This article introduces a novel system identification technique for determining the bulk modulus of cohesionless soils in the post-liquefaction dissipation stage following seismic excitation. The proposed method employs a discretization of Biot's theory for porous media using the finite difference method. The technique was validated using synthetic data from finite elements simulations of an excited soil deposit. These numerical simulations were performed using an advanced multi-yield surface elastoplastic model. Additionally, the technique was used to analyze a series of high-quality dynamic centrifuge tests performed on Ottawa F-65 sand as part of the LEAP- 2020 project. A comparative analysis between recorded and identified bulk modulus values highlights the effectiveness of the proposed technique across a wide range of conditions.

Past earthquakes have revealed that damage to sheet -pile walls under saturated conditions is closely linked to excess pore water pressure buildup in the surrounding soil. Nonlinear effective stress analysis (ESA) is commonly employed to assess the seismic performance of sheet -pile walls in liquefiable soils, incorporating constitutive models for liquefaction simulation. However, ESA results are sensitive to uncertainties in input parameters, model calibration, and modeling techniques. Dynamic centrifuge tests conducted in the Liquefaction Experiments and Analysis Project (LEAP) offer valuable insights into important response mechanisms and validate ESA. Seven centrifuge tests on a cantilevered sheet -pile wall model showed that liquefaction did not occur in the backfill near the wall due to net seaward wall displacement but did occur farther away. In addition, the mechanism of wall displacement was mainly due to the shear deformation of the softened backfill, with the displacement magnitude depending on the relative density of soil, peak ground acceleration of base motion, and wall displacement during gravity loading. Nonlinear ESA was performed for three centrifuge tests using FLAC2D and the PM4Sand constitutive model for soil. Gravity analysis captured static wall displacement and initial stress distribution in the soil. Two calibrations of the PM4Sand model were pursued at the element level: C1 calibration for liquefaction strength and C2 calibration for liquefaction strength and the post -liquefaction shear strain accumulation rate. System -level simulations showed similar liquefaction behavior as observed in the tests for both calibrations. However, the C2 calibration provided closer predictions of wall displacements, while the C1 calibration (default for PM4Sand) resulted in larger and more conservative displacements. Overall, the PM4Sand model performed well with minimal calibration, making it suitable for nonlinear ESA of sheet -pile walls.

This article evaluates the prediction capabilities and limitations of the ISA-hypoplasticity constitutive model for sands in the simulation of liquefiable sloping ground dynamic centrifuge tests from the LEAP -2017 project. For that purpose, the experimental results of three centrifuge tests performed at different centrifuge facilities are considered. The corresponding dynamic coupled predictions were carried out using the finite element software Abaqus Standard. The material parameters of the adopted constitutive model were determined based on a detailed laboratory characterization of the tested Ottawa F-65 sand, which included drained monotonic triaxial and undrained cyclic triaxial tests considering a wide range of initial conditions and testing characteristics. The comparison between measured and computed sloping ground accelerations and spectral response suggests reasonable predictions by the model. Furthermore, the results suggest that the constitutive model is only able to realistically reproduce the trends of the experimental excess pore water pressure when considering cyclic mobility effects.

This study presents the numerical results of a series of laboratory and dynamic centrifuge tests conducted by the team at Universidad del Norte, as part of the LEAP -2022 project. The soil ' s mechanical behavior was simulated using a pressure -dependent multi -surface plasticity constitutive model, which was carefully calibrated based on cyclic soil tests performed on Ottawa F-65 sand. These tests covered a wide range of initial densities, initial effective stresses, and cyclic stress ratios. The comparison between laboratory and numerical element tests revealed that the adopted constitutive model reasonably replicated most features of the material ' s undrained cyclic response, including liquefaction occurrence and the progressive development of double -amplitude permanent shear strains. The calibrated constitutive model was then used to blindly predict the dynamic behavior of centrifuge experiments composed of a sheet pile -soil system using the OpenSees finite elements software framework; these simulations are referred to as Type -B predictions. The numerical simulation showed that the model provided reasonable representation of soil responses in terms of accelerations and pore water pressure build-up; however, the simulations consistently overpredicted the displacements of the sheet piles. Therefore, based on the centrifuge experimental results, minor adjustments of the material parameters were performed, and the centrifuge tests were re -simulated; these simulations are referred to as Type -C predictions. The comprehensive evaluation exposed both the strengths and weaknesses of the modeling approach for the simulation of liquefiable deposits. Despite the discrepancies in sheet pile displacement, the study instills confidence in the model ' s applicability to liquefaction -related projects with similar conditions.

