Loose Area Research Articles

A case study of displacement, stress condition and failure criterion of surrounding rock in deep super-large section double chambers in the Longgu Coal Mine, Shandong, China

To investigate the stability of a super-large section chamber group, an analysis was conducted based on the in-situ geological conditions of a super-large section chamber group utilized as a coal gangue separation system at the Longgu Coal Mine. Field measurement and numerical simulation were employed to analyze the failure area and stress state of the surrounding rock under varying chamber spacings. The results indicate that the extent of the plastic zone significantly expands when the spacing between chambers is less than 2.0 times the chamber width. When the distance between chambers is 1.5 times the chamber width, it results in the rock pillars being entirely within the plastic zone. As the chamber spacing decreases, the tangential stress within the rock pillar range increases. When the chamber spacing is 2.5, 2.0, and 1.5 times the chamber width, the maximum tangential stress is 1.19, 1.46, and 1.18 times that in the case of a single chamber, respectively. Based on the displacement analysis, it was observed that as the distance between the chambers decreases, there is a notable increase in the displacement of the pillar sides and chamber top, indicating a higher risk of collapse. Integrating the plastic area and stress analysis allows for the categorization of the rock pillar area into four sections: the broken area, loose area, stable area, and firm area. Drawing upon the theoretical solution of the plastic zone of a circular chamber and the equivalent radius method, an approximate solution for the plastic zone of a non-circular chamber has been provided. Furthermore, the minimum reasonable spacing between chambers in a super-large section chamber group is provided as a distance criterion for the failure of a double chamber.

Functional Failure Behavior of Submerged Entry Nozzle during the Continuous Casting Process of the Bearing Steel GCr15

The submerged entry nozzle (SEN) is an indispensable functional structural ceramic in the current continuous casting production. The stability and safety of the SEN is very important during the casting process. In this article, the functional failure of the SEN during the continuous casting process of the bearing steel GCr15 is studied. The results show that the functional failure of the SEN during the bearing steel GCr15 casting process is caused by the clogging inside the SEN which is led by the low cleanliness and the high impurities n the molten steel. The clogging in the SEN can be divided into solidified steel area, loose area, dense area, and surface area. To improve the castability of bearing steel or other high‐cleanliness steel, it is necessary to strengthen the refining process and treatment effect, strengthen the sealing and the effect of the protective casting of the molten steel, and moderate optimization of nozzle materials or the application of external fields on the SEN.

Effect of magnetic alternate stirring on solidification structure of the round billet

ABSTRACT In this study, a permanent magnet stirrer was constructed for the implementation of experiments on different magnetic field stirring modes. Through experiments, it can be observed that when the fixed speed of 200 rpm and the alternate stirring mode of magnetic field was adopted, the loose area in the core of ingots was reduced from about 72 mm2 to 21 mm2, which significantly improved the density and element uniformity of the ingot. A Φ220 mm SAE1527 round billet was selected as industrial trial steel. When the stirring current and frequency was 350 A and 3 HZ, the electromagnetic stirring of the mold was adjusted from continuous stirring to alternate stirring mode. The solidification structure of the billet has been improved to a certain extent. Furthermore, the number of spot segregation larger than 0.5mm2 was reduced from 43 to 26, thereby improving the uniformity of internal elements in the billet.

Experimental and practical investigation of reinforcement mechanism on permeable polymer in loose area of drainage pipeline

Permeation grouting is one of the important methods of anti-seepage reinforcement when the drainage pipes crosses loose diseases caused by leakage. With the development of grouting materials, permeable polymer slurry is widely used in engineering practice. Due to its low viscosity, fast reaction and micro-expansion, the diffusion and reinforcement law of slurry in loose area of drainage pipeline is more complex. To better understand the effects of water head pressure, grouting pressure, sand particle size and clay content on the anti-seepage and reinforcement effect of permeable polymer grouting in loose area of drainage pipeline, several types of tests, including permeability and uniaxial compressive strength tests, were performed. Then, based on the model test results, a BP neural network prediction model for the anti-seepage reinforcement effect of permeable polymer grouting in loose area of drainage pipeline is constructed, and the research results are applied to the treatment project of loose area of drainage pipeline for verification. The results show that: 1) after grouting, the order of magnitude of permeability coefficient of the consolidated body is reduced to 10-7cm/s, the anti-seepage performance of the sand layer is greatly improved, and the grouting pressure is the main controlling factor affecting the anti-seepage performance of the consolidated body. 2) The compressive strength of the consolidated body is obvious different under different working conditions. The water head pressure is the main controlling factor affecting the strength of the consolidated body. 3) Due to the limitation of test conditions, the relative error between the predicted value of BP neural network model and the actual value is about 20%, which can meet the general prediction needs.

