Wen Jong Chang

Development of an in situ dynamic liquefaction test

A new field-testing technique has been developed in which liquefaction and pore pressure generation characteristics of soil are measured in situ. The in situ dynamic liquefaction test utilizes a large, hydraulic shaker to load dynamically a soil deposit. The soil response is measured with embedded instrumentation. The embedded instrumentation includes newly developed liquefaction test sensors that incorporate velocity transducers (geophones) and pore pressure transducers in a single case. The recorded data are used to describe pore pressure generation and liquefaction characteristics in terms of the relationship between shear strain and induced pore pressure ratio. The analytical techniques used to compute shear strain from particle velocity measurements are discussed and compared. The results from testing a 1.2-m by 1.2-m by 1.2-m reconstituted field test specimen are presented. The shear strain—pore pressure relationships at selected numbers of loading cycles that were determined from the in situ dynamic liquefaction test are compared with those measured by other investigators in the laboratory. The field-measured relationships show the same shape as the lab-measured relationships, but the field data indicate a smaller threshold strain for pore pressure generation (∼0.005 %). This difference is attributed to the low effective stresses in the reconstituted field specimen.

In Situ Dynamic Model Test for Pile-Supported Wharf in Liquefied Sand

Pile-supported wharf is a general option in port design to provide lateral resistance and bearing capacity under both static and dynamic loadings. In situ large-scale physical modeling using surface wave generator was performed to study the dynamic soil-structure interactions in pile-supported wharves and to verify configuration of an in situ monitoring station. A wharf model consisting of two steel pipe piles welded on a steel slab was installed on a reconstituted underwater embankment. Due to screening of stress waves, the two piles are subjected to different loading conditions. Data reduction procedures were developed to analyze coupled shear strain-pore pressure generation behavior, pile responses, and soil-pile interaction characteristics. The results proved that the physical modeling can capture the interactions among the induced shear strain, generated excess pore pressure, and dynamic p-y behavior around piles. Preliminary results also show that evolutions of dynamic p-y curve with excess pore pressure variations should be included in soil-pile interaction modeling.

Development of IoT Sensing Modulus for Surficial Slope Failures

To improve the limitations of rainfall-based slope warning system, a new system that integrates the hydro-mechanical slope analysis and wireless sensing module for surficial ground response monitoring is under development. The proposed system aims to establish a customized, time-dependent warning system for shallow slope failures triggered by rainfalls. A coupled hydro-mechanical analysis considering both the hydraulic infiltrations and mechanical responses of unsaturated soils in slope stability analysis is adopted. A real-time, wireless sensing module adopting the internet of things (IoT) technology is developed. The sensing module integrates the micro-electro-mechanical system (MEMS) sensing components with wireless communication modules. The module measures in-situ surface inclination and water content profile and uploads the data to cloud storage. The wireless sensing modules have been deployed in a potential landslide site for more than one year and current progress shows that feasibility of a customized, time-dependent warning system is promising.

TXT-tool 2.886-1.2: Guidelines for Landslide Monitoring Systems

This report aims at providing guidelines for setting up field monitoring programs for landslides. Recognizing that many parameters may be involved in landslide monitoring, the report concentrates on ground displacement, rainfall, soil moisture and groundwater conditions as the key elements. The types of instrumentations involved and their field installations are presented. The options of using automated electrical or optical fiber sensor systems are described. A few cases of applying fully automated field monitoring schemes for slope stability monitoring are presented to demonstrate the capabilities of currently available techniques.

Evaluation of Liquefaction Resistance for Gravelly Sands Using Gravel Content–Corrected Shear-Wave Velocity

AbstractThe current practice of evaluating the liquefaction resistance of gravelly soils with shear-wave velocity relies on the assumption that liquefiable gravelly soils behave as sandy ones. Recent laboratory tests on gap-graded gravelly sands show that the cyclic resistance is dominated by the packing conditions of the sand matrix, while the shear-wave velocity is affected by the gravel content. Taking these findings into account, the gravel content–corrected shear-wave velocity is derived based on the time-average equation of lumped gravel particles and the sand matrix. Based on analyses of case histories, a three-step procedure, which includes screening of gravelly sands, computation of stress-normalized, gravel content–corrected shear-wave velocity, and cyclic resistance evaluation using the modified correlation between the corrected shear wave velocity and the cyclic resistance, is proposed for evaluating the cyclic resistance ratio of gravelly sands. Comparisons with case histories show that the p...