Dynamic preloading and loading construction method for asymmetric deformation of existing structure in pit excavation with zero distance close approach

Abstract

The present application relates to a kind of zero distance close foundation pit excavation construction to pit existing structure asymmetric deformation dynamic preloading construction method, including the following steps: the deformation influence of pit existing structure in the process of zero distance close foundation pit excavation is simulated and analyzed, obtain the overall deformation law of pit existing structure upheaval and local differential deformation law;Select uniform heaped load mode and uneven heaped load mode to carry out heaped load test, determine optimal heaped load parameter;Pit existing structure is simulated by grading preloading, and the grading preloading scheme of optimal control effect is determined;Pit existing structure is gradually loaded;The parameter of the grading preloading scheme of optimal control effect is dynamically adjusted.The present application carries out the construction of pit existing structure zero distance close foundation pit by the way of preloading before excavation, reduces the upheaval amount of pit existing structure and interval tunnel, ensures the safety of pit existing structure when two side foundation pits are excavated and normal operation of subway train.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of geotechnical engineering and underground engineering construction technology, in particular to deformation control in close construction in urban dense areas, and specifically relates to a dynamic preloading and loading construction method for asymmetric deformation of existing structures in a pit caused by zero-distance close pit excavation construction. BACKGROUND

[0002] The construction of a pit close to an existing subway station has gradually become a common form in the development of urban underground space. How to solve the influence of zero-distance close pit on the existing operating station is crucial to the construction of urban rail transit.

[0003] The basic principle of the pile-up control technology is to induce the settlement of soil or compensate for the deformation of foundation or structure by applying a certain load (pile-up) on the structure or ground. As an important civil engineering technology, the pile-up control technology is relatively simple to construct and has a lower cost. The application of traditional pile-up technology usually relies on manual operation, and some important parameters of pile-up (pile-up amount, pile-up timing and pile-up method, etc.) are often determined by experience. It is difficult to accurately control the pile-up. Too much or too little pile-up, the time and the position of the pile-up will affect the effect of structure deformation control. For example, too much load may cause excessive settlement, while insufficient load may not effectively control the heave deformation.

[0004] The existing pile-up control has the following problems:

[0005] (1) How to determine the important parameters of pile-up control. Traditional pile-up technology usually relies on manual operation to apply load, and key parameters such as pile-up amount, pile-up timing and pile-up method are often determined by experience. Although this method can deal with routine situations, it has a lag and is inefficient, often taking remedial measures after problems occur, lacking an effective prediction mechanism, leading to increased construction costs. More importantly, due to the reliance on manual operation, the pile-up process is easily affected by human factors. For example, insufficient experience or judgment errors of construction personnel may lead to inappropriate selection of pile-up amount and pile-up timing, and non-standard operation may cause deviations in the method, intensity and sequence of pile-up application, thereby affecting the stability of the structure. In addition, the lag in adjustment of manual operation makes it difficult to make appropriate adjustments in time once the structure deforms, leading to uneven deformation or cracks and increasing the risk of the project. Furthermore, the complexity of the construction site environment or the negligence or fatigue of workers may cause errors or unevenness in the application of pile-up, thereby causing stress concentration or structural damage. Therefore, the lack of a scientific and systematic pile-up control method makes the accurate control of pile-up face great challenges and is easily disturbed by human factors, affecting the safety and effectiveness of the project.

[0006] (2) How to control the high-precision deformation of the asymmetric deformation of the existing station in the pit caused by the excavation of the pit. Existing researches mostly focus on the case where there is a certain distance between the pit and the existing subway structure, or the case where the single-side pit is close to the existing subway structure. However, the subway station structure has a large span, and when the pit excavation is located on one side of the station, the unloading effect of the pit will cause the subway station to move horizontally towards the pit, and the station floor will rise in the vertical direction, and the station body will tilt away from the pit, especially when the pit and the station share the supporting structure. If pit excavation is carried out on both sides of the station, not only will it exacerbate the uplift effect of the subway station, but also will cause the station to deviate in the horizontal direction due to the difference in the size of the two pits. Although symmetric excavation can alleviate some problems caused by asymmetric excavation in theory, in actual construction, due to the narrow space of underground construction environment and the limited space for pit excavation, it is difficult to ensure sufficient operating distance, and the arrangement and adjustment of equipment are also limited. The size and number of construction equipment limit its flexibility in a small space, making it difficult to guarantee construction efficiency and accuracy. In terms of time, due to the influence of weather, equipment maintenance and other factors, it is difficult to achieve synchronous construction for symmetric excavation. Although symmetric excavation on both sides can better control the horizontal deformation of the station tunnel, it is more disadvantageous for the vertical deformation control of the station tunnel. Asymmetric excavation causes uneven deformation or local stress concentration of the subway station structure due to the uneven position or depth of the pit excavation, increasing the risk and difficulty in the construction process. Therefore, in the actual construction process, due to the influence of space, equipment and time, it is complex and difficult to achieve symmetric excavation, and asymmetric excavation faces more severe deformation control challenges. Therefore, it is urgent to develop a more suitable construction scheme for these restrictions, especially in the case of zero-distance asymmetric excavation, how to achieve high-precision deformation control is still a problem to be solved.

[0007] (3) How to actively control the deformation of the existing station in the pit caused by the excavation of the pit. The traditional preloading control method usually starts to gradually apply preloading when the structure starts to rise and deform after the excavation of the pit. This method is a passive control measure after deformation occurs. Although it can slow down the further development of deformation to some extent, it is difficult to discover and effectively control the deformation in the early stage, which often leads to an increase in the risk during construction. With the rapid development of computing power, intelligent technology has gradually penetrated into the traditional engineering field, leading to the transformation of construction methods. Compared with passive control, intelligent active control can not only achieve more efficient, intelligent and unmanned construction management, but also save costs and improve safety factors. In the aspect of preloading control of the pit, intelligent technology can actively and timely adjust important parameters such as preloading amount, preloading time and preloading position through real-time monitoring and data analysis, and timely predict the occurrence or excessive development of deformation. However, there is still a lack of a systematic and scientific preloading active control method that can predict the occurrence of deformation and timely adjust the preloading scheme according to real-time data to accurately control the deformation of the pit.

[0008] (4) How to dynamically adjust the preloading scheme. The traditional preloading control method usually needs to be determined before the construction of the pit, and once the load is applied, it cannot be dynamically adjusted according to the actual construction situation. This static scheme cannot cope with the complex changes in the construction process of the pit, such as the increase in excavation depth, the dynamic changes of soil deformation and the response of the surrounding environment, etc. The preloading amount and preloading position may need to be adjusted. However, once the traditional preloading control method is set, it is difficult to flexibly respond to these changes, which may affect the safety and stability of the structures around the pit, and even may cause more serious structural damage. Especially for the deformation control of existing operating stations, the requirements are extremely strict. There is a lack of a deformation control method that dynamically adjusts the preloading according to the actual construction situation in the prior art. SUMMARY

[0009] In view of the deficiencies of the prior art, the main purpose of the present application is to provide a dynamic preloading construction method for asymmetric deformation of existing structures in a pit caused by zero-distance close pit excavation construction, to solve the problems that the important parameters of the traditional preloading control are difficult to determine, mostly rely on engineering experience, the traditional preloading control is difficult to control the asymmetric deformation of the existing structures in the pit caused by the excavation of the pit with high precision, and the preloading active control of the deformation of the existing structures in the pit caused by the excavation of the pit is difficult to be achieved, and the traditional preloading control is difficult to be dynamically adjusted.