Transparent soil model test and numerical study on the effect of adjacent spring on the stability of tunnel face in composite strata

To study the instability and failure mechanism of tunnel face in composite stratum and the evolution law of supporting pressure in the areas with spring, this paper used two different types of transparent soil and a self-designed 3D model test system. Six large transparent soil model tests were carried out by considering different confined water heads of spring and tunnel burial depth. The optical laser and high-speed camera were controlled to move on a high-precision linear platform. CT scanning was performed to obtain the failure model under different conditions. The finite element method considering a two-way fluid–structure coupling was used to validate the model test. The research results indicate under spring, the support pressure curves can be divided into three stages: rapid decline, rebound-rise, and constant. There is no rebound-rise stage under the condition of no spring. With increased confined water heads or reduced tunnel burial depth, limit support pressure shows an increasing trend. 2D and 3D damage models for different working conditions were obtained by PIV technology and 3D reconstruction technology. If there is a spring, the maximum displacement moves to the top of the tunnel with the increase of water head and the failure mode is a combination of “silo shape” and “inverted prism”. When there is no spring, the maximum displacement appears at the interface of the soil layer, and the failure mode is a combination of “silo shape” and “wedge shape”. The presence or absence of springs and the change of the confined water head have no significant effect on the height of the loosening area. With the tunnel burial depth ratio of 0.5 to 2.0, the height of the loose area increases from 0.17 to 0.83 D, and the soil arch area develops outward.

Research on the Characteristics of Thermosyphon Embankment Damage and Permafrost Distribution Based on Ground-Penetrating Radar: A Case Study of the Qinghai–Tibet Highway

In order to research the special embankment (thermosyphon embankment) damages and the distribution of permafrost under the Qinghai–Tibet Highway (QTH) embankment. The section K2952–K2953, which is a typical representative of the QTH, was chosen for the detection and research of the permafrost and embankment damages in order to determine the sources of the damages. In this study, the performance characteristics of the embankment, the active layer, and the permafrost table found in ground-penetrating radar (GPR) images were researched, combined with multi-source. According to the research findings, the construction of the embankment in this section has stabilized the effect on the permafrost table. Under the embankment of the unemployed thermosyphon section, the permafrost distribution has good structural integrity and continuity, with the permafrost table at a depth of around 5 m. The continuity of the permafrost distribution under the embankment in the thermosyphon section was poor, and there was localized degradation, with the permafrost table being approximately 6 m deep. The main cause of the irregular settlement and other damage in this section is the presence of a loose area at the base of the embankment. Although the thermosyphon on both sides of the embankment also plays a role in lifting the permafrost table, it is not ideal for managing the damage to high embankments where the type of permafrost under the embankment is high-temperature permafrost with a high ice content and where the sunny–shady slope effect is obvious. The research results described in this article can therefore provide a crucial foundation for the detection of highway damage and permafrost under embankments in permafrost regions in the future.

