This paper presents a rigorous, semi-analytical solution for the drained cylindrical cavity expansion in transversely isotropic sand. The constitutive model used for the sand is the SANISAND-F model, which is developed within the anisotropic critical state theory framework that can account for the essential fabric anisotropy of soils. By introducing an auxiliary variable, the governing equations of the cylindrical expansion problem are transformed into a system of ten first-order ordinary differential equations. Three of these correspond to the stress components, three are associated with the kinematic hardening tensor, three describe the fabric tensor, and the last one represents the specific volume. The solution is validated through comparison with finite element analysis, using Toyoura sand as the reference material. Parametric analyses and discussion on the impact of initial void ratio, initial mean stress level, at-rest earth pressure coefficient and initial fabric anisotropy intensity are presented. The results demonstrate that the fabric anisotropy of sand significantly influences the distribution of stress components and void ratio around the cavity. When fabric anisotropy is considered, the solution predicts lower values of radial, circumferential and vertical stresses near the cavity wall compared to those obtained without considering fabric anisotropy. The proposed solution is expected to enhance the accuracy of cavity expansion predictions in sand, which will have significant practical applications, including interpreting pressuremeter tests, predicting effects of driven pile installation, and improving the understanding of sand mechanics under complex loading scenarios.

Precise calibration of constitutive models for cyclic liquefaction is essential but often time-consuming and requires significant expertise, limiting broader application in geotechnical practice. This paper introduces an automatic calibration tool designed to streamline the process for advanced constitutive models under both monotonic and cyclic loading. The tool supports various types of monotonic and cyclic laboratory test data, offers multiple choices of suitable comparison planes for error calculation, with a focus to also suit cyclic liquefaction problems, and employs advanced optimization techniques. The calibration follows a two-stage approach: first, optimizing parameters governing monotonic response using monotonic test data; second, refining these and additional parameters with both monotonic and cyclic data. The critical state parameters are fixed throughout, while the elasticity parameters are fixed in the second stage, all within defined bounds. Using this automatic calibration tool and the adapted calibration strategy, extensive element-level test data was used to determine the parameters of the SANISAND-MSf model for a given sand. These calibrated parameters were then used to simulate boundary value problems, including centrifuge tests of liquefiable sand slopes and sheet-pile-supported liquefiable sand deposits, all subjected to base excitations, demonstrating excellent alignment with experimental results. This validation highlights the robustness, reproducibility, and accuracy of the tool to model cyclic liquefaction while significantly reducing the expertise and time required for calibration. This represents a significant advancement toward the broader adoption of advanced constitutive soil models in geotechnical engineering practice.

The cyclic response in saturated sand is gaining increasing interest owing to the soil-structure interaction in seismic regions. The evolution of the pore water pressure in liquefiable soil can significantly reduce soil strength and impact the structural dynamic response. This paper proposes a semi-analytical solution for a cylindrical cavity subjected to cyclic loading in saturated sands, incorporating an anisotropic, non-associated SANISAND model. The problem is formulated as a set of first-order partial differential equations (PDEs) by combining geometric equations, equilibrium equations, stress-strain relationships and boundary conditions. Due to the non-self-similar nature of this problem, these PDEs are solved by the hybrid Eulerian-Lagrangian approach to determine the cyclic response of the cavity. Then finite-element simulations with a user-defined subroutine are performed to validate the proposed solution. Finally, parametric studies are presented with the focus on soil parameters and cyclic loading history. It is found that the cyclic responses of the cavity in saturated sands are sensitive to the initial void ratio, and the at-rest coefficient of earth pressure primarily affects the monotonic response but marginally affects the cyclic response. Cylindrical cavities are more likely to liquefy when the sands are compacted in a loose state and under lower displacement amplitudes. The proposed solution has potential use for future research on the cyclic response of the soil-structure interaction in geotechnical engineering.