[0010] The technical scheme of the present application is as follows:

[0011] The present application provides a dynamic preloading construction method for asymmetric deformation of existing structures in a pit caused by zero-distance close pit excavation construction, comprising the following steps:

[0012] According to the construction scheme and the stratum parameters, the influence of the zero-distance close foundation pit excavation process on the deformation of the existing structure in the pit is simulated and analyzed to obtain the overall deformation law and the local differential deformation law of the upheaval of the existing structure in the pit;

[0013] Based on the deformation law, a uniform loading method and a non-uniform loading method are selected for the loading test to determine the optimal loading parameters, wherein the uniform loading method corresponds to the overall deformation trend of the existing structure in the pit, a uniform load is applied to the roof of the existing structure in the pit, and the non-uniform loading method corresponds to the local differential deformation characteristics of the existing structure in the pit, a local load is applied to both sides of the identified deformation mutation position;

[0014] Based on the optimal loading parameters, a staged preloading simulation of the existing structure in the pit is performed to determine the staged preloading scheme with the optimal control effect;

[0015] In the excavation of the solid foundation pit, the staged preloading scheme with the optimal control effect is used for step-by-step loading of the existing structure in the pit;

[0016] The parameters of the staged preloading scheme with the optimal control effect are dynamically adjusted by using numerical simulation and combining with the field monitoring data and the construction process.

[0017] Preferably, the overall deformation law refers to the overall upheaval value and position distribution of the roof or the bottom plate of the existing structure in the pit, and the local differential deformation law refers to the non-coordinated deformation upheaval value and position distribution of the local small range area of the roof or the bottom plate of the existing structure in the pit deviating from the overall deformation law.

[0018] Preferably, the local small range area includes one or more of the plate corner area, the plate middle area, and the plate support joint area of the roof or the bottom plate of the existing structure in the pit.

[0019] Preferably, the selection of the uniform loading method and the non-uniform loading method based on the deformation law for the loading test to determine the optimal loading parameters includes:

[0020] The uniform loading method and the non-uniform loading method are used for loading numerical simulation test by using numerical simulation analysis software, specifically including:

[0021] The uniform loading of different intensity loads on the roof of the existing structure in the pit is changed, and the loading position is actively created on both sides of the local deformation mutation position of the existing structure in the pit, and the local loading of different intensity loads on the actively created loading position is increased;

[0022] The control effect of different loading intensities on the overall vertical deformation of the existing structure in the pit and the local asymmetric deformation of the existing structure in the pit is analyzed;

[0023] Determine the optimal uniform heaped load strength and the optimal non-uniform heaped load strength.

[0024] Preferably, the uniform heaped load is earth heaping; and the non-uniform heaped load is water storage.

[0025] Preferably, the determination of the optimal grading pre-press heaped load scheme comprises:

[0026] Based on the excavation construction step sequence, the optimal uniform heaped load strength and the optimal non-uniform heaped load strength are graded, wherein the grading number m is not more than the excavation step sequence number n.

[0027] Through numerical simulation trial, different grading combinations of heaped load are applied before each excavation step sequence.

[0028] The deformation response of the existing structure in the pit under each grading combination during the excavation process is analyzed.

[0029] The effects of different grading strategies on deformation control are compared to determine the optimal grading pre-press heaped load strength and the optimal grading pre-press heaped load timing.

[0030] Preferably, the step-by-step loading of the existing structure in the pit using the optimal grading pre-press heaped load scheme comprises:

[0031] Perform grading pre-press heaped load.

[0032] Excavation work is carried out on both sides of the pit for the existing structure.

[0033] Excavation applies the ith level of pre-heap load, where i = 1, 2,..., n, including the ith level of uniform pre-heap load and the ith level of non-uniform pre-heap load.

[0034] Perform the ith excavation work on both sides of the pit.

[0035] Analyze the deformation of the existing structure in the pit, including the deformation increment of each structure and the asymmetric deformation trend of the structure.

[0036] Dynamic adjustment of pre-press heaped load parameters.

[0037] Determine the next level of uniform pre-heap load, as well as the next level of non-uniform pre-heap load and the next level of non-uniform pre-heap load position.

[0038] Determine whether it is the last excavation, if not, return to "Excavation applies the ith level of pre-heap load" and continue to iterate and optimize the loading scheme; if yes, end.

[0039] Preferably, the dynamic adjustment of the parameters of the optimal grading pre-press heaped load scheme based on numerical simulation and combined with field monitoring data and construction process comprises:

[0040] Real-time monitoring and obtaining the vertical deformation and stress change data of the existing structure in the pit;

[0041] Using the data and combining the current excavation step, the numerical simulation inversion analysis is used to dynamically optimize the pile-up strength and arrangement position in the subsequent excavation stage;

[0042] According to the change of the excavation process and the pile-up condition, the pile-up strategy is actively adjusted, including preferentially using the roof of the existing structure in the pit at the initial stage of excavation, and gradually using the pile-up surface increase or adjusting the pile-up area as the excavation of the foundation pit advances;

[0043] A dynamic closed-loop feedback mechanism of monitoring-analysis-adjustment-control is formed to realize the continuous optimization of the grading preloading pile-up parameter construction process.

[0044] Preferably, the dynamic preloading pile-up construction method further comprises: step-by-step unloading the pile-up of the existing structure in the pit after the excavation of the foundation pit is completed.

[0045] Preferably, the step-by-step unloading the pile-up of the existing structure in the pit after the excavation of the foundation pit is completed is: after the completion of the excavation of the foundation pit, the completed pile-up is gradually unloaded step by step as the structures on both sides of the existing structure in the pit are completed, until the pile-up amount is zero.

[0046] The beneficial effects of the present application relative to the prior art are: the present application proposes a dynamic preloading pile-up construction method for the asymmetric deformation of the existing structure in the pit during the zero-distance close foundation pit excavation construction, which reduces the uplift amount of the existing structure in the pit and the interval tunnel, and ensures the safety of the existing structure in the pit and the normal operation of the subway train during the excavation of the foundation pit on both sides. Specifically, at least the following practical effects are achieved:

[0047] The present application simulates and analyzes the deformation influence of the zero-distance close foundation pit excavation process on the existing structure in the pit by using numerical simulation software, and simulates different pile-up schemes to predict the pile-up effect and optimize the application position and size.

[0048] The present application provides a plurality of pile-up methods, which are combined with different pile-up methods (such as uniform pile-up and uneven pile-up) through pre-pile-up. According to the real-time monitoring deformation data of the existing structure in the pit, the overall and local uplift deformation of the existing structure in the pit is summarized, and the numerical simulation results are flexibly selected to enhance the applicability of the method.

