High Crustal Stress Research Articles

Drill tools sticking prediction based on adaptive long short-term memory

As one of the most severe disasters in deep coal mining, rockburst can be prevented through drill-hole pressure relief. However, the coal mine is characterized by high crustal stress and changeable mechanical properties of surrounding rock, which will cause drill rod deflection phenomenon, then lead to rod-deflection sticking accidents. This paper proposes a prediction method based on adaptive long short-term memory (ALSTM) for rod-deflection sticking accidents to improve drilling efficiency and reduce sticking accidents. Firstly, the sticking data is collected through the intelligent drilling condition simulation experimental platform, and then the sticking features are extracted based on the sticking data. Secondly, the sticking factor is constructed, and the sticking critical line is set. Thirdly, the good-point set and the proposed random perturbation algorithm are employed to improve the spotted hyena optimizer (SHO) to obtain the improved SHO (ISHO). Finally, we use the ISHO to optimize the hyperparameters of the long short-term memory and then establish the sticking prediction model based on ALSTM. The experimental results show that the proposed prediction model meets the demands for sticking prediction very well.

Study on Shear Failure Process and Zonal Disintegration Mechanism of Roadway under High Ground Stress: A Numerical Simulation via a Strain-Softening Plastic Model and the Discrete Element Method

Fracture expansion in rock masses can be observed by monitoring the break of contacts between the bounding particles via the discrete element method. The latter’s realization in this study via the PFC2D program tracked the evolution process of the zonal disintegration in an exemplary roadway-surrounding rock affected by mining. Besides, the damage evolution pattern in a high-stress soft rock roadway was simulated by the FLAC2D program using a strain-softening plastic model, revealing the effects of rock mass strength, stress state, and anchor support on the zonal disintegration of the roadway. Numerical simulation results show that in a roadway with high-level stress, the obvious fractures spread from the roadway surface to the depth of the surrounding rock along a series of geometric planes and cut the surrounding rock into rock mass blocks. Under high crustal stress, conjugate shear fractures occur near the roadway surfaces and form a closed-loop fractured zone after intersecting the conjugate fracture faces. The closed fractured zone becomes a free face, from which conjugate shear fractures develop, forming new closed fractured zones in the deep surrounding rock. By repeatedly generating the closed fracture zones, a fracture network appears in the roadway-surrounding rock. The development of zonal disintegration of roadway-surrounding rock mainly depends on the rock mass strength and its stress state. Zonal disintegration only occurs when the crustal stress of the roadway-surrounding rock exceeds its strength. When the horizontal stress is low and the vertical stress exceeds the rock mass strength, zonal disintegration only occurs on two sides of the roadway. When the vertical stress is low and the horizontal stress exceeds the rock’s mass strength, it only appears on the roof and floor. When the values of cohesion, internal friction angle, and tensile strength are reduced in the same proportion, cohesion has the greatest impact on the expansion of the zonal disintegration zone, followed by the internal friction angle, while the tensile strength effect is the least. In anchor-supported roadways undergoing zonal disintegration processes, the intact zone blocks slide relatively along the fracture surface during the process of loosening and deformation of the surrounding rock, making the anchor rods susceptible to tensile, shear, and bending actions.

FRACTAL CHARACTERISTICS OF CORE DISKING FRACTURE SURFACES

The morphological characteristics of core disking can reflect the in-situ stress field characteristics to a certain extent, but a quantitative description method for disking-induced fracture surfaces is needed. The fractal geometry was introduced to refine the three-dimensional characteristics of the core disking fracture surfaces, and the disking mechanism was explored through morphological characteristics. The innovative concentric-different scale method was proposed to divide the circular surfaces into square surfaces of different sizes. Furthermore, the applicability of four cubic covering methods for single fractal calculation was studied. Finally, the relative differential cubic covering method and multifractal method were used to calculate the three-dimensional data of core disking fracture surfaces in the Jinping area. The results showed that the concentric-different scale method fits the fractal dimension changing law in the exploration of different surface sizes. Using the differential cubic covering method and the relative differential cubic covering method can obtain good results for smoother surfaces. The disking was caused by tensile stress due to high crustal stress unloading, and the cracks originated from the inside of the core. Fractal theory is conducive to analyzing the morphology of rock fracture surfaces and provides guidance for exploring the failure mechanism and influencing factors.

