Saturated Soft Soil Research Articles

Design and construction of a deep excavation in soft soils adjacent to the Shanghai Metro tunnels

This paper presents the design and construction of a deep excavation for building foundations in saturated soil. This deep excavation was of particular interest because it was located above and beside the Shanghai Metro tunnels. The twin Shanghai Metro tunnels had to be in full operation during the deep excavation. Potential large deformation of the twin tunnels was one of the main concerns during the design and construction for the deep excavation. The paper discusses in detail the criteria and measures for controlling the soil and tunnel deformation. The measures included cast-in-place concrete diaphragm walls with bracing structural members, pumping consolidation, cement–soil mix pile systems, and rational excavation procedures. A simplified theoretical method was proposed to estimate the increment in undrained shear strength in a soft clay layer due to pumping consolidation. Furthermore, conventional finite element methods were used to predict the soil vertical and horizontal displacements induced by the excavation. Using the design and construction methods discussed in the paper, the settlement and horizontal displacement of the tunnels were successfully controlled within 5.0 mm and 9.0 mm, respectively. The curvature of longitudinal deformation curve of the tunnels was less than 1/15 000. The horizontal displacement of the braced diaphragm walls was less than 0.12% of the total excavation depth. Key words: Metro tunnels, saturated soft soil, deep excavation, design, construction, ground improvement, case studies.

Time-dependent settlement analysis of a geosynthetic-reinforced soil

This paper presents a mechanical modelling approach to determining the settlement of a geosynthetic-reinforced engineered granular fill–saturated soft foundation soil system. In this approach, the geosynthetic-reinforced engineered granular fill is represented by a reinforced Timoshenko beam and the saturated soft foundation soil is idealised as a Terzaghi spring–dashpot system. A parametric study has been carried out to observe the settlement response of the reinforced soil system along with the tension in the geosynthetic reinforcement at different stages of consolidation of the saturated soil.

Time-dependent settlement analysis of a geosynthetic-reinforced soil

This paper presents a mechanical modelling approach to determining the settlement of a geosynthetic-reinforced engineered granular fill–saturated soft foundation soil system. In this approach, the geosynthetic-reinforced engineered granular fill is represented by a reinforced Timoshenko beam and the saturated soft foundation soil is idealised as a Terzaghi spring–dashpot system. A parametric study has been carried out to observe the settlement response of the reinforced soil system along with the tension in the geosynthetic reinforcement at different stages of consolidation of the saturated soil.

Time-Dependent Settlement Response of Granular Fill on Soft Soil

In this paper, the time-dependent settlement characteristics of granular fill on saturated soft foundation soil were studied using a mechanical model for the foundation. The model idealizes the behaviour of granular fill and saturated soft foundation soil with the Pasternak shear layer and spring-dashpot system respectively. The parametric studies revealed the effect of various parameters on the settlement response of the model at different stages of consolidation of the soft soil.

Settlement Response of Soft Soils Reinforced by Compacted Sand Columns

Stone/compacted sand columns is a technique of soil reinforcement that is frequently implemented in soft cohesive soils to increase the bearing capacity of the foundation soil, to reduce the settlement, and to accelerate the consolidation of the surrounding saturated soft soil. The soil‐column interaction depends on several parameters, including the loading process and the loading rate, the replacement factor, the group effect, and the partial consolidation of the soft soil due to radial drainage through the column. This paper presents the results of a laboratory study that was conducted to investigate the effect of these various parameters on the settlement response of a soft foundation soil reinforced by compacted sand columns. Triaxial compression tests under different boundary conditions were performed on composite soil specimens made of annular silty soil samples with a central, compacted river‐sand column. These tests, performed in a specially modified triaxial cell, show that the group effect, the replacement factor, and the consolidation of the soft soil have a significant effect on the vertical stress concentration on the column and on the settlement reduction of the foundation soil.

Field study of the use of the dynamic consolidation ground treatment technique on soft alluvial soil : Charles, J A; Watts, K S Ground Engng, V15, N5, July 1982, P17–25

Field observations have been made at a site where dynamic consolidation has been used in an attempt to increase the undrained shear strength of saturated soft alluvial soil. Pore water pressures and undrained shear strength have been monitored before, during and subsequent to dynamic consolidation. The effectiveness of this ground treatment technique on soft alluvial soil has been assessed. (Author/TRRL)