Deformation Of Strata Research Articles

Characteristics and simulation study of ground fissure activities in Gaoliying, Beijing

The ground fissures in Gaoliying, Beijing, has caused panic among local people, and also caused severe damage to buildings and public facilities in its affected area. This paper takes the ground fissures as the research prototype and reveals its development and activities characteristics by field investigation and trenching exploration; The Flac3D finite difference method has also been used to simulate and calculate the deformation and failure characteristics of model strata under different fault dislocations and varying descend amounts of groundwater level. The results show that the ground fissure in Gaoliying are linearly distributed and cause the destruction mainly by vertical dislocation and horizontal tension in the shallow strata; Moreover, the differential settlement of the upper and lower strata of the model near the fault increases with the increase of fault dislocation. Vertical displacement and stress of soils on both sides of the fault are quite different, and the difference increases with the decrease of groundwater level.

Water Inrush Mechanism and Safety Control in Drilling and Blasting Construction of Subsea Tunnel

Dai, C.-Q.; Long, Y.-X.; Lv, Y.-L.; Hou, W.-Z., and Sui, H.-T., 2019. Water inrush mechanism and safety control in drilling and blasting construction of subsea tunnel. In: Gong, D.; Zhu, H., and Liu, R. (eds.), Selected Topics in Coastal Research: Engineering, Industry, Economy, and Sustainable Development. Journal of Coastal Research, Special Issue No. 94, pp. 218–222. Coconut Creek (Florida), ISSN 0749-0208.Based on the water inrush (WI) patterns of shallow buried tunnels, this paper elaborates on the WI mode and mechanism during the drilling and blasting of subsea tunnels in consideration of the characteristics of high-water pressure and complex geology of submarine tunnels. Then, through the main analysis for the deformation law of surrounding rock caused by drilling and blasting, it establishes the relationship between subsea/tunnel vault crown settlement and WI in construction under the construction conditions of unfavourable geological body, to obtain the two main failure modes of submarine tunnel: stratum cracking and partial separation failure. Besides, according to the characteristics of stratum deformation, the deformation displacement analysis of the roof and side walls of the tunnel was conducted to establish the safety control risk early warming mechanism on the basis of the risk control relationship between the measured values, early warning values, alarm values and limit control values of the stratum deformation. Finally, based on the core safety risk factors of the planning, design and construction stages of the subsea tunnel, the corresponding safety risk control measures were formulated.

Application of Roadway Backfill Mining in Water-Conservation Coal Mining: A Case Study in Northern Shaanxi, China

The mining induced subsidence and strata deformation are likely to affect the stability of the aquiclude, resulting in loss of water resources in the mining area. In order to reduce the disturbance of coal mining to the overlying strata and to preserve the water resources in the coal mining area, the roadway backfill mining (RBM) method was trialed in Yuyang coal mine in Northern Shaanxi, China. Based on pressure arch theory and ultimate strength theory, a mechanical model was developed to analyze the stability of coal pillars. Then the maximum number of vacant roadways between the mining face and the backfilling face was determined according to the stability of coal pillar and filling body. The method to calculate aquiclude subsidence and deformation was also proposed. Furthermore, as indicated by FLAC3D numerical simulations, the maximum tensile stress subjected by the aquiclude was 0.14 MPa, which is smaller than its tensile strength; the horizontal deformation was 0.24 mm/m, which is also smaller than the critical deformation of failure. Field monitoring data demonstrated a maximum of 2.76 m groundwater level drop in the mining area after mining. The groundwater level was determined to be 4.45~10.83 m below surface, ensuring the normal growth of surface vegetation and realizing the water-conservation coal mining (WCCM).

Numerical Study on Groundwater Drawdown and Deformation Responses of Multi-Layer Strata to Pumping in a Confined Aquifer

Pumping artesian water from porous media inevitably reduces the groundwater head and promotes soil consolidation, which may result in regional land subsidence. In this study, a fluid-mechanical coupled numerical model is developed to investigate the dewatering-induced groundwater drawdown and deformation responses for multi-layer strata. The relation between the stratum deformation and groundwater drawdown is discussed. The results show that the pumping process can be divided into four stages. The development of vertical deformation is inconsistent with the change of the pore pressure for the strata except for the confined aquifer at the early stage of pumping. The strata expand while the pore pressures reduce. This inconsistency may be due to the large unloading in the confined aquifer at the early stage of pumping. Soil arch comes into being owing to the constraint of the surrounding soils when the large unloading occurs in the confined aquifer; this can reduce the stratum compression and cause the expansion of the layers. It can be concluded that as the pumping continues, the decrease of the pore pressure dominates the vertical deformation and results in the soil compression in all strata.

