Knowledge of particle shape and configuration-dependent thermal conductivity is necessary to investigate heat or water transfer in geomaterials, especially under freezing states. Thermal conductivity of a porous medium is affected by its matrix components and particle shapes. However, the particle shapes in geomaterials are various, and the effect of the ice phase on the thermal conductivity may increase substantially as ice content increases from unfrozen to freezing. In this study, a generalized thermal conductivity model for geomaterials is proposed based on phase transition theory and geometry approximation with respect to unfrozen and freezing states. Volumetric contents of each component and shape factors are required to predict thermal conductivities by the model. In order to evaluate the model, test results from both ours and previous literatures are employed to evaluate the calculated ones, and they match very well. In addition, compared with the other two models, i.e., a physical model and an empirical model, the proposed model is more reasonable and effective.

The paper presents experimental results of two Osterberg’s cell load tests (OLTs) and three conventional load tests (COLTs) in the same subsoil conditions on Continuous Flight Auger (CFA) piles carefully monitored during construction stages. The instrumentation along the pile shaft in all the tests allows interesting comparisons of both global behaviour and local load transfer. Significant differences in the stiffness of the soil-pile system with the different test procedures is outlined. The main differences between the two test procedures occur at the two opposite ends of the pile, as could have been expected, while the observed behaviour in the middle part of the tested piles is close for the two models. A relatively simple FEM model has been calibrated on the basis of the OLTs results. The same model is capable of accurately matching the experimental results of the COLTs, proving that the observed differences are not due to random factors. Furthermore, the same model has been used to simulate ideal load tests. Such a reliable simulation shows that both the experimental procedures are actually responsible for significant differences in the behaviour of the soil-pile system even in the simple case of a concentrated axial load. Large differences arise in terms of the stiffness of the system with the OLTs providing by far the stiffest response. Despite being intermediate between the OLT and the ILT, the COLTs provide a response of the pile-soil system, which is on the average about two times stiffer than the Ideal test, where the force applied on top of the pile does not depend on a tangible reaction system. Care should be thus taken when considering the results of such tests in the prediction of the settlement of a piled foundation. Correction factors should be applied to the experimentally observed behaviour.

Using pile foundations as heat exchangers with the ground provides an efficient and reliable energy source for the heating and cooling of buildings. However, thermal expansion or contraction of the concrete brings new challenges to the design of such structures. The present study investigates the impact of temperature variation on the mobilised bearing capacities of geothermal piles. The mechanisms driving the variations and redistribution of mobilised bearing forces along geothermal piles are identified using Thermo-Pile software. The EPFL and Lambeth College test piles are modelled and analysed as real-scale experiments. Three simple representative cases are used to investigate the impact of over-sizing geothermal piles on their serviceability. It is found that the mechanisms responsible for the variations and redistribution of mobilised bearing forces along the piles are unlikely to cause geotechnical failure, even if the ultimate bearing force of a pile is reached. Furthermore, over-sizing geothermal piles compared to conventional piles can have a negative impact on their serviceability.

The uncertainty in the spatial distributions of consolidation settlement (s_c) and time (t_p) for Songdo New City is evaluated by using a probabilistic procedure. Ordinary kriging and three theoretical semivariogram models are used to estimate the spatial distributions of geo-layers which affect s_c and t_p in this study. The spatial map of mean (μ) and standard deviation (σ) for s_c and t_p are determined by using a first-order second moment method based on the evaluated statistics and probability density functions (PDFs) of soil properties. It is shown that the coefficients of variation (COVs) of the compression ratio [C_c/(1 + e₀)] and the coefficient of consolidation (c_v) are the most influential factors on the uncertainties of s_c and t_p, respectively. The μ and σ of the s_c and t_p, as well as the probability that s_c exceeds 100 cm [P(s_c > 100 cm)] and the probability that t_p exceeds 36 months [P(t_p > 36 months)] in Sect. , are observed to be larger than those of other sections because the thickness of the consolidating layer in Sect. is the largest in the entire study area. The area requiring additional fill after the consolidation appears to increase as the COV of C_c/(1 + e₀) increases and as the probabilistic design criterion (α) decreases. It is also shown that the area requiring the prefabricated vertical drains installation increases as the COV of c_v increases and as the α decreases. The design procedure presented in this paper could be used in the decision making process for the design of geotechnical structures at coastal reclamation area.

