Construction Technology and Safety Risk Control Measures of Deep Foundation Pit Excavation

Deep foundation pit excavation is a basic and key step involved in modern building construction.In order to ensure the construction quality and safety of deep foundation pits,this paper takes a project as an example to analyze deep foundation pit excavation technology,including the nature of this construction project,the main technical measures in the construction of deep foundation pit,and the analysis of the safety risk prevention and control measures.The purpose of this analysis is to provide scientific reference for the construction quality and safety of deep foundation pits.

Dam foundation excavation techniques in China:A review

A protective layer(PL) is commonly reserved above foundation surface to protect the underlying rock mass during dam foundation excavation. In China, the PL of dam foundation is conventionally subdivided into two or three thin layers and excavated with the shallow-hole blasting method, even by pneumatic pick method in case of soft rock mass. The aforementioned layered excavation of the PL delays the construction of the whole project. After nearly 30-year practices, several safe and effcient methods for the PL excavation of dam foundation are gradually developed. They include shallow-hole bench blasting with cushion material(SBC) at the bottom of the hole, and horizontal smooth blasting(HSB). The PL is even cancelled on the condition that horizontal pre-split technique is employed during dam foundation excavation. This paper introduces the aforementioned two PL excavation methods(shallow-hole blasting and bench blasting) and horizontal pre-split technique of dam foundation without protective layer(HPP). The basic principles of blasting method, blasting geometry, charge structure, drill-and-blast parameters of typical projects are examined. Meanwhile, the merits and limitations of each method are compared. Engineering practices in China show that HSB is basically the optimal method for dam foundation PL excavation in terms of foundation damage control and rapid construction. Some new problems for dam foundation PL excavation arising, such as strong unloading and relaxation phenomenon that encountered in the gorge region of southwest China, are needed to be addressed; and the corresponding countermeasures are discussed as well.

Deep Foundation Pit Excavations Adjacent to Disconnected Piled Rafts: A Review on Risk Control Practice

Foundation pit excavation engineering is an old subject full of decision making. Yet, it still deserves further research due to the associated high failure cost and the complexity of the geological conditions and/or the surrounding existing infrastructure around it. This article overviews the risk control practice of foundation pit excavation projects in close proximity to existing disconnected piled raft. More focus is given to geotechnical aspects. The review begins with achievements to ensure excavation performance requirements, and follows to discuss the complex soil structure interaction involved among the fundamental components: the retaining wall, mat, piles, cushion, and the soil. After bringing consensus points to practicing engineers and decision makers, it then suggests possible future research directions.

Deformation analysis and safety assessment of existing metro tunnels affected by excavation of a foundation pit

The excavation of a foundation pit considerably affects the adjacent structures and underground pipelines owing to the change in the stress state of the surrounding soil,resulting in deformation.The study of an actual engineering case was conducted to examine the influence of excavation on the deformation of adjacent subway tunnels.The finite element analysis software PLAXIS 3D was used to simulate the entire excavation process.The structural design of the foundation pit was optimized based on the simulation results to ensure the stability of the foundation pit and the safety of the existing subway tunnel structure.Finally,the safety evaluation of the excavation of the foundation pit that caused the deformation of the adjacent subway tunnel was performed.The influence of the excavation and unloading of the foundation pit on the subway tunnel is closely related to the distance between the subway and the foundation pit,the amount of earthwork excavated at one time,and the engineering geological conditions.The results of this paper can provide useful reference for the design optimization and safety assessment of similar projects.

Influencing factors and control measures of excavation on adjacent bridge foundation based on analytic hierarchy process and finite element method

Many uncertain factors in the excavation process may lead to excessive lateral displacement or overlimited internal force of the piles,as well as inordinate settlement of soil surrounding the existing bridge foundation.Safety control is pivotal to ensuring the safety of adjacent structures.In this paper,an innovative method is proposed that combines an analytic hierarchy process(AHP)with a finite element method(FEM)to reveal the potential impact risk of uncertain factors on the surrounding environment.The AHP was adopted to determine key influencing factors based on the weight of each influencing factor.The FEM was used to quantify the impact of the key influencing factors on the surrounding environment.In terms of the AHP,the index system of uncertain factors was established based on an engineering investigation.A matrix comparing the lower index layer to the upper index layer,and the weight of each influencing factor,were calculated.It was found that the excavation depth and the distance between the foundation pit and the bridge foundation were fundamental factors.For the FEM,the FE baseline model was calibrated based on the case of no bridge surrounding the foundation pit.The consistency between the monitoring data and the numerical simulation data for a ground settlement was analyzed.FE simulations were then conducted to quantitatively analyze the degree of influence of the key influencing factors on the bridge foundation.Furthermore,the lateral displacement of the bridge pile foundation,the internal force of the piles,and the settlement of the soil surrounding the pile foundation were emphatically analyzed.The most hazardous construction condition was also determined.Finally,two safety control measures for increasing the numbers of support levels and the rooted depths of the enclosure structure were suggested.A novel method for combining AHP with FEM can be used to determine the key influencing aspects among many uncertain factors during a construction,which can provide some beneficial references for engineering design and construction.

Deformation monitoring and remote analysis of ultra-deep underground space excavation

The development and utilization of urban underground space is producing many deep foundation pits.On-site monitoring is a key issue to ensure the safety of the foundation excavation,especially the monitoring of the lateral displacement of the structure.The ultra-deep circular foundation excavation project(58.65 m deep,the deepest foundation pit in Shanghai)in the test section of the Suzhou River deep tunnel is one of the most challenging engineering around the world.The distributed optical fiber monitoring technology of Brillouin optical frequency domain analysis(BOFDA)was employed to monitor the lateral displacement of the deep foundation.The monitoring process lasted for 14 months,and a total of 19 times of monitoring was carried out following the progress of the excavation of the foun-dation pit.This paper introduces the process,methods and precautions of optical fiber monitoring from early installation,equipment debugging to data acquisition,data processing and data analysis.By comparing the fiber monitoring data with the manual monitoring data,the deformation of the deep foundation excavation is analysed.The analysis results not only obtain the deformation law of ultra-deep foundation excavation,but also prove the advantages of optical fiber monitoring in deep foundation excavation.Finally,with the support of the Smart Infrastructure Service System(iS3),the research combines optical fiber monitoring with an information platform.Under the framework of the iS3 platform,an integrated data processing and analysis module for fiber monitoring is developed,and the feasibility of remote real-time collection and analysis of monitoring data is discussed.With the support of the information platform,the monitoring data can be transmitted back to the computer terminal to realize remote monitoring.