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 Acta GeotechnicaJournal Prestige (SJR): 1.588 Citation Impact (citeScore): 3Number of Followers: 6      Hybrid journal (It can contain Open Access articles) ISSN (Print) 1861-1133 - ISSN (Online) 1861-1125 Published by Springer-Verlag  [2469 journals]
• A closed-form solution for the failure interaction diagrams of pile groups

Abstract: The work at hand proposes a method for assessing, under reasonable hypotheses from an engineering perspective, the failure envelope of a pile group subjected to generalized loading conditions involving a vertical and a lateral force along with a moment. Following different assumptions of increasing complexity, a simple closed-form expression, which is however capable of considering also the strong dependence of sectional yielding moment on the axial force, is derived. The use of such formula, which allows a practical hand calculation of the interaction diagrams at failure, returns conservative yet very accurate results. As a follow up, with reference to reinforced concrete piles, design considerations involving both structural and geotechnical failure under lateral load are reported. It is found that for most cases, if steel reinforcement is established to resist the design bending moment, the geotechnical Ultimate Limit State checks are automatically satisfied.
PubDate: 2022-01-19

• A high-cycle accumulation model for clay and its application to monopile
foundations

Abstract: A high-cycle accumulation (HCA) model predicting the accumulation of permanent strain or excess pore water pressure in clay under a large number of load cycles is presented. Data from an extensive laboratory testing program on kaolin under undrained cyclic loading has been analysed for that purpose. The influence of strain amplitude, void ratio, stress ratio, overconsolidation ratio and loading frequency on the accumulation rates is considered in the constitutive equations of the HCA model. The proposed model is validated first by the simulation of element tests. Subsequently, its application to offshore wind turbine foundations under long-term lateral cyclic loading is presented by the back-analysis of a centrifuge test on a monopile in soft clay. The results are in good accordance with the measurements in terms of pile displacement and bending moment versus number of applied cycles. It is concluded that the proposed model is feasible to describe the long-term behaviour of clay subjected to high-cyclic loading.
PubDate: 2022-01-18

• New interpretable shear strength criterion for rock joints

Abstract: Shear constitutive models of rock discontinuities have been viewed as an effective stability evaluation tool in the rock mass engineering application area. This paper proposes a new interpretable shear strength criterion for rock joints based on multivariate adaptive regression splines (MARS) algorithm. Sensitivity analyses are then performed on the developed shear strength criterion. As the second purpose of this research, the potential competence of five surrogate soft computing (SC) methods including Gaussian process (GP), alternating model tree (AMT), Cubist, radial basis function (RBF) networks, and elastic net (EN) paradigms for fast predicting the shear strength of rock discontinuities is also comparatively evaluated along with the MARS model. These approaches formulate nonlinear relations between input and output variables. The proposed methodologies consider eight input factors: sampling interval $$(l)$$ , maximum contact area ratio $${(A}_{0})$$ , distribution parameter $$(C)$$ , maximum apparent dip angle $$({\theta }_{\max}^{*})$$ , basic friction angle $$({\varphi }_{\text{b}})$$ , tensile strength ( $${\sigma }_{\text{t}}$$ ), uniaxial compressive strength $${(\sigma }_{\text{c}})$$ , and normal stress $$({\sigma }_{\text{n}})$$ to assess peak shear strength $$({\tau }_{\text{p}})$$ of rock joints. A dataset collected from the literature conducted on the direct shear test is used for training and evaluating proposed methods. Ten-fold cross-validation is utilized to enhance the robustness and generalization of the developed SC-based shear strength surrogate models. Statistical indices and comparative analyses with conventional criteria indicate that the proposed SC regressors can deliver good agreements with the measured data in terms of performance accuracy and outperform or achieve comparable performances to the conventional models. However, GP, AMT, and RBF models have a good prediction performance than MARS and EN models.
PubDate: 2022-01-17

• A predictive deep learning framework for path-dependent mechanical
behavior of granular materials

