Large Foundation Pit Research Articles

Data acquisition method for digital construction site of large foundation pit engineering

To ensure the construction safety of large foundation pit engineering (FPE) and optimize the data collection method, this paper applies sensors and automatic collection items to automatic data collection based on traditional manual measurement. Data processing and analysis are carried out through the large FPE detection system construction. In the early warning module, the improved Grey Model (GM) (1,1), namely the improved method G, is used to predict the settlement of buildings around the monitoring project, and its reliability is analyzed. The improved method G has a good test result. Compared with method G and the Autoregressive Integrated Moving Average model (ARIMA), the improved Method G has a better prediction effect and smaller prediction error. When compared with method G, the mean absolute error (MAE) of the method used in the paper is smaller, which is −0.01. The root mean square value of absolute error is smaller, which is 0.0.54 less than method G. Compared with the ARIMA model, the average RE of the method used in this paper is 3.97%, which is 0.05% less than that. This method can be used to collect and predict data on large foundation pit (FP) construction sites, which is conducive to ensuring construction safety.

Study of the Mechanical Behavior of Retaining Structures and Adjacent Buildings during the Excavation of Deep and Long Pits

Excavation of deep and long pits can cause strata deformation and settlement of adjacent buildings. The excavation of a deep foundation pit of a nearby building in Zhengzhou City, China, is taken as the research object. The foundation of the foundation pit is an independent foundation under the column, the depth of the foundation pit is 24.5∼26.3 m, and the support form of an underground continuous wall and four internal supports is adopted. The stress and deformation characteristics of retaining structures during the construction of deep and long pits and their impact on the deformation of nearby buildings were studied through on‐site monitoring and finite element simulation. The analysis focuses on the effects of different excavation stages on adjacent structures, with the main conclusions as follows. After excavation, the underground continuous wall far from the building undergoes a “rotating‐kick” displacement, while the underground continuous wall on the side near the building only shows a “kick” displacement. Adjacent buildings have little influence on the distribution of shear force and bending moment of the underground continuous wall of the foundation pit. The first horizontal strut experiences pressure, gradually shifting to tension as excavation continues, with the maximum stress reaching 3.6 × 103 kN. The second, third, and fourth horizontal struts mainly bear compressive forces, increasing with the depth of the struts. The building primarily undergoes settlement in the early stages of deep and long pit excavation. As the excavation progresses, the building points near the pit begin to bulge, but the building corners far from the pit continue to show settlement. During the excavation of the deep and long pit, the differential settlement of the long side of the nearby building first decreases and then increases, and the differential settlement of the short side changes from a slight decrease to a significant increase. The settlement evolution of the building is as follows: overall settlement ⟶ overall uplift ⟶ uplift of the side of the building near the pit ⟶ outward tilting away from the pit. The findings may provide references for designing, constructing, and operating deep and large foundation pits.

Numerical Simulation Study on Application of T-Shaped Composite Pile Support System in Super-Large Foundation Pit Support Engineering

To reduce the impact of the one-time excavation of deep and large foundation pits on nearby subway tunnels, the excavation should be performed separately; thus, a T-shaped pile support system was studied. First, several foundation pit support structures were compared and selected, and a pile support system was proposed. In terms of space, a T-shaped support structure was formed to reduce the spatial requirements of the foundation pit. Through finite element software, a 1:1 restoration of the foundation pit using a T-shaped pile support system was carried out. The stress characteristics and support effect of the support structure were studied under two working conditions of symmetric and asymmetric excavation. The study found that there was a central effect on the foundation pit using a T-shaped pile support system, that is, the support piles farther away from the center of the T-shaped structure gradually increased the maximum pile bending moment and displacement owing to the constraints of vertical piles and the influence of the pit angle effect, respectively. In the case of symmetrical excavation, the T-shaped structure was simplified into a triangular structure, and the stress form of this type of structure could be reduced to a cantilever double-row pile structure, which met the requirements of pit excavation. The application of a T-shaped pile support structure can provide new design ideas for foundation pit engineering near regional subway lines.

