Geochemistry and zircon U-Pb geochronology of the rhyolitic tuff on Port Island,Hong Kong: Implications for early Cretaceous tectonic setting

Early Cretaceous rhyolitic tuffs, widely distributed on Port Island, provide insights into the volcanism and tectonic setting of Hong Kong. In this paper we present petrological, geochronological and geochemical data of the rhyolitic tuff to constrain the diagenesis age and petrogenesis of the rocks, tectonic setting and early Cretaceous volcanism of Hong Kong. The first geochronological data show that the zircons in the volcanic rocks have U-Pb age of 141.1–139.5 Ma, which reveals that the rhyolitic tuff on Port Island was formed in the early Cretaceous (K₁). Geochemically, these acid rocks, which are enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), and depleted in high field strength elements (HFSEs), belong to the high K calc-alkaline to shoshonite series with strongly-peraluminous characteristic. The geochemical analyses suggest that the volcanic rocks were derived from deep melting in the continental crust caused by basaltic magma underplating. Based on the geochemical analysis and previous studies, we concluded that the rhyolitic tuffs on Port Island were formed in a back-arc extension setting in response to the subduction of the Paleo-Pacific Plate beneath the Eurasian Plate.     

Numerical and experimental studies of pressure-controlled cavity expansion in completely decomposed granite soils of Hong Kong

Compaction grouting is the injection of a viscous grout into a soil under high pressure, which then densifies the surrounding soil by reducing void space. Laboratory and field tests of compaction grouting have been carried out. In this paper, a numerical model is used to simulate the compaction grouting process with the primary purpose of investigating relationships among various control parameters, such as injection pressure, void ratio and excess pore water pressure at various radial distances from the injection point. The compaction process is treated as a cavity expansion process in the numerical simulation. The soil is modelled with an elasto-plastic Mohr–Coulomb model using the commercial finite element program ABAQUS. In addition to numerical simulations, pressure-controlled cavity expansion laboratory tests were carried out on completely decomposed granite (CDG) soil specimens. Data collected from laboratory tests are compared with the finite element simulation to validate the finite element analyses. Factors that control the compaction process, such as the coefficient of earth pressure (K), initial void ratio, number of loading cycles and effective confining pressure, are explored in the numerical simulations.     

香港区域地层划分

本文在研究前人大量工作的基础上,以香港地区的地质演变历史为主要线索,重新拟定了泥盆纪以来香港的地层层序;对各主要地层单位,尤其是近年来新建的地层单位进行了讨论;将香港的地层与广东和中国南方进行了对比,并对香港今后进一步地层工作的方向提出了一些建议。本文的目的是建立一个简要的、索引式的有关香港地层的回顾,以便使读者能迅速掌握香港地层划分和对比的概况以及基本的地质演化历史。     

Gamma emitters in Hong Kong water

Water samples, representing seawater, river water, reservoir water, drinking water, and underground water were studied through gamma-ray spectral analysis. Only gamma emitters in the²³⁸U and²³²Th series and⁴⁰K were detected. No fission product was detected with specific activity above 0.1 Bq/kg. The present data could be the baseline for future monitoring of the radioactivity released from a nuclear plant being built at a 50-km distance from Hong Kong. The variation of detected specific activities may be due to geological differences and the effect of plants.     

