H. Tolga Bilge

Simulation of contaminant migration through a soil layer due to an instantaneous source

Analytical and numerical simulation models help civil and environmental engineering students to understand the physical and chemical processes that influence contaminant transport through a saturated soil layer, including advective and dispersive transport as well as sorption. The basic principles for simulation of contaminant migration through a saturated soil were introduced. Using the spreadsheet program MS Excel, based on existing analytical solution for two‐dimensional transport of contaminants in a saturated soil layer, concentrations at several coordinates at several times were calculated. A MATLAB code was developed using finite difference approach for numerical solution. The programming steps followed for analytical and numerical solutions were explained. The analytical and numerical solution was compared. An example of the simulation models for the contaminant transport through a saturated soil layer is given. The study shows that the analytical solution and the numerical solution, for the given problem, match in an acceptable range.

Dataset on SPT-based seismic soil liquefaction

This data article provides a summary of seismic soil liquefaction triggering and non-triggering case histories, which were compiled, screened for data completeness and quality, and then processed for the development of triggering relationships proposed in “SPT-based probabilistic and deterministic assessment of seismic soil liquefaction triggering hazard” [1]. The database is composed of 113 liquefaction, 95 non-liquefaction, and 2 marginal liquefaction case histories, from seismic events with moment magnitude Mw values varying in the range of 5.9 to 8.3. A spreadsheet summary of these case histories are included along with a separate spreadsheet, by which maximum likelihood assessment was performed. These data transparently enable researchers to access case history input parameters and processing details, and to compare the case history processing protocols with the ones of different researchers (e.g.: “The influence of SPT procedures in soil liquefaction resistance evaluations.” [2], “SPT-based liquefaction triggering procedures.” [3]).

Stress Scaling Factors for Seismic Soil Liquefaction Engineering Problems: A Performance-Based Approach

Most of the widely used seismic soil liquefaction triggering methods propose cyclic resistance ratio (CRR) values valid at the reference normal effective stress (σ′v,0) of one atmosphere and zero static shear stress (τst,0) states. Then, a series of correction factors are applied on this reference CRR, for the purpose of assessing the variability due to normal effective and static shear stress states (i.e. Kσ and Kα corrections) acting on the horizontal plane. In the literature, a number of relationships suggested to be used as part of liquefaction triggering methodologies. However, the presence of a wide range of correction factors, some of which with even contradicting trends, suggests that more research needs to be performed to reduce this uncertainty. Additionally, these stress correction factors are treated as being strain-independent and are applied disjointedly to CSR or CRR. The main motivation of this on-going study is defined as to develop a strain-dependent semi-empirical framework to assess combined effects of i) σ′v,0, ii) τst,0 acting on the plane, where cyclic shear stresses either produce iii) shear stress reversal or not. For this purpose, cyclic simple shear tests were performed on laboratory reconstituted sand samples. Additionally, cyclic test data were compiled from the available literature. On the basis of probabilistic assessment of this data, a unified correction scheme, which incorporates the interdependent effects of both overburden and static shear stresses along with the degree of cyclic shear stress reversal, has been developed.

Recent Advances in Seismic Soil Liquefaction Engineering

The assessment of cyclic response of soils has been a major concern of geotechnical earthquake engineering since the very early days of the profession. The pioneering efforts were mostly focused on developing an understanding of the response of clean sands. These efforts were mostly confined to the assessment of the mechanisms of excess pore pressure buildup and corollary reduction in shear strength and stiffness, widely referred to as seismic soil liquefaction triggering. However, as the years passed, and earthquakes and laboratory testing programs continued to provide lessons and data, researchers and practitioners became increasingly aware of additional aspects, such as liquefaction susceptibility and cyclic degradation response of silt and clay mixtures. Inspired from the fact that these issues are still considered as the “soft” spots of the practice, the scope of this chapter is tailored to include a review of earlier efforts along with the introduction of new frameworks for the assessment of cyclic strength and straining performance of coarse- and fine-grained soils.

Liquefaction Triggering Response Under Wave-Induced Cyclic Loading

Cyclic response of saturated sands has become one of the most popular topics in geotechnical earthquake engineering due to the consequent damages of earthquakes. Related to this topic, detailed performance of offshore structures founded on saturated sands under the effect of cyclic loads carries vital economic importance. It is well-known that besides seismic loading; storm, wind and/or submarine slope failures have direct effect on the strength and deformation behavior of soils through induced sea-level variations. This study summarizes the results of a series of cyclic triaxial tests performed to simulate the behavior of fully-saturated coarse grained sands under wave-induced cyclic loading. Evaluating the excess pore water pressure generation and shear strain accumulation response along with the number of cycles required for liquefaction triggering for sands, having different relative densities, and being subjected to various cyclic shear stress ratios (CSR), the following observations are made; i) number of cycles to liquefaction increases with increasing relative density and decreasing CSR, ii) for medium dense foundation and backfill soils, liquefaction is not triggered for CSR values less than 0.1 under reasonable number of cycles, and iii) number of cycles to liquefaction decreases significantly for soils subjected to CSR values exceeding of 0.25. These results were used to express the effects of the variation in water level and liquefaction triggering response in terms of in-situ test data, wave height and number of waves for the granular backfill of a sample offshore structure.Copyright

Probabilistic Assessment of Cyclic Soil Straining in Fine-Grained Soils

This paper presents a probabilistically-based semi-empirical model for the assessment of cyclically-induced shear and post-cyclic volumetric (reconsolidation) straining of saturated fine-grained soils. Consolidated-undrained, strain-controlled static, and stress-controlled cyclic triaxial tests have been performed on undisturbed silty and clayey samples for the purpose of compiling a database composed of induced maximum cyclic shear and post-cyclic volumetric strains along with Atterberg limits, natural moisture content, undrained static shear strength. The maximum likelihood methodology is used to develop limit-state models incorporating the selected descriptive variables for the estimation of cyclically-induced soil straining. Results are summarized in the form of a semi-empirical stochastic model which enables the estimation of cyclically-induced maximum shear and post-cyclic volumetric straining as a function of liquid limit, plasticity index, natural moisture content, undrained shear strength, cyclic shear stresses.