Dynamic Optimization of Construction Time-Cost for Deep and Large Foundation Pit Based on BIM Technology and Genetic Algorithm

With the increasingly fierce market competition, optimizing the construction time-cost of deep and large foundation pit construction projects has become one of the key factors for construction enterprises to remain invincible. By dynamically optimizing the time-cost, the optimal time corresponding to the lowest engineering cost can be found. Based on a comprehensive transportation hub project, considering the time value of capital and the reward and punishment of construction time, a time-cost dynamic optimization model is constructed. Relying on BIM technology, the feasibility of construction plan is analyzed from both qualitative and quantitative perspectives, and the project parameters and resource information is obtained accurately and quickly. Using the MATLAB program, time-cost optimization based on genetic algorithm is carried out, and the static and dynamic optimization results are compared. The results show that the dynamic optimization scheme reduces the total cost by 1.68% while reducing the total construction time by 8.47%. The dynamic optimization scheme extends the construction period by 2 days while reducing the total cost by 89,500 yuan compared to static optimization. The peak value of the fund demand curve before and after optimization has decreased from 128,000 yuan to 127,000 yuan. The time-cost dynamic optimization, considering the time value of capital is more in line with engineering reality, and the optimization results are more reliable and accurate. BIM technology can accurately and quickly obtain project parameters and resource information, solving problems such as complex processes in super deep excavation and huge engineering data statistics. The genetic algorithm can efficiently and accurately search for the optimal solution within the global domain. This study combines BIM technology with the genetic algorithm to solve the dynamic optimization problem of construction period cost for deep and large foundation pits. The research results of this study provide a theoretical reference for the optimization of schedule cost for similar projects.

Review on the Research and Application Progress of TRD Construction Method in Foundation Pit

with the development of the times, the expansion of urban scale and the development and utilization of underground space, the building foundation pit is developing in the direction of "large and deep". The traditional deep foundation pit support construction technology can no longer meet people's needs for the construction of deep and large foundation pits, thus deriving a new construction technology TRD construction method, which has a wide range of application, guaranteed wall quality and depth, and high construction efficiency. This construction method has been born for more than 30 years and has been popularized and applied in China for more than 10 years. This paper will briefly introduce the trd method from the aspects of its development, characteristics and academic research process of related applications. It is not difficult to see from the relevant research that the trd method has broad application prospects in China.

Experimental study on the variation rule of water level outside the pit caused by dewatering in the pit and the rule of reinjection outside the pit

Studying the surface settlement caused by foundation pit dewatering has certain practical significance for engineering construction. When the aquifer in the foundation pit is located within a large burial depth range, the impermeable wall does not completely separate the water layer, resulting in water inside and outside the foundation pit communicating around the bottom of the impermeable wall. Taking the foundation pit project of a subway station in Shenzhen as the background, model experiments were conducted to reveal the changes in water level outside the pit caused by precipitation under different conditions inside the pit. (1) Considering the influence of surrounding seepage, the precipitation curve outside the pit presents a concave and then convex form, which is different from the Dupuit theory precipitation curve. (2) For large foundation pit dewatering in layered soil, the downward trend of the dewatering curve outside the foundation pit decreases with the increase of soil depth. (3) Compared to vertical reinjection in close proximity to dense buildings, inclined reinjection has a smaller impact on the side adjacent to the retaining wall, while it is far away from the retaining wall, with a larger impact range. The full well deep reinjection well with an angle of 20° from the vertical direction has the largest reinjection range and the best reinjection effect. It provides a research basis for reasonable control and prevention of surface settlement and adverse deformation of diaphragm walls in narrow spaces under subsequent surrounding seepage conditions.

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.

