Soft Clay Area Research Articles

Failure in anisotropic sensitive clays: finite element study of Perniö failure test

The railway network on coastal areas of Finland is predominantly located in soft clay areas. The undrained shear strength of such clays is generally low, highly anisotropic, and rate dependent, and it exhibits post-peak strain softening under undrained conditions. A full-scale failure test was performed by Tampere University of Technology in Perniö, Western Finland, in 2009. A shallow railway embankment built on a soft clay deposit was equipped with a loading structure and loaded to failure in about 30 h. The embankment collapsed 2 h after the last loading step. In this study, data collected from the experiment are used, together with laboratory test results on high-quality samples, to conduct advanced finite element analysis of the Perniö failure test. The NGI-ADPSoft model is used for this purpose, which is capable of simulating the strain-softening behavior of the clay. Even though the observed rate effect is not taken into account in the analyses, the failure load can be predicted reasonably well. Good agreement is also observed for calculated displacements and failure mechanism with experimental observations.

Parameters affecting the lateral movements of compound deep cement mixing walls by numerical simulations and parametric analyses

A compound deep cement mixing retaining wall system is a combination of deep cement mixing (DCM) columns and precast reinforced concrete walls. This type of retaining wall was used in a deep excavation for a reservoir construction project in a soft clay area in Thailand. During construction, an inclinometer casing was installed to monitor the lateral movement profiles of this retaining wall system until construction had been completed. Studies on the parameters that affect the lateral movements of retaining walls of this type are limited because of the complex geometry involved. In this paper, a three-dimensional numerical model is first calibrated using an instrumented case history. Then, an analysis of the results for this case history is presented to characterize the wall behavior in terms of the ground settlement induced by wall deflection during excavation and in terms of lateral wall movement. Finally, a parametric study is performed. The results provide information on the influence exerted on the lateral wall movement by the following factors: the elastic modulus of the DCM columns, the embedded length of the DCM columns, the size of the DCM columns, the thickness of the precast wall, the thickness of the soft clay layer and the berm size. The influences of these factors are compared and rated in terms of their degree of importance.

Influences of Vehicle Loads on Braced Excavation in Soft Clay

Economic development and urbanization give rise to the excavation complexion, and higher requirements on design work are put forward. The risk of excavation in soft clay area is high and the design shall be comprehensive. While in practice, the dynamic characteristic of vehicle loads is seldom calculated. In this paper, conventional one-side plane method (beam on elastic foundation method) and three-dimensional finite element method were adopted to analyze the effects of vehicle loads on the retaining strutting system of braced excavation. Moreover, the reinforcement scheme of excavation after collapse was given as references for similar situations.

Analysis of Excavation Monitoring for the Fu-Qing Road Station in Ningbo Urban Rail Transit

The foundation pit of Fuqing road station is the first one to be excavated in Ningbo urban rail transit project. To ensure the safety of the foundation pit, a detailed monitoring scheme is established according to the engineering geological condition and design scheme of foundation pit. Due to Ningbo city is located in the classical soft clay area, there may occur pre-warning and dangerous condition during the excavation. Therefore, reinforcement of structure and soil is executed from the aspects of designing, construction, supervision and monitoring. At last, the deformation of foundation pit is controlled and the construction safety is ascertained. Furthermore, the information construction is adopted during the excavation and many data are obtained during the process of monitoring, the displacement of diaphragm wall, ground settlement and axial force of the support are analyzed. In addition, the control measures are presented and can provide reference to the future construction of the other stations.