Advances in Unsaturated Soil, Geo-Hazard, and Geo-Environmental Engineering

Electrokinetics (EK) is the general term used to describe responses of soil water systems to the application of an external electric field, which includes three predominant components, i.e. electro-osmosis, electrophoresis and electrochemical reactions. Electro-osmosis generates water flow in soil mass, electrophoresis induces movement of soil solids and electrochemical reactions lead to emission of oxygen and hydrogen gases, corrosion of anodes, and pH gradients in soil. Although electrokinetics has been studied over more than a century, the recent advances of anode technology have made electrokinetics a viable tool in geo-engineering. The applications of electrokinetics in geotechnical engineering and recent development of electrical vertical drains are reviewed in this paper. It is demonstrated that with solid understanding to principles, sound engineering design and proper implementation and execution, electrokinetics can provide viable solutions for challenges facing today's geotechnical engineers.

This paper presents results of a preliminary investigation of utilizing recycled gypsum derived from gypsum waste plasterboard to improve the strength of clayey soil for embankment construction, while considering environmental impacts. A case study was conducted to investigate different recycled gypsum content percentages, cement types, and cement content percentages. Four different recycled gypsum content percentages range from 0 to 10% were investigated. In this case study, cement was added to develop solidification for recycled gypsum and to improve environmental properties. Two different types of cements, the Portland and Furnace slag type B with a content range from 0 to 3% were used. A series of unconfined compression tests were conducted to evaluate the strength of treated clay. In addition, a series of environmental tests were conducted to explore the solubility concentration of Fluorine, Boron, and Chromium in the untreated and treated clay specimens. Furthermore, hydrogen sulfide and pH were investigated. Results showed that compressive strength of treated clay increased with the increase of recycled gypsum content. The use of recycled gypsum within the investigated limits has no adverse effect on pH value. The hydrogen sulfide gas is less than the standard permitted limits. The solubility of Fluorine, Boron, and Chromium leached from soil-gypsum mixture within the investigated limits were found less than the approved standard values.

It is always difficult to accurately calculate the shape and size of CSA (combustion space area) in UCG (underground coal gasification) even by using existing measuring methods due to its deep burying. In the paper, we propose the shape model of CSA. Based on both high temperature of combustion CSA and the relatively constant temperature of underground, the influence mechanics of seepage on temperature field is analyzed, a control equation of temperature field influenced by seepage is established, and the solution of finite element is worked out. Aiming at the UCG in a certain area, this paper inverses the temperature field distribution with seepage effect by making use of in-situ detection data and finite element numerical software Comsol. During the process of inversion, the approximate volume of CSA is calculated by adjusting its section size to gain the temperature distribution of coal seam that most close to in-situ detection. This method is with certain practical significance.

The Mg²⁺ and Cl^– in the surrounding environment of cement-soil piles may affect the mechanical properties of cemented soil, which may cause some serious damage to structures. In order to simulate and study the erosion effect process, a series of unconfined compressive tests were conducted on the cemented soil blocks which were cured in the MgCl₂ solutions with various concentrations and ages. For comparison purposes, photos of the blocks were taken and the Mg²⁺ and Cl^– concentration of the MgCl₂ solution were recorded after the curing process. The testing results show that the MgCl₂ solution does make out-looks of the cement-soil samples change, but not seriously, mainly represent crystallization adhering to the surface. The unconfined compressive strength of cemented soil block is decreased with the increasing of solution concentration, increased with the curing time. A coefficient α is put forward to predict the modification of the compressive strength of cemented soil in various concentration of MgCl₂ solution. The Mg²⁺ concentration is increasing with the erosion time increasing, Cl^– concentration is increasing before first 7 days, then decreased after 7 days. Chemical analysis indicates that the corrosion of MgCl₂ solution to cemented soil is a composite action including resolving and crystallizing corrosions.

