Urban existing pipeline local updating combined foundation pit supporting method

Abstract

The application discloses a kind of urban existing pipeline local updating combined foundation pit support method, belong to municipal underground pipeline engineering construction field.For the limited space that conventional support cannot form continuous closed system due to the interference of existing pipeline, a combination of steel sheet pile enclosure and MJS all-around high-pressure jet grouting is used, the longitudinal lateral enclosure is provided by steel sheet pile, the bottom and end closure are provided by MJS grouting body, and the effective closed area is collaboratively constructed.The method comprises: surveying and positioning, surface treatment, steel sheet pile construction, MJS grouting reinforcement, layered excavation, pipeline construction and foundation pit backfilling.The application breaks through the limitation of existing pipeline on support layout, realizes the technical balance of avoidance and closure, significantly improves the anti-leakage performance and overall stability of foundation pit side wall, and provides a safe and reliable construction space for old pipeline replacement operation.

Description

Technical Field

[0001] This invention belongs to the field of municipal underground pipeline construction, specifically relating to a combined foundation pit support method for partial renovation of existing urban pipelines. Background Technology

[0002] As my country's urbanization process enters a critical stage of stock renewal, urban underground infrastructure is gradually showing signs of aging, and partial replacement of existing pipelines has become a routine requirement in urban renewal projects. However, the core difficulty in replacing old pipelines lies in the partial excavation and support of the foundation pit. Unlike the foundation pit excavation for new construction projects, the layout of existing underground pipeline networks is complex, and replacement work requires partial excavation in the area of ​​the existing pipelines. The excavation range is limited by the existing pipeline route, burial depth, and surrounding structures, making it difficult to form the complete working space required by conventional support techniques.

[0003] Traditional support methods, such as perimeter sheet pile driving, cannot form a continuous and closed support system around the excavation area due to the physical obstruction of existing pipelines, resulting in insufficient stability of the pit sidewalls. This is especially problematic when the construction area is sandy soil with a high permeability coefficient, easily leading to significant leakage and other adverse conditions. Currently, the industry's pit support technology for such situations is still in the exploratory stage. Existing solutions often employ double-row longitudinal sheet pile support, grouting at both ends, and internal dewatering of the pit. While these methods can achieve some degree of construction capability, they suffer from drawbacks such as insufficient support strength, susceptibility to leakage, and high safety risks, making them unsuitable for the stringent safety and efficiency requirements of replacing old pipelines in urban core areas.

[0004] In existing technology, CN111851466A discloses an overlapping structure and construction method for two support systems in deep foundation pits in soft soil. This method addresses the joint overlapping problem of two different support systems—SMW piles and Larssen sheet piles—in narrow, deep foundation pits. It achieves the interlocking connection of the two systems by setting plain piles at the junction of the SMW piles and sheet piles, and driving Larssen sheet piles within these plain piles as overlapping sheet piles. However, this technical solution focuses on the structural overlapping between the two support systems and does not address the avoidance and closure of existing pipeline interference scenarios. It cannot solve the overall closure problem when partially excavating areas with existing pipelines.

[0005] CN116876468A discloses a method for rapid sealing of gaps in trench sheet pile support for existing pipelines. Addressing the problem of gaps in sheet piles caused by existing pipelines crossing trenches, it employs on-site prefabrication of reinforced concrete tongue-and-groove panels to quickly assemble a retaining wall, and utilizes vertical and horizontal channel steel to form a support system for physical sealing of the gap. However, this technical solution is a passive gap-filling measure. Its sealing relies on the physical splicing of prefabricated panels and does not involve the synergistic effect of grouting reinforcement and sheet pile support. Furthermore, it lacks effective means for deep sealing at the bottom and ends of the pit, making it difficult to meet the seepage prevention requirements under high permeability conditions in sandy soil layers.

