Effect of Fines Content on Static Liquefaction Susceptibility of Sandy Soil
Investigation of liquefaction susceptibility of materials that have been used in embankments, slopes, dams, and foundations is very essential. Many catastrophic geo-hazards such as flow slides, declination of foundations, and damage to earth structure are associated with static liquefaction that may occur during abrupt shearing of these materials. Many artificial backfill materials are mixtures of sand with fines and other composition. In order to provide some clarifications and evaluations on the role of fines in static liquefaction behaviour of sand sandy soils, the effect of fines on the liquefaction susceptibility of sand was examined experimentally in present work over a range of fines content, relative density, and initial confining pressure. The results of an experimental study on various sand-fines mixtures are presented. Undrained static triaxial compression tests were conducted on saturated Perth sand containing 5% bentonite at three different relative densities, namely (10, 50, and 90 %), and saturated Perth sand containing both 5% bentonite and slag (2%, 4%, and 6%) at single relative density 10%. Undrained static triaxial tests were performed at three different initial confining pressures namely 100, 150, and 200 kPa. The brittleness index was used to quantify the liquefaction potential of sand-bentonite-slag mixtures. The results demonstrated that the liquefaction susceptibility of sand-5% bentonite mixture was more than liquefaction susceptibility of clean sandy soil. However, liquefaction potential decreased when both of two fines (Bentonite and Slag) were used. Liquefaction susceptibility of all mixtures decreased with increasing relative density and initial confining pressure.
Mechanism of Sinkhole Development on Water-Bearing Soft Ground Tunneling
Underground excavations in an urban area can cause various geotechnical problems such as ground loss and lowering of groundwater level. When the ground loss becomes uncontrollably large, sinkholes can be developed to the ground surface. A sinkhole is commonly known as the natural phenomenon associated with lime rock areas. However, sinkholes in urban areas due to pressurized sewers and/or tunneling are also frequently reported. In this study, mechanism of a sinkhole developed at the site ‘A’ where a tunneling work underwent is investigated. The sinkhole occurred in the sand strata with the high level of groundwater when excavating a tunnel of which diameter is 3.6 m. The sinkhole was progressed in two steps. The first step began with the local failure around the tunnel face followed by tons of groundwater inflow, and the second step was triggered by the TBM (Tunnel Boring Machine) chamber opening which led to the progressive general failure. The possibility of the sinkhole was evaluated by using Limit Equilibrium Method (LEM), and critical height was evaluated by the empirical stability chart. It is found that the lowering of the face pressure and inflow of groundwater into the tunnel face turned to be the main reason for the sinkhole.
The Effects of Time and Cyclic Loading to the Axial Capacity for Offshore Pile in Shallow Gas
An offshore platform was installed in 1977 at about 260km offshore West Malaysia at the water depth of 73.6m. Twelve (12) piles were installed with four (4) are skirt piles. The piles have 1.219m outside diameter and wall thickness of 31mm and were driven to 109m below seabed. Deterministic analyses of the pile capacity under axial loading were conducted using the current API (American Petroleum Institute) method and the four (4) CPT-based methods: the ICP (Imperial College Pile)-method, the NGI (Norwegian Geotechnical Institute)-Method, the UWA (University of Western Australia)-method and the Fugro-method. A statistical analysis of the model uncertainty associated with each pile capacity method was performed. There were two (2) piles analysed: Pile 1 and piles other than Pile 1, where Pile 1 is the pile that was most affected by shallow gas problems. Using the mean estimate of soil properties, the five (5) methods used for deterministic estimation of axial pile capacity in compression predict an axial capacity from 28 to 42MN for Pile 1 and 32 to 49MN for piles other than Pile 1. These values refer to the static capacity shortly after pile installation. They do not include the effects of cyclic loading during the design storm or time after installation on the axial pile capacity. On average, the axial pile capacity is expected to have increased by about 40% because of ageing since the installation of the platform in 1977. On the other hand, the cyclic loading effects during the design storm may reduce the axial capacity of the piles by around 25%. The study concluded that all piles have sufficient safety factor when the pile aging and cyclic loading effect are considered, as all safety factors are above 2.0 for maximum operating and storm loads.