Calculation of fracture number and length formed by methane deflagration fracturing technology

The innovative Methane in-situ deflagration fracturing technology offers several benefits. It can prevent formation pollution and eliminates the need for complex treatment procedures for backflow materials. Additionally, it reduces ground transportation expenses and is poised to become a highly effective and eco-friendly waterless fracturing technology. This paper suggests methods for determining the number and length of fractures in oil and gas well stimulation, considering the main influencing factors. The fracture number is calculated using mass conservation principles, while the fracture length is determined using the crack propagation model. The fracturing experiments with large-sized samples were conducted to verify the technical feasibility of the new fracturing technology and fill the gap in large-scale physical model experimental research for deflagration fracturing technology. Following the experiment, compare experimental data with calculated data, and analyze the factors that affect the fracture number and length. The results indicate that both methods are highly feasible and possess strong predictive accuracy. It is advised that to enhance the fracturing effect on formations with high crustal stress, it is beneficial to appropriately increase the peak pressure, reduce the pressure rate, and increase the fracturing time while ensuring that the wellbore remains undamaged. Moreover, these proposed methods are versatile and adaptable, making them suitable for explosive fracturing within hydraulically fractured formations and high-energy gas fracturing technology.

Damage and failure characteristics of coal and surrounding rock under shaped blasting

The high crustal stress in deep coal mining undermines the efficiency and safety of blasting operations conducted to increase gas permeability in the coal seam. Therefore, in this study, theoretical research, computer-based numerical simulations, and experiments were conducted to investigate the damage and fracture characteristics of a coal body and surrounding rock subjected to shaped blasting. ANSYS LS-DYNA was employed for numerical simulations to understand how a shaped jet is formed and how damage occurs in shaped blasting. A model of crack evolution under the influence of detonation gases that is based on fracture mechanics theory was constructed to analyze the mechanism underlying the directional propagation of detonation cracks in shaped blasting. In the conducted experiments, shaped blasting resulted in the creation of an oval-shaped fragmentation area, which was evidence that the shaped cartridge limited the loss of energy in fragmentation, allowed detonation cracks to evolve further in the specimen, and caused the formation of a main crack that propagated in the direction along which energy was concentrated (i.e., directional damage). Compared with ordinary blasting, shaped blasting facilitated more efficient blast energy use and reduced undesirable blast disturbance to the surrounding rock by 58% according to the computed tomography image of resistivity. The results of this study provide valuable insights on safe and efficient coal production.

In situ visualization of water transport in cement mortar with an ultra-low w/b ratio under the coupling conditions of osmotic pressure, confining pressure, and temperature

The deep underground environment has complex geological conditions, which result in cement-based materials under the coupling conditions of high crustal stress, high pressure, and high temperature for the long-term. Thus, the mechanism of water transport is more complicated and often accelerates the deterioration of cement-based materials. In this study, the rules of water transport in mortar with an ultra-low w/b ratio under the coupling conditions of osmotic pressure, confining pressure, and temperature were systemically investigated based on a novel experimental device and low-field NMR technology. Experimental results showed that the saturation of the pore structure and penetration depth of mortar increased rapidly in the early stage (the first 10 min), and the water was mainly filled in nano-scale pores. Low-field NMR imaging technology could be applied to the visualization study of water transport in WPC mortar. With the increase of osmotic pressure and ambient temperature, the penetration rate of water in mortar was significantly increased, and the water was preferentially filled in nano-scale pores with pore sizes less than approximately 200 nm. The increase of confining pressure could improve the permeability of mortar to a certain extent due to the decrease in the penetration rate of water. For water transport in mortar with an ultra-low w/b ratio, the descending order of influence degree of different factors was osmotic pressure, confining pressure, and temperature.

Experimental Study on Cyclic Hydraulic Fracturing of Tight Sandstone under In-Situ Stress

Sandstone oil–gas reservoirs in the Junggar Basin, China have great development potential. However, their ultra-deep formation depth leads to high crustal stress and high breakdown pressure. Therefore, in this research, we studied the cyclic hydraulic fracturing of tight sandstone with different combinations of “high-pressure duration + low-pressure duration” under high-stress conditions. Through laboratory experiments, the pump pressure curves, hydraulic fracture morphology, acoustic emission counts, and peak frequency of the samples were obtained. The results showed that: (1) Compared with conventional hydraulic fracturing, the breakdown pressure of cyclic hydraulic fracturing was reduced by more than 30%, the minimum threshold of cyclic pump pressure required for sample breakdown was between 60%Pb and 70%Pb, and cyclic hydraulic fracturing more easily formed complex and diverse hydraulic fractures. (2) In cyclic hydraulic fracturing, under the same upper limit of cyclic pump pressure, the shorter the high-pressure duration, the fewer the cycles required for sample breakdown. (3) Under the same “high-pressure duration + low-pressure duration” condition, the lower the upper limit of the cyclic pump pressure, and the greater the number of cycles required for sample breakdown. (4) The AE cumulative counts curves fluctuated greatly during cyclic hydraulic fracturing, rising in an obvious step-wise manner and the AE peak frequency was banded and mainly divided into three parts: low frequency, medium frequency, and high frequency.