Deformation Control of Subway Stations under the Influence of the Construction of Deep and Large Foundation Pits with Composite Support Systems

The excavation depth of a deep and large foundation pit of a composite support system is 25.5 m, the minimum clear distance from the main structure of the station is 10.6 m and the closest distance to the entrance and exit structure is only 3.6 m. Relying on this project, numerical simulation, field monitoring and other methods are used to study the deformation law of the self-supporting system, the ground settlement and the subway station under construction. Then, the influence of different support parameters on the deformation of the subway station and track is analyzed, and the internal relationship between the deformation value of the station and track and the support parameters is further discussed. The main work and achievements are as follows: (1) Through field measurement and analysis, the deformation history of the station and track in the excavation is studied. The obtained results show that the interbracing + pile–anchor composite support structure has better control over the deformation of adjacent stations and tracks. Comparing the simulated value of station and track deformation with the measured data, it is concluded that the simulated and measured deformation trends remain consistent, and the maximum deformation value corresponds to the middle position of the foundation pit. This confirms the rationality and reliability of the composite support system model. (2) The analysis of the influence of different support parameters on the maximum deformation value of the subway station and track shows that the deformation of the station and track is less affected by the pile diameter of the retaining pile and the size of the interbracing section. It is greatly affected by the embedding depth of the retaining pile and the number of support channels. It is suggested that the optimal parameters should be a pile diameter of 1.0 m, embedding depth of 8 m, four interbracings and an interbracing section of 1.0 m × 1.0 m.

Analysis of the Deformation Law of Deep and Large Foundation Pits in Soft Soil Areas

Taking a deep excavation in Suzhou soft soils adopting three support schemes as the background, the excavation performance metrics, including the heave and lateral deformation of diaphragm walls, surface vertical deformation, vertical deformation of surrounding buildings, and earth pressure, are thoroughly investigated based on 15 excavation cases collected in the soft soil area of Suzhou. Based on the analysis of monitoring data, some findings were achieved: the foundation pit deformation is greatly affected by the spatial effect. The existing station can constrain the foundation pit deformation. Benefiting from the combination of various support solutions, the average maximum deflection of the diaphragm wall is 0.10% He. The maximum lateral movement depth of the diaphragm wall (δhm) is mainly located at (He-7, He+12.5). The vertical deformation of the wall top is greatly affected by the excavation exposure time and soil conditions. The heave range of the wall top is (−0.08∼0.26%) He. Under the action of the displacement of the diaphragm wall to outside the pit and the upward displacement of the wall top, the ground surface is uplifted, and the maximum uplift is (0.02∼0.14%) He, ranging from 0.12δhm to 1.13δhm. The maximum surface settlement is (−0.01% ∼ −0.15%) He, ranging from −0.22δhm to −3.11δhm. The form of building heave is mainly affected by the surface heave and the distance from the diaphragm wall (d). When d is within a certain range, there is a heave settlement difference between the adjacent side and the opposite side of the excavation, and the adjacent side undergoes mostly subsidence, while the opposite side undergoes mostly uplift. The peak value of the apparent earth pressure (AEP) envelope is 0.59γHe, which falls within (0.47∼0.78) He. The calculation scheme proposed by Kim can be used to predict the AEP for multiple soil types.

Numerical Simulation Study on Construction Effect of Top‐Down Construction Method of Suspended Diaphragm Wall for Deep and Large Foundation Pit in Complex Stratum

In order to study the deformation of a diaphragm wall and the settlement of surrounding soil under the complicated conditions of the deep and soft soil layer, which is underlying inclined rock and top‐down construction method, the construction scheme of suspended diaphragm wall based on the engineering practice of Oujiang North Estuary deep and large foundation pit of Wenzhou S2 railway is proposed, and the research method of numerical simulation is adopted in this article. By using Midas GTS finite element software, a three‐dimensional model of deep and large foundation pit excavation with top‐down construction method is established, and the internal force, deformation, and surface settlement of surrounding soil of suspended diaphragm wall with different depths into rock (1 m, 2 m, and 4 m) are analyzed. Furthermore, the optimization simulation research on the anchor locking scheme is carried out for the determined footed diaphragm wall. Similarly, the anchor locking scheme at a depth of 1 m into the interface between soil and rock is selected as the supporting scheme of the footed diaphragm wall through the simulation results. The research results of this article can guarantee the safety of diaphragm wall construction of deep and large foundation pit in complex stratum.

