A calculation method for realizing displacement control of underground pipe gallery in deep foundation pit construction

Abstract

The application discloses a kind of in deep foundation pit construction, realize the calculation method of underground pipe gallery displacement control, belong to civil engineering construction field.City underground pipeline crisscross, require that foundation pit engineering not only considers its stability when designing construction, also need to control the influence of surrounding pipeline within a certain range.The application utilizes Geo-Studio software to establish a two-dimensional mathematical model of deep foundation pit, simulates the whole process of foundation pit excavation and dewatering construction, optimizes and determines the final construction steps and methods of foundation pit, reduces the disturbance of foundation pit construction to pipe gallery to the minimum, greatly improves the safety of pipe gallery during construction.The application is based on conventional foundation pit construction technology, without other high-end special equipment and construction materials and supporting professional construction personnel, without increasing engineering investment, has good popularization value.

Description

Technical Field

[0001] This invention belongs to the technical field of civil engineering construction, specifically relating to a calculation method for controlling the displacement of underground utility tunnels during deep foundation pit construction. Background Technology

[0002] With the accelerating pace of urbanization, underground pipelines for gas, water, sewage, electricity, and communications crisscross the city. These are vital infrastructures ensuring urban operation and are often referred to as the city's "lifeline." The construction of urban subways, high-rise buildings, and underground commercial areas requires the excavation of foundation pits, which often overlap with or even intersect with these underground pipelines. The excavation, drainage, and support of foundation pits inevitably lead to a redistribution of soil stress inside and outside the pit, causing soil deformation, displacement of underground pipelines, and even rupture, resulting in significant economic losses and adverse social impacts. Therefore, the design and construction of foundation pit projects must not only consider their own stability but also control the deformation of nearby municipal pipelines within a certain range. The influencing factors are complex, and numerous difficulties exist during construction.

[0003] Urban underground pipeline projects mostly employ pipe jacking construction techniques, which impose strict requirements on the absolute displacement of the pipeline, the settlement difference between each pipe section, and the tilt angle. In actual foundation pit projects adjacent to or intersecting with pipelines, the additional stress method is often used to solve for the stress on the pipeline. However, foundation pit construction is often carried out in layers and sections, with excavation and support occurring simultaneously. This calculation method fails to consider the impact of the entire construction process and cannot propose a foundation pit construction plan that ensures pipeline safety, thus failing to provide technical support for the actual foundation pit construction process. Summary of the Invention

[0004] (1) Technical problems to be solved

[0005] This invention provides a calculation method for controlling the displacement of underground utility tunnels during deep foundation pit construction. It overcomes the shortcomings of existing calculation methods that treat the foundation as an elastic foundation, cannot simulate complex actual geological conditions, fail to consider the dynamic effects of the entire foundation pit construction process, and cannot formulate a foundation pit construction scheme that effectively controls the deformation of the utility tunnel based on the calculation results.

[0006] (2) Technical solution

[0007] To address the aforementioned technical problems, a calculation method for controlling the displacement of underground utility tunnels during deep foundation pit construction is provided, comprising the following steps:

[0008] Step 1: Collect design data such as plan and section drawings of the proposed foundation pit, as well as design, operation and maintenance data of pipelines involved in the project;

[0009] Step 2: Collect information on the topography and geomorphology of the project area, the distribution of soil and rock layers, the calculation parameters of each soil and rock layer, and the distribution of groundwater in the site.

[0010] Step 3: Use Geo-Studio software to establish a two-dimensional finite element model of the longitudinal section of the foundation pit, initially formulate a construction plan for alternating dewatering and excavation of the foundation pit, and calculate the displacement deformation value and cumulative displacement value of the pipe gallery in each dewatering and excavation process under this plan.

[0011] Step 4: Compare and analyze the impact of each construction process on the displacement of the utility tunnel obtained from numerical simulation, summarize the relationship between the settlement value caused by dewatering and the rebound amount of the foundation pit caused by excavation, and strive to offset the floating value of the utility tunnel caused by excavation with the settlement caused by dewatering in one dewatering and excavation process, so as to ensure that the displacement of the utility tunnel remains relatively unchanged after one dewatering and excavation construction process is completed.