Triaxial creep damage characteristics of sandstone under high crustal stress and its constitutive model for engineering application

AbstractThe creep characteristics of rock under high crustal stress are of important influence on the long‐term stability of deep rock engineering. To study the creep characteristics and engineering application of sandstone under high crustal stress, this study constructed nonlinear creep damage (NCD) constitutive mode based on the triaxial graded loading‒unloading creep test of sandstone in the Yuezhishan Tunnel. A numerical NCD constitutive model and a breakable lining (BL) model were developed based on FLAC3D and then applied to the stability analysis of the Yuezhishan Tunnel. Based on the creep test results of sandstone, a power function of creep rate and stress level was constructed, by which the long‐term strength was solved. The results show that the long‐term strength of the red sandstone based on the related function of the steady‐state creep rate and stress level is close to the measured stress value in engineering. The NCD model considering damage factors reflects the instantaneous and viscoelastic plasticity deformation characteristics of the red sandstone. The numerical NCD constitutive model and the BL model can reflect surrounding rock deformation characteristics and lining failure characteristics in practical engineering. The research results provide theoretical references for long‐term stability analysis of rock engineering and the deformation control of surrounding rock under high crustal stress.

The Properties of a Coal Body and Prediction of Compound Coal-Rock Dynamic Disasters

Since the precise identification and prediction and early warning of compound coal-rock dynamic disaster remain difficult, a new coal characterisation and prediction method for compound coal-rock dynamic disasters was described based on theoretical analysis, laboratory experiment, field sampling, mathematical treatment, and industrial testing. The results implied that the physicomechanical properties of coal in a compound coal-rock dynamic disaster are between those pertinent to a typical rock burst and a coal-gas outburst, i.e., with high crustal stress surrounding pressure, high gas pressure, low permeability, bump proneness, and outburst risk. The predicted drilling data indicate moderate gas desorption indices. The gas desorption velocity and permeability of compound coal-rock dynamic disaster coal decrease with the increase in crustal stress, while increase and decrease with the increase in gas pressure, respectively, at the same time, and they change little with increasing temperature. Gas extraction leads to the increase in coal mass brittleness and bump proneness. Based on the unique physical-mechanical properties of compound coal-rock dynamic disaster coal, a reasonably sensitive predictive index and critical value for Donglin Coal Mine were determined.

Study on the 2D Optimization Simulation of Complex Five-Hole Cutting Blasting under Different Lateral Pressure Coefficients

With the decrease and depletion of shallow coal resources, the depth of mining is increasing. The mechanism of high crustal stress blasting is not clear, and the effect of crustal stress on blasting effect is obvious. The law of the differential detonation is similar without crustal stress. The crustal stress of rock masses increases linearly with the increase in excavation depth, and the influence of crustal stress on blasting effect is great. In order to study the rock-breaking process of complex differential blasting under deep high crustal stress, the instantaneous detonation of each model and the priority detonation of the central hole are numerically simulated. The evolution law of the blasting crack and the method of optimizing blasting effect by differential blasting and increasing the aperture of the priority detonation hole under high crustal stress are put forward. The authors proposed a study on the 2D optimization simulation of complex five-hole cutting blasting under different lateral pressure coefficients of 400 m and 800 m with software ANSYS/LS-DYNA and analyzed the evolution rules of blasting cracks and lateral pressure coefficients. The results show that setting delayed detonation and hole diameter and optimizing blasthole spacing can optimize the rock-breaking effect under high crustal stress and different lateral pressure coefficients.