Abstract: As we transition into an era of data generation and collection, empirical summaries in the classical continuum modeling of granular materials cannot take full advantage of the increasingly larger data sets. This work presents a data-driven model for modeling granular materials, with the material data being extracted from discrete element method (DEM) simulations. A long short-term memory (LSTM) network is then employed to learn the mechanical behaviors of granular materials from the material dataset. Particular emphasis is placed on three elements: modification of LSTM unit cell, phase space sampling, and material history parameterization. The LSTM unit cell is modified so that the initial hidden state can be specified as the initial states of granular materials. Massive DEM simulations are performed to consider the effects of particle size distribution, initial density, confining pressure, and loading path on the mechanical behaviors of granular materials. The history-dependency of the granular materials is well represented by the architecture of the LSTM network and internal variable-based history parameterization. We compare the model predictions against DEM simulations to assess the performance of the proposed data-driven model. The results demonstrate that the model can predict the material behaviors of granular materials with different microstructures and initial states and reproduce the material responses under complex nonmonotonic loading paths. This data-driven model exhibits good generalization ability and high prediction accuracy in various situations.
PubDate: 2022-01-17

• Effect of water content on permanent deformation of fine/coarse soil
mixtures with varying coarse grain contents and subjected to multi-stage

Abstract: An interlayer soil in ancient rail tracks was identified as a mixture of ballast grains and subgrade fines. As the permanent strain $${\varepsilon }_{1}^{p}$$ of such mixture was affected by water content, cyclic triaxial tests were performed, under varying water contents of fines wf and coarse grain contents fv. Comparison between present and previous studies showed the significant effect of sample preparation method on $${\varepsilon }_{1}^{p}$$ . In the present study, a constant fine dry density ρd-f was maintained, leading to an unchanged suction of mixture whatever the fv value. In this case, only the reinforcement effect of fv on $${\varepsilon }_{1}^{p}$$ was identified. By contrast, in previous studies, the global dry density of mixture ρd was kept constant, resulting in a decrease in ρd-f with increasing fv and consequently a decrease in suction. In this case, when the negative effect of decreasing suction prevailed on the positive reinforcement effect of increasing fv, the $${\varepsilon }_{1}^{p}$$ increased.
PubDate: 2022-01-17

• Automated calibration of advanced soil constitutive models. Part II:
hypoplastic clay and modified Cam-Clay

Abstract: This paper introduces an automated deterministic method for the calibration of the Modified Cam-Clay and hypoplastic clay model. The calibration is structured in a hierarchical order established based on the apriori sensitivity study performed. The proposed method favours the clear physical meaning of the model parameters to a complete optimization of the objective error function. The method requires only basic laboratory experiments and it is currently implemented in the free-to-use online application called ExCalibre.
PubDate: 2022-01-17

• Reverse fault slip through soft rock and sand strata by centrifuge
modeling tests

Abstract: The devastating damage after the 1999 Chi-Chi and 1999 Izmit earthquakes has greatly motivated soil–reverse fault interaction studies. However, most centrifuge modeling studies have employed a single homogeneous soil layer during testing, which does not represent in situ conditions. Indeed, while geological conditions vary spatially, engineering soils are often underlain by soft rocks. Therefore, four centrifuge models were developed to evaluate the effect of soft rock layers on the ground surface and subsurface deformation. Sand–cement mixtures of varying thicknesses with a uniaxial compressive strength of 0.975 MPa, simulating extremely soft rock, were overlain by pluviated sandy soil. The model thickness was 100 mm, corresponding to 8 m in the prototype scale when spun at 80 g. Every model was subjected to a vertical offset of 50 mm/4 m (0.5 H; H: total sedimentary deposit thickness) along a reverse fault with a 60° dip. The results indicate that the presence of a soft rock stratum results in the creation of a horst profile at the ground surface. Additionally, the thinner the soil layer on top of the soft rock stratum is, the longer and higher the horst created at the ground surface. Consequently, the fault deformation zone lengthens proportionally with the increasing thickness ratio of the soft rock. Furthermore, the presence of soft rock as an intermediary stratum between bedrock and soil causes the deformation zone boundary on the hanging wall side to move in the direction of fault movement.
PubDate: 2022-01-16

• Automated calibration of advanced soil constitutive models. Part I:
hypoplastic sand

