Non-isothermal behavior of excavation damaged zone around deep radioactive waste disposal

peer reviewedIndurated argillaceous rocks are being investigated as suitable hosts for high-level nuclear waste storage. An important aspect in evaluating the efficiency of waste disposal is the examination of the thermal impact's potential effects on the excavation damaged zone (EDZ) near the field. Increased temperatures could alter the EDZ's crack network, potentially leading to hydraulic failure through thermal pressurization. To accurately understand and model the EDZ surrounding repository cells at higher temperatures, it is essential to account for the coupled influence of thermal-hydraulic-mechanical (THM) phenomena in the constitutive model. Recent studies [1] underline two crucial behaviors in the thermomechanical response of argillaceous rocks: a gradual change in mechanical properties, such as strength and stiffness, with temperature that leads to a more ductile state at higher temperatures; and the occurrence of reversible expansive strains due to temperature increase, which, upon exceeding a specific threshold, turn into irreversible contractive strains

Working platforms for cranes – review of design approaches and recommendations for a safe design

peer reviewedThis paper provides a technical insight into the essential aspects to be considered in the proper design of a safe working platform for heavy construction machinery. Considering the complexity of the operational boundary conditions, the uncertainties of the ground characteristics and the variability of the loads applied by the construction machinery, a clear understanding of the possible failure modes and the definition of a criterion for the design of countermeasures seems to be essential in this application. This can be better achieved by considering the significant increase in cost and time delays associated with the failure of the working platforms. This paper discusses various possible failure mechanisms in the working platforms and examines the advantages of using geosynthetic reinforcing elements to avoid the risk of failure

The role of hydro-mechanical properties of the tail void grouting material in mechanized tunnelling

peer reviewedApplication of tail void grouting material during mechanized tunnelling has an influential effect on hydraulic and stress-deformation regime around the tunnel. In this study, the variation of the hydro-mechanical (HM) properties of the grout has been investigated through 3D Finite Element Method to better understand the interactions around the tunnel under various geological conditions. The model has been validated using available data of the hardening soil small strain (HSS) model. An advanced constitutive model accounting for time-dependent hardening has been assigned to the grouting material. The effect of the parameter variation in the grouting layer on the deformations and excess pore pressures is evaluated using a parametric analysis. According to the results, the hardening rate of the grouting material, compared to other input properties, has the most significant impact on the HM characteristics of the surrounding ground as well as axial forces in the lining

Automatic calibration of the SANISAND parameters for a granular material using multi-objective optimization strategies

peer reviewedThe parameter calibration of a constitutive model is a requisite to counter the uncertainty in the parameters and to approximate the simulation results effectively. Yielding a robust set of parameters for various test conditions is complicated as innumerable parameter combinations have to be investigated. In previous works, this calibration has been performed manually by trial and error without checking the robustness of the chosen parameters. Therefore, the present study introduces an automated calibration procedure using multi-objective optimization techniques. This assists in searching the parameter domain space extensively for better combinations that simulate the experiment results precisely. Though this approach is quite popular in various other engineering aspects, proposing the concept of calibrating the soil parameters and validating their efficiency has been always a challenge and interesting in this framework. In this research, SANISAND model parameters have been calibrated for crushed glass material under different triaxial conditions considering the barotropy, and pycnotropy effects. The results demonstrated that the optimized SANISAND parameters approximated the experiment results far better than manually calibrated results. This calibration approach facilitates in conserving the robust parameters besides dealing with time constraints and motivates the idea of adapting this automation platform to any constitutive model for significant approximations

Numerical investigation of geogrid back-anchored sheet pile walls

peer reviewedIn the last decades, geosynthetic reinforcement has been widely used in geotech-nical applications. Recently, geogrid has also been used to back-anchor sheet pile walls. However, this system has not received sufficient attention neither in research nor in construction. Due to the complex interactions between soil, geogrid and sheet pile wall, the applicability of common design guidelines for conventionally back-anchored walls to this particular system has to be proven. To develop a fundamental understanding about the influence of various components of the system on its behaviour, numerical investigations have been conducted within this study. In this paper the influence of geogrid inclination, design of geogrid-sheet pile connection including prestressing and geogrid position on the earth pressure distribution and wall deformation is discussed. The numerical results revealed that the position of geogrid and design of geogrid-sheet pile connection significantly affect the earth pressure distribution. The wall deformations are mainly influenced by the geogrid position

Behavior of closely spaced square and circular footings on reinforced sand

peer reviewedThis paper describes an experimental investigation conducted to evaluate the ultimate bearing capacity, the settlement and the tilt of two types closely spaced footings, one having square shapes and the other having circular shapes, on unreinforced and reinforced soil. To decrease the objectionable influence of interference on the performance of the closely spaced footings, the foundation soil is reinforced by geogrid layers. The results of this reinforcement show both positive and negative effects, namely, a positive effect because there is a considerable increase in the ultimate bearing capacity, and a negative effect because there is an increase in settlement and tilt. Regarding the experimental results, the negative effect of interference can be decreased considerably through the use of soil reinforcements. The ultimate bearing capacity of the interfering footings increased by about 25-40%, whereas the settlement of the interfering footings at the ultimate load increased in the range of 60-100%. However, the closely spaced footings tilted by approximately 45% and 75% for reinforced sand with one and two layers of geogrid, respectively. © 2012. The Japanese Geotechnical Society. Production and hosting by Elsevier B.V. All rights reserved