Full-Field Estimation of Cyclic Threshold Shear Strain
Cyclic threshold shear strain is the cyclic shear strain amplitude that serves as the indicator of the development of pore water pressure. The parameter can be obtained by performing either cyclic triaxial test, shaking table test, cyclic simple shear or resonant column. In a cyclic triaxial test, other researchers install measuring devices in close proximity of the soil to measure the parameter. This method can cause sample disturbance which can affect the result of the experiment. Although there are already existing methods in determining the parameter, the movement and behavior of the soil before and after reaching this parameter needs to be understood. A method that can be used is by applying full-field measurement technique. The technique uses a camera to monitor and measure the movement of the soil. This study is an attempt to estimate the cyclic threshold shear strain parameter. The applied technique has the capacity to monitor the behavior of the particles at cyclic loading. For this study, the technique was incorporated in a strain controlled consolidated undrained cyclic triaxial test. Two-dimensional image processing was implemented. Lucas and Kanade optical flow algorithm were applied to track the movement of the soil particles. Results from the full-field measurement technique were compared with the results from the linear variable displacement transducer.
Non-Contact Measurement of Soil Deformation in a Cyclic Triaxial Test
Deformation in a conventional cyclic triaxial test is normally measured by using point-wise measuring device. In this study, non-contact measurement technique was applied to be able to monitor and measure the occurrence of non-homogeneous behavior of the soil under cyclic loading. Non-contact measurement is executed through image processing. Two-dimensional measurements were performed using Lucas and Kanade optical flow algorithm and it was implemented Labview. In this technique, the non-homogeneous deformation was monitored using a mirrorless camera. A mirrorless camera was used because it is economical and it has the capacity to take pictures at a fast rate. The camera was first calibrated to remove the distortion brought about the lens and the testing environment as well. Calibration was divided into 2 phases. The first phase was the calibration of the camera parameters and distortion caused by the lens. The second phase was to for eliminating the distortion brought about the triaxial plexiglass. A correction factor was established from this phase. A series of consolidated undrained cyclic triaxial test was performed using a coarse soil. The results from the non-contact measurement technique were compared to the measured deformation from the linear variable displacement transducer. It was observed that deformation was higher at the area where failure occurs.
Coupled Hydro-Geomechanical Modeling of Oil Reservoir Considering Non-Newtonian Fluid through a Fracture
Oil has been used as a source of energy and supply to make materials, such as asphalt or rubber for many years. This is the reason why new technologies have been implemented through time. However, research still needs to continue increasing due to new challenges engineers face every day, just like unconventional reservoirs. Various numerical methodologies have been applied in petroleum engineering as tools in order to optimize the production of reservoirs before drilling a wellbore, although not all of these have the same efficiency when talking about studying fracture propagation. Analytical methods like those based on linear elastic fractures mechanics fail to give a reasonable prediction when simulating fracture propagation in ductile materials whereas numerical methods based on the cohesive zone method (CZM) allow to represent the elastoplastic behavior in a reservoir based on a constitutive model; therefore, predictions in terms of displacements and pressure will be more reliable. In this work, a hydro-geomechanical coupled model of horizontal wells in fractured rock was developed using ABAQUS; both extended element method and cohesive elements were used to represent predefined fractures in a model (2-D). A power law for representing the rheological behavior of fluid (shear-thinning, power index
A Guideline for Determining the Search Space of Optimization Techniques in Slope Stability Analysis
Optimization techniques are used to find the optimal solutions for a problem. These methods attempt to minimize or maximize their objective function by operating on various combinations of design variables. The union of all possible solutions within the limits of the variables is called search space. The problem of finding the critical sliding surface (CSS) of soil slopes needs a global optimization technique, since it requires to identify the CSS with minimum factor of safety among almost infinite potential surfaces. Different global optimization methods have been used by researchers to solve this problem. Although none of them indicated the importance of establishing an adequate search space, this is one of the critical issues when using a search technique. This article briefly reviews the application of different optimization techniques in slope stability analysis from the first well established to the most recent result, perceives their limitations and outcomes, and explains their search spaces applied to CSS. A guideline is then introduced based on the comparison of the studied papers to help researchers determine the most effective and appropriate search space in slope stability analysis. As a result of this study, it would be possible to compare in a fair way the results of different optimization techniques when finding the CSS for benchmark examples considering that they look in the same space.