Experimental study on forced response characteristics and anti-dislocation performance of articulated tunnel structure under dislocation action of normal fault

The stick–slip dislocation of normal faults will produce large permanent displacement. The tunnel lining structure crossing active normal faults is easily affected by fault dislocation. It is necessary to study the mechanical behavior of tunnel lining structure under fault dislocation. Therefore, taking the subway tunnel of Urumqi Rail Transit Line 1 crossing the Jiujiawan fault project as an example, based on the optimal mix ratio determined by the indoor similar material ratio test, the self-designed large-scale active fault dislocation simulation loading system is used to carry out the stick–slip dislocation model test of normal fault with 60° dip angle. The mechanical behavior difference between the conventional tunnel structure and the flexible articulated tunnel structure is compared and analyzed, and the cracking range, damage characteristics and failure mode of the tunnel lining structure are defined. The results show that: (1) The failure modes of the conventional tunnel structure and the flexible articulated tunnel structure are basically the same, including the large eccentric failure of the inverted arch and the wall foot, and the compression shear failure at the fault plane, which are longitudinal cracks and oblique cracks respectively. In addition, there are longitudinal cracks in the inner side of the invert and the lateral side of the wall foot, but few circumferential cracks. (2) Because the flexible articulated structure increases the overall longitudinal flexibility of the tunnel, the flexible joints between segments can share part of the fault dislocation displacement, so the deformation range, failure degree and number of cracks of the articulated tunnel structure are significantly reduced compared with the conventional tunnel structure, and the anti-dislocation performance is better. (3) Considering the influence of fault dislocation on tunnel structure, the loose area and empty area should be investigated and repaired in the rapid repair and reinforcement of post-disaster tunnel. At the same time, the case study ideas and test methods in this paper can provide some reference value and guidance for other similar tunnel engineering studies in the future.

Earth Pressure of the Trapdoor Problem Using Three-Dimensional Discrete Element Method

Load transformation from the yielding part of the soil to the adjacent part is known as the soil arching effect, which plays an important role in the design of various geotechnical infrastructures. Terzaghi’s trapdoor test was an important milestone in the development of theories on soil arching. The research on earth pressure of the trapdoor problem is presented in this paper using the three-dimensional (3D) discrete element method (DEM). Five 3D trapdoor models with different heights are established by 3D DEM software PFC 3D. The variation of earth pressure on the trapdoor with the downward movement of the trapdoor, the distribution of vertical earth pressure along the horizontal direction, the distribution of vertical earth pressure along the vertical direction, the distribution of lateral earth pressure coefficient along the depth direction, the magnitude and direction of contact force chain are studied, respectively. Related research results show that the earth pressure on the trapdoor decreases rapidly after the downward movement of the trapdoor, and then reaches the minimum earth pressure. After that, the earth’s pressure will rise slightly, and whether this phenomenon occurs depends on the depth ratio. For the bottom soil, due to the stress transfer caused by the soil arching effect, the ratio of earth pressure in the loose area decreases, while the ratio of earth pressure in the stable area increases. With the trapdoor moving down, the vertical earth pressure along the depth in the stable zone is basically consistent with the initial state, which shows an approximate linear distribution. After the trapdoor moves down, the distribution of earth pressure along with the depth in the loose area changes, which is far less than the theoretical value of vertical earth pressure of its self-weight. Because of the compression of the soil on both sides, the lateral earth pressure coefficient of most areas on the central axis of the loose zone is close to the passive earth pressure coefficient Kp. The existence of a ‘soil arch’ can be observed intuitively from the distribution diagram of the contact force chain in the loose zone.

Failure analysis and dislocation-resistant design parameters of mining tunnel under normal faulting

To investigate the mechanical response and failure characteristic of mining tunnel under the effect of normal fault dislocation and the effect of dislocation resistant design parameters on the tunnel forces, model tests with a geometric similarity ratio of 1:40 were carried out to thoroughly analyze the impact of section connection form and section length on the tunnel. The outcomes of numerical simulations performed at the same scale were then compared to the consequences of experiments. The effect of three anti-dislocation design parameters on the mechanical response and failure characteristic of the tunnel, namely the lining joint form, the lining section length (6 m, 12 m), and the deformation joint width between sections (0.1 m, 0.2 m), was examined on the basis of confirming the accuracy of the numerical model. The results revealed that the tunnel exhibits longitudinal tension-bending superimposed on the vertical extrusion load pattern under the influence of normal fault dislocation, and the longitudinal deformation of the tunnel is characterized by an inverted S-shape. The fault zone is where most of the tunnel devastation is located, and most of the cracks are longitudinal through cracks. The void area appears beneath the invert near the fault plane in the hanging wall, while the loose area appears above the crown near the adjacent fault plane in the footwall. By adopting flexible connections between sections, shortening sections, and increasing the width of deformation joints within a tolerable range, the tunnel can be kept in good operational condition. Due to the difficulties of construction and engineering viability, vertical joints should continue to be the preferred lining form for mining tunnels crossing normal faults. Inclined joints along the fault plane have no evident advantages over vertical joints in terms of internal force.

