General deformation behavior of deep excavation support systems: A review

In geotechnical engineering, ground movement caused by excavations is a challenging issue. The excessive differential settlement generated by soil movement induced by wall deflection may cause damage to nearby structures. A detailed literature review on the general deformation behavior of deep excavation support systems is presented in this paper. Many factors, such as normalized horizontal deflection (δh-max/He%), vertical displacement (δv-max/He%), δvmax/δhmax ratio, settlement influence zone (Do), etc., can play significant roles in describing the deflection behavior of the excavation system. A descriptive analysis of the reviewed data was carried out. The concluded δh-max/He% values range between 0.17 to 1.5, with a mean value of 0.58 for soft clay, while in the case of sands and stiff clay soils δh-max/He% value ranges between 0.07 to 0.40, with a mean value of 0.20. δv-max/He% values range between 0.13 to 1.10, with a mean value of 0.49 for soft soil, while its value ranges between 0.02 to 1.10, with a mean value of 0.24 in the case of sands and stiff clay soils. The settlement influence zone (Do) reaches a mean distance of 2.3He, which falls within Do=1.5-3.5He in the case of soft clays, while Do reaches a mean distance of 2.0He and 3.0He in the case of sands and other stiff clay soils, respectively. The relationship between system stiffness and excavation-induced wall and ground movements was discussed. Unfortunately, the literature review offers limited data regarding system stiffness, the 3-D nature of excavation support systems, excavation processes, and time effects.

Deformation Characteristic of a Supported Deep Excavation System: A Case Study in Red Sandstone Stratum

A complete case record of a deep foundation pit with pile-anchor retaining structure excavated in red sandstone stratum is presented in this study. The horizontal displacement of pile top, the horizontal displacement at various depths, the axial force of anchor cable, and ground settlement during construction are measured. A three-dimensional numerical model is established to analyze the additional stress and deformation induced by the excavation and the accuracy of the FEM model is verified by comparing with field measured results. Both the measured and numerical simulation results show that the deformation of the pile-anchor supported deep excavation is significantly affected by the spatial effect. The results show that the deformation in the middle of the foundation pit is greater than the pit angle and that the deformation of the long side is greater than that of the short side and gradually decreases from the middle to the pit angle. The deformation and stress in the middle of the long side of the foundation pit are the largest, which is the most unfavorable part. With the increase of vertical excavation depth, the spatial effects tend to increase, and the influence scope of spatial effects is about five times the vertical excavation depth in the red sandstone stratum. The ground settlement outside the pit is mainly distributed in a groove shape, and the maximum settlement occurs about 8.5 m away from the pit edge. Finally, parametric studies of reinforcement parameters indicated that 1.5–2.0 times the initial elastic modulus and cohesive force of soil should be used for reinforcement. It is recommended that the ranges for pile diameter, pile spacing, anchor cable prestressing and inclination angle should be selected as 0.8–1.2 m, 1.4–2.0 m, 100–150 kN, and 10°–20°, respectively.

Prediction of Ground Subsidence During Underground Construction of Metro Line 2, Section 1, Ben Thanh - Tham Luong

Urban metro line No. 2 from An Suong station to Thu Thiem is one of the six metro lines thatis planned to be built in Ho Chi Minh City (HCMC). The metro line goes through the area in which thestratigraphy consists of many units, distributed from 20-80 m. The hydrogeology mainly has 2 aquifers,namely Holocene, and Pleistocene which affecting the deep excavation. During construction, there willbe some problems that will affect the work on the surface such as settlement, cracking, and damage. Byfinite element method on Plaxis software, the article forecasts the surface settlement during this metroline No.2. The results show that the ground settlement is relatively large in areas with soft groundstructures. The settlement results depend on the geological structure characteristics, hydrogeologicalcharacteristics, and the shape and size of the tunnels.

Parametric Sensitivity Study of Deep Excavation in Singapore Old Alluvium Formation

Deep excavation supported by vertical retaining walls together with strutting system is commonly used in Singapore for the construction of underground infrastructure. In this paper, a series of numerical scenarios simulated by PLAXIS software are carried out to study the influence of different design parameters such as pre-auger loosening effect, the embedded depth of retaining wall into the stiff soil layer, and the elastic modulus of the ground improvement layer on excavation design especially on strut force, retaining wall deflection, and bending moment. The results show that there is high risk if only a single set of parameters are used as input to predict the performance of the retaining system. Sensitivity analysis shall be carried out to evaluate the effects of these parameter variations within a reasonable range on strut force, retaining wall deflection, and bending moment.

Forecasting the impact of buildings with multi-storey underground parts on the displacement of subsoil using modern numerical tools

The paper will analyse and review the experience to date in determining the impact range of implementation of deeply founded structures on the displacement of the subsoil in the vicinity. With the background of these experiences, primarily empirical, the present possibilities of using numerical modelling to forecast the displacements of the terrain surface in various stages of works, that is, execution of deep excavation support systems, excavation-deepening phases with successive adding of struts, construction of underground levels and erection of the above-ground part of the building, will be presented. Based on the results of own research, conclusions on the use of 3D numerical models in spatial shaping and designing the structure of underground parts of new buildings erected in dense urban development will be presented. The characterised 3D numerical models were verified, taking into account the actual results of geodetic measurements of the completed buildings. Determining the range and forecasting the displacements of the subsoil are necessary for the design and implementation of investments due to the need to ensure the safety of erection and use of a new building and the buildings located within the area of influence.