Abstract: This paper discusses an automated deterministic approach to parameters calibration of the hypoplastic model for sand. The calibration is performed on results from basic laboratory experiments such as the oedometric test, isotropic compression test, and the drained and undrained triaxial shear tests. The calibration method is structured in a hierarchical order and implemented into a free-to-use online application called ExCalibre. The method is based on the sensitivity study performed prior to the development of the calibration method. The calibration procedure respects the physical meaning of the calibrated parameters and their influence on the stiffness and asymptotic states, rather than performing a blind optimization of an objective function.
PubDate: 2022-01-16

• A modified state parameter for sands

Abstract: This paper presents arguments for using a modified state parameter, Ic, to describe the fundamental state of sand. The other reference state being the minimum void ratio is introduced in the expression of Ic in addition to the critical state. Shear properties of sands from a substantial body of triaxial tests were examined, showing better correlations with Ic than ψ, which was the original state parameter defined by Been and Jefferies (35(2):99–112, 1985). More importantly, the parameter (χc), introduced by the individual correlations with Ic, represents the limit values of sand properties associated with the sand densest state and the values of χc are within a justifiable range facilitating engineering applicability. The modified state parameter Ic can be readily incorporated into current constitutive models. This is demonstrated in the paper through the use of a new Ic based expression for dilatancy that captures better the response measured in triaxial compression, particularly when the loading is cyclic.
PubDate: 2022-01-15

• Transparent soil test evaluation of vertical–horizontal mixed
curtain during dewatering

Abstract: The vertical–horizontal curtain system (VH curtain) is sometimes utilized in foundation pit dewatering under complex hydrogeological conditions. However, the working mechanism of this system when the horizontal curtain is semi-permeable and cannot completely cut off the bottom aquifer remains unknown. A transparent soil physical model test was performed to reveal the water control mechanism of the VH curtain system with a semi-permeable horizontal curtain. A multi-point inert tracer with a high-speed camera was used to photograph the seepage process. The seepage mode was revealed via a model test. With the Shanghai deep tunnel project as background, a numerical simulation was performed to understand the utilization of the VH curtain. The influence of horizontal curtain position, horizontal curtain thickness, horizontal curtain hydraulic conductivity, and VH curtain combination form on the seepage path around the foundation pit and on the drawdown of water level inside and outside the pit were studied. Results provide a basis for the engineering application of the VH curtain pumping well system.
PubDate: 2022-01-05

• A general simple method for calculating consolidation settlements of

PubDate: 2022-01-04

• Hydro-mechanical coupled analysis of near-wellbore fines migration from
unconsolidated reservoirs

Abstract: Oil or gas production from unconsolidated reservoirs could be hampered by sand migration near the wellbore. This paper presents a numerical investigation of production-induced migration of fine sands towards a wellbore drilled in a gap-graded sediment. The solid–fluid interaction is simulated by coupling the discrete element method and the dynamic fluid mesh. With the merit of DEM and a dynamic mesh, the model is capable of naturally capturing particle movements and spatiotemporal variations of hydraulic properties of the sediment at the pore scale. The results show that fine particles are mobilized by radial flow under an imposed hydraulic gradient, and the increase in the hydraulic gradient causes an increase in the fines production. The microscopic pattern of sand migration is clearly visualized through the simulation. The presence of fine particles affects the process of fines migration through two competing mechanisms. Under a low fine content, fine sands mainly serve as the fines production source, and thus, fines production is enhanced as the fine content increases up to a critical value, beyond which fines production is weakened with a further increase in the fine content since the blocking effect gradually dominates. A barrier layer is likely formed during sand migration due to settling and jamming of fine sands at the throats of pores, as fine sands migrate with the radial flow towards the wellbore. This layer is helpful to slow down sand migration, while it could impede production due to reduced permeability in the affected reservoir.
PubDate: 2022-01-04

• Calibrating and validating a soil constitutive model through conventional
triaxial tests: an in-depth study on CSUH model

Abstract: This paper presents an approach for calibrating and validating a constitutive model via conventional triaxial tests. First, the consolidated drained triaxial compression test results are used for model calibration. The particle swarm optimization algorithm based on multiple adaptive strategies is then adopted to calibrate the best fitting parameters. Subsequently, the constitutive model is validated by considering its performance in modeling the consolidated undrained triaxial tests. The unified hardening model for clays and sands (CSUH model) proposed by Yao et al. (Comput Geotech 110:326–343, 2019. 10.1016/j.compgeo.2019.02.024) is considered. The results demonstrate that the CSUH model can well describe the dilatancy of clays and sands with different densities in both drained and undrained triaxial tests.
PubDate: 2022-01-03

