Increase Of Excavation Depth Research Articles

Repairing Performance of Polymer-Modified Cement-Based Thin Spray-On Liners on Pre-Cracked Rock-like Specimens

With the development of coal mining and the increase in excavation depth, the stress on roadway surrounding rock is also increasing. This creates conditions for crack development in the roadway, so it is urgent to develop rock repair materials with excellent performance. The ability of thin spray-on liner (TSL) to repair rock and concrete opens up the possibility of reusing abandoned roadways. The ability of TSL to support the surrounding rock is also important in preventing the generation of roadway waste. In this paper, styrene–acrylic emulsion (SAE), vinyl acetate–ethylene copolymer emulsion (VAE), and polyvinyl alcohol powder (PVA) were used to prepare three TSLs. Rock-like materials were configured using cement mortar according to similar principles. Three types of TSLs were tested for basic properties such as viscosity and mechanical strength, which provided data to support the explanation of the repair performance of TSLs. Three TSLs were used to repair pre-cracked rock-like specimens (PR). The number of brushing times and the angle of PR’s cracks were regarded as test variables. Changes in the mechanical strength of repaired PRs were tested by compressive and flexural tests. TSL repair performance was evaluated with the help of mechanical strength changes. Results show that polyvinyl alcohol powder modified cement-based thin spray-on liner is most suitable for repairing rock cracks; as the thickness of the brush slurry increases, its repair performance continues to improve. This paper can provide experience and a theoretical basis for the research of other rock repair materials, and it is also instructive for repairing shotcrete in the roadway.

Numerical Study on the Effect and Mechanism of Supporting Pile Equivalent Calculation Methods in Pile–Anchor Support System

In numerical analysis, the pile equivalent calculation method plays a key role in foundation pit calculation results. However, the effect and mechanism of different pile equivalent calculation methods in the foundation pit has remained unclear. To solve this question, based on FLAC3D, four pile equivalent calculation methods were introduced into a typical pile–anchor pit. This research was carried out from the perspective of soil displacement and stress, special points’ stress paths, and the plastic zone. The results revealed that there was a remarkable influence on the calculation results for different pile equivalent calculation methods. Specifically, compared with structural pile elements, displacements near the pile were smaller in solid pile element mode. Moreover, with the increase in excavation depth, stress concentration appeared in the solid pile element mode. The solid support pile with the interface, compared to that without the interface, had less displacement but more stress concentration around the pile, which led the special points’ stress paths around the solid pile to become irregular. Regarding the structural pile elements, it is suggested that both modeling approaches had a similar effect. These findings could help to provide a deeper insight into pile–anchor foundation pit numerical analysis.

Monitoring and Prediction of Horizontal Displacement of Underground Enclosure Piles in Subway Foundation Pits.

Urban rail transportation and underground space development and utilization are initiatives to solve urban traffic congestion. The monitoring and prediction of the stability of underground enclosure piles in foundation pits is a key index for the dynamic evaluation of the stability of underground space engineering. In this paper, we focused on the problem that the dynamic prediction accuracy and stability of foundation pit retaining piles in the Qingdao area are not high. Based on the analysis of various time function curves and the physical meaning of the parameters, we proposed the Adjusted-Logistic time function model, which introduces three physical parameters to adjust the deformation velocity and deformation acceleration in different stages for better accuracy. It could predict the deformation process of underground enclosure piles under different geological engineering conditions. It was verified in the field that the root-mean-square error (RMSE) of the Adjusted-Logistic function was 0.5316, MAE was 0.3752, and R2 was 0.9937, which were better than those of Gompertz, Weibull, and Knothe time function models. Meanwhile, it showed that with the increase of excavation depth, the maximum horizontal displacement of the underground enclosure piles gradually decreased and finally stabilized at 0.62-0.71 H. We established a catastrophe model of the horizontal displacement cusp at the observation point of the underground enclosure piles by using the time series of the measured data. It could determine the weak location of the underground enclosure pile stability and realize the multipoint warning of the foundation pit stability, which would ensure safe construction.

