Rock Stress Field Research Articles

Analysis of Supporting Mechanism of Steel Arch Frame in Tunnel Collapse

As the steel arch can withstand the rock load immediately, this is widely used in tunnel collapse treatment. Firstly, the steel arch mechanism and mechanical model in tunnel collapse supporting had been studied. Then the modeling points and solutions of the finite difference software FLAC3D were pointed out, and the effects of steel arches and steel arches with different spacings were simulated. This paper analyzed the stress field of rock, displacement field of rock and stress behavior of steel in different conditions, the following conclusions: (a) Steel arch can inhibit stress concentration of the foot arch, while the dome appears to reduce the scope of the low stress areas, and it can effectively inhibit the vertical displacement of the vault and floor; (b) The maximum axial force and bending moment were increased with the increase in the arch steel arch spacing; (c) The maximum axial force steel arch occurs mainly at the crown, while the maximum bending moment occurs mainly in the arch and vault at the waist, and arch at the moment was very small. There were basically consistent with the mechanics calculations.

Research on gas leakage mechanism and detection technology of coal mine gas drainage

Aiming at the low concentration of gas in the percolation borehole, the paper analyzes the mechanism of gas leakage in the sealing hole of the pumping hole based on the multi-physics coupling theory based on the distribution of the surrounding rock stress field of the mining borehole and the roadway. The drilling hole sealing detection device and the determination method are used to detect gas concentration at different depths in the borehole in the normal extraction state, and analyze the variation law of the gas drainage concentration along the hole depth distribution to achieve fast and accurate judgment of the leak position and sealing test of the pumping hole. The test proves that the method and the device can effectively detect the leaking position and sealing effect of the extraction drilling hole, and can provide a simple and rapid detection method and science for the improvement of the sealing process, the adjustment of the sealing depth and the fine management of the coal mine site.

Optimization Analysis of Over-Sized Section Open-Off Cut Failure and Support

The open-off cut section of 1105 working face in Zhaogu II mine is the largest in China, causing considerable difficulties to the support work. The failure process of surrounding rock deformation, stress field, and stress state under original support of open-off cut is analyzed using FLAC3D numerical simulation analysis software. Analysis results show the large displacement of the bottom heave and two sides of the roadway. Furthermore, the vertical stress of open-off cut is greater than the horizontal stress, whereas horizontal stress is larger in the upper roof part. The shearing failure range of the open-off cut surrounding rock is large, indicating that the original support scheme possesses weak restraint capability to the surrounding rock and fails to effectively control deformation. Based on analysis and research results, the technical scheme of coordinated support for super-long anchor rod and anchor cable of over-sized section open-off cut with high-stress broken surrounding rock is put forward. The field industrial test shows that the coordinated support scheme of super-long anchor rod and anchor cable is reasonable and safe under a 9.2 m open-off cut section. With improvement of the working face, the deep rock layer on the roof at the open-off cut position of goaf first occurs evidently, whereas the shallow rock layer is unremarkable, indicating the stable rock formation in the anchorage area of the shallow super-long anchor. The super-long anchor rod plays a satisfactory role in support, and the control effect of broken surrounding rock is similarly satisfactory. Such condition can achieve large deformation of broken surrounding rock with high stress and super large section.

Study on Dynamic Strain Distribution in Rock Broken by Abrasive Slurry Jet

To reveal the stress and strain field in rock under abrasive slurry jet (ASJ) impacting, this paper carried out experiments to measure the dynamic rock strain using a novel strain measurement approach, which is the non-contact strain measurement system. Moreover, it was compared with the theoretical analysis of stress propagation in rock. The results showed that dynamic strain will propagate within rock in the form of spherical waves, whose maximum value is proportional to the jet pressure and inversely proportional to the square of the propagation distance. In the process of ASJ impacting rock, strain will increase from zero to a maximum value in milliseconds. Dynamic strain in rock is fluctuates due to the release of internal stress caused by the rock crushing, which can reflect that rock will be broken by ASJ in the form of stepped-failure. The paper reveals the dynamic strain distribution in rock broken by ASJ and provides a new idea and method for studying the rock failure mechanism under ASJ impacting.

