Pore Water Pressure Development in Soft Soil due to Installation and Loading of Controlled Modulus Columns

L Bałachowski,J Konkol

doi:10.1061/(asce)gt.1943-5606.0002675

Abstract

Excess pore water pressure (EPWP) development and decay due to the installation and static loading tests of controlled modulus columns (CMC) in soft soil was measured with piezometers equipped with low air entry (LAE) filters and a piezocone (CPTU) equipped with a high air entry (HAE) filter. The HAE filter allows for detailed detection of EPWP in short time intervals during construction of CMC. The influence zone due to the installation of the CMC group extends up to 40D (D = column diameter) with significant installation effects and high EPWP within the zone of 7D. The influence zone during the static loading test is much narrower and does not exceed 2D. The presented research shows the applicability of using a CPTU in EPWP monitoring during CMC construction and clarifies some effects of CMC group installation.

Highlights

Development of excess pore water pressure (EPWP) plays a significant role in geotechnical design in soft cohesive soils (e.g., Croney and Coleman 1961; Dunlap et al 1978; Hiff 1956; Hunt 2005; Strout and Tjelta 2005) and piles in particular (e.g., Li 2019; Liu et al 2012; Pestana et al 2002; Tang et al 2003; Xu et al 2006)
This paper addresses EPWP changes in soft soil surrounding the controlled modulus columns (CMCs) group during all phases of its construction and during static loading tests
The EPWP measurements during pullout tests show no significant EPWP generation near the column base. These results suggests no tensile stress in soft organic silt during the pullout test, which is in agreement with, for example, Han and Ye (2006), who noted no influence of the pile tip in pullout tests in soft Shanghai clay

Summary

Introduction

Development of excess pore water pressure (EPWP) plays a significant role in geotechnical design in soft cohesive soils (e.g., Croney and Coleman 1961; Dunlap et al 1978; Hiff 1956; Hunt 2005; Strout and Tjelta 2005) and piles in particular (e.g., Li 2019; Liu et al 2012; Pestana et al 2002; Tang et al 2003; Xu et al 2006). Suleiman et al (2015) performed comprehensive series of measurements of horizontal stress changes, pore water pressure, and lateral displacement during the construction of CMC columns and static vertical loading tests. They used push-in pressure sensors fitted with a piezometer, allowing for measuring total horizontal stresses and pore water pressure in the soil and shape acceleration arrays to monitor the evolution of soil lateral displacements These measurements were recorded at different distances from the pile shaft in very soft sandy silt or silty clay. They observed a maximal increase in both lateral stress and pore water pressure when the mandrel passes the sensor level. A detailed description of the soil investigation and geotechnical parameters is given in Konkol et al (2019)

Method

Discussion and Interpretation of the Data

Conclusions