Numerical simulation research on bolt supports’ mechanical properties deformation in high-stress roadway

With the rapid development of domestic mining industry, it is necessary to consider the safety of the mine when mining. In order to improve the high stress environment and the frequent failure of bolts caused by the increase of excavation depth, in this experiment, FLAC3D is creatively proposed to establish the calculation model of bolt support roadway, analyze the basic geological environment and surrounding rock structure of the research area, and conduct the numerical simulation of the mechanical characteristics of bolt support deformation (BSD) in the high stress roadway (HSR). The basic geological environment and surrounding rock structure of the study area are analyzed, and FLAC3D is adopted for establishing a calculation model of the bolt-supported roadway, which can be used to simulate the axial and lateral forces of the bolt, and then determine the boundary conditions. It is found that the supporting bolt in the roadway needs to bear not only axial tension, but also transverse shear and bending. Based on the Winkler foundation beam principle, a calculation model of the bolt’s lateral bending force in the soft rock roadway is established, the lateral force characteristics of the bolt support are analyzed, the concept of “anchoring composite bearing body” is proposed, and the force characteristics of the bearing body are calculated. The research results show that in the HSR, the bolt mainly bears the combined forces of tensile and lateral bending; among them, the bolt’s axial force remains basically unchanged at the tail part near the pallet, and the bolt’s axial force at the end part deep into the rock mass decreases rapidly. The bending moment of the bolt is “wave-shaped” distributed along the length of the rod body in the positive direction and negative direction of the axis, and the comprehensive action of the axial tension and transverse bending of the bolt increases when the stress concentration increases. A smaller roadway radius will lead to longer bolts, denser arrangement and higher support strength.

Influence Law of Foundation Pit Excavation on Stress of Surrounding Tunnel Bolt

Due to the existence of a tunnel next to the foundation pit, the soil surrounding the foundation pit deforms into the foundation pit due to the excavation unloading during the process of foundation pit excavation, which causes the deformation of the tunnel. The supporting structure of the tunnel can ensure the deformation stability of the tunnel, so it is necessary to study the stress of the tunnel bolt supporting structure caused by the excavation of the foundation pit. In this paper, the numerical simulation method was adopted to study the influence of the distance between the foundation pit and tunnel and the width and depth of foundation pit excavation on the stress of the tunnel bolt, and the following results were obtained: (1) When the distance between the tunnel and the foundation pit changes, the axial force of the bolt changes accordingly. The axial force of the left bolt first increases and then decreases, and the largest axial force is located in the middle of the bolt. (2) With the increase in the excavation width of the foundation pit, the stress of the left bolt does not change much. For the left bolt, with the increase in excavation depth, the stress of the left bolt does not increase monotonically but shows a trend of increasing first and then decreasing. When the excavation depth exceeds a certain value, the influence of excavation depth on lateral soil displacement gradually decreases. With the increase in excavation depth, the axial force of the top bolt decreases first and then increases.

Analysis of stability law and optimization of slope angle during excavation of deep concave mine slope

Occasional collapse failure is a typical occurrence during mine slope excavation processes. This study aimed to investigate the disaster law in the process of mining slope excavation, and further explore the optimal selection of excavation angle. Based on the systematic analysis of the residual sliding force and deformation response characteristics during slope excavation, the increment of the residual sliding force increases and the stability coefficient decreases with the increase in excavation depth. Additionally, a numerical model of the Jinchuan mining area in Jinchuan City, Gansu Province, China was created using the Midas-GTS finite element software. The influence of different excavation slope angles on slope stability was analyzed via numerical simulation under certain step slope height and width. The results show that the force and deformation of the slope were unfavorable to slope stability, and the slope stability coefficient would decrease gradually with the increase in slope angle. In addition, the optimal excavation angle combination ranges were determined as 62°~ 65°, 64°~ 67°, 67°~ 69°, 70°~ 71°, 73°, 75°~ 76°, 77°~ 80°considering the stability and maximum recovery. Therefore, the above research results verify the loading effect of mine slope excavation, and can serve as a reference for studies on the optimal range of excavation angles for the mine slope.

Study on the Law of Influence of Seepage Field Anomalies on Displacement Field Induced by Leakage of Enclosure Structure

The leakage of an enclosure structure will cause abnormal changes in the seepage flow field, which in turn can lead to the deformation of the enclosure structure and affect the surrounding geotechnical body. In this paper, a fiber-optic temperature measurement system is used to detect the location of the seepage points in a station of the Qingdao subway during open pit excavation, and the abnormal variation of the seepage field caused by the seepage points is obtained by numerical calculation and field measurement. Then, numerical simulation is performed to analyze the effects of seepage field anomalies on the deformation of the enclosure structure and surface settlement. It is found that the seepage flow caused by the leakage point has a significant influence on the surface settlement and the deformation of the enclosure structure. With the increase of excavation depth, the deformation of the enclosure structure increases and the maximum deformation position shifts downward. The deformation of the enclosure structure decreases when the leakage point exists. The surface volume also increases gradually with the excavation, and the maximum surface settlement position shifts outward significantly. The settlement range becomes larger when the leakage point exists.