Mechanical Analysis of Large-span Tunnel Construction in Urban Seaside

Hou, F.-J.; Li, S.-C.; Li, W.-J.; Li, X.-Z., and Han, X.-M.; 2019. Mechanical analysis of large-span tunnel construction in urban seaside. In: Gong, D.; Zhu, H., and Liu, R. (eds.), Selected Topics in Coastal Research: Engineering, Industry, Economy, and Sustainable Development. Journal of Coastal Research, Special Issue No. 94, pp. 255–259. Coconut Creek (Florida), ISSN 0749-0208.A tunnel in urban seaside is designed as a two-way eight-lane with a span of nearly 20 meters. The stratum is a horizontal layered rock mass and a three-level surrounding rock. In order to achieve rapid construction of large-span tunnels, combined with engineering background, horizontal layered rocks. The constitutive calculation model of the body is optimized and analyzed, and the whole time and space analysis of the tunnel construction process is carried out. The results show that for the layered rock mass stratum, the tunnel surrounding rock stress field is also the displacement field and the plastic zone distribution, and the transversely isotropic medium model is adopted. The root can fully reflect the engineering characteristics of the horizontal layered rock mass; The deformation of the tunnel surrounding rock after excavation shows that the horizontal layered rock mass is beneficial to the stability of the tunnel arch and the cavern; The settlement of the surrounding rock dome of the horizontal layered rock mass tunnel .The convergence deformation (6.0 mm) accounts for about 50% of the final deformation. The horizontal layered surrounding rock should actively control the deformation of the front of the face to enhance the stability of the cavity.

Induced seismicity in geologic carbon storage

Abstract. Geologic carbon storage, as well as other geo-energy applications, such as geothermal energy, seasonal natural gas storage and subsurface energy storage imply fluid injection and/or extraction that causes changes in rock stress field and may induce (micro)seismicity. If felt, seismicity has a negative effect on public perception and may jeopardize wellbore stability and damage infrastructure. Thus, induced earthquakes should be minimized to successfully deploy geo-energies. However, numerous processes may trigger induced seismicity, which contribute to making it complex and translates into a limited forecast ability of current predictive models. We review the triggering mechanisms of induced seismicity. Specifically, we analyze (1) the impact of pore pressure evolution and the effect that properties of the injected fluid have on fracture and/or fault stability; (2) non-isothermal effects caused by the fact that the injected fluid usually reaches the injection formation at a lower temperature than that of the rock, inducing rock contraction, thermal stress reduction and stress redistribution around the cooled region; (3) local stress changes induced when low-permeability faults cross the injection formation, which may reduce their stability and eventually cause fault reactivation; (4) stress transfer caused by seismic or aseismic slip; and (5) geochemical effects, which may be especially relevant in carbonate-containing formations. We also review characterization techniques developed by the authors to reduce the uncertainty in rock properties and subsurface heterogeneity both for the screening of injection sites and for the operation of projects. Based on the review, we propose a methodology based on proper site characterization, monitoring and pressure management to minimize induced seismicity.

Linkage-induced mechanism and control technology of pressure bump and surface geological damage in shallow coal seam mining of gully area

Coal mining will cause pressure bump in mining face and surface landslide, subsidence, and another geological damage in shallow thick coal seam mining of gully region. To analyze the linkage-induced mechanism and mutual influence relation between underground pressure bump and surface geological damage. This paper proposes a novel approach to study the stress field, displacement field, and damage field distribution of overlying strata in coal seam mining under valley terrain. The influence of valley terrain on in situ rock stress field decreases with the increase of the buried depth of coal and rock. The coal and rock strata of different depth under gully terrain are divided into significantly affected area, moderately affected area, and non-influence area. Exploitation activities under a gully area are divided into uphill mining stage, slope top mining stage, and downhill mining stage. The pressure bump and surface geological damage are easily linkage induced at the uphill mining stage. Based on the control of underground and surface damage of shallow thick coal seam mining in gully region, the slicing mining and filling mining of thick coal seam are put forward.

Investigating the supporting effect of rock bolts in varying anchoring methods in a tunnel

Pre-tensioned rock bolts can be classified into fully anchored, lengthening anchored and point anchored bolts based on the bond length of the resin or cement mortar inside the borehole. Bolts in varying anchoring methods may significantly affect the supporting effect of surrounding rock around a tunnel. However, thus far, the theoretical basis of selecting a proper anchoring method has not been thoroughly investigated. Based on this problem, 16 schemes were designed while incorporating the effects of anchoring length, pretension, bolt length, and spacing, and a systematic numerical experiment was performed in this paper. The distribution characteristics of the stress field in the surrounding rock, which corresponded to various anchoring scenarios, were obtained. Furthermore, an analytical approach for computing the active and passive strengthening index of the anchored surrounding rock is presented. A new fully anchoring method with pretension and matching technology are also provided. Then, an isolated loading model of the anchored surrounding rock was constructed. The physical simulation test for the bearing capacity of the model was performed with three schemes. Finally, the strengthening mechanism of varying anchoring methods was validated. The research findings in this paper may provide theoretical guidelines for the design and construction of bolting support in tunnels.