[0006] In summary, existing technologies have not yet provided a combined support method that can achieve partial excavation and overall closure of foundation pits under the interference of existing pipelines. There is an urgent need for a new support technology that organically combines steel sheet pile retaining with deep grouting reinforcement to synergistically construct an effective closed area. Summary of the Invention

[0007] The purpose of this invention is to provide a combined foundation pit support method for the partial renovation of existing urban pipelines, in order to solve the technical problem that conventional support cannot form a continuous closed system due to interference from existing pipelines. By combining steel sheet pile support with MJS all-round high-pressure jet grouting, an effective closed area is constructed in the confined space, which significantly improves the seepage prevention performance and overall stability of the foundation pit sidewall, and fundamentally reduces the safety risks of the project.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A combined foundation pit support method for partial renovation of existing urban pipelines, in confined spaces where interference from existing pipelines prevents conventional support from forming a continuous closed system, employs a combination of steel sheet pile retaining and MJS all-round high-pressure jet grouting. The steel sheet piles provide longitudinal and lateral retaining, while the MJS grouting provides bottom and end sealing, collaboratively constructing an effective closed area. The method includes the following steps: Step S1, Survey and Positioning: Conduct on-site surveys based on the existing pipeline drawings to verify the actual location and burial depth of the existing pipelines and determine the construction location of the retaining piles; Step S2, Surface treatment: Remove the existing road or soil layer in the area to be excavated, and excavate to the steel sheet pile construction working surface; Step S3, steel sheet pile construction: steel sheet piles are driven on both sides of the existing pipeline longitudinally to the design elevation, and steel sheet piles are driven transversely at both ends of the existing pipeline to the top of the existing pipeline without affecting the height of the existing pipeline, so that the longitudinal sides and both ends of the existing pipeline form a retaining structure, and the transverse steel sheet piles at both ends maintain a safe distance from the existing pipeline. Step S4, MJS grouting reinforcement: The all-round high-pressure jet grouting method is adopted to grout and reinforce the soil at the bottom of the foundation pit and the soil between the transverse steel sheet piles at both ends of the existing pipeline and the existing pipeline, so that the gap between the bottom and both ends of the foundation pit and the existing pipeline is reinforced and filled, forming an effective closed area together with the retaining structure. Step S5, layered excavation: First, construct the horizontal steel walers. After the horizontal steel walers are installed and form a stable system, excavate the lower soil layer in layers to ensure that the support is provided before excavation. Step S6, Pipeline construction: Replace or construct pipelines within the effective closed area; Step S7, backfilling the foundation pit: backfill layer by layer, finally remove the sheet piles, and grout the gaps after the sheet piles are removed to restore the ground structure.

[0009] Preferably, in step S3, the transverse sheet piles at both ends are driven to 300mm~500mm above the top of the existing pipeline, thereby achieving end enclosure closure while avoiding the existing pipeline.

[0010] Preferably, in step S3, the sheet piles are connected with small toothed joints, and special corner sheet piles are used at the corners.

[0011] Preferably, in step S4, the all-round high-pressure jet grouting method uses an ultra-high pressure jet of about 40MPa to form a reinforced pile with a diameter of about 2.5m, so as to effectively reinforce and fill the soil gaps at the bottom and ends of the pit that cannot be directly protected by steel sheet piles.

[0012] Preferably, in step S5, the horizontal steel waler is constructed by trenching.

[0013] Preferably, in step S7, during backfilling layer by layer, the horizontal steel waler is removed when backfilling reaches the position of the horizontal steel waler, and then backfilling continues.

[0014] Preferably, in step S7, the gaps after the sheet piles are removed are filled with grout.

[0015] Compared with the prior art, the present invention has the following beneficial effects: First, this invention overcomes the limitations of existing pipeline support layouts by combining sheet piles with MJS all-around high-pressure jet grouting. The sheet piles provide longitudinal and end lateral protection, while the MJS grouting body reinforces and fills the gaps at the bottom and ends, working together to create an effective sealed area. The gaps between the pit bottom and the existing pipelines at both ends, which cannot be directly protected by sheet piles, are effectively filled and reinforced by the large-diameter MJS reinforced piles, forming a three-dimensional sealed system of "protection + bottom sealing + end sealing." This significantly improves the seepage prevention performance and overall stability of the pit sidewalls, fundamentally reducing engineering safety risks.

