1st International Conference on Geomechanics and Geoenvironmental Engineering (iCGMGE)
ISBN: 978-0-6480147-5-1

Abstract: Given the increasing demand for trains to carry heavier loads, current Australian ballasted rail networks require a significant amount of upgrading. Railroad ballast is an unbounded granular material that displaces laterally when subjected to repeated train loading. During track operations, ballast deteriorates due to progressive breakage and the infiltration of fine particles or mud-pumping from the underneath layers (e.g., capping, subgrade), which decreases the shear strength, impedes track drainage and increases the deformation of ballasted tracks. Rail track substructures can be reinforced by geosynthetics to reduce lateral displacements and optimise overall track performance. This paper presents the current state-of-the-art knowledge of rail track geomechanics based on research conducted at the University of Wollongong, including essential topics related to laboratory tests, computational modelling and field investigations undertaken to examine the improved performance of ballast by the use of geosynthetics. Full-scale monitoring of instrumented tracks supported by RailCorp and Australian Rail Track Corporation (ARTC) has been carried out to obtain data (i.e. measure the in-situ stresses and deformation of ballast embankments) that will reliably verify track performance as well as calibrate and validate introduced numerical simulations. This paper focuses on primary research and development of new design and construction concepts to enhance track performance using geosynthetics, whilst highlighting examples of innovations from theory to practice. These results provide promising approaches that can be incorporated into existing track design routines to cater for future high speed trains and heavier hauls.

Abstract: Traditional pipe installation and replacement involves extensive excavation of trenches along the full length of the pipeline that are both expensive and disruptive. To minimize those costs, many different ‘trenchless technologies’ have been developed by contractors and manufacturers, to permit pipe installation, pipe repair and pipe replacement using minimal earthworks. The inventive individuals and organizations that develop these techniques generally focus on development of the construction tools, materials and procedures, rather than the geotechnical (and structural) consequences of these methods, and so a variety of Geomechanics investigations are needed to establish how ground conditions influence the success or failure of such projects.
The presenter has worked for the last twenty years exploring the Geomechanics and soil-pipe interactions associated with trenchless technologies, and this lecture presents an overview of some of the associated research problems and their solutions. After introducing three of the commonest trenchless technologies, examples are presented illustrating how computational and experimental projects are being used to explain and quantify the underlying Geomechanics phenomena. First, pipe installation using horizontal directional drilling is introduced, and the Geomechanics research illustrated considering studies of mud transportation from the borehole as a result of blowout or hydrofracture. Next, pipe repair using liners is introduced, with description of research investigations of soil-pipe-liner interaction under earth loads. Finally, pipe replacement using static pipe bursting is explained, where studies have explained how cavity expansion and soil dilation lead to uplift at the ground surface and damage to overlying infrastructure.

Abstract: The landslides along the bank of the Three Gorges Reservoir can cause direct losses nearby the landslide, and threaten coastal people and properties due to potential landslide-triggered waves. Within the impoundment of reservoir water, many landslides reactivated or newly occurred during the rainy season and the annual periodic fluctuation. In this paper, it deals with the characteristics and deformation of Datangbang landslide which is located in the mid part of the reservoir. Based on historical data and field investigation, the deformations occurred mainly during the rainy season and the reservoir water level drawdown. For analyzing the influence of water level fluctuation and rainfall to the landslide stability, the factor of safety (Fs) under different situations is calculated. The key issue is to simulate the variation of groundwater level resulting from the influence of these two factors. The value Fs is calculated under the four summarized stages of reservoir water level combining with the corresponding rainfall or long-term rainfall at each stage. It is concluded that the stability of Datangbang landslide will be mainly affected by the reservoir water fluctuation and rainfall. The results show that the values Fs becomes higher at the rise stage and lower at the drawdown stage of reservoir water level. Moreover, rainfall generally causes the Fs to drop suddenly.

