Showing papers in "Geotechnical and Geological Engineering in 2018"

Applications of Particle Swarm Optimization in Geotechnical Engineering: A Comprehensive Review

Abstract: Particle swarm optimization (PSO) is an evolutionary computation approach to solve nonlinear global optimization problems. The PSO idea was made based on simulation of a simplified social system, the graceful but unpredictable choreography of birds flock. This system is initialized with a population of random solutions that are updated during iterations. Over the last few years, PSO has been extensively applied in various geotechnical engineering aspects such as slope stability analysis, pile and foundation engineering, rock and soil mechanics, and tunneling and underground space design. A review on the literature shows that PSO has utilized more widely in geotechnical engineering compared with other civil engineering disciplines. This is due to comprehensive uncertainty and complexity of problems in geotechnical engineering which can be solved by using the PSO abilities in solving the complex and multi-dimensional problems. This paper provides a comprehensive review on the applicability, advantages and limitation of PSO in different disciplines of geotechnical engineering to provide an insight to an alternative and superior optimization method compared with the conventional optimization techniques for geotechnical engineers.

A Risk-Based Technique to Analyze Flyrock Results Through Rock Engineering System

Abstract: Flyrock is an adverse effect produced by blasting in open-pit mines and tunneling projects. So, it seems that the precise estimations and risk level assessment of flyrock are essential in minimizing environmental effects induced by blasting. The first aim of this research is to model the risk level associated with flyrock through rock engineering systems (RES) methodology. In this regard, 62 blasting were investigated in Ulu Tiram quarry, Malaysia, and the most effective parameters of flyrock were measured. Using the most influential parameters on flyrock, the overall risk of flyrock was obtained as 32.95 which is considered as low to medium degree of vulnerability. Moreover, the second aim of this research is to estimate flyrock based on RES and multiple linear regression (MLR). To evaluate performance prediction of the models, some statistical criteria such as coefficient of determination (R2) were computed. Comparing the values predicted by the models demonstrated that the RES has more suitable performance than MLR for predicting the flyrock and it could be introduced as a powerful technique in this field.

Experimental Study on Effect of Waste Plastic Bottle Strips in Soil Improvement

Abstract: With rapid advancements in technology globally, the use of plastics such as polyethylene bags, bottles etc. is also increasing. The disposal of thrown away wastes pose a serious challenge since most of the plastic wastes are non-biodegradable and unfit for incineration as they emit harmful gases. Soil stabilization improves the engineering properties of weak soils by controlled compaction or adding stabilizers like cement, lime etc. but these additives also have become expensive in recent years. This paper presents a detailed study on the behavior and use of waste plastic in soil improvement. Experimental investigation on reinforced plastic soil results showed that, plastic can be used as an effective stabilizer so as to encounter waste disposal problem as well as an economical solution for stabilizing weak soils. Plastic reinforced soil behaves like a fiber reinforced soil. This study involves the investigation of the effect of plastic bottle strips on silty sand for which a series of compaction, direct shear and California bearing ratio (CBR) tests have been performed with varying percentages of plastic strips and also with different aspect ratios in terms of size. The results reflect that there is significant increment in maximum dry unit weight, Shear Strength Parameters and CBR value with plastic reinforcement in soil. The quantum of improvement in the soil properties depends on type of soil, plastic content and size of strip. It is observed from the study that, improvement in engineering properties of silty sand is achieved at 0.4% plastic content with strip size of (15 mm × 15 mm).

Performance Evaluation of Adaptive Neuro-Fuzzy Inference System and Group Method of Data Handling-Type Neural Network for Estimating Wear Rate of Diamond Wire Saw

Abstract: The wear rate of diamond wire saw plays a vital role in the performance of sawing process. Predicting the sawing performance is very important in the production’s cost estimation and planning of the dimension stone quarries. In this research, an adaptive neuro-fuzzy inference system (ANFIS) is applied to estimate the wear rate of diamond wire saw under uncertain processes; hence, indirect prediction in ANFIS is carried out using subtractive clustering method (SCM) and fuzzy c-means clustering method based on four effective rock properties, such as Shore hardness, Schimazek’s F-abrasivity, uniaxial compressive strength and Young modulus. For this purpose, 38 rock samples were selected to test the proposed model from Turkey quarries. The results of indirect prediction indicated that the best performed model was related to ANFIS-SCM with highly acceptable degrees of accuracy 0.998 and 0.59 for R2 of the train and test data sets, respectively. In addition, group method of data handling type of neural network is used to assess the factors influencing the wear rate of the diamond wire saw. A sensitivity analysis was performed on the laboratory test results of studied rocks using three methods. In comparison to the existing models, the estimated results showed that a satisfactory performance could be obtained using the proposed ANFIS-subtractive clustering method.

