## 4 Discussion
### Mechanical Properties of Diatomite Soil in Triaxial Test  
In the triaxial test, the sample is saturated. This test controls the water content of the sample by controlling the different dry densities under the same density. A change in the mechanical properties of the sample was obtained. The results show that the shear strength of soil samples will be different under different dry densities. During the whole failure process of the sample, the volume of diatomite soil is easy to expand because of its water swelling property. It can change the stress of the diatomite soil in the shear process and affect its mechanical strength characteristics. The failure form of the soil sample is shown in Figure 6, in which it can be seen when the shear failure displacement occurs.  
Comparing the stress-strain curves of diatomite soil under three kinds of dry densities, it is found that when the dry density of diatomite soil increases from 1.30 g/cm\({}^{3}\) to 1.50 g/cm\({}^{3}\), the stress-strain curve of diatomite soil changes from a weak softening type  
Figure 6: Failure of diatomite soil sample.  
to a weak hardening type when the confining pressure is above 200 kPa, the failure mode of diatomic soil changes from brittle failure mode to plastic failure mode. When the water content of the soil sample is low, strain hardening will occur while the soil sample is damaged. The stress-strain curve of soil can be preliminarily fitted by hyperbolic equation [35]. The abscissa and ordinate of the curve equation are the principal strain \(\varepsilon\) in the shearing process of diatomic soil and the ratio \(\varepsilon/(\sigma_{1}-\sigma_{3})\) of the difference between the principal strain and the principal stress, respectively. The hyperbolic equation is as follows (1). From the hyperbolic equation, the equation on both sides of the equal sign can be obtained by mathematical operation, as follows (2):  
\[\sigma_{1}-\sigma_{3}=\frac{\varepsilon}{a+b\varepsilon} \tag{1}\]  
\[\frac{\varepsilon}{\sigma_{1}-\sigma_{3}}=a+b\varepsilon \tag{2}\]  
In the formula:  
\(a\)--Reciprocal of initial tangent modulus;  
\(b\)--Reciprocal of limit deviation stress.  
According to the shear curves of diatomic soil under the confining pressures of 200 kPa, 300 kPa, and 400 kPa with dry densities of 1.40 g/cm\({}^{3}\) and 1.50 g/cm\({}^{3}\), the \(\varepsilon\) and \(\varepsilon/(\sigma_{1}-\sigma_{3})\) values of the samples are fitted in a straight line. The resulting curve under the representative confining pressure of 200 kPa is shown in Figure 7.  
It can be seen that the relationship between \(\varepsilon\) and \(\varepsilon/(\sigma_{1}-\sigma_{3})\) of the shear results of diatomic soil under different confining pressures shows a high linear correlation in the equation, and the linear fitting effect is good. The results show that when the dry density of diatomic soil is 1.40 g/cm\({}^{3}\) and 1.50 g/cm\({}^{3}\) under a high confining pressure condition, the stress-strain curve of diatomic soil conforms to the weak hardening relationship of the soil sample, and the overall curve trend is similar to a hyperbola.  
The values of \(a\) and \(b\) at each confining pressure obtained by fitting the linear equations of \(\varepsilon\) and \(\varepsilon/(\sigma_{1}-\sigma_{3})\) is shown in Table 3. It can be seen that the inverse of the initial tangent modulus \(a\) and the inverse of the limit deviation stress \(b\) for the equation will change, the trend is that the value of \(a\) increases gradually and the value of \(b\) decreases gradually with the increase in confining pressures.  
Figure 7: Fitting curve of diatomic soil with different dry density under 200 kPa confining pressure.