Search

The stability of rock slope is often controlled by the existing discontinuous surfaces, such as discrete fractures, which are ubiquitously distributing in a geological medium. In contrast with the traditional approaches used in soil slope with a continuous assumption, the simulation methods of jointed rock slope are different from that of in soil slope. This paper presents a study on jointed rock slope stability using the proposed discontinuous approach, which considers the effects of discrete fractures. Comparing with traditional methods to model fractures in an implicit way, the presented approach provides a method to simulate fractures in an explicit way, where grids between rock matrix and fractures are independent. To complete geometric components generation and mesh partition for the model, the corresponding algorithms were devised. To evaluate the stability state of rock slope quantitatively, the strength reduction method was integrated into our analysis framework. A benchmark example was used to verify the validation of the approach. A jointed rock slope, which contains natural fractures, was selected as a case study and was simulated regarding the workflow of our framework. It was set up in the light of the geological condition of the site. Slope stability was evaluated under different loading conditions with various fracture patterns. Numerical results show that fractures have significant contributions to slope stability, and different fracture patterns would lead to different shapes of the slip surface. The devised method has the ability to calculate a non-circular slip surface, which is different from a circular slip surface obtained by classical methods.

Low-rank coal reserves account for nearly 55% of the national coal reserves in China, and it is extremely important to understand their anisotropic microstructure and coalbed methane storage and sorption characteristics. In this study, microstructures that develop parallel to and perpendicular to bedding of low-rank coals are studied through scanning electron microscopy. The micromorphology and microfracture and mineral distributions are examined. Based on fractal theory and digital image processing technology, the fractal box-counting dimensions of microfracture distributions that form parallel as well as perpendicular to the coal bedding planes are calculated, and the anisotropic fractal characteristics of these microfracture distributions are characterized. The pore-size distribution and the fractal characteristics of the microscopic pore structure are systematically examined by means of nitrogen adsorption and mercury intrusion tests. The results of the fractal box-counting dimension calculations indicate that microfractures distributed perpendicular to coal bedding are rougher and more irregular than those distributed along a bedding plane, with the former exhibiting higher space filling and methane adsorption capacity. The fractal dimension of the microscopic pore structure reveals two inflection points measuring approximately 5 and 80 nm, thereby indicating that the low-rank coal exhibits a microscopic pore structure with a three-level fractal characteristic.

Foamed concrete has attracted increasing attention in civil engineering due to its unique properties. Permeability is one of the significant material properties that governs its long-term d...

Water inrush disasters originating from completely weathered granite are strongly affected by its physical and mechanical properties, such as the porosity, permeability, and water stability. The porosity and permeability are heavily affected by the particle composition. Meanwhile, a large amount of particles with poor cementation, are transferred by water, which may affect the flow properties and water inrush. This study investigates the mass transfer and flow properties of water inrush in completely weathered granite for different particle size distributions. To this end, a series of tests was performed by designing a new testing system, which can induce mass transfer and apply external pressures during the tests. The results demonstrate the following: (1) the flow properties and water inrush are related to the mass transfer. In the experiments, it was found that the permeability of the samples increases by a factor of 14–53.3, compared with the initial permeability. Thus, a notable signal to forecast water inrush can be obtained, which represents the change in water quality from muddy water to clear water. (2) With an increase in Talbot index n, the mass transfer and porosity first decrease and then increase. However, the permeability and water inflow increase and a critical value of n = 1.0 is required to induce the water inrush. (3) Three flow stages, namely, a Darcy flow, rapid flow, and stable flow, can be utilized to describe the water inrush evolution. Non-Darcy flow properties and high water inrush risk are observed in the second stage, where the water inflow increases to 551 mL/min, which is more than thrice that in the Darcy flow for n = 1.0. The obtained results can provide an important reference to understand the mechanisms, forecast the risks, and implement effective control measures for water inrush (e.g., optimum control time).

The support of rock bolt plays a significant role in maintaining the stability of a roadway in steeply inclined geological formations, yet choosing a reasonable support scheme of rock bolt in this situation is still not well understood. To reveal the force or stress distribution mechanism of anchor bolts and design an effective support scheme, an in situ anchorage experiment was conducted in a deep-buried roadway in steeply inclined rock strata. This results of this study demonstrate that in the steeply inclined rock formations, the intersection angle of a bolt length direction and the interface of rock layers have a great effect on the distribution and variation of axial force in bolts. The axial forces at the positions near the intersection of the interface and bolt increase a lot with time. In addition, the existence of no small or non-zero axial force at the end of anchor bolts indicates that much longer bolts should be used to prevent further deformation in steeply inclined rock.