[0049] The present application proposes a pre-pressing and loading method, before the foundation pit is excavated, the numerical simulation software is used to simulate and analyze the deformation influence of the zero distance close foundation pit excavation process on the existing structure in the pit, and the deformation law of the existing structure in the pit is obtained, then different loading intensities are set, and the uniform and non-uniform loading is applied in the area exceeding the deformation standard, and the loading is applied before each layer of earthwork is excavated, the control effect of different pre-pressing intensities and pre-pressing loading time on the uplift deformation of the existing structure in the pit is analyzed according to the simulation results, and the best pre-pressing loading time and the best pre-pressing loading amount are obtained. Through the pre-pressing and loading method, the passive control method can be changed into an active control method, the unfavorable deformation trend can be recognized earlier, and the loading is adjusted and intervened actively, so that the deformation is controlled in a smaller and safer range.

[0050] The present application realizes the dynamic management of "monitoring, analyzing, adjusting and controlling" by real-time monitoring data and feedback to the numerical simulation, timely adjusting the loading scheme, actively creating the loading conditions according to the excavation construction engineering, and completing the dynamic closed-loop management of construction and the dynamic coordination of excavation construction and loading, so that the disturbance to the existing structure in the pit is minimized, and the overall construction quality is ensured.

[0051] The loading materials (such as earth and water storage) of the present application are easy to obtain and low in cost, and through the optimization of loading parameters and graded loading, the resource waste is reduced, the orderliness and rationality of the loading operation are ensured, and the construction efficiency is improved.

[0052] It should be understood that the content described in the summary section is not intended to limit the key or important features of the embodiments of the present application, nor to limit the scope of the present application. Other features of the present application will become apparent through the following description. In addition, the implementation of any embodiment of the present application does not mean that multiple or all of the above beneficial effects are simultaneously or simultaneously achieved. BRIEF DESCRIPTION OF DRAWINGS

[0053] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only exemplary, and for those skilled in the art, other drawings can be derived from the provided drawings without creating labor.

[0054] The structures, proportions, sizes, etc. shown in the specification are only used to cooperate with the content disclosed in the specification, to be understood and read by those skilled in the art, and are not intended to limit the limiting conditions under which the present application can be implemented, so they do not have technical significance. Any modification of structure, change of proportion relationship or adjustment of size, without affecting the effect and purpose that the present application can produce, should still fall within the scope of the technical content disclosed by the present application.

[0055] Figure 1 The overall flow framework schematic diagram of the dynamic preloading and heaping construction method for the non-symmetrical deformation of the existing station in the pit in the zero-distance close pit excavation construction of some embodiments of the present application;

[0056] Figure 2 The detailed flow schematic diagram of steps S1-S3 of the dynamic preloading and heaping construction method for the non-symmetrical deformation of the existing station in the pit in the zero-distance close pit excavation construction of some embodiments of the present application;

[0057] Figure 3 The detailed flow schematic diagram of steps S4-S5 of the dynamic preloading and heaping construction method for the non-symmetrical deformation of the existing station in the pit in the zero-distance close pit excavation construction of some embodiments of the present application;

[0058] Figure 4 The typical spatial relationship schematic diagram of the existing station structure and the two-side non-symmetrical zero-distance close pit of some embodiments of the present application;

[0059] Figure 5 The existing station roof uniform heaping schematic diagram of some embodiments of the present application;

[0060] Figure 6 The existing station two-side structure local differential deformation position increases non-uniform heaping schematic diagram of some embodiments of the present application under the premise of uniform heaping;

[0061] Figure 7 The existing station two-side structure non-symmetrical uniform heaping schematic diagram of some embodiments of the present application;

[0062] Figure 8 The existing station comparison schematic diagram of some embodiments of the present application under the two working conditions of “non-heaping” and “dynamic preloading and heaping”. DETAILED DESCRIPTION

[0063] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear and explicit, the embodiments of the present application are further described in detail below in combination with the embodiments and the drawings. Herein, the schematic embodiments of the present application and the descriptions thereof are used to explain the present application, but not as the limitation to the present application.

[0064] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connecting", "fixing" and the like should be understood in a broad sense, for example, can be fixed connection, can also be detachable connection, or integral; can be mechanical connection, can also be electrical connection; can be directly connected, can also be indirectly connected through an intermediate medium, can be internal communication of two elements or interaction relationship of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0065] It should be understood that the terms "including / containing", "consisting of" or any other variant are intended to cover non-exclusive inclusion, so that the product, device, process or method including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such product, device, process or method. Without more limitation, the elements defined by the statement "including / containing", "consisting of" do not exclude the presence of additional identical elements in the product, device, process or method comprising the elements.

[0066] It should also be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices, components or structures referred to must have a particular orientation, be constructed or operated in a particular orientation, and cannot be understood as a limitation on the present application.

[0067] Referring to Figures 1 to 8 The present application proposes a dynamic preloading construction method for non-symmetrical deformation of existing structures in a pit caused by zero-distance close pit excavation construction. The method mainly solves the following problems:

[0068] (1) For the problem that important parameters of traditional preloading control are difficult to determine, mostly relying on engineering experience, the present application simulates and analyzes the deformation influence of zero-distance close pit excavation on the existing structures in the pit by using numerical simulation software, and simulates different preloading schemes to predict the preloading effect and optimize the application position and size.

[0069] (2) For the problem that traditional preloading control is difficult to control the non-symmetrical deformation of existing structures in the pit caused by pit excavation construction with high precision, the present application provides various preloading methods, which are combined with different preloading methods (such as uniform preloading and uneven preloading) through preloading. According to the real-time monitoring deformation data of the existing structures in the pit, the overall or local uplift deformation of the existing structures in the pit is summarized, and the numerical simulation results are flexibly selected to enhance the applicability of the method.

[0070] (3) To address the issue that surcharge loading cannot be used to actively control the deformation of existing structures within the excavation pit, this invention proposes a preloading method. Before excavation, numerical simulation software is used to simulate and analyze the deformation impact of near-field excavation on existing structures within the pit, revealing the deformation patterns. Then, different surcharge intensities are set and applied uniformly or non-uniformly to areas exceeding deformation standards. Loading is performed before each layer of earthwork excavation. Based on the simulation results, the control effects of different preloading intensities and timing on the bulging deformation of existing structures within the pit are analyzed to obtain the optimal preloading timing and the optimal preloading amount. By using preloading, passive control can be transformed into active control, allowing for earlier identification of unfavorable deformation trends and proactive adjustment of the surcharge for intervention, thereby controlling deformation within a smaller and safer range.

[0071] (4) In view of the problem that traditional load control is difficult to dynamically adjust, this invention monitors data in real time and provides feedback to verify the numerical simulation, adjusts the load scheme in a timely manner, realizes dynamic management of "monitoring, analyzing, adjusting and controlling at the same time", and actively creates load conditions according to the excavation and construction project, completes the dynamic closed-loop management of construction and the dynamic coordination of excavation and construction and load, minimizes the disturbance to the existing structure in the pit, and ensures the overall construction quality.

[0072] The implementation of the present invention will be described in detail below with reference to preferred embodiments.