• Seismic response for an isosceles triangle hill subjected to anti-plane
shear waves

Abstract: This paper presents an exact, analytical solution to the boundary value problem of the anti-plane (SH) waves scattering by an isosceles triangle hill on an elastic half-space by using the wavefunction expansion method. An appropriate region-matching technique is introduced to divide the half-space containing a triangle hill into two subregions. Then, the wavefield expression of each subregion is constructed in terms of an infinite series in two coordinate systems, respectively. Furthermore, a Graf’s addition formula is derived to unify the coordinate system and solve the unknown coefficients in the wave functions. Finally, numerical results are calculated to illustrate the effects on ground motion due to the existence of an isosceles triangle hill. This paper revises the existing analytical methods, and aims to provide a benchmark for numerical method verification and a reference for engineering practice.
PubDate: 2022-01-01

• Stability analysis of geosynthetic-reinforced soil structures under steady
infiltrations

Abstract: Conventional approach for evaluation of the stability of geosynthetic-reinforced soil structures (GRSSs) is performed under either completely dry or saturated conditions, whereas soils are usually unsaturated in practice. Owing to the suction-induced effect, the behavior of soil is quite different, consequently leading to various stability conditions of GRSSs. This study presents a useful analytical solution for assessing the reinforcement effect of geosynthetics on the internal stability of unsaturated GRSSs under steady infiltration conditions using the kinematical approach of limit analysis, aiming at determining the reinforcement strength required for preventing slope failure. This analytical solution can take the effect of suction stress, unit weight of soil and tensile strength cut-off simultaneously into account. By comparing with the results of other solutions, the validity of the analytical solution is verified. An extensive parametric study is conducted in this paper. The obtained results show that the suction stress has a more significant effect than the tensile strength cut-off on the required normalized reinforcement; additionally, the required normalized reinforcement obtained by the extended M-C yield criterion is more conservative than that of the tension cut-off model in the presence of suction stress, and the hysteresis effect should be considered in the routine design.
PubDate: 2022-01-01

• A Caputo variable-order fractional damage creep model for sandstone
considering effect of relaxation time

Abstract: Establishing a fractional creep model with few parameters and explicit physical interpretation is of significant meaning for predicting rheological deformation of rock. In this study, based on the Caputo variable-order fractional derivative, a Caputo variable-order fractional creep model is proposed, whose physical interpretation is clearly stated by setting a varying-order function related to relaxation time. The significance of relaxation time is firstly highlighted to reveal the evolution mechanism of viscoelasticity of creep and relaxation response by constructing equivalence between rheological responses of constant-order fractional Maxwell model and that of time-varying viscosity Maxwell model. Meanwhile, considering the importance of relaxation time in rheology, a modified damage factor is also presented and introduced in proposed model. Next, for verifying the applicability of proposed damage creep model, a series of uniaxial creep experiments were conducted on sandstone under step by step loading, the creep data predicted by proposed damage creep model are well agreement with experimental creep data. And then, a comparative study with constant-order fractional damage creep model was performed to present the advantages of proposed Caputo variable-order fractional damage creep model, which gives further references for application of Caputo variable-order fractional derivative in rheological model. Finally, the variations and influence of elastic modulus and relaxation time on creep response based on proposed Caputo variable-order fractional damage creep model are discussed and expounded deeply.
PubDate: 2022-01-01