Prediction of Uniaxial Compressive Strength of Some Sedimentary Rocks by Fuzzy and Regression Models

Abstract: The purpose of this research is to construct predictive models to estimate the uniaxial compressive strength (UCS) of grainstone, wackestone-mudstone, boundstone, gypsum, and silty marl in the Qom area (central Iran). For this purpose, a series of rock mechanics tests were applied and indices such as block punch index, point load strength index (Is(50)), Schmidt rebound hardness and ultrasonic P-wave velocity (Vp) were determined for these rocks. Then, linear multiple regression and the Sugeno-type fuzzy algorithm were compared to check their accuracy. To improve the accuracy of the Sugeno fuzzy inference system, the weighted if-then rules are extracted. In addition to correlation coefficient, the variance account for (VAF) and the root mean square error (RMSE) were also calculated to check the predictive performances of these models. Obviously, performances of all four indices are reasonably good in predicting UCS (R2 > 0.76) from simple regression analyses. However, ultrasonic P-wave velocity does not give appropriate value (R2 = 0.67). The VAF and RMSE were calculated as 90% and 10.80 for the uniaxial compressive strengths obtained from the multiple regression model and 90% and 12.82 for uniaxial compressive strengths obtained from the fuzzy inference system, respectively. Thereby, both multiple regression analyses and fuzzy inference system exhibit better predictive performances for UCS than simple regression analyses. The predictive performances of multiple regression analyses and the fuzzy inference system show both models are comparable. Seemingly, fuzzy inference system is an efficient approach to predict UCS of rock materials from indices due to its efficiency in handling uncertainties of test results with transparency.

Effect of Fly Ash and Rice Husk Ash on Index and Engineering Properties of Expansive Clays

Abstract: Many innovative ameliorating techniques including chemical stabilization have been in practice for improving the behaviour of problematic, highly expansive clays. This paper presents a comparative study on the effect of fly ash (FA) and rice husk ash (RHA) on index and engineering properties of an expansive clay. Liquid limit (LL), plastic limit, plasticity index (PI) and free swell index (FSI), and coefficient of permeability (k), unconfined compressive strength and swelling pressure were determined at varying quantities of FA and RHA. Coefficient of permeability, swelling pressure and unconfined compressive strength of the FA-clay and the RHA-clay blends were determined at their respective OMC and MDD obtained from Proctor compaction tests. LL, PI and FSI decreased significantly with increasing FA and RHA contents. Coefficient of permeability, however, increased with additive content. Further, swelling pressure of the blends decreased with increasing additive content.

Laboratory Study of the Effect of Degrees of Saturation on Lime Concrete Resistance Due to the Groundwater Level Increment

Abstract: Lime concrete and lime treatment are two attractive techniques for geotechnical engineers in the construction of rail tracks and pavement layers, in slope protection of earth dams, and as a support layer for shallow foundations. The present study investigates the influence of different degrees of saturation upon the unconfined compressive strength (qu) of lime concrete. At first, the characteristics of used materials were determined. Then, the optimum amounts of water and clay soil were determined based on flow table tests and uniaxial compression tests. Specimens with an optimum level of clay, sand, lime, and moisture were prepared. After processing durations of 14, 28, 45, and 60 days in laboratory condition, the specimens were exposed to saturation levels ranging from 0 to 100%. The uniaxial compressive strength tests were then carried out on all specimens. The diagram of strength reduction of lime concrete versus different depths and saturation degrees (Sr) were developed. The results showed that the moisture has a significant effect on decreasing the strength of lime concrete. The specimens that placed in 100% of saturated condition failed completely, and in 20% of saturated condition, the strength value of specimens decreased about 42%. Also, the optimum percentages of clay and water for application in lime concrete with 7% lime, respectively 23 and 24.04% were determined. Based on the results of SEM test it was observed that the specimen was characterized by a rather well-structured matrix since both the filling of a large proportion of the coarse-grain soil voids by clay and the pozzolanic activity of lime led to retain less pore water in the specimen, increasing the uniaxial compressive strength, and consequently resist against swelling and shrinkage of the clay soil.