Load Carrying Capacity of Soils Reinforced with Encased Stone Columns
Stone columns are effectively used to improve bearing strength of soils and also for many geotechnical applications. In soft soils when stone columns are loaded they undergo large settlements due to insufficient lateral confinement. Use of geosynthetics encasement has proved to be a solution for this problem. In this paper, results of a laboratory experimental study carried out with model stone columns with and without encasement. Sand was used for making test beds, and grain size of soil varies from 0.075mm to 4.75mm. Woven geotextiles produced by Gareware ropes India with mass per unit area of 240gm/M2 and having tensile strength of 52KN/m is used for the present investigation. Tests were performed with large scale direct shear box and also using scaled laboratory plate load tests. Stone column of 50mm and 75mm is used for the present investigation. Diameter of stone column, size of stones used for making stone columns is varied in making stone column in the present study. Two types of stone were used namely small and bigger in size. Results indicate that there is an increase in angle of internal friction and also an increase in the shear strength of soil when stone columns are encased. With stone columns with 50mm dia, an average increase of 7% in shear strength and 4.6 % in angle of internal friction was achieved. When large stones were used increase in the shear strength was 12.2%, and angle of internal friction was increased to 5.4%. When the stone column diameter has increased to 75mm increase in shear strength and angle of internal friction was increased with smaller size of stones to 7.9 and 7.5%, and with large size stones, it was 7.7 and 5.48% respectively. Similar results are obtained in plate load tests, also.
Sloping Seabed Behavior Due to Water Surface Waves
Wave-induced seabed instability can cause serious damage to coastal infrastructure and offshore structures. The issue has been studied vastly for the flat or slightly sloped seabeds. However, with the deployment of Marine Hydrokinetic devices near and offshore, with potential deployment of some near the edge of the continental shelf, there is a need to consider steeper slopes and full interaction between the anchoring foundation and the seabed. In this work, a numerical model is developed to examine the failure potential of seabed with various inclination angles due to general shear failure and instantaneous liquefaction due to wave action. For this objective, first, the horizontal seabed response is evaluated by solving Biot’s equations in the framework of finite element analysis and verified by analytical solution. In this case, no interaction between the wave-induced water pressure and the soil response was considered. Second, the fluid domain is modeled assuming linear wave theory and a progressive water surface wave. A two-way coupling of pressure and flux between the two media is implemented. A parametric study is conducted to evaluate the effect of interaction on the system response. In addition, the effect of the sloping seabed and the shoaling waves is investigated. The results indicated that for typical values of sediment permeability and wave characteristics, the interaction of domains does not have a significant impact on soil response in comparison to decoupled approach when flat seabed is assumed. However, for modeling the inclined bed, the full interaction is required to achieve an accurate response characterization.
The Effect of Sand Content on Behavior of Kaolin Clay
One of the unknowns in the design of zoned earth dams is the percentage of sand which can be present in a clay core and still retain the necessary plasticity to prevent cracking in response to deformation. Cracks in the clay core of a dam caused by differential settlement can lead to failure of the dam. In this study, a series of Atterberg Limit tests and unconfined compression strength tests have been conducted in the ISU soil mechanics laboratory on prepared mixes of quartz sand and commercial clays (Kaolin and Smectite) to determine the relationship between sand content, plasticity and squeezing behavior. The prepared mixes have variable percentages of sand ranging between 10 and 90% by weight. Plastic limit test results in which specimens can be rolled into 1/8 in. threads without crumbling and plasticity index values which represent the range of water content over which the specimens can be remolded without cracking were used to evaluate the plasticity of the sand-clay mixtures. The test results show that the design mixes exhibit plastic behavior with sand contents up to 80% by weight. However, the plasticity of the mixes decreases with increasing sand content. For unconfined compression strength tests, the same mixtures of sand and clay (Kaolin) were made in plastic limit. The results which were concluded from the UCC tests represent the relationship between sand-clay content and chance of having squeezing behavior, also according to the results from UCC, strength of different samples and stress-strain curves can be obtained.
Slope Stability Assessment of Himalayan Slope under Static and Seismic Conditions
Stability of slope in Chamoli Distt. near River Alaknanda in Uttarakhand is essential to safeguard the infrastructure of the slope where a dam is proposed to be built near this slope. Every year the areas near the slope have been facing severe landslides (small or big) due to intensive precipitation inflicting substantial damages as per Geological Survey of India records. The stability analysis of the slope under static and pseudo static conditions are presented in this study by using FEM software PHASE2. As per the earthquake zonation map of India, the slope is found in zone V, and hence, pseudo static stability of slope has been performed considering pseudo static analysis. For analysing the slope Mohr-Coulomb shear strength criteria is adopted for soil material and self-drilling anchors are modelled as bolts with parameters like modulus of elasticity, diameter of anchors and peak pull-out resistance of the anchors with the soil present there. The slope is found to be unstable under pseudo static conditions with computed factor of safety= 0.93. Stability is provided to the slope by using Self Drilling Anchors (SDA) which gives factor of safety= 1.15 under pseudo static condition.