Abstract: This paper discusses the role of the degree of capillary saturation in modelling the coupled hydro-mechanical behaviour of unsaturated soils and proposes a new constitutive model for unsaturated soils by using the degree of capillary saturation and the effective inter-particle stress. In the proposed constitutive model, the shear strength, yield stress and deformation behaviour of unsaturated soils are governed directly by the above two constitutive variables. The model is then validated against a variety of experimental data in the literature, and the results show that a reasonable agreement can be obtained using this new constitutive model.

Abstract: Considering the context of sustainable building, energy consumption and greenhouse gas reduction, compacted earth is regarded as a promising non-industrial construction material. However, due to lack of scientific knowledge, there is currently no clear recognized guidance for their set-up, or means of measurement to guarantee their performance. In particular, the mechanical behaviour of earthen materials is strongly influenced by the water molecules which are adsorbed on the pore surfaces. In that context, in order to explore the hydro-thermo-mechanical behaviour of compacted earth, triaxial apparatus at controlled temperature and equipped with non-contacted sensors measuring system, was developed. The results show that the relative humidity at which the samples were stored have a strong impact on the mechanical characteristics of earthen material: both the maximum deviator stress fc and Young’s modulus E decrease with the increase of relative humidity, meanwhile, more plastic characteristics are observed. Non negligible swelling/shrinkage phenomena induced by variations of relative humidity are also observed. These results are eventually analysed in the light of a fully coupled poromechanical model which allows quantifying the evolution of the mechanical behaviour induced by daily variations of temperature and humidity.

Abstract: Common approaches to obtaining material parameters from soil water retention curves (SWRCs) are discussed and the typical mistakes made in the literature are highlighted. Particular attention is given to the evaluation of the air entry value (AEV) from the gravimetric water content based SWRCs. A consistent graphical approach for the determination of AEV based on an understanding of the effects of stress history and volume change on gravimetric water retention behaviour is presented. The robustness and application of the approach are demonstrated using an extensive set of experimental data from the literature.

Abstract: The design and construction of the underground Sydney Metro Northwest stations is delivered under two separate contracts. The temporary support (10 years) for the excavation, part of the Tunnels and Station Civils (TSC) contract, typically comprises prestressed ground anchors and soldier pile walls. The permanent support (100 years) and station structure, part of the Operations Trains and Systems (OTS) contract, comprises reinforced concrete station walls propped by station slabs constructed in front of the temporary support. Due to the limited design life of the temporary support, the ground pressure will ultimately be transferred to the permanent station structure. Therefore, the design of the station permanent walls requires modelling of the ground stress history due to the excavation, followed by modelling of the load transfer from the temporary support onto the permanent walls. Capturing this, as well as the beneficial effects of the stress relaxation due to the initial excavation, is crucial in achieving an optimised design for the permanent walls. This paper presents the integrated ground-structure interaction approach adopted for the permanent walls design at Norwest Station, which resulted in optimised design ground pressures and station wall thicknesses.

Abstract: This paper examines the failure and subsequent reinforcement design of the retaining structures under special conditions for a railway square in a mountainous area. The cause of the failure of the original design is discussed. A new scheme of keeping soils in front of retaining piles + diagonal bracing is proposed to re-design the retaining structures for railway square construction. A finite-element modelling is used to carry out detailed numerical analyses for different loading cases and verify the reliability of the reinforcement design. It is shown from the analyses that special attentions should be paid to the horizontal forces induced by diagonal braces. The construction results indicates that the proposed reinforcement scheme is effective and reliable.

Abstract: Operation of a chlorine manufacturing plant near Botany Bay, NSW, Australia resulted in mercury contamination in soil and groundwater. Site remediation included design and construction of an integrated groundwater and soil vapour containment system comprising a subsurface barrier wall up to 25 m deep, and a multi-layer cap designed to be compatible with ongoing site use as a paved hardstand for stockpiling operations. This paper presents a case history focusing on geoenvironmental engineering aspects of the design of the containment system. The paper presents the rationale for components of the design, including for the groundwater barrier wall: geometry, depth, hydraulic and vapour properties, construction method, and mix design. For the multi-layer cap design, topics covered include selection of material layers for vapour and infiltration control, design features for vapour monitoring and venting contingency, and landform shaping. Construction of the containment system occurred in 2015-2016, with the groundwater barrier wall formed using the cutter soil mixing method. The containment system notably provides combined groundwater and soil vapour management at a deep sand site with ongoing site use for industrial stockpile operations.