[0016] Secondly, this invention addresses the interference scenario with existing pipelines by controlling the transverse steel sheet piles at both ends to a certain height above the top of the existing pipeline. This achieves end protection without affecting the existing pipeline, while simultaneously reinforcing and sealing the end gaps through MJS grouting. This achieves a technical balance between avoidance and sealing, providing a safe and reliable construction space for replacing old pipelines.

[0017] Third, this invention simplifies the support construction process, reduces disturbance to the surrounding environment, shortens the construction cycle, and reduces additional costs incurred due to construction delays and accident handling, thus possessing significant economic value. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the plan layout of the combined foundation pit support method described in this invention.

[0019] Figure 2 This is a cross-sectional schematic diagram of the combined foundation pit support method described in this invention.

[0020] Figure 3 This is a schematic diagram illustrating the stability verification of the foundation pit against confined water as described in this invention.

[0021] In the diagram: 1. Existing pipeline; 2. Steel sheet pile; 3. H-beam waler; 4. MJS large-diameter mixing pile. Detailed Implementation

[0022] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structure, features and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0023] like Figure 1 and Figure 2 As shown in the figure, this embodiment provides a combined foundation pit support method for partial renovation of existing urban pipelines, which specifically includes the following steps: Step S1, Survey and Positioning: Based on the existing pipeline drawings, conduct an on-site survey to verify the actual location and burial depth of the existing pipeline 1. Then, using surveying instruments such as a total station and theodolite, perform surveying and setting out to determine the construction location of the retaining piles.

[0024] Step S2, Surface treatment: Using hydraulic picks and other machinery, break up the existing road or soil layer in the area to be excavated, and excavate to the working face of the steel sheet pile 2.

[0025] Step S3, Sheet Pile Construction: (e.g.) Figure 1As shown, sheet piles 2 are driven to the design elevation on both sides of the existing pipeline 1 longitudinally to form a longitudinal lateral retaining structure. Sheet piles 2 are also driven laterally at both ends of the existing pipeline 1, extending 300mm-500mm above the top of the existing pipeline 1 to ensure no impact on the existing pipeline 1. The sheet piles 2 should use small-toothed connections, and specially designed corner sheet piles should be used at corners to ensure the continuity and airtightness of the retaining structure. Through the above construction, a retaining structure is formed on both sides and ends of the existing pipeline 1 longitudinally, and the transverse sheet piles 2 at both ends maintain a safe distance from the existing pipeline 1.

[0026] Step S4, MJS grouting reinforcement: as follows Figure 2 As shown, the MJS method (all-around high-pressure jet grouting) is used to reinforce the soil at the bottom of the foundation pit and the soil between the transverse sheet piles 2 and the existing pipeline 1 at both ends. The MJS method uses ultra-high pressure jetting of approximately 40 MPa, typically forming reinforced piles with a diameter of about 2.5 m. This effectively reinforces and fills the gaps in the soil at the bottom and ends of the pit that cannot be directly protected by the sheet piles 2. Through MJS grouting reinforcement, the gaps between the bottom and ends of the foundation pit and the existing pipeline 1 are reinforced and filled, forming an effective sealed area together with the sheet pile 2 retaining structure, preventing leakage at the bottom and ends.

[0027] When a confined aquifer exists below the excavation surface of the foundation pit, such as Figure 3 As shown, the stability against confined water can be verified using the following formula: γ s P wk ≤ (1 / γ Ry )Σγ i h i In the formula: γ s - Partial factor for the effect of confined water, taken as 1.0; P wk -Standard value of water pressure at the top of a confined aquifer (kP) a ); γ i -Unit weight of each soil layer from the top of the confined aquifer to the bottom of the pit (kN / m³) 3 ); h i - The thickness (m) of each soil layer between the top surface of the confined aquifer and the bottom of the pit; γ Ry - The coefficient for resistance to pressure moisture is taken as 1.05.

[0028] Step S5, Layered Excavation: During trench excavation, first construct the horizontal steel walers 3, which are generally constructed using a cut-out method. After the horizontal steel walers 3 are installed and a stable system is formed, excavate the lower soil layer, ensuring that support is provided before excavation.

[0029] Step S6, Pipeline Construction: According to design requirements, replace or construct the pipeline in the effective enclosed area. When working in the trench, the space is generally small, involving confined space operations, so appropriate ventilation, anti-toxic and safety protection measures must be taken.