1D Infiltration Behavior of Two-Layered Hydrophobic Recycled Concrete Aggregates in a Column Apparatus
One-dimensional (1D) vertical infiltration column tests have been carried out to study the infiltration characteristics of two different hydrophobic materials, fine and coarse recycled concrete aggregates (RCA) and if they are helpful to be used in a capillary barrier system. The tests were carried out on fine RCA over coarse RCA, fine RCA over coarse RCA with oil, and fine RCA over coarse RCA with wax. The column apparatus was instrumented with tensiometer-transducer system, data acquisition system, soil moisture sensor, and electronic weighing balance to measure various parameters viz pore-water pressure, water content, and outflow rate of water. The instruments facilitated the measurement of all these parameters instantaneously and automatically. The experimental results indicated that the rate of flow of within the RCA is modified upon coating with oil or wax. It was observed that the water flowed faster within the layer of coarse RCA with oil and wax as compared to that within the layer of coarse RCA without oil and wax. This could be attributed to the hydrophobicity of each solid particle of coarse RCA that was coated with oil and wax.
Influence of Ground Granulated Blast Furnace Slag on Geotechnical Characteristics of Jarosite Waste
The quick evolution of industrialization causes the scarcity of precious land. Thus, it is vital need to influence the R&D societies to achieve sustainable, economic and social benefits from huge utilization of waste for universal aids. The current study promotes the influence of steel industries waste i.e. ground granulated blast furnace slag (GGBS) in geotechnical properties of jarosite waste (solid waste residues produced from hydrometallurgy operations involved in extraction of Zinc). Numerous strengths tests (unconfined compression (qu) and splitting tensile strength (qt)) are conducted on jarosite-GGBS blends (GGBS, 10-30%) with different curing periods (7, 28 & 90 days). The results indicate that both qu and qt increase with the increase in GGBS content along with curing periods. The increased strength with the addition of GGBS is also observed from microstructural study, which illustrates the occurrence of larger agglomeration of jarosite-GGBS blend particles. The Freezing-Thawing (F-T) durability analysis is also conducted for all the jarosite-GGBS blends and found that the reduction in unconfined compressive strength after five successive F-T cycles enhanced from 62% (natural jarosite) to 48, 42 and 34% at 7, 14 and 28 days curing periods respectively for stabilized jarosite-GGBS samples containing 30% GGBS content. It can be concluded from this study that blending of cementing additives (GGBS) with jarosite waste resulted in a significant improvement in geotechnical characteristics.
A Semi-Automated GIS-Based Implementation of Slope Angle Design Reconciliation Process at Debswana Jwaneng Mine, Botswana
The mining of pit slopes is often associated with some level of deviation from design recommendations, and this may translate to associated changes in the stability of the excavated pit slopes. Therefore slope angle design reconciliations are essential for assessing and monitoring compliance of excavated pit slopes to accepted slope designs. These associated changes in slope stability may be reflected by changes in the calculated factors of safety and/or probabilities of failure. Reconciliations of as-mined and slope design profiles are conducted periodically to assess the implications of these deviations on pit slope stability. Currently, the slope design reconciliation process being implemented in Jwaneng Mine involves the measurement of as-mined and design slope angles along vertical sections cut along the established geotechnical design section lines on the GEOVIA GEMS™ software. Bench retentions are calculated as a percentage of the available catchment area, less over-mined and under-mined areas, to that of the designed catchment area. This process has proven to be both tedious and requires a lot of manual effort and time to execute. Consequently, a new semi-automated mine-to-design reconciliation approach that utilizes laser scanning and GIS-based tools is being proposed at Jwaneng Mine. This method involves high-resolution scanning of targeted bench walls, subsequent creation of 3D surfaces from point cloud data and the derivation of slope toe lines and crest lines on the Maptek I-Site Studio software. The toe lines and crest lines are then exported to the ArcGIS software where distance offsets between the design and actual bench toe lines and crest lines are calculated. Retained bench catchment capacity is measured as distances between the toe lines and crest lines on the same bench elevations. The assessment of the performance of the inter-ramp and overall slopes entails the measurement of excavated and design slope angles along vertical sections on the ArcGIS software. Excavated and design toe-to-toe or crest-to-crest slope angles are measured for inter-ramp stack slope reconciliations. Crest-to-toe slope angles are also measured for overall slope angle design reconciliations. The proposed approach allows for a more automated, accurate, quick and easier workflow for carrying out slope angle design reconciliations. This process has proved highly effective and timeous in the assessment of slope performance in Jwaneng Mine. This paper presents a newly proposed process for assessing compliance to slope angle designs for Jwaneng Mine.
