Influence of groundwater drawdown on excavation responses e A case history in Bukit Timah granitic residual soils

Performances of a braced cut-and-cover excavation system for mass rapid transit （MRT） stations of the Downtown Line Stage 2 in Singapore are presented. The excavation was carried out in the Bukit Timah granitic （BTG） residual soils and characterized by significant groundwater drawdown, due to dewatering work in complex site conditions, insufficient effective waterproof measures and more permeable soils. A two-dimensional numerical model was developed for back analysis of retaining wall movement and ground surface settlement. Comparisons of these measured excavation responses with the calculated performances were carried out, upon which the numerical simulation procedures were calibrated. In addition, the influences of groundwater drawdown on the wall deflection and ground surface settlement were numerically investigated and summarized. The performances were also compared with some commonly used empirical charts, and the results indicated that these charts are less applicable for cases with significant groundwater drawdowns. It is expected that these general behaviors will provide useful references and insights for future projects involving excavation in BTG residual soils under significant groundwater drawdowns.

Effect of joints on microwave fracturing of the Bukit Timah granite using an open-ended antenna

Microwave fracturing of rocks before mechanical breakage could improve the performance of mechanical excavators and reduce environmental impacts.Previous research focused on the microwave fracturing of intact rock blocks.By using an open-ended antenna,this paper investigates the effect of pre-existing joints on the microwave fracturing of the Singapore Bukit Timah granite blocks.The results show that the specimens are weakened in the manners of cracking,spalling,melting,or a combination of them.The crack number and the total crack length produced by microwave treatment of jointed rock blocks are slightly smaller than those in the intact rock blocks.The interaction between joints and microwave-induced cracks can be summarized into the following four patterns:(1)microwave-induced cracks become arrested so that the crack propagation is terminated;(2)microwave-induced cracks penetrate the joints and continue to propagate;(3)microwave-induced cracks become deflected along the joints;and(4)microwave-induced cracks propagate forward following the joints.The smaller the approach angle between the microwave-induced crack and the preexisting joint is,the more microwave-induced cracks tend to be arrested at the joint.Increasing the approach angle between the microwave-induced crack and the joint can increase the chance of microwave-induced crack penetrating the joint.The results also show that the smaller the distance is between the microwave radiation point and the joint,the easier it is for microwave-induced cracks to penetrate the joints;otherwise,the microwave-induced crack is more likely to be arrested at the pre-existing joint.

Engineering properties of the Bukit Timah Granitic residual soil in Singapore

Extensive site investigations were conducted prior to the construction of a Mass Rapid Transit project in Singapore that was predominantly in the Bukit Timah Granite(BTG)formation residual soil.This paper evaluates the engineering properties of the BTG formation residual soil based on data from 208 site investigation boreholes from four different sites.Based on the results from 2481 conventional laboratory tests and 1192 in-situ tests,this paper summarizes the engineering properties of the highly variable BTG residual soil,including conventional composition analysis,index and hydraulic properties,and strength and deformation parameters required for geotechnical analysis and design.Based on these results,the BTG formation is found to be quite heterogeneous.As the degree of weathering decreases with depth from the top of the formation,the BTG residual soil becomes sandier,with reduced silt and clay fractions.The coefficient of permeability and the compression index of the BTG residual soil vary significantly.In addition,the empirical equations relating the shear strength(index)to the standard penetration test(SPT)-N,as well as the equations and charts for determining stiffness,are proposed.These findings,together with the proposed equations or charts,can be used for design guidance of similar projects related to granitic residual soils in Singapore.

印尼玻雅项目厂外取水方案研究

印尼玻雅项目厂址附近有Lematang河和Enim河两种水源可以选择。根据水文资料,提出两个供水方案:方案一为采用开敞式取水泵房从Lematang河取水;方案二为采用开敞式取水泵房从Enim河取水,雨季由河水补充水泵向厂区供水的同时,向Bukit Kendi矿坑补水;旱季矿坑作为河水的补充及备用水源,采用泵船取水方式。通过对两个方案的经济技术比较,推荐用Enim河作为水源,旱季由Bukit Kendi矿坑与河水联合供水的取水方式。