Macro-Micro Response Characteristics of Surrounding Rock and Overlying Strata towards the Transition from Open-Pit to Underground Mining

The macro-micro mining response of the surrounding rock and overlying strata towards the transformation from open-pit to underground mining is examined in the present study, based on the engineering background of the Jinning phosphate mine (Yunnan Phosphate Chemical Group Co., Ltd.) via simulations involving similar materials, digital photographic measurement technology, and numerical simulation. The mining deformation of the surrounding rock underground, and of the overlying strata, is shown to develop in three stages, namely: (1) small and local deformation, (2) continuous linear increase, and (3) the violent nonlinear collapse of the entire system. The internal distribution of stress in the surrounding rock and adjacent overlying strata of the inclined mined-out area is complicated. The degrees of pressure increase and pressure relief have an important relationship with the size of the mining space. The pressure relief is more complete close to the mined area, and the stress reduction decreases with increasing distance. The cracks propagate in arc shapes and have a tendency to penetrate into the upper and lower ends of the stope. The size of the excavation space plays a key role in the generation, propagation, and penetration of the cracks. Due to the disturbance of the first mining level and the increase in excavation depth, the rate of damage to the surrounding and overlying rock increases in the second mining level. This process generates more cracks, which accelerate the instability of the surrounding rock and overlying strata.

Comparative investigation on deformation monitoring and numerical simulation of the deepest excavation in Beijing

The investigation on the mechanical mechanism of the retaining and protection structure of superdeep excavations is an important subject, and its deformation control research is particularly important. Taking the deepest foundation pit with full-section overall excavation in Beijing as an example, this paper studies the stress and deformation characteristics of composite soil nailing wall and anchored soldier pile wall combined retaining system under complex geological conditions of multi-layer groundwater during the process of excavating 31.4 m deep. The Midas simulation software and monitoring data are used to analyze the construction process of foundation excavation. The simulated results and monitored values of anchor force, ground settlement, and soil deformation during foundation excavation are analyzed and discussed to verify the reliability of the model. The spatial effect of internal force and deformation of composite retaining and protection structure for superdeep foundation excavation is discussed, and the parameters affecting the retaining structure are analyzed and investigated. The research shows that with the increase of excavation depth, both the extremum of the bending moment and the extremum of lateral displacement of retaining piles are increasing, and the position of the extremum of bending moment is located near the excavation face; then, the bending moment reaches the maximum when the foundation pit is excavated to the bottom. Within a certain range, increasing the rigidity or the embedded depth of the retaining pile or the prestress of the anchor can effectively control the lateral displacement of the excavation. However, when the rigidity of retaining pile is too large, its lateral displacement does not change significantly. Similarly, when the embedded depth is too long or the prestress of the anchor is too powerful, the effect of controlling deformation is also not obvious. The research results will provide theoretical basis and practical experience for the design and construction of superdeep excavations.

Experimental investigation on rockburst process and failure characteristics in trapezoidal tunnel under different lateral stresses

In general, the in-situ stress increases with the increase of excavation depth, and it significantly affects the safe and long-term stability of tunnels and chambers. To study the influence of the in-situ stress on the rockburst process and failure characteristics, three different lateral stresses were loaded to perform biaxial compression experiments on sandstone specimens with a trapezoidal opening. The results indicate that the high lateral stress accelerates the formation of localized damage around the trapezoidal opening, which can effectively consume the elastic strain energy. The deep surrounding rock at the roof and floor are basically in a compressive stress state, and the tangential compressive stress in the deep surrounding rock of the sidewall is greater than that in the deep surrounding rock of the roof and floor, which can cause the deep surrounding rock of the sidewall to be damaged more severely. For the corners of the trapezoidal opening, the high lateral stress can restrain the rotation of the principal stress, which lead to the reduction of the crack density around the corners. AE signals and CT scanning show that the failure mode of the model specimen shifts from tensile fracture to mixed tensile and shear fracture with the increase of the lateral stress. Under different lateral stresses, the outlines of failure zones on both sidewalls of trapezoidal opening are V-shaped, and the damage degree at the sidewall of the trapezoidal opening increases with the increase of the lateral stress when the rockburst occurs. Additionally, the failure zones on both sidewalls are larger than those of circular opening, which indicate that the supporting area on the sidewall of trapezoidal opening needs to be larger than that on the sidewall of circular opening.