Interference effect of shallow foundations constructed on sand reinforced with geosynthetics

peer reviewedThis paper numerically examines the bearing capacity ratio for rough square footings located at the surface of a homogeneous sandy soil reinforced with a geogrid. The failure stage in the sand was controlled using the Mohr-Coulomb criterion and a non-associated flow rule. Numerical results were compared with those obtained from other experiments and were found to be in good agreement. A parametric study revealed the role of the distance between reinforcing layers and footings and the width and depth of reinforcing layers on the bearing capacity. The distribution of shear strain and displacement in the soil for both reinforced and unreinforced footings was investigated. In short, the results showed that the bearing capacity of interfering footing increases with the use of geogrid layers, depending on the distance between two footings. The best geometry and orientation of the geogrid layers were determined to achieve maximum bearing capacity for closely spaced square footings. Parametric studies demonstrated that the efficiency of reinforcement on the bearing capacity of interfering footings is greater than that on an isolated reinforced footing. In addition, reinforcement caused the bearing capacity of interfering footings to increase by about 1.5 and 2 for one and two reinforcement layers, respectively. Design charts are presented. © 2008 Elsevier Ltd. All rights reserved

Tail void grouting material: A parametric study on the role of hydro-mechanical characteristics in mechanized tunneling

peer reviewedThis paper investigates the influence of the hydro-mechanical properties of the tail void grouting material on short and long-term behavior of the tunnel. These characteristics are of high importance affecting the deformations and pore pressure regime around the tunnel as well as forces and deformations in the linings. Various properties of the tail void grouting material including thickness of grouting layer, permeability, stiffness, hardening ratio, shrinkage, and creep behavior are investigated using 3D Finite Element Method. The effect of each parameter variation on the representative surface settlements as well as deformations and excess pore pressures around the tunnel along with the axial forces and radial displacement of the linings has been thoroughly investigated. According to the results, a high hardening ratio corresponding to a fast-hardening grout could lead to 75% lower surface settlement. Utilization of a low permeable grout results in excess pore pressure remaining in the system which is 4.5 times higher than using a high permeable grout. The magnitude axial forces of the lining will depend on the direction of dissipation, when the permeability of the grout is concerned

Analysis of interfering circular footings on reinforced soil by physical and numerical approaches considering strain-dependent stiffness

peer reviewedThis paper numerically examines the bearing capacity, settlement, and failure kinematics of two closely spaced circular footings on reinforced soil. A number of large-scale tests are performed to identify the influence of the tilt of interfering footings on their ultimate bearing capacity and settlement, and these experimental results are used to verify the numerical model. Because the mobilization of shear strength in soil and tensile resistance in the geogrid depend to a large extent on the strain level (especially in small strains), a nonlinear elastic-plastic constitutive model in conjunction with a nonassociated flow rule is proposed. In addition, themodel accounts for the dependency of the friction and dilation angles on the strain level in the plastic domain. The constitutive parameters are calibrated for the triaxial loading test, whereas the numerical model for the closely spaced footings is verified with reference to the large-scale test results. Thereafter, the ultimate bearing capacity and settlement of interfering circular footings on reinforced soil are studied for different configurations, and the critical size and position of reinforcements that maximize the bearing capacity are characterized. Results show that the ultimate bearing capacity increases up to a maximum of 40 and 90% by the use of one and two layers of geogrid, respectively. Beyond the bearing capacity, the settlement of adjacent circular footings increases up to 45%(compared with a single footing with the same safety factor). Finally, the influence of reinforcing soil on failure kinematics and soil deformation pattern is investigated

Evaluation of the Installation Effect on the Performance of a Granular Column

The procedure of granular column installation impacts soil properties such as stress state, stiffness, and permeability in the near-field of the column. For an accurate and efficient design of relatively costly geostructures on improved subsoil with granular columns, a reliable estimation of the column installation effects on the properties of natural subsoil deposits is necessary. To achieve this goal, two phases are adopted in numerical simulations: (1) the installation phase based on the cavity expansion method using a 2D model, and (2) the construction phase in conjunction with the improved soil properties after column installation using a 3D model. The latter phase includes the construction of an embankment and the column is considered as an independent unit. The soil profile, i.e., stress and stiffness, is spatially updated from the first simulation (i.e., installation phase). In this frame, the stiffness was calculated according to a procedure suggested by the authors to determine the final stiffness based on the formulation of the Hardening Soil constitutive model. The numerical models were validated through a comparison with the recorded data of a field test obtained from the Klagenfurt site. Results of numerical analyses for the case study indicated that application of proposed methodology led to a more accurate estimate of the settlement, demonstrating that the installation effects have be taken into consideration to assure reliable evaluation of granular-column performance