Abstract: Large diameter (>900mm) driven tubular steel piles have become a preferred footing system for support of buildings, bridges and other structures because of their relative ease of installation, high capacity and low cost and have played an important role in the Pacific Highway upgrade project. This paper will discuss a few case histories on driven steel tubular piles on recent highway upgrade projects on the east coast of Australia. Common practice, issues with design, installation and quality assurance via Pile Dynamic Analyzer (PDA) test and pile dynamic monitoring (PDM) will be discussed; drivability, unit shaft and base resistance as indicated from PDA tests will be compared with published data.

Abstract: A concrete arch culvert with reinforced soil wing wall structures was constructed on soft soil treated with nonconforming short dynamic replacement columns. A novel remedial design solution was developed which comprised (i) installation of remedial stone columns in the vicinity of the culvert and wing wall structures, (ii) provision of a detached connection system to allow for greater tolerable movement at the culvert-wing wall interface, and (iii) the use of a dead-man anchorage system to tie-back the ground beam that underpins the wall facing. This paper focuses on the numerical analyses of the arch culvert and wing wall structures, and compares the predictions with actual performance under short term loading conditions.

Abstract: In this paper, a number of infrastructure applications of ground improvement techniques used to address risk associated with construction over poor ground are discussed. In each case, the key design issues and associated risks are described, and the ground improvement methods used described. This paper outlines the projects, discusses geotechnical risks associated with soft ground, presents details of the ground improvement works, and discusses ground improvement selection, design, and construction monitoring. Examples from projects in Asia and Australia of how requirements for cost and programme savings have driven innovations in design and new developments in ground improvement are discussed. Established approaches to managing geotechnical risks on projects are briefly reviewed.

Abstract: Predicting water flow in partially-saturated soils, using the Richards equation, is important for a range of science and engineering problems. Unsaturated material properties, such as the water retention curve and the unsaturated hydraulic conductivity function, are usually expensive, time-consuming and difficult to measure experimentally. Inverse solutions of the Richards equation offer one alternative to experimental determination. However, the doubly-iterative process of inverting a highly non-linear partial differential equation such as the Richards equation leads to computationally expensive algorithms, and the choice of inverse solvers is critical in developing efficient inverse solution tools.
The paper assesses the performance of two popular inverse solution algorithms, the Levenberg-Marquardt Algorithm and Genetic Algorithms, and evaluates their comparative ability to invert the Richards equation accurately and efficiently. Tools are built using a forward-solver of the Richards equation based on the Finite-Element Method developed at the University of Sydney, and inverse algorithms available in Matlab. Using a simple 1D infiltration problem as a case, the inverse solver is assessed for a range of values for the difference between number of unknowns and number of observation points, as well as different levels of proximity of initial estimate to actual solution. For the case studied here, both algorithms generate accurate solutions; however, the Levenberg-Marquardt algorithm appears to be more computationally efficient.

Abstract: In this study, the influence of an underground opening at different depths on seismic performance of a 15-storey moment resisting building subjected to the 1995 Kobe earthquake is investigated. The numerical model consists of a superstructure, soil medium, and an underground opening, all simulated using finite element method in time domain considering soil nonlinearity and soil-structure interaction. The results are presented in terms of foundation rocking angle, distribution of maximum shear force developed in the structure, maximum lateral deflection as well as inter-storey drifts of the building. The results indicate that the underground opening has a notable influence on seismic response of the building. Particularly, the maximum foundation rocking angle is reduced with the presence of the underground opening with stiff concrete lining and the reduction is more significant when the underground opening is constructed at a lower depth. In addition, for a shallower underground opening, as the foundation rocking decreases, seismic energy dissipation is reduced, which in turn, causes more seismic energy transmitted to the structure and consequently larger shear forces are developed in the structure, which reveals the importance of consideration of underground structure in the seismic design of superstructures. Moreover, according to the results, the building constructed above a shallow underground opening experiences relatively smaller lateral displacement and inter-storey drifts subjected to earthquake excitation.

