Characterization of Lime and Polymer Treated Ultra-Soft Clay Soils Using the Modified Vane Shear and Correlating the Shear Strengths to the Electrical Resistivity and CIGMAT Miniature Penetrometer for Nondestructive Field Tests

Abstract

With the growth in construction along the coastal regions, ports and offshore deepwater sea beds, ultra soft clay soils are encountered and are affecting the performance of the pipelines and other anchor systems placed in it. In this study, untreated and treated ultra-soft clay soils shear strengths were quantified using the modified vane shear device and correlated the shear strength to the CIGMAT miniature penetrometer penetration and electrical resisitivity. The ultra-soft clay soils were prepared by varying the bentonite content from 2 to 10%. The soil with 10% bentonite was treated with 2–10% lime and with 1–10% polymer separately to enhance the shear strength. The shear strength, pH, CIGMAT miniature penetrometer and electrical resistivity were used to characterize the untreated and treated ultra-soft clay soils. Untreated soft soil strength varied from 0.01 to 0.17 kPa when the bentonite content in the ultra-soft clay soil was increased from 2 to 10%. With 2% lime treatment the shear strength of 10% bentonite soil was increased to 0.27 kPa. Adding 10% lime to the 10% bentonite ultra-soft soil reduced the shear strength to 0.15 kPa. With 10% polymer treatment, the shear strength was increased by 45 times to 6.8 kPa for the 10% bentonite ultra-soft soil. The CIGMAT miniature penetrometer penetration varied linearly with the shear strength of the untreated ultra-soft clay soils and treated ultra-soft clay soils with 10% bentonite. pH was almost constant for untreated ultra-soft clay soils while it increased by 22% and 35% for the 10% lime and 10% polymer treated ultra-soft clay soilss respectively. Relative electrical resistivity decreased by 246% when the bentonite content was increased from 2 to 10% in the ultra-soft clay soils. Addition of 10% of lime to the ultra-soft clay soil with 10% of bentonite content decreased the relative electrical resistivity by 171%. Addition of 10% of polymer to the ultra-soft clay soil with 10% of bentonite content reduced the relative electrical resistivity by 545%. Power law, linear and Vipulanandan correlation models were used to predict the shear strength-resistivity relationship for the untreated, lime-treated and polymer-treated ultra-soft clay soils respectively. In addition, linear model was used to predict the water content relationship with electrical resistivity for the untreated and treated ultra-soft clay soils. The CIGMAT miniature penetrometer was modeled using 3-D axisymmetric finite element method, which predicted the penetration of CIGMAT penetrometer that agreed well with the experimental results of the untreated and treated ultra-soft clay soils. The CIGMAT miniature penetrometer penetration and the electrical resisitivity monitoring are two non-destructive methods that can be easily adopted in the field and the property correlations can be used to determine the shear strength of the ultra-soft caly soils in the field.