The Elastic–Plastic Damage Analysis of Underground Research Laboratory Excavation for Disposal of High Level Radioactive Waste

The deep geological disposal is an internationally recognized method for the disposal of high level radioactive waste. As an essential facility, the construction safety of underground research laboratory (URL) is very important. Taking the China’s first URL in Beishan, Gansu Province as engineering background, considering the influence of arranged joints in rock mass, an elastic–plastic damage numerical method for fractured rock mass is presented and the corresponding subprogram in Flac3D is developed. Based on the numerical calculation of underground research laboratory construction, the optimized excavation scheme of URL is obtained and the distribution rules of surrounding rock displacement field, stress field and plastic damage zone are studied. The research result can provide important guidance for the construction of Beishan URL.

Mathematical model of rock stress under abrasive slurry jet impact based on contact mechanics

With development of water jet technology, abrasive water jet (AWJ) has become a new tool for cutting hard rock, which is widely used in stone processing, tunneling, and mining. Abrasive slurry jet (ASJ) is superior to AWJ in its ability and efficiency of rock cutting and breaking due to the addition of high-polymer. However, the stress field of rock impacted by ASJ directly affects the cutting and breaking efficiency, but there is no unified microscopic mechanism of rock failure under ASJ impact due to the uncertain contact type between the rock and the abrasive particles. In this paper, contact mechanics is used to establish a new mathematical model of rock stress under ASJ impact, which shows the rock stress distribution. Moreover, the mathematical model was solved numerically and presented in a rectangular coordinate system, from which the rock stress concentration area and failure type can be obtained. The results show that rock stress concentration appears at four areas (the center, edge, axis of particle indentation, and the edge of slurry jet), where rock is apt to be broken with axial compressive failure, radial tensile failure, shear failure, and radial tensile failure, respectively. Moreover, the rock stress caused by abrasive particle impact is much larger than that by slurry jet impact.

On the link between stress field and small-scale hydraulic fracture growth in anisotropic rock derived from microseismicity

Abstract. To characterize the stress field at the Grimsel Test Site (GTS) underground rock laboratory, a series of hydrofracturing and overcoring tests were performed. Hydrofracturing was accompanied by seismic monitoring using a network of highly sensitive piezosensors and accelerometers that were able to record small seismic events associated with metre-sized fractures. Due to potential discrepancies between the hydrofracture orientation and stress field estimates from overcoring, it was essential to obtain high-precision hypocentre locations that reliably illuminate fracture growth. Absolute locations were improved using a transverse isotropic P-wave velocity model and by applying joint hypocentre determination that allowed for the computation of station corrections. We further exploited the high degree of waveform similarity of events by applying cluster analysis and relative relocation. Resulting clouds of absolute and relative located seismicity showed a consistent east–west strike and 70° dip for all hydrofractures. The fracture growth direction from microseismicity is consistent with the principal stress orientations from the overcoring stress tests, provided that an anisotropic elastic model for the rock mass is used in the data inversions. The σ1 stress is significantly larger than the other two principal stresses and has a reasonably well-defined orientation that is subparallel to the fracture plane; σ2 and σ3 are almost equal in magnitude and thus lie on a circle defined by the standard errors of the solutions. The poles of the microseismicity planes also lie on this circle towards the north. Analysis of P-wave polarizations suggested double-couple focal mechanisms with both thrust and normal faulting mechanisms present, whereas strike-slip and thrust mechanisms would be expected from the overcoring-derived stress solution. The reasons for these discrepancies can be explained by pressure leak-off, but possibly may also involve stress field rotation around the propagating hydrofracture. Our study demonstrates that microseismicity monitoring along with high-resolution event locations provides valuable information for interpreting stress characterization measurements.

Experimental simulation of water-inrush disaster from the floor of mine and its mechanism investigation

Mine water inrush is very common in China and can cause hysteretic and severe damages to the safety production of coal mines. Essentially, water inrush from coal floor can be attributed to the connection of cracks and the formation of water channel in floor rocks under the interaction of stress field and seepage field. In this paper, the interaction between cracks, stress field, and seepage field in floor rocks was studied by physical simulation; the evolution law of water inrush from floor cracks was obtained under the fluid-solid coupling effect, and the monitoring of rock stress and seepage pressure was realized by virtue of soil pressure and pore-pressure sensors. The results indicated that the permeability of floor rocks had regional and temporal characteristics due to the cyclical variation of in-situ floor stress. The high-permeability zone occurred under the early mining stress area, and gradually extended and connected inside the floor. As a result, more confined water could flood into the connected cracks and thus changed the seepage field in front of working face. This work provides new approaches and knowledge for researching coal floor water inrush and has important significances for the prevention of coal water disasters.

