Foundation Pit Dewatering Research Articles

Barrier Effect of Existing Building Pile on the Responses of Groundwater and Soil During Foundation Pit Dewatering

In regions with abundant groundwater resources, pre-excavation dewatering on deep foundation pits often leads to the deformation of the enclosure wall and settlement of the surrounding ground. Based on a series of engineering measurements, we conducted a series of numerical simulations to investigate the behaviors of wall and soil during pre-excavation dewatering with and without the existing pile foundations and under different distances between the existing pile foundations and foundation pits (D). Numerical results indicated that when the foundation pit is adjacent to existing building pile foundations, the soil was restricted by the pile foundations (i.e., soil-blocking effect). When D ≤ 40 m, the soil-blocking effect grows stronger as D gets smaller; while when D > 40 m, the soil-blocking effect is significantly weakened and the water-blocking effect (i.e., the blockage of groundwater seepage by the building pile foundation) gradually appears, which intensifies the ground surface settlement. The maximum settlement position of the soil behind the pile foundation of the existing building is farther away from the foundation pit as the soil-blocking effect becomes stronger. The coupling effect of soil-blocking and water-blocking on the ground deformation should be considered in the design of the foundation pit project to get a more reasonable support and dewatering scheme.

A Study on the Influence of Dewatering in the Excavation of Adjacent Tunnels under Lateral Soil Effects

The dewatering of foundation pits leads to changes in the water level and effective stress within the surrounding strata. When existing tunnels are present within the dewatering influence zone, the impact of dewatering on these tunnels cannot be ignored. The Vlasov foundation beam model was used to simulate the interaction between the tunnel and the soil, and the key parameters of the model were precisely investigated. In addition, the constraining effect of the lateral soil on the tunnel was also considered. By integrating the principles of effective stress and Dupuit’s assumption, in this work we calculated the additional load on the tunnel caused by foundation pit dewatering, which was then applied to determine the tunnel stress and deformation induced by dewatering. The accuracy of this approach is validated through comparative analysis with finite element results. Furthermore, the relationships between the permeability coefficient (kt), the spacing (d) between the tunnel and the dewatering well, the water level drop (sw), and tunnel stress and deformation were further studied. The key findings are summarized as follows. Firstly, accounting for lateral soil effects enhances computational accuracy. Secondly, an increase in soil kt leads to a greater tunnel settlement with relatively minor changes in bending moments. Thirdly, as d increases, both tunnel settlements and bending moments decrease. Additionally, as the water level dropped from 10 m to 30 m, the maximum additional stress on the tunnel increased by 94.50%, and the settlement increased by 127.43%. Consequently, it is essential to pay close attention to the tunnel segment nearest to the water level.

Numerical Simulation of Artificial Recharge Groundwater Effect on Overlying Soft Clay Compression Control

Soil deformation is prone to occur in the process of the foundation pit dewatering. A large number of metro existing tunnels are located in soft soil layers. The compression of soft soil poses a threat to metro existing tunnels. Previously, plenty of research on foundation pit dewatering is focused on the hydraulic head and deformation characteristics of the aquifer. However, the law of water releasing and compression deformation of overlying soft soil has not been taken seriously. In order to study the artificial recharge groundwater effect on overlying soft clay, a three-dimensional seepage–soil deformation coupling numerical model was established. The theoretical basis of the model is Darcy’s law and the principle of effective stress. A foundation pit located in Nanjing, China was selected as an example. The numerical model was used to simulate the hydraulic head and soil deformation caused by foundation pit dewatering and artificial recharge groundwater outside. The result shows that, due to the difference of hydraulic head between the aquifer and the aquitard reducing, it also has a good control effect on the deformation of the soft soil by recharging water into the aquifer. The location of recharge wells around the metro existing tunnel can control the soil deformation effectively, which could help to reduce the impact on the metro existing tunnel.

