A retaining construction method of cement-soil mixing pile combined with light well point dewatering

Abstract

The application discloses a retaining construction method of cement-soil mixing pile combined with light well-point dewatering, which improves the independent construction of cement-soil mixing pile construction and light well-point dewatering into an integrated process flow of interpenetrating construction, sequentially comprising dam body part pre-dewatering, cement-soil mixing pile construction, internal dewatering of a foundation pit, secondary dewatering around the pile body and earthwork excavation. The dam body part pre-dewatering before construction reduces the free water content of the dam body and the wall toe part, accelerates the cement hydration reaction and compresses the dam body strength age; after construction, the original dewatering pipe is used for secondary dewatering inside the pile body and continues until the main structure is capped, so that the water level rise is prevented from causing the soil uplift and the uneven settlement of the building. The application improves the dam body strength, enhances the anti-overturning stability, is beneficial to the early earthwork excavation, shortens the overall construction period, and the secondary dewatering uses the original facilities, thus being good in economy.

Description

Technical Field

[0001] This invention relates to the field of building engineering technology, specifically to a retaining construction method that combines cement-soil mixing piles with lightweight wellpoint dewatering. Background Technology

[0002] In industrial plant and soft soil foundation pit support projects, cement-soil mixing piles are widely used as retaining structures for foundation pits due to their advantages such as simple construction, soil and water retention, and good economy. Especially in soft soil areas, where the foundation soil has high water content and high compressibility, cement-soil mixing piles can effectively form continuous water-stop curtains and gravity retaining walls, making them one of the preferred solutions for shallow foundation pit support.

[0003] However, engineering practice in soft soil areas shows that the strength and stability of cement-soil mixing pile dams are closely related to the soil moisture content. In conventional construction processes, cement-soil mixing pile construction and lightweight wellpoint dewatering are usually carried out as two independent procedures: large-scale dewatering is conducted first, and mixing pile construction is carried out after the water level meets the requirements. After construction is completed, dewatering is stopped, and the foundation pit is excavated only after the dam body has cured to the design strength. This independent construction mode has the following technical drawbacks: First, during the construction of cement-soil mixing piles, if the soil in the dam area is still saturated with water, the cement slurry will mix with the soil with high water content after injection. The free water content of the dam will be too high, making it difficult for the cement hydrolysis and hydration products to fully react with the soil. This will result in a slow increase in the strength of the dam and a longer age required to reach the design strength, which will in turn delay the subsequent earthwork excavation time.

[0004] Secondly, during dewatering in soft soil areas, the flow of groundwater and the high moisture content in the soil significantly affect the strength and stability of cement-soil mixing piles. It is particularly noteworthy that when the dam body becomes unstable, its center of rotation is not at the toe of the wall. If only conventional dewatering is carried out inside the foundation pit without targeted pre-dewatering of the dam body and toe, the soil at the toe will remain saturated, resulting in insufficient strength of the mixing piles in that area and creating a hidden weak zone in terms of overturning stability.

[0005] Third, if dewatering is stopped immediately after the cement-soil mixing piles have reached their design strength, the soil will rise as the water level gradually returns to its original height. Meanwhile, the load on the main structure continues to increase, and the combined effect of soil rise and increased load will amplify the risk of uneven settlement of the building.

[0006] While existing technologies include the separate application of cement-soil mixing pile construction methods and lightweight wellpoint dewatering methods, no technical solution has yet been found to integrate the two into a unified process. In particular, there is a lack of technical means to coordinate and control the pre-dewatering of the dam body, the dewatering inside the foundation pit, and the secondary dewatering around the pile body in stages, regions, and time sequences. Summary of the Invention

[0007] The purpose of this invention is to provide a construction method for a retaining system that combines cement-soil mixing piles with lightweight wellpoint dewatering. This method improves the construction of cement-soil mixing piles and lightweight wellpoint dewatering from independent construction to an integrated process of overlapping construction. The process includes, in sequence, pre-dewatering of the dam body, cement-soil mixing pile construction, dewatering inside the foundation pit, secondary dewatering around the pile body, and earthwork excavation. Pre-dewatering before construction reduces the free water content of the dam body to accelerate cement hydration, and secondary dewatering after construction prevents the water level from rising and causing the soil to lift, thereby improving the strength of the dam body and enhancing its anti-overturning stability.