[0012] Step 5: Taking into account the impact of construction technology and excavation zoning, optimize processes with significant displacement. ① If the pipe gallery floats significantly after a single dewatering and excavation process, reduce the excavation depth for that process or increase the dewatering intensity to lower the water level. ② If the pipe gallery settles significantly during a single dewatering and excavation process, reduce the excavation depth for that process or decrease the dewatering intensity to raise the water level. ③ Select excavation areas appropriately or add auxiliary engineering measures. For example, first excavate the soil on both sides of the pipe gallery to the bottom elevation of the pit, retain the backfill soil above the pipe gallery for weight, and finally use a slicing excavation method for the backfill soil, using steel beams to lock the pipe gallery while excavating to prevent it from floating.

[0013] Step 6 involves using model calculations to analyze and optimize the displacement changes of the utility tunnel in each construction process under the construction plan. This process is continuously refined until the displacement of the target utility tunnel is controlled within 10mm under the recommended construction plan, which can successfully reduce the risk of damage to the utility tunnel during construction. Beneficial effects

[0014] The beneficial effects of this invention are as follows: This invention proposes a calculation method for controlling the displacement of underground utility tunnels during deep foundation pit construction. A two-dimensional mathematical model of the deep foundation pit is established using Geo-Studio software to simulate the entire process of excavation and dewatering, optimizing and determining the final construction steps and methods. This minimizes the disturbance to the utility tunnel during construction, significantly improving its safety. Based on conventional foundation pit construction techniques, this invention does not require expensive specialized equipment, materials, or specialized personnel, thus not increasing project investment and possessing significant potential for widespread application. Attached Figure Description

[0015] The accompanying drawings are provided to further understand the present invention and form part of the specification. They are used together with the embodiments of the present invention to explain the invention and do not constitute a limitation thereof.

[0016] Figure 1 This is a plan view showing the intersection of the deep foundation pit and the power utility tunnel in the Jin'an River Direct Discharge Channel Project in Fuzhou City.

[0017] Figure 2 This is a cross-sectional view of the intersection of the deep foundation pit and the power utility tunnel in the Jin'an River Direct Discharge Channel Project in Fuzhou City.

[0018] Figure 3 A two-dimensional mathematical model of the deep foundation pit for the Jin'an River direct discharge channel project into the Minjiang River in Fuzhou.

[0019] Figure 4 This is a simplified diagram of the foundation pit excavation process for the initial construction plan.

[0020] Figure 5 This is a simplified diagram of the foundation pit excavation process for the final construction plan.

[0021] Figure 6 This is a cloud map showing the displacement changes of the pipe gallery after the completion of the first step in the final construction plan for the foundation pit.

[0022] Figure 7 This is a cloud map showing the displacement changes of the pipe gallery after the completion of the second step in the final construction plan for the foundation pit.

[0023] Figure 8 This is a cloud map showing the displacement changes of the pipe gallery after the completion of the third step in the final construction plan for the foundation pit.

[0024] Figure 9 This is a cloud map showing the displacement changes of the utility tunnel after the completion of step 4 in the final construction plan for the foundation pit.

[0025] Figure 10 This is a cloud map showing the displacement changes of the pipe gallery after the completion of step 5 of the final construction plan for the foundation pit.

[0026] Figure 11 This is a cloud map showing the displacement changes of the pipe gallery after the completion of step 6 in the final construction plan for the foundation pit.

[0027] Figure 12 This is a cloud map showing the displacement changes of the utility tunnel after the completion of step 7 in the final construction plan for the foundation pit.

[0028] Figure 13 This diagram shows the excavation process of the foundation pit and the calculation results of the settlement value of the power utility tunnel for construction scheme 1.

[0029] Figure 14 The diagram shows the settlement results of the foundation pit excavation process and the settlement value of the power utility tunnel, in order to optimize the construction plan.

