Background
The construction of urban rail transit effectively drives the development and utilization of various peripheral underground spaces, and a large number of deep and large foundation pit engineering projects are continuously emerging. Meanwhile, the foundation pit engineering around the urban rail transit is developing towards the direction of large-depth excavation. When the deep and large foundation pit engineering construction is carried out on the adjacent existing subway tunnel, the tunnel deformation caused by the foundation pit construction is controlled, and the method is a great problem in the foundation pit engineering in weak soil.
In the process of excavation of the foundation pit, the enclosure structure can generate horizontal displacement towards the inner direction of the pit under the combined action of water pressure and soil pressure inside and outside the pit, and simultaneously cause uplift deformation of the bottom of the foundation pit, and influence is generated on the surrounding environment to a certain extent, the influence is firstly expressed as settlement and horizontal displacement of the surface outside the pit, and further coordinated deformation of the existing subway tunnel in the field can be caused. The urban subway tunnel usually adopts shield construction, and the section of jurisdiction of assembling is highly sensitive to the deformation, if design construction is improper, causes too big tunnel deformation, will seriously threaten its operation safety.
In engineering practice, the following two methods are often used for tunnel deformation control: (1) increasing the design rigidity of a foundation pit supporting structure to control the deformation of the foundation pit and further control the deformation of the tunnel; (2) and (4) driving an isolation pile between the foundation pit and the tunnel to carry out the deformation propagation control of the soil body in the active area, thereby achieving the purpose of controlling the deformation of the tunnel. However, the traditional method often has the following problems in the practical process: (1) the traditional method has unclear stress mechanism and is difficult to carry out quantitative design analysis; (2) passive control measures are adopted, the control effect is poor, and the fine control of the whole process of tunnel deformation is difficult; (3) the construction measures are high in manufacturing cost and are mostly permanent measures, and the foundation pit is considered to be a temporary engineering structure, so that the engineering economy is poor.
The traditional design method of the barrier system is usually based on engineering experience, the stress mechanism is unclear, professional quantitative design analysis is difficult to perform, and then the deformation control effect is optimized. Meanwhile, the traditional separation measures mostly adopt a through-long rigid structure design (such as a row pile or an underground continuous wall), the construction cost is high, and the permanent underground structure in the field can not be recycled after the use, so that the economical efficiency is poor. Based on the research results completed by the applicant, the traditional rigid barrier system has a blocking effect on the shallow soil mass of the active region outside the pit and a pulling effect on the deep soil mass of the active region, and the pulling effect of the rigid section has an opposite effect on the horizontal deformation control of the deep tunnel outside the pit.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a method for controlling the deformation of a tunnel outside a foundation pit based on a liquid grout blocking wall, which aims to solve the problem of poor tunnel deformation control effect caused by unloading of foundation pit excavation by traditional engineering measures in the background art.
In order to achieve the purpose, the invention provides the following technical scheme:
a deformation control method for a tunnel outside a foundation pit based on a liquid-state slurry blocking wall is characterized in that the liquid-state slurry blocking wall is adopted to replace a traditional rigid blocking system, the 'traction effect' of an active area outside the pit is effectively controlled, and the deformation energy of a displacement field of the active area outside the pit is released through the shearing deformation of liquid; and after the foundation pit construction is finished, the liquid blocking slurry wall is subjected to landfill treatment, so that the site is restored to the original state.
The method specifically comprises the following steps:
(1) determining design parameters of the barrier slurry wall by combining site engineering conditions and site soil conditions; the design parameters comprise the design depth L of the liquid slurry wall, the design width w of the liquid slurry wall, the distance D from the foundation pit support structure, the excavation depth H of the foundation pit, the clear distance D between the tunnel and the foundation pit support structure, the center burial depth S of the tunnel and the internal friction angle of the soil body in the active area of the field
Comprehensively determining the design parameters of the barrier slurry wall;
(2) constructing the barrier slurry wall based on the determined design parameters; excavating a separation slurry wall by adopting underground continuous wall excavation grooving equipment, and preparing slurry while excavating; after the construction of the blocking slurry wall is finished, preparing slurry in the blocking slurry wall, and sealing the top of the blocking slurry wall by using a steel plate;
(3) and excavating the foundation pit, and after the excavation of the foundation pit is finished and the tunnel is deformed stably, carrying out backfill construction on the separation slurry wall.
