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15 December 2018, Volume 40 Issue 6
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    Review
    RESEARCH PROGRESS OF LOCKED-IN STRESS IN ROCKS1)
    GENG Hansheng, XU Hongfa, CHEN Xiao, BAI Zhun
    2018, 40(6):  613-624.  doi:10.6052/1000-0879-18-195
    Abstract ( 349 )   PDF (1949KB) ( 506 )  

    The influence of the locked-in stress on the rock mechanical properties cannot be ignored. Since Chen Zongji proposed the definition of the locked-in stress in rocks, there were very few related studies. Starting from the definition, combined with the current development of the rock mechanics, this paper expands the concept of the locked-in stress,in a new definition of the locked-in stress in rocks. The forms of the stress in accordance with the new definition of the locked-in stress in the rock mechanics research are classified. The variation law of various kinds of locked-in stress and its empirical formula are summarized. The correlation between the locked-in stress and the excavation of the underground engineering and its influence are discussed. This paper provides a new way to explain the special phenomenon of deep rock mechanics.

    Applied Research
    EXPERIMENT STUDY OF I TYPE CRACK BLUNT EXTENSION INDUCED BY WEAK PLANE1)
    DONG Kangxing, WANG Suling, LI Jinbo, FANG Xinyao
    2018, 40(6):  625-629.  doi:10.6052/1000-0879-18-194
    Abstract ( 474 )   PDF (16211KB) ( 332 )  
    Shear failure of weak interface as natural cracks or bedding is the key factor for the formation of crack network. Based on the principle of a three-point bending test, this paper sets up the test bed of mode I crack extension weak plane. The digital image correlation method is used to obtain the specimen surface displacement and strain field changes when the crack extends through the weak plane. The experiment results show that: when the crack extended at the weak interface, the extension stopped transitory, the COD (crack opening displacement) increased rapidly, the crack blunted, the shear strain increased rapidly, the mode I crack transforms to a mixed mode I-II crack and the crack extended deflective.
    GALLOPING BEHAVIORS OF SECTOR-SHAPE ICED EIGHT BUNDLE CONDUCTORS1)
    CAI Mengqi, XU Qian , ZHOU Linshu , LIU Xiaohui , YAN Bo
    2018, 40(6):  630-638.  doi:10.6052/1000-0879-18-061
    Abstract ( 233 )   PDF (11770KB) ( 339 )  
    The sector-shape iced eight UHV (ultra-high voltage) bundled conductors are in a condition more similar to the heavy ice conditions than that of the crescent-shape ice. Test models of sector-shape cross section iced eight bundled conductors are prepared. The aerodynamic coefficients of the sector-shape iced conductor models varying with the wind attack angle are obtained by the wind tunnel test. Based on the wind tunnel test results of sector-shaped iced eight bundle conductors, the numerical methods are used to study the effects of critical parameters on the galloping of eight sector-shaped iced conductors. The effects of the wind velocity, the span length and the initial wind attack angle on the galloping of sector-shaped iced eight bundled iced conductors are investigated. The result shows that the sector-shaped iced eight conductors can reflect the galloping characteristics of eight bundle conductors under heavy ice conditions.
    REBOUNDING OF GALILEAN CANNON FROM A RIGID WALL1)
    LIU Lizhi, WANG Bingxiang, ZHENG Yuxuan, YU Tongxi, ZHOU Fenghua
    2018, 40(6):  639-646.  doi:10.6052/1000-0879-18-203
    Abstract ( 266 )   PDF (9530KB) ( 365 )  
    The Galilean Cannon involves a chain of different size balls rebounding on a rigid wall. Three mechanical models are used to analyze the rebound process: (1) The rebounding is treated as a series of separated one-to-one "elastic" impacts; (2) The rebounding is treated as a one-dimensional multi-body impact, using the Hertzian contact model to describe the rigid body interactions; and (3) The rebounding process is simulated using a 3-D FEM software. Each model reveals a disintegration phenomenon of the ball-chain after impact. It is shown that the rebound speed of the smallest ball in the far end of the chain can be several times larger than the incident speed. The increase of the rebounded speed is more significant when a spacing is assigned between the balls so that the multi-impacts occur as "separated" impact events. Also the differences among the three analytical models are discussed. Experiments are conducted with agreeable results as compared with the theoretical analysis.
    2018, 40(6):  647-652.  doi:10.6052/1000-0879-18-198
    Abstract ( 357 )   PDF (3964KB) ( 348 )  
    This paper extends the p-type superconvergent recovery method to the finite element elastic stability analysis of Euler beams. Based on the superconvergence properties of the buckling loads and the nodal displacements in the buckling modes in regular FE solutions, a linear ordinary differential boundary value problem (BVP) is set up, which approximately governs the buckling mode in each element. This linear BVP within an element is solved with a higher order element, and a more accurate buckling mode is recovered. Then by substituting the recovered buckling mode into the Rayleigh quotient in analytic form, the buckling load is recovered. This method is simple and clear. It can improve the accuracy and the convergence rate of the buckling loads and the buckling modes significantly with a small amount of computation. Numerical examples demonstrate that this method is reliable and efficient and is worth further extending to other skeletal structures.