This chapter presents a summary of the calibration exercises (i.e., element test simulations) submitted by nine numerical simulation teams that participated in the LEAP-ASIA-2019 prediction campaign. The standard sand selected for the campaign is Ottawa F-65, and researchers have developed several efforts to increase the database of laboratory tests to characterize the physical and mechanical properties of this sand (Carey TJ, Stone N, Kutter BL, Grain Size Analysis and Maximum and Minimum Dry Density of Ottawa F-65 Sand for LEAP-UCD-2017. Model tests and numerical simulations of liquefaction and lateral spreading: LEAP-UCD-2017. Springer, 2019; El Ghoraiby MA, Park H, Manzari MT. Physical and mechanical properties of Ottawa F65 sand. In: Model tests and numerical simulations of liquefaction and lateral spreading: LEAP-UCD-2017, Springer, 2019; Ueda K, Vargas RR, Uemura K, LEAP-Asia-2018: Stress-strain response of Ottawa sand in Cyclic Torsional Shear Tests, DesignSafe-CI [publisher], Dataset, https://doi.org/10.17603/DS2D40H, 2018; Vargas RR, Ueda K, Uemura K, Soil Dyn Earthq Eng 133:106111, 2020; Vargas RR, Ueda K, Uemura K, Dynamic torsional shear tests of Ottawa F-65 Sand for LEAP-ASIA-2019. Model tests and numerical simulations of liquefaction and lateral spreading: LEAP-ASIA-2019, Springer, 2023). The objective of this element test simulation exercise is to assess the performance of the constitutive models used by the simulation teams for simulating the experimental results of a series of undrained stress-controlled cyclic torsional shear tests on Ottawa F-65 sand for two different relative densities (Dr = 50% and 60%) (Ueda K, Vargas RR, Uemura K, LEAP-Asia-2018: Stress-strain response of Ottawa sand in Cyclic Torsional Shear Tests, DesignSafe-CI [publisher], Dataset, https://doi.org/10.17603/DS2D40H, 2018; Vargas RR, Ueda K, Uemura K, Soil Dyn Earthq Eng 133:106111, 2020; Vargas RR, Ueda K, Uemura K, Dynamic torsional shear tests of Ottawa F-65 sand for LEAP-ASIA-2019. Model tests and numerical simulations of liquefaction and lateral spreading: LEAP-ASIA-2019, Springer, 2023). The simulated liquefaction strength curves demonstrate that majority of the constitutive models are capable of reasonably capturing the measured liquefaction strength curves both for Dr = 50% and 60%. However, the simulated stress paths and stress-strain relationships show some differences from the corresponding laboratory tests in some cases.

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.

In this chapter, Class-C numerical simulations were performed for LEAP-ASIA-2019 centrifuge experiments that took place at different universities testing facilities. A comparative study was conducted among the simulated and experimental seismic responses of a mildly sloping ground of medium-dense to dense Ottawa-F65 sand under ramped sinusoidal acceleration input motions. A pressure dependent multi-yield surface model that can simulate the liquefaction potential of sand soils under earthquake loading was chosen for the numerical simulations through the OpenSees finite element modeling software. An initial calibration of the soil constitutive model, namely Phase I, was performed against different cyclic torsional shear tests for Ottawa-F65 sand under various Cyclic Stress Ratios (CSRs). Numerical modeling of centrifuge experiments Phase II was carried out after a few adjustments to the estimated model parameter values for the sake of providing proper computed output responses. The adopted soil model and simulation technique provide adequate numerical predictions of the liquefaction potential for the mildly sloping ground problem and accurately simulate the time histories of excess pore water pressure, accelerations, and surface deformations, regardless of experiencing a few undesirable responses for simulated Kyoto University centrifuge tests. The capabilities and limitations of the selected constitutive soil model and computational technique are analyzed and discussed through the context.

Short-lived climate pollutants (SLCPs) including black carbon (BC), methane (CH4), and tropospheric ozone (O-3) are major climate forcers after carbon dioxide (CO2). These SLCPs also have detrimental impacts on human health and agriculture. Studies show that the Hindu Kush Himalayan (HKH) region, which includes Nepal, has been experiencing the impacts of these pollutants in addition to greenhouse gases. In this study, we derive a national-level emission inventory for SLCPs, CO2, and air pollutants for Nepal and project their impacts under reference (REF) and mitigation policy (POL) scenarios. The impacts on human health, agriculture, and climate were then estimated by applying the following: (1) adjoint coefficients from the Goddard Earth Observing System (GEOS)-chemical transport model that quantify the sensitivity of fine particulate matter (PM2.5) and surface O-3 concentrations in Nepal, and radiative forcing in four latitudinal bands, to emissions in 2 x 2.5 degrees grids, and (2) concentration-response functions to estimate health and crop loss impacts in Nepal. With the mitigating measures undertaken, emission reductions of about 78% each of BC and CH4 and 87% of PM2.5 could be achieved in 2050 compared with the REF scenario. This would lead to an estimated avoidance of 29,000 lives lost and 1.7 million tonnes of crop loss while bringing an economic benefit in present value of 2.7 times more than the total cost incurred in its implementation during the whole period 2010-2050. The results provide useful policy insights and pathways for evidence-based decision-making in the design and effective implementation of SLCP mitigation measures in Nepal.