The paper presents a theory of non-linear consolidation for radial flow of a clay deposit treated with PVDs considering linear void ratio-log effective stress relationship, constant coefficient of consolidation but with ramp or construction loading. The governing equation of consolidation is solved numerically by the finite difference method. Parametric study quantifies the effects of magnitude of surcharge load and construction time on the variations of degree of settlement and degree of dissipation of excess pore pressures with time. The maximum induced excess pore water pressure is sensitive to the construction time for a given surcharge load. The variation of degree of settlement is dependent on both applied load intensity and the construction time. While the rate of building up of pore pressure with time during the construction is almost independent of stress increment ratio, the dissipation rate is shown to be dependent on stress increment ratio.

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The design of a soil improvement system, by preloading with wick drains, is formulated as a constrained optimization problem. The drain spacing, length, embankment height, and time required to achieve a specified consolidation settlement are selected as design variables whereas, the total cost of the system is adopted as an objective function. The cost function includes excavation, sand blanket, engineering fill, surcharge, wick drains, instrumentations and observation cost components. For a given site dimensions, soil profile, targeted settlement, and maximum allowed time to achieve, a computer program is coded in Fortran-90 to solve the problem of consolidation in vertical and radial directions based on Hansbo's (1981) and Olson (1977) methods, with different options to include the effects of smear, well resistance, ramp loading, and wick drains characteristics. In conjunction with the modified Hooke and Jeeves optimization method, the program is applied to a real project under construction in Basra province-Iraq. The real site dimensions, soil profile, and soil characteristics, as obtained from the site investigation program, are adopted. For the unit prices assigned, the results support the capability of the optimization method in manipulating such a decision-making problem. They also revealed failure of decision taken of canceling the inclusion of wick drains and adopting preloading only as a technique to improve the site soil. Studying the effects of the values of coefficients of consolidation in two directions on the behavior highlighted the vital importance of conducting a preliminary site investigation to evaluate foundation proposals. After arriving to a decision regarding soil improvement, the detailed phase of site investigation should be oriented towards finding the first order soil parameters associated with the selected soil improvement method, instead of wasting the efforts and money through conducting an exaggerated number of traditional less important tests. It is concluded that increasing the coefficient of consolidation in the vertical direction and the ratio of its radial value to the vertical one will increase the optimum drain spacing and decrease the drain length, the time required to achieve a specified settlement, and the required cost of the system. Embankment height, time of consolidation and total cost are proportional to the required settlement.

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In the excess pore water pressure dissipation method (referred to as EPWPD method hereafter), ground settlement occurs to some extent due to compaction, because vertical drains in the ground could prevent the pore water pressure from rising during earthquake. Therefore, in this method, it is particularly important to predict the amount of ground deformation under liquefaction as well as to discuss whether liquefaction could be prevented. In this study, the fundamental characteristics of this method were examined by a series of numerical simulations to quantitatively predict the ground deformations. The macro element method, which had been applied only to consolidation phenomena, was mounted on a soil-water coupled finite deformation analysis code GEOASIA which is capable of handling inertial forces and utilizes the SYS Cam-clay as the elasto-plastic constitutive model of the soil skeleton. The main conclusions obtained in this study are outlined next. 1) It was evident that the macro element method that had been only used for quasi-static problems has satisfactory approximation accuracy even in dynamic problems. 2) Basic characteristics of EPWPD method (i.e., liquefaction/compaction during earthquake and consolidation settlement after earthquake) can be adequately reproduced even when a comparatively rough finite element mesh without accounting the drains pitch is used in the macro element method mounted on the analysis code GEOASIA. 3) It is possible to efficiently design the effective drain pitch under the EPWPD method by conducting 1-dimentional mesh analysis prior to multi-dimensional mesh analysis.

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The disposal of the dredged soil has recently become a worldwide problem. In order to utilize high water content soil material, it is essential to dewater and increase the soil strength. There are urgent demands for developing an alternative new method to dewater the dredged soils in more economical and environment-friendly viewpoint. In this paper, siphon method with porous filter material is proposed to dewater the high water content dredged soil. In order to clarify the availability and effectiveness of this method, a series of tests were performed to investigate the dewatering behavior and strength of the dredged soil with vacuum and siphon methods. It was found that there is some possibility to dewater the dredged soil by using siphon method with vertical pressure.

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The ground surface of reclaimed land with dredged clay settles due to self-weight consolidation for a long term. If the ground surface settles rapidly, the settled space can receive additional dredged clays. In this paper, the ground improvement project with vertical drains for such a disposal pond is introduced. The determination of model ground using the reclamation analysis is a key point because the ground condition at the installation of plastic board drain is not different from that at the design of ground improvement. The adequacy of proposed method is confirmed in comparison with the measured excess pore water pressure distributions at the installation of vertical drains.

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This paper covers a development of volume reducing method for natural cohesive soil ground by disturbance, generated by mixing machinery as utilized for cement deep mixing method. This method is based on the basic knowledge that compressibility of natural clay will be changed by sample disturbance. This paper summarizes basic effect of compressibility of natural clay on artificial disturbance by a series of laboratory oedometer tests. Through the tests using undisturbed clay samples taken in Japan, effects of disturbance on compressibility is examined. Then, simple estimation of potential settlements due to ground disturbance by mixing machinery is studied using liquid limit of clay sample, as basic clay intrinsic parameter. In addition, effect of coefficient of consolidation due to the disturbance is confirmed to control the consolidation speed in subsequent soil improvement work by pre-fabricated vertical drain. Finally, some probable application of this proposed method is mentioned.

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