Method for rainwater and sewage diversion of soft soil foundation

Abstract

The present application relates to the technical field of urban drainage pipe network reconstruction engineering, in particular to a reconstruction method for rain and sewage separation of soft soil foundation, which is implemented in a way of simultaneous implementation of sewage channel cofferdam flow guiding and soft soil foundation pit excavation construction. The cofferdam of the present application can be quickly constructed in the sewage channel, and has simple and practical structure, easy construction, and higher stability compared with existing soil cofferdam or soil-rock cofferdam. In the process of foundation pit excavation, the supporting structure of cement mixing pile combined with high-pressure rotary jet pile can avoid adverse phenomena such as sidewall sand flow, pipe gushing at pit bottom, large deformation of foundation pit, and large stress on pile body in excavation engineering, and is convenient for construction machinery to work above the foundation pit. The simultaneous implementation of sewage channel cofferdam flow guiding and soft soil foundation pit excavation significantly shortens the construction period of rain and sewage separation reconstruction.

Description

Technical Field

[0001] This invention relates to the field of urban drainage network renovation engineering technology, specifically a method for rainwater and sewage separation renovation on soft soil foundations. Background Technology

[0002] my country's urban drainage systems mainly consist of three types: combined sewer systems, intercepted combined sewer systems, and separate sewer systems. Currently, most old urban areas in my country use combined sewer systems, where untreated rainwater and sewage are directly discharged into water bodies, causing serious pollution. Alternatively, the discharge of mixed rainwater and sewage into sewage treatment plants increases the impact load on these plants, severely disrupting their stable operation. Therefore, once conditions permit, it is necessary to implement rainwater and sewage separation upgrades to urban combined sewer systems.

[0003] Existing stormwater and sewage separation renovation projects require systematic dredging of the municipal combined sewer network and the establishment of new separation channels. Since these projects are often located in densely populated urban areas and commercial districts, construction causes significant inconvenience to surrounding residents. Particularly in areas with complex foundation conditions, landslides are prone to occur during excavation, with landslide thrust often exceeding the maximum allowable horizontal thrust of the existing support structure. This leads to foundation pit deformation, further extending the construction workload and timeline, and exacerbating the living and transportation difficulties of nearby residents. Therefore, a stormwater and sewage separation renovation method suitable for soft soil foundations is urgently needed. Summary of the Invention

[0004] To address the issues of large engineering workload and long construction period in the renovation of drainage pipe networks for soft soil foundations, this invention proposes a method for the renovation of rainwater and sewage separation in soft soil foundations.

[0005] The present invention relates to a method for renovating soft soil foundations by separating rainwater and sewage, characterized in that the method is implemented by simultaneously carrying out the construction of sewage channel cofferdam diversion and soft soil foundation pit excavation:

[0006] The steps for diverting the sewage ditch using a cofferdam are as follows: Steel grating is fixed to the bottom of the sewage ditch using bolts; soil bags are placed in front of the steel grating to form a water-stop layer. Once the soil bags are compacted, the sewage ditch is cut off. During construction, a diversion pipe needs to be installed upstream of the cofferdam to connect with the downstream section, preventing sewage from overflowing into the sewage ditch during the rainwater and sewage separation process; after the sewage downstream of the grating is drained, a brick wall is constructed, and the cohesive soil at the bottom of the brick wall is transferred. After the brick wall is completed, final water isolation is achieved, and observation is conducted through observation wells to avoid the risk of significant seepage during construction; after waterproofing the brick wall on the water-facing side, cohesive soil is finally filled between the brick wall and the steel grating to form the cofferdam; after the cofferdam is formed, a pipe jacking inverted siphon technique is used to divert the original sewage ditch.

[0007] The excavation steps for the soft soil foundation pit are as follows: Cement mixing piles are used as water-stopping piles, arranged closely to form a cement mixing wall. A shotcrete surface layer is installed on the corresponding inner side of the cement mixing wall, with a steel mesh embedded within it. H-beams are inserted into the cement mixing wall, with a central circular hole drilled in the web of the beam from the top. Reinforcing steel plates are welded to both sides of the beam, with the center of the hole in the reinforcing steel plate aligned with the center of the hole in the beam. After excavating the foundation pit, a capping beam is poured. Horizontal steel supports are installed between the capping beams. After the foundation pit excavation is completed, high-pressure jet grouting piles are installed at the bottom of the pit, ultimately forming the foundation pit support. Several drainage pipes are installed within the foundation pit for rainwater and sewage separation, connecting to the sewage system and rainwater system upstream of the drainage ditch, completing the rainwater and sewage separation modification. Finally, the foundation pit is backfilled with earth.

[0008] The cofferdam of this invention can be quickly constructed within the sewage ditch. It is simple, practical, and easy to construct, and the resulting cofferdam exhibits higher stability compared to existing earthen or earth-rock cofferdams. During the excavation of the foundation pit, a support structure combining cement mixing piles and high-pressure jet grouting piles is used, which avoids adverse phenomena such as sidewall sand flow, bottom piping, large foundation pit deformation, and excessive pile stress during excavation. This also facilitates the operation of construction machinery above the foundation pit. The simultaneous implementation of the sewage ditch cofferdam diversion and soft soil foundation pit excavation significantly shortens the construction period for the rainwater and sewage separation renovation project. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of the cofferdam structure used in this invention.

[0010] Figure 2 This is a schematic diagram of the foundation pit support structure used in this invention.