Integral bridges with longer spans experience an increased cyclic interaction with their granular backfills, particularly due to seasonal thermal fluctuations. To accurately model this interaction behaviour under cyclic loading, it is crucial to employ appropriate constitutive models and meticulously calibrate and test them. For this purpose, in this paper two advanced elastoplastic (DeltaSand, Sanisand-MS) and two hypoplastic (Hypo+IGS, Hypo+ISA) constitutive models with focus on small strain and cyclic behaviour are investigated. The soil models are calibrated based on a comprehensive laboratory programme of a representative highly compacted gravel backfill material for bridges. The calibration procedure is shown in detail and the model capabilities and limitations are discussed on the element test level. Additional triaxial tests with repeated un- and reloading reveal significant over- and undershooting effects for the majority of the investigated material models. Finally, cyclic finite element analyses on the soil-structure interaction of an integral bridge are conducted to compare the performance of the soil models. Qualitatively similar cyclic evolution of earth pressures are detected for the soil models at various bridge lengths and test settings. However, a substantially different cyclic settlement behaviour is observed. Additionally, the investigation highlights severe overshooting effects associated with the tested hypoplastic soil models. This phenomenon is studied in detail using a single integration point analysis. Supplementary studies reveal that the foot point deformation of the abutment significantly influences the lateral passive stress mobilisation and the amount of its increase with growing seasonal cycles.

Damage to buried pipes under seismic landslide actions has been reported in many post-earthquake reconnaissance. The landslide-pipe problem in the technical literature has been often investigated using simplified analytical methods. However, the analytical methods ignore the real mechanism of pipe response under natural dynamic slope instability. The dynamic slope instability is significantly influenced by its lateral boundary interface (LBI) characteristics. In this study, slope-pipe interaction (SPI) under seismic loading, focusing on the effect of LBI properties, is evaluated by continuum numerical simulation using the SANISAND constitutive model in FLAC3D. The results show that the geometry of the failure mass varies from 2D to 3D by increasing the stiffness at the slope boundaries (from smooth to hard) and the maximum pipe deformation decreases by around 40%. Moreover, the response components of maximum axial stress, bending moment, and shear stress of the pipe occur at the end sections of the buried pipe and near the boundaries of the landslide zone. However, the maximum pipe deflection occurs in the middle of the pipe. The results of shear force-shear displacement curves demonstrate that the soil-pipe interaction stiffness is variable along the pipe length and can be estimated by a hyperbolic equation.

The paper introduces a semi-analytical approach for predicting the pile-soil response under cyclic lateral loads in sands, incorporating the cavity expansion/contraction theory with an anisotropy and non-associated constitutive model, Simple ANIsotropic SAND (SANISAND). The pile hole is regarded as a cylindrical cavity, and the cyclic loading process is reasonably treated as a cavity expansion/contraction problem. A superposition principle is introduced to determine the superimposed stress states around the cavity. The geometric relationship, quasistatic equation, and boundary conditions are integrated into a standardized solving procedure to obtain the stress-strain distribution surrounding the pile. Subsequently, the derived cyclic p-y curve is used in conjunction with the deflection equilibrium differential equation and finite-difference method to determine the pile-soil response under lateral cyclic load. The method's validity and capacity are further demonstrated through two well-examined centrifuge tests, which shows a good agreement with the experimental data. The cumulative deformation, hardening and ratcheting behaviors of pile-soil system can be captured in this study, which provides a novel approach to figure out the pile-soil response in sands under cyclic lateral loads.