Research on Multi-Objective Optimization Model of Foundation Pit Dewatering Based on NSGA-II Algorithm

This study focuses on optimizing the foundation pit dewatering scheme using the foundation pit dewatering theory and the principles of multi-objective optimization. It explores the development of a multi-objective optimization model and efficient solution technology for foundation pit dewatering. This research focuses on the foundation pit dewatering project at the inverted siphon section of Xixiayuan canal head, specifically from pile number XZ0+326 to XZ0+500. It establishes an optimized mathematical model for foundation pit dewatering that incorporates three objectives. Additionally, a dewatering optimization program is developed by utilizing the MATLAB optimization toolbox and the multi-objective optimization algorithm program based on the NSGA-II algorithm (Gamultiobj). The multi-objective optimization mathematical model is solved, and a Pareto-optimal solution set with uniform distribution is obtained. The multi-objective optimization evaluation system based on AHP is constructed from the three aspects of dewatering cost, the impact of settlement on the environment, and the safety and stability of the foundation pit. The optimization scheme of the Pareto-optimal solution set is selected as the decision result to provide multiple feasible schemes for the dewatering construction of foundation pits. The optimization scheme is verified by using the GMS software. The simulation results demonstrate that the optimization scheme fulfills the requirements for water level and settlement control. Moreover, the developed optimization program efficiently solves the multi-objective optimization problem associated with foundation pit dewatering. Lastly, an evaluation system incorporating the NSGA-II algorithm and AHP is developed and utilized in the context of dewatering engineering in order to offer multiple viable optimal dewatering schemes.

Field Experiments on 3D Groundwater Flow Patterns in the Deep Excavation of Gravel-Confined Aquifers in Ancient Riverbed Areas

In ancient riverbed areas, the hydro-geological conditions are extremely complex because of the cutting of ancient river channels during the sedimentary process. How to lower groundwater level in water-riched gravel-confined aquifer during deep excavation is vital for underground engineering. Groundwater flow patterns had to be understood during foundation pit dewatering. This paper presents a field case study conducted at the deep foundation pit of the Qianjiang Century City station on Hangzhou Metro Line 6, which is notable for its 52 m deep unclosed waterproof curtain. A total of 34 pumping wells were installed within the pit. During the tests, one well was subjected to a pumping well, while the others served as observation wells. The research included two sets of multi-depth pumping tests, which differed in terms of their filter lengths, aimed at investigating the flow pattern around pump wells and the roots of diaphragm walls. The study found that the use of longer filters, higher pump rates, and filters placed nearer to aquifer roofs enhances dewatering efficiency and minimizes impact on the surrounding geological environment. This paper introduces a novel concept known as the diaphragm wall–pumping well effect, which regulates the water head outside the pit and the subsidence, thereby optimizing the drawdown of the deep foundation pit with an unclosed waterproof curtain. The findings were applied in the foundation pit dewatering of Qianjiang Century City station, and the drawdown in and outside the pit was effectively controlled.

Numerical Simulation of Foundation Pit Dewatering Based on FEFLOW-taking Pumping Station a as an Example

Numerical Simulation of Foundation Pit Dewatering Based on FEFLOW-taking Pumping Station a as an Example

Experimental Study on Groundwater Dewatering and Recharge of Deep Foundation Pit of a Subway Station in Jinan Water-Rich Area

A large amount of groundwater dewatering is beneficial to the foundation pit construction, but it will cause surface collapse, waste groundwater resources and damage the groundwater environment. In order to maintain the stability of groundwater level and the safety of surrounding buildings in the construction of deep foundation pit, the combination of dewatering and recharge is adopted. Taking the construction of deep foundation pit of a subway station in Jinan water-rich area as an example, the theoretical model of recharge quantity, stratum parameters and groundwater level was obtained through the backward derivation of the precipitation calculation model. 78 dewatering wells and 78 recharge wells were designed, and the on-site dewatering and recharge teat was carried out. The test results show that the water level of a single dewatering well decreases sharply in the initial stage of precipitation, and then the depth drops gradually to a stable level, and finally maintains a fixed value. The water inflow of a single well ranges from 34.54~57.07 m³/d, and the groundwater level can be lowered to 1.53~2.79 m below the foundation pit floor. The recharge volume of a single well in the natural recharge state is 146.88~ 241.44 m3/d, and the higher the recharge pressure, the stronger the recharge capacity of the recharge well. Through field test research, it is found that the recharge capacity of single well of recharge well is much greater than the pumping capacity of single well of dewatering well, and 56 recharge wells can make the recharge rate reach 100%, which optimizes the dewatering and recharge design of deep foundation pit.

