Rainfall-induced landslides in Hulu Kelang area, Malaysia   总被引：5，自引：2，他引：3  

Min Lee Lee  Kim Yeong Ng  Yuk Feng Huang  Wei Chao Li 《Natural Hazards》2014,70(1):353-375

Hulu Kelang is known as one of the most landslide-prone areas in Malaysia. The area has been constantly hit by landslide hazards since 1990s. This paper provides an insight into the mechanism of rainfall-induced landslide in the Hulu Kelang area. Rainfall patterns prior to the occurrences of five selected case studies were first analyzed. The results showed that daily rainfall information is insufficient for predicting landslides in the area. Rainfalls of longer durations, i.e., 3–30 days prior to the landslides should be incorporated into the prediction model. Numerical simulations on a selected case study demonstrated that both matric suction and factor of safety decreased steadily over time until they reached the lowest values on the day of landslide occurrence. Redistribution of infiltrated rainwater in the soil mass could be a reason for the slow response of failure mechanism to rainfall. Based on 21 rainfall-induced landslides that had occurred in the area, three rainfall thresholds were developed as attempts to predict the occurrence of rainfall-induced landslide. The rainfall intensity–duration threshold developed based on the local rainfall conditions provided a reasonably good prediction to the landslide occurrence. The cumulative 3- versus 30-day antecedent precipitation index threshold chart was capable of giving the most reliable prediction with the limiting threshold line for major landslide yielded a reliability of 97.6 %.  相似文献   

A modified analytical solution of soil stress distribution for XCC pile foundations     

Yaru Lv  Hanlong Liu  Charles W. W. Ng  Anthony Gunawan  Xuanming Ding 《Acta Geotechnica》2014,9(3):529-546

X-section cast-in-place concrete pile (XCC pile) is a new type of pile foundation, which has an X-shaped cross section. Compared to the traditional circular pile of the same cross-sectional area, the bearing capacity of an XCC pile is higher due to increased cross-sectional perimeter. Since Geddes solution is based on St. Venant’s principle, leading to the results independent of the cross-sectional geometry and size, large differences are induced when estimating the soil stress distribution for XCC pile foundations. This paper derives a modified analytical solution, which is dependent on the cross-sectional geometry of XCC pile, from Geddes solution. Validation of this modified solution was conducted through three-dimensional numerical analysis and proven more suitable for XCC pile foundations. Parametric study on three geometrical parameters is conducted using this modified solution. The results indicate that the stress in founding soil due to skin friction decreases with increasing pile radius and central angle of concave, but increases with increasing length of flat side. The stress due to end-bearing decreases with increasing pile radius and length of flat side, but increases with increasing central angle of concave. From the parametric studies, the recommended dimensions of XCC pile radius, length of flat side, and central angle of concave are recommended ranges from 200 to 600 mm, 30 to 60 mm, and 90° to 150°, respectively.  相似文献   

Distribution, classification, petrological and related gochemical (SRA) characteristics of a tropical lowland peat dome in the Kota Samarahan-Asajaya area, West Sarawak, Malaysia     

Mohamad Tarmizi Mohamad Zulkifley  Ng Tham Fatt  Wan Hasiah Abdullah  John Kuna Raj  S. Paramanathan Param  Roslan Hashim  Muhammad Aqeel Ashraf 《Central European Journal of Geosciences》2013,5(2):285-314

Petrographic studies indicate that lateral variations in the decomposition levels of peat are associated with the predominantly occurring peat macerals. Source Rock Analyzer (SRA) results indicate lateral variation in peat organic matter types from type II to III and back again to type II, occurring laterally within the top 0-m to 0.5-m layer at the basin margin to the midsection and further towards the near-center areas of the peat dome. This variation is most likely caused by a combination of factors: (a) Horizontal zonation and lateral variation of the dominant species of plant assemblages (b) Fibric (marginal) peats and hemic to sapric peats associated with type II organic matter (kerogen). Sample organic matter (coal-equivalent kerogen) typing indicates that the relative abundance of phytoclasts and palynomorphs generally supports the organic matter classification obtained by the SRA method. Lateral variations in the peat organic matter types may support the lateral vegetation variation concept. The classification of peat organic matter types (interpreted from visual analyses of palynological slides) occurring from the basin periphery to the mid-section and further towards the basin center yields organic matter of type II to type III and mixed types II to III (coal kerogen-equivalent), respectively.  相似文献   