Research on Numerical Simulation of Top‐Down Construction Effect of Diaphragm Wall of Deep and Large Foundation Pit under Different Working Conditions in Complex Stratum

In order to study the construction effect of deep and large foundation pit excavation and its impact on the surrounding environment under complex stratum conditions, the deep and large foundation pit of the top‐down construction method of shield exit shaft of S2 line of Wenzhou City railway is taken as the research object in this paper. According to the complex geological conditions of deep soft soil layer with underlying inclined rock surface in Wenzhou, the numerical simulation method is used to carry out the related research. The simulation results of the deformation characteristics of the diaphragm wall under two different working conditions which are the same length diaphragm wall and the suspended foot diaphragm wall are compared and analyzed. According to the analysis results, the suspended foot diaphragm wall is determined as the final construction scheme of the diaphragm wall, and it is verified by field measurement. The research results can provide technical support for the construction of similar projects. At the same time, it can also provide basic accumulation for the construction of major projects in Wenzhou.

Research on Monitoring Information Management of Deep Foundation Pit Engineering Based on BIM Technology

With the rapid development of construction industry, there are more and more deep and large foundation pit projects with complex architectural environment and geological conditions. Deformation monitoring in deep foundation pit as a basic element of engineering quality assurance is becoming more and more important. At present, the management and expression form of monitoring data in deep foundation pit still stays in the stage of two-dimensional form and curve expression, and it can not reflect the deformation of deep foundation pit in real, fast and effective way.Take the 3#, 4# high-rise residential and underground garage project of a college in Xi'an as an example. Based on Revit software, taking BIM technology and Revit API as the theoretical basis, and taking Microsoft Visual Studio 2012 and Autodesk Revit 2014 as the development platform, we use C# programming language to carry out the two development of information management module for deep foundation pit engineering monitoring. Combining BIM technology with monitoring data management of deep foundation pit, the information management mode of monitoring data of deep foundation pit is improved, which makes express expression of deep foundation pit construction monitoring more rapid and effective, and has guiding significance for safety construction of deep foundation pit engineering.

Analysis of deformation monitoring results of a deep and large foundation pit

Taking a deep and large foundation pit project as an example, the paper analyzed some developmental characteristics of its deformation during construction. The deformation included vertical displacements of the ground surface and horizontal displacements of deep soil surrounding the foundation pit. At the same time, the trends of the ground settlement were predicted based on the monitoring data. The analysis and predictions showed that: (1) The soil around the foundation pit was influenced by the excavation and supporting construction; (2) The vertical and horizontal displacements appeared some regular patterns of gradual development over time. In addition, there were certain differences in the trends of measuring points at different locations; (3) By fitting the monitoring data, the deformation of the foundation pit could be effectively predicted and offer a guidance to the engineering practice.

A Numerical Investigation of the Deformation Mechanism of a Large Metro Station Foundation Pit under the Influence of Hydromechanical Processes

