Large Dip Angle Research Articles

Incipient particle motion in the expansion of water-inrush channel by considering the 3D relative exposure degree

Water inrush is a high-risk disaster in the construction of water-rich tunnels. The loss of particles on the sidewall of the water inrush channel is the key factor. To study the incipient particle motion in the expansion of water-inrush channel by considering the 3D relative exposure degree, the analysis for incipient flow velocity of the water inrush channel is conducted. The BP neural network and triaxial test are used to get the mesoscopic parameters. Through the DEM–CFD coupling, numerical simulation for the incipient particle motion is implemented. The effects of the 3D relative exposure degree on the incipient flow velocity are analyzed. Finally, the incipient flow velocity in the expansion of water inrush channel is verified by the laboratory test and engineering field test. The results show that: (1) the large particles have greater incipient flow velocity; (2) the particles in large dip angle are easier to move; (3) the 3D relative exposure degree of particle conforms to the Weibull distribution and the exponential distribution; (4) the incipient flow velocity of particles is closer to the critical flow velocity of rolling instability; (5) the incipient flow velocity is determined by the particles at the bottom of expansion channel.

Modeling Subduction With Extremely Fast Trench Retreat

AbstractThe Tonga‐Kermadec subduction zone exhibits the fastest observed trench retreat and convergence near its northern end. However, a paradox exists: despite the rapid trench retreat, the Tonga slab maintains a relatively steep dip angle above 400 km depth. The slab turns flat around 400 km, then steepening again until encountering a stagnant segment near 670 km. Despite its significance for understanding slab dynamics, no existing numerical model has successfully demonstrated how such a distinct slab morphology can be generated under the fast convergence. Here we run subduction models that successfully reproduce the slab geometries while incorporating the observed subduction rate. We use a hybrid velocity boundary condition, imposing velocities on the arc and subducting plate while allowing the overriding plate to respond freely. This approach is crucial for achieving a good match between the modeled and observed Tonga slab. The results explain how the detailed slab structure is highly sensitive to physical parameters including the seafloor age and the mantle viscosity. Notably, a nonlinear rheology, where dislocation creep reduces upper mantle viscosity under strong mantle flow, is essential. The weakened upper mantle allows for a faster slab sinking rate, which explains the large dip angle. Our findings highlight the utilizing rheological parameters that lead to extreme viscosity variations within numerical models to achieve an accurate representation of complex subduction systems like the Tonga‐Kermadec zone. Our study opens new avenues for further study of ocean‐ocean subduction systems, advancing our understanding of their role in shaping regional and global tectonics.

Experimental and numerical study on the mechanical behavior of layered rock anchored by CRLD anchor cable

The study of the mechanical behavior of layered anchored rock is essential for addressing the stability control challenges of surrounding rock of the roadway in layered rock masses. This paper focuses on a novel constant resistance large deformation (CRLD) anchor cable and conducts a comparative study on the uniaxial compressive mechanical behavior of unanchored rock, conventional high-strength (HS) anchor cable, and CRLD anchor cable anchored rock under different bedding dip angles α (30°, 45°, 60°, 75°, and 90°). The strength characteristics, failure characteristics, and acoustic emission characteristics of various specimen types were analyzed with emphasis. The results indicate that with the increase of bedding dip angle, the elastic modulus, peak strength, and residual strength of all specimen types exhibit a trend of decreasing first and then increasing. Compared to unanchored and HS anchored rock, the values of various mechanical parameters for CRLD anchored rock show varying degrees of improvement. The failure modes of various specimen types under different bedding dip angles can be classified into five categories based on the characteristics of the crack distribution. Through comparison, it was found that the CRLD anchor cable can effectively restrict the occurrence of bedding shear failure within the anchored zone in layered rocks with smaller dip angles (30°, 45°). It also transforms the failure mode of layered rocks with larger dip angles (60°, 75°) from a single mode of bedding shear failure to a mixed mode of bedding-bedrock failure. However, under a bedding dip angle of 90°, the two types of anchored rocks exhibit similar failure forms. Comparing the acoustic emission characteristics of the two types of anchored rocks, it is observed that under different bedding dip angles, CRLD anchored rocks exhibit a more uniform distribution of acoustic emission counts, a smoother energy release process, and significantly lower peak count and cumulative energy values. Finally, a numerical model for layered CRLD anchored rocks was constructed based on the discrete element method. The reliability of the experimental results from the physical model in this study was verified by statistically analyzing the quantity evolution process and orientation distribution of microcracks in the numerical model.