Sample Preparation and Coring of Highly Friable and Heterogeneous Bonded Geomaterials
Most of the Earth’s crust surface rocks are technically categorized as weak rocks or weakly bonded geomaterials. Deeply weathered, weakly cemented, friable and easily erodible, they demonstrate complex material behaviour and understanding the overlooked mechanical behaviour of such materials is of particular importance in geotechnical engineering practice. Weakly bonded geomaterials are so susceptible to surface shear and moisture that conventional methods of core drilling fail to extract high-quality undisturbed samples out of them. Moreover, most of these geomaterials are of high heterogeneity rendering less reliable and feasible material characterization. In order to compensate for the unpredictability of the material response, either numerous experiments are needed to be conducted or large factors of safety must be implemented in the design process. However, none of these approaches is sustainable. In this study, a method for dry core drilling of such materials is introduced to take high-quality undisturbed core samples. By freezing the material at certain moisture content, a secondary structure is developed throughout the material which helps the whole structure to remain intact during the core drilling process. Moreover, to address the heterogeneity issue, the natural material was reconstructed artificially to obtain a homogeneous material with very high similarity to the natural one in both micro and macro-mechanical perspectives. The method is verified for both micro and macro scale. In terms of micro-scale analysis, using Scanning Electron Microscopy (SEM), pore spaces and inter-particle bonds were investigated and compared between natural and artificial materials. X-Ray Diffraction, XRD, analyses are also performed to control the chemical composition. At the macro scale, several uniaxial compressive strength tests, as well as triaxial tests, were performed to verify the similar mechanical response of the materials. A high level of agreement is observed between micro and macro results of natural and artificially bonded geomaterials. The proposed methods can play an important role to cut down the costs of experimental programs for material characterization and also to promote the accuracy of the numerical modellings based on the experimental results.
Probabilistic Analysis of Fiber-Reinforced Infinite Slopes
Fiber-reinforcement is an effective soil improvement technique for applications involving the prevention of shallow failures on the slope face and the repair of existing slope failures. A typical application is the stabilization of cohesionless infinite slopes. The objective of this paper is to present a probabilistic, reliability-based methodology (based on Monte Carlo simulations) for the design of a practical fiber-reinforced cohesionless infinite slope, taking into consideration the impact of various sources of uncertainty. Recommendations are made regarding the required factors of safety that need to be used to achieve a given target reliability level. These factors of safety could differ from the traditional deterministic factor of safety.
Virtual Approach to Simulating Geotechnical Problems under Both Static and Dynamic Conditions
Recent studies on the numerical simulation of geotechnical problems show the importance of considering the soil micro-structure. At this scale, soil is a discrete particle medium where the particles can interact with each other and with water flow under external forces, structure loads or natural events. This paper presents research conducted in a virtual laboratory named SiGran, developed at IREQ (Institut de recherche d’Hydro-Quebec) for the purpose of investigating a broad range of problems encountered in geotechnics. Using Discrete Element Method (DEM), SiGran simulated granular materials directly by applying Newton’s laws to each particle. The water flow was simulated by using Marker and Cell method (MAC) to solve the full form of Navier-Stokes’s equation for non-compressible viscous liquid. In this paper, examples of numerical simulation and their comparisons with real experiments have been selected to show the complexity of geotechnical research at the micro level. These examples describe transient flows into a porous medium, interaction of particles in a viscous flow, compacting of saturated and unsaturated soils and the phenomenon of liquefaction under seismic load. They also provide an opportunity to present SiGran’s capacity to compute the distribution and evolution of energy by type (particle kinetic energy, particle internal elastic energy, energy dissipated by friction or as a result of viscous interaction into flow, and so on). This work also includes the first attempts to apply micro discrete results on a macro continuum level where the Smoothed Particle Hydrodynamics (SPH) method was used to resolve the system of governing equations. The material behavior equation is based on the results of simulations carried out at a micro level. The possibility of combining three methods (DEM, MAC and SPH) is discussed.