[0030] Figure 15 This is a diagram showing the settlement results for the foundation pit excavation process (section 6) and the power utility tunnel. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be further described clearly and completely below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Example 1

[0032] This embodiment provides a calculation method for achieving full-process control of underground utility tunnels during deep foundation pit construction. This embodiment further illustrates the invention in detail with the deep foundation pit excavation calculation of the box culvert in the tail section of the Jin'an River Direct Discharge to Minjiang River Channel Project in Fuzhou City.

[0033] The construction content of this project is to build a water-passing box culvert connecting to the sluice gate on Paiwei Road. The water-passing box culvert intersects with the high-voltage cable jacking pipe of the substation in the Paiwei Road section. The minimum vertical distance between the pipe gallery and the water-passing box culvert is only 0.3m. The project plan and section are as follows. Figure 1 , 2 As shown. During the construction period, the foundation pit is planned to be excavated to the 0m elevation soil layer until the soil above the utility tunnel is exposed. Steel beams will be installed above the utility tunnel, and a water culvert will be arranged. The displacement and deformation of the cable utility tunnel will be greatly affected by the foundation pit construction.

[0034] First, we collected design data such as the plan layout of the intersection of the box culvert and the pipe gallery at the proposed Paiwei Road section, the cross-sectional view of the foundation pit excavation and support, the topography and geomorphology of the project area, the distribution of soil and rock layers, the calculation parameters of each soil and rock layer, the distribution of groundwater on the site, and the design, operation and maintenance data of the pipelines.

[0035] A two-dimensional mathematical model of the foundation pit and pipe gallery was created using Geo-Studio software. Drainage wells were arranged, and geotechnical mechanics parameters and groundwater levels were input. Figure 3 As shown in the figure. One dewatering and one excavation are defined as one construction sequence. The preliminary dewatering and excavation construction plan for this foundation pit is as follows: Figure 4 As shown. The displacement and deformation of the pipe gallery in this scheme were calculated using the Geo-Studio two-dimensional finite element model, as shown. Figure 13 As shown, when using this construction scheme, the maximum displacement of the power utility tunnel in a single operation is 8.0 mm. After a cumulative excavation of 3.0 m in the foundation pit, the maximum displacement of the tunnel reaches 13.0 mm. At this point, the water level in the foundation pit has been lowered by 2.5 m. This construction scheme has a significant impact on the deformation and safety of the tunnel within the foundation pit. The calculation results of this scheme reveal a pattern: in this project, the soil is more affected by excavation unloading than by dewatering the manholes. The soil rebound caused by excavating 1.0 m of soil is greater than the soil settlement caused by dewatering 1.0 m. Therefore, the construction scheme alternating between dewatering 1.0 m and excavating 1.0 m will lead to significant upward floating of the tunnel during construction, and involves numerous procedures; therefore, it should be optimized.

[0036] like Figure 14As shown, the optimized scheme involves three stages of dewatering and three stages of excavation from the ground to the overburden layer. Each stage involves dewatering 1.6m and excavating 1.3m, with dewatering and excavation alternating. Afterwards, the soil on both sides of the overburden layer is excavated twice, followed by further excavation of the overburden layer, and the installation of locking steel beams. The soil on both sides of the overburden layer above the utility tunnel is excavated twice. Before excavating the overburden layer, the groundwater level at the location of the utility tunnel is lowered to -1.1m. Calculations show that the cumulative displacement after the first three stages does not exceed 1mm, achieving a good balance between the pit settlement and rebound values. After excavating the soil on both sides of the overburden layer to the bottom elevation of the box culvert, the cumulative displacement of the utility tunnel within the pit is -5.5mm.

[0037] In the optimized scheme, step 6, a single construction step, causes the power utility tunnel to float upwards by 6mm, with a cumulative upward float of 0.5mm. To reduce the tunnel displacement caused by step 6, while keeping other construction steps unchanged, step 6 is optimized by increasing the dewatering within the tunnel. The calculated conditions and results are as follows. Figure 15 As shown. After comprehensive analysis, when the water level at the location of the power utility tunnel is lowered to -1.3m, the uplift value of the tunnel in the excavated area is still too large, while when the water level is lowered to -1.9m, the settlement value of the tunnel below the retained soil is too large. Therefore, in this process, it is advisable to lower the water level below the power utility tunnel to 1.5~1.7m.

