## 3 Creep Characteristics of the Strongly Weather Argillaceous Sandstone
### Analysis of the Experimental Results
#### 3.2.2 Influencing Factors of the Creep Characteristics  
Many factors affect the creep characteristics of rock and soil (e.g., mineral composition, particle gradation, moisture content, and stress level). The variables tested in the creep tests performed here included moisture content, stress level, and confining pressure. Figure 8: Loading curves. (**a**) Natural state with 100-kPa confining pressure, (**b**) Saturated state with 100-kPa confining pressure, (**c**) Natural state with 200-kPa confining pressure, (**d**) Saturated state with 200-kPa confining pressure, (**e**) Natural state with 300-kPa confining pressure, (**f**) Saturated state with 300-kPa confining pressure. Figure 9: The full creep process curve. (a) Moisture content Table 4 shows the ratios of instantaneous strain to total strain. The percentage of instantaneous strain to total strain is relatively small for creep specimens with 13% moisture content compared with the saturated specimens, ranging from 49% to 83%. The unsaturated specimens required longer times to reach stable deformation and showed a slow overall adjustment process. The instantaneous strain of the saturated specimens accounted for a relatively high percentage (56-89%) and the time required to reach stable deformation was short, exhibiting a relatively fast overall adjustment process. This is because water can reduce the cementation between particles, thus playing a lubricating role in the movement of soil and stone. The cementation effect and friction between particles in the saturated state are strongly weakened when an external force is applied, with a low resistance to movement, rotation, and overturning between particles, thus increasing the speed at which internal adjustments can be completed. Figure 7 shows that the creep specimens with a 13% moisture content exhibited better regularity than the saturated specimens at the same proportionally increasing stress level. The strain increase with stress level and deformation were similar, except at the fourth loading level, when those of the less-saturated sample were slightly larger. The strain increase at each stress level varied for the saturated creep specimens. At low stress levels, the displacement variation was small; at moderate stress levels, the displacement change tendency increased; and at high stress levels, the displacement increased rapidly. The shear strength of the saturated specimens was smaller than that of the natural specimens, and the displacement of the saturated specimens at high stress levels showed rapid growth and poor stability. Moisture content therefore has an important influence on the creep characteristics of strongly weathered argillaceous sandstone, and effective hydrophobic drainage is required for slope protection management. (b) Stress level Stress level exerted the most notable effect on the specimen's creep characteristics. Higher stress levels were associated with larger instantaneous displacement, larger creep displacement, and longer times required to enter steady-state deformation. The stress level also determined the creep state of the specimens; when the stress level (SL) was low (0.2 \(\leq\) SL \(\leq\) 0.4) the specimens showed decay creep; at a medium stress level (0.6 \(\leq\) SL \(\leq\) 0.8) the specimens showed steady creep; and when the stress level was very high (SL = 1.0) the specimens exhibited accelerated creep and quickly experienced shear damage. (c) Confining pressure The effect of confining pressure on the creep of the specimens was more complex. Higher confining pressures were associated with shorter times required for a specimen to enter stable deformation. However, at the same stress level, a higher confinement pressure resulted in larger creep deformation. This occurred because, with increasing confining pressure, the stress level corresponding to the deviator stress also increased, the stress state increased, the specimen deformation accelerated, and the overall deformation increased.