• A constitutive model for municipal solid waste considering mechanical

Abstract: A constitutive model is developed to describe the stress–strain–time behavior for decomposing municipal solid waste (MSW) within a critical state soil mechanics framework. The model is an extension of the Modified Cam-Clay plasticity model. In this model, three sources contribute to the hardening of MSW due to volumetric strain: time-independent plastic volumetric strain, time-dependent volumetric mechanical creep strain, and time-dependent volumetric strain due to the biodegradation (decomposition) of MSW. The MSW model was evaluated through numerical analyses of large-scale one-dimensional compression tests in the laboratory and the field and the reported vertical and horizontal deformations of a MSW landfill. The associated model parameters were obtained by compositional analysis of the waste, from values reported in the literature, and by fitting numerical results to observed behavior. For the laboratory compression test, the best-fit numerical simulation over-predicted the early settlement but converged on the experimental values after 200 days. Initially, the calculated vertical strains in the field-scale test deviated from the measured strains by up to 10% over the 398-day period of the test. However, numerical results after adjusting model parameters to provide the best fit with the measured strains resulted in a maximum deviation of less than 3% over the test duration. The calculated vertical displacements of the MSW landfill were consistent with field measurements. However, the calculated horizontal displacements were significantly lower than the measured values. Sensitivity studies showed that the time-dependent settlement predicted by the model is highly sensitive to the biodegradation rate of MSW. The good agreement between numerical values and observed vertical deformations for the SWEAP section on the MSW landfill suggests that the model has the potential to assess the performance of subsystems in landfills (e.g., the performance of a side slope liner system subject to landfill settlement). However, the discrepancy between predicted and observed horizontal displacements suggests that the numerical model can be improved by incorporating deviatoric creep deformations in the constitutive model.
PubDate: 2022-01-01

• Coupled thermal–hydraulic modeling of artificial ground freezing with
uncertainties in pipe inclination and thermal conductivity

Abstract: Artificial ground freezing (AGF) has been widely used as a temporary soil stabilization and waterproofing technique in geotechnical practices (e.g., tunnel construction). Many sources of uncertainty exist during AGF. Firstly, groundwater seepage flow can adversely affect the freezing efficacy. Secondly, freeze pipe inclination inevitably occurs during installation, which is likely to yield an unfrozen path and elevate construction risk. Thirdly, as a key soil parameter, the spatial variability in thermal conductivity can also affect the freezing process. In this work, a unit cell model of freeze pipes is established by a coupled thermo-hydraulic finite element method to examine the effects of these sources of uncertainty. The pipe inclination is considered in the unit cell model by prescribing various values of freeze pipe spacing. The thermal conductivity of soil solid is simulated as a three-dimensional lognormal random field to account for the spatial variability of soil. Results are tabulated to evaluate the additional freezing time required in the AGF system due to the existence of these uncertainties. The findings are capable of determining a reasonable range of freeze pipe spacings and the corresponding critical seepage velocity, and can offer practitioners a rule of thumb for estimating freeze pipe spacing.
PubDate: 2022-01-01

• Seismic risk assessment of a steel building supported on helical pile
groups

Abstract: Designing structures to be the least vulnerable within earthquake-prone areas is a serious challenge for structural engineers. One common and useful tool that structural engineers use to predict the vulnerability of a structure during an earthquake is a fragility curve. However, most structural fragility curves do not take into consideration the contribution of pile foundation systems in the structural vulnerability. Therefore, this study aims to modify existing fragility curves of a six-story fixed-base steel frame hospital building with buckling-restrained braces, to incorporate the effect of helical pile group behavior on the fragility of the structure. To that end, a finite element model of the investigated structure was modified with results from a full-scale shake table test performed on two groups of helical piles embedded in dense sand supporting a superstructure. The primary results show that fixed-base design may not be conservative for all conditions and soil–foundation interaction should be considered when creating fragility curves, especially for a stiff structure on soft soils where a high-intensity earthquake is anticipated.
PubDate: 2022-01-01

• Significance of flow rule for the passive earth pressure problem

Abstract: Determination of earth pressures is one of the fundamental tasks in geotechnical engineering. Although many different methods have been utilized to present passive earth pressure coefficients, the influence of non-associated plasticity on the passive earth pressure problem has not been discussed intensively. In this study, finite-element limit analysis and displacement finite-element analysis are applied for frictional materials. Results are compared with selected data from literature in terms of passive earth pressure coefficients, shape of failure mechanism and robustness of the numerical simulation. The results of this study show that passive earth pressure coefficients determined with an associated flow rule are comparable to the Sokolovski solution. However, comparison with a non-associated flow rule reveals that passive earth pressure coefficients are significantly over predicted when following an associated flow rule. Moreover, this study reveals that computational costs for determination of passive earth pressure are considerably larger following a non-associated flow rule. Additionally, the study shows that numerical instabilities arise and failure surfaces become non-unique. It is shown that this problem may be overcome by applying the approach suggested by Davis (Soil Mech 341–354, 1968).
PubDate: 2022-01-01

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