[0073] See Figures 1 to 3 The flowchart shown illustrates the following steps: S1: Based on the construction plan and geological parameters, simulate and analyze the deformation impact of the zero-distance close-proximity excavation process on the existing structure within the pit, deriving the overall deformation law and local differential deformation law of the existing structure within the pit; S2: Based on this deformation law, select uniform loading and non-uniform loading methods for loading tests to determine the optimal loading parameters. The uniform loading method corresponds to the overall deformation trend of the existing structure within the pit, applying a uniformly distributed load to the top plate of the existing structure within the pit. The non-uniform loading method corresponds to the local differential deformation characteristics of the existing structure within the pit, applying local loads on both sides of the identified deformation abrupt change locations; S3: Based on the optimal loading parameters, conduct graded preloading simulation on the existing structure within the pit to determine the graded preloading scheme with the best control effect; S4: During the actual excavation of the foundation pit, gradually load the existing structure within the pit using the graded preloading scheme with the best control effect; S5: Dynamically adjust the parameters of the graded preloading scheme with the best control effect using numerical simulation combined with on-site monitoring data and the construction process.

[0074] The present application adopts the above technical scheme, fully masters the existing structure in the pit and the external foundation pit excavation mode before construction, determines the pre-loading before construction through numerical simulation inversion analysis: the influence of foundation pit excavation on the heave of the existing structure in the pit is analyzed by numerical simulation, the initial (first level) pre-loading amount is determined and applied to pre-control the heave; dynamic adjustment during construction: during the foundation pit excavation process, simulation of pre-pressing loading is required before each layer of soil is excavated, the pre-loading amount is actively adjusted according to the simulation results before each excavation to ensure that the heave is always maintained within the allowable range, and the safety of the tunnel structure and the normal operation of the subway train are ensured.

[0075] The following will take the existing station in the pit as an example to elaborate the specific implementation of each link.

[0076] Step S1, according to the construction scheme and stratum parameters, the numerical simulation software is used to simulate and analyze the deformation influence of the zero-distance close foundation pit excavation process on the existing station structure to obtain the overall deformation law and local differential deformation law of the heave of the existing station structure.

[0077] It is easy to understand that the construction scheme generally refers to the field construction scheme, and the core content covers two key paths of foundation pit engineering and main structure construction. Specifically, it specifies the layered and segmented excavation process of the foundation pit on both sides of the line, including the step sequence of earthwork excavation, the coordinated installation of supporting structures and key auxiliary processes such as dewatering and drainage. On this basis, the scheme further specifies the construction sequence of the main structure inside the foundation pit, from cushion pouring, bottom plate construction, to the sequential operation of side walls, middle plates and top plates, and finally to the installation of secondary structures and auxiliary facilities inside, forming a complete, coherent and executable field construction instruction system. The stratum parameters generally include geological conditions, structural parameters and load conditions.

[0078] In this step, finite element software such as PLAXIS 3D, Midas GTS NX, ABAQUS, etc. is generally used to simulate and analyze the deformation influence of the zero-distance close foundation pit excavation process on the existing station structure.

[0079] In some embodiments, the overall deformation law refers to the overall heave value (heave size) and position distribution of the top plate or bottom plate of the existing station structure; the local differential deformation law refers to the non-coordinated deformation heave value and position distribution of the local small range area of the top plate or bottom plate of the existing station structure that deviates from the overall deformation law, and the core is "small range, mutation, and no change in overall deformation trend".

[0080] More specifically, the overall deformation law refers to the uniform trend and gradual distribution of deformation of the existing structure in the pit, which is usually covered by most of the area of the plate (such as more than 70-80% of the total area of the plate), and the deformation direction (such as bulging) is consistent with the macroscopic law of the pit side (such as high deformation value near the large pit side and low deformation value near the small pit side), and the deformation values at different positions in the plate show a "gentle gradient" without abrupt local jumps.

[0081] The local differential deformation law is a non-coordinated deformation that deviates from the overall gradient law in a small range (usually less than 20% of the total area of the plate) in the plate under the background of overall deformation--the deformation is limited to a certain part of the plate (such as the corner area of the plate, a small piece in the middle of the plate, or the local area where the plate contacts the support), and the deformation value of the area and the adjacent area has a significant "mutation", and does not follow the overall gradient trend. The local differential deformation law mainly expresses the difference after comparison with the overall deformation law, for example, the overall deformation is 3-4mm, and part of the deformation is 5-7mm, then the difference deformation is 2-3mm.

[0082] In this step, before the excavation of the foundation pit, numerical simulation is used Figure 4 to excavate the existing station on both sides and preliminarily determine the deformation law and adverse position of the existing station structure, so as to effectively control the bulging deformation of the existing station structure during construction.

[0083] Step S2, based on the deformation law, selecting Figure 5 the uniform loading method and Figure 6 , Figure 7 the uneven loading method shown in the figure to carry out the loading test, and determining the optimal loading parameters.

[0084] In the present application, the uneven loading method is carried out on the premise of the uniform loading method, that is, the uneven loading is carried out on the basis of the uniform loading.

[0085] In this step, the uniform loading method corresponds to the overall deformation trend of the existing station, and a uniform load (the last layer of soil excavation section) is applied to the top plate of the existing station. More specifically, the uniform loading (different loading intensities): according to the overall deformation law in S1, different loading intensities are set on the upper part of the top plate structure of the subway station before the excavation of the last layer of soil, and the loading is uniformly applied. According to the simulation results, analyze the control effect of different loading intensities on the bulging deformation of the existing station, and find the best uniform loading intensity.

[0086] The unevenly piled manner corresponds to the local differential deformation characteristics of the existing station, and a local concentrated load is applied on both sides of the identified deformation mutation position. In more detail, the unevenly piled (different piled positions): in the overall deformation rule background, in order to eliminate the relative differential deformation between each part of the subway, firstly, the piled position limitation condition is defined - because the existing station has been put into operation, the bottom plate space is limited by operation and cannot be piled, so the unevenly piled is only carried out on both sides of the existing station structure (the operable space of the top plate, the local area of the bottom plate related to the structure on both sides of the station wall, etc. need to be determined in combination with the actual structure layout of the station and the operation safety boundary.); secondly, according to the differential deformation rule of the station structure (such as the larger amount of heave on one side, or the deformation difference on both sides exceeds the control threshold) and the unfavorable position (such as the structure section where the differential deformation is concentrated) obtained in S1, through numerical simulation trial, on the basis of the applied uniform piled, the local piled counterpressure of different intensities is increased on the structure positions corresponding to the areas with large differential deformation on both sides; finally, the simulation results are compared (such as the reduction of the deformation difference on both sides, whether the overall deformation meets the limit value), and the unevenly piled (local piled) strength and specific position with the best control effect are determined.

[0087] In some embodiments, based on the overall deformation rule, the numerical simulation analysis software is used to carry out piled numerical simulation trial by using the uniformly piled manner, and the optimal piled parameters include:

[0088] (1) changing the load of different intensities to carry out uniform piled on the top plate of the existing station;

[0089] (2) analyzing the control effect of different piled intensities on the overall vertical deformation of the existing station;

[0090] (3) determining the uniformly piled intensity with the optimal control effect.

[0091] In some embodiments, based on the local differential deformation rule, the numerical simulation analysis software is used to carry out piled numerical simulation trial by using the unevenly piled manner, and the optimal piled parameters include:

[0092] (1) actively creating piled positions on both sides of the local deformation mutation position of the existing station, and changing the load of different intensities to increase local piled on the actively created piled positions;

[0093] (2) analyzing the control effect of different piled intensities on the local asymmetric deformation of the existing station;

[0094] (3) determining the unevenly piled intensity with the optimal control effect.