Size and shape characteristics of drumlins,derived from a large sample,and associated scaling laws     

Chris D. Clark  Anna L.C. Hughes  Sarah L. Greenwood  Matteo Spagnolo  Felix S.L. Ng 《Quaternary Science Reviews》2009,28(7-8):677-692

Ice sheets flowing across a sedimentary bed usually produce a landscape of blister-like landforms streamlined in the direction of the ice flow and with each bump of the order of 10² to 10³ m in length and 10¹ m in relief. Such landforms, known as drumlins, have mystified investigators for over a hundred years. A satisfactory explanation for their formation, and thus an appreciation of their glaciological significance, has remained elusive. A recent advance has been in numerical modelling of the land-forming process. In anticipation of future modelling endeavours, this paper is motivated by the requirement for robust data on drumlin size and shape for model testing.From a systematic programme of drumlin mapping from digital elevation models and satellite images of Britain and Ireland, we used a geographic information system to compile a range of statistics on length L, width W, and elongation ratio E (where E = L/W) for a large sample. Mean L, is found to be 629 m (n = 58,983), mean W is 209 m and mean E is 2.9 (n = 37,043). Most drumlins are between 250 and 1000 metres in length; between 120 and 300 metres in width; and between 1.7 and 4.1 times as long as they are wide. Analysis of such data and plots of drumlin width against length reveals some new insights. All frequency distributions are unimodal from which we infer that the geomorphological label of ‘drumlin’ is fair in that this is a true single population of landforms, rather than an amalgam of different landform types. Drumlin size shows a clear minimum bound of around 100 m (horizontal). Maybe drumlins are generated at many scales and this is the minimum, or this value may be an indication of the fundamental scale of bump generation (‘proto-drumlins’) prior to them growing and elongating. A relationship between drumlin width and length is found (with r² = 0.48) and that is approximately W = 7 L ^1/2 when measured in metres. A surprising and sharply-defined line bounds the data cloud plotted in E–W–L space, and records a scale-dependent maximum elongation limit (approximated by E_max = L^1/3, when L measured in metres). For a given length, for some reason as yet unknown, drumlins do not exceed the elongation ratio defined by this scaling law. We also report and compare our statistics to an amalgamated sample (25,907 drumlins) of measures derived from around 50 published investigations. Any theory must be able to explain the drumlin statistics and fundamental scaling properties reported herein and they thus provide powerful tests for drumlin modelling.  相似文献   

Developing an empirical model of canopy water flux describing the common response of transpiration to solar radiation and VPD across five contrasting woodlands and forests     

Rhys Whitley  Daniel Taylor  Catriona Macinnis‐Ng  Melanie Zeppel  Isa Yunusa  Anthony O'Grady  Ray Froend  Belinda Medlyn  Derek Eamus 《水文研究》2013,27(8):1133-1146

A modified Jarvis–Stewart model of canopy transpiration (E_c) was tested over five ecosystems differing in climate, soil type and species composition. The aims of this study were to investigate the model's applicability over multiple ecosystems; to determine whether the number of model parameters could be reduced by assuming that site‐specific responses of E_c to solar radiation, vapour pressure deficit and soil moisture content vary little between sites; and to examine convergence of behaviour of canopy water‐use across multiple sites. This was accomplished by the following: (i) calibrating the model for each site to determine a set of site‐specific (SS) parameters, and (ii) calibrating the model for all sites simultaneously to determine a set of combined sites (CS) parameters. The performance of both models was compared with measured E_c data and a statistical benchmark using an artificial neural network (ANN). Both the CS and SS models performed well, explaining hourly and daily variation in E_c. The SS model produced slightly better model statistics [R² = 0.75–0.91; model efficiency (ME) = 0.53–0.81; root mean square error (RMSE) = 0.0015–0.0280 mm h^‐1] than the CS model (R² = 0.68–0.87; ME = 0.45–0.72; RMSE = 0.0023–0.0164 mm h^‐1). Both were highly comparable with the ANN (R² = 0.77–0.90; ME = 0.58–0.80; RMSE = 0.0007–0.0122 mm h^‐1). These results indicate that the response of canopy water‐use to abiotic drivers displayed significant convergence across sites, but the absolute magnitude of E_c was site specific. Period totals estimated with the modified Jarvis–Stewart model provided close approximations of observed totals, demonstrating the effectiveness of this model as a tool aiding water resource management. Analysis of the measured diel patterns of water use revealed significant nocturnal transpiration (9–18% of total water use by the canopy), but no Jarvis–Stewart formulations are able to capture this because of the dependence of water‐use on solar radiation, which is zero at night. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