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.

Numerical simulation method for vibration response of blasting excavation of deep-buried rock mass

In order to solve the safety problems caused by in-situ stress unloading and blasting impact in blasting excavation of deep-buried rock mass, the initial stress field and dynamic response of excavation unloading of deep-buried rock mass are calculated by ANSYS implicit and explicit solver. The results show that the stress wave induced by in-situ stress unloading diffracts at the foot of the wall and produces stress wave superposition in the surrounding rock above the wall. The vibration of surrounding rock caused by excavation of buried rock mass consists of blasting shock and ground stress unloading. With the increase of excavation depth, the vibration of surrounding rock caused by ground stress unloading exceeds blasting effect and gradually dominates the measured vibration.

MECHANICAL PERFORMANCE OF COMPOSITE RETAINING AND PROTECTION STRUCTURE FOR SUPER LARGE AND DEEP FOUNDATION EXCAVATIONS

The reliable retaining methods and a good stress system are the key to the success of super large and deep excavation engineering. In this paper, the deepest foundation pit in Hainan province is taken as an example. The method of mutual verification between in-situ monitoring and numerical simulation is adopted. The mechanical performance of composite retaining structure composed of reinforced concrete cast-in-situ soldier pile wall, diaphragm wall and prestressed anchor cable are studied. The interaction between the reinforced concrete cast-in-situ pile retaining structure at the upper part and the diaphragm wall retaining structure at the lower part is revealed, and the variation of internal forces of the diaphragm wall retaining structure in the time and space is demonstrated. And then the influence of insertion ratio and rigidity on the mechanical properties of diaphragm wall is discussed. Research shows, the range of interaction between the upper and lower retaining structures is limited. During the excavation process, the maximum bending moment of the diaphragm wall is always near the excavation surface, and the curvature of the bending moment curve decreases gradually with the increase of excavation depth and axial tension of anchor. When the insertion ratio of diaphragm wall increases, the maximum bending moment moves upward. With the rigidity of the diaphragm wall increases moderately, the bending moment of the retaining structure increases, but the lateral displacement decreases. The research results can provide theoretical basis and practical experience for the composite retaining structure design of super large and deep foundation excavations.

Research on Failure Mechanism and Parameter Sensitivity of Zonal Disintegration in Deep Tunnel

With the increase of excavation depth, the zonal disintegration phenomenon appears in the deep rock mass, which is quite different from the failure mode of shallow tunnel. In order to analyse the failure mechanism of this phenomenon, an elastoplastic softening damage model was put forward based on the softening damage characteristics of deep rock mass. The constitutive equations, the equilibrium equations, and the failure criterion were deduced. The theoretical solutions of radial displacement and radial stresses and tangential stresses of deep surrounding rock mass were calculated. The distribution law of zonal disintegration in deep tunnel was obtained. The theoretical solutions presented an oscillating mode. The theoretical calculated widths of fracture zones were in good agreement with the in situ test data. Besides, the sensitivity of different parameters to fracture morphology was calculated and analysed. The results show that the relative loading strength has a controlling role in the zonal disintegration morphology, followed by the cohesion force and deformation modulus, and the internal friction angle is the least. This study reveals the morphological characteristics and influencing factors of zonal disintegration, which provides a basis for the prediction and support control of fracture modes.

Field Monitoring Analysis of Construction Process of Deep Foundation Pit at Subway Station

Taking the excavation of deep foundation pit of a subway station in Ji’nan city as the background, and the measured data of the deep-horizontal displacement, support axis force and the surface settlement of the retaining pile body during the excavation was analyzed. It was shown that with the increase of excavation depth of the foundation pit, the position of the maximum horizontal displacement of the pile gradually moved downward from the top of the pile, and the pile deformation curve gradually changed from a similar cantilever beam to a “bow shaped” curve, the phenomenon of moving to the outside of the pit occurred at the top of the pile in the end-well of subway station. It is necessary to prevent the first reinforced concrete support and the retaining structure from being broken due to the lateral displacement of the top of the pile. The foundation pit excavation caused the settlement of the surrounding surface. The maximum settlement point was about 15 m from the boundary of foundation pit. The maximum surface settlement value was located in the middle of the standard section. The maximum settlement was 18.5 mm. The maximum horizontal displacement of ZQT37 measuring point at the standard section was 23.79 mm, and the location of maximum horizontal displacement was approximately 17 m from the top of the foundation pit. The axial force of the concrete support and the third steel supports at the ZCL20 section of the standard section were the largest. All supports were in safe working condition during excavation of the foundation pit.