Damage Characteristics and Constitutive Model of Deep Rock under Frequent Impact Disturbances in the Process of Unloading High Static Stress

During the mining of deep mineral resources, the rock is in the complex mechanical environment of high crustal stress and blasting excavation unloading, and the improved SHPB test system is used to carry out frequent impact disturbance test of deep rock in the process of unloading high static stress. Firstly, the general characteristics of dynamic stress-strain curve envelope of the whole process trend can be divided into four stages: the stable development stage of micro cracks, the non-stable development stage of micro cracks, the fatigue damage stage, and the fatigue failure stage. Then, the damage variables of the rock are defined by continuous factors, strain equivalence principle and statistical damage theory, which are based on the whole deformation characteristics of rock during the test. And the derived damage variable equation of rock in the damage process is proved to be reasonable, and the damage constitutive model of rock under frequent disturbances in the process of unloading high static stress is established by the combined model method. Finally, the rationality of constitutive equation is verified by test data, which shows that the dynamic stress-strain curve envelope is in good consistency with the theoretical curve of constitutive equation.

Quantitative analysis of rockburst in the surrounding rock masses around deep tunnels

Rockbursts in deep tunnels subjected to high crustal stress were investigated using a general particle dynamics (GPD) code with the Holmquist–Johnson–Cook damage model (HJC). Under dynamic excavation disturbance, several numerical tests were carried out to investigate the dynamic failure patterns of surrounding rock masses with different preexisting cracks around deep tunnels. The numerical results showed that the GPD code can satisfactorily simulate the phenomenon of rockburst caused by crack evolution, including predicting the ejection velocity, rockburst location and ejected rock block volume. Moreover, the analysis of the circumferential stress in the surrounding rock of deep tunnels at the Jinping II Hydropower Station shows the efficiency of the GPD code. In addition, four typical rockburst, which occurred under different geological conditions at the Jinping II Hydropower Station, were analyzed by using the GPD code. The numerical simulations suggested that the GPD code can efficiently reproduce the 2D and 3D crack growth in the surrounding rock, which eventually leads to the occurrence of rockburst.

Dynamic mechanical characteristics and failure mode of serpentine under a three-dimensional high static load and frequent dynamic disturbance.

The improved split Hopkinson pressure bar (SHPB) was used to study the dynamic mechanical properties and failure characteristics of surrounding rock in deep rock mass engineering that is under high stress and affected by blasting excavation and other dynamic disturbances. In a three-dimensional high static load and frequent dynamic disturbance test, the preload high axial pressure and confining pressure are used to simulate the high crustal stress of deep rock, and the effect of small disturbances on the rock is simulated by the low impact load. The results show that there are two types of dynamic stress-strain curves of deep rock: an elastic-plastic curve and plastic-elastic-plastic curve. The curves consists of five parts: the compaction stage, micro-crack steady development stage, micro-crack unstable propagation stage, fatigue damage stage, and fatigue failure stage. Reductive phenomena of constringent strain after dynamic peak stress appear because of the different degrees of rock damage. Moreover, these phenomena include two conditions, namely, whether rebound occurs or not. The impact resistance of rock is strongest when the ratio of the confining pressure to axial pressure is optimal, and the dynamic average strength of rock and accumulative impact times decrease with the increase of the preloaded axial compression and increase with the increase of the preloaded confining pressure. Both the dynamic deformation modulus and dynamic peak stress decrease with the increase of the accumulative impact time, while the maximum strain and the dynamic peak strain increase. The corresponding rebound strain as a whole first increases and then decreases with the increasing impact times. For deep rock, tensile failure and single-bevel plane shear failure are the main failure modes, and pull-compression mixed friction failure is the auxiliary failure mode. Additionally, the lumpiness of broken rock decreases with the increase of the preloaded axial compression and increases with the increase of the preloaded confining pressure.

A Control Method of Rock Burst for Dynamic Roadway Floor in Deep Mining Mine

Roadway floor rock burst is an important manifestation of rock bursts in deeply buried mines. With the increase of mining depth and mining intensity, rock burst disasters in the roadway floor such as floor heaves are becoming more serious. The article investigated the roadway floor severe heave caused by floor rock burst during excavation of the No. 3401 working face, which was controlled by an anticlinal structure and deep mining in Shandong Mine, China. Firstly, by analyzing geological conditions of the working face, roadway support parameters, and characteristics of coal and rock, it was revealed that high tectonic stress and high crustal stress were main causes of the floor rock burst. Secondly, based on the Theory of Mechanics and Theory of Energy, the energy conversion process in the roadway floor was discussed, and the rock burst condition caused by elastic energy in the roadway floor was analyzed. The failure characteristics of roadway‐surrounding rock were also inspected, using a borehole recorder. The roof and sidewalls of roadway mainly contained fissures and cracks, whereas cracks and broken areas are distributed in the roadway floor. Finally, based on the deformation and failure characteristics of roadway‐surrounding rock, a method termed “overbreaking‐bolting and grouting‐backfill” was proposed to control roadway floor rock burst. The method was tested in the field, and the results showed that it could effectively control the deformation of roadway floor and rock burst, guaranteeing the stability of roadway floor. This impact control method for the roadway floor can provide a reference for the prevention and control of roadway rock burst in mines with similar geological conditions.