Sustainable Improvement of Marine Clay Using Recycled Blended Tiles

Abstract: The usage of recycled material for improving problematic soil as a construction and pavement material has been a sustainable interest. Recycled blended tiles (RBT), a waste from ceramic tiles factories containing high amount of sodium and magnesium, was used as a soil stabilizer for marine clay improvement in this study. This research investigated the effects of sizes and percentages of RBT on the physical and strength properties, which included particle size distribution, Atterberg limits, compaction, and unconfined compressive strength (UCS) of marine clay. Microstructural characterization, including the scanning electron microscopic, energy dispersive X-ray spectroscopy, and X-ray diffraction was conducted on both untreated and treated marine clay-RBT samples to examine the mechanism of strength development. The addition of RBT reduced the water holding capacity, which then caused the reduction in soil plasticity (from 18 to 11%) and optimum water content (from 20 to 16%) along with the increase in peak dry density (from 1.66 to 1.74 Mg/m3). The UCS of marine clay increased from 50 to almost 220 kPa. The optimum RBT contents, providing the highest UCS, were at 20 and 30% for 0.063 mm RBT and 0.15 mm RBT, respectively. The UCS improvement of treated marine clay is attributed to the formation of cementation compounds, mainly aluminum magnesium silicate hydrate (A–M–S–H). The outcome of this research will allow the use of RBT as a low-carbon soil stabilizer across civil engineering applications.

Landslide Susceptibility Mapping Using Fuzzy-AHP

Abstract: Landslides are as the movement of soil on slopes that they are one of the most common natural hazards in many mountainous areas. Landslides are recognized as an important natural hazard in many countries. So in the study, the geographic information system-based the fuzzy quantifier is used to determinate the landslide susceptibility modeling in the north of Khorramabad, west of Kermanshah Province, Iran. To determine the landslide susceptibility modeling generated aspect, some input data were prepared such as the digital elevation model, lithology, slope, land use, river, road, fault, and precipitation maps. Fuzzy map showed that almost all of the area was medium landslide susceptibility that had the value close to 1. Fuzzy-AHP model showed that 77.62% of the study area had medium landslide susceptibility and this method was a useful tool for forecasting of landslide susceptibility status in each case study.

The Risk Assessment of Tunnels Based on Grey Correlation and Entropy Weight Method

Abstract: In the process of tunnel construction, many kinds of geological disasters are frequently occur. Among them, tunnel collapse is one of the most serious geological disasters. Seven controlling factors were determined by analyzing 76 large or medium tunnel collapses in China. By means of synthesizing all kind of index parameters, grey relational coefficients were calculated based on grey correlation theory. Entropy weight method was used to compute the weight coefficients. And a comprehensive risk evaluation model of tunnel collapse was established based on entropy weight and grey relational degree. The paper gives the correctional coefficients depending on rainfall conditions during construction of the tunnel. At last the collapse risk level of tunnels was obtained. Based on the actual project cases of risk assessment, the results indicated that the comprehensive risk evaluation model of tunnel collapse was scientific and reasonable. And it was shown that the method was easy to master and has a great significance on engineering practice.

Time-Dependent Behaviour of Brittle Rocks Based on Static Load Laboratory Tests

Abstract: Cumulative elastic and inelastic strain and associated internal stress changes as well as damage evolution over time in brittle rocks control the long-term evolution of the rockmass around underground openings or the land surface settlement. This long-term behaviour is associated with time-dependent deformation and is commonly investigated under static load (creep) conditions in laboratory scale. In this study, low Jurassic and Cobourg limestone samples were tested at different static load levels in unconfined conditions to examine the time to failure. Comparisons are made with longterm testing data in granites and limestones associated with the Canadian nuclear waste program and other data from the literature. Failure typically occurred within the time limits of the test program (4 months) with axial (differential) stress levels near or above the crack damage threshold (CD) estimated from baseline testing. The results also suggest that the time to failure of limestone is longer than that of granite at a given driving stress. Further insight into samples that did not reach failure was investigated and it was found that there was a clear division between failure and no failure samples based on the Maxwell viscosity of the samples tested (indicating that viscosity changes near the yield threshold of these rocks. Furthermore, samples showed a clear tendency towards failure within minutes to hours when loaded above CD and no failure was shown for samples loaded below CI (crack initiation threshold). Samples loaded between CD and CI show a region of uncertainty, with some failing and other not at similar driving stress-ratios. Although such testing is demanding in terms of setup, control of conditions, continuous utilization of test and data acquisition equipment and data processing, it yields important information about the long-term behaviour of brittle rocks, such as the expect time to failure and the visco-elastic behaviour. The information presented in this paper can be utilized for preliminary numerical studies to gain an understanding of potential impact of long-term deformations.