Rain-induced slope instability in Hong Kong

Catastrophic geological disasters frequently occur on slopes with obliquely inclined bedding structures (also referred to as obliquely inclined bedding slopes), where the apparent dip sliding is not readily visible. This phenomenon has become a focal point in landslide research. Yet, there is a lack of studies on the failure modes and mechanisms of hidden, steep obliquely inclined bedding slopes. This study investigated the Shanyang landslide in Shaanxi Province, China. Using field investigations, laboratory tests of geotechnical parameters, and the 3DEC software, this study developed a numerical model of the landslide to analyze the failure process of such slopes. The findings indicate that the Shanyang landslide primarily crept along a weak interlayer under the action of gravity. The landslide, initially following a dip angle with the support of a stable inclined rock mass, shifted direction under the influence of argillization in the weak interlayer, moving towards the apparent dip angle. The slide resistance effect of the karstic dissolution zone was increasingly significant during this process, with lateral friction being the primary resistance force. A reduction in the lateral friction due to karstic dissolution made the apparent dip sliding characteristics of the Shanyang landslide more pronounced. Notably, deformations such as bending and uplift at the slope’s foot suggest that the main slide resistance shifts from lateral friction within the karstic dissolution zone to the slope foot’s resistance force, leading to the eventual buckling failure of the landslide. This study unveils a novel failure mode of apparent dip creep-buckling in the Shanyang landslide, highlighting the critical role of lateral friction from the karstic dissolution zone in its failure mechanism. These insights offer a valuable reference for mitigating risks and preventing disasters related to obliquely inclined bedding landslides.     

Devonian fluviodeltaic sedimentation in Hong Kong

Twenty-three distinct sedimentary facies have been distinguished in the Devonian Bluff Head Formation exposed around the Tolo Channel area of northeastern Hong Kong. These facies have been combined into five facies associations: channel, aeolian, sheetflood, deltaic and palaeosol, with the bulk of the formation belonging to the channel association. The lower part of the Bluff Head Formation, around Plover Cove, consists of upwards-coarsening cycles, each typically 3 m thick. The basal parts of some cycles contain distinctive marine fossils of Early to Middle Devonian age. Sedimentation occurred on a marine-influenced delta plain, with eustatic sea level rises controlling cycle development. The middle and upper parts of the formation contrast strongly with the lower part and show a distinct change to alluvial plain sedimentation. Upward-fining cycles, each approximately 40 m thick, comprise basal multistorey, braided, conglomerate-filled channel deposits at the base passing upwards into finer-grained sheetflood, aeolian and channel sandstones at the top. Palaeosols in the higher parts of the cycles indicate periods of non-deposition under semi-arid climatic conditions. These cycles represent repeated abandonments of the fluvial system which we suggest were controlled by tectonic pulses.     

Ecological modernisation and policy learning in Hong Kong

Whilst ecological modernisation theory emphasizes the potential for modern societies to recognize and respond to their environmental impacts by finding new ways of governing environment-economy relations, concepts of policy learning focus on the scope for new forms of environmental policy to be generated within and transferred between different contexts. Within this paper we explore the conceptual and practical linkages between the two areas of debate - a hitherto neglected area in the literature - and we set this discussion in the context of environmental policy-making in Hong Kong. We suggest that the practical relevance of the concepts of ecological modernisation and policy learning depends upon the presence of a reflexive society with rational, responsive institutions. While many theorists assume that such institutions exist, our analysis of policies for water and air quality management in Hong Kong highlights the need for theories to consider the embeddedness of existing institutions and the significance of the capacities for, and the barriers to, change more fully. We find that capacities for some forms of ecological modernisation and policy learning do exist in Hong Kong. However, we argue that the nature of these capacities often limits the potential for change to those local environmental problems that can be addressed through more technically and economically viable forms of policy intervention and that can be easily accommodated within existing political and economic structures. We also conclude that the capacities for ecological modernisation and policy learning that are needed if Hong Kong is to tackle the effects of the trans-boundary environmental problems that it is increasingly encountering have yet to emerge.     

香港安山-英安质古火山颈群

香港中侏罗世屯门组火山岩主要由安山质熔岩、凝灰岩和凝灰角砾岩夹少量凝灰质砂岩组成。其中凝灰角砾岩初期曾误认为是沉积砾岩。1990年香港地质调查组重新研究后,确认是火山成因的凝灰角砾岩。按岩相分析,屯门组火山岩可分为火山通道相安山-英安质熔岩和爆发角砾岩,还有爆发空落相凝灰角砾岩。火山通道相又可分为火山颈相和岩墙相,分布在屯门组东西两侧。在青山东麓,出露一列NNW向呈断续、线状分布的火山颈群。近年来新出版的《香港地质考察指引》和《香港工程地质实践》等地质著作仍将该区爆发角砾岩误认为是沉积成因的砾岩,在地质勘探和工程设计上造成混乱,导致不应有的经济和时间上的损失。本文综合最新研究成果并与世界各地同类火山岩的特征进行对比,确证火山通道相爆发角砾岩的存在,并发现呈线状分布的古火山颈群。     

