Experimental and theoretical investigation of constant rate of strain consolidation

Abstract

The Constant Rate of Strain (CRS) test provides an efficient and a relatively rapid method to determine properties (stress history, compressibility, hydraulic conductivity, and rate of consolidation) of a cohesive soil and possess many advantages over the incremental oedometer test. Ease of operation and the ability to take frequent readings provides tremendous labor savings and a better definition of the compression curve. However, the test has some disadvantages including, pore pressure measurement errors, initial transient conditions, and strain rate dependent soil behavior. There is also no set standard for the method of analysis to be used for interpretation of the CRS data. This experimental and theoretical study evaluates parameters that affect CRS test results, including strain rate sensitivity, testing device effects, and different methods used to interpret the data. An extensive program was conducted on Resedimented Boston Blue Clay (RBBC) and Resedimented Vicksburg Buckshot Clay (RVBC) to study the behavior during constant rate of strain consolidation. Strain rate sensitivity was measured using the Wissa Constant rate of strain device. Two special CRS tests were performed to evaluate the pore pressure measuring system and to. assess transient conditions. Two analysis methods proposed by Wissa et al. (1971) were scrutinized using a numerical simulation on a model soil. The stiffness of the pore pressure system relative to the soil stiffness is extremely important in tests with high ... Both soils were found to be strain rate sensitive. The softer RVBC had little sensitivity in compression and c, behavior. However, the k, decreased with increasing hydraulic gradient. Stiffer RBBC had a high sensitivity in compression and cv behavior. kv was insensitive to gradient but this observation is believed to be an error caused by the system stiffness. The findings support the use of either the linear or nonlinear theory provided the ... is kept below 0.15. The system stiffness, relative to the soil stiffness, is very important and negatively impacts results as the ... increases. The transient duration is well predicted by Wissa's F3 = 0.4 limit. Based on numerical simulation, it was shown that the established equations to compute k, and c, should be modified to account for large deformations.