In expressway engineering, the environmental impacts of the drainage and leachate collected from the road surface or road bank have attracted public attentions about their potential risks on human health. The maintenance of the expressway always requires considerable amount of chemicals, e.g. CaCl₂. Thus there is need to design pools along the expressway to collect and treat the road drainages. Due to the low hydraulic conductivity, compacted clay liners are primarily used in waste disposal facilities. It is still lack of complete knowledge about compacted clay liners. In this study, the effect of salt solutions on the hydraulic conductivity of compacted Kaolin column was experimentally investigated by laboratory tests. The changes in electrical conductivity and pH values of the leachates were also monitored. The results might be helpful to the engineering designers in this field.

The rate of moisture flow in an unsaturated soil regime is governed by a single diffusion material parameter, α. The unsaturated diffusivity coefficient controls transient moisture flow conditions within a soil in response to suctions or fluxes imposed at the boundaries of the soil mass. Seasonal moisture fluctuations in the soil profile depend on the diffusion properties of the soil mass and the amplitude of moisture variations at the ground surface. Mitchell (1979) proposed a periodic function that can be used to investigate how diffusivity parameters and seasonal fluctuations affect the moisture active zone. This research study shows that distribution of suction with depth within an unsaturated subgrade soil surface is greater for wetting diffusion coefficients than drying diffusion coefficients. In the paper, an investigation of how diffusivity parameters and seasonal moisture fluctuations affect the predicted moisture active zone is presented.

Cracks are easily initiated in unsaturated expansive soil slopes due to evaporation process and the development of these cracks affects greatly the deformation and stress of soil slopes due to rainfall infiltration/evaporation. Consolidation theory for unsaturated soils is employed here to investigate crack evolvement and deformation of unsaturated expansive soil slopes. By using reduced suction and introducing a new elastic-plastic constitutive equation of the soil skeleton, the simplified consolidation theory for unsaturated soils are employed and incorporated into an in-house finite element method code. Initial cracking of the soil slopes is simulated and analyzed in detail and then the seepage-deformation analysis for unsaturated soil slope accompanying the initiating of crack is explored using FEM code developed here under evaporation conditions and rainfall infiltration.

A series of pocket penetrometer (PP) tests were carried out to measure the compression strength of fine-grained soil (i.e., Indian Head till) specimens that were compacted with different water contents (i.e., matric suction values) and compression stresses. Based on the experimental results, a simple technique is developed to estimate matric suction of the as-compacted soil specimens using the unique relationship between the matric suction and compression strength determined from the PP tests. The proposed technique is simple, promising and can be extended towards estimating the matric suction of different types of unsaturated fine-grained soils (i.e., with different plasticity index, I_p) compacted both in the laboratory and in field conditions.

Unsaturated soil mechanics has rapidly become a part of geotechnical engineering practice during recent decades. Hence a considerable number of studies focusing on determination of unsaturated soil property functions have been conducted on unsaturated soils. This paper presents the study of the unsaturated behavior of a granite residual soil from China by performing a series of tests. Experimental results show that the degree of saturation and shear strength are all related to the applied suctions at unsaturated states. The extended Mohr-Coulomb failure criterion can be adopted for unsaturated soil strength to consider variations in strength due to the presence of matric suction. To illustrate the effects of unsaturated behavior on geotechnical engineering practice, numerical analysis was used to investigate the seepage of the embankment taking into account the unsaturated seepage. Obtained results are valuable to correlative practical engineering when considering unsaturated problem.

Compacted soils are extensively used in engineering projects and the volume change of compacted soils is of great interest to engineers. Most compacted soils have collapsible soil behaviors when subjected to wetting or loading. Volume change of compacted soil is therefore a consolidation problem for unsaturated collapsible soils. At present, the existing consolidation theory for unsaturated soils is based on the assumption that the soil is elastic while unsaturated soils are well-known elastic-plastic materials. This paper compares the differences in results of consolidation when elastic and elasto-plastic analysis are used.