Investigation on coal seam distribution and gas occurrence law in Guizhou, China

In order to enhance the management level of coal mine safety production and promote the “safe, accurate and efficient” preventive treatments for gas in Guizhou of China, the occurrence and other prominent features of coal and gas are investigated. The characteristics and regularities of coal mine accidents in Guizhou during 2001–2015 are summarized to analyze the commonness of gas accidents in general and determine the characteristics of gas preventive treatment. Geological data, gas basic parameters, and physical properties of coal of 386 mines and 761 sets of coal seams in Guizhou are also statistically analyzed. Based on step control theory of gas occurrence structure and the regionally tectonic regularity of coal-bearing stratum distribution, the deformations of coal measures in Guizhou mine area are mainly caused by great variation of stratigraphic occurrence, complicated geological structure, and high crustal stress. The regional occurrence of coal seam is obvious with the highest content of Tongzi–Zunyi–Liuzhi–Xingyi line, which gradually reduces to the both east and west sides. Influence factors and weights of gas occurrence are expounded from geological and coal factor by mathematical statistics, and the main influence factors of gas occurrence are the sedimentary environment, syncline structure, and metamorphic grade in proper sequence. Combined with the risk prediction of coal and gas outburst area, the prediction of gas pressure by gas content is not suitable under the special occurrence conditions. The initial velocity of gas emission, the solidity coefficient, and the damage type in more than 77% of minable seams all exceed the critical value. This work provides guidance in improvement of the governance situation for gas control in Guizhou. The index prediction system which is suitable for mining conditions of special coal mines in Guizhou should be established.

Spatiotemporal development of mine water inrush and its mechanism—a case study in Ganhe coal mine, Shanxi, China

Mine water inrush is one of the main hazards in coal mining industry. The mechanism and the processes are complex. Investigation of the spatiotemporal development of the hydrological process could lead to a better understanding of mine water inrush and effective countermeasures. For this reason, we investigated spatial and temporal characteristics (i.e., the changes of flow rate, groundwater level, and water quality) during a water inrush event in China, which had a flow rate of 730 m3/h at maximum and 300m3/h under a steady condition. The result shows that the water inrush developed in several stages. A mathematical model of the dynamic change between the water table and the inrush flow rate was constructed. Based on this model, we found the relationship of highly conductive flow channels between some observation boreholes and the water inrush point. In addition, the recharge velocity of the highly conductive flow channels and the equivalent mean flow velocity of the whole mine were determined. A comprehensive analysis of geological, hydrodynamic, and crustal stress conditions was conducted to study the development of the water channel near the F13 fault and the nonlinear process from seepage stage to inrush stage. The result reveals the water inrush is likely caused by activation of faults under combined influences of high crustal stress and high hydraulic pressure.

ANALYSIS ON CHARACTERISTIC AND FORMATION MECHANISM OF LARGER DEFORMATION FOR THE TUNNEL OF CHENGDU-LANZHOU RAILWAY

The larger deformation of soft rock tunnel of the Chengdu-Lanzhou railway presented not only the common larger deformation characteristics, such as the lining crack, steel torsion, transect of tunnel reduced in size, and so on; but possessed the regional particularities of the tectonic conditions were intricate and active, for the Chengdu-Lanzhou railway pass through the following three tectonic elements of Longmen Mountain tectonic belt, Songpan-Ganzhi fold tectonic belt and west Qinling Mountains fold structural belt included 10active faults; of the formation lithology condition were extremely weak and cracked, for the 70 percent of rock mass of Chengdu-Lanzhou railway were soft rock of slate, phyllite, schist and carbon slate, suffered seriously by the tectonic and took on the intense crumpled deformation and strong crushing cracked; of the Wenchuan seismic effect were outstanding, for the Chengdu-Lanzhou railway run through the Wenchuan 512 meizoseismal area, the seismic wave damaged to rock mass, which resulted to reduce integrity of rock mass and increase water permeability of rock mass. The crustal stress field of Chengdu-Lanzhou railway were extremely complex, with the tectonic stress field characteristic of obvious high crustal stress. The formation mechanism of larger deformation of the Chengdu-Lanzhou railway were the interaction of the complex tectonic stress, soft and cracked formation lithology, bias of disadvantage discontinuous surface and softening effect of groundwater, summarized the three kinds of the loose large deformation, squeezed large deformation and structural large deformation in high stress field. And the conclusions of this paper is great guiding significance for the building Chengdu-Lanzhou railway and others tunnel construction in similar engineering geological conditions.