Numerical investigation on the deformation of railway embankment under normal faulting

Active faults in the earthquake region are consistently regarded as a potential geological hazard to the construction and operation of railway engineering. However, the effects of normal faulting on railway embankments have not been investigated thoroughly. For bridging this knowledge gap, three-dimensional finite element analysis considering the influence of faulting offset, the soil layer’s thickness, the fault dip angle and the embankment cross-fault angle are conducted to clarify the normal faulting effects on the railway embankment. Emphasis is given to the stress and strain characteristic in the fault rupture outcropping regions on the embankment, the deformation of the embankment centerline for design purposes, and the determination of the affected zones for railway embankment preservation. The analysis shows that the normal fault rupture outcropping regions on railway embankment are tensile yield in most cases. The existence of the soil layer and its thickening would widen the affected zones and the regions where the fault ruptures outcrops. The fault dip angle and the cross-fault angle of the embankment have a complex effect on the behaviors of the crossing embankment. The depth of the subsidence zone of the embankment would increase with the decrease of the fault dip angle and the large fault dip angle would change the primary fault rupture to be a compressive one directly above the fault line. If the embankment crosses the fault line obliquely, the curvature radius of the centerline would hardly meet the design code.

Research on grouting reinforcement technology of fault crossing roadway in fully mechanized mining face with large dip angle

Research on grouting reinforcement technology of fault crossing roadway in fully mechanized mining face with large dip angle

Research on the slip deformation characteristics and improvement measures of concrete-faced rockfill dams on dam foundations with large dip angles

The pumped storage power station (PSPS) is an important measure to achieve the strategic goal of “dual carbon”. As one of the preferred types for the upper reservoir dams of PSPSs, the concrete-faced rockfill dam (CFRD) often has a dam foundation on a steep transverse slop and is prone to produce slip deformation along the slope, resulting in poor anti-sliding stability of the dam slope. It is dangerous for the operation safety of PSPSs. Therefore, the slip deformation of CFRDs on dam foundations with large dip angles is investigated. The mechanism for the initiation of slip deformation is revealed. The design measures of physical mechanic and geometric structure are proposed to reduce slip deformation. The results show that the larger sliding forces and smaller anti-sliding forces are the fundamental reasons that CFRDs on dam foundations with large dip angles are prone to produce slip deformation. The larger the dip angle of the dam foundation, the larger the slip deformation of the dam body and face slab, and the smaller the safety factor of the dam slope. When the dip angle of the dam foundation is greater than 15°, the safety factor of the dam slope is less than the minimum value of 1.5 required by codes. The addition of pressure slopes can effectively reduce the slip deformation of the dam body or face slab and significantly improve the anti-sliding stability of the dam slope. When the height or width of the pressure slope platform is greater and the cohesion or internal friction angle of the pressure slope is larger, the slip deformations of the dam body and face slab are smaller, and the safety factor of the dam slope is greater. It is recommended that the height and width of the pressure slope platform be 1/2 times the maximum height of the main dam, and the density (cohesion and internal friction angle) of the pressure slope be equivalent to that of the main dam’s rockfill material. The research results can provide theoretical and technical support for the design and construction of CFRDs for the upper reservoir of PSPSs.