Determining a position parameter D of the blocking slurry wall according to the clear distance D between the tunnel and the foundation pit support structure, wherein when the D is 0.6-0.8D, the deformation control effect of the blocking slurry wall is obvious; secondly, determining the design depth L of the barrier slurry wall, and working according to the stress diffusion angle of the soil body in the field
When the control effect is optimal, the blocking paste wall reaches the optimal control effect if the control effect is optimal
At this time, the value L is equal to S; and finally, determining the design width w of the barrier slurry wall according to the excavation depth H of the foundation pit, and taking w as (0.1-0.12). H, so that the deformation control effect of the barrier slurry wall can be maximized.
And (2) preparing the slurry by adopting water, cement and bentonite, wherein the bentonite comprises the following components in volume ratio: cement: water 1: 1.52: 3.13, and the specific gravity of the slurry is controlled to be 1.12-1.34.
And (3) backfilling the groove by using fine sand, and discharging the prepared slurry, wherein the backfilling is preferably performed by using the fine sand with the average particle size of 0.3-0.6 mm, and the backfilling pore ratio is controlled within the range of 0.67-0.95.
And (3) the steel cover plate and the peripheral soil body are in free lap joint in the step (2).
Compared with the prior art, the invention has the beneficial effects that:
1. the design concept of the liquid barrier slurry wall adopting the prepared slurry as the main body is provided. The invention adopts the prepared slurry as the barrier in the designThe system body replaces a rigid structure in a traditional barrier system and effectively blocks the principal stress sigma in the horizontal direction3When the tunnel is spread in a field, the deformation energy of the displacement field of the active region outside the pit is released through the shear deformation of the liquid, the 'traction effect' of the active region outside the pit is reduced, and the horizontal deformation of the tunnel outside the pit caused by the unloading of the foundation pit is further controlled.
2. The traditional design method of the barrier system is usually based on engineering experience, the engineering stress mechanism is unclear, and quantitative design analysis is difficult to carry out. Based on research results of the applicant, the method can be used for excavating the foundation pit according to the excavation depth H of the foundation pit, the clear distance D between the tunnel and the enclosure structure, the center burial depth S of the tunnel and the internal friction angle of the soil body in the ground active region
And the engineering characteristics and the physical and mechanical parameters of the soil body are equal, the optimized design parameters of the liquid barrier slurry wall are provided, and the deformation control effect on the tunnel outside the foundation pit is maximized.
3. The invention provides the optimized design parameters of the grout wall and simultaneously gives consideration to construction feasibility and economy. The underground diaphragm wall grooving equipment is used for construction, and the specialized prepared slurry is used as a filling main body. In the construction process, slurry wall grooving construction is carried out firstly, professional slurry preparation is carried out while grooving is carried out, and after the construction is completed, a steel cover plate is adopted for sealing the top of the slurry wall. And after the foundation pit construction is finished and the tunnel is deformed stably, backfilling the groove by adopting fine sand, and discharging the prepared slurry. The invention is easy to construct in actual operation, can effectively reduce the construction cost, and can ensure that the planning and use at the later stage of the site are not influenced after the fine sand is backfilled.
The novel liquid-state blocking slurry wall provided by the method divides the soil body of the active area outside the pit into 'traction effect' influence areas according to the characteristics of the soil body of the field, and a section of liquid-state blocking slurry wall taking slurry as a main body is arranged in the liquid-state blocking slurry wall, so that the main stress sigma in the horizontal direction is effectively blocked3When the field is spread, the deformation energy of the field is released by adopting liquid shearing deformation, and the horizontal deformation spreading is effectively blocked. Through setting reasonable design parameters, the deformation control of the liquid separation slurry wall is effectively improvedThe effect is achieved, and meanwhile, the construction cost can be effectively reduced.
Detailed Description
The technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.
The construction and post-backfilling of the liquid barrier slurry wall of the present invention will be further described with reference to the accompanying drawings and the specific embodiments. The following examples are given for the purpose of illustration only and are not intended to be limiting.