Fracture Initiation of an Inhomogeneous Shale Rock under a Pressurized Supercritical CO2 Jet

Due to the advantages of good fracture performance and the application of carbon capture and storage (CCS), supercritical carbon dioxide (SC-CO2) is considered a promising alternative for hydraulic fracturing. However, the fracture initiation mechanism and its propagation under pressurized SC-CO2 jet are still unknown. To address these problems, a fluid–structure interaction (FSI)-based numerical simulation model along with a user-defined code was used to investigate the fracture initiation in an inhomogeneous shale rock. The mechanism of fracturing under the effect of SC-CO2 jet was explored, and the effects of various influencing factors were analyzed and discussed. The results indicated that higher velocity jets of SC-CO2 not only caused hydraulic-fracturing ring, but also resulted in the increase of stress in the shale rock. It was found that, with the increase of perforation pressure, more cracks initiated at the tip. In contrast, the length of cracks at the root decreased. The length-to-diameter ratio and the aperture ratio distinctly affected the pressurization of SC-CO2 jet, and contributed to the non-linear distribution and various maximum values of the stress in shale rock. The results proved that Weibull probability distribution was appropriate for analysis of the fracture initiation. The studied parameters explain the distribution of weak elements, and they affect the stress field in shale rock.

The Behaviour of Fracture Growth in Sedimentary Rocks: A Numerical Study Based on Hydraulic Fracturing Processes

To capture the hydraulic fractures in heterogeneous and layered rocks, a numerical code that can consider the coupled effects of fluid flow, damage, and stress field in rocks is presented. Based on the characteristics of a typical thin and inter-bedded sedimentary reservoir, China, a series of simulations on the hydraulic fracturing are performed. In the simulations, three points, i.e., (1) confining stresses, representing the effect of in situ stresses, (2) strength of the interfaces, and (3) material properties of the layers on either side of the interface, are crucial in fracturing across interfaces between two adjacent rock layers. Numerical results show that the hydrofracture propagation within a layered sequence of sedimentary rocks is controlled by changing in situ stresses, interface properties, and lithologies. The path of the hydraulic fracture is characterized by numerous deflections, branchings, and terminations. Four types of potential interaction, i.e., penetration, arrest, T-shaped branching, and offset, between a hydrofracture and an interface within the layered rocks are formed. Discontinuous composite fracture segments resulting from out-of-plane growth of fractures provide a less permeable path for fluids, gas, and oil than a continuous planar composite fracture, which are one of the sources of the high treating pressures and reduced fracture volume.

Study of the bottom-hole rock stress field under water jet impact

ABSTRACTOn the basis of analysis of the bottom-hole rock stress field under water jet impact, there are three types of coupling, which include the coupling of pore fluid and water jet, the coupling of pore fluid and rock matrix, and the coupling of water jet and rock matrix. The fluid-solid coupling model with the four main factors of three-dimensional in-situ stress, fluid column pressure, pore pressure, and water jet velocity is established and calculated by the finite element method and the finite volume method. The results show that the maximum principal stress of the bottom-hole increases with the increase of bottom-hole differential pressure. The maximum jet impact force is proportional to the square of the jet velocity; the pore pressures on the impact surface and along impact axis decrease in the form of cubic parabola with the increase of the distance. The local effect is obvious under water jet impact; the main affected area of the water jet is 2 times jet radius on the impact surface and 2.5 to 3.5 times jet radius along the impact axis when water jet velocity increases from 50 to 250 m/s, which is consistent with the stress wave attenuation theory. Study of the bottom-hole rock stress field under water jet impact provides a numerical research method for study of the water jet rock breaking mechanism under actual drilling conditions and the theoretical basis for faster and more efficient drilling.

Force State of Country Rock and Supporting Structure in Multi-Arch Tunnel under Central Hole + CRD Method

The reason situ stress is very complicated, and it is still not very clear question. In this paper, the construction process through practical engineering analysis on a variety of construction methods and steps arch tunnel to study the effects of different excavation methods and deep anchor support large section tunnel under guard by theoretical analysis of surrounding rock stress field, strain field and variation of the displacement field, analysis of different rock excavation methods, supporting stress state characteristics, in order to optimize the choice of tunneling method provides a theoretical basis. Under the conditions all kinds of rock reasonable steps to secure construction methods put forward and lay the foundation for long-term safety arch tunnel.