Monitoring and Characterization of Mining-Induced Overburden Deformation in Physical Modeling With Distributed Optical Fiber Sensing Technology

Facing increasingly large and discontinuous structural evolution under the influence of extensive mining activities, some traditional geophysical technical methods of monitoring overburden deformation have become of restricted use. As an advanced sensing technology, the distributed optical fiber sensor has been introduced into rock deformation monitoring by virtue of its good adaptability and high precision. In this paper, an overburden stratum deformation monitoring experiment was performed within a physical model test to explore the deformation characteristics of mining-induced overburden stratum based on distributed optical fiber sensing. The results indicate that distributed optical fiber monitoring is effective, and the Brillouin frequency shift (BFS) variation distribution reflects every aspect of the space-time and movement laws of the overburden stratum. The comparison of measurements of the distributed optical fiber, fiber Bragg gratings, and dial gauges proved the feasibility and reliability and revealed the ability of optical fiber measurement to monitor large-scale macroscopic deformation, and capture subtle deformation along the entire overburden stratum. More importantly, the BFS variation distribution presents a three-step form, which explicitly identifies the zoning development of overburden stratum. In turn, a conceptual model for describing the overburden deformation process is provided; it illustrates the inversion mechanism of the BFS variation distribution in reaction to the typical overburden deformation structure. This study aims to provide a theoretical and methodological foundation for the application of distributed optical fiber sensing (DOFS) measurement in mining ground control research.

Three-dimensional numerical analysis of the interaction of two crossing tunnels in soft clay

Recently, with the development of underground construction, multi-tunnel engineering has become a matter of concern since the interaction between tunnels at close ranges could cause additional deformation in strata as well as surrounding structures and even serious damage to surface buildings. These tunnel displacement and soil deformation problems can be effectively predicted using numerical methods considering the influence of various factors, such as the anisotropic nature of soft clay. To this end, the anisotropic elastoplastic constitutive S-CLAY1 is implemented in finite element code to investigate deformation problems in the strata and nearby structures caused by the excavation of multi-tunnels. This paper focuses in particular on configurations of two crossing tunnels. Multiple 3D numerical simulations using ABAQUS enable successive analyses conducted for tunnels at different spacings (1.5D, 2.5D, 3.5D and 4.5D, where D is the tunnel diameter) of configurations aligned vertically. The results, including the ground settlement, lining force and moment, and tunnel convergence, are analyzed. For each aspect, the most unfavorable case is determined by comparing the results of different simulations. This investigation can provide a reference for multi-tunnels design and construction.

The Influence of Earth Pressure Balanced Shield Tunnel Underpassing Coastal Water Body on Stratum Deformation

ABSTRACT Guo, C.; Guan, X.; Shi, L., and Qiu, S., 2018. The influence of earth pressure balanced shield tunnel underpassing coastal water body on stratum deformation. In: Liu, Z.L. and Mi, C. (eds.), Advances in Sustainable Port and Ocean Engineering. Journal of Coastal Research, Special Issue No. 83, pp. 237–246. Coconut Creek (Florida), ISSN 0749-0208. The complexity of construction technology and the surrounding soil environment of shield tunnel, especially the construction of soil pressure balanced shield tunnel in soft foundation, will inevitably cause the settlement of the overlying soil stratum and surface of tunnel. When there is coastal water body on the surface above the tunnel, it will change the distribution and size of pore water pressure in the soil stratum below the coastal water body, thus affecting the settlement of the overlying soil stratum of tunnel. However, most urban subway tunnels are double-tunnel single-track shield tunnels, and successive tunnel construction will also cause the ...