3D Reverse-Time Migration Imaging for Multiple Cross-Hole Research and Multiple Sensor Settings of Cross-Hole Seismic Exploration

The two-dimensional (2D) cross-hole seismic computed tomography (CT) imaging acquisition method has the potential to characterize the target zone optimally compared to surface seismic surveys. It has wide applications in oil and gas exploration, engineering geology, etc. Limited to 2D hole velocity profiling, this method cannot acquire three-dimensional (3D) information on lateral geological structures outside the profile. Additionally, the sensor data received by cross-hole seismic exploration constitute responses from geological bodies in 3D space and are potentially affected by objects outside the well profiles, distorting the imaging results and geological interpretation. This paper proposes a 3D cross-hole acoustic wave reverse-time migration imaging method to capture 3D cross-hole geological structures using sensor settings in multi-cross-hole seismic research. Based on the analysis of resulting 3D cross-hole images under varying sensor settings, optimizing the observation system can aid in the cost-efficient obtainment of the 3D underground structure distribution. To verify this method’s effectiveness on 3D cross-hole structure imaging, numerical simulations were conducted on four typical geological models regarding layers, local high-velocity zones, large dip angles, and faults. The results verify the model’s superiority in providing more reliable and accurate 3D geological information for cross-hole seismic exploration, presenting a theoretical basis for processing and interpreting cross-hole data.

Research on the key technology of Turkish gas storage shaft

The construction procedure of the gas storage well is complicated, and each technical index request is extremely high, does not allow any mistake. The well deviation is difficult to control. Because of the large dip angle of formation, it is difficult to ensure the wellbore quality by conventional anti-deviation measures, and the change of well deviation and azimuth can not be monitored at any time. So it's almost impossible for conventional anti-incline measures to satisfy the design. In the upper large hole section, the tower pendulum bha is used. In the section below the second open hole, the MWD steering system is used to prevent deviation and reduce deviation, and in the second open large hole section, the slim hole is used first, after reaming, the difficulty of deviation control is reduced, the ROP is increased, and the contradiction between wellbore quality and ROP can be solved by using MWD steering system to prevent deviation and straighten, because the casing and the surface casing and the production casing belong to the large diameter thick wall casing, the rigidity is very big, and the casing is also the abnormal oil drilling pipe, this well summarizes the experience, after strengthening the well opening measures, the safe and smooth running.

An insight into the effect of primary hidden microfissures on mechanical behaviors and failure characteristics of brittle basalt

The anisotropy of mechanical properties of hard rocks is usually affected by the internal primary hidden microfissure structures, which tend to induce secondary rock fracture propagation even surrounding rock instabilities in deep underground excavation. This research attempts to reveal the control effect of primary hidden microfissures on the mechanical behaviors and failure characteristics of cryptocrystalline basalt with hidden microfissures (CBWHM) through a series of laboratory tests. Firstly, a geometric feature extraction method for primary hidden microfissures of basalt rock has been proposed, by which 20 groups of three-dimensional (3D) visualization models of cylindrical basalt samples were established, and the distribution location and volume crack rate (KV) of hidden microfissures were simultaneously determined. On this basis, a series of the uniaxial compression tests of basalt samples with synchronous acoustic emission (AE) were carried out. Results show that the location and development degree of primary hidden microfissures significantly control the mechanical characteristics of basalt, with the relevant micro-fracture events occurring earlier and throughout the whole loading process compared with intact samples. In general, there exists a uniaxial polynomial fitting relationship between the strength of basalt samples and KV. The larger the KV, the lower the peak strength (σc) of basalt, which could decrease by 30–50% compared to that of the intact rock when KV is more than 5‰. However, when the hidden microfissures with large dip angles are located close to the central axis, the influence of KV on the rock strength becomes less, but the crack propagation and failure morphology are still obviously controlled by the hidden microfissures. The statistical analysis results of surface cracks and rock fragment characteristics of the damaged basalt samples further show that the basalt rock is easy to expand, penetrate and eventually fail along the hidden microfissures under loading, and it is tensile fracture that controls the failure of CBWHM. With an increase of KV, the mass percentage (W) of the coarse particle of the sample fragments increases gradually, and the fractal dimension (D) of the rock fragments and KV of the hidden microfisures show an obvious logarithmic curve relationship. The research could provide effective guidance for the interpretation of the meso-mechanism of hard rock failures.