Malaysian Experiences of Peat Stabilization, State of the Art

Abstract: Peat has been considered as an organics remnant that suffers decomposition process throughout times under overburden pressure. Composition of peats normally consists of organics materials which sometimes exceed 75% specifically from woods that grows in marshes and places in conditions where deficiencies of oxygen exist. Usually peat area related with swampy and normally a low shear strength region. High compressibility is significant and often related to problematic soil for construction purposes. In this article, extensive number of studies are reviewed to understand the behavior of the peat after being stabilized. New findings indicated that the peat contents differs from one location to another, thus inevitably gives different behavior. Many improvisation methods have been put forward such as chemical stabilization, cement stabilization, deep mixing and fiber reinforcement to name a few to enhance the strength properties of the peat. This is mainly for construction reliability purposes. However, the suitability of the ground improvement for peat thus depend on its fundamental properties and cost involve for any dedicated ground construction work. This paper review the properties of peat in Malaysia and reviewed recent development in the peaty soil stabilization in Malaysia. It is also compared the materials used for the peat stabilization and the expansive clay soils as the main two problematic soils.

Numerical ANFIS-Based Formulation for Prediction of the Ultimate Axial Load Bearing Capacity of Piles Through CPT Data

Abstract: This study explores the potential of adaptive neuro-fuzzy inference systems (ANFIS) for prediction of the ultimate axial load bearing capacity of piles (Pu) using cone penetration test (CPT) data. In this regard, a reliable previously published database composed of 108 datasets was selected to develop ANFIS models. The collected database contains information regarding pile geometry, material, installation, full-scale static pile load test and CPT results for each sample. Reviewing the literature, several common and uncommon variables have been considered for direct or indirect estimation of Pu based on static pile load test, cone penetration test data or other in situ or laboratory testing methods. In present study, the pile shaft and tip area, the average cone tip resistance along the embedded length of the pile, the average cone tip resistance over influence zone and the average sleeve friction along the embedded length of the pile which are obtained from CPT data are considered as independent input variables where the output variable is Pu for the ANFIS model development. Besides, a notable criticism about ANFIS as a prediction tool is that it does not provide practical prediction equations. To tackle this issue, the obtained optimal ANFIS model is represented as a tractable equation which can be used via spread sheet software or hand calculations to provide precise predictions of Pu with the calculated correlation coefficient of 0.96 between predicted and experimental values for all of the data in this study. Considering several criteria, it is represented that the proposed model is able to estimate the output with a high degree of accuracy as compared to those results obtained by some direct CPT-based methods in the literature. Furthermore, in order to assess the capability of the proposed model from geotechnical engineering viewpoints, sensitivity and parametric analyses are done.

Prediction of Rock Brittleness Using Genetic Algorithm and Particle Swarm Optimization Techniques

Abstract: Determining the rock brittleness is often needed in a wide range of rock engineering projects; however, direct measurement of the brittleness are expensive, time consuming and also the test devices is not available in every laboratory. Due to that, assessing the brittleness of rock as a function of some rock properties such as uniaxial compressive strength, Brazilian tensile strength and density of rock is unavoidable. The aim of this paper is to develop predictive models for estimating the rock brittleness using two techniques, genetic algorithm (GA) and particle swarm optimization (PSO). For this aim, four different models including linear and non-linear were developed using GA and PSO techniques. Further, in order to validate the accuracy of proposed models, various statistical indices including the root mean square error (RMSE), the variance account for (VAF), the coefficient of determination (R2) and performance index (PI) were computed and utilized herein. The values RMSE, VAF, R2 and PI ranged between 2.64–5.25, 82.58–93.06%, 0.851–0.932 and 1.480–1.708, respectively; with the quadratic form of the GA approach indicating the best performance. It is concluded that both the GA and PSO techniques could be utilized for predicting the rock brittleness; however, GA-quadratic model is superior.