Experimental Study on the Application of BOTDA in the Overlying Strata Deformation Monitoring Induced by Coal Mining

The coal mine working face overlying strata is often disturbed by multiple mining, leading to adverse effects on the working face’s safe production and ground surface movement. In the three-dimensional physical model test with the size of 3000×2000×2000 mm, after the overburden gets stable when the first working face had been extracted, by using three vertical distributed optical fibers based on the BOTDA principle, the deformation law of the overburden caused by the contiguous coal face mining is studied. Results show that, before the working face advanced to 840 mm (near the fiber), the stress law of the overburden was as follows: the middle of the model was under pressure state and the remaining part was under tension state, and the key stratum produced stress concentration phenomena caused by the secondary mining; when the face advanced to 840 mm (through the fiber), the frequency shift curve of the key stratum and the strata on it combined, and the stress concentration in the key stratum disappeared, indicating that the bearing structure of the key stratum gets unstable; compared with the previous monitoring data, when the working face far away from the fiber, the information reflected by the frequency shift data gradually gets single when the working face is far away from the fiber compared with the previous measurement data. The overburden deformation increased dramatically after the key stratum gets unstable. The surrounding rock and fiber will detach when the stratum goes though large deformation such as abscission layer, fracture, and collapse, and the frequency shift monitored by BOTDA cannot characterize the rock deformation in this situation. The experimental method and the results of this paper serve as useful reference for the application of BOTDA technology in geotechnical engineering.

Experimental Study and Estimation of Groundwater Fluctuation and Ground Settlement due to Dewatering in a Coastal Shallow Confined Aquifer

The coastal micro-confined aquifer (MCA) in Shanghai is characterized by shallow burial depth, high artesian head, and discontinuous distribution. It has a significant influence on underground space development, especially where the MCA is directly connected with deep confined aquifers. In this paper, a series of pumping well tests were conducted in the MCA located in such area to investigate the dewatering-induced groundwater fluctuations and stratum deformation. In addition, a numerical method is proposed for the estimation of hydraulic parameter, and an empirical prediction method is developed for dewatering-induced ground settlement. Test results show that groundwater drawdowns and soil settlement can be observed not only in MCA but also in the aquifers underneath it. This indicates that there is a close hydraulic connection among each aquifer. Moreover, the distributions and development of soil settlement at various depths are parallel to those of groundwater drawdowns in most areas of the test site except the vicinity of pumping wells, where collapse-induced subsidence due to high-speed flow may occur. Furthermore, the largest deformation usually occurs at the top of the pumping aquifer instead of the ground surface, because the top layer is expanded due to the stress arch formed in it. Finally, the proposed methods are validated to be feasible according to the pumping well test results and can be employed to investigate the responses of groundwater fluctuations and stratum deformations due to dewatering in MCA.

Study on the mechanism of “separation stratum water-inrush” induced by impact energy of the key stratum sudden breaking

Subsidence deformation of the bottom rock stratum of the bending belt was different due to deflection difference; the separation stratum space was easy to form between the soft and hard rock stratum, and the separation stratum water formed under the water supplies. Based on catastrophe theory and the mechanics theory, the pointed catastrophic model of key stratum (the rock beam structure overlying the separation stratum space) was established. The impact energy released by the key stratum breaking was calculated. The “crushing” modes and “cleavage” modes of separation stratum water-inrush were proposed under the impact energy of key stratum. The periodic step distance of two kinds modes of separation stratum water-inrush was calculated. At last, separation stratum water-inrush of extra-thick coal of Guo Jiahe mine was taken as an example to study, and the aim was to provide technical reference for the prevention and treatment of separation stratum water-inrush.

Effect of Near-Wave Field Mining Tremors on the Rock Bolt Support Behaviour within Stress Domain

One of the most serious hazard in the underground copper mining in Poland is the roof fall hazard. The scale and intensity of this type of events depends on several factors. Due to seismic activity, weaker roof strata can loosen and deform, generating additional load on the rock bolt support. The type of load depends strictly on the course of stratum deformation as well as on the intensity of the dynamic effect in the form of a seismic wave. Continuous monitoring is then necessary to determine the risk level of stability loss within existing excavations in order to minimize the probability of serious accidents. The following study analyses the impact of tremors recorded within the near-wave field upon the stress change in the instrumented rock bolts.

Water Inrush from Pregrouting Fractures Induced by Mining Activities and Its Engineering Control Method Optimization

Water inrush accidents during coal mining still occur after reinforcement of fissured water bearing strata underlying coal seams through grouting, which seriously troubles field technicians. In order to further prevent the water inrush, especially the water inrush after grouting reinforcement, the grouting technique needs to be improved. Experimental design, theoretical analysis, and numerical simulation have been carried out in sequence. On the microscale level, the relationship between strains and water flow rate was analyzed through laboratory experiments; on the macroscale level, the propagation mechanism of grouting cracks resulting from the rock strata deformation during coal production was analyzed with rock beam theory, and then a new model of casing pipes preventing water inrush by controlling deformation of the floor rock strata is proposed. The laboratory test results show that the response of the radial strain and the water flow rate to mining operation is consistent and positively correlated and verify that it is feasible to reduce water inrush disaster by controlling deformation of the rock strata. The deformation governing equation of the casing pipes is deduced theoretically. At last, the numerical calculation was done to prove the effectiveness of controlling the floor rock strata deformation by the casing pipe group, which indicated that the displacement of the monitoring points after grouting is smaller than that before grouting practice. It is practicable to realize grouting technique optimization by the innovative adoption of the grouting casing pipes in the future.