[0038] After numerical simulation optimization, the final construction sequence of the deep foundation pit project for direct discharge into the Minjiang River is as follows:

[0039] Step 1: After the original ground elevation is 6.6m and the water level in the foundation pit is lowered by 1.6m, a 1.3m thick soil layer is excavated. (At this point, the excavation level is 5.3m.)

[0040] Step 2: After lowering the water level in the foundation pit by 1.6m, excavate a 1.3m thick soil layer. (At this point, excavation reaches an elevation of 4.0m.)

[0041] Step 3: After further dewatering by 1.6m in the foundation pit, excavate a 1.3m thick layer of soil, leaving a 1.5m thick layer of topsoil for the pipe gallery. (At this point, the excavation reaches an elevation of 2.7m.)

[0042] Step 4: Excavate the soil on both sides of the reserved cover to an elevation of 1.205m.

[0043] Step 5: Dewater the pit to an elevation of 0.8m to -0.6m, excavate the cover soil above the pipe gallery, and excavate and lock the cover soil in sections (1.0m each) along the direction perpendicular to the water flow. After each 1.0m wide section of cover soil is excavated, lock one anti-buoyancy steel beam. After the steel beam is welded and locked, proceed to the next excavation and locking step. Repeat the construction cycle until all excavation and locking are completed.

[0044] Step 6: Excavate the soil outside the jet grouting piles to an elevation of 0.1m. In this step, a certain degree of dewatering can be considered based on the actual stress monitoring of the pipe gallery and anti-buoyancy steel beams.

[0045] By following the above construction procedures, the displacement of the power utility tunnel can be successfully controlled within 10mm, reducing the risk of damage to the tunnel.

Claims

1. A calculation method for controlling the displacement of underground utility tunnels during deep foundation pit construction, characterized in that, Includes the following steps: Step 1: Collect the plan and section design data of the proposed foundation pit, as well as the design, operation and maintenance data of the pipelines involved in the project; Step 2: Collect information on the topography and geomorphology of the project area, the distribution of soil and rock layers, the calculation parameters of each soil and rock layer, and the distribution of groundwater in the site. Step 3: Use Geo-Studio software to establish a two-dimensional finite element model of the longitudinal section of the foundation pit, initially formulate a construction plan for alternating dewatering and excavation of the foundation pit, and calculate the displacement deformation value and cumulative displacement value of the pipe gallery in each dewatering and excavation process under this plan. Step 4: Compare and analyze the impact of each construction process on the displacement of the utility tunnel obtained from numerical simulation, summarize the relationship between the settlement value caused by dewatering in the foundation and the rebound amount of the foundation pit caused by excavation, and strive to offset the floating value of the utility tunnel caused by excavation with the settlement caused by dewatering in one dewatering and excavation process, so as to ensure that the displacement of the utility tunnel remains relatively unchanged after one dewatering and excavation construction process is completed. Step 5: Taking into account the construction process and the impact of excavation zoning, optimize the displacement procedures: ① If the pipe gallery floats after the first dewatering and excavation procedure, reduce the excavation depth of this procedure or increase the dewatering intensity to lower the water level; ② If the pipe gallery settles during the first dewatering and excavation procedure, reduce the excavation depth of this procedure or increase the dewatering intensity to raise the water level; ③ Select excavation areas reasonably or add auxiliary engineering measures; first excavate the soil on both sides of the pipe gallery to the bottom elevation of the pit, retain the backfill soil above the pipe gallery for weight, and finally use a slice-type excavation for the backfill soil, using steel beams to lock the pipe gallery while excavating to prevent it from floating. Step 6 involves using model calculations to analyze and optimize the displacement changes of the utility tunnel in each construction process under the construction plan. This process is continuously refined until the displacement of the target utility tunnel is controlled within 10mm under the recommended construction plan, which can successfully reduce the risk of damage to the utility tunnel during construction.

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