Abstract: In this study the smear zone were characterised using undisturbed samples collected at various locations after vertical drains were installed in the field. The aim was to determine more realistic smear zone characteristics in relation to the in-situ structure of soil. The extent of the smear zone for Ballina clay was determined on the basis of normalised permeability (kh/khu), the change in soil compressibility and a reduction in the water content. The permeability and compressibility of the soil were investigated to determine the extent to which the soil surrounding the PVD had become disturbed.

Abstract: Dynamic wetting and dewetting behaviours in multiphase flow have a significant influence on many geotechnical applications, such as unsaturated soil mechanics, carbon geosequestration, and oil recovery. In this paper, a smoothed particle hydrodynamics (SPH) method with an inter-particle force formulation is applied to simulate capillary interactions, involving surface tension and dynamic contact angle effects. In particular, the frictional boundary condition at liquid-solid interface is critical in dynamic simulations, while the traditional treatment requiring arbitrary friction or dragging force can neither reflect the complex interaction between different phases nor contain direct links to physical quantities. Therefore, we introduced an interfacial viscous force in the SPH to replicate realistic dynamic behaviour of fluid-solid interactions. The interface of fluids with different surface tension and wettability between different phases can be reproduced by adjusting liquid-liquid and liquid-solid inter-particle force parameters respectively. Through parametric studies, other physical properties predicted from the model including density, viscosity and compressibility are also implemented and can be altered for various constituents. The capillary tube scenario was studied, containing fluid particles with shifting substrate to generate wetting and dewetting phenomena. Dynamic contact angles were recorded under different moving speeds of the contact line. After analysing results from different moving speeds, the dynamic contact angles and corresponding capillary numbers can be correlated by a power law. This result is in a good agreement with the experimental observations under dynamic loading conditions. The simulations have demonstrated that the proposed numerical model accounts for the pore-scale effects, including dynamic contact angle and surface tension, and can be used for simulating multiphase flow in geomaterials.

Abstract: In recent years, utilisation of geothermal energy is becoming more popular worldwide. Such technique helps people to reduce the carbon footprint by less consumption of air-conditioning and it can be considered as one of sustainable energy resources. The geothermal energy pile is one of solutions combining properties of ground heat source exchangers (GHSE) and structural functions. In this paper, thermo-mechanical behaviour of geothermal energy piles was studied by using finite element analysis (FEM). To find mechanical response of energy piles, the numerical simulation is established to investigate safety performance of geothermal energy piles under different loading conditions. The thermal expansion for energy piles and surrounding soil are considered during operation. Individual thermal loading cycles and multiple thermal loading cycles are also presented in this study for short- and long-term performance. As the pile is heated and cooled, axial displacement of pile settles and heaves, respectively. It was found that relatively stationary settlement will be achieved after several heating and cooling cycles. Stabilised settlement behaves linearly with temperature variation and formed a different stiffness slope with the pile free expansion line. Moreover, 30 thermal cycles were performed to study long-term behaviour of the energy pile settlement. The preliminary results could warrant further studies for the serviceability design of geothermal energy piles.

Abstract: In unsaturated granular media, the flow phenomena and patch formation of the liquid involve interactions among different constituent phases, including gas, liquid and solid, and are of significance in geotechnical and geo-environmental engineering, including unsaturated soil mechanics, groundwater remediation and oil production. In this paper, in order to study these multiphase flow phenomena in granular media, we adopted an open-source CFD platform (OpenFOAM, in particular the interFoam solver for considering multiple fluid phases) and implemented the specific material parameters, including the contact angle, density, viscosity and surface tension, which were obtained from corresponding experiments. Inside the pore space, the classic Navier-Stokes equations considering the mass and momentum balance are solved by the Volume of Fluid (VOF) method tracking the temporal and spatial evolution of liquid-gas interfaces. Drainage procedure under different conditions in granular media with specified grain size and porosity have been simulated. It is found that the patch formation phenomena are controlled by capillary force and the wettability of the granular packing, i.e., the surface tension and contact angle, as well as the viscous force, i.e., the viscosity. Finally, the results of direct numerical simulation presented here quantitatively study the laws of water patch formation.