A comparison study of face stability between the entering and exiting a shallow-buried tunnel with a front slope

Worldwide, it is a great challenge to tunnel in portal section, where excessive deformation, cracking, or even collapse often occurs during the construction process. This paper presents a comparison study of face stability between entering and exiting a shallow-buried tunnel with a front slope. Firstly, the theoretical solutions of support pressure σT and safety coefficient FS of the excavation face considering surface slope are derived by upper-bound limit analysis method. Secondly, for different slope angles, buried depth and surrounding rocks of the exit and entrance sections, the σT and FS are obtained. The results show that when the burial depth of the tunnel crown h remain constant, the σT increased first and then decreased while the FS increased gradually, and both become steady when the slope angle α arrive at a certain value. In addition, the thicker the h is, the smaller the certain value α is. When the h and α remain constant, the loose area in front of the excavate face will decreased apparently with the increase of the internal friction angle φ, thus the σT will decrease and FS will increase. Moreover, the σT decreased linearly with the increase of cohesion c and unit weigh γ of surrounding rock, while the FS is the opposite. Compared with the entrance section, the construction risk at the exit section is greater.

Evolution law and application of permeability in gob without coal pillar and self‐formed roadway

AbstractRoof‐cutting and pressure‐releasing technology are used to cut out the pressure transmission line of the critical blocks in the roof, causing the roof to totally collapse in the gob, while the NPR large deformation anchor cable support keeps the highway in its self‐formed state. The gangue compactness has increased greatly when fully collapsed and filled to the gob's edge. At the end of the working face, the void ratio between rock blocks and the loose area is decreased, resulting in an observable shortening of the airflow disturbance distance at the working face and a change in the disaster gas accumulation law in the deep gob. It is critical to obtain the permeability characteristics of gob to avoid hazardous gas migration. The evolutionary model of the permeability of the mined‐out region is created based on the analysis of the movement law of the overburden strata and the collapsed law of the gangue in the gob, and the “Z” ventilation model is built to research the airflow law in the gob. The following are the key conclusions reached: The 0–10 m airflow exchange zone is severe, the 10–45 m airflow return face is weak, the 45–190 m section airflow exchange is weak, and the 190–280 m section airflow confluence gob enhances the top corner's weak air area. The 0–50 m part of the self‐formed Roadway has a wide air leakage channel, and good sealing methods have a significant impact on air leakage in the working face. The two‐dimensional model constructed by comprehensive quantification of the main controlling factors, such as broken‐expand, pressure, and filling degree, can represent the law of gas migration in the panel to a significant extent, and the reliability of the permeability evolution law is confirmed through data comparison and analysis.

Three-Dimensional Theoretical Model for Soil Arching with Inclined Slip Surfaces

Terzaghi proposed two-dimensional (2D) arching theory through trapdoor tests based on the assumption of a vertical slip surfaces. However, the original 2D assumption is different from a real three-dimensional (3D) excavation condition and actual slip surfaces caused by the downward movement of a trapdoor are inclined surfaces. Therefore, a 3D theoretical model was proposed in this study considering inclined slip surfaces. Horizontal thin-layer differential element method was used to obtain the loosening soil pressure. Using the 3D theoretical model, the effects of the buried depth ratio of loose area, length of loose area, soil parameters, and lateral earth pressure coefficient were investigated. The loosening earth pressure was highly affected by inclination angle of slip surface, buried depth ratio and length of loose area. Neglecting the inclined slip surface will underestimate the value of the loosening earth pressure, which will lead to the insecurity of the design. Loosening earth pressure calculated by this study was also compared with trapdoor tests. Results from this study was in good agreement with the experimental results. Compared with the traditional 2D solution, results from this study can more accurately analyze the soil arching effect in 3D excavation cases.