On the basis of a series of indoor stress relaxation tests for Nanning expansive soils, the characteristics of stress relaxation under the condition of direct shearing for the unsaturated remolded expansive soils have been investigated. The results show that relaxation curves of stress belong to non-completed decay type under different water contents, and the stresses tend to be stable. The relaxation curves can be obviously divided into three stages: accelerating relaxation stage, uniformly speeding relaxation stage and stable relaxation stage. The nonlinearity degree of stress-strain isochronal relationship curves are increased gradually with the increase of water content, while the ultimate displacements at soil's failure are smaller. Through the comparative analysis of experimental relaxation model and test data, we find that this experimental model could well reflect nonlinear relaxation characteristics of Nanning unsaturated remolded expansive soil.

Based on the existing research results, there is a linear relationship between adsorption strength and swelling force, and the method to obtain the effective shear strength of the expansive rock/soil by routine shear test is studied. Soil samples were taken from K9+800 of Beijing western sixth ring highway and prepared under different water contents. Then the saturated and unsaturated consolidation slow shear tests were carried out on the conventional direct shear apparatus to obtain the effective cohesive, effective internal fiction angle and total cohesion including adsorption strength of the soil. Swelling force of the soil under the corresponding water content was determined by pressure balanced method. The results indicated that, there was a good linear relationship between the adsorption strength and the swelling force of Beijing expansive rock/soil, and a good exponential relationship between the swelling force and the water content; the cohesion decreased exponentially with the increment of water content, while the variation of the internal friction angle with the water content were different. At last, the shear strength formula of Beijing expansive rock/soil was proposed.

To simulate the dual subsoil layers foundation of levee on the middle and lower reaches of Yangtze River which always present with shallow relative impermeable layer and thick permeable layer, a new kind of seepage box has been conducted indoors for simulating seepage field of the dual subsoil layers foundation. The seepage prevention scheme has been designed to study the seepage prevention function on the effect of seepage failure prevention for the suspended seepage prevention wall. The different kinds of impermeable materials and the different depth of suspended wall are used to check the effect of suspended seepage prevention wall. The following conclusions are inferred from the testing results: (1) It is equivalent in seepage prevention function by two different kinds of materials of suspended seepage prevention wall. Generally, clay grouted cut-off wall is economical and convenient for construction. However, impermeable suspended seepage prevention wall such as concrete wall is safer and more stable for the higher flood control standard area. (2) The seepage prevention function of suspended seepage prevention wall increases obviously the increase of the depth of wall. However, the depth is not needs too much for the control of the development of seepage failure.

Piping is the results of soil internal erosion by seepage. In this paper, a mathematic model for the development of piping is formulated based on the principle of mass conservation and the consideration of the solid-fluid interactions. Soil particles are divided into three types, i.e., framework particles, movable particles and moving particles. The moving particles are derived from the movable particles after its statical balancing broken caused by the drag force of the water flow. The transforming of the movable particles to moving ones is considered as the source item of the particle transporting model. A mechanical model for a movable particle is proposed to determine the source item corresponding to the previous studies. As the complex of the model, it is solved by numerical method (The Finite Volume Method in this paper). The finite volume equations for the 2-D model are deduced. With the model and method discussed in the paper, a 2-D example's been solved. The result about the variation of the source item, seepage velocity, permeability coefficient, porosity, and the remaining movable particles density during the piping process are discussed and considered, which are all agreeing with the fact.

Deep excavation induces groundwater table varied from inside to outside of the foundation pit and groundwater may flow around the bottom of retaining wall. In this paper, a practical engineering with a deep excavation in Shanghai was studied. PLAXIS program was applied to analyze earth pressures and lateral wall displacements considering the fluid-structure coupling interaction. The computed earth pressure distributions with PLAXIS program were compared with results of conventional Rankine's theory and measured data. The results illustrate that the computed results of considering fluid-structure coupling coincided with measured data. Earth pressure and lateral wall displacements computed by FEM through fluid-structure coupling are appropriate to multi-braced excavation in soft clay.