Experimental Study of Sand-Silt Mixtures with Torsional and Flexural Resonant Column Tests
Dynamic properties of soils, especially at the range of very small strains, are of particular interest in geotechnical engineering practice for characterization of the behavior of geo-structures subjected to a variety of stress states. This study reports on the small-strain dynamic properties of sand-silt mixtures with particular emphasis on the effect of non-plastic fines content on the small strain shear modulus (Gmax), Young’s Modulus (Emax), material damping (Ds,min) and Poisson’s Ratio (v). Several clean sands with a wide range of grain size characteristics and particle shape are mixed with variable percentages of a silica non-plastic silt as fines content. Prepared specimens of sand-silt mixtures at different initial void ratios are subjected to sequential torsional and flexural resonant column tests with elastic dynamic properties measured along an isotropic stress path up to 800 kPa. It is shown that while at low percentages of fines content, there is a significant difference between the dynamic properties of the various samples due to the different characteristics of the sand portion of the mixtures, this variance diminishes as the fines content increases and the soil behavior becomes mainly silt-dominant, rendering no significant influence of sand properties on the elastic dynamic parameters. Indeed, beyond a specific portion of fines content, around 20% to 30% typically denoted as threshold fines content, silt is controlling the behavior of the mixture. Using the experimental results, new expressions for the prediction of small-strain dynamic properties of sand-silt mixtures are developed accounting for the percentage of silt and the characteristics of the sand portion. These expressions are general in nature and are capable of evaluating the elastic dynamic properties of sand-silt mixtures with any types of parent sand in the whole range of silt percentage. The inefficiency of skeleton void ratio concept in the estimation of small-strain stiffness of sand-silt mixtures is also illustrated.
The Effect of Spatial Variability on Axial Pile Design of Closed Ended Piles in Sand
While significant improvements have been made in axial pile design methods over recent years, the influence of soils natural variability has not been adequately accounted for within them. Soil variability is a crucial parameter to consider as it can account for large variations in pile capacity across the same site. This paper seeks to address this knowledge deficit, by demonstrating how soil spatial variability can be accommodated into existing cone penetration test (CPT) based pile design methods, in the form of layered non-homogeneous random fields. These random fields model the scope of a given property’s variance and define how it varies spatially. A Monte Carlo analysis of the pile will be performed taking into account parameter uncertainty and spatial variability, described using the measured scales of fluctuation. The results will be discussed in light of Eurocode 7 and the effect of spatial averaging on design capacities will be analysed.
Concept of the Active Flipped Learning in Engineering Mechanics
The flipped classroom has been introduced to promote collaborative learning and higher-order learning objectives. In contrast to the traditional classroom, the flipped classroom has students watch prerecorded lecture videos before coming to class and then “class becomes the place to work through problems, advance concepts, and engage in collaborative learning”. In this paper, the active flipped learning combines flipped classroom with active learning that is to establish an active flipped learning (AFL) model, aiming to promote active learning, stress deep learning, encourage student engagement and highlight data-driven personalized learning. Because students have watched the lecture prior to class, contact hours can be devoted to problem-solving and gain a deeper understanding of the subject matter. The instructor is able to provide students with a wide range of learner-centered opportunities in class for greater mentoring and collaboration, increasing the possibility to engage students. Currently, little is known about the extent to which AFL improves engineering students’ performance. This paper presents the preliminary study on the core course of sophomore students in Engineering Mechanics. A series of survey and interviews have been conducted to compare students’ learning engagement, empowerment, self-efficacy, and satisfaction with the AFL. It was found that the AFL model taking advantage of advanced technology is a convenient and professional avenue for engineering students to strengthen their academic confidence and self-efficacy in the Engineering Mechanics by actively participating in learning and fostering their deep understanding of engineering statics and dynamics
Method of Calculating Thermal Cracking Probability for Mass Concrete
This paper describes the method of the calculating thermal cracking probability for mass concrete. Generally, in Japan, thermal cracking for mass concrete is verified by computing thermal cracking probability, and by applying limit values for control target. If the goal of the control target is to prevent thermal cracking, the verification is carried out by confirming that the calculated value of thermal cracking probability is equal to or less than 5%. In practice, however, thermal cracking index which is equivalent to thermal cracking probability is applicable. The thermal cracking index is a ratio of splitting tensile strength of concrete to thermal tensile stress obtained by 3D-FE analysis in concrete. In fact, an equation and the figure are declared to estimate the thermal cracking index which meets the required thermal cracking probability. Therefore, it is shown that one thermal cracking index decides one thermal cracking probability. But originally one cracking index decides an endless number of thermal cracking probability. Since, the thermal cracking probability is calculated according to 3 variables, thermal cracking index and the coefficient of variation for tensile strength, the coefficient of variation for tensile stress. In Japan, the one standard coefficient of variation for tensile strength and for tensile stress is applicable so that thermal cracking probability is calculated easily. But the one standard coefficient of variation is unapparent. Since that, an equation and the figure declared are established by comparing thermal cracking index with observed data in actual structures on whether thermal cracks occurred or not. In actual structures, it cannot declare whether the coefficient of variation is standard or not. So, this paper shows that the one standard coefficient of variation in Japan is computed, analyzing that the equation and the figure. And then, it offers a versatile method of the calculating thermal cracking probability, taking any other coefficient of variation for tensile strength and for tensile stress. If the variation for tensile strength by the high-quality control is smaller than by the standard quality control, the thermal cracking probability calculated is exactly small by this offering method of the calculating, even though the thermal cracking index on the high-quality control is the same as on the standard quality control. Bivariate normal distribution modeling the tensile strength and the tensile stress is used in this offering a versatile method of the calculating thermal cracking probability.