[0030] Step S7, backfilling the foundation pit: The trench should be backfilled layer by layer. When backfilling reaches the position of the horizontal steel waler 3, the horizontal steel support should be removed, and then backfilling should continue. Finally, the sheet piles 2 should be removed. The gaps after the sheet piles 2 are removed should be grouted to restore the stratum structure and avoid stratum loss.

[0031] This embodiment utilizes the synergistic combination of sheet piles 2 and MJS all-round high-pressure jet grouting to construct an effective closed area within the confined space affected by the existing pipeline 1. This solves the problem of support and closure of the foundation pit under the interference of the existing pipeline, significantly improves the seepage prevention performance of the foundation pit sidewall and the stability of the foundation pit, and provides a safe and reliable construction space for the replacement of old pipelines.

[0032] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A combined foundation pit support method for partial renovation of existing urban pipelines, characterized in that, In confined spaces where existing pipeline interference prevents conventional support from forming a continuous closed system, a combination of sheet pile support and MJS all-around high-pressure jet grouting is used. The sheet piles provide longitudinal and lateral support, while the MJS grouting provides bottom and end sealing, collaboratively constructing an effective closed area. This includes the following steps: Step S1, Survey and Positioning: Conduct on-site surveys based on the existing pipeline drawings to verify the actual location and burial depth of the existing pipelines and determine the construction location of the retaining piles; Step S2, Surface treatment: Remove the existing road or soil layer in the area to be excavated, and excavate to the steel sheet pile construction working surface; Step S3, steel sheet pile construction: steel sheet piles are driven on both sides of the existing pipeline longitudinally to the design elevation, and steel sheet piles are driven transversely at both ends of the existing pipeline to the top of the existing pipeline without affecting the height of the existing pipeline, so that the longitudinal sides and both ends of the existing pipeline form a retaining structure, and the transverse steel sheet piles at both ends maintain a safe distance from the existing pipeline. Step S4, MJS grouting reinforcement: The all-round high-pressure jet grouting method is adopted to grout and reinforce the soil at the bottom of the foundation pit and the soil between the transverse steel sheet piles at both ends of the existing pipeline and the existing pipeline, so that the gap between the bottom and both ends of the foundation pit and the existing pipeline is reinforced and filled, forming an effective closed area together with the retaining structure. Step S5, layered excavation: First, construct the horizontal steel walers. After the horizontal steel walers are installed and form a stable system, excavate the lower soil layer in layers to ensure that the support is provided before excavation. Step S6, Pipeline construction: Replace or construct pipelines within the effective closed area; Step S7, backfilling the foundation pit: backfill layer by layer, finally remove the sheet piles, and grout the gaps after the sheet piles are removed to restore the ground structure.

2. The combined foundation pit support method for partial renovation of existing urban pipelines according to claim 1, characterized in that, In step S3, the transverse sheet piles at both ends are driven to 300mm~500mm above the top of the existing pipeline, so as to achieve end enclosure closure while avoiding the existing pipeline.

3. The combined foundation pit support method for partial renovation of existing urban pipelines according to claim 1 or 2, characterized in that, In step S3, the sheet piles are connected with small toothed joints, and special corner sheet piles are used at the corners.

4. The combined foundation pit support method for partial renovation of existing urban pipelines according to claim 1, characterized in that, In step S4, the all-round high-pressure jet grouting method uses an ultra-high pressure jet of about 40MPa to form a reinforced pile with a diameter of about 2.5m, so as to effectively reinforce and fill the soil gaps at the bottom and ends of the pit that cannot be directly protected by steel sheet piles.

5. The combined foundation pit support method for partial renovation of existing urban pipelines according to claim 1, characterized in that, In step S5, the horizontal steel waler is constructed by trenching.

6. The combined foundation pit support method for partial renovation of existing urban pipelines according to claim 1, characterized in that, In step S7, during backfilling layer by layer, the horizontal steel waler is removed when backfilling reaches its position, and then backfilling continues.

7. The combined foundation pit support method for partial renovation of existing urban pipelines according to claim 1 or 6, characterized in that, In step S7, the gaps after the sheet piles are removed are filled with grout.

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