Filled road embankment along riverbank or widen riverbank as road embankment is often used in the project of highway construction. The road embankment built along riverbank has what influences to the stability of riverbank, and has what characteristics on the stability, deformation and destroy mode to the road embankment. These are the main questions to be solved for the construction of river levee highway extent. Based on the results of local reconnaissance, in-situ test and laboratory experiment, a new finite element model is built to carry out the analogy calculation and the analysis of the stability of the riverbank and the road embankment under different water level and whether the road embankment is built. The calculation results indicate that: 1) the build of road embankment is propitious to enhance the stability of the riverbank. The safety factors are increased about 26%. 2) the embankment built along riverbank is easy to generate differential settlements and large settlement. The total settlement may increase 35% for the widen project of road embankment. 3) the road embankment may occur shear destroy on the slope from the river bank behind the road embankment. The seepage has little influence to the stability and cannot change the failure mode of the embankment. Numerical simulation can forecast the stability and the failure modes of the road embankment before the project built. Numerical simulation with the new mode is useful to the design of building road embankment along riverbank or widening the riverbank as road embankment.

A series of compression creep and unloading tests have been conducted for unsaturated Nanning expansive soils and red clay. The creep and rebounding curves of different soil samples are obtained and compared. According to the characteristics of the curves, the multi-component visco-elastic-plastic creep model for expansive soils and red clay are proposed, respectively. The relevant parameters in both models are measured from the tests. It is showed that the calculated curves fit well with the measured curves, which proves the correctness of the proposed models and provides reliable theoretical basis for analyzing the deformation and strength behaviors of expansive soils.

Carpet shreds and carpet shred-soil mixtures can be used as alternative backfill material in many geotechnical applications. In this study an experimental testing program was undertaken using small scale model tests with goal of evaluating the lateral resistance of a single pile located near a reinforcing sandy slope. A broad series of conditions including unreinforced cases, was tested by varying parameters such as: carpet shred content, aspect ratios of carpet shreds, pile distance from the slope crest, relative density of sand, angle of the slope, embedded length, skin friction and cross section of pile. The carpet shred content and aspect ratio were found to influence the lateral resistance of single pile located near reinforcing sandy slope. The optimum carpet shred content and aspect ratio of carpet shred were 1.5 and 3 respectively, and with these values a good improvement in lateral resistance of piles was reached.

The Xi'an city metro system is located within an active geological area containing several ground fissure sites. This potential geological hazard can cause serious threats to construction of the new metro system. In this research study, prototype model tests were conducted to investigate the effects of the ground fissures on the metro system under earthquake forces. The prototype model box was loaded with several seismic forces of different characteristics and the changes in the ground fissures were surveyed. Test results showed that 1) The existing ground fissures opened wider under the applied seismic forces and new fissures appeared close to the existing cracks, 2) The seismic forces caused larger soil settlements within the vicinity of the ground fissures and the long duration earthquake forces resulted in larger soil settlements, 3) The laboratory prototype model tests resulted in very useful information in terms of the behavior of the ground fissures and their interactions with the metro system under the simulated seismic forces.

The application of Smoothed Particle Hydrodynamics (SPH) method to the simulation of granular materials under large deformation is presented. The Drucker-Prager constitutive model with non-associated flow rule is implemented into the SPH formulations to model the granular flow in a continuum framework. Simulations of the collapse of 3-D axisymmetric sand columns with various aspect ratios are conducted to validate the developed model. Numerical results of the granular flow pattern and final runout distance are in good agreement with the experimental observations as reported in literature. This study indicates that despite being a continuum-scale model, the developed SPH model can be used to effectively simulate large deformation and dense flow of granular materials, and geomaterials in general if proper constitutive models are implemented. Therefore, the developed model may find applications in various problems involving dense granular flow such as landslides and debris flow.