[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A construction method for a retaining system combining cement-soil mixing piles and lightweight wellpoint dewatering is disclosed. This method transforms the independent construction of cement-soil mixing piles and lightweight wellpoint dewatering into an integrated process of simultaneous construction. The process sequentially includes pre-dewatering of the dam body, cement-soil mixing pile construction, dewatering inside the foundation pit, secondary dewatering around the piles, and earthwork excavation. Pre-dewatering reduces the free water content of the dam body to accelerate cement hydration, and secondary dewatering prevents soil uplift caused by water level rise, thereby improving dam strength and enhancing overturning stability. The construction method includes the following steps: Before the construction of cement-soil mixing piles, dewatering is carried out on the inner side of the dam body to lower the water level below the foundation pit elevation, so that the soil of the dam body and the toe of the wall is constructed under dewatering conditions, thereby reducing the free water content of the dam body and reducing the risk of dam instability. After the water level drops, cement-soil mixing piles are constructed at the dam site to mix the cement slurry with the soil with low water content, accelerate the reaction of cement hydrolysis and hydration products with the soil, and compress the dam body to reach the required age for the design strength. Dewatering was carried out inside the foundation pit to bring the water level inside the pit up to the design height required before earthwork excavation. After the cement-soil mixing piles reach their designed strength and before earthwork excavation, secondary dewatering is carried out around the piles at the original dewatering pipe locations inside the pile bodies, and dewatering continues until the main structure is capped, in order to prevent uneven settlement of the building caused by soil lifting during the water level rise.

[0009] Preferably, during dewatering of the pile section, the water level drops to a certain height below the foundation pit elevation to ensure that the soil at the toe of the foundation pit wall has been dewatered before the pile construction.

[0010] Preferably, the dewatering step inside the foundation pit is selected based on the area inside the foundation pit. If the area of ​​the foundation pit is small and the water level in the foundation pit has reached the design height required before earthwork excavation during the dewatering process, this step is omitted.

[0011] Preferably, the secondary dewatering around the pile body is carried out using the existing dewatering pipes laid during the dewatering construction of the pile body.

[0012] Preferably, during the construction of the cement-soil mixing pile, the cement content is determined by observing the gloss of the cement slurry, so as to control the construction quality of the cement-soil mixing pile.

[0013] Preferably, earthwork excavation is carried out after the cement-soil mixing piles have reached their design strength.

[0014] Compared with the prior art, the present invention has the following advantages: 1. Interleaved construction to shorten the construction period. The construction of cement-soil mixing piles and lightweight wellpoint dewatering is changed from independent construction to an integrated process of interleaved construction. Pre-dewatering before construction creates conditions for the construction of mixing piles, and secondary dewatering is used to maintain water level control after the construction of mixing piles is completed. The close connection between each process can shorten the curing period of cement-soil mixing piles, which is conducive to the early excavation of earthwork, thereby shortening the overall construction period of the project.

[0015] 2. Pre-watering accelerates hydration and improves dam strength. Targeted pre-watering is carried out on the dam body and toe areas before the construction of the mixing piles. This effectively reduces the free water content of the dam body, allowing the cement slurry to mix with the low-moisture soil. The cement hydrolysis and hydration products react with the soil earlier, accelerating the increase in dam strength. Furthermore, the reduction of excess saturated free water in the gaps between the dam body skeletons improves the stability of the dam body.

[0016] 3. Dewatering at the toe enhances overturning stability. Dewatering at the pile body ensures that the soil at the toe has been fully dewatered, eliminating the weak areas formed at the toe due to insufficient dewatering in traditional construction, and thus enhancing the overall overturning stability of the cement-soil mixing pile dam.

