Strength-deformation and pore pressure characteristics Of fine sand stabilized with various additives

Abstract

This research presents a cost effective and environmental friendly chemical solution to stabilize fine sand against excessive pore water pressure generation during an undrained loading condition. Seven additives were chosen to find suitable sand additive combinations for stabilization purpose. Series of consolidated undrained triaxial tests and unconfined compression tests were conducted on different sand additive combinations on specimen size of 38.1 mm diameter and 76.2 mm height prepared by the moist tamping method using 10% moisture content. Curing was done by spraying water at an equal time interval. During triaxial test back pressure, saturation was done and pore pressure parameter B value was kept between 0.90~0.95. A preliminary test program was conducted before starting the stabilization phase. A group of samples with relative density 50% were prepared with fine sand and 5% of seven different additives, namely ordinary Portland cement(OPC), Portland cement(PC), bentonite, gypsum, lime, slag and fly ash to observe the individual performance of additives. Almost 50 unconfined compression tests were conducted on 7, 14 and 28 days cured samples and 7 consolidated undrained triaxial were conducted on 28 days cured samples. From the test results, it was observed that cement mixed samples exhibited the highest strength and lowest pore water pressure in all curing ages. Bentonite and gypsum mixed samples showed good strength and less pore water pressure after 28 days curing. Lime, slag and fly ash treated samples showed very poor strength and high pore water pressure in all curing ages. On stabilization phase considering the future availability of fly ash in Bangladesh it was attempted to utilize fly ash to stabilize fine sand. To stabilize fine sand another group of samples with relative density 25% were prepared with sand and combinations of different percentage of additives as (slag, lime, fly ash and Portland cement). It was observed that sand treated by increasing the percentage of fly ash decreased the strength of samples and generate more pore water pressure. To reduce pore water pressure slag, lime and Portland cement were added and the observation was addition of Portland cement was more effective than the addition of lime and slag. Because only 7% to 14% Porlant cement increased the strength of sand-fly ash sample a lot and decreased pore water pressure while the percentage of fly ash is high. On the basis of test results, suitable combinations as sand combined with 20% fly ash and 7% PC and sand combined with 40% fly ash and 14% PC were proposed for improving loose sandy deposits against liquefaction and other possible hazards.