Plasticity Index Ip Research Articles

A NEW MODEL OF FROST HEAVE PREDICTION FOR CLAYEY SOILS

After analysing the results of systematic experimental research on frost susceptibility tests, a new frost heave prediction model, including the heave ratio η and rate R, is first proposed in this paper. Six main factors influencing frost heave are considered: initial water content W, initial dry unit weight γd, frost penetration rate Vf, groundwater level Hw, plasticity index Ip and ion content S. The model could be expressed by: η= B0WB1γBd2VB31·exp(B4Hw)exp(B5Ip)exp(B6S) and R = B'0WB'1γB'2dexp(B'3Hw)exp(B'4Ip)exp(B'5S) with a good reliability, where B0 to B6 and B'0 to B'5 are the characteristic constants of clayey soils. The effect of each factor on frost susceptibility of soils is discussed also.

A new model of frost heave prediction for clayey soils

After analysing the results of systematic experimental research on frost susceptibility tests, a new frost heave prediction model, including the heave ratio η and rate R, is first proposed in this paper. Six main factors influencing frost heave are considered: initial water content W, initial dry unit weight γd, frost penetration rate Vf, groundwater level Hw, plasticity index Ip and ion content S. The model could be expressed by: η= B0WB1γBd2VB31·exp(B4Hw)exp(B5Ip)exp(B6S) and R = B'0WB'1γB'2dexp(B'3Hw)exp(B'4Ip)exp(B'5S) with a good reliability, where B0 to B6 and B'0 to B'5 are the characteristic constants of clayey soils. The effect of each factor on frost susceptibility of soils is discussed also.

Effects of Plasticity and Sample Disturbance on Statistical Properties of Undrained Shear Strength

ABSTRACT Statistical properties of undrained shear strength cu are investigated through laboratory and in-situ tests. In laboratory, a series of unconfined compression tests and triaxial UU tests are performed using mixed soil samples. Concerning in-situ soil samples, comparative study is made between disturbed and undisturbed soil specimens. Following findings and method are obtained : (1) When plasticity index Ip is greater than 15%, the difference of cu between unconfined compression test and triaxial UU test is less than 2% and is almost negligible. However, when Ip is smaller than 15%, unconfined compression test always provides smaller strength than triaxial UU test. cu of unconfined compression test is about 15% smaller than that of triaxial UU test when Ip≒ 10. (2) Concerning the coefficient of variation of strength V(cu), however, there is no significant difference between these two testing methods. Moreover, V(cu) is found almost independent of both plasticity index and consolidation pressure. (3) When soil specimens are disturbed, the mean value of qu becomes small while the coefficient of variation becomes large. In the case of E50, however, the coefficient of variation holds constant during disturbance procedure. (4) The method of predicting statistical values of strength of undisturbed specimens from those of disturbed samples is newly presented.

Influence of Strain Rate on Undrained Shear Characteristics of K0-Consolidated Cohesive Soils

In order to investigate the influence of strain rate on undrained shear characteristics of normally consolidated cohesive soils, K0-consolidated undrained triaxial compression and extension tests were performed on three kinds of cohesive soils with different plasticity index IP under different strain rate. The conclusions from this study are: The maximum principal stress difference and axial strain at failure increase with the increase of strain rate, whereas the pore pressure coefficient Af decreases. The magnitude of excess pore pressure, both in the compression and extension tests, at the same strain is found to be smaller as the strain rate increases in the case of plastic clay. This trend does not become clear as the plasticity index decreases. Initial portion of effective stress path progresses approximately elastically from the point of K0-consolidation for all the specimens, irrespective of different strain rates. The undrained shear strength anisotropy at high strain rate becomes smaller than that at low strain rate.

Undrained Shear Strength Anisotropy of Normally Consolidated Cohesive Soils

ABSTRACT In order to investigate the undrained shear strength anisotropy of cohesive soils of intermediate grading between sands and clays, a series of consolidated undrained triaxial compression and extension tests is performed on soil samples which are prepared by mixing Kawasaki clay and Toyoura sand (with crushed fraction) so as to obtain a wide range of soil type expressed in terms of plasticity index Ip. Four kinds of cohesive soil samples with Ip of 30, 20, 15 and 10 are tested. The conclusions from this study are: 1) Undrained shear strength anisotropy increases with decrease in Ip. And difference between values of (cu/p)E/ (cu/p)c obtained by CIU and CK0U tests increases as the plasticity index increases. 2) Relationship between cu/p values obtained by four types of consolidated undrained triaxial tests and Ip is quantitatively shown. 3) In view of either shape of effective stress paths and the undrained shear strength anisotropy, shear properties of cohesive soils of Ip of 20 and 30 are seen to be those of clays, however, soils of Ip of 15 and 10 are considered the intermediate soils. Based on results of the present study, a way of accounting for the anisotropic undrained shear strength in stability analysis is proposed, with assumption that the in situ undrained compression strength of vertical sample is known.