Performance of Bored Pile on Alluvial Deposit
Bored cast in-situ pile is a popular choice amongst consultant and contractor due to the ability to adjust the pile length suitably in case if any variation found in the actual geological strata. Bangladesh geological strata are dominated by silt content. Design is normally based on field test such as Standard Penetration test N-values. Initially, pile capacity estimated through static formula with co-relation of N-value and angle of internal friction. Initial pile load test was conducted in order to validate the geotechnical parameters assumed in design. Initial pile load test was conducted on 1.5m diameter bored cast in-situ pile. Kentledge method is used to load the pile for 2.5 times of its working load. Initially, safe working load of pile has been estimated as 570T, so test load is fixed to 1425T. Max load applied is 777T for which the settlement reached around 155mm which is more than 10% of diameter of piles. Pile load test results was not satisfactory and compelled to increase the pile length approximately 20% of its total length. Due to unpredictable geotechnical parameters, length of each pile has been increased which is having a major impact on the project cost and as well as in project schedule. Extra bore holes have been planned along with lab test results in order to redefine the assumed geotechnical parameters. This article presents detailed design assumptions of geotechnical parameters in the design stage and the results of pile load test which made to redefine the assumed geotechnical properties.
Numerical Investigation on Performance of Expanded Polystyrene Geofoam Block in Protecting Buried Lifeline Structures
Expanded Polystyrene (EPS) Geofoam is often used in below ground applications in geotechnical engineering. A most recent configuration system implemented in roadways to protect lifelines such as buried pipes, electrical cables, and culvert systems could be consisted of two EPS geofoam blocks, 'posts' placed on each side of the structure, an EPS block capping, 'beam' put atop two posts and soil cover on the beam. In this configuration, a rectangular void space will be built atop the lifeline. EPS blocks will stand all the imposed vertical forces due to their strength and deformability, thus the lifeline will experience no vertical stress. The present paper describes the results of a numerical study on the post and beam configuration subjected to the static loading. Three dimensional finite element analysis using ABAQUS software is carried out to investigate the effect of different parameters such as beam thickness, soil thickness over the beam, post height to width ratio, EPS density, and free span between two posts, on the stress distribution and the deflection of the beam. The results show favorable performance of EPS geofoam for protecting sensitive infrastructures.
Experimental Study on Stabilisation of a Soft Soil by Alkaline Activation of Industrial By-Products
Utilising waste materials, such as fly ash (FA) and slag (S) stockpiled in landfills, has drawn the attention of researchers and engineers in the recent years. There is a great potential for usage of these wastes in ground improvement projects, especially where deep deposits of soft compressible soils exist. This paper investigates the changes in the strength development of a high water content soft soil stabilised with alkaline activated FA and S, termed as geopolymer binder, to use in deep soil mixing technology. The strength improvement and the changes in the microstructure of the mixtures have been studied. The results show that using FA and S-based geopolymers can increases the strength significantly. Furthermore, utilising FA and S in ground improvement projects, where large amounts of binders are required, can be a solution to the disposal of these wastes.
Electromagnetically-Vibrated Solid-Phase Microextraction for Organic Compounds
A newly-developed electromagnetically vibrated solid-phase microextraction (SPME) device for extracting nonpolar organic compounds from aqueous matrices was evaluated in terms of sorption equilibrium time, precision, and detection level relative to three other more conventional extraction techniques involving SPME, viz., static, magnetic stirring, and fiber insertion/retraction. Electromagnetic vibration at 300~420 cycles/s was found to be the most efficient extraction technique in terms of reducing sorption equilibrium time and enhancing both precision and linearity. The increased efficiency for electromagnetic vibration was attributed to a greater reduction in the thickness of the stagnant-water layer that facilitated more rapid mass transport from the aqueous matrix to the SPME fiber. Electromagnetic vibration less than 500 cycles/s also did not detrimentally impact the sustainability of the extracting performance of the SPME fiber. Therefore, electromagnetically vibrated SPME may be a more powerful tool for rapid sampling and solvent-free sample preparation relative to other more conventional extraction techniques used with SPME.
