## 2 Materials and Methods
### Test Methods
Figure 2: Test processes: (**a**) Cylindrical mold under hydraulic uniaxial compression; (**b**) Packaged sample to be tested; (**c**) High-precision electronic scale; (**d**) Water absorption process of samples; (**e**) Saturated sample at the end of the tests. water content in a very short time, and the curve is linear and almost vertical. (2) Section II: deceleration water absorption section; within the time equivalent to several tens of times of Section I, the water content reaches 80% of the saturated water content and the curve is concave. (3) Section III: slow water absorption section; compared with the first two sections, the water absorption time was significantly increased and the change rate of water absorption velocity is significantly reduced. \[w=A_{1}\times e^{-\frac{t}{t_{1}}}+A_{2}\times e^{-\frac{t}{t_{2}}}+w_{0}, \tag{3}\]  
where, \(w\) is the water content. \(w_{0}\) is the offset, which is close to the saturated water content, and the value here is 17.6. \(t\) is the water absorption time. \(A_{1}\) and \(A_{2}\) are the amplitudes, which are negative values of all experiments, and the values here are \(-12.1\) and \(-6.1\), respectively. \(t_{1}\) and \(t_{2}\) are water absorption time fitting parameters and the values here are 7.1 and 430.7, respectively. According to the average water absorption velocity, a linear function is fitted (Equation (4), the corrected coefficient of determination \(R_{adj}^{2}=0.983\)) in the double logarithmic coordinate axis (base 10), and the rock water absorption velocity model is obtained. Additionally, according to the parameters \(t_{1}\) and \(t_{2}\) in Equation (3), the whole curve is divided into three sections. (1) Section I: the water absorption velocity is greater than 0.4%/min. (2) Section II: the water absorption velocity is between 0.004-0.4%/min. (3) Section III: the water absorption velocity is less than 0.004 %/min. Equation (4) can also be written in the form of Equation (5). \[y=a+bx, \tag{4}\]  
where \(y\) represents \(\lg(v)\). \(x\) represents \(\lg(t)\). \(a\) is the intercept and is always positive, and the value here is 0.54. \(b\) is the slope and is always negative, and the value here is \(-1.14\). \[v=10^{a}\times 10^{b\times\lg(t)}, \tag{5}\]  
where \(v\) is the water absorption velocity. Under the premise of considering the scale problem, the above laboratory test results can be applied to engineering. Reasonable measures are taken to prevent and control engineering disasters by judging the section of rock water absorption. When the water absorption of the rock is in Section I, the water content is small and the water absorption velocity is large, and the water source needs to be cut off in time to prevent the water content from increasing rapidly. When the water absorption of the rock is in Section II, the water can be cut off while absorbing water. At this time, the operability time for taking engineering measures is sufficient. When the water absorption of the rock is in Section III, the influence of water can be ignored in a short period of time because the rock is basically saturated and the project has not been damaged. This kind of situation is suitable for short-term use of rock engineering. For example, on the premise of exploring the fault and other failure surfaces of Norwegian subsea tunnel, the rock water absorption model proposed in this study can be used to judge the water absorption stage of the surrounding rock during tunnel construction and certain measures can be taken to prevent and control tunnel water inflow [16].