The objective of this research is to study dynamic behavior and responses of rock avalanche. A series of small-scale flume tests was performed on a shaking table subjected to sine waves. Simple constrained flows were generated by releasing granular materials down a flume with two inclined portions at an assigned position. Material type and the frequency and amplitude of input sine waves were varied respectively to investigate their influences on run-out. Besides, superposition mode (simultaneous release and shake) was proposed to reflect the superposition of static and dynamic effects, comparing non-superposition mode (release first and then shake). Results show that run-out increased with decreasing frequency and increasing amplitude. The difference in run-out at various amplitudes reduced when the frequency increased. The run-out was more sensitive to frequency at large amplitude than that at small amplitude. Coarse materials went further than fine materials under dynamic condition. The increment of run-out in superposition mode was larger than that in non-superposition mode at 200 and 300 gal, and was smaller at 400 gal. The increment of run-out increased as the frequency reduced and the amplitude increased in these two modes.

Model test plays an important role in the research of rock avalanches. However, there is a problem that test results are sometimes too scattered to establish a trend. A series of small-scale flume tests on shaking table were conducted to analyze the influencing effects of dynamic factors acting on the rock avalanches, and the similar problem was found. Efforts were paid to obtain much more reasonable test results by adopting adjustments for operations, especially those that would affect the test results with high sensitivity. It was found that releasing geometry performed a much more obvious influence on the results in the dynamic tests than in the static tests and acquired a sample emplacement method with higher standard. Some individual particles would be forced out of the flume by shaking, with much higher speed than in static tests. Attention should be paid to recycle these particles, or it would result in shorter run-out in the next tests. Besides, attentions were suggested to pay in many manual operations which were regards as key technologies of the tests, such as sample arrangement, vibration applying and sample releasing, run-out measurement, et al. The introductions of the operating techniques in our tests would form a basis for future test design and help to understand the mechanism of earthquake induced rock avalanches.

The huge destruction of the earthquake of 7.6 and 6.2 MW in Padang, West Sumatra, Indonesia on September 30, 2009 caused widespread death of more than 1,200 people and destruction to the heavily populated and relatively prosperous region. In this paper a summary of earthquake effects to structural damage on road infrastructure and geofailures, i.e., landslide and debris flow, during the earthquake were identified based on direct field observation at several districts, i.e. the city of Padang, Padang Pariaman, Pariaman and Agam. The levels of earthquake damage were classified from low to severe destruction level for road pavement and bridges. The earthquake also caused events of landslides and debris flows close to road networks which killed hundreds of people while hundred kilometers of road pavement were made inaccessible. Some road networks were totally collapsed and as a result, several villages became isolated areas.

A three-dimensional numerical model for rock slope of Lixian-Xiaojin highway in Sichuan province was established by FLAC3D. The seismic wave in Wenchuan earthquake on 12th May in 2008 measured at the Lixian seismic station was an 8.0 magnitude earthquake The Wenchuan earthquake was adopted to analyze dynamic stability of the slope. The calculation results show the slope was stable and the maximum value of acceleration time histories of slope face was amplified, and the range of the amplification multiple for PGA (peak of ground acceleration) is from 2.16 to 3.48. The max amplification multiple appeared around the slope middle which was the most unstable position under seismic load and permanent displacement in slope ground surface was 2.584mm ~5.141mm. Both of horizontal permanent displacement and acceleration response peak have vertical amplification effects. Furthermore, permanent displacement had 14 times amplification and acceleration response peak have 1.3 times amplification at the top of slope.

The Pastor and Zienkiewicz (P-Z) model was adopted here as the constitutive model to study the dynamic responses of the Liyutan dam subjected to the Chi-Chi earthquake. For numerical simulation, the shell materials of the earth dam are assumed to satisfy the P-Z model. The optimal material parameters of P-Z model were judged according to the experimental results by Center Region Water Resource Office in Taiwan. Staged construction, seepage, static equilibrium and dynamic response are sequentially analyzed. A comparison is performed between the P-Z model and Mohr-Coulomb model through the dynamic analysis of the Liyutan dam under Chi-Chi earthquake. The influence of permeability of shell on the generation of pore water pressure under earthquake loading was studied. The results show that the large horizontal permanent movements at the upstream shell were resulted and the larger vertical settlement took place at the top of dam after the earthquake. The Mohr-Coulomb model results in higher pore water pressure compared to those obtained of the P-Z model during the earthquake shaking. The pore pressure parameter in upstream shell slightly decreases with the increase of the permeability of shell.