[0017] 4. Secondary dewatering prevents soil uplift and avoids uneven settlement. Secondary dewatering is carried out after the mixing piles reach the design strength and before earthwork excavation, and continues until the main structure is capped. This effectively prevents soil uplift during water level rise and avoids the risk of uneven settlement caused by the combined effect of soil uplift and increased load on the main structure.

[0018] 5. Utilize existing dewatering pipes to control costs. Secondary dewatering construction directly utilizes the existing dewatering pipes laid during the pre-dewatering of the pile body, eliminating the need to re-lay dewatering facilities. This avoids significant fluctuations in the project budget and is economical.

[0019] 6. Simple process and controllable quality. The construction process of cement-soil mixing piles is mature. On-site, the cement content can be judged by observing the gloss of the cement slurry. Based on random checks, the construction quality can be further guaranteed. The operation is simple and highly reliable. Attached Figure Description

[0020] Figure 1 This is an integrated construction process flow diagram of the present invention, which shows the sequential relationship between the construction of dewatering at the pile body, cement-soil mixing pile construction, dewatering inside the foundation pit, secondary dewatering around the pile body, and earthwork excavation. Detailed Implementation

[0021] 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, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0022] Step 1: Construction site preparation and surveying / layout After the construction site is leveled, the location of the dam body is measured and laid out according to the design drawings to clarify the construction scope of the cement-soil mixing piles and the location of the dewatering wells.

[0023] Step 2: Dewatering at the pile location First, dewatering is carried out at the pile body. In soft soil areas, the sedimentary soil below the water level is saturated with water. If targeted pre-dewatering is not carried out, the cement slurry injected during the construction of cement-soil mixing piles will mix with the high-water-content soil, resulting in an excessively high free water content in the dam body, which will seriously affect the cement hydration reaction and the development of dam strength.

[0024] Specifically, dewatering is carried out on the inner side of the dam body to lower the water level to a certain height below the foundation pit elevation. It is particularly important to ensure that the soil at the toe of the foundation pit wall has been dewatered before the pile construction, and the water level drop should cover the toe area. This is because, in the event of dam instability, the center of rotation is not at the toe, but the toe remains a critical area for overturning stability. If the soil in this area is not adequately dewatered, it will create a weak point, reducing the overall stability of the dam.

[0025] Once the water level drops to the designed height, dewatering will cease, and preparations will begin for cement-soil mixing pile construction.

[0026] Step 3: Construction of Cement-Soil Mixing Piles Cement-soil mixing piles were constructed at the dam site after dewatering. Because the pre-dewatering effectively reduced the moisture content of the soil in the dam area, the free water content of the dam body was greatly reduced after the cement slurry was mixed with the low-moisture soil. The cement hydrolysis and hydration products could react with the soil earlier, thereby compressing the dam body to reach the required age for design strength.

[0027] During construction, the design drawings and specifications must be strictly followed. During the mixing of the cement slurry, the gloss of the slurry will gradually increase as the cement content increases. In addition to random quality checks, the gloss of the cement slurry can be observed during on-site construction to help determine its cement content, thereby ensuring the construction quality of the cement-soil mixing piles to a greater extent.

[0028] Step 4: Dewatering inside the foundation pit After the cement-soil mixing pile construction is completed, it is determined whether separate dewatering of the pit is required based on the internal area and water level of the foundation pit.

[0029] If the area inside the foundation pit is large and the water level inside the foundation pit cannot meet the design requirements during the dewatering process at the dam site, then dewatering will be carried out again inside the foundation pit to bring the water level inside the foundation pit up to the design requirements before earthwork excavation, thus providing conditions for earthwork excavation.

[0030] If the area of ​​the foundation pit is small and the water level in the foundation pit has reached the design height required before earthwork excavation during the dewatering process of the dam body, this step can be omitted to reduce the amount of dewatering work.

[0031] Step 5: Secondary dewatering around the pile After the cement-soil mixing piles reach their design strength, secondary dewatering should be carried out at the locations of the existing dewatering pipes inside the pile bodies before earthwork excavation. This secondary dewatering must continue until the main structure is capped.