The Use of Nanoclay Particles for Stabilization of Dispersive Clayey Soils

Abstract: Common strategies for improvement of dispersive soils include chemical stabilization with various additives such as lime, cement, bitumen, resin, etc. Application of the mentioned materials in terms of technical and economic considerations has advantages and certain limitations. Recently, due to improvements in nano-materials production and application, use of this type of materials in different sciences especially geotechnical engineering has been considered. In this research, the effect of nanoclay on dispersivity potential of two types of clayey soils with low plasticity and high plasticity has been studied. For this purpose, first identification tests were implemented on two types of clayey soils and nanoclay, and then pinhole tests were conducted on soil samples with different amounts of nanoclay including (0, 0.25, 0.5, 1, 2 and 4% by dry weight) with respect to curing ages of 1, 3 and 7 days. Based on the results obtained from different tests, it was found that the addition of nanoclay to dispersive clayey soils could decrease their dispersivity potential considerably.

A Critical Review on Filter Design Criteria for Dispersive Base Soils

Abstract: Dispersive soils have become common materials for the construction industry. Highly susceptible to internal erosion and piping, dispersive soils must only be used with specific engineering measure in order to avoid failures that were often catastrophic. In an earth dam, clayey soils are used for the core and sandy materials are used for the filter to retain the eroded core soils and prevent their migration. In the absence of first-rate core material, dispersive soils have been used instead. This paper provides a review of the current knowledge and experiences regarding filtration of core soils, particularly the dispersive ones. The engineering problems associated with the use of dispersive soils are discussed and significant findings from previous studies on protective filters are summarized. It is worthy to note that the current review considers both, the conventional, rather empirical filter design criteria based on particle sizes and the current, quite theoretical state-of-the-art filter design criteria based on constriction sizes, with discussion given on the advantages and disadvantages of both. The information provided by this review should be handy for the study, design, construction, and operation of related geotechnical and geo-environmental projects.

Stability Analysis of Rock Slope with Small Spacing Tunnel under Earthquakes and Influence of Ground Motion Parameters

Abstract: A numerical analysis model of layered rock slope with small spacing tunnel was established with MIDAS GTS/NX finite element program, and the validity of numerical simulation was validated with a large-scale shaking table experiment On this basis, the dynamic stability of the model slope and the influence of ground motion parameters on the seismic dynamic responses were analyzed The results show that the maximum horizontal displacement occurs at the top of the slope The existence of the tunnel markedly changes the stress distribution inside the slope The tensile failure and shear failure may appear at the middle wall, at the foot of the slope and at the conjugate 45° direction of the surrounding rock of tunnel The seismic failure of the slope is the dynamic development process with the increase of excitation time and the slope is more likely to be damaged under coupled earthquake The peak ground acceleration (PGA) amplification coefficients along the slope surface decrease with the increase of earthquake amplitudes under coupled earthquake, but they increase with the increase of amplitudes under horizontal earthquake The PGA amplification coefficients along slope surface decrease with the increase of earthquake frequencies The duration has little influence on the PGA amplification effect

Effect of Geological Structure on Flyrock Prediction in Construction Blasting

Abstract: Blasting is sometimes inevitable in civil engineering work, to fragment the massive rock to enable excavation and leveling. In Minyak Beku, Batu Pahat also, blasting is implemented to fragment the rock mass, to reduce the in situ rock level to the required platform for a building construction. However, during blasting work, some rocks get an excessive amount of explosive energy and this energy may generate flyrock. An accident occurred on 15 July 2015 due to this phenomenon, in which one of the workers was killed and two other workers were seriously injured after being hit by the flyrock. The purpose of this study is to investigate the causes of the flyrock accidents through evaluation of rock mass geological structures. The discontinuities present on the rock face were analyzed, to study how they affected the projection and direction of the flyrock. Rock faces with lower mean joint spacing and larger apertures caused excessive flyrock. Based on the steoreonet analysis, it was found that slope failures also produced a significant effect on the direction, if the rock face failure lay in the critical zone area. Empirical models are often used to predict flyrock projection. In this study five empirical models are used to compare the incidents. It was found that none of the existing formulas could accurately predict flyrock distance. Analysis shows that the gap between predicted and actual flyrock can be reduced by including blast deign and geological conditions in forecasts. Analysis revealed only 69% of accuracy could be achieved if blast design is the only parameter to be considered in flyrock projection and the rest is influenced by the geological condition. Other causes of flyrock are discussed. Comparison of flyrock prediction with face bursting, cratering and rifling is carried out with recent prediction models.

