C.W.W. Ng

C.W.W. Ng
The Hong Kong University of Science and Technology | UST · Department of Civil and Environmental Engineering

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581
Publications
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Publications

Publications (581)
Article
Biochar amended clay layer has emerged as a sustainable hydraulic barrier for hazardous municipal waste containment system. The effects of pore fluid salinity on soil shrinkage and water retention characteristics of biochar amended clay are unknown. This study aims to investigate the behavior of soil shrinkage and water retention of biochar amended...
Article
Full-text available
Phosphorus (P) deficiency in agricultural soil is a worldwide concern. P modification of biochar, a common soil conditioner produced by pyrolysis of wastes and residues, can increase P availability and improve soil quality. This study aims to investigate the effects of P-modified biochar as a soil amendment on the growth and quality of a medicinal...
Article
Full-text available
Steep creek hazards are characterised according to their solid fraction ν s , which governs the flow dynamics. To arrest these hazards, rigid multiple barriers are installed along a channel. However, existing design guidelines are deficient because the fundamental overflow and landing mechanisms are not well understood. In this study, experiments w...
Article
Full-text available
This paper compares the field performance of non-grassed and grassed three-layer landfill cover systems utilising construction waste but without geomembrane at the Shenzhen Xiaping landfill site under humid climates over a monitoring period of 54 months. The top layer of each cover system was constructed by coarse-grained completely decomposed gran...
Article
Full-text available
Due to climate change, extreme rainfalls happen more frequently with different patterns. Biochar and plant roots can affect soil water retention curve (SWRC) and hence slope stability. Until now, no available SWRC model considers soil–plant-biochar interaction, which can also be used for slope stability analysis under extreme rainfalls with differe...
Article
PurposeThe common mycorrhizal fungi associated with plant roots can reach a wide region in soil free of roots. The fungal hyphae and the generated organic matter affect soil hydraulic conductivity. Such an influence is so far not rigorously studied in the context of geotechnical systems subjected to the ecological process.Methods Here, we designed...
Article
Deep excavations inevitably induce stress relief and ground movement, which may affect the safety and serviceability of nearby pile foundations. Although research attention was paid to the basement-soil-pile interaction, most of the previous studies focused on responses of end-bearing piles due to a single basement excavation. In this study, centri...
Article
A basal clearance is usually designed beneath barriers to enable sufficient discharge to minimise the maintenance work over service life. Current design guidelines for multiple barriers usually neglect the influence of basal clearance, resulting in either an over-conservative or a non-conservative design impact force acting on the subsequent barrie...
Article
Compacted clay possesses a low water permeability and has been widely used in geo-environmental facilities such as landfill cover systems. Recent studies revealed the potential applications of compacted biochar-amended clay (BAC) as an alternative landfill cover soil. However, the effects of biochar on the soil water retention curves (SWRCs) of cla...
Article
The destructive nature of debris flows is mainly caused by flow bulking from entrainment of an erodible channel bed. To arrest these flows, multiple flexible barriers are commonly installed along the predicted flow path. Despite the importance of an erodible bed, its effects are generally ignored when designing barriers. In this study, three unique...
Article
Heat transfer from/to energy piles can cause plastic contraction of soft clay with a low overconsolidation ratio (OCR) during heating and cooling. This can lead to thermally induced excess pore water pressure and changes in the lateral stress acting on a pile. These thermally induced phenomena cause additional plastic settlement of the soil and pil...
Article
Full-text available
Baffles and check-dam systems are often used as granular flow (rock avalanches, debris flows, etc.) control structures in regions prone to dangerous geological hazards leading to massive landslides. This paper explores the use of numerical modelling to simulate large volume granular flow and the effect of the presence of baffles and check dam syste...
Article
Tunneling results in stress relief and arching in the ground. New tunnel excavation beneath an existing tunnel but at different angles can lead to different patterns of stress redistribution. Studies on multi-tunnel interaction have mainly focused on perpendicular tunnels, and the effects of tunneling skew angle remain poorly understood. Three-dime...
Article
The use of steel flexible barriers to mitigate landslide risk on natural hillsides is becoming common in the last decade in Hong Kong. The current design approach for this kind of barrier structure involves the adoption of the hydrodynamic load model to predict dynamic impact forces, followed by non-linear structural analyses of flexible barriers u...
