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Advanced Engineering Science

Gongcheng Kexue Yu Jishu/Advanced Engineering Science
Journal ID : AES-16-10-2021-23
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Abstract :

With the increasing depth of underground engineering, the accurate evaluation of the depth and the degree of excavation damage zone (EDZ) in deep rock engineering is gradually influenced by the high geostress field and it is important to assess the impact reasonably. Relying on the excavation of a deep diversion tunnel, the drilling plan of distressing the in-situ stress step by step was adopted. At the outer zone of sampling area, conventional sampling holes were drilled in the form of a circular closed boundary. And boreholes and low stress coring were also carried out at the centre of the sampling area. The acoustic detection results of the depth and the degree of the damage area under different in-situ stress levels were obtained at the same location by acoustic detection device, and laboratory tests were carried out based on the core samples from the holes above. The uniaxial compressive strength of rock mass under different in-situ stress levels were given from acoustic wave velocity results by Hoek-Brown strength empirical formula to represent rock mechanics properties. These above contributed to judge the influence of the different in-situ stress levels on acoustic detection and damage degree evaluation in blasting EDZ. Researches showed that the conventional acoustic detection of excavation damage zone in high stress area would underestimate the depth of surrounding rock and the damage degree, which would be underestimated about 10% to 30% when the initial stress was 45 MPa. When the local stress level was reduced from 45 MPa to 30 MPa, the uniaxial compressive strength of rock mass would be seriously overestimated about 30% to 100%. Therefore, the high in-situ stress level had a significant impact on the results of acoustic detection and damage zone evaluation of surrounding rock. The effect of in-situ stress level on acoustic detection must be taken into account and corrected properly by reducing and increasing in evaluating rock mass quality by using wave velocity index in engineering.

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Gongcheng Kexue Yu Jishu/Advanced Engineering Science
Journal ID : AES-16-10-2021-22
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Abstract :

In order to analyze the effect of coupling relationship between joint stiffness parameters on the dynamic performance of machine tool bolt joints surface, a response surface method which is based on the theory of response surface statistics was proposed to fit the natural frequency of generalized modal states and the dynamic stiffness of the joints. In this method, the natural frequency was taken as the critical index to describe the object dynamic characteristics, with which the mathematic relationship between dynamic characteristics and the stiffness parameters between the joints were analyzed. The response surface model of predicating the varying dynamic characteristics with the finite element models of single and two nodes was established by central composite experiment design and response surface method theory. The least square method with the response function and the experimental test value were taken as the optimization objective, the nonlinear programming and genetic algorithm were combined to realize the stiffness parameter identification of the joint part. The type of response surface function expression was selected to display the stiffness coupling relationship between multiple pairs of nodes, and the influence with the coupling of stiffness on the dynamics of components was revealed. In order to verify the feasibility of the method, one bolt assembly was taken as the research object. The central composite experiment was designed to determine the different combination values of the stiffness between the joints, and the natural frequencies related to the first 11 orders were acquired by conducting the modal analyses with the ANSYS software. Utilizing the acquired dynamic data, a second-order polynomial response surface model was established to describe the connections between the stiffness and the natural frequencies. The accuracy of the established model was validated after calculating the valuating indexes, the influence of the coupling of stiffness on the dynamic characteristics of the components was analyzed, and the effects of multiple rigidness coupling, uncoupling and single stiffness on the dynamic performance of structures were compared and analyzed. The results showed that the dynamic modeling simulation with multi-stiffness coupling is in good agreement with the modal frequency and mode of vibration measured in the test. The first 11 mean modal frequency error is only 1.6%, which proves the necessity of considering the coupling relation between equivalent stiffness.

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