## 5 Other Applications
### Rock Load  
In underground excavations, generally, the load on installed support is known as rock load. It indicates the rock pressure that results from the rock-load height above the underground excavation. Reliable forecast of rock load is one of the toughest jobs in rock engineering. [PERSON] was the first whose rock-mass classification system,--that is, rock-load classification--was used to estimate the rock load to be carried by the steel arches installed to support a tunnel [5], as shown in Figure 2.  
Since then, different methods, including empirical, analytical, numerical and experimental approaches, were used for prediction of the rock load [9; 124; 125; 126]. According to [PERSON] [9] and supported by [PERSON] [88], the rock load is free of the tunnel size in rock and [PERSON] expressed this using Equation (65).  
\[P=\frac{2\times J_{n}^{1/2}\times Q^{-1/3}}{3\times J_{r}}\ (\mathrm{kg/cm^{2}}) \tag{65}\]  
The correlation of Equation (65) has proven useful, except in cases of squeezing-ground conditions. For squeezing ground, three adjustment factors were applied to [PERSON]'s original equation, including the tunnel depth factor, tunnel radius factor and correction factor for time [127; 128]. The application of the _RMR_ system was introduced for the support load by [PERSON] [124] based on the old version of _RMR_ and extended for _RMR_\({}_{89}\) using Equation (66). He defined the rock load as unstable zone height above the excavation crown, which tends to collapse ultimately.  
\[P=\frac{100-RMR_{89}}{100}\gamma B, \tag{66}\]  
where \(p\) is the support load (kN), \(B\) is the tunnel width (m) and \(\gamma\) is the rock density (kg/m\({}^{3}\)).  
Since the above equation is based on a coal mine roadway, the evaluation of this equation for rock tunnel applications shows that the estimated support pressure is unsafe in squeezing conditions [128]. Furthermore, the estimates for the non-squeezing condition are unsafe in the case of a small tunnel and are overestimated for a large tunnel. The following correlations (Equations (67) and (68)) have been  
Figure 2: Development of loosened ground zone in response to tunnel construction. \(B\) and \(H_{t}\) are the width and height of the tunnel, respectively, \(H_{p}\) and \(B_{i}\) are the height and width of the arching zone, respectively and \(H\) is the depth of the tunnel from the ground surface.  
proposed for a rock tunnel, taking the tunnel depth and tunnel radius as two additional parameters with _RMR_ for non-squeezing and squeezing conditions [128].  
For non-squeezing ground:  
\[P=\left(2.32-0.035\times RMR_{89}+0.001\times H+0.03\times a\right),\,MPa \tag{67}\]  
For squeezing ground:  
\[P=\left(f(RMR_{89})/12\right)\times 10^{\left(1.8H^{0.4}\times d^{0.1}/RMR_{89} ^{1.2}\right)},MPa, \tag{68}\]  
where \(P\) is the ultimate support pressure, \(f(RMR_{89})\) is the correction factor for the tunnel closure, \(H\) is the tunnel depth (m) and \(a\) is the radius of the tunnel (m).  
Due to the widespread acceptance of _GSI_ in rock engineering, Equation (66) is considered the core origin for the Equation (69), which is based on _GSI_ for the calculation of support pressure [129].  
\[P=\frac{100-\left[\left(1-\frac{D}{2}\right)\sqrt{\frac{\sigma_{cr}}{100}}GSI \right]}{100}C_{s}S_{q}\gamma D_{e}, \tag{69}\]  
_GSI_ defines the quality of rock-mass, \(D\) is the disturbance factor, \(\sigma_{cr}\) is the residual compressive strength of the rock mass in the broken zone around the tunnel, \(D_{e}\) is the equivalent diameter of the excavation, \(\gamma\) is the unit weight of rock mass, \(C_{s}\) is the correction factor for the horizontal-to-vertical field stress ratio and \(S_{q}\) is the correction factor for the squeezing-ground condition.