Flow Characteristics of Cemented Paste Backfill

Abstract: Cemented paste backfill (CPB) is primarily used for backfilling underground voids at George Fisher Mine (Mount Isa, Australia). The objective of this paper is to summarise the geotechnical characterisation of the tailings and the rheological properties of the CPB as determined from a laboratory testing program undertaken at James Cook University. Two binders were examined [a General Purpose cement and a slag blend cement] over a range of dosages from 0 to 6% and CPB mix solids content in the range of 72–78%. The slump tests were carried out using the standard cone (ASTM C 143) used for concrete and a cylinder with 110 mm (diameter) × 110 mm (height), whereas the yield stress was measured using a shear vane (Brookfield vane spindle V-73). The index characteristics of the tailings including the grain size distribution, liquid limit, plastic limit, specific gravity were determined as per ASTM standards. This paper will then discuss the interrelationships among the solid content, slump, saturated density and the yield stress of the CPB. It is shown that there is strong correlation between the two different slump test devices used in this study. The smaller cylindrical device appears to have good potential for slurries like mine tailings or dredged mud that have high water content for slump test. There is also strong inter-relationship among solid content, slump, yield stress, and bulk density. Increasing the solid content increases the bulk density and yield stress, but reduces the slump. While there is hardly any difference between the two binder types used in this study in terms of flow parameters, namely the yield stress and slump, the binder dosage has an effect. At any specific solid content, higher binder dosages lead to a drop in the slump and increase in the yield stress. The difference is more pronounced in dense slurries. It is also strongly believed that the trends and relationships developed in this study may be valuable for the other mining operations using CPB.

High Strain Rate Response of Rocks Under Dynamic Loading Using Split Hopkinson Pressure Bar

Abstract: In the present work, dynamic stress–strain response of five sedimentary and three metamorphic rocks from different regions of India, e.g. Kota sandstone, Dholpur sandstone, Kota limestone, Himalayan limestone, dolomite, quartzite, quartzitic gneiss and phyllite have been investigated through split Hopkinson pressure bar test at different strain rates. The dry density, specific gravity, static compressive strength and tensile strength values of the rocks have also been determined. Petrological studies of the rocks have been carried out through X-ray diffraction test and scanning electron microscope test. It is observed from the stress–strain response of the rocks that the peak stress increases with increasing strain rate. Dynamic increase factors for the strength of these rocks have been determined by comparing the dynamic and the static peak compressive stresses and correlation equations are proposed.

Effect of Saturation Time on the Coal Burst Liability Indexes and Its Application for Rock Burst Mitigation

Abstract: Coal seam water infusion is one of the widely used techniques for rock burst mitigation, and the saturation time of coal is one of the essential factors influencing the effectiveness of water infusion. To analyze the effect of saturation time on coal burst liability indexes, bursting liability indexes of coal specimens taken from No. 2 mining face in Changgouyu Mine in Beijing were tested under natural state and different saturation time. Compared with coal specimens under natural state, the uniaxial compressive strength, elastic strain energy index, and bursting energy index all decrease in different degrees as the saturation time increases. The dynamic failure duration, however, shows an opposite tendency. When the saturation time is 0–6 days, the bursting liability indexes vary significantly, but when the saturation time is longer than 6 days, this phenomenon is not very obvious. When the saturation time increases from 0 to 6 days, the uniaxial compressive strength, elastic strain energy index, and bursting energy index decreases from 18.31 to 7.15 MPa, 2.59 to 1.25, 3.04 to 1.20, respectively, but when the saturation time increases from 6 to 8 days, their corresponding increments are only 0.02–0.05. Moreover, the time of coal seam water infusion in No. 2 mining face was designed 6–8 days based on the test results. Practical experiences show that excellent destress effect was achieved by water infusion. After coal seam water infusion, the average moisture content of coal seam increases from 0.85 to 1.26%, and the width of destress zone increases from 0–4 to 0–6 m.

Physicochemical and Mechanical Properties of Lime-Treated Loess

Abstract: This paper studies the changes in physicochemical and mechanical properties of lime-treated loess at different lime contents and curing days. The physical tests were conducted in particle size distribution, Atterberg limits, specific gravity, specific surface area and cation exchange capacity of lime-treated loess, while its chemical tests included electrical conductivity, total dissolved solids, pH, and oxidation reduction potential of extracts from 1:5 soil to water. Finally, the relevant mechanical tests were performed in unconfined compressive strength. The results showed that the physicochemical and mechanical properties of lime-treated loess were altered during hydration and pozzolantic reactions, which caused the formation of aggregation and new cementitious minerals. As a result, the performance of lime-treated loess acquired great improvement compared to that of untreated loess. The improvement can attribute to the first immediate aggregation formation due to flocculation induced by cation exchange, and then the filling between the aggregations or particles due to the formation of new cementitious minerals. In addition, the results indicated that the chemical properties of lime-treated loess are more relatively sensitive to environmental change than their physical and mechanical properties.