Analysis on construction deformation characteristics of Da-Puling tunnel by monitoring measurement

Tunnel monitoring and measurement is the guarantee of tunnel construction safety and implementation of dynamic parameter design; relying on the surface settlement, vault settlement and convergence deformation in the tunnel during the construction of Da-Puling tunnel on Guangxi expressway, based on the monitoring data, the stress situation and deformation characteristics of the tunnel are analyzed; the results show that the construction parameters of Da-Puling tunnel are basically reasonable, and the portal section is the key to the control of the whole construction parameters, the settlement of the tunnel vault in the V-Class surrounding rock of the portal section is about 4 times of the convergence deformation, which is mainly caused by the gravity of the overlying soil layer. The settlement of the tunnel vault in the IV-class surrounding rock is close to the convergence deformation, and the stress release deformation in the loose area of the tunnel surrounding rock is the main one. The monitoring and analysis in the construction process provides reliable data for design and construction in time, and ensures the smooth progress of tunnel construction.

Underground Structure Inspection in Geological Groundwater Environment Base on Geologic Radar Technology

How to accurately detect the anti-slide pile and the surrounding rock hole is the key to the correct application of the concrete quality treatment method, at the same time, it can ensure the control effect to a certain extent, and make the treatment project more economical and effective. The presence of water in the reinforced concrete layer, coupled with the void shape, and the irregular nature of the water in the hole, may be filled with air, mud, soil and other media factors, so there is considerable complexity. The number of abnormal bodies in the contrast enhancement diagram increases significantly, which is helpful for us to observe the loose area of anti-slide pile. We can find the pixel value corresponding to the feature by detecting the abnormal data of the pile one by one.

PERIPHERAL DENTINOGENIC GHOST CELL TUMOR: A RARE CASE REPORT

Peripheral dentinogenic ghost cell tumor (PDGCT) is a rare and locally infiltrating benign odontogenic tumor with only 20 cases reported in the literature. A 75-year-old woman with total dental prosthesis had a nodular and fibrous lesion of 3 mm, normochromic, and sessile with a year of evolution near tooth 38. The clinical hypothesis was inflammatory fibrous hyperplasia, and an excisional biopsy was made. Microscopically, nests of odontogenic epithelium were observed in which the periphery exhibited palisaded columnar cells with a loose central area similar to the stellate reticulum. In addition, squamous metaplasia and sometimes fused phantom cells were observed. The stroma composed of dense fibrous connective tissue had few mononuclear inflammatory cells, and the lesion was merged with the surface parakeratinized stratified squamous epithelium. Thus, the diagnosis of peripheral PDGCT was stated. The patient is under follow-up without showing signs of recurrence after 5 months.

Influence of Backfill Compaction on Mechanical Characteristics of High-Density Polyethylene Double-Wall Corrugated Pipelines

For flexible pipelines, the influence of backfill compaction on the deformation of the pipe has always been the focus of researchers. Through the finite element software, a three-dimensional soil model matching the exterior wall corrugation of the high-density polyethylene pipe was skillfully established, and the “real” finite element model of pipe-soil interaction verified the accuracy through field test. Based on the model, the strain distribution at any position of the buried HDPE pipe can be obtained. Changing the location and extent of the loose backfill, the strain and radial displacement distributions of the interior and exterior walls of the HDPE pipe under different backfill conditions when external load applied to the foundation were analyzed, and the dangerous parts of the pipe where local buckling and fracture may occur were identified. It is pointed out that when the backfill is loose, near the interface between the backfill loose region and the well-compacted region, the maximum circumferential strain occurs frequently, the exterior wall strain is more likely to increase greatly on the region near crown or invert, the interior wall strains increase in amplitude at springline, and the location of the loose region has a greater influence on the strain of the pipe than the size of the loose area.