Considering the unique conditions of deep and large subway foundation pit excavation affected by heavy rainfall in soil-rock composite strata, this paper employs finite element numerical simulation methods to study foundation pit instability under the influence of heavy rainfall. According to the hydraulic coupling conditions caused by rainfall, a fluid-solid coupling numerical model for a deep and large subway foundation pit in soil-rock composite strata is established in this paper. By selecting the Anshan road station of Qingdao subway line 4 as the engineering background, various parameters related to foundation pit excavation affected by heavy rainfall at different excavation depths were analyzed. The study found that after the foundation pit was excavated, the surrounding pore water pressure decreased and the pore water pressure near the ground surface increased rapidly due to rainfall. As the horizontal distance from the foundation pit increased, the pore water pressure at the same depth also increased. The excavation of the foundation pit caused uplift of the bottom of the pit. After rainfall, the uplift value decreased compared with that before rainfall. With increasing excavation depth, the decreased value of the bottom uplift decreased and then increased. The rainfall caused the horizontal displacement of the pit walls on both sides of the pit to increase. When the excavation depth was 10 m, the horizontal displacements on both sides of the pit were equivalent. When the excavation depth was 20 m, the horizontal displacement was concentrated in the first 10 m; when the excavation depths were 30 m and 40 m, the horizontal displacement was concentrated in the first 13 m. This finding shows that when the foundation pit was affected by rainfall, the sidewall collapsed at a distance of 13 meters from the ground. As the excavation depth increased, the depth of excavation instability was closer to the bottom of the pit. The research in this paper can provide a reference for the construction of deep and large foundation pits in similar composite ground conditions that are affected by rainfall.

Construction Technique of Vertical Shafts Excavation Above Subway Tunnel

Taking the foundation pit construction of the section K0 + 700 ~ + 900 of Shuangjiehe Road, Tinghai Road and other underground roads in Qianhai District of Shenzhen as an example, this paper introduces a new key construction technology of deep and large foundation pit excavation in the coastal area of reclamation to control the uplift and deformation of underground subway, which effectively utilizes the principle of space–time effect. Based on the number of finite difference software FLAC 3D numerical analysis, the skip excavation method and key construction parameters are simulated and optimized. The monitoring data show that the excavation method, sequence and construction protection measures have significant effect on the deformation control of subway tunnel, which can provide reference for similar projects.

Theoretical analysis and engineering application of the new pile-soil-support system

The Plaxis 2D finite element software is used to analyze the deformation laws of new pile-soil-support system with HS model based on a foundation pit in Shanghai. Contrastive analysis is conducted between finite element and measured values. The results show that the Plaxis 2D can predict the deformation of the new pile-soil-support system. The existence of steel tube inclined brace changes the deformation laws of the traditional double- row piles and can reduce the displacement of top of the double-row piles effectively. The deformation of retaining piles of the new pile-soil-support system satisfies the safety and deformation requirements of the foundation pit. The new support system has no inner supports and it avoids a lot of construction waste generated by the construction and demolition of temporary supports. It is safe, economy and green environmental protection, and it can provide reference for the deep and large foundation pits in soft soil areas.

Research and Engineering Application of Soft Soil Unloading and Deformation Model

Soft soil is a multiphase medium composed of solid soil particles, pore water, pore gas and combined water film adsorbed on the surface of particle group and colloid between particles. It is widely distributed in coastal, middle and lower reaches of rivers and delta of lakes. Its physical and mechanical properties and engineering characteristics are complex and regional differences are obvious. With the rapid development of social economy and urbanization, it will inevitably lead to serious problems such as urban land tension, traffic congestion and environmental pollution. These coastal cities are the leaders of China’s economic development. After more than 30 years of rapid economic development, the construction scale of these cities in China is also expanding, and the supply and demand of construction land is becoming increasingly tight. The contradiction between supply and demand is more prominent. With the scarcity of land resources and the rapid development of economy, a large number of construction projects in Qianhai area have been started, among which the construction of subway is also on a large scale. The shortage of land resources and the increase of land development make the high density and high strength building development along the subway line. The development of these building properties is bound to appear a large number of complex deep foundation pit projects, and the excavation of deep and complex foundation pit near the side of subway tunnel is a common form of excavation. In practical construction projects, due to the influence of external factors such as complex construction site conditions and urgent time requirements, people often pursue the progress of foundation pit excavation too much in actual construction, ignoring the research and application of mechanical properties of soft soil foundation, which leads to the safety accidents of subway tunnel structure from time to time. This is closely related to the mechanical properties of soft soil with high moisture content, high compressibility and low bearing capacity. Therefore, deep and large foundation pit engineering in soft soil area is prone to heavy engineering safety problems such as underground continuous wall and other retaining structures. Therefore, the further study of the unloading deformation model of soft soil, the physical and mechanical properties and engineering characteristics of soft soil has a positive and important economic value and social role in engineering in the future.