Numerical Simulation and Analysis of the Influencing Factors of Foundation Pit Dewatering under a Coupled Radial Well and Curtain

It is crucial to use a suitable dewatering technique to prevent land subsidence and substantial decreases in groundwater levels caused by the dewatering of groundwater during the construction of underground projects. Therefore, in this study, a generalized three-dimensional numerical model of groundwater flow was implemented for an underground station pit project. The dewatering efficiency of the coupled radial well-curtain method was investigated and compared with that of a traditional method. In addition, the influence of different structures and parameters (radial pipe diameter, conductance, number of radial pipes, and shaft drawdown) on the dewatering efficiency was assessed. The results showed the following: (1) radial wells caused less disturbance to the groundwater seepage field and extracted less groundwater during the dewatering process compared with pumping wells; (2) the structure and parameters of the radial wells positively correlated with the dewatering efficiency; (3) the curtain improved the dewatering efficiency, resulting in lower amounts of groundwater discharged and less disturbance to the groundwater flow field; and (4) the coupled radial well-curtain method is an efficient dewatering method that could effectively prevent the lowering of groundwater level outside the foundation pit, thus reducing the risk of land subsidence in the surrounding area.

Research on the Control of Excavation Deformation of Super Deep Foundation Pit Adjacent to the Existing Old Masonry Structure Building

In order to ensure the safety and stability of the existing old masonry structure houses in the process of dewatering and excavation of the super deep foundation pit of the subway, the support form of a water stop curtain combined with bored cast-in-place piles and internal support is adopted, and the rotary jet grouting piles are constructed around the houses, and sleeve valve pipes are embedded, and the soil and house foundation are grouted and strengthened. The deformation of the building foundation is analyzed by the finite element method. The results show that the deformation of adjacent buildings is mainly uniform at the initial stage of foundation pit dewatering and excavation. With the increase of foundation pit dewatering and excavation depth, the deformation of adjacent buildings shows significant differential characteristics, and the maximum displacement of buildings is settlement deformation. The field monitoring data show that the actual deformation trend and value range of the building structure are basically consistent with the finite element calculation results, and no new damage is found in the building structure during the construction process. Effective foundation pit support method and soil layer reinforcement method can effectively reduce the impact of foundation pit on the deformation of adjacent buildings.

Research on Subsidence Induced by the Dewatering–Curtain Interaction in the Deep Foundation Pit of the Shield Launching Shaft in Shenzhen, China

The waterproof curtain plays an important role in the dewatering of a deep foundation pit. Recognition of the depth of the waterproof curtain inserted into the confined aquifer at different depths may help control ground subsidence due to dewatering, but subsidence analysis of the interaction between dewatering and the waterproof curtain requires further study. In this study, we mainly analyze the relationship between ground subsidence and dewatering based on the shield shaft pit of the Qianhai-Nanshan deep tunnel project in Shenzhen. Our numerical simulation results show that the ground subsidence around the foundation pit decreases with an increase in the depth of the waterproof curtain inserted into the confined aquifer, and when the waterproof curtain completely penetrates the confined aquifer, the ground subsidence caused by pit dewatering is minimal. Our numerical simulation results are consistent with the actual on-site dewatering monitoring data. Our results suggest that the diaphragm wall is an effective measure to control the ground subsidence in deep foundations, helping to reduce excessive dewatering.