The effect of a shield crossing an existing underground infrastructure needs to be evaluated, yet there are few studies on this subject. In this study, to model the influence of a shield crossing on a large diaphragm wall, a detailed three-dimensional numerical model with special methods considering the effects of the panel joints and the shield crossing has been developed. The panel joints have been simulated by a HINGE mode of the connection type, and the effect of shield crossing has been realized by modelling the excavated concrete using the solid elements, which interact with the surrounding soils that have been simulated with the ground springs. After analysing the characteristics of the deformation, maximum and minimum principal stresses, vertical and circumferential bending moments in the diaphragm wall, the maximum deformation, and the largest maximum and minimum principal stresses are at the perimeter of the shield tunnel. Further, for the bending moment, the largest negative vertical and circumferential bending moments are at the perimeter of the shield tunnel, yet the largest positive vertical and circumferential bending moments are distributed around the perimeter of the shield tunnel. For the largest tensile stress and vertical bending moment, there are large changes in the diaphragm wall around the shield tunnel, which is detrimental to the diaphragm wall. Considering the effect of the shield crossing, the diaphragm wall should be reinforced according to the results of the numerical analysis during the design and construction stages.

Water inrush from completely weathered granite has presented a significant challenge for tunnel construction, suggesting the urgency and importance of revealing the water inrush mechanism. In this ...

This paper presents a case study of the countermeasures of water and mud inrush disasters in the Junchang Tunnel in Guangxi, China. This tunnel was constructed in a weathered granite formation, and four serious water and mud inrush disasters occurred during construction. The geological and hydrological conditions are first reviewed to understand their effects on the water and mud inrush disasters. Four potential causes of the serious water and mud inrush disasters in the Junchang Tunnel were proposed, including the poor stability of the completely weathered granite, the high groundwater level and large groundwater flow rate, insufficient pre-reinforcement of the surrounding rock and the disturbances caused by tunnel construction. Water-sealing and ground reinforcement measures were suggested before excavation to improve the stability of the surrounding rock and plug the water outflow channels, and full-face curtain grouting was considered as the first choice. Furthermore, several improvements, including the combined utilization of various grouting materials, supplementary grouting with steel pipes in collapsed boreholes and dynamically optimized grouting methods, were implemented to solve the serious water inflow and collapse problems experienced during the drilling and grouting work. A detailed curtain grouting scheme was proposed and applied in practice. A comprehensive evaluation based on inspection borehole investigations and P–Q–t analysis indicated that the curtain grouting method yielded satisfactory performance in water sealing and ground reinforcement. In addition, the groundwater level and settlement data collected in the field validated the effectiveness of the proposed countermeasures.

During tunnel construction, groundwater inrush from completely weathered granite strata is a significant challenge to geotechnical engineers. Up to the present, prevention of water inrushing hazards is almost exclusively based on the experience of engineers. This paper presents a coupled seepage–erosion water inrush model to investigate the characteristics of seepage–erosion properties. The proposed model is based on classical theories of solute transport and fluid dynamics in porous media. In the model, changes of porosity link permeability with the accumulation of particle loss in the seepage–erosion process. The coupled seepage–erosion model was applied to examine the influence of curtain grouting thickness on the seepage–erosion process. The results showed that the seepage–erosion process was attenuated as thickness increased. The results also showed that the porosity and permeability visibly changed and the water inflow clearly exceeded the acceptable engineering criterion when the thickness was less than 6 m. However, with a further increase in thickness, the seepage–erosion process was suppressed and little changes of the relative parameters were showed. The numerical results demonstrated that a curtain grouting thickness of 6 m was suitable for curtain grouting in completely weathered granite. Field investigation of Cenxi tunnel verified the effectiveness of the thickness determined by the proposed model.

Hydraulic fracture behaviours when a fracture reaches stratum interfaces and penetrates into adjacent layers are so complicated that they have not been well studied, particularly for three-dimensions. In this paper, cohesive zone theory (which controls the fracture propagation progress and describes the fluid characteristics when flowing within an open fracture channel and diffusing into permeable rock) is used to simulate hydraulic fracturing. Regarding the simulation method, the pore pressure nodes constraint method is introduced, and seven zero-thickness pore pressure cohesive element layers are built to simulate the initiation and propagation of hydraulic fractures by which the hydraulic fracture in a coal seam is able to propagate within stratum interfaces and even penetrate into adjacent layers. The actual propagation evolution of a crack underground could be presented as well. The hydraulic fracture morphological characteristics during the entire propagating process are analysed, and the damage evolution of the rock around the hydraulic fracture is studied based on linear damage theory. Combined with the injection pressure curve characteristics, the propagation trajectory of a ǂ-shaped hydraulic fracture is divided into seven stages, and the propagating process is described in detail for each stage. The initialization and propagation characteristics of a hydraulic fracture at different fluid injection rates are well studied.

