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The Mechanism and Application of Pre-tensioned Bolts Supporting Joints Rock Mas

Author: YangHuiMin
Tutor: DaiXingGuo
School: Central South University
Course: Engineering Mechanics
Keywords: joint rock mass pre-tensioned bolt Consolidation mechanism Finite element method contact element
CLC: TU476
Type: Master's thesis
Year: 2010
Downloads: 236
Quote: 1
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Abstract


Rock mass is the assembly of rock blocks with different size and position,The length,direction and angle of the joints exist in which are the critical factors to the rock mass condition.Therefore,when studying the damage and the stability of rock,solely based on the rock is not enough,we should thoroughly study the joint effects on rock mass strength. In order to ensure the rock excavation,the necessary measures must be taked to ensure their safety,Anchor technique is widely used in geotechnical engineering. Rock bolting is the most effective and also the most economical means of supporting excavations in rock. However,the mechanism of anchorage is still not known well.Analogical method or semi-theoretical,semi-empirical method are often adopt in most of the anchoring designs in engineering practice. The entire mechanical property of the joints rock mass after pre-tensioned bolts supporting should be studied basing on present theory foundation and applying to the rockmass engineering stability analysis.Firstly,the mechanical properties and status of joints causes are overviewed.According to the theory that Three failure models were proposed,and the mechanism and the failure strength criteria of the models was also analyzed.The extend direction of crack tips is given by the judgment of mini-plastic zone displacement.Subsequently,the supporting mechanism of the anchor are summed up.According to the theory that the bolt and the joint plane have the same distortion,the effective length and the optimal anchoring angle are discussed. Furthermore,by using of FEA code ANSYS,the mechanism of the pre-tensioned bolts are studied. The unrestricted segment of anchor cable is simulated with three dimension link element Link10,the interior anchoring part is simulated with usual link element Link8.A problem should be paid attention is that the nodes of anchoring part should coincide with the nodes of rock mass in order to keep harmony with displacement. The prestress ce applied by the equivalent temperature method. At last,the reinforce mechanism and effect of pre-tensioned bolts on roadway roof is explored. Main conclusions are as follows:(1)The reinforcement action of pre-tensioned bolts supporting joints rock mass mainly externalizes in creasing the interlayer-pressure and roadway roof pressure.(2) The prestress which is imposed on the anchor is mainly undertaked by the free section.Only a part of the restricted segment of anchor is effective. The position of the shear stress peak within the anchorage section is not changed with the various factors changing,but the magnitude of the peak is decreased with the stiffness increasing,or the pre-stressed of anchor and the shear modulus of rock decreasing.(3)The rock which in the surrounding of the tension-type prestressed cable anchorage’s restricted segment is pulled, therefore, a long range anchor should be adopted when anchot groups.(4) A contact element method based on the nonlinear contact theory is used to simulate the mechanical characteristics of the interface. The pre-tensioned bolts increase the joints pressure which is the mechanics of strengthening the joints roof. Thereby the joints sliding distance, the roof separation value and the roadway displacement is reduced.

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