In pile foundation response due to horizontal vibration, it is known that the original Novak's method overestimates the dominant frequency and underestimates the dominant amplitude of pile head responses. It is found that reducing the pile-foundation system stiffness and damping coefficients would lead to a smaller dominant frequency and higher dominant amplitude, respectively. The objective of this paper is to evaluate and determine appropriate correction factors for stiffness and damping coefficients for the analytical model developed by Novak and El-Sharnouby (1983) to improve the theoretical predictions of pile foundations subjected to dynamic forces. The reduction factors were determined by continuously reducing the shear modulus of the soil and system damping until the computed and filed responses matched. Three sets of field pile tests were analyzed.

This paper presents practical approaches for developing site-specific design seismic parameters and acceleration response spectral (ARS) curve for a bridge foundation design in liquefiable soils. A 15-span bridge, cast-in-place, prestressed box girder structure supported on Abutment 1, Bents 2 through 15, and Abutment 16 is proposed to cross a creek where alluvial soils are present to a deep depth that are susceptible to liquefaction subject to the design earthquakes. Both conventional liquefaction analysis using the industrial standard approach and a nonlinear effective-stress analysis with pore pressure generation were performed to determine liquefaction depth. A neutral plane is estimated above which the pile is subject to negative skin friction (downdrag force) and below which the pile has positive skin friction. After liquefaction depth and downdrag forces are determined, the pile lengths, axial and lateral capacities were analyzed using the industrial standard design approaches.

Cyclic dynamic field tests simulating the high-speed train vibration effect were conducted in a water-rich loess tunnel (called Zhang Mao Tunnel) located on the Zhengzhou-Xi'an Passenger Dedicated Line with a design speed of 350 km per hour (km/h). The forced excitation tests were performed on the top of the backfill of the tunnel invert arch with 12 different vibration frequencies (5 to 27 Hz). During testing, measurements were taken at various locations below the tunnel invert for the vertical vibration velocity, the earth pressure, and the excess pore pressure. The testing results indicate that the maximum vertical vibration velocity at the excitation surface is approximately 1.55 mm/s. At the same depth, the vibration velocity increases with the vibration frequency. The increase is small when the vibration frequency is equal to or less than 21 Hz, but becomes greater when the vibration frequency is higher than 21 Hz. Under different vibration frequencies, the earth pressure versus depth remains basically unchanged. Under the constant vibration frequency, the earth pressure at the same depth remains basically unchanged for different loading numbers. Under cyclic loading, negative values for the excess pore pressure appear below the tunnel invert; but the absolute value is small.

Site amplification essential for seismic zonation between ground surface and a base layer was investigated using vertical array records in a number of KiK-net arrays in Japan during recent destructive earthquakes. Based on soil investigation data available for individual downhole arrays, theoretical amplifications for surface arrays consistent with the vertical array records were calculated. A good and unique correlation was found between the peak amplification thus obtained and S-wave velocity ratio, defined as S-wave velocity in a base layer divided by average S-wave velocity, <emph type="32">Vs for different sites and different earthquakes. The value of <emph type="32">Vs was evaluated from fundamental mode frequency and a thickness of equivalent surface layer in which peak amplification was exerted. The conventional parameter Vs₃₀ often used in current practice, showed poorer correlation than <emph type="32">Vs with the obtained amplifications. It is suggested that <emph type="32">Vs may be determined from microtremor measurements.