Abstract: Modern engineering solutions which exhibit a change in the natural ground temperature require a better understanding of the fundamental behaviour of soils with respect to temperature. Examples include; energy piles, nuclear storage, and novel construction techniques such as freezing or heating. A temperature change can affect soil settlement/volume, as well as its strength characteristics. The response is complex, a function of numerous factors including; material type/composition, stress history, drainage condition, loading, and time. This paper presents results from triaxial tests performed on reconstituted kaolinite using multiple stress histories to investigate the impact of temperature on consolidation behaviour and undrained shear strength.

Abstract: The most realistic approach to numerically simulate a Deep Cement Mixed (DCM) column-supported field embankment is the use of a three-dimensional (3D) finite element model. However, two-dimensional (2D) plane-strain numerical models are popular compared to 3D models due to the efficiency in computational time and computer memory. When a column-supported embankment is modelled using a 2D plane-strain model, the individual columns are converted into equivalent column walls and it is assumed that the strains do not change in cross sections along the longitudinal direction of the embankment. During the conversion, material properties or the geometry of the columns are modified based on the conversion method applied. According to the literature, 2D plane-strain idealisation based on equivalent area (EA) method yields the results closest to the 3D model predictions and field measured data. However, all these studies are carried out considering the elastic or elasto-plastic behaviour for columns. As far as the mechanical behaviour of DCM columns is concerned, DCM columns experience strain-softening beyond yielding. The column strength reduces during the strain-softening resulting large deformations in the improved ground. If a constitutive model, which has the ability to simulate strength reduction based on the level of plastic strains, is adopted to simulate the softening behaviour, the accuracy of predicted embankment behaviour is largely depend on the plastic strains developed in DCM columns. Hence, results of a 2D model and a 3D model differ to a large extent. The aim of this study is to investigate this problem in detail and to propose an approach to obtain an equivalent set of parameters for the softening incorporated constitutive model to obtain realistic predictions for a field problem using both 3D and 2D numerical models.

Abstract: The construction of underground expressway has been receiving a great attention as the solution to unban traffic congestions in Korea. In this study, a main double-deck tunnel with a ramp tunnel constructed as a part of the underground expressway is considered. A numerical analysis using FDM was performed for the case in which a right directional ramp tunnel of 1-level is diverging from a main double-deck tunnel of 2-level. For the main tunnel and the diverging tunnel in different geometrical configurations at the divergence section depending on diverging conditions, the stability was investigated by using the Mohr-Coulomb failure proximity approach. The results showed that horizontal divergence condition is the most unfavorable in terms of stability.

Abstract: Integral abutment bridges (IABs) provide an attractive alternative to bridges with expansion joints as they minimise the construction cost and eliminate the costly and traffic retarding maintenance works associated with the expansion joints. However, the settlement of the soil at the bridge approach and the escalated lateral earth pressure acting on the abutment are inherent problems in IABs. These problems are induced by the abutment movements in response to the thermally induced expansion and contraction of the superstructure of the bridge. The aforementioned issues have limited the lengths of IABs in practice. The approach settlement and lateral stress ratcheting effects vary from one IAB to another depending on the factors such as the length of the bridge, the amplitude and number of abutment displacement cycles, in addition to the way in which the abutment moves. In this research, a small wall experimental model has been used to study the effects of different modes of wall movements. The first part of this article investigates the influence of the mode of wall movement on the soil settlement and the lateral earth pressure acting on the wall. In the second part, the effectiveness of expanded polystyrene geofoam (EPS) as a compressible inclusion, to alleviate the approach problems in IABs, has been discussed.