[0011] Among them, steel grating 1, soil bags 2, brick wall group 3, cohesive soil 4, cement mixing wall 5, shotcrete surface layer 6, capping beam 7, horizontal steel support 8, high-pressure jet grouting pile 9, H-beam 10, steel plate 11. Detailed Implementation

[0012] Example 1: To further accelerate the improvement of urban sewage collection and treatment facilities, achieve full coverage of sewage pipe networks as soon as possible, and realize the goal of full collection and treatment of domestic sewage, thereby achieving long-term cleanliness of urban black and odorous water bodies and changing the current situation of mixed rainwater and sewage flow in a certain area, it is necessary to carry out rainwater and sewage separation renovation. The specific construction method adopts a scheme of simultaneous diversion of sewage channels with cofferdams and excavation of soft soil foundation pits, as follows:

[0013] The steps for diverting the sewage ditch using a cofferdam are as follows: Steel grating is fixed to the bottom of the sewage ditch using bolts; soil bags are placed in front of the steel grating to form a water-stop layer. Once the soil bags are compacted, the sewage ditch is cut off. During construction, a diversion pipe needs to be installed upstream of the cofferdam to connect with the downstream section, preventing sewage from overflowing into the sewage ditch during the rainwater and sewage separation process; after the sewage downstream of the grating is drained, a brick wall is constructed, 1.5m high, using red bricks and 75# cement mortar. Simultaneously, the cohesive soil at the bottom of the brick wall is removed. After the brick wall is completed, it achieves final water isolation, and observation is conducted through observation wells to avoid the risk of significant seepage during construction; the water-facing side of the brick wall is plastered with a 20mm thick layer of 1:2 cement mortar, with the mortar used for jointing on the water-facing side. The water-facing side is also waterproofed. Finally, cohesive soil is filled between the brick wall and the steel grating to form the cofferdam; after the cofferdam is formed, a pipe jacking inverted siphon technique is used to divert the original sewage ditch.

[0014] The excavation steps for the soft soil foundation pit are as follows: Cement mixing piles are set on both sides of the foundation pit, and several cement mixing piles are closely arranged to form a cement mixing wall. A shotcrete surface layer is set on the inner side of the cement mixing wall, and a capping beam is set on the top of the cement mixing wall along the length of the cement mixing piles; horizontal steel supports are set between the capping beams on both sides; high-pressure jet grouting piles are set at the bottom of the foundation pit. H-beams are inserted into the cement-soil mixing wall. Reinforcing steel plates are welded to both sides of the web of the H-beam at 30cm from the top. Corresponding circular holes are opened in the center of the web and the center of the reinforcing steel plate. The top of the H-beam is higher than the capping beam; steel plates are laid on the H-beams, and the H-beams are welded to the steel plates to support the engineering machinery for excavation and dredging operations above the foundation pit. In the later stage of the project, the welded positions of the H-beams and steel plates are cut, the steel plates are removed, and the H-beams are pulled out using hoisting machinery and filled with cement grout to fill the gaps.

[0015] The parameters selected in this embodiment are merely preferred embodiments of the present invention. Any technical features adopted from the content of the invention should fall within the protection scope of the present invention.

Claims

1. A method for reconstructing rainwater and sewage separation of a soft ground foundation, characterized by The method is implemented by the way of simultaneous implementation of the diversion of the sewage channel cofferdam and the soft soil foundation pit excavation construction: The diversion of the sewage channel cofferdam is as follows: the steel grating plate is fixed to the bottom of the sewage channel by planting bolts; the soil bags are placed in front of the steel grating plate to form a water stop layer; when the soil bags are densely stacked, the sewage channel is cut off; during the construction, a diversion pipeline is arranged on the upstream of the cofferdam and connected to the downstream to avoid sewage overflow from the sewage channel during the rainwater and sewage diversion reconstruction; after the sewage downstream of the grating plate is drained, the brick wall group is built, and the cohesive soil at the bottom of the brick wall group is transferred; after the completion of the brick wall group, the final water stop is realized, and the observation is carried out through the observation well to avoid the risk of large water seepage during the construction; after the waterproof treatment of the brick wall on the water side, the cohesive soil is finally filled between the brick wall group and the steel grating plate to finally form the cofferdam; after the cofferdam is formed, the pipe jacking inverted siphon technology is used to guide the original sewage channel; The soft soil foundation pit excavation is as follows: the water stop pile is made of cement mixing pile, the cement mixing piles are closely arranged to form a cement mixing wall, a sprayed concrete surface layer is arranged on the corresponding inner side of the cement mixing wall, and a steel mesh is arranged in the sprayed concrete surface layer; the H-shaped steel is inserted into the cement mixing wall, the center circular hole is opened at the top web of the steel, and the reinforcing steel plates are welded on both sides of the steel; the center holes of the reinforcing steel plates are aligned with the center holes of the steel; after the excavation of the foundation pit, the crown beam is poured; the horizontal steel support is arranged between the crown beams; after the completion of the foundation pit excavation, the high-pressure rotary jet pile is buried at the bottom of the foundation pit; finally, the foundation pit support is formed; a plurality of drainage pipelines are arranged in the foundation pit for rainwater and sewage diversion, the drainage pipelines are respectively connected to the upstream sewage system and the rainwater system of the sewage channel, and the rainwater and sewage diversion reconstruction is completed; finally, the earthwork of the foundation pit is backfilled.

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