Mumtaz A Usmen

EVALUATION OF RESILIENT MODULUS FOR LIME- AND CEMENT-STABILIZED SYNTHETIC COHESIVE SOILS

The effects of deviator stress, molding moisture content, stabilizer type and content, curing period, and soil type on the resilient modulus (Mr) of lime- and cement-stabilized cohesive soils were investigated by using Hydrite R (kaolinite) and sodium bentonite (montmorillonite) blends. It was found that Mr increases with decreasing deviator stress, increasing lime and cement content, and extended curing period. Moisture variations around optimum had little effect on Mr with higher lime contents. Multiple regression analyses and Students t-tests indicated that all the factors investigated were significant and could be related to Mr by predictive regression equations. For a given stabilizer type and content, the low-plasticity clay (CL) soil produced the best results. The cement-stabilized CL soil normal cured for 28 days produced the highest Mr value. However, cement stabilization was not found to be very effective for the high-plasticity clay (CH) soil. Mineralogical composition has a marked effect on the Mr of lime and cement-stabilized cohesive soils. Kaolinitic CL soils work better than montmorillonitic CH soils with both lime and cement.

Ultrasonic Testing for Evaluation of Stabilized Mixtures

Tests were conducted to evaluate the feasibility of using ultrasonic testing for stabilization applications. The ultrasonic testing consisted of determining primary-wave (P-wave) velocities of stabilized mixtures. The ultrasonic method involves a simple and fast test procedure that allows for repeated assessment of a sample over time. For the testing program, tests were conducted on a high plasticity clay stabilized with lime, cement, and fly ash and a Type F fly ash stabilized with lime and cement. Compaction characteristics of the mixtures were determined using modified Proctor tests. Unconfined compression tests were used to determine compressive strength and modulus of the mixtures immediately after sample preparation and after 7-day and 28-day curing periods. Ultrasonic tests were conducted on the compaction and compression test samples, and the test results were correlated. Variation of velocity with water content demonstrated a similar trend to the variation of dry density with water content for the soil. The velocity increased with increasing density for both soil and fly ash. For compression characteristics, velocity increased with increasing modulus for both soil and fly ash. The velocity correlated well with the unconfined compressive strength of fly ash samples. However, this trend was not as well defined for the soil. Overall, the test program demonstrated that ultrasonic testing can be used effectively to evaluate stabilized materials. P-wave velocity correlations can be used to verify the quality of field placement of stabilized mixtures and to improve mixture design procedures.

Ultrasonic Assessment of Stabilized Soils

The feasibility of using ultrasonic testing, in particular P-wave velocities, to evaluate stabilized soils was investigated. A high-plasticity clay soil that was stabilized with lime, cement, and lime — fly ash mixtures was used in the study. The testing program consisted of determination of P-wave velocities and compression characteristics of the stabilized soils immediately after compaction and subsequent to 7 days and 28 days of curing. Variation of velocity with stabilizing agent, curing time, and also with the compression characteristics of the soils was investigated. It was observed that P-wave velocities were higher for samples stabilized with cement compared with samples stabilized with lime and fly ash. In addition, velocities increased with curing time for all the stabilized mixes. In general, the velocities of the samples increased as the unconfined compressive strength of the samples increased. However, there was a substantial amount of scatter in the data. The trends observed in the modulus data were better and the P-wave velocities of the stabilized soils increased as the modulus of the soils increased. Also the variation of modulus with time was similar to the variation of velocity with time. In addition, the P-wave velocities increased as the densities of the samples increased.