The determination of the effective stress coefficient of porous media (such as coal) remains a controversial issue. The purpose of this paper is to determine the effective stress coefficient of coal during gas penetration and to investigate the impact of effective stress and gas slippage on coal permeability under cyclic loading conditions. Analyzing the evolution law of coal anisotropic permeability with effective stress allows the deformation characteristics of the coal's internal structure, such as cleat or bedding, to be studied. The effective stress coefficient of long flame coal is obtained through modified permeability models based on experimental data. Test results show that the slippage effect significantly influences the permeability of coal samples, specifically in the range of low pore gas pressure, and that the effect of gas slippage is larger than that of effective stress. Permeability decreases gradually when effective stress increases, but it increases during unloading, and ascending and descending curves show significant irreversibility of permeability. Moreover, PLR (permeability loss rate) and IPLR (irreversible permeability loss rate) results indicate that the influence of effective stress on permeability perpendicular to bedding is greater than that of permeability parallel to bedding and that the ability of the cleat to resist deformation induced by effective stress is weaker than that of bedding. Under identical pressure conditions, the cleat shows more vulnerability and produces larger plastic deformation.

The effective thermal conductivity (ETC) of rocks is crucial for many geological and engineering applications and projects. In this study, a three-component ETC model was proposed, which includes seven parameters, that are, the thermal conductivities of water ( λ w ), gas ( λ g ) and solid phase ( λ s ), the porosity (φ), the coefficient of shape factor ( n ), the weighted harmonic parameter (η) and saturation degree (Sr). The methods to establish the parameters of the proposed model were described with validation carried out using several experiments including X-ray diffraction (XRD) test, porosity test and thermal conductivity test. Comparisons performed indicated that the new proposed model was flexible enough to reflect the variation of the ETC with saturation degree. Furthermore, the sensitivity analysis and grey correlation analysis were given in examining the effect of the parameters included in the model. The results showed that: 1) The parameter sensitivity analysis and grey correlation analysis of ETC show that the ETC is most sensitive to the thermal conductivity of solid phase ( λ s ), followed by coefficient of shape factor ( n ), weighted harmonic parameter (η) and saturation degree ( S r ), and less sensitive to the porosity (φ). 2) When the pore shape of the porous media is irregular or the thermal conductivity ratio of the continuous phase and discontinuous phase is larger than 100, n is a key parameter that can tremendously influence the value of ETC. 3) Although the change of η does not influence the maximum and minimum values of ETC, it can greatly affect the variation of ETC when 0

In order to solve the problems in the surface casing removal, the casing milling process is proposed to be used. Through the size and material selection of casing milling pipe, mechanical analysis of connection thread and the innovative design of casing milling shoes, a series of casing milling tools and the efficient casing milling process are formed. The field application results show that the milling process can smoothly mill to the predetermined position. After the milling process, the surface casings can be successfully removed by cutting and fishing. The efficient milling process studied in this paper can make the removal of the surface casing with low cast and high efficiency. Both social and economic benefits are remarkable and it has a broad application prospect.

The growing use of foamed concrete for building materials and geotechnical fills raises the question of suitable durability and performance standards. In order to analyse the degradation characteristics of foamed concrete with lightweight aggregate and polypropylene fibre under freeze–thaw cycles, specimens are frozen and thawed in a temperature and humidity-controlled container where the temperature varied from +40 to −40°C and the humidity was kept constant (about 100%). The freeze–thaw tests are performed; they consist of around 40 cycles of freezing and thawing, with each cycle lasting 8 h. The deterioration of the specimens is examined according to changes of strength and deformation characteristics in a series of uniaxial compression tests. The experimental results show that: (a) the compressive strength of samples decreases and the axial strain corresponding to the peak stress increases with increasing of freeze–thaw cycles, and the compressive strength decays exponentially with the number of freeze–thaw cycles; (b) the compressive strength of foamed concrete decreases with increase in foam and perlite content, increases with increased polypropylene fibre content; their fitting relationship is also provided.