Sung-Woo Moon

Stress Dependency of Shear-Wave Velocity Measurements in Soils

AbstractBased on an extensive in situ shear-wave velocity (Vs) database, this study aims to not only examine the stress-dependent characteristics of in situ Vs from a generalized Vs-stress model [Vs=α×(σc′)β], but also provide valuable reference information on site-specific stress-dependency of Vs for global geotechnical sites. For in situ Vs, the site-specific material constants (α and β) at each site had wider ranges when compared to typical values reported from laboratory tests. This is mainly attributed to different test conditions and inherent in situ site characteristics. The in situ-based site-specific material constants in this study are compared with laboratory-based material constants suggested in previous studies. Evidently, each α–β trend varies on laboratory tests and in situ tests and a unified relationship is appropriate only when β is less than 0.5. Thus, separate relationships between material constants are proposed for laboratory-based and in situ-based measurements. The results imply th...

Estimating spatial variations in bedrock depth and weathering degree in decomposed granite from surface waves

AbstractIn Singapore, sudden changes of bedrock depth and highly variable weathering degrees in residual soils are commonly observed. This study employed the dispersive characteristics of Rayleigh-...

Numerical Investigation of Drilled Shafts near an Embankment Slope under Combined Torque-Lateral-Load Scenario

Generally, cantilevered structure-foundation systems supporting highway signs, signals, and luminaires in the areas exposed to severe wind loadings (e.g., hurricane) have been designed under coupled torsion and lateral load scenario. Especially, mast arm cantilevered structures constructed near or on an embankment slope may have more concerns on the torsional and lateral resistance of the foundation. However, most research works have merely considered drilled shaft foundations under torsion-lateral load case with an embankment in proximity. In this study, a numerical study is performed with different soil layers to: (1) understand the combined torque-lateral load behavior of drilled shafts near an embankment slope; (2) examine the effect of both the torsion and lateral resistances in the proximity of an embankment slope. It was found that torsional stiffness decreases with increase in slope angles. Finally, design criteria (e.g., minimum allowable distance from the embankment, maximum allowable point load near the embankment) of the mast arm assembly and loads are provided.

Effect of Fine Particles on Cement Treated Sand

Cement treated sand improves mechanical properties through the cementitious bonding between cohesionless particles, thus allowing several geotechnical applications such as soil stabilization against slope failure and liquefaction. Since pure sand without any fine particles is seldom available in nature, this study aims to investigate the effect of fine particles (kaolin) in a very small proportion (<5%) on cement treated sand. Two types of cements are used: (i) Ordinary Portland cement (OPC) and (ii) Calcium sulfoaluminate cement (CSA). OPC is the widely used cementitious binder whereas CSA is a rapid hardening cement that is becoming popular due to its low carbon foot print. Three different cement contents (3%, 5% and 7%) and four different fine contents (0%, 1%, 3% and 5%) for each cement content are chosen. The stiffness and strength of the cement treated sands are measured through shear wave velocity and unconfined compressive strength respectively, after 1-day and 7-day curing periods. The results show that the influence of fine particles is visible even with fine content as low as 1%. However, the effect is different between the two types of cements used and between low and high cement contents. As the fine content increases, the increase in strength and stiffness is more for OPC than CSA and more significant at low cement content (3%) than high cement content (5% and 7%).

Undrained Shear Strength in Cohesive Soils Estimated by Directional Modes of In-Situ Shear Wave Velocity

The estimated undrained shear strength (su) is often not a unique value because it can be evaluated by various test types and/or procedures, such as different failure modes, shear strain rates, and boundary conditions. This study explores (1) the relationship between reference undrained shear strength and in situ shear wave velocity in terms of the effective overburden stress, and (2) the independent relationships to evaluate the undrained shear strength with special consideration of different directional and polarization modes (VH, HV, HH shear waves), which has not been reported. This evaluation is done via a worldwide database compiled from 43 well-documented geotechnical test sites associated with soft ground. Finally, new correlation models are proposed to estimate the undrained shear strength based on the in situ shear wave velocity as well as the plasticity index or the overconsolidation ratio. The application of the shear wave velocity–undrained shear strength relation is illustrated through two independent case studies. The proposed relationships are expected to contribute to reasonable estimates of undrained shear strength as well as offer practical guidance on even extrapolation beyond the data that is available to geotechnical engineers.

From Direct Simple Shear Test to Soil Model Development and Supported Excavation Simulation: Integrated Computational-Experimental Soil Behavior Characterization Framework

AbstractA constitutive model that represents soil behavior under a wide range of loading conditions is necessary for the simulation of complex boundary value problems. However, most laboratory tests are interpreted with an assumption of uniform stresses and strains within the tested soil specimen even when the specimen is known to experience nonuniform stress-strain distribution as in the direct simple shear (DSS) test. Numerous tests are often needed to fully characterize a soil’s nonlinear and anisotropic behavior and to develop an appropriate soil model. This paper utilizes an evolutionary inverse analysis approach to extract nonuniform stresses and strains within K0 consolidated-undrained direct simple shear (CK0UDSS) test specimens on Boston blue clay (BBC) and directly develop soil constitutive models. The extracted soil behavior is consistent with known behavior of BBC including anisotropic stress-strain response and small strain nonlinearity obtained under complex laboratory loading conditions. Th...