Numerical Simulation to Select Proper Strain Rates during CRS Consolidation Test

Abstract

Constant rate of strain (CRS) and incremental loading (IL)consolidation [3]. Constant rate of strain consolidation test reduces the required time for consolidation test using standard oedometer test (IL) from almost two weeks time to few hours. During CRS test the load is applied continuously; continuous record of stress and deformation are made, which improves the accuracy of consolidation properties determination in particular the preconsolidation pressure P c .Because of its many advantages, the CRS test is in many countries, a standard test for the determination of consolidation properties of clayey soils. It is adopted by the Swedish geotechnical institute, the Norwegian geotechnical institute, the French Laboratoire Central des Ponts et Chaussées (LCPC), and the American Society of Testing and Materials (ASTM) [4]. However, prior selection of a suitable strain rate for a given soil specimen, is still a problem to an extensive use of the CRS test in practice [4,5], and many researches were conducted to examine strain rate effect on measured CRS consolidation parameters [6][7][8][9].Comparison of CRS test results with those of conventional oedometer test has permitted to develop some criteria for the CRS test results acceptance. These criteria are essentially the relative pressure criterion R u [2,3,10], the liquid limit LL criterion [11], and the standardized strain rate parameter β based on the large strain theory [4,12]. The relative pressure criterion R u defined as the ratio of excess pore water pressure at the base of specimen ∆u H to applied vertical stress ∆σv is generally the most used criterion. However, literature survey shows important differences in the acceptable range of relative pressure values. Table 01 summarizes some relative pressure values recommended by authors for some types of soils, with relative pressure range varying from 5 to 50%. ASTM standard (ASTM 4186-06) recommends values of relative pressure to be between 3 and 15% during steady state stage of CRS test [13]. Similar range of relative pressure is also recommended by the French Laboratory (LCPC) [14].

An Investigation of Soil Void Ratio Effect on Liquid Limit Values Determined by Different Test Methods

“…There is no statement on the void ratio of specimens in relevant standards for the liquid limit tests. As the motivation for this study, the void ratio was thought to have a significant role on the liquefaction because it is an important parameter for strength and deformability properties of soil materials [18][19][20].…”