Engineering Application and In-situ Monitoring Analysis of Retaining Structures of New H-section Steel Support System in Foundation Pit

A new H-section steel support system is introduced based on a foundation pit project in Shanghai. In-situ monitoring was carried out to measure the displacement of supporting piles. The monitoring results showed that the displacement of pile-top was closely related to the excavation depth and time. It is basically no longer developing after the foundation slab concreted finished. Horizontal displacement of the pile body increased gradually with the increase of excavation depth. The maximum horizontal displacement was about 25 mm and the position was about 1 m below the bottom of the foundation pit. Finally, the horizontal displacement of the pile body was presented as a "bow" with a small displacement at two ends and a large displacement in the middle. Compared with those at reinforced concrete support area, it showed that the deformation law and final displacement value of pile-top and pile body in the new H-section steel support area was basically the same as that of reinforced concrete support area. And all of the monitoring data were within the security range, meeting the design and code requirements. Moreover, new H-section steel support system construction period was short and the cost was low. It could effectively improve the green construction level. The conclusions obtained in this paper could be referred for other familiar projects.

A Computational Analysis on the Ambient Environment Effect Caused by Excavation of Foundation Pit of Lock Extension Project

A study is carried out on ambient environmental changes caused by excavation of foundation pit of Huzhou lock extension project based on ABAQUS finite element software. The result indicates that the excavation depth of foundation pit has a large impact on ambient environment. The analysis on foundation pit enclosure structures of different excavation depths and the soil horizontal displacement in the rear of retaining wall suggests that the enclosure structure and the soil horizontal displacement in the rear of retaining wall increase gradually with the increase of excavation depth. However, the horizontal displacement of the same excavation depth decreases significantly after a horizontal support of steel pipes is applied. The depth of the enclosure structure has a certain effect on the ambient environment. The enclosure structure and the soil horizontal displacement in the rear of retaining wall decrease gradually with the increase of the insertion ratio of the enclosure structure. The reduction of horizontal displacement is small when the insertion ratio of the enclosure structure is larger than 2.0.

Underground exploitations inside safety pillar shafts when considering the effective use of a coal deposit

Abstract Underground mining exploitation creates damage in surface building structure and in underground constructions as well. For this reason, many mining companies gave up carrying out excavations in safety pillar shafts. Currently, the situation on the market is changing. The continuous increase in excavation depth combined with an increase in exploitation costs resulted in many mining companies trying to find cheaper solutions. One of the methods is to carry out partial exploitations inside safety pillar shafts. Such exploitation is much cheaper than ordinary, because it decreases the exploitations depth, the length of transportation drifts, etc. The functionality of the shaft and its infrastructure have to be fulfil. The authors present a methodology for calculating the effects of mining on mine shafts using geometric integral methods. The paper presents the assumption of the first method developed by Bals (1939), a method based on the so-called Professor Knothe Theory (1951) and the German method of Ruhrkohle (Ehrhardt and Sauer 1961). Based on these methods, operational planning rules are given for mining in protective pillars during coal bed exploitation; additionally, the dimensioning method for shaft pillars is specified. Presented solutions are illustrated with examples from mining practice, where the continuous miner system was planned in the direct area of the mining shaft.

Study on Active Earth Pressure of Sheet Pile Model Test on Foundation Pit Engineering

In recent years, building density in the city is increasing as the promoting of urban modernization. Deep foundation pit excavation and bracing is a topic in geotechnical engineering, including strength and stabilization of soil mechanics, and transmutation and sedimentation of deep foundation, and common effect between soil and shoring structure. The paper based on the design and fabrication of indoor model test device. This paper respectively explored the destroy mechanism of cantilever and anchored sheet pile support structure on the soil pressure under the different loads, and comprehensively carried through cantilever and anchored sheet pile support test under four-grades excavation depth and four-grades load combination, and specially researched the transformation of soil pressure. At the same time, the piles spacing changed among 3cm, 4cm and 5cm. Theoretical results showed that the active earth pressure increased with the increase of load and excavation depth. Model test results showed that the earth pressure behind the piles increased with the increase of excavation depth and the load. The biggest earth pressure was 19.38kPa when loading 40kPa. The changing curves of soil pressure were similar when piles spacing was 3cm and 4cm. Earth pressure after the piles was negative when piles spacing exceeded 4cm, which illustrated that active earth pressure had changed into passive soil pressure.