降雨型与地震型滑坡试验研究

为了研究和探索降雨和地震诱发滑坡灾害的成因机理,对降雨型滑坡和地震型滑坡进行了物理模拟试验,系统地研究了坡度、坡体结构、降雨量、振动强度等因素对斜坡破坏变形的影响规律,探讨了降雨和地震诱发斜坡失稳破坏的主要模式和过程.对于降雨型滑坡,通过实验确定不同坡度滑坡的临界降雨量,发现临界降雨量与滑坡坡度呈幂指数关系.对于地震型...     

四川岷江上游滑坡触发因素分析

以高山峡谷为地貌特征的岷江上游地区人口密集,在晚更新世以来发生了数以万计的滑坡,探讨该地区滑坡发生的主要触发因素对该地区的地质灾害防治意义重大。文中从区域降雨特点、滑坡坡形特点、地震震级大小与滑坡面积的对应关系以及叠溪已恢复地震记录的周期性分析等方面入手展开探索性研究。在降雨方面,与滑坡灾害严重的尼泊尔相比,岷江上游无论是累积降雨量还是日降雨量均未达到触发滑坡的关键阈值。在坡形方面,岷江上游的滑坡不具有暴雨触发滑坡形成的坡底峡谷地形特征,而具有地震触发滑坡形成的自上而下较为平坦的坡面特征。在震级大小与滑坡面积的对应关系中,岷江上游的大面积滑坡分布支持地震触发,与暴雨触发的局部小面积滑坡形成鲜明对比。在叠溪已恢复地震记录的周期分析中,我们获得能够导致该地区软沉积物变形的5.0或5.5级地震的复发周期集中于二三十年,而引发大面积滑坡的可能类似汶川特大地震的平均复发间隔为2.6ka。这与中等—特大地震以及滑坡面积随地震震级一般呈现指数增长关系相吻合。据此,我们初步认为,岷江上游地区晚更新世以来发育的大量滑坡由降雨触发的可能性很小,绝大部分可能为地震触发。这一初步认识有待今后的细致研究进一步验证。     

基于降雨入渗的Newmark模型改进及地震滑坡危险性预测研究

滑坡是一种破坏性非常强的地质灾害,其中地震与降雨均为诱导滑坡发生的关键因素。从降雨期间发生地震的角度考虑,基于Green-Ampt降雨入渗模型对Newmark模型进行改进,推导两因素耦合作用下的边坡安全系数F_S。以云南省鲁甸县某一区域为例,分别开展无降雨、降雨无积水与降雨积水三种情况下的地震滑坡危险性预测及坡度与入渗深度因子对位移影响分析。通过比较上述三种情况,得到研究区域内的Newmark累积位移分布及危险性区划。结果表明：与未降雨情况相比,后两种情况下地震滑坡高危险程度区域面积占比计算区域随着降雨时间的增加从1%分别提高至9%、12%,滑坡低危险程度区域面积从51%分别降低至35%、33%;坡度值与入渗深度值越大,滑坡位移越大,危险性越高。Newmark改进模型充分考虑了降雨对地震滑坡产生的促进作用,能更好地反映出研究区每个场点相对的滑坡危险性,对滑坡危险性预测具有一定指导意义。     

云南鲁甸溶蚀堆积体滑坡研究——以龙头山镇葫芦桥滑坡为例

中国西南山区的可溶岩地区侵蚀、溶蚀谷地的溶蚀堆积体斜坡坡面露头看似完整,内部实则松散、透水且易滑。云南鲁甸县龙头山葫芦桥滑坡属于典型溶蚀堆积体滑坡,通过对其水文地质条件、工程地质条件和降雨等影响因素的分析,认为持续降雨和地震是该滑坡灾害发生的主要诱发因素。在取样测得岩土层物理力学参数的基础上,采用Geo-Slope软件进行稳定性分析。计算结果表明,该滑坡在天然状态下处于较稳定状态,稳定性系数为1.287;降雨、地震、降雨+地震三种工况下稳定性系数均小于1,处于不稳定状态。计算结果与该滑坡实际滑动状况相符,可为同类型滑坡的调查研究提供实例借鉴。     

降雨和地震耦合作用对滑坡稳定性的影响——以甘肃西和Ⅲ号滑坡为例

以甘肃省西和县西山Ⅲ号滑坡为例分析了地震与降雨耦合作用对滑坡稳定性的影响。采用GEOSTUDIO软件对其进行了天然及地震降雨耦合作用两种条件下的数值模拟。通过计算结果对比可知,西山Ⅲ号滑坡在天然状态下处于稳定状态;地震降雨耦合作用对西山Ⅲ号滑坡的稳定会起到很强的削弱作用,滑坡将处于失稳状态。在此处采用的计算条件下,相同降雨量下地震与不同降雨强度的耦合作用显示,降雨强度越小雨水入渗相对越多,地震作用下超孔隙水压力影响区域越大,滑坡越不稳定。     

