Electroosmosis Treatment on Composite Soils

As an alternative to stone column in fine grained soils, it is possible to create stiffened columns of soils using electroosmosis (electroosmotic piles). This technique has already been proven. This program of this research is to establish the effectiveness, and the efficiency of the process in different soils. The aim of this study is to assess the capability of electroosmosis treatment in a range of composite soils in terms of the vertical settlement, expelled water, electrical current and power consumption, treatment time and final water content.
The equipment developed by Nizar and Clarke (2013) was used with an octagonal array of anodes surrounding a single cathode in a nominal 250mm diameter 300mm deep cylinder of soil and 80mm anode to cathode distance. The equipment was modified to allow radial and vertical temperature profiles to be monitored during the electroosmotic treatment.
Twenty-four tests were performed on China Clay Grade E kaolin and calcium bentonite (Bentonex CB) mixed with sand fraction C (BS 1881 part 131) at different ratios; (0, 23, 33, 50 and 67%) by weight subjected to different applied voltages (5, 10, 15 and 20). The soil slurry was prepared by mixing the dry soil with water to 1.5 times the liquid limit of the soil mixture. The electroosmotic tests are divided into three phases. In Phases 1 and 2, 15 kPa was applied to simulate a working platform, 50 kPa was used in Phase 3 to simulate a surcharge load. The electroosmotic treatment was only performed during Phase 2. Control tests for each soil mixture were carried out to assess the behaviour of the soil samples subjected to only an increase of vertical pressure, which is 15 kPa in Phase1 and 50kPa in Phase 3
Analysis of the experimental results from this study showed a significant dewatering effect on the soil slurries. The water discharged by the electroosmotic treatment process decreased as the sand content increased. Soil temperature increased significantly when an electrical power was applied and drops when an applied D.C power turned off or when the electrode degraded. The highest increase in temperature was found in pure clays at higher applied voltage after about 8 hours of electroosmosis test.