[0095] In the present application, before the foundation pit is excavated, the numerical simulation is used to excavate the foundation pit on both sides of the existing station, and the piled parameters of different piled manners are preliminarily determined, so that the piled scheme is more scientific, accurate and flexible.

[0096] In some embodiments, the uniform piling manner is piling soil.

[0097] In some embodiments, the non-uniform piling manner is water storage.

[0098] In the present application, the piling is performed in the manner of piling soil and water storage, which is easy to obtain materials and has low cost, and is operable and flexible, facilitating the implementation of partial and zoned loading.

[0099] In step S3, a hierarchical preloading simulation is performed on the existing station structure based on the optimal piling parameters to determine a hierarchical preloading scheme with optimal control effect.

[0100] In this step, the hierarchical preloading parameters refer to hierarchical preloading strength and preloading timing, and the optimal uniform piling strength and non-uniform piling strength obtained in S2 are classified according to the excavation step sequence (the classification order m≤ the construction excavation step sequence n); numerical simulation is used to calculate the application of different classification combinations before each excavation to obtain the optimal hierarchical preloading strength and preloading timing, i.e., the hierarchical preloading scheme with optimal control effect.

[0101] In some embodiments, determining the hierarchical preloading scheme with optimal control effect specifically includes:

[0102] Based on the excavation construction step sequence, the optimal uniform piling strength and the optimal non-uniform piling strength are classified, wherein the classification number m does not exceed the excavation step sequence number n;

[0103] Through numerical simulation calculation, the piling of different classification combinations is applied before each excavation step sequence;

[0104] The deformation response of the existing station in the excavation process under each classification combination is analyzed;

[0105] The effects of different classification strategies on deformation control are compared to determine the optimal hierarchical preloading strength and hierarchical preloading timing.

[0106] In this step, the preloading piling manner can change the passive control mode to an active control mode, identify the adverse deformation trend earlier, and actively adjust the piling to intervene, so as to control the deformation in a smaller and safer range. The hierarchical loading of preloading can avoid damage to the existing structure in the pit caused by sudden large loading under the premise of ensuring the piling effect.

[0107] In step S4, the hierarchical preloading scheme with optimal control effect is used to load the existing station structure step by step in the entity foundation pit excavation.

[0108] Referring to Figure 3, step S4 is carried out around the dynamic linkage control of staged pre-pressing pile loading and foundation pit excavation, and the specific implementation steps are as follows in combination with the flowchart logic:

[0109] Performing staged pre-pressing pile loading;

[0110] Excavation is carried out on both sides of the existing station;

[0111] The i-th level of pre-pressing pile loading (i=1, 2,..., n) is applied, including the i-th level of uniform pre-pressing pile loading (a predetermined intensity of uniform load applied on the roof of the existing station) and the i-th level of non-uniform pre-pressing pile loading (a predetermined intensity of local load applied on both sides of the identified deformation mutation position);

[0112] Performing the i-th excavation operation on both sides of the foundation pit;

[0113] Analyzing the deformation of the existing station structure, including the deformation increment of each structure and the asymmetric deformation trend of the structure;

[0114] As can be easily understood, the structure here includes the roof and the floor, and the deformation increment refers to the vertical deformation increment of the structure compared with the previous excavation. The asymmetric deformation trend is because the excavation on both sides of the existing station is asymmetric, and the deformation caused by the existing station is also asymmetric, and the influence trend on the existing station structure after one excavation.

[0115] Dynamic adjustment of pre-pressing pile loading parameters (see S5 for specific adjustment steps, which are described in detail below);

[0116] Determining the next level of uniform pre-pressing pile loading, as well as the next level of non-uniform pre-pressing pile loading and the next level of non-uniform pre-pressing pile position;

[0117] Judging whether it is the last excavation, if not: the process returns to "applying the i-th level of pre-pressing pile loading (i=1, 2,..., n)", and the loading scheme is continuously iterated and optimized; if yes: the whole process of "staged pre-pressing pile loading + foundation pit excavation" linkage control is completed.

[0118] Step S5: dynamically adjusting the parameters of the staged pre-pressing pile loading scheme that optimizes the control effect by using numerical simulation and combining with the field monitoring data and the construction process.

[0119] This step actively adjusts the size and position of the pile loading according to the real-time monitoring of the vertical deformation trend and stress change of the existing structure in the pit as the excavation of the foundation pit on both sides of the existing station proceeds, so as to realize the dynamic closed-loop management of "monitoring, analyzing, adjusting and controlling".

[0120] In this step, according to the excavation construction mode, in the initial stage of excavation, due to the limited position of the stack, the stack is mainly placed on the upper part of the existing station roof; with the advancement of excavation, additional stack positions and conditions are actively created (preferably constructing the structure on both sides of the existing station and stacking on the structure on both sides of the existing station), to realize the dynamic adjustment of excavation and stacking.

[0121] The present application actively creates a stack position by preferentially constructing the structure on both sides of the existing station structure and applying asymmetric uniform stacking on both sides according to the size of the two-side foundation pit excavation, to realize the dynamic adjustment of excavation construction and stacking, and better achieve the effect of bump control.

[0122] In this step, first, deformation sensors are installed on the existing subway station structure and track bed, then the deformation of the existing subway station structure during the construction of the double-side foundation pit is monitored in real time, and finally the deformation trend of each structure of the station is determined. If the vertical deformation of the bottom plate track area is monitored to increase, the stack amount is increased, if the vertical deformation is monitored to decrease, the stack amount is decreased, and if the asymmetric deformation trend of the structure (the two-side foundation pit of the existing station is asymmetrically excavated, the deformation of the larger side is greater than that of the smaller side, resulting in asymmetric deformation, and the position of asymmetric deformation may change or the number of deformation positions may increase during the excavation process), the asymmetric stack position and stack amount need to be changed or increased.

[0123] In some embodiments, the dynamic adjustment of the parameters of the hierarchical preloading stack scheme optimized for control effect by using numerical simulation and combining field monitoring data and the construction process includes:

[0124] Real-time monitoring and obtaining the vertical deformation and stress change data of the existing station structure;

[0125] As can be easily understood, the monitoring of the project is in the bottom plate track area. The plates actively creating the stack position and the existing station plates are cooperatively stressed, and all of them utilize the monitoring of the bottom plate track area.

[0126] Using the data and combining the current excavation step, the stack strength and arrangement position in the subsequent excavation stage are dynamically optimized through numerical simulation inversion analysis;

[0127] According to the changes of the excavation process and the stack conditions, the stack strategy is actively adjusted, including preferentially using the existing station roof for arrangement in the initial stage of excavation, and gradually using the stack surface to increase or adjust the stack area with the advancement of foundation pit excavation;

[0128] A dynamic closed-loop feedback mechanism of monitoring-analysis-adjustment-control is formed to realize the continuous optimization of the hierarchical preloading stack parameters in the construction process.

[0129] In this step, numerical simulation and field monitoring are combined, field monitoring data are used for verification and improvement of the numerical simulation model, so as to obtain more accurate simulation results. According to the optimized simulation model and real-time monitoring data, the size, position and loading / unloading time sequence of the preloading are dynamically adjusted to realize the dynamic closed-loop management of'monitoring, analysis, adjustment and control'.

[0130] In some embodiments, the dynamic preloading and heaping construction method further comprises S6: step-by-step unloading of the heaping of the existing station structure after the foundation pit excavation is completed.