Experimental Study on the Movement and Evolution of Overburden Strata Under Reamer-Pillar Coal Mining Based on Distributed Optical Fiber Monitoring

Focusing on the deterioration of the surface ecological environment caused by large-scale exploitation of the Jurassic coal field in northern Shaanxi, the three-dimensional similar material test model is made to simulate the extraction of shallow coal seam. Using Brillouin optical time-domain analysis (BOTDA) optical fiber distributed sensing technology, this paper studied the strain distribution rule and movement characteristics of strata under reamer-pillar mining, analyzed the stability of the remaining coal pillars in the mining area, and obtained the strain contour graph of strata through calculations. The research result shows that the deformation of coal pillars in a safety-critical state under reamer-pillar mining experiences three stages. The stratum deformation is distributed in the shape of a pyramid with the mining area as the center. On the basis of the strain distribution of strata, the settlement curve and subsidence curve of strata deformation are determined to obtain the rupture angle and angle of draw. After being compared with the measured data, the angle values are almost the same.

Deformation characteristics and safety assessment of a high-speed railway induced by undercutting metro tunnel excavation

Stratum deformation (settlement) is a challenging issue in tunnel engineering, especially when construction of metro tunnels has to undercut high-speed railway. For this purpose, we used the FLAC3D software to analyze the stratum settlement characteristics of high-speed railway at different crossing angles intersected by metro tunnel, in terms of ground settlement trough, stratum slip line and irregularity of ballastless tracks. According to the evolution of the stratum settlement at different angle regions, an optimized angle is proposed for the actual project design. In order to reduce the influence of stratum settlement on the safety of high-speed railway, an approach of safety assessment is proposed for the shield engineering undercutting high-speed railway, as per Chinese specifications using numerical results and on-site conditions. A case study is conducted for the shield tunnel section crossing the Wuhan – Guangzhou High-speed Railway between the Guangzhou North Railway Station and the Huacheng Road Station, which represents the first metro tunnel project passing below a high-speed railway in China. A series of measures is taken to ensure the safe excavation of the shield tunnel and the operation of the high-speed railway. The results can provide a technical support for performing a safety evaluation between high-speed railways and metro tunnels.

Optimization Analysis of Construction Scheme for Large-Span Highway Tunnel Under Complex Conditions

AbstractThe construction process of the tunnel ground deformation regularity of surrounding rock, stability, deformation control of tunnel surface based on the requirements, combined with the characteristics of shallow tunnel with large-span. Used three-dimensional numerical simulation software, established a dynamic tunnel analysis program to simulate the construction process of center cross-diagram method and double sidewall drift method. Based on the stratum deformation, supporting force and analysis of plastic zone distribution, comparative analysis of engineering adaptability of different construction methods from the construction process and construction mechanics, get optimization tunnel construction scheme.

Research Study on Mechanics Mechanism of Roadbed Grouting for Shallow Buried Tunnel

The traffic congestion has become a prominent problem in many cities under the rapid development of urbanization at present in China. In order to solve it, more and more cities have accelerated the development of the subway traffic. In consequence of that, there will be a large number of tunnel construction technical problems to be solved. The strata deformation caused by the tunnel construction, especially in the dense urban area, has always been a subject of great concern. Especially in shallow tunnel construction, the surface will form a settlement trough due to the excavation of the stratum. The construction sink may inflict the road pavement damage, underground pipeline damage, as well as the damage of buildings. The grouting process is one of the most effective methods to solve the construction settlement. The grouting process has been widely used in tunnel construction because it may contribute to the reinforcement of the rock and the soil in situ and will change their inherent physical and mechanical properties. In this paper, combined with the construction of one shallow buried tunnel in a city, the method of roadbed grouting has been adopted to make the reinforcement for the roadbed. This paper studies the precautions which are needed when the soft soil roadbed does not interrupt the traffic. The study may provide some certain guiding significance for the construction of other city underground road on soft soil foundation [1-4].