As shown in fig. 1 and 2, the invention relates to a liquid barrier grout wall for controlling the deformation of a tunnel caused by unloading. The device disclosed by the invention is a pure liquid barrier system which takes prepared slurry as a main body, and maximizes the control effect on the deformation of the tunnel caused by unloading by utilizing the physical and mechanical characteristics of the prepared slurry. Firstly, determining design parameters of the barrier slurry wall by combining site engineering conditions and site soil conditions, wherein the distance D between the barrier slurry wall and the foundation pit enclosure structure is 0.6-0.8D, and the design depth of the barrier slurry wall
When in use
At the moment, the value L is equal to S, the design width w of the blocking slurry wall is equal to (0.1-0.12) H (wherein D is the clear distance between the tunnel and the foundation pit enclosure structure, H is the excavation depth of the foundation pit, S is the center buried depth of the existing tunnel,
the inner friction angle of the soil body in the active area of the field) is obtained, and the deformation control effect of the grout blocking wall is optimal under the condition of the design parameters. And then, constructing the blocking slurry wall based on the determined design parameters and excavating a foundation pit, as shown in the attached drawing 1. And after the foundation pit is excavated and the tunnel is deformed stably, backfilling construction of the blocking slurry wall is carried out, as shown in the attached figure 2. Firstly, the construction of the foundation
pit support structure 2 is completed before the foundation pit is excavated into the
soil body 3 in the pit. The main body 1 and 6 of the separation grout wall is constructed before the
soil body 3 in the pit is excavated. And (3) adopting underground continuous wall grooving equipment to perform the groove forming construction of the blocking slurry wall between the foundation
pit enclosure structure 2 and the existing
tunnel 4 outside the pit, and preparing the slurry 1 in the slurry wall while forming the groove on the blocking slurry wall. In the process of forming the groove, slurry circulation is carried out by adopting a slurry circulation method, and the inside of the groove is filled with prepared slurry 1 along with the completion of excavation of the
soil body 3 in the groove. In order to optimize the fluidity of slurry 1 in the separation slurry wall, simultaneously ensure that the specific gravity of the slurry meets the requirements and prevent the
soil body 5 of the 'traction effect' affected area outside the pit from collapsing, water, cement and bentonite are adopted for preparing the slurry, and the volume ratio of the three components is bentonite: cement: water 1: 1.52: 3.13, the specific gravity of the slurry 1 is controlled to be 1.12-1.34. After the construction of the separation slurry wall is finished, the interior of the separation slurry wall is filled with the prepared slurry 1, and the top of the separation slurry wall is sealed by a steel cover plate 6, so that the steel cover plate 6 is in free lap joint with the
peripheral soil body 5 to ensure the deformation control effect. In order to prevent hole collapse caused by overload, the site in the range of 10-15 m around the hole is forbidden to be loaded. So far, this separation thick liquid wall construction is accomplished, can dig the
interior earthwork 3 of hole. In the process, the blocking slurry wall can effectively control the horizontal deformation of the existing
tunnel 4 outside the pit. And after the whole construction of the foundation pit is finished and the
tunnel 4 outside the pit is deformed and stabilized, backfilling the isolation slurry wall, which is shown in the attached figure 2. And removing the steel cover plate 6 at the top of the slurry wall, backfilling the slurry wall in the groove by adopting the fine sand 7, preferably adopting a replacement method for backfilling, and circularly replacing the fine sand 7 and preparing the slurry 1 in the groove. In order to ensure the backfilling quality, the backfilling is preferably made of fine sand with the average grain diameter of 0.3-0.6 mm, and the backfilling pore ratio is controlled within the range of 0.67-0.95. After the prepared slurry 1 in the groove is completely discharged and the fine sand 7 is backfilled to the ground surface, the backfilling construction of the slurry blocking wall is finished, the site is recovered to the original state, and the subsequent site planning is not influenced so that the subsequent site planning is not influencedThe application is as follows.
Although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that various changes in the embodiments and/or modifications of the invention can be made, and equivalents and modifications of some features of the invention can be made without departing from the spirit and scope of the invention.