[0131] More specifically, after the foundation pit excavation is completed, the completed heaping is gradually unloaded in steps and stages as the structures on both sides of the existing station are completed, until the heaping amount is zero.

[0132] It is easy to understand that when the completed heaping is unloaded, it should be unloaded in sections and zones according to the construction conditions of the structures on both sides of the existing station and the real-time monitoring conditions of the existing station structure.

[0133] It should be noted that whether to unload after completing all the foundation pit excavation or to continuously unload while excavating and building should be determined according to the construction conditions, real-time monitoring results and soil quality.

[0134] In the present application, after the foundation pit excavation is completed, the structures inside the foundation pits on both sides of the existing station are gradually constructed, and are unloaded in sections and zones according to the real-time monitoring results and construction conditions, so as to achieve flexible unloading and ensure the overall stability of the existing station structure.

[0135] In summary, the zero-distance close proximity foundation pit excavation construction method of the present application has the following advantages:

[0136] (1) Precise heaping deformation control is the most direct and effective way to solve the problems of construction safety, construction cost and slow construction progress caused by the heaving of the existing station during close proximity excavation of the foundation pit.

[0137] (2) By preloading before excavation and dynamically adjusting the heaping, the heaving of the existing station structure is actively controlled, the heaving amount of the existing subway structure and the interval tunnel is significantly reduced, and the normal operation of the existing subway during excavation of the foundation pit is ensured.

[0138] (3) In actual construction, through real-time monitoring and review, the loading measures can be adjusted in real time, which helps to improve the accuracy of heaving amount control, prevent the actual heaving amount from deviating greatly from the predetermined plan, and realize fine construction.

[0139] (4) The method provides multiple loading modes, and by preloading and matching different loading modes (such as uniform loading and non-uniform loading), flexibility can be achieved according to the overall or local uplift deformation of the existing station structure, and the applicability of the method is enhanced.

[0140] (5) The loading materials (such as earth and water storage) are easy to obtain and low in cost, and by optimizing the loading parameters and grading loading, resource waste is reduced, the orderliness and rationality of the loading operation are ensured, and the construction efficiency is improved.

[0141] (6) Through the dynamic management of “monitoring, analyzing, adjusting, and controlling” and the creation of loading conditions according to the excavation construction project, dynamic closed-loop management of construction and dynamic coordination of excavation construction and loading are realized, the disturbance to the existing station is minimized, and the overall construction quality is ensured.

[0142] Specific implementation

[0143] Engineering background: The subway Lize Business District Station (Line 14, Line 16, Airport Line, Line 11, Lijing Line and terminal) project is located under two plots 64# and 65# and surrounding roads. At present, Line 14 and Line 16 have been completed and opened to traffic, and the station of the Daxing Airport Line is under construction, and the main structure of the Line 11 and Lijing Line stations is reserved in this station. In the development process of the Lize City Terminal Integrated Transportation Hub, excavation work on the existing two-side foundation pits of Line 16 is involved. In this process, the unloading effect caused by the excavation of the foundation pit and the disturbance to the soil layer during construction will inevitably destroy the original stress state of the soil. The change of soil stress will cause uneven deformation of the surrounding soil, and then cause the uplift deformation of the already operating Line 16 station and tunnel structure, affecting its stability and safety. Especially during the construction process, Line 16 needs to remain in normal operation, which puts forward very high requirements for deformation control. According to relevant design specifications and operation requirements, the amplitude of the deformation of Line 16 tunnel must be strictly controlled between ±2mm and -3mm, which poses a huge challenge to accurate monitoring and deformation control during construction.

[0144] This embodiment takes the asymmetric foundation pit excavation on both sides of the already operating Line 16 station in the Beijing subway Lize Business District Hub project as the background. The dynamic preloading and loading construction method includes the following steps:

[0145] S1: According to the construction scheme and stratum parameters, the numerical simulation software is used to simulate and analyze the influence of zero-distance close foundation pit excavation on the deformation of the existing station structure, and the deformation law of the uplift of the existing station structure is obtained.

[0146] The specific method is: before construction, the engineering and hydrogeological detailed parameters of the foundation pit excavation area need to be fully investigated and obtained, including: ① stratum physical and mechanical parameters, such as the unit weight (natural unit weight, saturated unit weight), cohesion, internal friction angle, compression modulus, and permeability coefficient of each soil layer; ② groundwater parameters, including the confined water level elevation, phreatic water depth, and groundwater permeability characteristics; and ③ existing station structure parameters, including the main structure size (roof, floor, side wall, etc.), concrete strength grade, and structure connection node form.

[0147] Subsequently, the appropriate numerical simulation software (such as PLAXIS 3D, Midas GTS NX, ABAQUS, etc.) is selected, and in this project case, PLAXIS 3D software is used for modeling analysis. The constitutive model for numerical simulation needs to be determined in combination with the stratum characteristics (Morrison-Culhane, hardening soil, HSS, etc.), and in this project case, the HS model is mainly selected. This model can more accurately simulate the nonlinear deformation and hardening characteristics of the soil body through the tangent stiffness modulus E50 (50% offset stress secant modulus), unloading / reloading modulus E ur , and triaxial drainage test shear strength parameters; the existing station structure uses a linear elastic model.

[0148] According to the construction scheme, the influence of foundation pit excavation on the heave of the existing station structure (roof, floor, etc.) is analyzed through numerical simulation. The structure vertical deformation and horizontal deformation cloud maps obtained from the model calculation results show the deformation law of the existing station structure, which can be divided into overall deformation law and local differential deformation law.

[0149] The overall deformation law refers to the heave of the entire roof of the existing structure in the pit as a complete unit, which is affected by the macro unloading of the foundation pit excavation (especially the stress release dominated by the large foundation pit side when the two sides are not symmetrically excavated). The deformation shows a unified trend and a gradual distribution, usually covering most of the area of the plate (such as more than 70%-80% of the total area of the plate), the deformation direction (such as heave) is consistent with the macro law of the foundation pit side (such as high deformation value near the large foundation pit side and low deformation value near the small foundation pit side), and the deformation values at different positions in the plate show a "gentle gradient" without abrupt local jumps. For example, a 4mx6m roof, from the edge of the plate near the large foundation pit side to the edge of the plate near the small foundation pit side, the heave gradually decreases from 18mm to 7mm, and the displacement difference between any two adjacent measuring points (1-2m apart) is within 2-3mm, and the deformation rhythm of all measuring points is synchronized with the excavation progress of the large foundation pit. This deformation of the main area of the cover plate, which follows a unified gradient, is the overall deformation.

[0150] Local differential deformation is a non-uniform deformation that deviates from the overall gradual change rule and appears in a small range (usually less than 20% of the total area of the plate) in the plate in the context of overall deformation - the deformation is limited to a certain local area in the plate (such as a corner of the plate, a small piece in the middle of the plate, or a local area in contact with the support), and the deformation value of the area and the adjacent area around it has a significant "jump" and does not follow the overall gradient trend. For example, the top plate described above has a gradient of "high on the side of the large foundation pit and low on the side of the small foundation pit", but in one corner of the plate (about 0.5mx0.5m range), the amount of bulging suddenly increases from 12mm to 17mm around the periphery, or in a 2mx2m area in the middle of the plate, the amount of bulging decreases from 10mm to 5mm around the periphery. This small range, which deviates from the overall gradient trend, is the local differential deformation. The core is "small range, non-uniform, and sudden change", and it does not change the overall deformation trend of the plate.