跨越走滑断层黏土地层动力响应离心机试验研究     

蔡奇鹏  吴宏伟  胡平  陈星欣  李升才 《岩土力学》2018,39(7):2424-2432

地震中基岩走滑断层活动引起跨断层地下结构物破坏,上覆土层的非一致响应机制尚不明确,隐伏裂缝影响规律认识不足。基于可模拟走滑断层活动的层状剪切箱,针对黏土地层展开两个离心机振动台试验,对比上覆土体中隐伏裂缝的影响。试验结果表明,当地层中不存在隐伏裂缝时,基岩走滑断层错动对两盘地层的非一致振动的影响不显著。当地层中存在隐伏裂缝,错动盘一侧土体的振动加速度幅值随振动循环次数的增加逐渐减小,固定盘和错动盘两侧土体出现非一致振动响应,固定盘一侧土体产生的超静孔压大于错动盘一侧。隐伏裂缝对土体非一致振动响应的影响范围受限于其在地层中的分布范围,探明隐伏裂缝上断点的埋深具有重要工程意义。  相似文献   

Monitoring ground deformation in Beijing, China with persistent scatterer SAR interferometry   总被引：1，自引：1，他引：0  

Alex Hay-Man Ng  Linlin Ge  Xiaojing Li  Kui Zhang 《Journal of Geodesy》2012,86(6):375-392

This paper investigated the long term ground deformation in Beijing, China, using persistent/permanent scatterer interferometry (PSI) techniques. GEOS-PSI (Geodesy and Earth Observing Systems-PSI), an in-house software developed at UNSW for PSI, has been applied to 41 ENVISAT ASAR images acquired over the metropolitan area of Beijing City between June 2003 and March 2009 and 24 ALOS PALSAR images (two Paths: 10 acquisitions from January 2007 to October 2008 and 14 acquisitions from February 2007 to September 2009). The results generated using these datasets from the two satellites were cross-validated. Correlations between the results of ENVISAT ASAR and ALOS PALSAR agreed very well. The horizontal and vertical displacement rate maps over Beijing City were obtained from the results generated with data acquired by both satellites over the period from 1st February 2007 to 1st November 2008. The results indicate that the displacements in Beijing City were mainly in the vertical direction. The majority of the easting displacement rates were in the range of ?10 mm/year to 10?mm/year, while the vertical rates were in the range of ?115 mm/year to 6?mm/year. The possible cause for the ground deformation is groundwater extraction based on our research as well as earlier published studies.  相似文献   

Burrowing responses of the short-neck clam Ruditapes philippinarum to sediment contaminants     

