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Tripe R.,Atkins Boreas | Kontoe S.,Imperial College London | Wong T.K.C.,Geotechnical Engineering Office
Soil Dynamics and Earthquake Engineering | Year: 2013

An extensive investigation has been made into the interaction between topographic amplification and soil layer amplification of seismic ground motion. This interaction is suggested in the literature as a possible cause for the differences between topographic amplification magnitudes observed in field studies and those obtained from numerical analysis. To investigate this issue a numerical finite element (FE) parametric study was performed for a slope in a homogeneous linear elastic soil layer over rigid bedrock subjected to vertically propagating in-plane shear waves (Sv waves). Analyses were carried out using two types of artificial time history as input excitation, one mimicking the build-up and decay of shaking in the time histories of real earthquake events, and the other to investigate the steady-state response. The study identified topographic effects as seen in previous numerical studies such as modification of the free-field horizontal motion, generation of parasitic vertical motion, zones of alternating amplification and de-amplification on the ground surface, and dependence of topographic amplification on the frequency of the input motion. For the considered cases, topographic amplification and soil layer amplification effects were found to interact, suggesting that in order to accurately predict topographic effects, the two effects should not be always handled separately. © 2013. Source


Chan R.K.S.,Geotechnical Engineering Office
14th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering | Year: 2011

Landslides pose a significant threat to many communities in different parts of the world. A comprehensive Slope Safety Management System has been developed and implemented to tackle the unique landslide problems in Hong Kong. While the System has been able to cope with the prevailing nature of the landslide problems so far, climate change brings Hong Kong and other parts of the world new challenges, especially the impact of extreme rainfall. The number, scale and mobility of landslides could be unprecedented under an extreme rainstorm. To better understand the potential impact of extreme rainfall on slope safety, many research initiatives are underway in different parts of the world. In the interim, a pragmatic approach in engineering design could be adopted to cater for some of the uncertainties. An emergency response and preparedness system should be in place taking into account the potential impact of appropriate extreme rainfall events. Source


Ng C.W.W.,Hong Kong University of Science and Technology | Wong H.N.,Geotechnical Engineering Office | Tse Y.M.,Hong Kong University of Science and Technology | Pappin J.W.,Arup | And 3 more authors.
Geotechnique | Year: 2011

It is well recognised that field measurements of stressdependent soil-water characteristic curves (SDSWCCs) and the permeability function (coefficient of permeability with respect to the water phase) are vital for assessing transient seepage, pore water pressure changes and the stability of unsaturated soil slopes. In this study, SDSWCCs and the permeability function were measured by using the instantaneous profile method on a saprolitichillside in Tung Chung, Hong Kong. The ground profile comprises colluvium and completely decomposed tuff (CDT). A 3 m diameter circular plot was instrumented and subjected to two wetting-drying cycles. Throughout a 48-day monitoring period, variations of volumetric water content and matrix suction in the uppermost 3 m of soil were measured continuously using time-domain reflectometry moisture probes and jet-fill tensiometers, respectively. The field observations reveal that there is a clear trend of decreasing sizes of hysteretic loops of SDSWCCs with depth. In a comparison of the field- and laboratory-measured SDSWCCs, general agreement can be seen in the first wetting-drying cycle but not in the second cycle. The field-observed unsaturated permeability function is highly dependent on suction history (wetting- drying cycles). The field-measured permeability ranges from 4 × 10-7 m/s to 3 × 104 m/s in the colluvium, whereas the corresponding measured values vary from 4 × 10-7 m/s to 1 × 104 m/s in the CDT. Predictions of SWCC and permeability function using existing empirical approaches based on particle size distributions (PSDs) should be treated with caution. There is a clear qualitative and quantitative inconsistency between predictions of permeability function from PSD and field measurements. Source


Sewell R.J.,Geotechnical Engineering Office | Davis D.W.,University of Toronto | Campbell S.D.G.,Geotechnical Engineering Office | Campbell S.D.G.,British Geological Survey
Journal of Asian Earth Sciences | Year: 2012

Sixteen new high precision U-Pb zircon ages are reported from Jurassic and Early Cretaceous silicic volcanic and plutonic rocks of Hong Kong. When combined with the existing age dataset, the new ages constrain more tightly the timing of major periods of volcanism and plutonism at 162.6 ± 4.5. Ma, 146.7 ± 1.1. Ma, 143.0 ± 1.0. Ma and 140.8 ± 0.6. Ma. However, two ages of 151.9 ± 0.2. Ma and 148.1 ± 0.2. Ma, from eastern New Territories and southern Hong Kong indicate additional and therefore more continuous, albeit pulsed, magmatic activity than previously thought. © 2011 Elsevier Ltd. Source


Sewell R.J.,Geotechnical Engineering Office | Tang D.L.K.,Geotechnical Engineering Office | Campbell S.D.G.,British Geological Survey
Geochemistry, Geophysics, Geosystems | Year: 2012

Exceptional exposures of four, precisely dated, Middle Jurassic to Early Cretaceous, silicic volcanic centers and their plutonic equivalents in Hong Kong have provided an excellent opportunity to examine close connections in time and space between magma chambers and their overlying calderas. Here, we describe a ∼14 km crustal section through a collapsed caldera in southeastern Hong Kong where the intracaldera fill suggests that the magmatic discharge was of supereruption scale. The main subvolcanic components that link a magma chamber with surface are revealed by well-established field relationships, supplemented by high precision geochronology, whole-rock geochemistry, and geophysical data. Exposures and outcrop patterns reveal kilometer-scale caldera subsidence and evidence of the simultaneous evacuation of hundreds of cubic kilometers of high-silica rhyolite magma through dike-like conduits from a shallow subcrustal reservoir. The resultant volcanotectonic depression, within which is preserved a single cooling unit of massively columnar-jointed densely welded tuff (High Island tuff), is interpreted to form part of a larger tilted Early Cretaceous nested caldera complex. The High Island eruption signaled the end of a 24 Myr-period of voluminous, pulsed Middle Jurassic to Early Cretaceous silicic magmatism in the Hong Kong region characterized by four discrete ignimbrite flare-ups. Copyright 2012 by the American Geophysical Union. Source

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