Numerical Modeling in the Structural Study of Technogenic Rock Array

Abstract: The relevance of research underlies in the fact that numerical models of technogenic rock arrays can predict and evaluate structural and mechanical properties, which are very difficult or even impossible to study instrumentally. It is possible to simulate the technogenic rock array’s structure by the method of discrete elements, where each particle in the array structure is described separately. The article contains the method of numerical simulation of structure of bulk disjointed rock array, describes the basic initial and boundary conditions of the model; represents the visualization of numerical model of the array created with peripheral dumping (as the array with more textured and visual segregated granulometric composition). The ways of application of technogenic rock array numerical modeling in the mining process are described. Comparative analysis of real and simulated array structure shows the adequacy of the numerical model and the algorithm developed for its creation. In addition, the adequacy of the model is supported by a high convergence of the experimental and calculated dependence of the filtration rate values upon the particle size distribution of technogenic rock arrays.

Influence of Drying on the Stiffness and Strength of Cement-Stabilized Soils

Abstract: Nowadays, improving the strength and deformation properties of soft soils by deep soil mixing is a commonly used technique. There is also an increasing interest in the use of this technique for foundation/structural elements and excavation retaining walls applications. The compressive strength and elastic modulus of the soil mix material are key parameters in the design of these structures. However, there is very limited information available on the impact of exposure to air drying (in the case of retaining wall) on the strength and stiffness of cement stabilized soils. The aim of this study is to investigate the effects of different curing conditions (immersion in water, cycles of wetting and drying, continuous air drying) on the mechanical properties of soils treated with cement in the laboratory. Free–free resonance tests and unconfined compression tests were performed on specimens of silt and sand treated with blastfurnace slag cement. Strength increases more rapidly than stiffness between 7 and 30 days. The strength of stabilized soils submitted to cyclic wetting and drying before the cement hydration process is complete continues to increase. As long as the periods of drying do not induce microcracks, the stiffness of the treated soil specimens also increases with time. However, the stiffness is lower than for the specimens cured in water indicating a disruptive effect of the imposed wetting–drying cycles on stiffness. Continuous exposure to air drying inhibits strength development due to insufficient water for hydration. Significant stiffness decreases were observed on specimens of stabilized silt and are attributed to microcracking.

The Derivation and Validation of TBM Disc Cutter Wear Prediction Model

Abstract: The problem of disc cutter wear is inevitable when shield or TBM excavating hard rock for a long distance, thus, the study of disc cutter wear model has an important project value on predicting its service life and replacement opportunity. It is put forward by analyzing disc cutter wear mechanism that the main wear form is abrasive wear, which is based on plastic removal mechanism. Then, disc cutter wear rate and linear wear rate prediction models are obtained by approximate calculation and mathematical deduction, which are based on Rabinowicz equation and CSM model. At last, the two models are verified through field test data from three projects, and the results show that the prediction model can accurately reflect the real wear situation of disc cutter.

Nonlinear Variation Parameters Creep Model of Rock and Parametric Inversion

Abstract: Traditional Nishihara model is a linear constant parameters model, and it is difficult to describe nonlinear accelerated creep characteristics of rock with this model. Therefore, an improved Nishihara model is proposed in the way of replacing, cascading elements and substituting parameters in the original model. Firstly, fractional differential elements are used to replace viscous elements in the traditional Nishihara model; then a viscous plastic element with assumption exponential relationship between the rock nonlinear rheological deformation and time power function is cascaded; finally, the viscosity coefficient of the traditional model is rewritten to a variable parameter related to stress and time, thus obtaining the nonlinear variation parameters creep model of rock. The improved model is verified with data from creep test to frozen soft rock during Cretaceous period, which shows that this model can describe the rock nonlinear accelerated creep characteristics more accurately and more comprehensively.

