Geotechnics, Volume 2, Issue 2 (June 2022) – 11 articles

In this paper, the design of a new laminar shear box at the Laboratory of Earthquake Engineering and Dynamic Analysis (L.E.D.A.) of the University of Enna “Kore” (Sicily, Italy), is presented. The laminar box has been developed to investigate the liquefaction phenomenon and to validate advanced numerical models and/or the numerical approaches assessed to simulate and prevent related effects. The first part of the paper describes in detail the types of soil containers that have been used in the last three decades around the world. Particular attention is paid to laminar shear box and liquefaction studies. Moreover, the most important factors that affect the performance of a laminar shear box are reported. The last part of the paper describes components, properties, and design advantages of the new laminar shear box for 1g shaking table tests at L.E.D.A. The new laminar box has a rectangular cross section and consists of 16 layers. Each layer is composed of two frames: an inner frame and an outer frame. The inner frame has an internal dimension of 2570 mm by 2310 mm, while the outer frame has an internal dimension of 2700 mm by 2770 mm. Between the layers, there is a 20 mm gap, making the total height 1600 mm. Full article

Historically, empirical relations are the basis of everyday foundation design. These relations, however, rely on specific datasets, which may not represent the true conditions observed in the field. Even in situ tests rely on empirical correlation formulas, which link observed phenomena to soil properties. These correlations should be updated according to the specific design conditions. Big data (BD) workflows enable the use of massive data available to update the correlations and to provide more accurate predictions of the parameters studied. Thus, in this paper, a BD approach is used to study the relation between the drilling process of continuous flight auger piles and the shear strength properties (SSPs) of the surrounding soils. Soil surveys were carried out to identify the soil strata in the site and to validate the estimates of the SSPs. The results show that indirect measurements are in accordance with typical undrained shear strength and friction angles of the materials considered. Full article

The Screw Driving Sounding (SDS) is a recently developed in-situ testing method for soil/site characterisation. To better understand the mechanism of testing, it is essential to create a simulation model for the SDS test to assist in better understanding the response and in improving the testing process, not to mention the development of empirical correlations to estimate geotechnical parameters for use in design. Complex problems involving large deformations are usually difficult to solve with the classical finite element (FE) method because large deformations can lead to large mesh distortions and contact problems. In this paper, a computational model using the finite element method is developed to simulate the drilling process involved in SDS tests; the Coupled Eulerian-Lagrangian (CEL) approach is used to deal with large deformation problems. The SDS drilling process in a sandy deposit with defined stress states (i.e., relative density and effective confining pressure) is simulated, and the SDS-derived parameters are monitored. Based on the simulation results, a chart was established to correlate the measured SDS parameter with the internal friction angle for different vertical effective overburden stresses. The derived chart is validated with the results of laboratory tests performed on samples taken from several sites in Christchurch, NZ, adjacent to the locations of the SDS tests. The results show that the CEL FE framework can model complex physical processes encountered during the SDS drilling. Moreover, the developed chart can be used to estimate the friction angle of the sandy soil based on the SDS-measured torque at a given depth. Full article

This paper reports on preliminary yet consistent studies and results around the concept of meta-material applied to the protection of buried gas transmission pipelines. The capacity of the proposed meta-material layout in attenuating and dissipating the energy induced by a surface explosion is described in general terms, and then it is examined for a set of nine realistic cases. The formulation of the band gaps, which are considered zones of mitigation for the incident waves of certain frequencies, composes the core of the analysis. For the calculation of the band gaps that target a specific range of frequencies, the 1D periodic structures’ theory is adopted, and the results have been verified numerically via COMSOL. The layout is tested for nine cases of surface explosions via finite element analyses in ABAQUS, using the CONWEP model for simulating the surface explosions. Extremely satisfying results are demonstrated regarding the reduction in the vertical and horizontal displacements of the buried steel pipe. The outer goal of the present study is to spotlight the implementation of meta-material concepts for the efficient blast protection of underground structures, addressing a major hazard for this type of structure and a gap in the current literature. Full article

An assessment of evaporation losses from soils is critical for sustainable agriculture in semi-arid regions. The purpose of this research was to determine the effect of desaturation and shrinkage on evaporative flux from representative soils. Results indicated that the surface area did not change for silty sand (6% volume reduction) and substantially increased for lean clay (17% volume reduction). The evaporative flux for silty sand decreased from 31 to 25 mg/m²∙s in Stage II, remained constant during Stage III, and decreased to 11 mg/m²∙s in Stage IV. In contrast, the lean clay showed a longer Stage II (34 to 14 mg/m²∙s), a near constant Stage III, albeit a similar Stage IV (13 to 3 mg/m²∙s). The air entry and residual suction values were 1 kPa and 100 kPa for silty sand and 5 kPa and 1400 kPa for lean clay. In both soils, the total suction merged with the matric suction at Stage II–Stage III boundary. Furthermore, the shrinkage curve was J-shaped for silty sand with the only void ratio decrease in Stage II, whereas that for the lean clay showed a significant void ratio decrease in Stage II, marginal decrease in Stage III, and no decrease in Stage IV. Under high demand, the silty sand exhibited Stage III and Stage IV evaporation, whereas the lean clay also showed significant flux during Stage II. For the investigated range of water content, the total water loss under high demand was found to be 7 times that under low demand. Full article

