# One-Dimensional Consolidation Properties of Soft Clay under Multi-Stage Loading
## 3 Test Results and Discussion
### Variation Law of Consolidation Coefficient  
Excess pore pressure is generated in soil when it is subjected to external loads. The water present in the soil pores is gradually discharged, leading to a reduction in excess pore pressure ([PERSON] and [PERSON], 2013; [PERSON], 2013). The rate at which this dissipation occurs is commonly quantified using the consolidation coefficient (\(C_{v}\)). In this study, a one-dimensional compression test was conducted to determine the relationship between the deformation of undisturbed soil specimens over time under different consolidation pressures. The consolidation coefficient was calculated using Equation (2):  
\[C_{v}=0.848\frac{H^{2}}{t_{90}} \tag{2}\]  
where \(C_{v}\) is the vertical consolidation coefficient; \(H\) is the maximum drainage distance; \(t_{90}\) is the time required for the degree of consolidation to reach 90%, which can be obtained by drawing the curve between the reading of the dial indicator of the consolidation test and the square root of time. Figure 3 illustrates the variation in the consolidation coefficient of saturated soft soil under multi-stage loading. As the consolidation pressure (\(P\)) increases, the consolidation coefficient (\(C_{v}\)) gradually decreases. This decrease can be observed in two stages: an initial rapid decrease followed by a slower decrease. During the first stage of loading (\(P\) = 50 kPa), the soil undergoes a rapid discharge of pore water and the compaction of pores, transitioning from a soft plastic state to a plastic state. This stage is known as the rapid consolidation stage. Subsequently, after consolidation and stabilization from the first stage, the soil enters a stage of slow consolidation. In the second, third, and fourth stages of loading, the discharge of pore water is hindered, resulting in a slower rate of consolidation deformation. Studies conducted by [PERSON] et al. (2013) on soft soils in Shenzhen, [PERSON] et al. (2013) on soft soils in Singapore, and by [PERSON] et al. (2013) on soft soils in Gemas and Kluang have indicated that the consolidation coefficient decreases with increasing consolidation pressure. However, [PERSON] et al. (2013) have demonstrated that the consolidation coefficient is also influenced by the stress history. Both overconsolidated and underconsolidated soft soils exhibit distinct patterns of change. The process of consolidation deformation of soft soil can be analyzed using the microstructural model of soft soil established by [PERSON] et al. (2013). In its natural state, the soil contains a significant amount of pore space, including overhead macropores and micropores. The soil particles mainly consist of silt and sand particles, which do not form the soil skeleton. During the rapid consolidation stage, the external load is primarily supported by the pore water in the overhead macropores. The soil contains numerous interconnected macropores, resulting in a considerable permeability coefficient (\(k_{v}\)) and consolidation coefficient (\(C_{v}\)). As pore water is discharged, the macropores gradually compress. The compression of macropores in the soil allows larger consolidation pressures to compact and block more drainage channels compared to under smaller pressures, resulting in a significant decrease in \(k_{v}\). This decrease in \(k_{v}\) bis the main reason for the sharp decrease in \(C_{v}\) when \(P\) increases from 0 to 50 kPa. The error between the theoretical calculation and experimental values is significant, as depicted in Figure 3. This discrepancy can be better understood by examining the definition and calculation formula of the soil's consolidation coefficient. The consolidation coefficient is a crucial parameter that indicates the rate at which soil consolidates.