Abstract: Soil liquefaction during earthquakes is one of the most destructive and complicated phenomena and has caused extensive damage to buildings, lifelines and earth embankments. The energy based procedure, which defines potential of liquefaction in saturated sandy soil subject to dynamic loads, is used in this study to present new equation for evaluating strain energy for triggering liquefaction. To achieve this goal, a dataset of high quality laboratory test of cyclic simple shear, cyclic triaxial, and cyclic torsional tests were collected from the literature with 6 input soil parameters and strain energy for triggering liquefaction as a target. Then, through a new tool, namely the Response Surface Method (RSM) new equation was presented. The RSM equation is generated on full quadric base due to main Designs of experiment (DOE) of Central Composite. Foremost, an Artificial Neural Network (ANN) was employed to model correlations between soil parameters and liquefaction resistance determining coded input values for design of experiment (DOE) for the RSM. Next, to demonstrate the accuracy and capability of the presented equation, they were applied to calculate strain energy with a new dataset and results were compared with other correlations and models published previously. Finally, a sensitivity analysis is performed using Monte Carlo Simulation (MCS) to show the influence of soil parameters and their uncertainties on the probability of liquefaction.

Abstract: Sulfuric acid induced volume changes and consequent distress to the industrial structures has been reported in a number of cases in the past few decades. The exponential growth of costs required for repair of such structures necessitates a better understanding of soil behavior subjected to acid contamination to plan proper control measures. Thus, an attempt is made in the present study to evaluate the influence of sulfuric acid contamination on the volume change behavior of black cotton soil and to assess the potential of fly ash to control the induced volume changes. Formation of sulfate based minerals leads to an increase in swelling and a decrease in compressibility of soil during sulfuric acid contamination. Results of fly ash amended soils subjected to sulfuric acid contamination indicate a marginal reduction in swelling and compressibility than the original soil. The mineralogical and morphological studies indicated that the formation of sulphate minerals and consequent microstructural changes were similar in original soil and fly ash amended soil during sulfuric acid contamination. Based on the study, it can be concluded that the addition of fly ash did not show a supplementary advantage in soil prone to sulfuric acid contamination.

Abstract: The construction of underground expressway has been receiving a great attention as the solution to unban traffic congestions in Korea. In this study, a main double-deck tunnel with a ramp tunnel constructed as a part of the underground expressway is considered. A numerical analysis using FDM was performed for the case in which a right directional ramp tunnel of 1-level is diverging from a main double-deck tunnel of 2-level. For the main tunnel and the diverging tunnel in different geometrical configurations at the divergence section depending on diverging conditions, the stability was investigated by using the Mohr-Coulomb failure proximity approach. The results showed that horizontal divergence condition is the most unfavorable in terms of stability.

Abstract: Clay minerals exhibit mineralogical transformations when interacted with chemicals. Alkalis used in industries are one such example. Understanding the mechanism of change in plasticity properties of soils due to alkali interaction would be of great use to explain the variations in their geotechnical properties, as plasticity properties are always an indicative of engineering properties. Type and concentrations of alkali, duration of interaction and type of the mineral are the prime factors causing mineral transformations. So, in the present study efforts are made to understand the influence of alkali solutions on the plasticity properties and also on the mineralogy of red earth possessing kaolinite mineral at different periods of interaction. Two types of alkalis namely sodium hydroxide and potassium hydroxide of 8N have been selected in this study. Duration of interaction maintained was 7, 14, 28 and 56 days. The results showed that changes in the plasticity properties of red earth in the presence of NaOH are comparatively more than that of KOH. The changes observed have been explained with the help of new mineral formations by X-ray diffraction studies. Detailed XRD analysis revealed that sodalite at all curing periods are majorly formed in NaOH where as in KOH muscovite (hydrogen aluminum potassium silicate), microcline (potassium aluminum silicate) and rectorite (potassium aluminium silicate hydroxide hydrate) are formed. Effect of 8N NaOH on mineralogical transformations is predominant when compared to 8N KOH. Thus the type and intensity of new mineral formations largely depend on type of alkali and the duration of interaction period.

