S.L. Lee’s research while affiliated with National University of Singapore and other places

Two methods are presented to estimate the load-carrying capacity of driven piles. These methods use a new wave equation model that incorporates the loss of energy to the soil mass through radiation damping of the soil. Conventional soil parameters are used in this new model. Both methods use the load-test result of a test pile to estimate the soil parameters at the site by set matching. These soil parameters are then used to predict the load-carrying capacity of similar piles at the site in subsequent analyses from set measurements. The two methods are demonstrated by the prediction of the load-carrying capacity of 21 piles at four sites. Key words: load-carrying capacity, pile foundations, pile driving, soil setup, wave equation model.

Vertical drains and surcharge were used to accelerate the consolidation of soft marine clay under the second runway at the Changi Airport site. To study this problem further, the consolidation of a strip of layered clay deposit under a large reclamation is analysed as a two-dimensional problem in accordance with Biot's theory using the finite difference method. The soil with vertical drains is replaced with an equivalent soil having an enhanced vertical hydraulic conductivity obtained by equating the surface settlement of the real soil with that of the equivalent soil. The soil modulus and the hydraulic conductivity of the real soil are varied with the prevailing effective stress in the soil. The operating soil parameters determined by back analysing the field observations in a pilot test were then utilized to predict the behaviour of the main works. Soil displacement at any point in the plane of strain could be determined within a reasonable accuracy. As the equivalent soil is obtained by equating the average degree of consolidation, pore pressures cannot be predicted accurately within the drain area. However, the trend of pore pressure variation across the test site is implied by the analysis. The trend showed that pore pressures outside the drain area are found to influence the settlement and pore pressure inside the drain area, causing retardation in the consolidation of the drain area. Key words: Biot's analysis, consolidation, flexible drains, numerical analysis, soft clay.

The economic growth of a country depends significantly on its transportation system. The highways that form part of this system sometimes pass over compressible soft soil deposits. Two major geotechnical problems associated with the construction of road embankments on these soil deposits are stability during construction and long-term settlement. If the latter problem is not addressed adequately, excessive post-construction settlement will have serious consequences for the maintenance of road pavement, in addition to the unwarranted downdrag force (negative skin friction) and lateral pressure on the piles supporting the bridge abutments and ancillary structures. To mitigate these adverse effects, deep-seated saturated clays are pre-consolidated with Fibredrain, a vertical drain manufactured with biodegradable jute and coir fibre, and surcharge, and surface deposits of granular, clayey or peaty materials are treated by high-energy impact (HEI) application to enforce settlement and improve their bearing capacity. If post-construction secondary compression is significant it can be reduced by placing a higher surcharge than required for primary consolidation. Because of their cost-effectiveness these techniques have been and are being used in several soil improvement projects in the Southeast Asian region. Details of the treatment, the properties of and design procedure for Fibredrains, and the application of HEI are discussed.

Experimental programs were designed carefully and appropriate testing materials were selected for the parametric study on the flow of cement grout through aggregate media during the preplaced aggregate grouting process in concrete-construction. Experimental investigations include the testing and evaluation of the viscosity of cement grout, the intrinsic permeability coefficient, and the porosity of the aggregate media. The time dependency and shear history dependency of the Theological properties of the cement grout are incorporated in the viscosity tests so as to be able to simulate more accurately the grouting process. The average shear rate of the flow is estimated from the flow velocity by determining the average nominal radius of the imaginary flow channel from the permeability testing. The resulting parameters include the yield stress and plastic viscosity of the cement grout and their time dependency, intrinsic permeability and porosity of the aggregate media, and the average nominal radius of the imaginary flow channel.