Propagation and arrest of collapse failures in a buried offshore pipeline crossing reverse fault areas

Offshore pipelines crossing fault rupture areas suffer the risk of local buckling, which can in turn initiate propagating buckles. This study presents the results of evaluating several series of local collapses, subsequent propagating buckles, temporary buckling arrests, and crossover simulations of a deformed (due to reverse fault displacements) offshore pipeline under external overpressure. A numerical model of a buried pipeline with a single (twin) integral arrestor(s) was developed using a nonlinear vector form intrinsic finite element method. The residual external pressure capacity of a deformed pipeline after reverse fault displacements was assessed. Single integral arrestors at different installation sites and twin integral arrestors of different lengths were tested. Effects of fault dip angles on the propagation and arrest of collapse failures were investigated. The longitudinal and bending deformations caused by reverse fault displacements result in a significant decrease in the external pressure resistance of offshore pipelines. Four weak areas appeared around the bending regions, the size relationship of their collapse pressures determined the sequence of multiple local collapses and directions of the subsequent propagating buckles. Integral arrestors are effective designs with significant arresting efficiency in such scenarios. The flexure curve of the pipeline changed significantly only when an arrestor was installed in the left- or right-bending region. A large fault dip angle leads to both higher first collapse pressures and crossover pressures due to smaller bending deformations. A flipping crossover occurs when a downstream reverse ovality develops, which rotates the collapse direction by 90°. The material efficiency of integral arrestors will decrease with the occurrence of flipping crossovers.

Research on Stability Control of Shields at Working Face with Large Dip Angle

Coal is the main energy source in China. As flat and shallow coal seams are being depleted, adverse coal seams such as inclined and steeply inclined coal seams account for larger proportion of seams that are mined. For these coal seams, instability such as slip and tipping of mining equipment due to the large inclination is a significant challenge for the productive operation of intelligent or smart mines. Therefore, this paper serves to provide some insights into improving their stability. In this paper, research on the anti-tipping and anti-slip technology of shields is carried out on an intelligent working face with a large dip angle. A mechanical model of “support-surrounding rock” was established. Through the analysis of the influence of the self-weight of the support on its stability and through theoretical analysis and field practice, it was found that the critical tipping angle of the support in the free state is 27.8, the critical slip angle is 16, and the support is more prone to slip in the free state; the shields in the middle of the working face are the key area for stability control. Suitable technical measures are taken to ensure the stability of the supports, which provides the management and practical basis for safe and efficient mining in the intelligent working face with a large dip angle.

Dynamic sublevel caving technology for thick seams with large dip angle in longwall top coal caving (LTCC)

Dynamic sublevel caving technology for thick seams with large dip angle in longwall top coal caving (LTCC)

Multi-scale Fractures and Their Influence on Shale Gas Deliverability in the Longmaxi Formation of the Changning Block, Southern Sichuan Basin, China.

The capacity and deliverability of shale gas are closely linked to the presence of multi-scale fractures, including fractures and faults, within organic-rich shales. This study aims to investigate the fracture system of the Longmaxi Formation shale in the Changning Block of the southern Sichuan Basin and quantify the influence of multi-scale fractures on shale gas capacity and deliverability. The fracture system was analyzed through outcrop, core observations, and 3D seismic interpretation. Criteria for fault classification were established based on the horizon, throw, azimuth (phase), extension, and dip angle. The Longmaxi Formation shale mainly comprises shear fractures that form under multi-phase tectonic stress, characterized by large dip angles, small extensions, small apertures, and high density. The high content of organic matter and brittle minerals in the Long 1-1 Member facilitates the occurrence of natural fractures, which somewhat enhance shale gas capacity. Reverse faults with a dip angle of 45-70° exist vertically, while laterally, there are early-stage nearly E-W faults, middle-stage NE faults, and late-stage NW faults. Based on the established criteria, faults that cut upward through the strata in and above the Permian with a throw greater than 200 m and a dip angle greater than 60° have the greatest influence on shale gas preservation and deliverability. These results provide important guidance for shale gas exploration and development in the Changning Block and contribute to our understanding of the relationship between multi-scale fractures and shale gas capacity and deliverability.