香港地区边坡防护与治理

自开埠以来香港地区边坡事故一直不断。香港政府多年来积极进行边坡的防护治理,成效显著。讨论了香港地区岩土边坡破坏的主要原因、防治滑坡的工程措施及边坡管理系统。香港的边坡防治经验值得内地借鉴。     

Land reclamation in Singapore,Hong Kong and Macau

The spatial and temporal significance of land reclamation from the sea in relation to the development of the three SE Asian small coastal territories of Singapore, Hong Kong and Macau are examined and compared. In all three territories the rate of reclamation has been an index of the rate of economic development. Four phases of land reclamation are identified: (1) pre-1900: involved relatively unplanned and uncostly projects in shallow water and swamplands around the main focus of settlement; (2) 1900–1945: involved military projects outside the main settlement core; (3) 1945–1980: this phase of large-scale projects unconstrained by natural conditions because of advances in technology and high rate of reclamation was driven by rapid industrial and population growth; (4) 1980 to date: a period marked by large infrastructure projects designed to maintain and extend the status of the territories as world economic and commercial centres. Currently 10%, 5% and 33% of the total land surfaces of Singapore, Hong Kong and Macau respectively comprise land reclaimed from the sea and these proportions will continue to rise.     

Groundwater and geotechnical aspects of deep excavations in Hong Kong

Consideration of groundwater is a key element in almost every construction project. The design of deep excavations for basements or underground railway station concourses below the water table require that the water pressures are taken into account. Whilst these can be considered to be hydrostatic in soil, the decreasing permeability of rock with depth and the fact that groundwater flow is invariably along discrete fractures means that the water pressure is unlikely to be hydrostatic at depth.

Groundwater control for deep excavations can be achieved by a number of methods such as grouting, pumping or structural walls or a combination of these. For tunnelling projects grouting is extensively used, but the development of sophisticated tunnelling machines has led in many cases to the demise of compressed air as a means of groundwater control.     

Rockfall Hazard Analysis for Hong Kong Based on Rockfall Inventory

Summary ¶This paper compiles and analyzes the rockfall data in Hong Kong in the last fifty years. A simple rockfall hazard analysis is presented based on this rockfall inventory. A frequency-magnitude relation, which is analogous to the Gutenberg-Richter relation for earthquake occurrence, is proposed for rockfall, and direct correlation between rockfall frequency and the daily rainfall is observed. Data analysis shows that a threshold daily rainfall of about 150–200mm is expected in order to trigger rockfall events in Hong Kong. Among the 368 rockfall events in the 13 year period from 1984 to 1996 in Hong Kong, 35% of the incidents lead to blockage of or damage to roads, 22% lead to damages or evacuation of squatter huts, 21% lead to blockage of pedestrian pavement and footpath, and 15% affect buildings, such as housing apartments and schools. Only 15% of these rockfalls fell onto open space and caused negligible effects on human activities. Most of these rockfall events occurred during heavy rain and when landslide warning should has been issued by the Hong Kong Observatory, thus only 6% of these events led to injury or casualty, car damages, and damages to public utilities. Rockfall hazard zonation maps in terms of the spatial distribution of previous rockfalls are proposed for both Kowloon Peninsula and Hong Kong Island.     