Dynamic Response of Shallow-Buried Small Spacing Tunnel with Asymmetrical Pressure: Shaking Table Testing and Numerical Simulation

Abstract: A series of shaking table tests were designed and carried out to study the seismic behaviors of a shallow-buried small spacing tunnel with asymmetrical pressure. The key details to shaking table model test, including test equipment, model similarity relation, similarity constant, model box, physical model, layout of transducers, seismic waves, and loading system were presented. The numerical simulation of the shaking table test was also carried out by using a finite element simulation software. The results show that: (1) the Fourier spectrums in the vertical direction and horizontal direction are different at the same measuring point. The structure of tunnel transforms the Fourier spectrum of horizontal direction. (2) The stability of middle rock pillar is poor under seismic wave action. The anchor plays an important role in strengthening the stability of middle rock pillar. The dynamic strain of anchor has accumulative effect. (3) The numerical simulation results are in significant agreement with the shaking table test results. (4) Compared with type of seismic wave, peak seismic wave has a significant effect on acceleration response of tunnel. The peak acceleration response of the tunnel is linear with the peak seismic wave, in the horizontal direction. The peak acceleration response is nonlinear in the vertical direction. (5) The axial force of cross section at arch foot is larger than other position. The shock absorption effect of 10 cm seismic isolation layer is better than 5 and 20 cm.

Identifying the Main Control Factors for Different Deformation Stages of Landslide

Abstract: Water level fluctuations and rainfall, as external factors, are typically the two dominant causal factors of landslide deformation in the Three Gorges Reservoir Area. A quantitative model capable of evaluating landslide deformation processes is critical for early warning of landslide. The primary purpose of this paper is to take the Zhujiadian landslide as an example to determine the main control factors for different deformation stages of landslide. Original field date collected from the Zhujiadian landslide was examined using the grey relational grade analysis (GRGA). The approach consists of three steps: determination of landslide type, data processing, and identifying the main control factors of landslide deformation. The results obtained suggest that the Zhujiadian landslide is typical retrogressive landslide, and its deformation occurred first at the front part of the landslide and progressed upslope due to drawdown of reservoir water level and heavy rainfall. In the whole deformation process, the main control factors of different parts of landslide changed with the landslide development. Thus, the findings of the study are useful for rapidly predicting landslide deformation relating to water level fluctuations and rainfall, and the GRGA is useful for interpreting the main control factors of landslide deformation from a quantitative point of view.

Prediction of California Bearing Ratio from Index Properties of Soils Using Parametric and Non-parametric Models

Abstract: This work proposes a methodology to obtain from the soils properties the best prediction model for the California bearing ratio index. The methodology proposes three different prediction techniques: (1) the multiple linear regression, a classical parametric technique; and two non-parametric techniques: (2) the local polynomial regression (LPR) and (3) the radial basis network. The LPR is a known statistical method, but in the geotechnical engineering field is not in common use. Besides, although several research works have been published in this field, they do not include a robust procedure for making good comparison between different models. Here, a cross validation method is proposed with this aim. A data set of 96 samples from Peruvian soils is used to illustrate the methodology. To validate the proposed methodology, a data set from the literature is also analyzed.

Relevance of SEM to Long-Term Mechanical Properties of Cemented Paste Backfill

Abstract: This paper is an attempt to relate the microstructure to long-term mechanical properties of the cemented paste backfill produced from a hard rock mine tailing from North Queensland in Australia bound with flyash-based geopolymer (geopolymer), flyash-blended cement (FBC), and general purpose cement (GPC). A relatively high slump (260 mm) paste backfill mix with 74 wt% solids has been used to prepare cylindrical paste backfill samples with a diameter of 50 mm and a height of 100 mm. The uniaxial compressive strength tests were conducted on all samples after curing for 112 days to obtain their strength, failure strain and Young’s modulus. Fractured samples were examined under scanning electron microscope to understand the failure mechanisms at the microstructural scale. The results show that binders significantly affected the mechanical properties of paste backfills (ANOVA, p < 0.05). The paste backfill bound with geopolymer gave the lowest strength and Young’s modulus, while the paste backfills bounded with FBC and GPC showed comparable higher strength and modulus values. This was attributed to the relatively well-packed paste backfills with less cracks and smaller pore sizes in these paste backfills bound with FBC and GPC binders. In particular, needle-shaped particles, which were originally identified in GPC, highly influenced the mechanical property of paste backfills. These results indicate that fly ash can be used to partially replace the cement as a binder for paste backfills to achieve economic and environmental benefits.