Inferring the in situ stress regime in deep sediments: an example from the Bruchsal geothermal site

Knowledge of the ambient state of stress is of crucial importance for understanding tectonic processes and an important parameter in reservoir engineering. In the framework of the 2,500-m deep geothermal project of Bruchsal in the central part of the Upper Rhine Graben, new evidence is presented for the stress field in deep-seated sedimentary rocks. With a sophisticated data analysis based on the concept of critical stress ratios, we evaluate the quality and uncertainty range of earlier stress field models in the Bruchsal area. New data from borehole logging and leak- off tests in deep sediments are used to propose an alternative stress profile for this part of the Upper Rhine Graben. The revised stress field model for the Bruchsal area predicts a normal with transition to strike-slip faulting regime. Stress field perturbations and potential decoupling process within specific clay-, salt-, and anhydrite-bearing units of the Keuper can be observed. By comparison with other models, we can show a regional consistency of our stress field model that is reliable throughout the central Upper Rhine Graben extending from Bruchsal in the East to the Soultz-sous-Forêts EGS site in the West.

Modelling the internal stress field in argillaceous rocks under humidification/desiccation

SUMMARYThis paper deals with analytical and numerical modelling of the internal stress generated in argillaceous rocks during humidification/desiccation processes, which is an essential issue for damage study. This local stress field arises from two mechanisms: (i) complex interactions between free swelling/shrinking clay matrix and non‐strained inclusions of carbonate and quartz and (ii) a self‐restraint effect induced by the moisture gradient during the transient moisture exchange process. The inclusion–matrix interaction is investigated in different cases. Firstly, the analytical solution of the stress around a cylindrical inclusion embedded in an infinite swelling matrix is derived: The inclusion would suffer tension (compression) under humidification (desiccation), and the resulting cracking patterns are discussed. Then, the problem of two inclusions with different distances in an infinite swelling matrix is considered, and it is shown that the local stress around an inclusion will be perturbed and amplified by neighbouring inclusions. Finally, an inclusion outcropping at the free surface of a swelling matrix is modelled as to investigate the effect of free surface: The inclusion–matrix interface undergoes shear stresses of which the maximum is found at the free surface. In addition to the inclusion–matrix interaction, the self‐restraint effect is investigated: The induced stress is maximal at the beginning of humidification/desiccation processes and vanishes gradually with time. The quantity of the self‐restraint stress is strongly controlled by the hydric loading rate. Copyright © 2014 John Wiley & Sons, Ltd.

Zonal disintegration of rock mass around an underground excavation

In focus is mathematical modeling of zonal disintegration of rocks around a deep-level excavation. In the framework of the elastic model of isotropic material, the author analyzes the two-dimensional case of stress field in rocks around a circular cross-section excavation. The effective compressive stresses at infinity depend on the depth of the excavation occurrence. The shear stress analysis has shown that in rocks around the excavation, the increased shear stress circle zone appears at the distance \(r = \sqrt 3 R\) from the excavation center. The increased stresses come before the rock mass disintegration and create conditions for next destruction circles. The author dwells on probable influence of initial hydrostatic stress on the disintegration law. In modeling, the zonal disintegration circles appear at larger distance from the excavation center than in the experiment, due to the idealization of the classical problem formulations in rock mechanics.

A Study on the Effect of Bottom-hole Differential Pressure on the Rock Stress Field

Bottom-hole differential pressure is one of the most important factors that affects the drilling penetration rate. The purpose of the article is to study the effect of bottom-hole differential pressure on the vertical bottom-hole stress field. On the basis of mechanical analysis of the bottom-hole rock, the fluid-solid coupling model with the bottom-hole differential pressure is established under axisymmetry condition and is solved by using a numerical method. The comparison of the distribution of borehole wall stress between the numerical and theoretical solution is performed to verify the feasibility and rationality of the model. Then analysis of the stress state of the whole bottom-hole rock to break is carried out. The results show that the numerical solution is consistent with the theoretical solution and the fluid-solid coupling model is reasonable. With the increasing of the bottom-hole differential pressure, the bottom-hole tensile stress increases and compressive stress decreases and tensile region becomes larger. The whole bottom-hole rock to break is divided into three regions: triaxial tension region, biaxial compression and unidirectional tension region, and triaxial compression region. Qualitative and quantitative analysis of the bottom-hole stress field under different differential pressure provides the theoretical basis for rock breaking mechanism and faster and more efficient drilling.