Control and prevent land subsidence caused by foundation pit dewatering in a coastal lowland megacity: indicator definition, numerical simulation, and regression analysis

Land subsidence has to be controlled under global climate change and sea level rising for coastal megacities. Land subsidence caused by lowering groundwater level during underground excavation has become a dominant influence factor for land subsidence during urbanization and city renewal. How to manage the land subsidence induced by foundation pit dewatering (FPD) on an urban scale was urgent. Shanghai was selected as the research background. A subsidence and drawdown double control (SDDC) partition was established. The position of three times excavation depth (3H) horizontally away from the foundation boundary in the plane was defined as the boundary between dewatering subsidence and excavation settlement. Land subsidence of 3H (LS-3H) and groundwater drawdown on 3H (GD-3H) were defined as the evaluating and controlling indicators. An FPD conceptual model was summarized by the estimating and investigating of foundation pit information and numerical simulations were performed. A total of 6540 FPD scenarios were simulated for the LS-3H and GD-3H. Multi-factor regression analysis was conducted to obtain relations between the GD-3H and the shape, area, depth, and curtain depth of foundation pit on the basis of the numerical simulations. The regression models can be used to estimate the GD-3H and compared with the threshold specified by land subsidence prevention and control (LSPC) law, which can provide a reference for similar cases.

Numerical Simulation of Forming MICP Horizontal Seepage Reducing Body in Confined Aquifer for Deep Excavation

The drawdown outside of a deep foundation pit has to be controlled during excavation. However, the vertical curtain cannot cutoff a deep and thick confined aquifer during deep excavation. In this study, a microbial-induced carbonate precipitation (MICP) horizontal seepage reducing body (HSRB) was proposed to control drawdown combined with a partially penetrating curtain. MICP HSRB is formed by using the seepage field generated by the recharge wells to drive the migration of a Sporosarcina pasteurii solution, stationary solution, and cementation solution into the deep confined aquifer. The migration of each solution was numerically simulated to study the HSRB formation process. The influence of different factors on solute migration was studied. The results show that the solutes in the fixed fluid and cementation fluid can reach the area under the driving of the seepage field, which proves that MICP HSRB can be formed. The calcium ions and urea in the cementation solution are more likely to migrate to the designated area than the bacterial solution. Increasing the injection rate of bacterial solution and adding recharge wells both made the bacterial solution migrate more quickly to the designated area. In the case of multiple grouting, the solute migration in the later stage will be hindered by the plugging of pores caused by calcium carbonate generated in the earlier stage. Therefore, different grouting methods need to be designed to drive the seepage field so that the solute injected in the later stage can continue to migrate. The MICP HSRB grouting technology can be used in foundation pit dewatering, providing reference for similar engineering.

Zoning design of a deep and large foundation pit adjacent to the Yangtze River in Wuhan

Taking the design of a deep and large foundation pit near the Yangtze River in Wuhan as an example, combining with the complex environment around the foundation pit and considering the development sequence of the construction unit, the work scheme of "zoning design, zoning construction, supporting pile + internal support" is adopted. In order to reduce the influence of foundation pit excavation on adjacent excavation, piles with large diameter and small pile spacing are used as isolation piles. Using 90 deep dewatering Wells and cement mixing pile (local CSM) as water stop curtain, the calculation can meet the requirements of foundation pit dewatering. The existing monitoring data show that the design of the foundation pit is safe, reasonable and economical, which can provide a certain reference for similar projects.

