Experimental evaluation of soft soil compaction process using Cement - Fly Ash - Marine Sand piles in Vietnam

Abstract

Cement fly ash marine sand (CFMS) piles are a new solution for improving soft soils in Vietnam, utilizing marine sand and f ly ash to address riverbank erosion and environmental challenges caused by river sand extraction and waste from thermal power plants. Evaluating the effectiveness of this solution is essential for practical implementation. This study analyzes the theoretic al aspects of soil compaction process and presents the results of field experimental evaluation. A square network of CFMS piles was constructed at Lai Cach Industrial Park, Hai Duong Province, Vietnam to evaluate the actual effectiveness of soil reinforcem ent for two types of soft soil: clay and sandy clay, both in their soft state. The CFMS piles, with a diameter of 300mm and a depth of 7.0m, were divided into three groups based on varying adhesive content (ADH) and the fly ash (FM)/cement (CM) ratio: Grou p 1 (ADH of 5% and FM/CM of 0%), Group 2 (ADH of 10% and FM/CM of 10%), Group 3 (ADH of 15% and FM/CM of 20%). Theoretical analysis indicated that two compaction processes occurred in soft soils: instantaneous compaction and time - dependent compaction. The effectiveness of the soft soil reinforcement was evaluated th rough laboratory tests on soil samples taken before and immediately after reinforcement . The results revealed th e following changes: the moisture content decreased by 2.39% in clay and 7.07% in s andy clay, the unit weight increased by 1.04% in sandy clay and 1.06% in clay, the void ratio decreased by 2.22% in clay and 6.58% in sandy clay, the coefficient of compressibility decreased by 2.86% in clay and 3.13% in sandy clay. Dynamic penetration tes ts (DCP) were conducted at three different stages: before reinforcement, immediately after reinforcement and 10 days after reinforcement. The results indicated that the dynamic penetration resistance (q d ) increased by 9.8% in sandy clay and by 14.8% in cla y immediately after reinforcement; after 10 days of reinforcement, q d in Group 1 (q d - 10 - 1 ) increased by 19.3% in sandy clay and by 27.7% in clay; in Group 2 (q d - 10 - 2 ), it increased by 52.3% in sandy clay and by 47.9% in clay; and in Group 3 (q d - 10 - 3 ), q d increased by 67.0% in sandy clay and by 59.1% in clay.