Pavement thickness is a very vital component during the design stage of a road construction project. Pavement design helps to determine the costs of the project over a certain period to ascertain how the cost of road pavement construction affect the life cycle cost of the road. Road pavements are designed based on the type of subgrade material and the expected traffic load to help clients and decision-makers make decisions on the project. In this study, expansive road subgrade materials were improved using lime and cement and their California Bearing Ratio (CBR) was used in road pavement design. The study used the Design and Manual for Roads and Bridges (DMRB) as a guide to investigating the effect of stabilised expansive road subgrade with varying CBR values on road pavement design. The mineral structure, characteristics, Atterberg limit, compaction CBR, swell and microstructural analysis (scanning electron microscopy (SEM) and Energy Dispersive X-ray (EDX)) of stabilised subgrade materials were investigated. The results show an increase in California Bearing Ratio (CBR) values and a reduction in swell values while curing age increased for stabilised subgrade materials. Treated samples show high Calcium Silicate Hydrate (C-S-H) gel formation after 7 and 28 days of curing. The thickness of road pavement was observed with an increase in CBR values. The study established that the thickness of road pavement and overall construction cost can be reduced using cement and lime as additives in subgrade stabilisation. Full article

There are many empirical equations published for unsaturated fine-grained soils. However, there is only one empirical equation established for silty sand using the shear-box test and filter-paper-based suction test, but with the suction range of 0 to 200 kPa. It is reported that there is a significant discrepancy between the predicted values and test results of apparent cohesion within the range of 0 to 100 kPa for unsaturated coarse-grained soils. The purpose of this research is to study the effect of water content on apparent cohesion and predict apparent cohesion for coarse-grained soils within the range of 0 to 100 kPa using shear-box test and suction test results without much inconsistency. In this research, soil samples from the rainfall-induced landslide sites were obtained; laboratory tests such as soil-classification tests, shear-box tests and consolidated undrained triaxial tests were carried out. Test results were analyzed, and the findings are presented. When the water content is increased from 0% to 30%, there is a reduction of 89% in apparent cohesion on average. A newly developed prediction model for apparent cohesion based on the low range of matric suction from 0 to 100 kPa for unsaturated coarse-grained soils is introduced in this paper and compared with published models. Full article

In this article, a quantitative numerical study of the random distribution of the soil material parameters to the probability density functions of the failure load and failure displacements of a shallow foundation is presented. A modified Cam-Clay yield function is used for this scope into a stochastic finite element numerical formulation. Several hypotheses for the random distribution of the compressibility factor $\kappa$, of the material constitutive relation, the critical state line inclination c of the soil, as well as of the permeability k of the continuum, have been tested and assessed with Monte Carlo simulation accelerated with Latin hypercube sampling. It is validated that both failure load and failure displacements follow Gaussian normal distribution despite the non-linear behaviour of the soil. Furthermore, as the soil depth increases, the mean value of failure load decreases and the failure displacement increases. The failure mechanism of clays can be determined with accuracy using this numerical implementation, without the restrictions imposed by analytical solutions, taking into consideration the eccentricity of the load in combination with non-linear constitutive relations. Full article

Groundwater level plays an important role in triggering landslides. In this paper, Distinct Element Method is used to investigate the impact of groundwater table fluctuation on the stability of jointed rock slopes. For this purpose, 110 cases including different number of joint sets, joint friction angles, joint spacings, and joint angles are considered and the influence of changing groundwater level on the stability of a jointed rock slope is investigated through a series of parametric studies. This study shows that the factor of safety for slopes can decrease significantly with increasing the groundwater level, and the impact is more significant on slopes with steeper joints. Furthermore, as the spacing of the joints decreases, the impact decreases. However, as the joint spacing increases, the groundwater table should rise to a higher elevation to be able to have an impact. Moreover, the impact on the factor of safety is similar for different joint friction angles when the groundwater level elevation is high. This study provides a better understanding of the impact of groundwater table fluctuation on the stability of jointed rock slopes. Full article

The goal of this paper is to review the research advances in deformation and permeability evolution during the creep of rocks in geoengineering problems through aspects of experiments, models, and methods. On the experimental side, we reviewed the reports related to creep-permeability evolution in resolving real geoengineering problems. In the section on the constitutive model, we summarized the equations of the relationship between creep deformation and permeability evolution in reproducing the interaction mechanism of creep-permeability. In addition, in the section on the numerical modeling method, we examined the modelling methods able to apply the mechanism of creep-permeability evolution as a real problem. Our report concludes that it is important to conduct experiments to demonstrate the deformation and permeability evolution during the creep of heterogeneous rocks in multi physics fields (Thermal-Mechanics-Hydraulic-Chemical). Additionally, we confirm that it is necessary to improve the proposed equation of permeability evolution by considering strain and damage. Finally, this paper suggests that the DEM (Discrete Element Method) is available to evaluate the influence of the heterogeneousness of rocks on deformation and permeability evolution. Full article

Natural soils are often modelled as a continuum characterized by the composition of the soil, a particulate material. Yet, in situ, the fabric and structure of soil may govern its behavior. Discrete element modelling is used to simulate the composition of soil as a particulate material and develop fabric quantities. These quantities are presented as average quantities for a volume of particles. It is possible to use DEM to study the evolution of fabric at the particle level. This paper describes a state-of-the-art fabric term, referred to as geometrical stability index, $ʎ$, which can measure the contacts deviation of each particle from the most stable contacts arrangement during loading. The parameters required to define this new fabric term were attained from a designed algorithm. 2D discrete element method (DEM) biaxial test simulations were performed to validate the effectiveness of the geometrical stability index in defining the local instability. As the sample is loaded, a shear band is formed. The geometric stability index in that band increases relative to the surrounding relatively intact soil. Thus, a brittle failure is associated with an increase in the variation of inter-particle contacts from a stable configuration. The geometric stability index is able to model the development of discontinuities in a particulate material at the particle level. The DEM modelling results demonstrate the correlations between the new fabric term and the progressive of localized failure in densified particulate systems such as over consolidated clay, where the failure is a function of progressive development of local fissure spacing. Full article