# Creep Model of Weakly Cemented Soft Rock Considering Damage and Secondary Development in FLAC3D
## 2 Experimental Study on Weakly Cemented Soft Rock
### Creep Test Result  
Referencing the aforementioned experimental protocol, creep tests on weakly cemented mudstone under different confining pressures were conducted, yielding full-stage creep curves under varying confining pressures, as shown in Figures 5a and 6a. [PERSON]'s loading method was used to process graded creep curves for different stress levels under distinct confining pressures, as presented in Figures 5b and 6b. The results indicate that, from the first to the fifth stress levels, the specimens exhibited only decaying and steady-state creep behaviors. Upon reaching the steady-state creep phase, the creep rate remained essentially constant, with axial, circumferential, and volumetric strains progressively increasing over time. At the sixth stress level (i.e., axial stress of 9.5 MPa under uniaxial conditions and 20 MPa under 2 MPa confining pressure), the axial stress exceeded the long-term strength of the rock. The specimen initially displayed decaying creep upon loading; however, once the axial strain reached a critical threshold, a rapid increase in the  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Confining** & **Elastic** & **Cohesion/MPa** & **Angle of Internal** & **Poisson** & **Compressive** \\
**Pressure/MPa** & **Modulus/GPa** & **Crisation/\({}^{\circ}\)** & **Ratio** & **Strength/MPa** \\ \hline
0 & 1.96 & 4.2 & 24.3 & - & 10.31 \\
2.0 & 2.24 & 4.2 & 24.3 & 0.46 & 21.19 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Mechanical parameters of weakly cemented mudstone samples.  
Figure 4: RLJW-2000 rock rheometer.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Confining** & **Level 1/MPa** & **Level 2/MPa** & **Level 3/MPa** & **Level 4/MPa** & **Level 5/MPa** & **Level 6/MPa** \\ \hline
0 & 5.5 & 6.3 & 7.1 & 7.9 & 8.7 & 9.5 \\
2.0 & 11.5 & 13.2 & 14.9 & 16.6 & 18.3 & 20 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Creep test stress level.  
axial strain rate was observed, transitioning to accelerated creep and ultimately leading to rapid failure over time.  
Under uniaxial conditions (Figure 5a), volumetric strain exhibited a four-stage evolution. During the initial loading phase, there was a rapid increase in volumetric strain. At low stress levels (\(\sigma_{1}\) = 5.5-6.3 MPa), the volume was compressed by 0.15% to 0.009%, indicating internal crack closure. In the intermediate stress stage (\(\sigma_{1}\) = 7.1-8.7 MPa), volumetric strain reversed and peaked at 0.21%, signifying that microcrack propagation surpassed pore compaction. As the stress level reached the late fifth stage (\(\sigma_{1}\) = 8.7 MPa) to pre-failure (\(\sigma_{1}\) = 9.5 MPa), volumetric compression began, with strain decreasing from 0.21% due to fracture network coalescence, leading to volume contraction and specimen failure. Under 2 MPa confining pressure (Figure 6a), the volumetric strain evolution differed markedly. In the low-stress stage (\(\sigma_{1}\) = 6.3-14.9 MPa), there was continuous volumetric expansion up to 0.85%, reflecting the confining pressure-induced suppression of lateral deformation and internal crack-dominated damage. When the stress reached \(\sigma_{1}\)\(\geq\) 16.6 MPa, volumetric strain decreased, while circumferential strain increased (Figure 6a), indicating the breakdown of confining constraints and axial plastic flow-dominated deformation prior to failure.  
Figure 5: Strain creep characteristics at \(\sigma_{3}\) = 0 MPa. (**a**) Total strain–time history curve. (**b**) Axial strain graded creep curve.  
Figure 6: Strain creep characteristics at \(\sigma_{3}\) = 2 MPa. (**a**) Total strain–time history curve. (**b**) Axial strain graded creep curve.