[0032] The purpose of secondary precipitation is to prevent water levels from rising. Without continuous precipitation, as the water level gradually rises back to its original height, the soil will experience uplift. Meanwhile, the load on the main structure is constantly increasing. The combined effect of soil uplift and increased load will increase the risk of uneven settlement of the building. Secondary precipitation effectively mitigates this risk by keeping the water level continuously below the design height.

[0033] It should be noted that the secondary dewatering directly utilizes the existing dewatering pipes laid during the dewatering construction of the pile body in step two, without the need to re-lay dewatering facilities, and will not cause too much fluctuation in the project budget.

[0034] Step Six: Earthwork Excavation After the cement-soil mixing piles reach their design strength and the water level inside the foundation pit meets the excavation requirements, earthwork excavation will commence. Because the interleaved construction process compresses the curing period of the cement-soil mixing piles, earthwork excavation can be carried out earlier, which helps to shorten the overall project duration.

[0035] 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 retaining wall construction method combining cement-soil mixing piles and lightweight wellpoint dewatering, characterized in that, The construction process of cement-soil mixing piles and lightweight wellpoint dewatering has been improved from independent construction to an integrated process of simultaneous construction. This process includes, in sequence, pre-dewatering of the dam body, cement-soil mixing pile construction, dewatering inside the foundation pit, secondary dewatering around the piles, and earthwork excavation. Pre-dewatering reduces the free water content of the dam body to accelerate cement hydration, and secondary dewatering after construction prevents water level rise and soil uplift, thereby improving the dam's strength and enhancing its anti-overturning stability. The construction method includes the following steps: Before the construction of cement-soil mixing piles, dewatering is carried out on the inner side of the dam body to lower the water level below the foundation pit elevation, so that the soil of the dam body and the toe of the wall is constructed under dewatering conditions, thereby reducing the free water content of the dam body and reducing the risk of dam instability. After the water level drops, cement-soil mixing piles are constructed at the dam site to mix the cement slurry with the soil with low water content, accelerate the reaction of cement hydrolysis and hydration products with the soil, and compress the dam body to reach the required age for the design strength. Dewatering was carried out inside the foundation pit to bring the water level inside the pit up to the design height required before earthwork excavation. After the cement-soil mixing piles reach their designed strength and before earthwork excavation, secondary dewatering is carried out around the piles at the original dewatering pipe locations inside the pile bodies, and dewatering continues until the main structure is capped, in order to prevent uneven settlement of the building caused by soil lifting during the water level rise.

2. The retaining wall construction method of cement-soil mixing piles combined with lightweight wellpoint dewatering as described in claim 1, characterized in that, When the pile body is dewatered, the water level is lowered to a certain height below the foundation pit elevation to ensure that the soil at the toe of the foundation pit wall has been dewatered before the pile body construction.

3. The retaining wall construction method of cement-soil mixing piles combined with lightweight wellpoint dewatering as described in claim 1, characterized in that, The dewatering step inside the foundation pit is selected based on the area inside the foundation pit. If the area of ​​the foundation pit is small and the water level in the foundation pit has reached the design height required before earthwork excavation during the dewatering process, this step can be omitted.

4. The retaining wall construction method of cement-soil mixing piles combined with lightweight wellpoint dewatering as described in claim 1, characterized in that, The secondary dewatering around the pile body is carried out using the existing dewatering pipes laid during the dewatering construction of the pile body.

5. The retaining wall construction method of cement-soil mixing piles combined with lightweight wellpoint dewatering as described in claim 1, characterized in that, During the construction of the cement-soil mixing piles, the cement content is determined by observing the gloss of the cement slurry in order to control the construction quality of the cement-soil mixing piles.

6. The retaining wall construction method of cement-soil mixing piles combined with lightweight wellpoint dewatering as described in claim 1, characterized in that, After the cement-soil mixing piles reach their designed strength, earthwork excavation will commence.

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