(1) Principle of roadway support

In the soft rock roadway support, the soft rock enters the plastic state is inevitable, and it should be the best to achieve its maximum plastic load capacity; at the same time its huge plastic properties (such as expansion deformation energy) must be released in some form. One of the keys to soft rock support design is the choice of deformation release time and support time.

(2) Best support time and time

The theory of rock mechanics and engineering practice show that after the excavation of the chamber, the deformation of the surrounding rock gradually increases. Different from the deformation speed, it can be divided into three stages; namely, the deceleration deformation stage, the approximately linear constant speed deformation stage and the accelerated deformation stage. The optimal support time is the maximum of the engineering force P _R and the surrounding rock self-supporting force P _D transformed by the deformation, and the minimum support time of the engineering support force.

Figure 7-34 Best Support Time T _S

(two)   Common support form for soft rock roadway

(1) Anchor spray net support

The anchor spray net support series is an effective and practical support form for soft rock roadway. Shotcrete can close surrounding rock and isolated water in time. The net can not only support the surrounding rock between the anchors, but also connect a single anchor to the entire anchor group, and form a thin-walled reinforced concrete retaining ring with certain flexibility. The anchor spray net support allows a certain deformation of the surrounding rock, and the support performance meets the requirements for one support of soft rock. According to the surrounding rock conditions, it is also possible not to spray the concrete, but only the anchor net, the truss anchor net, the steel ladder anchor net, the steel belt anchor net support, or the secondary shotcrete support.

(2) metal stent yieldable

The U-shaped steel shrinkable metal bracket has the structural adjustability of the shrinkage and load-bearing capacity, and the surrounding rock stress is adjusted by the contraction and elastic deformation between the members. During the deformation and contraction of the support, the support resistance to the surrounding rock is maintained, and the surrounding rock stress tends to be in equilibrium. China has carried out a lot of research work on U-shaped steel shrinkable metal bracket post filling, inter-frame support, support material quenching and tempering treatment, standardization of support technology, etc. U-shaped steel shrinkable metal bracket has been widely used. .

(3) Arc plate support

In the soft rock, a round and shrinkable carcass support can be used to prevent water erosion and weathering, and the bottom sill can be effectively controlled. The measures for making the carcass contractible are "wood bricks, sewing stones, rounds" and strips. The arc plate bracket utilizes high-strength concrete construction technology to form a full-section closed, dense continuous high-strength reinforced concrete slab structure roadway support.

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