Author collect a lot of informations about stability calculation. model test and monitoring on site for surrounding rock in the Laxiwa. Ertan. Lubuge underground plant etc. and Jingchuan tunnel.trying to find out its deformational law in high in-situ stress region and trying to put forward some suggestions about the design of plant.
It is a vital technical problem to keep stability of surrounding rock in an underground project. As the in-situ stress is higher and its horizontal stress component is bigger in the high in-situ stress region. the problem is noticeable.
We collect a lot of informations about stability calculation, model test and monitoring on site for surrounding rock in the Laxiwa, Ertan, Lubuge, Beishan, Dongfong and Longtan undergound plant, and Jinchuan tunnel, trying to find out its deformational law in high in-situ stress region and trying to put forward some suggestions about the design of plant.
1.1 Becase of the excavation of chamber, there exists a redistributive region of stress. The informations of Ertan and Longtan show that its depth is as much as width of the main generator room and its width is as much as the higth of the main generator room.
There is an area of stress concentration of the vault and botton of chamber mass. The strain energy is 7–8 times greater than the original. There is an area of stress relaxation in side of chamber mass, the strain energy is sixty percent as much as the original.
1.2 Except that deformation in part corner, generally speaking, along with excavation of chamber the deformation of surrounding rock always points to free boundary. Generally, the displacement of vault and bottom is less than one of central section of side wall. The maximum displacement very often happens at central section of side wall in upper side of main generator room or in lower side of tailrace surge chamber. It aforesaid is 2–5cm.
As the effect of shear stress, freguently, the desplacement in the some derection as shear stress is just a litter bigger than that in the opposide direction.
In addition, the monitoring result on site of Lubuge shows that along with the distance increasing to boundary, the displacement of rock mass shows a trend to zero.
1.3 Generally, there is a compressive region at vault. The tress concentration factor is 3.3–3.7. The bottom of main generator room and tailrace surge chamber is also the concentrated region of compressive stress. The stress concentration factor is 2.92 at Lubuge test in site. But there is lower compression stress or tension region in the central area of rock mass.
In the cross parts of main generator room and tailrace surge chamber with tail tunnel or with traffic tunnel, the stress is much complicated. In accordance with three dimensional calculation of Ertan, the maximum principal stress is 110Mpa, which is 4.9 times higher than the orignal.