The effective coefficient of consolidation C h , and hence the effective discharge capacity, of prefabricated vertical drains (PVDs) is a function of the hydraulic conductivity and compressibility of the clay as well as of the field performance of the PVD. The field performance is influenced by the deformation of the core and the filter, clogging of the filter, and kinking of the PVD during the consolidation process. The design of soil improvement projects using PVDs is a function of the effective C h , the final settlement, the drain spacing, and the lateral pressure on the drain. Prefabricated vertical drains should possess sufficient tensile strength to withstand the installation stresses associated with thick clay deposits, as well as the densification of granular soil layers at the surface by heavy tamping. Fibredrain is a PVD that is biodegradable and ecologically harmonious. Several selected projects in East and South East Asia are discussed to illustrate the field performance of Fibredrain. Le coefficient de consolidation effective C h et, de là, la capacité de décharge effective des drains verticaux préfabriqués (PVD) est fonction de la conductivité et compressibilité hydrauliques de l'argile ainsi que de la performance de terrain des PVD. La performance de terrain est influencée par la déformation du cur et du filtre, l'occlusion du filtre et la déformation des PVD pendant le processus de consolidation. La conception des projets de consolidation des sols utilisant les PVD dépend du C h effectif, du tassement final, de l'espacement des drains et de la pression latérale sur le drain. Les drains verticaux préfabriqués devront posséder une résistance à la traction suffisante pour supporter les contraintes d'installation dans des dépôts d'argile épais ainsi que la densification en surface des couches de sol granulaires, densification causée par un compactage lourd. Le Fibredrain est un PVD biodégradable et sans danger pour l'environnement. Nous avons choisi pour notre étude plusieurs projets en Asie orientale et Asie du sud-est afin d'illustrer la performance sur le terrain du Fibredrain.

The effective coefficient of consolidation Ch, and hence the effective discharge capacity, of prefabricated vertical drains (PVDs) is a function of the hydraulic conductivity and compressibility of the clay as well as of the field performance of the PVD. The field performance is influenced by the deformation of the core and the filter, clogging of the filter, and kinking of the PVD during the consolidation process. The design of soil improvement projects using PVDs is a function of the effective Ch, the final settlement, the drain spacing, and the lateral pressure on the drain. Prefabricated vertical drains should possess sufficient tensile strength to withstand the installation stresses associated with thick clay deposits, as well as the densification of granular soil layers at the surface by heavy tamping. Fibredrain is a PVD that is biodegradable and ecologically harmonious. Several selected projects in East and South East Asia are discussed to illustrate the field performance of Fibredrain.

A tall building comprising frames and shear walls coupled together is idealized as a shear–flexure cantilever through the continuum approach. The effects of axial deformation as well as axial force in the frames are considered and incorporated in the formulation of the governing equations. Numerical examples are solved through the Galerkin method and the results compared with finite element solutions. The study indicates that the effect of axial deformation in the frame should be considered for tall and/or slender buildings while the effect of axial force in the column should be included for buildings with soft-storeys resulting from the termination of core walls in the lower portion of the building. Copyright © 2002 John Wiley & Sons, Ltd.

The ability of cement grout to penetrate voids of aggregate media, during the injection process of prepacked concrete construction, is strongly dependent on its viscosity. This paper reports experimental work on the viscometric characteristics Of cement grout for the prediction of prepacked grouting process. Various factors influencing the measured results have been identified. Shear history dependent viscosity of cement grout requires that an experimental programme should be designed: (a) to ensure repeatability; and (b) to obtain meaningful results for the concerned construction process. Due consideration has been given to establish proper mixing and measuring programmes. Results were obtained through a set of carefully selected parameters to simulate the shear history during the grouting process. The Bingham model was adopted to characterise the shear rate dependency of the apparent viscosity. Time dependency of the Bingham parameters was obtained from a series of tests of the same batch under the specified initial mixing condition and subsequent agitation. Thixotropy loop tests were also carried out to analyse the sensitivity of the internal structure of cement grout to further shearing, thus comparing the mixing effect on rheological property of cement grout.

An investigation on the movement of water in 100% Portland cement concretes is presented. The water diffusion and sorptivity tests, together with the accelerated water permeability test, are performed to determine the transport parameters that characterise the mechanisms of water diffusion, sorptivity and permeability in concrete respectively. The effects of pore humidity, ambient temperature, environmental relative humidity, applied hydrostatic pressure gradient and water-cement ratio are also explored. The results obtained from the tests on water diffusion, sorptivity and permeability show good agreement with those reported in the literature. The study of water movement has practical implications on the prediction of transport and distribution of aggressive chemical agents in concrete, as well as on the development of rational and quantitative durability assessment for concrete structures exposed to different climatic and environmental conditions.