# New Method to Estimate Rock Mass Deformation Modulus Based on BQ System
## 3 Engineering and Geological Background, Test Methods, and Results  
### Maerdang Hydropower Station  
The Maerdang dam and hydropower project is located in the main channel of the Yellow River, about 5 km upstream of the town of La Jia, Ma Qin County, Qinghai province, in the hinterland of the Qinghai Tibet Plateau. The area has a seismic intensity level VII. Its barrage is a rock-fill dam with a maximum height of 215 m, and a normal water level of el. 3275 m.  
The rock mass of the dam foundation is mainly Middle and Upper Triassic metasandstone, along with Mesozoic monzonite and tertiary breccias, all of which can be classified as hard rock. The development law of discontinuities in the three rock masses is basically the same, which can be generally divided into four groups, all in a flat, straight, and closed state.  
The deformational properties of the dam foundation rock mass were investigated using a total of 26 plate loading deformation tests, of which 11 were on metasandstone, 13 on monzonite, and 2 on breccia. Additionally, to obtain the BQ value and subsequently establish the relationship between this and the deformation modulus of the rock mass, the seismic wave velocity along the adult wall near each test site was measured, and a detailed survey was performed on joints in the rock mass. The experimental methods strictly followed the guidelines outlined in the Code for rock tests in water and hydropower projects (SL/T 264-2020) [21].  
Because an intensely weathered rock mass cannot normally be used as a dam foundation, the deformation tests were mainly carried out in slightly or moderately weathered rock masses: 19 were slightly weathered, 6 were moderately weathered, and only 1 was intensely weathered. The tests were divided into horizontal and vertical tests, according to  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**BQ Ratings** & **I** & **II** & **III** & **IV** & **V** \\ \hline Suggested value & \textgreater{}33 & 33–16 & 16–6 & 6–1.3 & \textless{}1.3 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Suggested value of rock mass deformation modulus for different ratings (in GPa).  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**BQ Ratings** & **I** & **II** & **III** & **IV** & **V** \\ \hline Number of samples & 89 & 184 & 262 & 184 & 178 \\ Minimum value & 20.6 & 5.24 & 0.92 & 0.57 & 0.003 \\ Maximum value & 72.19 & 57.50 & 25.10 & 9.55 & 2.32 \\ Average value & 42.70 & 26.30 & 10.82 & 4.12 & 0.56 \\ Mean square deviation & 11.36 & 10.96 & 5.19 & 1.92 & 0.58 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Statistical results of rock mass deformation modulus for different ratings (in GPa).  
the loading direction; the former was conducted on the adit wall, and the latter on the floor (shown in Table 5).  
All test points were machined by hand. The diameter of the rock surface was in the order of 60 cm, and that of the bearing plate was 40 cm. Surface undulation was limited to less than 5 mm. A total of five loading and unloading cycles were carried out at a time-controlled loading rate, with a minimum load of 1.280 MPa and a maximum of 9.088 MPa. The deformation modulus of the rock mass was calculated according to the formula of the local load on the surface of a semi-infinite elastic body assumed to be uniform, continuous, and isotropic. Considering that the actual load of a tall dam is generally very high and the deformation modulus is relatively higher at low stress, the final deformation modulus for each test point was determined as the mean value of the deformation modulus calculated for the last three loading stages.