Research on Mining Pressure Dynamic Effect of the Large Dip Angle Working Face

In order to study the mining pressure law of the large dip angle working face, prevent the topping accident of the working face, and cause the roof accident, through the observation of the mining pressure of the working face of Xiaogou coal mine, the law of mine pressure appearance and dynamic effect of the large dip angle working face are obtained. The results show that the initial support force of the working face support is not less than 24 MPa, the lower part of the working face is larger, and the falling rock has not been effectively filled in the middle and lower part of the working face. Therefore, the daily observation of the top and bottom goaf is carried out to determine whether it is a large area of suspended ceiling appears. Taking effective measures for safe mining in a timely manner has great practical significance for reducing roof accidents.

The Influence of Cross-Section Shape on Failure of Rock Surrounding the Main Tunnel in a Water-Sealed Cavern

The influence of cross-section shape on rock stability was investigated by designing a similar model test and numerical simulation using particle flow code (PFC). The test results showed that the left- and right-hand sides of the entrance are subjected to tension, mainly forming vertical cracks or oblique cracks with a large dip angle. The vicinity of the entrance is subjected to the shear effect and the overall failure of the model is brittle in the similar test. Mesoscopic fractures mainly appear as tensile fractures, and a small number of shear fractures are found in the vicinity of the entrance. A long narrow coalescent-fracture zone is separately formed at the left- and right-hand sides of the entrance when approaching peak load in PFC test. Stress concentration occurs at the end of the long axis of the elliptic cross-section. The stress is high at the arch foot and spandrel of a horseshoe-shaped cross-section and a coalescent fracture zone formed at the arch foot on the right-hand side caused the tunnel to fail. The ovoid-shaped and vertical-wall-arched cross-sections are under significant tension, owing to the force chains distributed along the tunnel wall, show a large included angle with the tunnel wall. From the perspective of bearing capacity, a circle is the best section. From the perspective of failure mode, the horseshoe-shaped section is more suitable for use in corresponding practical engineering.

Computed Tomography Observation and Image-Based Simulation of Fracture Propagation in Compressed Coal

In this study, the fracture propagation characteristics and associated mechanisms of coal are investigated by using computed tomography (CT) observation and image-based simulation. The spatial distribution and the structural morphology of original fractures provide significant influences on the failure behavior of fractured coal. The fractures with small dip angles and large openings result in more-obvious fracture closure and stable propagation stages, while failure pattern is more sensitive to those with large dip angles. The coal tends to experience brittle failure, which transits from a splitting to mixed-splitting faulting mode because of the difference in original fracture distribution. The final failure fracture network originates mainly from the propagation of original fractures, driven by localized tensile stress. Fracture interaction and mineral influence tend to increase the complexity in the failure fracture network. Moreover, image-based numerical models are established on the basis of CT reconstruction, where the spatial distribution and the structural morphology of original fractures are properly considered. Numerical modeling reproduces similar stress–strain responses and failure fracture networks to that observed in the experiment. The predicted distribution of tensile stress shows a similar evolution trend to the failure fracture network, implying that the fracture propagation of coal is dominated by tensile failure. Shear cracks emerge mainly after the large fracture running through the coal sample has been formed.

Investigation of effect of the profile of screw flight on chocolate flow in 3D printing using an improved lattice Boltzmann method.

3D printing provides a new way of molding chocolate with complex geometrical structures. The screw extruder can efficiently transport the liquid chocolate, which has been adopted to investigate the effect of the profile of the screw flight on the flow. First, the rheological behavior of the liquid chocolate is measured and the Cross equation is demonstrated as the proper rheological model. Then, based on the rheological behavior, an improved lattice Boltzmann method is creatively proposed, for which the effectiveness is validated by the classical Poiseuille flow. Third, the geometrical structure of the screw extruder is analyzed and transformed. The possible changes in the profiles of the screw flights are listed. Finally, the fluid analysis is conducted and the necessary streamlines figures, cloud charts and velocity distributions are obtained. The large dip angle in straight cases has an obvious effect on the velocity distribution and the common flow area. The position of the convex point is the additional important factor, whereas the concave profiles are the most moderate in the proposed cases. The changes in the profiles will affect the chocolate flow. The work is significant for extrusion theory in 3D printing. © 2022 Society of Chemical Industry.