Article
In natural slopes, apart from isotropic and transversely anisotropic soil fabric, rotated anisotropic soil fabric is also commonly observed due to deposition and weathering. Previous studies mainly focused on the effects of copula selection on transversely anisotropic soil slope stability. However, the influence of copula selection on rotated aniso...
Article
Stomatal conductance (SC) and chlorophyll concentration (CC) are sensitive to soil matric suction (ψ). The relationship between these two plant parameters and ψ in root zone can help understand the water uptake efficiency and photosynthetic capacity of a plant. This paper aims to quantify the relationships between SC and CC with ψ, for Schefflera a...
Article
Natural terrain landslides are mainly triggered by rainstorms in Hong Kong, which pose great threats to life and property. To mitigate landslide risk, building a prediction model which could provide information on both spatial and temporal probabilities of landslide occurrence is essential but challenging. In this paper, real-time rainfall conditio...
Article
Full-text available
Heavy metal contamination in soil is a great threat to medicinal plant. Ground granulated blast furnace slag (GGBS) is a potential soil pH adjuster to reduce heavy metal toxicity. However, how GGBS affects the quality and yield of herbal plants under heavy metal stress is not clear. This study aims to investigate the quality and yield of a medicina...
Article
Enzyme induced carbonate precipitation (EICP) is an innovative ground improvement technique which can enhance soil properties including soil strength, stiffness and hydraulic conductivity by cementing and filling soil pores. The calcium carbonate precipitation has the potential to influence the water retention ability through altering pore-size dis...
Article
Boulders entrained in debris flow induce high impact forces on a rigid barrier. In current design practice, the concentrated load from boulders is estimated using the Hertz equation with a load reduction factor (Kc). Separately, the distributed load from the debris is estimated using the hydrodynamic equation. The existing design practice is simply...
Article
There is an increasing interest and use of energy foundation worldwide. Full-scale tests, physical model tests at one Earth’s gravity and at elevated gravity in a geotechnical centrifuge and numerical simulations have been widely reported in the literature. Almost all studies have focused on single energy piles (EPs) and pile groups subjected to sy...
Article
Excavation induces stress changes and soil movement on existing floating piled rafts and elevated pile groups. Limited investigation of the effects of deep excavations has resulted in an incomplete understanding of pile foundation performance at the serviceability state. A series of three-dimensional (3D) centrifuge model tests and numerical simula...
Article
Full-text available
Purpose Soil matric suction, or negative water potential, contributes to soil physical stability (e.g., slope). Plants retain soil matric suction as they take up and transpire water in soil. This study investigated the effects of the common plant root-fungi symbiosis on the changes of the low-range matric suction (i.e., 0–100 kPa), which is relevan...
Article
In the design of multiple rigid barriers, the height of the first barrier governs the impact dynamics of debris flow on the next barrier in a channel. However, current design approaches neglect the height of the first barrier, and no specific guideline is given on the design of the impact load on the second barrier. In this study, a new impact equa...
Chapter
Debris flows pose threats to sustainable development in many countries worldwide, including China, Japan, Switzerland and USA. To mitigate these flows, rigid and flexible barriers are commonly installed along the predicted flow paths. To arrest large volumes of debris flow, several barriers may be installed in series to create a cascading effect to...
Article
Full-text available
Lateritic clay is well recognized to contain significant amount of iron and aluminium oxides (sesquioxide). These oxides enhance the formation of soil aggregates which would greatly affect soil structure. So far, no study has been carried out purposely to investigate the influence of aggregate-dependent structure on the mechanical behaviour of the...
Article
The influence of root hydro-mechanical reinforcement on slope stability has commonly been modelled two-dimensionally. Moreover, the differentiation between primary and secondary roots is always ignored. This paper proposes a new three-dimensional (3D) theoretical model describing the effects of hydro-mechanical reinforcement of root systems on the...
Article
In this study, resonant column tests carried out to investigate the influence of suction on the shear modulus and damping ratio of two compacted lateritic sandy clays from Ghana (GL) and Nigeria (NL) are reported. Each type of soils was tested under two confining pressures and at three suctions. The microstructure of the soils was also studied thro...
Article
Full-text available
An unsaturated soil is a three-phase material that is ubiquitous on the earth’s surface. The fully saturated and completely dry states are just two limiting conditions of an unsaturated soil. The state and properties of unsaturated soils can change significantly with external loads, weather conditions and groundwater level. Proper modelling of the...