[0151] S2: Based on the deformation rule, select uniform and non-uniform stacking methods for stacking test to determine the optimal stacking parameters.

[0152] Based on the overall deformation rule, the numerical simulation analysis software is used to perform stacking numerical simulation test to determine the optimal stacking parameters. The specific method is as follows: ① The stacking application time is clear before the last layer of soil is excavated (the specific construction scheme can be divided, and in this project case, the excavation is roughly divided into four layers, each layer corresponds to the height of the subsequent internal structure of the foundation pit, and each layer is excavated by 2 meters each time). At this stage, the existing station structure has already borne most of the bulging deformation caused by the previous excavation, and the structure deformation trend has fully emerged. By applying the stack at this stage, the deformation increment of the subsequent excavation stage can be directly controlled, which can not only accurately evaluate the control effect by comparing the deformation data before and after the stack, but also effectively offset the unloading bulging effect caused by the excavation of the last layer of soil by using the additional pressure generated by the stack, making the control more targeted and verifiable.

[0153] ②Stacking range coverage Figure 5 The subway station top plate structure shown is a full section, and the stacking area boundary is consistent with the edge of the station top plate structure (deviation not more than 0.5m), ensuring that the load is uniformly applied to the top plate. The stacking strength is set according to the gradient test scheme, and the initial value is determined according to the maximum bulging amount predicted in S1, usually in the range of 10-20kPa gradient (such as 50kpa, 60kPa, 70kpa, 80kPa, 90kPa five groups of schemes).

[0154] ③ The coupling effect of the heaping and excavation process should be considered in the numerical simulation: when simulating the excavation of the last layer of soil, a pre-set uniform heaping load is applied, and the heaping state is kept stable for 12-24 hours (to simulate the actual heaping construction and settlement stabilization time), and then the last layer of soil excavation process is executed. The uplift deformation data of the station structure (roof, floor, side wall) is analyzed throughout the process.

[0155] ④ The control effect evaluation indicators include: maximum uplift reduction rate ((maximum uplift without heaping - maximum uplift after heaping) / maximum uplift without heaping x 100%), deformation rate peak (maximum deformation rate during the excavation stage after heaping), and structural stress response (whether the additional bending moment and shear force of the roof are within the design allowable range). Through multiple scheme comparison, the optimal uniform heaping strength that meets the following conditions is selected. When the indicators of two schemes are similar, economic conditions can be considered.

[0156] Based on the local differential deformation law, the numerical simulation software is used to perform heaping numerical simulation trial with uneven heaping, and the specific method to determine the optimal heaping parameters is as follows:

[0157] ① Heaping position limitation and space verification: Since the existing station is in operation, the floor and track area space are limited by train passage and equipment maintenance, and heaping operation is strictly prohibited. Therefore, uneven heaping operation is strictly limited to the workable area of the structure on both sides of the existing station. For example, the structure on both sides of the existing station can be prioritized for construction, and heaping conditions can be actively created, as shown in Figure 6 、 Figure 7 .

[0158] ② Reference data collection: based on the numerical simulation results of S1, the key indicators of differential deformation of the station structure are extracted, including: maximum uplift difference on both sides (Δh≥3mm needs to be controlled), and differential deformation area.

[0159] ③ Heaping strength gradient setting: based on the uniform heaping that has been applied, a 5-level local heaping strength gradient (8kPa, 10kPa, 12kPa, 16kPa, 20kPa) is set for the significant differential deformation area.

[0160] ④ Heaping implementation process (using water reservoir weight heaping)

[0161] Heaping range demarcation: using the principle of "deformation extreme value area corresponding to heaping core area", the single heaping area is controlled within 8-15㎡, and a 0.6m wide transition zone (strength decreases linearly to the uniform heaping strength) is set at the edge, and the distance between adjacent heaping areas is >1.5m to avoid stress superposition.

[0162] Material selection: water reservoir weight is used on both sides of the structure to form regular cubic heaping units, and the heaping strength is changed by changing the water depth.

[0163] ⑤ In numerical simulation, the coupling effect of surcharge and excavation process should be considered simultaneously: When simulating the excavation of the last layer of soil, on the basis of the applied uniform surcharge (the optimal uniform load strength obtained in the previous step can be selected), apply a uniformly distributed surcharge of preset strength in the differential deformation area, keep the surcharge state stable for 12-24 hours (simulating the actual surcharge construction and settlement stabilization time), and then execute the excavation process of the last layer of soil. Analyze the heave deformation data of the station structure (top slab, bottom slab, side walls) throughout the entire process.

[0164] ⑥ The evaluation indicators for control effectiveness include: the differential deformation reduction rate of the base plate ((difference before loading - difference after loading) / difference before loading × 100%), and the structural stress response (whether the additional bending moment and shear force of the base plate are within the design allowable range). Through comparison of multiple schemes, the optimal non-uniform loading strength that meets the following conditions is selected. Economic considerations can be taken into account when the indicators of two schemes are similar.

[0165] S3: Based on the optimal surcharge parameters, perform graded preloading simulation on the existing station structure to determine the graded preloading scheme with the best control effect.

[0166] Specific implementation plan: For the optimal uniform load strength determined by S2 (taking 80 kPa as an example), at least 3 typical grading schemes are proposed, and multiple preloading timings (load initiation nodes) are matched simultaneously:

[0167] ①Grading scheme:

[0168] Option 1: 20kPa→40kPa→60kPa→80kPa (increasing step by step, with the difference between steps increasing from small to large);

[0169] Option 2: 30kPa → 40kPa - 60kPa - 80kPa (Initial load is relatively large, subsequent loads increase gradually)

[0170] Option 3: 25kPa→35kPa→50kPa→80kPa (uniform transition in stages).

[0171] ② Timing of pre-compression:

[0172] Timing Group A: Apply initial surcharge before excavation of the first layer.

[0173] Timing Group B: Apply the initial surcharge after the first layer of excavation and before the second layer of excavation.

[0174] Timing Group C: Apply the first-stage surcharge after the second layer of excavation and before the third layer of excavation.

[0175] ③ Optimal solution selection: By comparing simulation results from multiple dimensions, the optimal combination is selected from three aspects: deformation control effect, structural safety, and construction feasibility.

[0176] S4: In the entity foundation pit excavation, the optimal control effect of the hierarchical preloading and surcharge scheme is used to gradually load the existing station structure.

[0177] Due to the actual foundation pit excavation, the actual deformation of the station may deviate from the simulation results. Therefore, real-time monitoring of the deformation of the existing station structure is needed, and numerical simulation inversion analysis of the existing station structure is needed again, and the original design construction excavation model and subsequent loading measures are optimized. At the same time, during the foundation pit excavation process, after excavating a part of the earthwork, the real-time monitoring of the station body and the uplift data and change trend of each section are carried out, the deformation and loading amount are reviewed, and the loading measures (such as loading position, loading amount, loading opportunity) are adjusted in real time according to the review results.

[0178] S5: Use numerical simulation and combine with field monitoring data and construction process to dynamically adjust the parameters of the hierarchical preloading and surcharge scheme with the optimal control effect.