Experimental study on pore-fracture evolution law in the thermal damage process of coal

High temperature causes thermal damage to coal and alters its physical and mechanical properties. In this paper, in order to study the influence of thermal damage on coal mechanical properties and pore-fracture development, uniaxial compression experiments were performed on coal samples treated under different temperatures. Meanwhile, the evolution law of coal fracture in the heating process was quantitatively studied from macroscopic and microscopic perspectives by using a CT scanning electron microscope (SEM), and evolution characteristics of coal pore structure under high temperature were tested and analyzed. In addition, the influence mechanism of thermal damage to the mine fire was discussed in combination with the characteristics of coal mine fire. The results show that the failure mode of coal sample changes from splitting failure to splitting-tensile combined failure and shear-tensile combined failure with the rise of temperature. As the temperature goes up, the number and length of fractures both grow, while the fracture rate and width increase first and then decrease. The porosity of coal exhibits an upward trend on the whole. Under the action of thermal damage, the internal micropore surfaces of coal become notably rougher. The high temperature thermal damage causes the formation of a loose area at the edge of fire area. This loose area not only affects the fracture field and airflow field of the fire area, but also further induces the fire to spread deeper. The research results can be used as a reference for on-site fire prevention work.

Simulation Study on Different Bucket Wide in Shoveling Loading Process Based on EDEM

The study is based on the bucket wide in shovel loading process, to know about mechanism about different bucket wide in shovel loading process through the motion regularity of the material. Then simulation experiment was applied by a shovel-loader for different bucket wide in the discrete software EDEM. The results show that the new windrow frontier is loose when inserting material. As a result of the bucket disturbance, slope material is moved downward. The impact area is greater as material bucket width is larger. With the increase of bucket insert depth, bucket goes forward extrusion materials, material goes toward small loose zone and stress area. During the process of inserting, material is squeezed into a dense zone and then solid zone is in damaged state. The smaller bucket width is, the smaller the impact is on the material, vice versa. In the phase of ascension, the bucket shear extrusion windrow, shearing effect is obvious. The affection of the shearing area of the particles becomes greater because of the increase of bucket width. The more obstacles the shovel can overcome, with the rotation of the bucket to ascend, area is decreased about interacting with bucket, material goes toward the loose area and tends to stability.

Impact of shield tunneling on adjacent spread foundation on sandy cobble strata

The section of shield tunnel of the Chengdu Metro line passes primarily through sandy cobble strata. There are many buildings with spread foundations along the lines. Shield tunnel construction will disturb the ground, causing displacement or stress to adjacent spread foundations. Based on the similarity theory, a laboratory model test of shield tunnel driving was carried out to study the influence of shield tunnel excavation on the displacement of adjacent spread foundation. The results show that foundation closer to the tunnel has greater displacement or settlement than that further away. The horizontal displacement is small and is influenced greatly by the cutting face. The displacement along the machine driving direction is bigger and is significantly affected by the thrust force. Settlement occurs primarily when shield machine passes close to the foundation and is the greatest at that time. Uneven settlement at the bottom of the spread foundation reaches a maximum after the excavation ends. In a numerical simulation, a particle flow model was constructed to study the impact of shield tunnel excavation on the stresses in the ground. The model showed stress concentration at the bottom of the spread foundation. With the increasing ground loss ratio, a loose area appears in the tunnel dome where the contact force dropped. Above the loose area, the contact force increases, forming an arch-shaped soil area which prevents the loose area from expanding to the ground surface. The excavation also changed the pressure distribution around spread foundation.

Stretching and Chamfering Finite Element Analysis of Rotor Loose Compaction Based on DEFORM

DEFORM is a software used for FEA (Finite Element Analysis) simulation. By using this software, I take a research on the procedure when a steel billet with defect of artificial loosening is drawn out in a simulated environment. Then I build a FEA model about the loosening and compaction of a large-sized rotor and stimulate the procedure in accordance with current craft card involving rotor forging. Finally, I get a result: the relative density of the loose area reaches up to 85% after the first drawing-out process (note: forging ratio 1.47). After simulating the procedure of chamfering on a billet which has been already drawn out, I found that chamfering had little substantial impact on the its loosening and compaction.