Design, construction and analysis for super-wide, deep and large foundation pit

Both developing and developed countries are facing a series of difficulties and challenges in the process of urbanization. In recent years, in order to alleviate the problem of urban congestion, underground space has developed rapidly, and the excavation of foundation pit is the most important step in the development of underground space. This paper takes the foundation pit of the tunnel under construction in Suzhou as a research object. The design width of the foundation pit reaches 61.5 m and the depth reaches 18 m, so it belongs to the super wide and deep foundation pit. Numerical analysis is performed by finite element software to calculate the deformation of the foundation pit. The research shows that the main problem to be solved is the deformation of the foundation pit, and the deformation of side wall of foundation pit tunnel is the most obvious. The maximum deformation of the side wall of the main tunnel and the auxiliary tunnel reached the maximum at 15 m. The maximum deformation of the main tunnel is about 1.3 cm, and that of the auxiliary tunnel is about 0.9 cm. Through targeted design and construction, the mechanical performance of the foundation pit retaining structure is optimized, and the stability of the foundation pit is strengthened. The reasonable retaining structure can ensure the good construction quality. The design and construction of the project can provide reference for related engineering construction.

Study on Deep and Large Foundation Pit of a National First‐Class Key Tomb Protection Project

For the support engineering of the deep and large foundation pit (DLFP) due to tomb protection, there are still no clear standards. The construction of DLFP will introduce large‐range transverse and longitudinal disturbance on the stratum; therefore, it should be reinforced. In this paper, the reinforcement of the deep and large foundation pit of a national first‐class key tomb protection project is studied. By comparing the existing supporting scheme and the stress conditions of the reinforced tomb, the combination reinforcement scheme by bored pile and pile slab retaining wall is found to be safe and feasible. Furthermore, according to the simulated bending moment, displacement, and axial force of the tomb by numerical analysis, an economic and reasonable mixed anchor support scheme is selected. In order to ensure the stability of the tomb during the supporting process of the foundation pit, a maximum value of 10 mm for the overall settlement of the tomb can be treated as the control benchmark based on the support and anchorage schemes in each specification and the in‐site measured settlement values of the tomb. The determined support, anchorage schemes, and the control benchmark can provide certain technique guidance and research significance for the protection of similar ancient buildings in the future.

Effects of Partial Supporting Pile Removal from Deep Foundation Pits by Shallow Excavation Method in Loess Areas

Partial supporting piles removal from deep foundation pit may lead to large‐scale foundation pit collapse, resulting in severe consequences. Various studies have investigated the underpinning technology of cutting abutment piles by combining field monitoring and numerical simulation, but there are few studies on cutting supporting piles of foundation pit by the shallow excavation method. Taking an actual deep and large foundation pit as an example, the finite element method (FEM) was adopted to study the surface settlement and the changing trend of the force and displacement of the supporting pile caused by cutting piles during the shallow excavation of double tunnels. The FEM results were verified with the field monitoring data. The simulation results show that the surface settlement around the foundation pit mainly occurs at the pile cutting stage under different excavation sequences (0D, 1D, 2D), and the main distribution area is the one‐fold diameter area outside the double tunnel. After the supporting piles are partially cut, the bending moment and displacement of the lower part of the broken piles differ significantly due to different excavation sequences, but the bending moment and displacement of the upper part of the broken piles are basically similar. In the process of removing the supporting piles, the Earth pressure behind the piles is redistributed, and the load is mainly transferred to the adjacent supporting piles outside the tunnel within the radius of one time of the tunnel diameter. However, the load is not evenly transferred to the adjacent supporting piles. Some recommendations for the reinforcement scheme of the supporting structure during cutting supporting piles in deep foundation pit are also proposed. The research results can provide theoretical basis and practical guidance for the construction of similar projects in the future.