    ANALYSIS OF MECHANICAL CHARACTERISTICS OF FROZEN CLAY AND MODIFIED S-M CREEP MODEL1)
    GUO Mengyuan, YAO Zhaoming, LI Mengjie, CHEN Junhao
    2018, 40(6):  653-660.  doi:10.6052/1000-0879-18-107
    Abstract ( 240 )   PDF (2893KB) ( 236 )  
    To describe the mechanical characteristics of the mine soil layer constructed by the artificial freezing method, the uniaxial compressive strength test and the uniaxial compression creep test are carried out by using the remolded soil samples of a certain mine, and the stress-strain curves and the creep curves of the remolded frozen clay at different temperatures and loading grades are obtained. Experimental results show that the uniaxial strength of the soil is higher at a lower frozen temperature; The creep deformation of the soil increases with the increase of the stress level at the same frozen temperature; The isochronous stress-strain curve of the uniaxial compression creep deviates with respect to the strain axis with time. The soil sample experiences two stages of the initial creep and the stable creep, with a tendency to enter the accelerated creep stage in a higher stress level. By modifying the meaning of the parameters in the Singh-Mitchell model and with consideration of the influence of temperature, the improved S-M creep explicit model of the artificial frozen clay is obtained. Then the parameters of the S-M creep explicit model are optimized by using the particle swarm algorithm. Compared with the modified S-M explicit model, the calculated values are in good agreement with the experimental data, which indicates that the modified S-M creep explicit model can well simulate the creep characteristics of the deep frozen clay. The modified S-M creep explicit model provides a new method for the creep calculation of the artificial frozen soil.
    MECHANICAL MODEL OF COLUMN BASE CONNECTION IN ANCIENT TIMBER STRUCTURES1)
    WANG Ziang, GUO Rui, QIAN Xingjian, YANG Ruixin, DAI Jianbo, HE Jiayong
    2018, 40(6):  661-665.  doi:10.6052/1000-0879-18-141
    Abstract ( 578 )   PDF (423KB) ( 290 )  
    According to the investigation of earthquake damage over the years, the slippage of the column foot is a typical damage of the column base connection part of ancient timber structures in Sichuan areas. In order to predict the slippage of the column foot and determine the degree of earthquake damage of ancient timber structures, the column base connection is chosen as the research object. The connecting part is simplified into horizontal and rotating springs, then the dynamic equations of structures are established accordingly. In the solution process, the irregular seismic excitation is simplified, and the peak excitation is used as the constant input. The equivalent stiffness and the correction coefficient are introduced to modify the equation and the solution results, and finally the expressions of the slip distance of the column foot, the maximum slip distance and the maximum inclination angle of the column are obtained.
    MODEL ESTABLISHMENT AND LOAD TRANSFER OF SEMI ARTICULATED FLEXIBLE DRILLING TOOL1)
    LUO Min, DONG Xiaona, XU Tingting, LI Qiaozhen
    2018, 40(6):  666-670.  doi:10.6052/1000-0879-17-444
    Abstract ( 239 )   PDF (4913KB) ( 275 )  
    The load transfer law of the semi articulated flexible drilling tool directly affects the drilling in ultra short radius horizontal wells. In this paper, firstly, the element stiffness equation is deduced and the bending moment transfer rule of the semi articulated flexible drill is obtained. Then, combining the theoretical analysis and the numerical simulation, the semi articulated flexible drill rod model is verified. Finally, the semi articulated flexible drill mechanical model is established in the build section and the load transfer under different borehole curvature radius conditions is discussed. The analysis results show that with the same well depth, with the increase of the radius of curvature, the bottom hole torque value increases, when the semi articulated flexible drill rod is not locked, the semi articulated flexible drill rod does not transfer the bending moment and increase the large fluctuate torque at the bottom hole . The research results provide a theoretical basis for the design of flexible drilling tools.
    2018, 40(6):  671-675.  doi:10.6052/1000-0879-17-437
    Abstract ( 337 )   PDF (709KB) ( 372 )  
    In order to establish the calculation theory of flexural buckling critical loads for axial compression members under normal conditions, First of all, the total potential energy equation for bending buckling of bars was derived, then the critical loads for four kinds of end constraint conditions were obtained by employing Rayleigh-Ritz method and based on the principle of potential energy stationary value theory, and the formula of critical load amplification coefficient was given by comparing the Euler's critical load, which was able to consider the influence of slenderness ratio, compression deformation, shear deformation and cross-sectional shape coefficients, and the formula was derived in this paper can be used to calculate the critical loads for compression bars in possession of smaller slenderness ratio. The analysis of the critical loads between the circular-section and the biaxial symmetric I-section axial compression members show that the slenderness ratio of the member is the dominant factor affecting the amplification coefficient.
    2018, 40(6):  676-682.  doi:10.6052/1000-0879-18-101
    Abstract ( 436 )   PDF (7216KB) ( 489 )  
    A floating object is just supported at the buoyant center, which varies with the equilibrium attitude of the object. It is stability at the least distance between the gravity center and the buoyant center. A floating cylinder may have two to five equilibrium positions, of those one or two are stable. The stable posture is related to its specific gravity and the ratio of length to diameter, and catastrophe maybe induced as the system parameters change continually.