Earthquake-induced liquefaction and consequent failure of geomaterials have been recognised as a geohazard that causes significant damage to geotechnical infrastructures. Predicting such large deformation events has proven to be a challenging topic, which requires the development of powerful numerical tools and advanced soil models. The Smoothed Particle Hydrodynamics (SPH) method has been successfully applied to simulate large deformations and post-failure processes of geotechnical problems, including seismic large deformation analyses. However, the SPH simulation of earthquake-induced liquefaction and large deformation of geotechnical problems remains challenging, primarily due to the lack of a stabilised computational framework capable of capturing the complex responses of soil liquefaction. This study addresses this research question with the developments and applications of a fully coupled flow-deformation SPH framework incorporating the SANISAND model for solving earthquake-induced liquefaction problems. Several stabilisation techniques, including Rayleigh damping, stress diffusion and pore-pressure diffusion, are introduced to improve the stability and accuracy of SPH simulations. Additionally, a robust stress update method, combining the sub-stepping technique and cutting-plane algorithm, is proposed to effectively integrate the constitutive laws of the SANISAND model during large deformation SPH simulations. Verification of the proposed SPH framework against theoretical solutions shows its effectiveness before being applied to simulate several shaking table tests reported in the literature. The proposed SPH framework and model are able to reproduce experimental results in several simulations, demonstrating their potential and capability for the future prediction of earthquake-induced liquefaction and failure of geoinfrastructures.

Ground response analysis under earthquakes is a critical part of earthquake engineering. Experimental or numerical techniques are commonly applied to implement seismic soil response analysis. However, due to the expensive and time-consuming implementation and also uncertainties in experimental tests and numerical analyses, in this study, deep learning methods are proposed as a good alternative for nonlinear seismic soil response analysis. Long short-term memory network (LSTM) and bidirectional long short-term memory network (BiLSTM) are selected as potential candidates. Input features for the deep LSTM and Bi-LSTM structures are input ground motions at the base of the soil model. And, output features are responses in terms of time series at different locations along the depth of the soil medium. It is noted that all the responses are simultaneously predicted. A limited number of real earthquakes with various characteristics are chosen for training, validation, and testing datasets in the deep learning methods. The datasets are formed by using numerical results. The nonlinear behavior of the soil in numerical models is simulated by employing a sophisticated constitutive model of simple anisotropic SAND (SANISAND). The effectiveness of numerical results is demonstrated with the assistance of the centrifuge test. The results confirm the good performance of the proposed deep learning models for nonlinear seismic ground response prediction. The capacity of the deep learning models is inspected in both the time domain in terms of time series and the frequency domain.

In seismic regions both in Iran and around the world, subterranean gas pipelines inevitably extend through highrisk areas prone to seismic landslides. The seismic landslide-pipe failure mechanism constitutes a continuum geomechanical challenge influenced by factors such as sliding mass configuration, pipe positioning relative to potential slope failure surfaces, and seismic input characteristics. In this study, response of steel pipeline buried in sand under seismic landslide action is analyzed by finite difference models using an advanced soil constitutive model. The numerical model is first validated based on the shaking table test results and then several dynamic analyses are performed using the selected records of the Iranian ground motions database. The outcomes of the dynamic analysis demonstrate that Arias Intensity (Ia) can be identified as an optimal intensity measure (IM) for predicting the seismic response of a slope-pipe system in terms of maximum pipe deflection, axial strain, and shear stress. Predictive models are then developed based on the optimal IM for estimating the pipe deflection, axial strain, and shear stress subjected to a seismic landslide. These proposed predictive models offer valuable insights for assessing the response of buried pipelines to seismic landslides in Iran within the framework of performance-based earthquake engineering.

This chapter presents Type-C numerical simulations of prototype-scale centrifuge tests on gently sloped liquefiable deposits of Ottawa F65 sand for the LEAP-ASIA-2019 project. The simulations aim to assess the performance of the numerical modeling approach and a SANISAND-type constitutive model for large post-liquefaction shear deformation of sands. The constitutive model is calibrated against cyclic torsional shear tests conducted at different relative density levels and cyclic shear stress amplitudes. The laboratory-determined hydraulic conductivity of sand is doubled and kept constant during the dynamic stage of the analyses to account for the increase in permeability experienced during liquefaction. The simulations successfully capture the acceleration response and excess pore water pressure generation and dissipation of the slope deposit when soil liquefaction is observed. However, accurately modeling lateral displacements remains challenging in most cases. The results provide insights into the capabilities and limitations of the adopted Type-C numerical simulations, numerical modeling approach, and constitutive model.