Article
This paper presents a field test on the axial and radial thermal responses of friction-type energy piles embedded in clay under monotonic thermal loads (2.5 and 5.0 kW). The inlet and outlet water temperature, pile temperature, and strain were monitored. The heat exchange efficiency and thermal response of the energy pile are discussed and analyzed...
Article
Leachate transport through municipal solid waste (MSW) landfill liners can be slowed considerably by adsorption. MSW landfill leachate contains a large variety of pollutants at very different concentrations, and there will be competitive adsorption as these pollutants are transported through the landfill's compacted clay liner (CCL). In this study,...
Conference Paper
New insights into three-dimensional tunnel–tunnel interaction and tunnel–pile interaction are revealed and summarised in this lecture. Recent advances in the centrifuge modelling technique to facilitate the simulation of both volume and weight losses due to in-flight tunnel construction are described. Moreover, novel physical model tests are analys...
Article
Although the effects of tunnel excavation on nearby existing pile foundations have been extensively studied, previous studies mainly focused on response of single piles and elevated pile groups. In this study, three-dimensional centrifuge model tests were carried out to investigate the effects of side by side twin tunneling on an existing two by tw...
Article
Many lateritic soils contain goethite and hematite, which have a low thermal expansion coefficient and also enhance the formation of soil aggregates. The influence of these minerals on the thermo-mechanical soil behaviour, however, has not been well understood. In this study, cyclic thermal strain of a small number of specimens of saturated laterit...
Article
Root water uptake induces additional soil suction by soil water extraction. However, induced soil suction restricts root water uptake when beyond a threshold (st) and tend to stop water uptake at limiting suction (sl). This process is called root-soil hydraulic interactions, whose relationship with plant morphology (e.g., plant height, leaf area an...
Article
Existing solutions for analyzing one‐dimensional (1‐D) consolidation of unsaturated soil are only derived to cater to two extreme drainage conditions (fully drained and undrained). This study presents a new explicit solution for 1‐D consolidation of unsaturated soil with semi‐permeable drainage boundary. Based on the assumptions of two independent...
Article
Bio-engineered slopes use vegetation as “live” protection elements against the triggering forces of landslides, erosions and debris flows. In this paper, the effects of basic plant traits (both root and shoot) on their slope stability functions in compacted and planned green slopes have been reviewed. This review is based on over 200 papers on area...
Article
Rock-filled gabions are widely used to attenuate concentrated impact loads exerted by boulders entrained in debris flows. However, rock fragments used to construct gabion may not always be available and the performance of rock-filled gabion can be highly variable, depending on size and angularity of the rock fragments used. In this study, light-wei...
Article
Any tunnel construction inevitably causes differential soil movements, resulting in additional adverse effects to existing pipelines. Although there are many jointed pipelines in practice, previous studies commonly simplified existing pipelines as continuous structures. In this study, centrifuge tests were designed and conducted to investigate the...
Article
Granular flows, such as debris flows, are commonly arrested by using deformable barriers, but their designs rely heavily on empiricism. The fundamental impact mechanisms between a granular flow and a deformable barrier have yet to be elucidated. Thus, estimating the impact load on deformable barriers remains a key scientific and engineering challen...
Article
A full-scale test was carried out to investigate the interactions between an energy pile and four traditional piles connected to the same overlying reinforced beam. A series of sensors was installed in the energy pile, surrounding soil, traditional piles, and beam to monitor their thermal and mechanical responses. The interactions between the energ...
Article
Volumetric behavior of loess induced by isotropic compression and wetting was investigated through stress- and suction-controlled triaxial tests. To assist in the interpretation of test results, X-ray diffraction (XRD), Scanning Electron Microscope (SEM) and Mercury Intrusion Porosimeter (MIP) tests were carried out to determine the mineral composi...
Article
Thermal softening is generally referred as the reduction of yield stress with increasing temperature. Previous experimental studies of thermal softening focus on a single type of specimen (either intact or recompacted). In this study, thermal softening of saturated intact, recompacted and reconstituted loess specimens was investigated through tempe...
Article
Although various researchers have reported that scaling effects should be considered carefully when modelling mechanical behaviour of pile in sand by a geotechnical centrifuge, scaling effects on the coupled thermo-mechanical behaviour of energy pile have not been reported. In this study, the scaling effects on centrifuge modelling of floating ener...
