Dongseop Lee

Analytical interpretation of slug test in a vertical cutoff wall.

An analysis method for slug tests performed in a partially penetrating well within a vertical cutoff wall is presented. A steady-state shape factor for evaluating hydraulic conductivity of the material within the wall was derived by applying the method of images to the previously developed analytical solution of Zlotnik et al. (2010) for an infinite aquifer. Two distinct boundary conditions were considered: constant-head boundary for the case of direct contact between the wall and the aquifer, and no-flux boundary representing an impermeable filter cake on the sides of the wall. The constant-head and no-flux boundary conditions yield significantly higher and lower shape factors, respectively, than those for the infinite aquifer. Consequently the conventional line-fitting method for slug test analysis would yield an inaccurate estimate of the hydraulic conductivity of a vertical cutoff wall.

Effect of Real Bentonite Cake on Slug Test Analysis for Slurry Trench Wall

The slug test is a viable method in estimating the hydraulic conductivity of the slurry trench wall backfill because of its ability to consider a more representative volume of the backfill and to reflect the in situ performance of the construction. A three-dimensional numerical model is developed to simulate the slug test in a slurry trench wall with the presence of bentonite cake on the interface boundary between the wall and the surrounding soil formation. Influential factors such as wall width (i.e., proximity of wall boundary), well deviation, vertical position of the well intake section, and compressibility of the wall backfill are taken into account in the model. The experimentally obtained hydraulic properties of the bentonite cake are also incorporated in a series of slug test simulations. The simulation results are then examined to evaluate the bentonite cake effect in analyzing practical slug test results in the slurry trench wall. The simulation results show that the modified line-fitting method can be used without any reduction factor for the slug test in the slurry trench wall with the presence of bentonite cake. A case study is reanalyzed with the assumption of existing bentonite cake. The results are compared with the previously reported results by the approaches used for the case of no bentonite cake (constant-head boundary) and upper-bound solution (no-flux boundary). The modified line-fitting method and the type curve method produce similar results for slurry walls with bentonite cakes. The case study results demonstrate the importance of the bentonite cake effect in estimating the hydraulic conductivity of the slurry wall backfill.

Optimum configuration of helical piles with material cost minimized by harmony search algorithm

Helical piles are a manufactured steel foundation composed of one or multiple helix plates affixed to a central shaft. A helical pile is installed by rotating the central shaft with hydraulic torque motors. There are three representative theoretical predictions for the bearing capacity of helical piles: individual bearing method, cylindrical shear method, and torque correlation method. The bearing capacity of helical piles is governed by the helical pile’s configuration, geologic conditions and penetration depth. The high variability of influence factors makes an optimum design for helical pile configuration difficult in practice. In this paper, the harmony search algorithm is adopted to minimize the material cost of helical piles by optimizing the components composing a helical pile based on the proposed bearing capacity prediction. The optimization process based on the combined prediction method with the aid of the harmony search algorithm leads to an economical design by saving about 27percent of the helical pile material cost.

Nonlinear Finite-Strain Self-Weight Consolidation of Dredged Material with Radial Drainage Using Carrillo’s Formula

AbstractEstimation of the time-rate consolidation of dredged deposits is considerably complicated when vertical drains are installed to enhance the consolidation process of the soft-soil stratum, because the vertical drains are commonly installed before self-weight consolidation is complete. In this paper, two new methods are proposed to take into account both vertical and radial drainage conditions during the nonlinear finite-strain self-weight consolidation of dredged soil deposits (i.e., precise prediction of the self-weight consolidation behavior considering radial flow to the vertical drain). For one-dimensional nonlinear finite-strain consolidation in the vertical direction, the simplified Morris’s analytical solution and the primary consolidation, secondary compression, and desiccation of dredged fill (PSDDF) analysis are adopted. In addition, to consider the radial drainage, Barron’s vertical drain theory is used. The overall average degree of self-weight consolidation of the dredged soil is estim...

The Unique and Interactive Effects of Employees’ Trust in Leader and Felt Trust on Voice Behavior

Although research has emphasized that interpersonal trust in the employee-leader relationship is the prime consideration for employees’ likelihood to speak up to their leaders, the extant literatur...

Case Studies of PSDDF for Phased Placement of Dredged Soils

Use of Terzaghis one-dimensional consolidation theory is not suitable for consolidation of highly deformable soft clays such as dredged soils. To model this condition, it is necessary to consider non-linear finite strain consolidation behavior, i.e., changes in compressibility and permeability with increasing stress. A one-dimensional non-linear finite strain numerical model, Primary Consolidation, Secondary Compression, and Desiccation of Dredged Fill (PSDDF), has been used to predict the stress-dependent settlement of fine-grained dredged materials. In this paper, two case studies of using PSDDF are discussed to illustrate the applicability and accuracy of PSDDF. The first case study involves PSDDF simulations of laboratory-phased placement of a marine clay dredged from Busan, Korea. PSDDF results are in good agreement with the corresponding results of the laboratory large strain consolidation tests. The other involves estimating the service life of the Craney Island Dredged Material Management Area near Norfolk, Virginia, in the United States. The excellent agreement between measured and calculated values shows that PSDDF is a reliable tool for predicting settlement of dredged material.