Abstract: The time-dependent response of rocks is strongly influenced by the presence of pore fluids, particuarly for unsaturated materials. This paper presents a theoretical framework for modelling the coupled creep and damage behaviour of unsaturated rocks based on thermodynamic principles. The coupled phenomena of delayed inelastic strains and microcracks are modelled using the theories of viscoplasticity and continuum damage mechanics, both governed by a plastic effective stress. This framework strikes a balance between different requirements in constitutive modelling: capability to reproduce experimental observations, simplicity for practical use and thermodynamic consistency. The relevance of the model is illustrated by confronting its predictions to experimental data.

Abstract: In this paper, a new type of elements called radiation discs is introduced to model dynamic pile-soil-pile interaction and to deal with the radiation conditions at infinite domains. The pile group system can be modelled using beam-column elements, while the radiation discs are defined at the nodal points of the elements to model the pile-soil-pile interaction. A Boussinesq-type loading distribution is proposed to act on the discs to achieve the proper mode of deformation at the cross sections of piles. Using radiation discs, the discretisation of the domain is only required along the length of piles, while the discretisation of soil medium, top free surface boundary, and cross sections of piles are avoided. Numerical examples are presented to demonstrate the application of the method and to investigate the influence of excitation frequency and pile spacing on dynamic response of pile groups.

Abstract: In this paper, an extended finite element (X-FEM) framework is proposed to explore the influence of the laminar and turbulent flow regimes for the fracturing fluid inflow on hydraulic fracturing process. The fracturing fluid flow is modelled by taking advantages from the flow and continuity equations within the fracture faces. The momentum balance of the bulk governs the overall behaviour of the surrounding bulk. The X-FEM enrichment strategy is adopted in order to account for the discontinuous displacement field due to the fracture body. Meanwhile, the nonlinearities associated with the stress field in the vicinity of the crack tips is captured by using the cohesive fracture model. The coupling between the fluid and solid phases is carried out by employing the staggered Newton procedure. The development of the laminar or turbulent flow regimes along the flow path line is recognized by using the well-known Reynolds number. Energy loss due to friction along the fracture faces is incorporated by applying the Darcy-Weisbach equation. Using the proposed formulation, the profile for the fluid pressure associated with the laminar/turbulent fracturing flow regimes is deduced. Finally, through several numerical simulations the robustness of the developed framework is illustrated. Meanwhile, the significance of the current study is highlighted by comparison of the results with those neglecting the effects of the turbulent flow regime.

Abstract: Diaphragm wall or Trench-cutting & Re-mixing Deep wall (TRD) directly embedded into the bedrock have been primarily adopted in Wuhan as a form of waterproof cut-off wall for excavations. However, the installation of diaphragm wall is expensive; the corners of TRD wall are vulnerable to seepage and the advantages of TRD method cannot be fully taken for an irregular cut-off wall involving more corners. This paper will discuss the constructability, quality and waterproof properties of a Cutter Soil Mixing (CSM) cut-off wall under high groundwater pressure through a case study of deep excavation for a medical complex construction in Wuhan. By investigating the technical scheme, construction method, costs and effect on the environment, CSM wall has been found to possess sound waterproof properties and can be installed in advance which will shorten the construction time. CSM wall is more cost-effective and environmentally-friendly than diaphragm wall or TRD wall and offers an new option for cut-off wall design in Wuhan.

Abstract: The need for sustainable asphalt mixture design is becoming a priority within pavement industry. This trend is necessitated by high rate of construction and demolition waste, pressing demand on landfill sites. Recycled Construction Aggregate (RCA) is one of the potential options for utilization in pavement construction. Therefore, the feasibility of partial substitution of virgin aggregate in hot-mix asphalt (HMA) with RCA is investigated in this research project. RCA differs from virgin aggregate because of the cement paste which is attached to the surface of the virgin aggregates as well as the variety in its composition. This highly porous cement paste and the variation in quality of RCA results in the lower particle density and higher porosity, and subsequently higher bitumen absorption and wet/dry strength variation.
However, the test results demonstrate that some parameters such as flakiness Index and particle shape have a smaller value in RCA compared to virgin aggregates. These parameters are two dominant characteristics which have significant impact on asphalt mixture strength and stability. This paper presents some of the results of an investigation on the feasibility of utilization of RCA in asphalt mixtures. For this purpose, firstly, a preliminary experimental study is conducted to evaluate the properties of RCA as an alternative for natural aggregate in asphalt mixture under different combination and percentages with virgin aggregates. The aggregate properties studied in this preliminary level were flakiness index, particle shape, water absorption and particle density, wet/dry strength variation, crushing value, and weak particles.
Based on the results obtained from the aggregate specification tests on unbound RCA, in the second step, different asphalt mixtures incorporating substitutions of coarse virgin aggregate with 25% and 50% RCA were prepared and evaluated through gyratory compaction method; the optimum bitumen contents were found to be 5.1%, 5.8 and 6.2% of C320 bitumen, respectively.

