively analyzed.

5. The method according to claim 1, wherein the method is characterized by: In step seven, the caisson pot bottom is gradually converted from a small pot bottom to a large pot bottom sinking state; at the same time, the water level in the cabin is adjusted to not less than 2m above the ground level outside the caisson.

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