Since Changsha Economic Development Zone was set up in Xingsha district of Changsha City in 1992, Xingsha district has become a new eastern satellite town of Changsha city, P.R.China. The construction of Xingsha district, especially road construction has been producing a great impact on the landscape of the city. Through investigation, we find the landscape system has been changed. A continuous habitat is subdivided into smaller sections, ecological connectedness is reduced, and the road layout with chessboard form damages and interdicts the transferring path and habitat of biology so as to reduce the ecological function of corridor. The construction of auxiliary landscape of urban road did not combine with local humanities landscape, which results in the disconnection between natural landscape, humanities landscape and the complexity and diversity of humanities landscape. Land use is unreasonable and land resource is wasted severely. To solve these problems, the paper puts forward a few available solutions for ecological restoration of roads in Xingsha. This paper studies the environmental influence, land use, protection of ecological diversity and landscape culture of Xingsha satellite town in order to provide scientific basis for road ecological design and construction while urban expands.

CO₂ sequestration in abandoned coal seams is regarded as an effective potential approach to mitigate the ever-increasing CO₂ levels in the atmosphere. The injection of CO₂ into abandoned coal mines not only provides a solution for the long-term storage of CO₂ but it also has the added advantage of using coal bed methane as an energy source. Adsorption is the main criterion for storage in coal seams, where it constitutes to about 95–98% of total storage. The coal matrix is heterogeneous and consists of three porosity systems: micropores, mesopores and macropores. Therefore, the inherent mechanical properties such as permeability and other in-situ attributes such as fractures complicate storage capacity estimation. Earlier studies have shown that the injection of supercritical CO₂ offers higher storage capacity. However, there is a lack of experimentally verified storage capacity estimation methodologies, especially for supercritical CO₂. In this paper, various parameters such as coal rank, carbon content, pressure, moisture and temperature found in earlier studies for supercritical CO₂ are presented for clarification of the estimation of supercritical CO₂ storage capacity in coal seams. Methodologies suggested by earlier studies as better suited for supercritical conditions are also reviewed.

Carbon dioxide (CO₂) sequestration in deep coal seams has been identified as one of the potential methods to reduce CO₂ emission into the atmosphere. In this paper, a commercial coalbed methane reservoir simulator, COMET 3, was used to study the effects of seam conditions such as temperature and moisture content of the coal, and injection pressure and gas composition on CO₂ sequestration in coal. A 500x500x20 m coal layer, which is lying 1000m below the ground surface, was simulated in the model. CO₂ was injected from the bottom center of the coal layer for 10 years using a well of 0.1 m diameter. Four scenarios were simulated by changing the temperature and moisture content of the coal seam, and injection pressure and gas composition. The model results show that the amount of CO₂ that can be injected into the coal seam decreases by around 75% when the temperature of the coal seam changes from 10 °C to 50 °C; decreases by 99% when the moisture content of the coal seam was changed from 0.1 (cm³/cm³) to 0.5 (cm³/cm³); and increases by around 40000% when the gas injection pressure increases from 10 to 20 MPa, and increases by 80% when the percentage of CH₄ in the injection gas changes from 0% to 10%.

In order to minimize the environmental and physical hazards of rock slope failures in deep open cut mines, evaluation of rock mass strength with a reasonable degree of accuracy is required. The task is made much more difficult due to the presence of discontinuities or joints, as the strength of a rock mass depends on both the strength of intact rock and of the discontinuities. The main objective of this study was to review the applicability and accuracy of existing models for the prediction of the strength of a jointed rock mass. Therefore, some experimentally-determined strength results with corresponding outcomes derived from five different existing models were analysed. The experimental results reviewed in this paper were obtained from physical model tests. In the empirical models, the influence of joint properties was aggregated into one parameter, called the "joint factor". The analysis shows that the effect of joint orientation on the strength of a rock mass is overestimated by existing empirical models for joint angles smaller than 20° and larger than 40° , measured with direction of the major principal stress. Therefore, a modification is suggested to determine the joint factor, and subsequently the unconfined compressive strength, more precisely.