Laboratory Experiment on Formation of MICP Horizontal Seepage-Reducing Body in Confined Aquifer for Deep Excavation

Using a soil improvement biotechnology based on microbial-induced carbonate precipitation (MICP) to form a horizontal water barrier in foundation pit dewatering can not only achieve a good dewatering control effect, but also control the cost and obtain good economic and environmental benefits. In this study, taking the Shanghai layer ⑨ sand as the research object, the solution injected into the layer ⑨ sand by MICP grouting technology includes bacterial solution (Sporosarcina pasteurii) and cementation solution (urea and CaCl2 solution). The migration mechanism of the bacterial solution and cementation solution in groundwater was analyzed through batch experiment and column test, and the mathematical model of migration was established. The dynamic adsorption characteristics of the S. pasteurii, Ca2+, and urea were obtained by dynamic adsorption test. Through isothermal adsorption test, the Freundlich isotherm was used to describe the isothermal adsorption of S. pasteurii onto fine sand, and the partition coefficient of the S. pasteurii was found to be 1.5 × 10−7 L/mg. The Langmuir isotherm can be used truly reflect the isothermal adsorption of Ca2+ onto fine sand. The distribution coefficient of the Ca2+ was 7 × 10−8 L/mg. The maximum adsorption capacity of the solute was 2404.8 mg/kg. The adsorption capacity of the urea was very small. According to the sand column test, the vertical dispersion was 11.5 cm. Due to the obvious size effect of dispersion, the sensitivity of dispersion in actual working conditions should be analyzed in a subsequent numerical simulation. The determined solute transport parameters provide support for the further study of the numerical simulation of the solute transport process of the HSRB formed by MICP grouting technology and provide a basis for further field application.

Analytical Analysis of the Groundwater Drawdown Difference Induced by Foundation Pit Dewatering with a Suspended Waterproof Curtain

The dewatering of foundation pits with a suspended waterproof curtain causes different groundwater drawdowns inside and outside the pit, resulting in the drawdown difference between the inside and outside the pit. Maintaining a groundwater drawdown difference between the inside and outside of a foundation pit can eliminate the adverse effects of dewatering on the surrounding environment. According to previous studies on unsteady flow, an analytical solution of the groundwater drawdown with a suspended waterproof curtain under unsteady flow has been proposed. The analytical solution of unsteady flow and the formula of groundwater drawdown difference with a suspended waterproof curtain were validated by comparing pumping tests and finite-element method (FEM), in which a good agreement was observed. The magnitude of the drawdown difference generally represents the extent of surrounding groundwater affected by groundwater drawdown inside the pit. This paper also investigated the effects of sensitivity parameters on the drawdown difference for minimizing the effect of surrounding environment. During the process of dewatering with a suspended waterproof curtain, the groundwater drawdown (Sh) should not exceed the length of the waterproof curtain (L), and the optimal radius of foundation pit (Rw) and length of waterproof curtain (L) were found, i.e., Rw/H0 = 0.781 and L/H0 = 0.813 (H0 is 32 m). Beyond these values, the drawdown difference tends to be stable. The drawdown difference is also significantly affected by the dewatering time. When t < 48 h, the groundwater drawdown difference decreases rapidly; when t > 48 h, the groundwater drawdown difference stabilizes.

Analysis on Key Points of Foundation Pit Dewatering Construction in High-rise Building Engineering

Analysis on Key Points of Foundation Pit Dewatering Construction in High-rise Building Engineering

Optimization schemes for deep foundation pit dewatering under complicated hydrogeological conditions using MODFLOW-USG

The design and optimization of the dewatering scheme for deep foundation pits in a highly permeable heterogeneous layer are critical to protect water resources, control subsidence and mitigate environmental impacts. Numerical simulation is an important and sometimes the only tool in the design of dewatering schemes, especially when the dewatering projects are planned under complex hydrogeological conditions with limited data. The open excavation method was chosen for a project to drain a deep foundation pit (35–44 m) in an upland river valley landscape. Quaternary alluvial deposits (129.0 m thick) are generally distributed in the riverbed and the overburden consists mainly of alluvial-diluvial sandy gravel cobbles, clayey soils, sandy clay, and silty fine sand, making the study area very heterogeneous. There may be water inrush from foundation pit, uneven subsidence and deformation due to the uneven structure of the sand and slope stability. MODFLOW-USG (Unstructured Grid) and Subsidence and Aquifer-System Compaction (SUB) Package were used to create a coupled 3-D groundwater flow-subsidence numerical model for foundation pit dewatering. MODFLOW-USG provides greater flexibility in the design of the grid to achieve a high degree of accuracy in numerical simulation, while effectively reduces computational costs. A combination of waterproof curtain and a partial penetrating well was proposed for lowering the groundwater table. The optimized dewatering scheme with a curtain depth of 60 m and a hydraulic conductivity of 0.00518 m/d, and four rows of dewatering wells with an equal row spacing of 40 m, well depth of 50 m, and well spacing of 12.5 m in each row can meet the dewatering requirements with minimum groundwater discharge in the scenarios. The numerical simulation of this study provides a powerful and useful tool for dewatering and subsidence control of deep foundation pit under complex hydrogeological conditions.

