Yieldable technology of lengthened bolts for high-stress soft rock roadways

Due to their large deformation and plastic zones, the high-stress soft rock roadways, for stability control, need the support materials which have high elongation, and are anchored to the deep layer of the roof rock. Based on the theory of “strong support and yield pressure”, a new type of lengthened bolt is invented to adapt to the deformation and failure of the soft rock roadways. Its length, elongation and broken load are 4 m, 17% and 195 kN, respectively. The constitutive models for lengthened bolt support system and bolt-cable support system are established. The result shows that the upper limit strain of constitutive model for support system should not exceed the maximum strain of support materials in order to guarantee the stability of support structure. The new lengthened bolt can provide more yield-pressure distance than the cable, which exactly assures both the stability and the support strength of the lengthened bolt support system in soft rock roadways. Under the experimental conditions, the resistance of the lengthened bolt support is about 170.2 kN, and the theoretical rock deformation, 0 m to 4 m away from the roadway roof, is 264 mm, which is close to the actual deformation value. The goal of “yield support” in high-stress soft rock roadways is effectively achieved.