Article
Analytical solutions are proposed considering the hydrological and mechanical effects of roots with different root architectures on shallow slope stability. Analytical parametric studies show that an exponential root has more prominent hydrological and mechanical effects than a uniform one. At drying conditions, the hydrological effect becomes more...
Article
Retaining wall back-filled with fine-grained soil such as silt is vulnerable to failure due to its low water permeability under heavy rainfall. Based on unsaturated soil mechanics, a new capillary barrier concept is proposed to form a back-filled retaining wall to reduce water infiltration under rainfall. The capillary barrier retaining system cons...
Article
Due to shortage of usable spaces in congested urban cities, deep basements for buildings are frequently constructed above or at a side of existing tunnels. Although much attention was paid to the basement-tunnel interaction, previous studies mainly simplified it as a plane strain problem and focused on excavation-induced tunnel responses in sand. I...
Article
Lateritic clay is widely distributed in tropical areas and extensively used as foundation materials. Compared to other soils, it is rich in iron and aluminum oxides (sesquioxide), which enhance the formation of soil aggregates. The principal objective of this study is to investigate the hydro-mechanical behaviour of a lateritic sandy lean clay. All...
Article
The coefficient of restitution (COR) is an important input parameter in the numerical simulation of granular flows, as it governs the travel distance, the lateral spreading and the design of barriers. In this study, a new custom-built micro-mechanical impact loading apparatus is presented along with impact experiments on engineered and natural mate...
Article
Lateritic soils generally have high content of iron and aluminium oxides (i.e., content of sesquioxides), which are found able to enhance soil aggregation and therefore to alter pore size distributions. So far, however, there is no study on the influence of sesquioxides on the stress-dependent soil water retention curves (SDSWRCs) of unsaturated so...
Article
Although numerous studies have been carried out on investigating thermal volume changes in different soils, limited attention has been paid to loess. This study aims to investigate the effects of clay content on the deformation of loess under heating-cooling cycles. Three soils with different clay contents (i.e. SA: 7%; SB: 13%; SC: 35%) were prepa...
Article
Full-text available
Purpose Temperature has a significant influence on water retention curve (WRC) because temperature affects surface tension of water and volumetric behaviour of soil. However, in previous studies on thermal effects on WRC, the difference in suction-induced volume change of soil specimen at various temperatures is always insignificant. With increasin...
Article
Although various researchers have reported that scaling effects should be considered carefully when modelling the mechanical behaviour of pile in sand by a geotechnical centrifuge, scaling effects on the coupled thermo-mechanical behaviour of the energy pile have not been reported. In this study, the scaling effects on the centrifuge modelling of f...
Article
A large amount of waste glass is generated every year and contributes significantly to landfills. Large-scale physical model tests were carried out to study the dynamic response of recycled crushed glass (RCG) contained in gabion baskets and its performance against successive boulder impacts at energy levels of up to 70 kJ. The cushioning performan...
Article
Full-text available
Random field theory has been increasingly adopted to simulate spatially varying environmental properties and hydrogeological data in recent years. In a two-dimensional (2D) stochastic analysis, variation of the environmental properties or hydrogeological data along different directions can be similar (i.e., isotropic) or quite different (i.e., anis...
Article
When the ground is subject to dynamic compaction such as aircraft wheel loading and pile driving, the wave dissipates in soil, which has not been fully understood qualitatively and quantitatively. This paper reports a series of split-Hopkinson pressure bar (SHPB) tests on silica and calcareous sands with various length-to-diameter ratios, initial v...
Article
Three-dimensional numerical parametric study is conducted to investigate stress transfer mechanisms and settlement of a floating pile due to multi-propped basement excavation by using hypoplastic sand model. Centrifuge test results are adopted to validate the soil model and model parameters. Effects of excavation depth, pile location with respect t...
Article
Full-text available
The impulse load of boulders at the front of debris flows is critical to the design of structural defense measures, which are commonly constructed on hillsides to mitigate landslide risk. Field evidences have demonstrated the capability of some steel flexible barriers in intercepting debris flows with bouldery inclusions. However, there is still a...
Article
Microbial aerobic methane oxidation (MAMO) has been considered as an environmental-friendly method for mitigating methane emission from municipal landfill sites. Soil column has in a landfill cover under one-dimensional (1-D) condition. However, most of the published soil column tests failed to simulate 1-D heat transfer due to the use of thermal c...