Analysis of the influence of groundwater seepage on the deformation of deep foundation pit with suspended impervious curtain

Taking the deep foundation pit of a metro station with rich water environment as the research background, a three-dimensional model of seepage-stress coupling is established. Numerical simulation is used to study the deformation process and influencing factors of deep foundation pit dewatering and excavation of the station, and the influence of dfferent pre-dewatering conditions and different depths of the water-stop curtain on the deformation of the foundation pit is analyzed. The results show that during the dewatering and excavation of foundation pits, seepage-stress has an obvious coupling effect in dewatering and excavation. The stress concentration position of retaining structure and the maximum displacement of lateral displacement are about 0.5–0.6 excavation depth of pile body. With the depth of precipitation increases, the seepage effect in the soil layer is obviously enhanced, which is not conducive to the stability of the foundation pit.

Numerical simulation of foundation pit dewatering using horizontal seepage reducing body

Groundwater level has to be lowered during deep excavation. A vertical curtain is usually adopted to control the drawdown inside and outside a foundation pit in a built-up area. However, the cost and working difficulty increases substantially with the rise in depth of vertical curtains. In the manuscript, a man-made horizontal seepage reducing body (HSRB) was introduced to shorten the vertical curtain depth and control drawdown. With the No. 4 shaft foundation pit of Guangyuan Project, Shanghai as background, HSRB was proposed in foundation pit dewatering. Microbially induced carbonate precipitation grouting technology was recommended to form an environment-friendly HSRB. Numerical method was used to simulate and understand the influence of position, thickness, and hydraulic conductivity of HSRB on groundwater level. The non-separated HSRB was better than the separate HSRB. Decreasing HSRB hydraulic conductivity was better than increasing HSRB depth. Four seepage modes were summarized considering vertical curtain penetration conditions into multi-aquifer, and the fifth seepage mode was formed for vertical curtain using man-made HSRB, which can be referred by similar engineering applications.

Research on the Effective Control of Ground Settlement during Double‐Layered Foundation Pit Dewatering Based on Seepage Control‐Recharge Coupling Model

This study focuses on the settlement of buildings around the foundation pit caused by foundation pit dewatering. Within the study context, a test is conducted on the control of ground settlement during double‐layered foundation pit dewatering based on the seepage control‐recharge coupling effect. Moreover, a large indoor seepage test device is developed to accurately simulate in‐situ three‐dimensional seepage conditions of double‐layer foundations. The study results showed that compared to the antiseepage conditions, upon the additional recharge, the head of the upper row of the pressure measuring tubes outside the foundation pit is raised by nearly 10.7%, and the water level of the lower row of pressure measuring tubes is raised by about 3.1%. Additionally, the head of the outer side of each pressure measuring tube is higher than that of the inner side by about 2.75% on average, indicating that the recharge outside the pit can effectively increase the head height in the area above the soil layer at the bottom of the recharging well outside the foundation pit and reduce the settlement of the building outside the foundation pit. The numerical calculation of the settlement outside the pit using FLAC3D software further confirms the effect of the seepage control‐recharge coupling model on the ground settlement during foundation pit dewatering. The research results are important for the infiltration deformation and foundation settlement control in composite foundations precipitation.