Shin PK  Ng AW  Cheung RY 《Marine pollution bulletin》2002,45(1-12):133-139

The burrowing responses of a common tropical bivalve, the short-neck clam Ruditapes philippinarum, to cadmium (Cd)-spiked sediment, variations of sediment grain size and natural sediments collected from 15 locations in Hong Kong's inshore waters were investigated through a series of laboratory tests. Results showed that the burrowing response exhibited a negative relationship with an increase in Cd concentration in the spiked sediments. The level of Cd was also found to be directly proportional to the percent mortality of the clam. However, there was no significant difference (p>0.05) in the time elapsed for the clam to burrow into sediments with different grain size composition. The elapsed time for 50% of the test clams to burrow into the sediment (ET₅₀) over a period of 48 h was calculated for the sediment samples collected from the 15 locations. Results of ANOVA showed significant difference (p<0.05) among the sediment samples. Tukey's multiple comparison test revealed two groups of sediments: group 1 containing 3 sediment samples collected from Victoria Harbour and group 2 containing 12 samples obtained from other coastal areas of Hong Kong. The ET₅₀ value for group 1 sediments was found to be greater than 2880 min whilst the ET₅₀ for group 2 sediments had a mean of 173.9 min. Agglomerative classification of the sediment samples, based on metal content (As, Cd, Cr, Cu, Ni, Pb, Zn), also showed two similar groups, suggesting that the ET₅₀ values were correlated with the metal level of the sediment samples. Group 1 sediments collected from Victoria Harbour had greater concentrations of Cd, Cr, Cu, Ni and Zn as compared to that in group 2. The present study demonstrated that high metal content in the sediment tends to inhibit the burrowing responses of the clam and that there is potential to develop the burrowing responses of R. philippinarum as a sublethal sediment toxicity test.  相似文献   

Magnetic properties and heavy-metal contents of contaminated seabed sediments of Penny's Bay, Hong Kong   总被引：12，自引：0，他引：12  

Chan LS  Ng SL  Davis AM  Yim WW  Yeung CH 《Marine pollution bulletin》2001,42(7):569-583

Magnetic properties and heavy-metal concentrations of vibrocore samples were found to be potential indicators of shipping contamination in seabed sediments in Hong Kong Harbour. Geochemical results of 74 vibrocores located off Penny's Bay on Lantau Island revealed an enrichment of heavy metals in the upper 1-2 m of the cores within the eastern part of the study site. Whole-core magnetic susceptibility measurements also showed a greater concentration of magnetic particles in the surficial layer of these cores. A significant correlation exists between the magnetic susceptibility and the concentrations of Pb, Zn and Cu, as well as the Tomlinson pollution load index (PLI). The proximity of these cores to a major navigation fairway and an anchorage site suggests probable contamination of the surficial seabed sediments by shipping-related wastes. A study of the magnetic properties of one of the cores, VT60, revealed a difference in the magnetic properties between the contaminated and the uncontaminated sediments. Samples from the contaminated zone exhibited relatively stronger magnetic remanence and susceptibility. The two groups of samples also formed distinct trends on the hysteresis ratios plot. A level of unusually high magnetic susceptibility within the contaminated zone was attributable to the presence of strongly magnetized granules, which were probably refuse from shipping-related activities. Geochemical and magnetic results were also conducted on samples of different size-fractions from this core. The < 63 microns fraction was found to contain a relatively higher magnetic susceptibility and greater heavy-metal content.  相似文献   

Propagation of solar-flare cosmic rays along corotating interplanetary flux-tubes     

C. K. Ng  L. J. Gleeson 《Solar physics》1975,43(2):475-511

The propagation of solar-flare cosmic rays along a corotating spiral mean interplanetary magnetic flux-tube is investigated under a variety of initial, inner and outer boundary conditions, by solving the transport equations numerically. The inner boundary condition is shown to have negligible effects on the redistribution of the cosmic rays in interplanetary space, apart from a proportionality constant. The diffusion coefficients have been classified into type I and type II: for type I the peakalong-spiral stays at a finite heliocentric distance, while for type II it travels to infinity. The time dependence of the anisotropy vector is characteristically different in each type and in the case of type I is a function of the observation point. The general propagation characteristics with a free-escape outer boundary are like those of type I. It is shown that closely exponential decay can be produced without a free-escape boundary. The concept of an ‘equilibrium shape’ at late time is introduced. With a source that decays slowly, a maximum and minimum pair appears in the spatial distribution; the maximum subsequently propagates outward and the minimum inward. The impulsive models given do not reproduce satisfactorily all the observed characteristics of solar burst events and a solar source extended in time appears to be indicated.  相似文献