Mechanism of anomalous low friction phenomenon in deep block rock mass

Deep rock mass has the unique ＂self-stressed＂ block-hierarchical structure, anomalous low friction （ALF） was one of the typical nonlinear get-mechanical and dynamic responses in deep block rock mass, which occurred as the result of movements of large-scale get-blocks under the impact of external pulses （such as a deep confined explosion, earthquakes, rock bursts and etc.）. ALF phenomenon obtained its name to describe the curious phenomenon that the friction between interacting get-blocks qua- si-periodically disappears at some discrete points in time along the direction orthogonal to the direction of the external pulse. With the objective to confirm the existence of the ALF phenomenon and study the get-mechanical conditions for its occurrence experi- mentally and theoretically, laboratory tests on granite and cement mortar block models were carried out on a multipurpose testing system developed independently. The ALF phenomenon was realized under two loading schemes, i.e., blocks model and a working block were acted upon jointly by the action of a vertical impact and a horizontal static force, as well as the joint action of both ver- tical and horizontal impacts with differently delayed time intervals. We obtained the rules on variation of horizontal displacements of working blocks when the ALF phenomenon was realized in two tests. The discrete time delay intervals, corresponding to local maxima and minima of the horizontal displacement amplitudes and residual horizontal displacements of the working block, satis- fied canonical sequences multiplied by （√2）＇. Some of these time intervals satisfied the quantitative expression （√2）＇ ,alva. At last, 1D dynamic theoretical model was established, the analytical results agreed better with the test data, while the quantitative expression drawn from test data was not validated well in theoretical analyses.

Zonal disintegration phenomenon in rock mass surrounding deep tunnels

Zonal disintegration is a typical static phenomenon of deep rock masses. It has been defined as alternating regions of fractured and relatively intact rock mass that appear around or in front of the working stope during excavation of a deep tunnel. Zonal disintegration phenomenon was successfully demonstrated in the laboratory with 3D tests on analogous gypsum models, two circular cracked zones were observed in the test. The linear Mohr-Coulomb yield criterion was used with a constitutive model that showed linear softening and ideal residual plastic to analyze the elasto-plastic field of the enclosing rock mass around a deep tunnel. The results show that tunneling causes a maximum stress zone to appear between an elastic and plastic zone in the surrounding rock. The zonal disintegration phenomenon is analyzed by considering the stress-strain state of the rock mass in the vicinity of the maximum stress zone. Creep instability failure of the rock due to the development of the plastic zone, and transfer of the maximum stress zone into the rock mass, are the cause of zonal disintegration. An analytical criterion for the critical depth at which zonal disintegration can occur is derived. This depth depends mainly on the character and stress concentration coefficient of the rock mass.

Mechanism of zonal disintegration phenomenon in enclosing rock mass around deep tunnels

In order to study the mechanism of the zonal disintegration phenomenon(ZDP),both experimental and theoretical investigations were carried out.Firstly,based on the similarity law,gypsum was chosen as equivalent material to simulate the deep rock mass,the excavation of deep tunnel was modeled by drilling a hole in the gypsum models,two circular cracked zones were measured in the model,and ZDP in the enclosing rock mass around deep tunnel was simulated in 3D gypsum model tests.Secondly, based on the elasto-plastic analysis of the stressed-strained state of the surrounding rock mass with the improved Hoek-Brown strength criterion and the bilinear constitutive model,the maximum stress zone occurred in vicinity of the elastic-plastic interface due to the excavation of the deep tunnel,rock material in maximum stress zone is in the approximate uniaxial loading state owing to the larger tangential force and smaller radial force,the mechanism of ZDP was explained,which lay in the creep instability failure of rock mass due to the development of plastic zone and transfer of the maximum stress zone within the rock mass.Thirdly,the analytical critical depth for the occurrence of ZDP was obtained,which depended on the mechanical indices and stress concentration coefficient of rock mass.

Pendulum waves and basics of «geomechanical thermodynamics»

It is shown that modern achievements in the field of experimental and theoretical researches and developments of innovative measuring systems for monitoring of non-linear dynamic and kinematic characteristics allow to formulate basics of new academic discipline,designated as“geomechanical thermodynamics”.The following circumstances can be considered as the most important prerequisites for development of this new discipline.(1)Practical completeness of the classical thermodynamics,based on kinetic gas theory and molecular movements in solid bodies;(2)Creation of“formular construction tool”for the description of dynamic and kinematic characteristics of pendulum waves and energy conditions of their occurrence and propagation from dynamic sources,located in multi-phased stressed rock mass and geomaterials with block-hierarchical structure;(3)Principal opportunity to establish formal relations between substantial energy carriers of“packages”of nonlinear pendulum waves(geoblocks of certain hierarchical levels according to their diameters)and“molecules”:their movement,velocity and acceleration of the“molecules”↔“geoblock”;“force interactions between molecules”↔“non-linear elastic interaction between geoblocks”,etc.The term of“geomechanical temperature”is introduced and its analytical expression,which is proportional to kinetic energy of movement of geoblocks with defined volume for their hierarchical subsequence at“confined”conditions of the stressed rock mass,is shown.The similar aspects are discussed,when emission acousticelectromagnetic fields are fixed using corresponding coefficients of mechanical-electrical and mechanicalacoustic transformations.In order to quantitively describe the evolution of energy state of local zones of stressstrain concentration and surroundings of their non-linear influence from catastrophic events at the natural and mine-engineering systems(earthquakes,rock bursts,etc.),the terms of their geomechanical and thermodynamic stages are introduced and specified:Tiei 20;t;;;*T‒with background states ei 20;*T and three major stages ei2t;;T outlined,where(t)is the concentration,(,‒)are the failure and relaxation and(*)is the quasirecovering up to“background”level after the occurred catastrophic event.Using certain examples,the existence of critical elastic energy content of local zones with“meta-stable state”,which is transforming to quasiresonance process of failure and relaxation of“excessive”energy,is shown eTT.