Seismicity and Stress State in the Ryukyu Islands Subduction Zone

Based on the newly compiled and mostly complete unified earthquake catalogue for China’s seas and adjacent areas, further information was obtained about the structural shape and dip angle of the Benioff zone in the Ryukyu Islands subduction zone during the different subduction stages. In addition, using the damped regional stress tensor inversion method, we were able to investigate the complex stress field characteristics and the dynamic significance of the shallow and intermediate earthquakes in the Ryukyu Islands subduction zone. The results show that the tectonic stress field of the Ryukyu Islands subduction zone was extensional along the subduction direction in the northern area of the Tokara Strait and was compressional along the subduction direction in the southern area of the Tokara Strait. The R value of the shallow stress field of the Okinawa Trough was low, and the σ3 was stable in the NNW direction with a small dip angle (>30°). The type of stress field in the shallow part of the Okinawa Trough transitioned from strike-slip type to normal fault type from north to south, reflecting the difference in the degree of development of the trough, and the southern segment of the trough began to transform into the expansion stage. The northeastern portion of the study area and southeast Taiwan constituted the high R value (0.68–0.87) region where the σ2 had tensile components. The stress state was biaxial tension–uniaxial compression, and the principal compressive stress was determined to be in the SEE direction with a large dip angle (>30°). The σ1 in northeast Taiwan exhibited a nearly vertical (>60°) plunge, while the σ2 and σ3 were nearly horizontal. The σ2 was thrust in the ENE–WSW direction, and the σ3 was extended in the NNW direction. Through this research, a greater understanding has been gained of the seismicity characteristics and shape of the Ryukyu Islands subduction zone. Supplementary research has also been completed on the focal mechanism solution and stress field of the Ryukyu Islands subduction zone. Finally, this research is important for earthquake hazard analysis and earthquake engineering safety evaluation in this area.

Salt diapirism in the eastern margin of the Pre-Caspian Basin: Insight from physical experiments

Since the 1950 s, salt diapirism has been shown to be closely related to hydrocarbon accumulation and has been a hot spot of research activity in structural and petroleum geology. Many salt structural, such as salt wall, roller, pillow, welt and anticline have been formed in the Pre-Caspian Basin during the post-Kungurian (Lower Permian) times. Meanwhile, mechanisms of salt structure deformation and the influence of the sub-salt strata on salt diapirism is still unclear. Based on seismic data and a geological model of the eastern margin of the Pre-Caspian Basin, physical simulation experiments of salt diapirism have been conceived. Performed to analyze, the dynamic process of salt structure deformation, and to clarify mechanisms of the salt diapirism and the relationships between the salt structures and the underlying strata. Differential loading seems to a principal mechanism accounting for sediment. The sedimentation rate of the overburden formations had a great impact on the salt structure forms and geometry. The physical experiments showed that: salt diapirism starts in the basin margin with progradation of sediments and then continues down-slope toward the basin center. The height and width of the salt structures are influenced by dip angle of the sub-salt. The larger-scale salt structures occurred in the inner basin zones, followed the central slope zone and the basin margin with a large dip angle.

Model Test of TBM Tunnel Crossing Large Dip Angle Fault Zone under High In Situ Stress

In order to study the effect of fracture zone on tunnel stability under high ground stress and to reveal the disaster mechanism of fracture zone surrounding rock compressor, the TBM tunnel of Fragrant Furnace Mountain Tunnel in the F12 fracture zone in Dali I section of central Yunnan was experimentally studied. The results show that the TBM cutter head has a significant effect on the surrounding rock pressure in the range of 0.43 D~0.5 D (hole diameter), with a maximum increase of 1.19-fold. As the measurement point approaches the tunnel contour, the displacement of surrounding rock increases. As TBM traverses the fracture zone interface, the displacement of surrounding rock increases at the maximum rate. The effect of TBM shear rock formation failure on the internal displacement of rock formation is 1.21 D in the front and not more than 1.5 D in the top. Sliding and loosening of the fault zone looser above the interface can easily lead to blockage of the fault zone, and the pressure of the surrounding rocks at front edge does not affect more than 1.73 H (the length of horizontal projection of the fault zone interface). Therefore, in the course of construction, the interface of fracture zone should be promoted to reduce the construction risks.