This paper is devoted to numerical analysis of strength and deformation of cohesive granular materials. The emphasis is put on the study of effects of confining pressure and loading path. To this end, the three-dimensional discrete element method is used. A nonlinear failure criterion for inter-granular interface bonding is proposed, and it is able to account for both tensile and shear failure for a large range of normal stress. This criterion is implemented in the particles flow code. The proposed failure model is calibrated from triaxial compression tests performed on representative sandstone. Numerical results are in good agreement with experimental data. In particular, the effect of confining pressure on compressive strength and failure pattern is well described by the proposed model. Furthermore, numerical predictions are studied, respectively, for compression and extension tests with a constant mean stress. It is shown that the failure strength and deformation process are clearly affected by loading path. Finally, a series of numerical simulations are performed on cubic samples with three independent principal stresses. It is found that the strength and failure mode are strongly influenced by the intermediate principal stress.

Discontinuities in brittle geomaterials, including concrete and rock, represent localized zones of weakness and enhanced hydraulic transmissivity that often control the hydromechanical behavior of the medium. The shearing of discontinuities and the resulting morphological changes can significantly alter this behavior. In this work, a procedure is developed to characterize sheared discontinuity replicas as a function of the applied normal load using X-ray micro-computed tomography (micro-CT) imagery. A specimen design and testing procedure that facilitates CT scanning is presented along with an image processing procedure to quantify the morphological changes in the specimens. Subsequently, the results of direct shear testing and image-based measurements of mean fracture aperture, surface area, median effective aperture, and the preferential orientation of fracture void space are presented and discussed. Application of the procedure developed herein yields characteristics of the morphology of sheared discontinuities that were previously not possible to obtain or that were time consuming to collect with destructive sectioning methods.

This paper investigates the face stability of shield-driven tunnels shallowly buried in dry sand using 1-g large-scale model tests. A half-circular tunnel model with a rigid front face was designed and tested. The ground movement was mobilized by pulling the tunnel face backwards at different speeds. The support pressure at tunnel face, settlement at ground surface, and internal movement of soil body were measured by load cells, linear variable differential transducers, and a camera, respectively, and the progress of face failure was observed through a transparent lateral wall of model tank. The tests show that, as the tunnel face moves backwards, the support pressure at the tunnel face drops sharply initially, then rebounds slightly, and tends to be stabilized at the end. Similarly, the ground surface settlement shows a three-stage variation pattern. Using the particle image velocimetry technique, the particle movement, shear strain, and vortex location of soil are analyzed. The variation of support pressure and ground surface settlement related to the internal movement of soil particles is discussed. The impact of the tunnel face moving speed on the face stability is discussed. As the tunnel face moves relatively fast, soil failure originates from a height above tunnel invert and an analytical model is developed to analyze such failure.

The presented results of cyclic triaxial tests on sand demonstrate that the cumulative effects due to small cycles obey a kind of flow rule. It mainly depends on the average stress ratio about which the cycles are performed. This so-called “cyclic flow rule” is unique and can be well approximated by flow rules for monotonic loading. Amongst others it is shown that the cyclic flow rule is only moderately influenced by the average mean pressure, by the strain loop (span, shape, polarization), the void ratio, the loading frequency, the static preloading and the grain size distribution curve. A slight increase of the compactive portion of the flow rule with increasing residual strain (due to the previous cycles) was observed. These experimental findings prove that the cyclic flow rule is an essential and indispensable concept in explicit (N-type) accumulation models.

This paper presents results of an experimental work to determine a relationship between swelling pressure and suction of heavily compacted bentonite–sand mixtures. For comparison, tests were also carried out on heavily compacted bentonite specimens. A series of swelling pressure tests were performed using multi-step constant-volume method where suction of the specimens tested was reduced in a stepwise manner toward a zero value. The suction reduction was induced using vapor equilibrium and axis-translation techniques. It is shown that compacted specimens did not exhibit any collapse upon suction decrease and exhibited maximum swelling pressures at zero-equilibrium suction. The development of swelling pressure with decreasing suction of the specimens showed threshold suctions below which a further reduction in suction yields an increase in the swelling pressure of the same magnitude. The magnitude of threshold suction was found to be a function of bentonite content in compacted specimens.

Behaviour of granular soils subjected to internal erosion involves complex coupling between solid–fluid interaction, skeleton deformation and microstructural evolutions. This paper presents a micro–macro investigation on suffusion in idealized gap-graded and well-graded soils using the coupled computational fluid dynamics and discrete element method. The interaction between soil particles and seepage flow is modelled via momentum exchange between two phases. The progressive loss of fine particles subjected to upward seepage flow at various hydraulic gradients is investigated. The fines content, volumetric contraction and void ratio are monitored to identify the changes of macroscopic states of the soil skeleton. In addition, the microstructural evolution is tracked via particle-scale descriptors such as coordination numbers and force chain statistics. Several clogging–unclogging events which are responsible for the sudden changes of fines content and skeleton response are observed during suffusion. A parametric study indicates that the initial fines content and the hydraulic gradient significantly affect the kinetics of suffusion. Microstructural analyses reveal that the removal of fines is accompanied by the reduction in weak contact pairs and particles with low connectivity.