The Use of Piezocone Penetration Test Data for the Assessment of Iron Ore Tailings Liquefaction Susceptibility
The Iron Ore Quadrangle, located in the state of Minas Gerais, Brazil is responsible for most of the country’s iron ore production. As a result, some of the biggest tailings dams in the country are located in this area. In recent years, several major failure events have happened in Tailings Storage Facilities (TSF) located in the Iron Ore Quadrangle. Some of these failures were found to be caused by liquefaction flowslides. This paper presents Piezocone Penetration Test (CPTu) data that was used, by applying Olson and Peterson methods, for the liquefaction susceptibility assessment of the iron ore tailings that are typically found in most TSF in the area. Piezocone data was also used to determine the steady-state strength of the tailings so as to allow for comparison with its drained strength. Results have shown great susceptibility for liquefaction to occur in the studied tailings and, more importantly, a large reduction in its strength. These results are key to understanding the failures that took place over the last few years.
The Failure and Energy Mechanism of Rock-Like Material with Single Flaw
This paper investigates the influence of flaw on failure process of rock-like material under uniaxial compression. In laboratory, the uniaxial compression tests of intact specimens and a series of specimens within single flaw were conducted. The inclination angle of flaws includes 0°, 15°, 30°, 45°, 60°, 75° and 90°. Based on the laboratory tests, the corresponding models of numerical simulation were built and loaded in PFC2D. After analysing the crack initiation and failure modes, deformation field, and energy mechanism for both laboratory tests and numerical simulation, it can be concluded that the influence of flaws on the failure process is determined by its inclination. The characteristic stresses increase as flaw angle rising basically. The tensile cracks develop from gentle flaws (α ≤ 30°) and the shear cracks develop from other flaws. The propagation of cracks changes during failure process and the failure mode of a specimen corresponds to the orientation of the flaw. A flaw has significant influence on the transverse deformation field at the middle of the specimen, except the 75° and 90° flaw sample. The input energy, strain energy and dissipation energy of specimens show approximate increase trends with flaw angle rising and it presents large difference on the energy distribution.
Experimental Simulation of Soil Boundary Condition for Dynamic Studies
This paper studies the free-field response by adopting a flexible membrane container as soil boundary for experimental shaking table tests. The influence of the soil container boundary on the soil behaviour and dynamic soil properties under seismic effect were examined. A flexible container with 1/50 scale factor was adopted in the experimental tests, including construction, instrumentation and determining the results of dynamic tests on a shaking table. Horizontal face displacements and accelerations were analysed to determine the influence of the container boundary on the performance of the soil. The outputs results show that the flexible boundary container allows more displacement and larger accelerations. The soil in a rigid wall container cannot deform as similar as the soil in the real field does. Therefore, the response of flexible container tested is believed to be more reliable for soil boundary than that in the rigid container.
Liquefaction Assessment of Marine Soil in Western Yemen Region Based on Laboratory and Field Tests
Liquefaction is a major threat for sites consists of or on sandy soil. But this present study concentrates on the behavior of fine soil under cyclic loading. This paper presents the study of liquefaction susceptibility of marine silty clay to clayey silt for an offshore site near western Yemen. The submerged and loose sediment condition of marine soil of an offshore site can favour liquefaction during earthquakes. In this regard, the liquefaction susceptibility of the site was carried out based on both field test results and laboratory test results. From field test results of seismic cone penetration test (SCPT), liquefaction susceptibility was assessed considering normalized cone tip resistance, and normalized friction ratio and results give an idea regarding both cyclic mobility and flow liquefaction. Laboratory cyclic triaxial tests were also conducted on saturated undisturbed and remoulded sample to study the effect of cyclic loading on strength and strain characteristics. Liquefaction susceptibility of the marine soft soil was also carried out based on index properties like grain size distribution, natural moisture content and liquid limit of soil.
Using Micropiles to Improve the Anzali's Saturated Loose Silty Sand
Today, with the daily advancement of geotechnical engineering on soil improvement and modification of the physical properties and shear strength of soil, it is now possible to construct structures with high-volume and high service load on loose sandy soils. One of such methods is using micropiles, which are mostly used to control asymmetrical subsidence, increase bearing capacity, and prevent soil liquefaction. This study examined the improvement of Anzali's saturated loose silty sand using 192 micropiles with a length of 8 meters and diameter of 75 mm. Bandar-e Anzali is one of Iran's coastal populated cities which are located in a high-seismicity region. The effects of the insertion of micropiles on prevention of liquefaction and improvement of subsidence were examined through comparison of the results of Standard Penetration Test (SPT) and Plate Load Test (PLT) before and after implementation of the micropiles. The results show that the SPT values and the ultimate bearing capacity of silty sand increased after the implementation of the micropiles. Therefore the installation of micropiles increases the strength of silty sand and improving the resistance of soil against liquefaction.