Construction Mechanical Mechanism of Shallow Subway Tunnel Group with Large-Span Variable Cross Section

The number of tunnel crossings or line switchings in the vicinity of subway transfer stations is increasing with the construction of subway tunnels. The construction interaction of the subway tunnel group with variable cross section and the time and space effects of strata deformation has become a major problem that limits the development of subway tunnel spaces. Thus, this study analyzed the deformation law of the upper strata and surrounding rocks in a subway tunnel group with large-span variable cross section caused by different construction processes using ABAQUS numerical simulation analysis. The research focused on the construction interaction mechanism and stratum deformation law of such a subway tunnel group and considered Shenzhen Metro Line 7 as the study subject. The stratum deformation law caused by twin tunnels excavation was referred. Results showed that (1) the construction process significantly influenced the construction safety of tunnel groups with large-span variable cross section; (2) constructing small cross-sectional tunnels first increases the lateral deformation and settlement of the vault in large cross-sectional tunnels, which are far from small cross-sectional tunnels, but reduces the settlement of the vault in the small cross-sectional tunnels and the lateral deformation of the surrounding rock between the large and small cross-sectional tunnels, which benefits tunnel groups with large-span variable cross section; and (3) as shown by the comparison of the final numerical simulation data that in which the large cross-sectional tunnel was constructed after the completion of the small cross-sectional tunnel construction had the lowest project risk.

Physical Simulation of Strata Failure and Its Impact on Overlying Unconsolidated Aquifer at Various Mining Depths

Underground mining severely lowers the water table and worsens the ecological environment. To determine the mechanism influencing drawdown in unconsolidated aquifers induced by deep mining combined with overburden movement, with a view to environmental protection, physical simulations for three different depths were designed to investigate and contrast deformation and fracture distribution characteristics at diverse depths after mining. The impacts on overlying unconsolidated aquifers were then analyzed by monitoring overburden movement and ground water level data, and the deformation limit was estimated. Modeling results indicated that coal mining had different impacts on the overlying unconsolidated aquifer via various mechanisms of groundwater level reduction. The aquifer outside the fractured water-conducting zone could be affected by coal mining, and the water tables dropped rapidly. The failure and the deformation features of the aquitard floor were the key to revealing the mechanism of groundwater depletion in deep mining. The effects on aquitard decreased as the distance from the working face increased. A relationship between the strata deformation and the drawdown rate was established; that is, the rate of decline of the groundwater level did not accelerate until the maximum subsidence of the aquitard floor exceeded approximately 0.9 m, or the subsidence-bending area of the aquitard floor exceeded approximately 156 m2.

Displacement characteristics for a “π” shaped double cross-duct excavated by cross diaphragm (CRD) method

This paper presents a lateral launching scheme of shield with oblique-curve shaped (“π” shaped) double cross-duct excavated by cross diaphragm (CRD) method. A series of in-situ tests, theoretical analysis and numerical simulations were performed to obtain the displacement characteristics of the surface and the underground. Finally, an economic comparison of the traditional scheme and the proposed scheme was conducted. The investigation results show that: (1) The change of the tunnel curvature has an obvious influence on stratum stress distribution and deformation characteristics. (2) The ground loss, surface subsidence and horizontal convergence in the curve segment are correspondingly smaller than that in the straight section and the arching effect is also more easily formed in the curve segment. (3) On the contrary, the curvature change has little influence on the crown settlement. (4) The application of this proposed scheme improves the efficiency of shield tunneling, with also economical advantages.

Research on mining-induced deformation and stress, insights from physical modeling and theoretical analysis

The dynamic change of mining-induced stress is the main reason for large deformation of surrounding rock. To investigate the influence of mining-induced stress and deformation is important for appropriate supportive design. It also helps to raise the safety and productivity of longwall mining operations. In this paper, Weijiagou Coal Mine in Southwest China was selected as the case study. In order to research on the deformation and breakage of overlying strata, physical modeling test was carried out on the self-developed rotatable physical similar test system. By using digital image correlation (DIC) technique, the deformation of strata and development of cracks in the process of coal seam excavation were acquired, meanwhile, mining-induced stress was also monitored by pressure cell and strainmeter. According to the mechanical structure of stope, the height of the destressed zone has a significant influence on stress distribution. In order to minimize the discrepancy between the physical model test and theoretical analysis, the dimension of the plastic zone of roadway was added into the mining panel width, and the gap between the experimental and theoretical results reduced.