人工边坡绿化种植技术及其在香港的应用

在人工边坡上进行绿化种植不仅美化环境，而且有控制冲蚀和稳定斜坡的作用，设计人员应考虑将植被作为所有土和风化岩石的人造斜坡的基本保护方法。香港在边坡绿化种植方面积累了成功的经验。文章概述了在人工边坡表面进行绿化种植的基本原理及其综合效应，详细介绍香港地区的人工边坡绿化种植技术，包括设计思路、设计过程、施工技术和维护管理等方面，并为当前中国内地人工边坡绿化种植技术的推广和研究提出了建议。     

Structurally controlled landslides in saprolitic soils in Hong Kong

A number of large slope failures which have occurred in Hong Kong have highlighted the important influence that discontinuities in saprolitic soils can have on slope stability. Conventional stability analyses normally adopted for such soils, which assume failure through intact materials of uniform shear strength, are not appropriate if discontinuity-controlled failures can be postulated. Stress history and present-day weathering effects should also be taken into consideration in the assessment of the long-term stability of slopes in weathered rocks in tropical and subtropical regions. © Rapid Science Ltd. 1998     

Hydrographic surveys and sedimentation in Deep Bay,Hong Kong

Three hydrographic surveys were carried out in Deep Bay, which is located in the eastern part of Pearl estuary between Shenzhen, the most successful special economic zone of PRC, and Hong Kong. Data on current, size distributions of bottom sediment, suspended solids, and some water quality parameters were obtained. This information is of value for mathematical modeling of tidal circulation and sediment transport in the bay, and also useful in the planning of further development in this area. The sedimentation rate in Deep Bay was estimated by two different approaches, viz. comparison of historical navigation maps and²¹⁰Pb dating. Information obtained from the maps indicated that average sedimentation rate between 1898 and 1949 was about 8 mm/yr, while a 15 mm/yr figure was obtained from the²¹⁰Pb dating for recent years.     

花岗岩风化程度的化学指标及微观特征对比——以香港九龙地区为例

据香港九龙3个不同工程场地取得的149件不同级别的风化花岗岩样品的化学分析结果,用统计学方法,从反映岩石风化程度的18项化学指标中选取9项进行了分析计算.对其结果及其与风化程度分级的关系的研究表明有4种指标比较理想.通过对样品微观特征的观察研究和矿物成分、微孔隙率以及综合显微岩石指标(Ip)进行了描述和定量分析,发现其中一些指标有一定相关性.这些化学指标和微观特征相关的统计值在一定程度上可定量表征花岗岩的风化程度,即:随风化作用进行,碱、碱土金属组分逐渐淋失,脱硅、富铝铁化作用逐渐加强;相应地,先是钠长石风化成高岭石,其次为云母和钾长石的风化.粘土矿物所占体积百分比随风化程度增高而变大,至残积土(Ⅵ级)时已达50%左右;Ip指标值下降,微孔隙率增高.文章综合出各个风化级别的指标变化范围及平均值供花岗岩分布区花岗岩风化野外调查和研究工作参考.     

香港九龙复活破火山的鉴别及其地质意义

香港主城区座落在香港岛一九龙地区的九龙花岗岩体上,该花岗岩体平面形态呈直径约11km的圆形,周边火山岩群山环绕,构成特殊的圆形盆地地貌,以往曾有人认为是陨石坑。笔者根据前人地质资料分析并经实地考察,认为该地貌形态实为大致以尖沙咀为中心的一个大型晚中生代复活破火山机构,九龙花岗岩体为破火口塌陷后侵位的中央侵入体,周围火山地层产状围斜内倾,发育环形断裂（主要为高角度正断层）和放射状断裂,具典型复活破火山特征,可称之为“九龙复活破火山”。     

香港九龙破火山的地层结构与划分讨论

香港岛—九龙半岛地区以往火山地层的划分主要依据岩性特征,基本不考虑火山构造和火山岩相的鉴别,由于陆相火山岩区特有的岩性岩相时空上的复杂多变,导致地层组越划越多,不能合理进行区域地层对比,更无法通过火山地层划分恢复古火山活动过程。笔者等在该地区开展了野外路线地质调查和火山构造—火山岩相研究,鉴别出九龙复活破火山机构,在此基础上确定火山地层主要由同一期普林尼式喷发形成的冷却单元构成,有类似的地层结构,结合年龄资料和区域地质对比,它们基本上可归入同一地层组;同时,分析了陆相火山地层的划分方法,指出岩石地层单位划分不能作为主要方法;冷却单元或流动单元才是合理划分陆相火山地层的基本单位。