# Static Properties of Kaolinite Samples from Different Structures and the Influence of Strain Rate
###### Abstract  
This paper conducts triaxial undrained tests on flocculated and dispersed kaolin samples at strain rate range 0.005-1%/min to investigate the effects of structure and strain rate on shear strength. The test results show that the flocculated samples exhibit strain hardening behaviour, while the dispersed samples show strain softening behaviour. The strain rate sensitivity parameter reflects the degree to which shear strength increases with increasing strain rate. The structure affects the strain rate sensitivity parameter, with values of 4.79% and 2.31% for flocculated and dispersed samples, respectively. When the strain rate is 1%/min, due to the low permeability of the dispersed sample, the high strain rate causes a rapid increase in local pore pressure, while the postponed dissipation of excess pore pressure destroys the sample. When studying the influence of clay structure, it is important to use the same strain rate; otherwise, the differences in shear strength may be underestimated. structure; clay; triaxial test; strain rate; shear strength +
Footnote †: journal: Applied sciences  
0000-0002-4115, 0000-0002-4  
on soils with two different plasticity indices. The results showed that, for small specimens, the shear strength increases with the increase in strain rate. Previous studies have shown that the physical and mechanical properties of clay are highly correlated with its micro-pore structure. The latest research findings also indicate that the ionic concentration and pH value of pore fluids can alter the microstructure of clay, thereby affecting its mechanical properties [13]. Some macroscopic mechanical properties can be explained using microscopic structures. In the past, scholars studied the microstructure of clay using optical microscopes, scanning electron microscopes (SEM), and mercury intrusion porosimetry (MIP) [14; 15; 16]. [PERSON] and [PERSON] [17] proposed the concepts of flocculated and dispersed structures. In a flocculated structure, the static interaction forces between adjacent particles during sedimentation are attractive, and soil particles are primarily arranged edge-to-edge (EE) and edge-to-face (EF). A dispersed structure refers to a structure in which the static interaction forces between adjacent particles during sedimentation are repulsive and soil particles are arranged face-to-face (FF). Subsequent researchers conducted a series of tests on flocculated and dispersed samples and indicated that structure affects the mechanical characteristics of clay [18; 19; 20; 21; 22; 23; 24]. Their research results found that the deviatoric stress-axial-strain relationship of dispersed samples exhibited strain softening, whereas flocculated structure samples exhibited strain hardening. Moreover, the shear strengths of the dispersed samples were greater than those of the flocculated samples. It is worth noting that, when conducted triaxial undrained shear tests on flocculated and dispersed samples, [PERSON] [18] and [PERSON] et al. [19] used the Germaine and [PERSON] formula [25] to calculate strain rate, and based on the calculated results, used different strain rates; whereas [PERSON] [21] used the same strain rate (0.05%/min). As mentioned earlier, the shear strength of clay measured at different strain rates varies. Therefore, determining the strain rate when comparing the two structures is worth discussing. Different countries and regions have adopted different standards for triaxial tests to determine strain rates, and there are major differences between these standards. Consequently, various scholars used different strain rates when they conducted triaxial undrained tests on clay, and there is a considerable discrepancy between the loading rates of actual engineering projects and conventional loading rates in laboratories. [PERSON] [26] suggested that the construction process may take a few days to several weeks, which means that the strain rates in the field are three orders of magnitude less than in the laboratory.