Abstract: The slip line theory is applied to the problem of an axisymmetric retaining wall interacting with unsaturated soil. The slip line governing equations express the limiting equilibrium condition of a Mohr-Coulomb soil. A linear variation of the contribution of suction to the effective stress with depth is assumed. Both active and passive failure modes of a rigid wall are considered. The plastic critical depth for unsaturated soil failing in an active failure mode is discussed. Assuming the circumferential stress to be the minor principal stress causes higher passive lateral earth pressure. It is shown that adopting the effective stress concept enables the influence of suction in unsaturated soils to be considered in a simple way. The influence of the contribution of suction to the effective stress is found to be significant.

Abstract: An integral barrier-retaining wall system is a reinforced concrete retaining wall with a fully integrated traffic barrier. When a vehicle hits the barrier, this collision impact must be resisted by the barrier, the retaining wall and the soil foundation. In fact, the vehicle collision is a very short transient dynamic loading over a small impact zone. However, for geotechnical design, when considering stability of the whole system, the establishment of equivalent uniformly distributed loads for the plane-strain case is perhaps more important than the ultimate dynamic loading. To obtain these equivalent loads, it is essential to understand fundamentally how the impact loading transmits from the impact point and time to the broader structure. Hence, in this paper, a full-scale Test Level 4 (TL-4, corresponding to regular traffic in AS5100.2) vehicle crash test on a 3-m-high concrete retaining wall integrated with a 1.2-m-high traffic barrier was performed numerically and the effects of the impact loading on such integral barrier-retaining wall system were studied. The magnitude and duration of the impact loading from vehicle collision were obtained from the model. An influence length, which is used to establish equivalent uniformly distributed loads, has been discussed. According to the numerical results, the maximum loads in the transverse, longitudinal and vertical (downwards) directions are 279.65 kN, 78.44 kN and 71.04 kN, respectively. These forces correspond to the design loads specified in AS 5100.2:2004.

Abstract: Drying induced cracking in colloidal films is of fundamental interest in nature and various industrial applications. The cracking morphologies are in varied forms from the planet surface to the oil painting. A lot of industrial raw materials come in the granular form, and are used to mix with the liquid. For all the above, the first thing is to understand the details of the desiccation procedure. Evaporation from porous media is a complex pore scale transport process, which can be affected by many factors such as temperature, liquid phase distribution, the scales of the particles. Especially, evaporation from soil affects energy balance, land surface-atmosphere interactions. It is known that the crack patterns are the signature of the particles, solvent and substrate type, the drying conditions and the film thickness. Lazarus(2011) studied the influence of layer thickness on the crack patterns induced by desiccation, and found that the crack patterns can vary from craquelures to spiral with different thickness. Smith(2011) performed experiments on compliant elastomer surfaces in which the level of constraint was varied by changing the substrate modulus and gave a theory to describe the substrate modulus dependence of the cracking length scale. Lucas(2016) investigated how a substrate’s shape affects the appearance of cracks above it by preparing mud cracks over sinusoidally varing surfaces and found that the observed crack patterns changed from wavy to ladder-like to isotropic as the thickness of the cracking layer increased. Shokri(2015) found that the crack spacing could be changed by putting salt into the colloidal film, and the crack spacing had a positive correlation with salt concentration. However, the effect of water content on the crack pattern induced by desiccation has yet to be quantified.

Please click here to download iCGMGE2017 Proceeding.