[0179] During the entire construction process, the specific surcharge position, surcharge amount and surcharge timing should be judged according to the real-time deformation data and change trend of the station obtained by real-time monitoring, and used to verify and improve the numerical simulation model to obtain more accurate simulation results. According to the optimized simulation model and real-time monitoring data, dynamically adjust the scale, position and application / unloading timing of surcharge (preloading), realize the dynamic closed-loop management of "monitoring, analysis, adjustment and control".

[0180] S6: After the foundation pit excavation is completed, the surcharge of the existing station structure is unloaded step by step.

[0181] After the completion of surcharge and excavation on both sides of the existing structure in the pit, the internal structure to be built in the pit is gradually constructed, and the existing structure in the pit is gradually unloaded at the same time. The real-time deformation of the station structure is monitored in real time, and according to the real-time monitoring results, the upper part of the station is gradually unloaded, and the vertical deformation (uplift and settlement) of the existing station is reduced.

[0182] In this case, the change law of the deformation value with the dynamic surcharge time of the existing station under the two working conditions of "no surcharge" and "dynamic preloading and surcharge" is shown in Figure 8, the horizontal axis is the dynamic preloading time, and the vertical axis is the deformation value of the existing station. The dashed line represents the deformation trend of the “non-preloading” condition, and the solid line represents the deformation trend of the “dynamic preloading” condition. The “critical value” is the safety threshold of the deformation of the station. As can be seen from the figure, compared with the “non-preloading” condition, the deformation peak value of the existing station under dynamic preloading is significantly reduced, and the final stable deformation is much smaller than the “critical value”. This means that dynamic preloading can actively limit the deformation of the station and avoid the stress redistribution of the soil caused by the excavation of the foundation pit, which may cause the deformation of the station to exceed the limit (such as structural cracking and excessive track settlement), thereby ensuring the safety of the station structure.

[0183] It is easy for those skilled in the art to understand that the above-mentioned preferred schemes can be freely combined and superimposed without conflict.

[0184] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A dynamic preloading method for zero-distance close-proximity excavation of a foundation pit, characterized in that, Includes the following steps: Based on the construction plan and geological parameters, the impact of the zero-distance close-to-the-pit excavation process on the deformation of the existing structure in the pit was simulated and analyzed, and the overall deformation law and local differential deformation law of the existing structure in the pit were obtained. Based on the aforementioned deformation law, uniform and non-uniform loading methods were selected for loading tests to determine the optimal loading parameters. The uniform loading method corresponds to the overall deformation trend of the existing structure in the pit, and a uniformly distributed load is applied to the top plate of the existing structure in the pit. The non-uniform loading method corresponds to the local differential deformation characteristics of the existing structure in the pit, and a local load is applied to both sides of the identified deformation abrupt change location. Based on the optimal loading parameters, a staged preloading simulation was conducted on the existing structure in the pit to determine the staged preloading scheme with the best control effect. In the excavation of a solid foundation pit, the existing structure inside the pit is gradually loaded using the graded preloading scheme with the best control effect. The parameters of the graded preloading scheme with optimal control effect are dynamically adjusted by using numerical simulation and combining on-site monitoring data and construction process.

2. The dynamic preloading surcharge construction method according to claim 1, characterized in that, The overall deformation law refers to the overall uplift value and location distribution of the existing structural top or bottom plate within the pit; and the local differential deformation law refers to the non-coordinated deformation uplift value and location distribution that deviates from the overall deformation law in a small local area of ​​the existing structural top or bottom plate within the pit.

3. The dynamic preloading surcharge construction method according to claim 2, characterized in that, The localized small area includes one or more of the corner area, middle area, and joint area of ​​the existing structural top or bottom plate within the pit.

4. The dynamic preloading surcharge construction method according to claim 1, characterized in that, The process of selecting uniform and non-uniform loading methods for surcharge tests based on the deformation law to determine the optimal surcharge parameters includes: Numerical simulation analysis software was used to conduct load simulation trials under both uniform and non-uniform loading methods, specifically including: The loads of different intensities are uniformly applied to the top plate of the existing structure in the pit, and load positions are actively created on both sides of the location of a sudden change in local deformation of the existing structure in the pit. The loads of different intensities are then applied to the actively created load positions to increase local load. The effects of different surcharge intensities on the overall vertical deformation and local asymmetric deformation of the existing structure within the pit were analyzed. Determine the uniform load strength and non-uniform load strength that provide the best control effect.

5. The dynamic preloading surcharge construction method according to claim 1, characterized in that, The uniform loading method is soil piling; the non-uniform loading method is water storage.

6. The dynamic preloading surcharge construction method according to claim 1, characterized in that, The staged preloading scheme that determines the optimal control effect includes: Based on the excavation construction sequence, the optimal uniform load strength and the optimal non-uniform load strength are classified into levels, where the number of levels m does not exceed the number of excavation steps n. Through numerical simulation, different graded combinations of surcharges were applied before each excavation step. Analyze the deformation response of the existing structure in the pit under each grade combination during the excavation process; By comparing the effects of different grading strategies on deformation control, the optimal grading preloading strength and timing of grading preloading are determined.

7. The dynamic preloading surcharge construction method according to claim 1, characterized in that, The stepwise loading of the existing structure within the pit using the staged preloading scheme with optimal control effect includes: Implement graded preloading; Excavation work was carried out on the foundation pits on both sides of the existing structure inside the pit; The excavation applies the i-th level of preload, where i = 1, 2, ... n, including the i-th level uniform preload and the i-th level non-uniform preload; Perform the i-th excavation operation on both sides of the foundation pit; The deformation of the existing structures within the pit was analyzed, including the deformation increments of each structure and the trend of asymmetric deformation. Dynamic adjustment of preload parameters; Determine the next level of uniform preload, as well as the next level of non-uniform preload and the location of the next level of non-uniform preload; Determine if this is the last excavation. If not, return to "Excavation with i-th level preload" and continuously iterate to optimize the loading scheme; if yes, end.

8. The dynamic preloading surcharge construction method according to claim 1, characterized in that, The dynamic adjustment of the parameters of the staged preloading scheme with optimal control effect using numerical simulation combined with on-site monitoring data and construction process includes: Real-time monitoring and acquisition of data on vertical deformation and stress changes of existing structures within the pit; Using the data and the current excavation sequence, the load intensity and layout in subsequent excavation stages are dynamically optimized through numerical simulation and inversion analysis. Based on the changes in the excavation process and loading conditions, the loading strategy is proactively adjusted, including prioritizing the use of the existing structural top slab in the pit during the initial excavation phase, and gradually increasing or adjusting the loading area by utilizing the loading surface as the excavation progresses. A dynamic closed-loop feedback mechanism of monitoring, analysis, adjustment, and control is formed to achieve continuous optimization of the construction process of graded preloading parameters.

9. The dynamic preloading surcharge construction method according to claim 1, characterized in that, The dynamic preloading construction method also includes: unloading the load on the existing structure in the pit in stages after the foundation pit is excavated.

10. The dynamic preloading surcharge construction method according to claim 9, characterized in that, The step-by-step unloading of the load on the existing structure inside the pit after the excavation is completed is as follows: as the structures on both sides of the existing structure inside the pit are completed after the excavation, the completed load is gradually unloaded in stages until the load is zero.

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