（2.26）
And
                               （2.27）
Or
                              （2.28）
Hence,
                            （2.29）
Where  = vertical pressure
        = unit weight of rock mass
 = thickness of overlying rock mass
  = internal friction angle of rock mass
Note that when , , which indicates the sliding force of the block is totally overcomed by the friction along surface AB or CD.
        
●Vertical pressure of deep structures

Figure 2.6 shows a deep structure with vertical pressure. In such condition, the lateral friction is far exceed the weight of the sliding block column. So the part of ABCDE as shown in Figure 2.6 is called rock arching or pressure arching and only the lower rock masses of AED can produce pressure on the structure.

 
Figure 2.6 Vertical pressure of a deep structure

（a）Curve of pressure arching
As shown in Figure 2.7.  is assumed to be a uniform load along the axis of the pressure arch, and from the law of Zero force moment, we have 
 
Figure 2.7 Pressure arching
        
                                      （2.30）
Where  = horizontal force at the crown of pressure arching. And the curve of the pressure arching is a second-degree parabola.
（b）Height of pressure arching
In Figure 2.7, the pressure at the crown is balanced by the horizontal reaction force  and when T≥H,，the pressure arching is stable. The force T is produced by friction resulting from pressure  . The total vertical reaction force A produced by pressure q can be expressed as
                                                       （2.31）
    And the horizontal friction is
                                              （2.32）
When T=H，the pressure arching is at a limit state, and the equation for pressure arching can be expressed as
                                       （2.33）
If x=a1，solving equation (2.33), the height of pressure arching is equal to
                                        （2.34）
The height   at any point of the pressure arching is 荷载设计英文文献和中文翻译(6):http://www.751com.cn/fanyi/lunwen_34334.html