New insights into the generation of the 2013 Lushan Earthquake (Ms 7.0), China

AbstractGlobal seismic waveform inversion can provide information on where the 2013 Ms 7.0 Lushan earthquake occurred in Sichuan Province, China, and how its aftershock sequence expanded. To investigate the generation mechanism of the Lushan earthquake and its relation to the 2008 Wenchuan earthquake (Ms 8.0), 50 temporary seismic stations were installed in the source area following the Lushan earthquake. Crustal stress data were also collected along the Longmen‐Shan Fault zone (LMFZ) to reveal its influence on the generation of the Lushan earthquake. Seismic imaging and crustal stress analysis have revealed that the Lushan earthquake occurred in a distinct area with high velocity (Vp, Vs), low Poisson's ratio (σ), and high crustal stress. The high‐velocity zone at the Lushan source may reflect Precambrian metasedimentary or igneous rock in the seismogenic layer, which enables the accumulation of high crustal stress to generate large earthquakes. However, a sharply contrasting gap zone with low‐velocity, high‐σ anomalies is clearly imaged in the upper crust under the concatenated area between the Lushan and Wenchuan earthquakes. Seismic images indicate that the low‐velocity gap zone is associated with fluid‐bearing ductile flow from the lower crustal materials of Tibet being pushed into a weakened segment of the LMFZ. This study suggests that the 2013 Lushan earthquake may have been triggered by high crustal stress accumulation together with high coseismic stress further increased by the Wenchuan earthquake in the metamafic seismogenic layer. Contrasting rheological variations in the crust and crustal stress changes along the LMFZ control the rupture processes that generated the Lushan and Wenchuan earthquakes, as well as the generation of new earthquakes in the future.

Numerical Simulation on Hard and Stable Roof Control by Means of Directional Hydraulic Fracturing in Coal Mine

Hydraulic fracturing is a method which combines a natural action with a factitious means to alter rock structure. In order to control the extending direction of fracture in the process of hydraulic fracturing, directional hydraulic fracturing is necessary. According to fracture initiation and extension mechanism, taking fully into account the flow-stress-damage coupling effect, simulating with numerical way and analyzing a law of the roof under the dynamic failure process on a working face with a hard and stable roof in 2 cases, the one is the non-directional directional hydraulic fracturing, and the other one is wedge groove directional hydraulic fracturing by RFPA2D-Flow. Based on analyzing the distribution law of the primary stress field on roof surrounding rock, we reveal the control mechanism and behavior law of directed by wedge groove directional fracturing. The study results shows that: First, under the coupling effect from the high hydraulic pressure and crustal stress, failure of roof is not simply a shearing failure, but a compound stress effect from tensile and compress failure which tension contributes more. Second, the directional fracturing by wedge-groove guides to the main fracture progressing into directional expansion, relying on man-made weak plane, it also makes the roof directional hierarchically, timely and fractionated carving come true.

Analysis on the Characteristics of Displacement Field Distribution around the Deep Buried and Great Complex Section Tunnel

Taken the excavation of TBM assembly underground chamber with deeply buried super large and complex section in Jinping Ⅱ Hydropower Station as the background, apply theoretical analysis and experimental method to study the rock deformation and displacement analysis. The result shows that, drilling and blasting method is used for construction which is divided into four layers from top to bottom according to the excavation, they are 8.5m, 5.5m, 6.0m,7.0m from top to bottom, respectively. the displacement of surrounding rock generally moves toward the direction of the free surface. The rock possesses spring back deformation pointing to internal underground chamber. The displacements of arch crown and floor are mainly vertical, and displacement of retaining wall is mainly horizontal. This is significantly different from the rock deformation of underground chamber under general stress after excavation. The chamber displacement distribution under high crustal stress is closely related to stress direction. Location axis of underground chamber should parallel the direction of maximum principal stress. Under the complex and great deeply buried condition, excavation of large section tunnel by digging from the top layer can better release the rock stress, and the rock displacement changes gently, which is conducive to rock mass stability and structure security.