玉树地震滑坡分布调查及其特征与形成机制

2010年4月14日青海省玉树县发生了MS7.1地震.文中基于现场考察与遥感影像目视解译的方法,对玉树地震滑坡进行分析,并制作了玉树地震滑坡空间分布图.结果表明,该地震触发了约2 036处滑坡灾害,总面积约1.194km2;地震滑坡分布受主地表破裂控制作用强烈;滑坡类型多样,但以崩塌型滑坡为主;滑坡有5种成因机制:人工开挖坡脚型、地表水入渗致坡体震动滑动型、断裂错断震动型、震动型、后期冰雪融化或降雨入渗型;除地震主地表破裂外,还有许多坡体裂缝,主要分布在主地表破裂带SE端的SW盘,该部位在地震中受到了强烈的挤压作用.     

岷县漳县6.6级地震典型滑坡特征及其诱发机制

地震和降雨是滑坡产生的两大诱因。一般认为二者的耦合作用概率小,在现实中也较少发现有此种实例。岷县漳县6.6级地震中黄土地震滑坡广泛发生,本文通过现场调查,在相关降雨量数据、航空影像空间分析的基础上研究了两个地点(永光村滑坡和堡子村滑坡)的典型地震黄土滑坡的空间展布特征和发生、发展过程,分析了诱发机制。结果发现:(1)地震滑坡呈带状分布与地震发震构造走向一致;(2)位于极震区范围的永光村黄土滑坡具有泥流特征,土体含水量可达塑限以上,是由于过量降水和强地震动耦合作用下发生;(3)堡子村黄土地震滑坡则主要为强地震动所诱发,滑距较短,并具滞后发生特性。本结果对未来地震中滑坡的预防与防治具有借鉴意义。     

黄土地震滑坡卫星影像识别方法

为获得详细的地震滑坡数据和分布特征,揭示黄土地震滑坡的成灾模式和防治措施,需要对黄土地区地震滑坡进行详细的编录,利用卫星影像的识别方法是重要的手段之一。通过总结黄土地震滑坡特有的空间分布特征、平面形态特征、地震滑坡发育特征和伴生水文特征,归纳利用卫星影像识别黄土地震滑坡的7种识别标志。利用该方法,研究通渭地区黄土地震滑坡的空间分布与规律,结果表明：黄土地震滑坡卫星影像识别方法获得的滑坡与野外现场调查结果相近;通渭地区滑坡拥有缓坡发育、低角度、中远滑距、大体积、方向性明显等特点。     

降雨型滑坡时空预报新方法

地质条件和降雨是引起重庆地区山体滑坡的两个最主要条件. 文中在分析降雨型滑坡形成条件的基础上, 提出了将地质条件和降雨因素进行分级叠合的降雨型滑坡时空预报新方法. 首先, 利用多因素相互作用关系矩阵, 对某个地区或者某个边坡所在位置的地质条件进行半定量的评价和分级. 然后, 根据日最大降雨量和降雨过程的总降雨量, 对该地区降雨的严重程度进行分级. 最后将“地质条件影响因子”和“降雨影响因子”进行分级叠合, 得到了“滑坡易滑程度判别因子”, 并据此将滑坡按照其易滑度分为滑坡极易发生、滑坡易发生、滑坡不易发生和滑坡基本不发生4级. 通过对某个地区的一些危险边坡进行地质勘察, 结合比较准确的天气预报, 可以对该地区的降雨型滑坡进行较为准确的时空预测预报. 以鸡扒子滑坡为例, 验证了利用“双因素”分级叠合方法进行降雨型滑坡时空预报的可靠性和可行性.     

四川德阳地区龙风水库西岸滑坡稳定性分析及防治

本文在对四川德阳地区龙风水库西岸滑坡的地质地貌条件及变形迹象进行深入调查的基础上,对该滑坡的主要成因及稳定性进行了分析与评价,并有针对性地提出了工程防治方案。研究表明,疏松透水的土层、较强的降雨以及人类耕作活动是导致滑坡发生的主要因素。在天然状态下该滑坡稳定或基本稳定;在天然＋地震状态下,该滑坡欠稳定或不稳定;在连续高强度降雨状态下,该滑坡不稳定。故采取截、排水及抗滑桩等工程措施是防治该滑坡的有效方案。     

A Monte Carlo study of rainfall forecasting with a stochastic model

A procedure for short-term rainfall forecasting in real-time is developed and a study of the role of sampling on forecast ability is conducted. Ground level rainfall fields are forecasted using a stochastic space-time rainfall model in state-space form. Updating of the rainfall field in real-time is accomplished using a distributed parameter Kalman filter to optimally combine measurement information and forecast model estimates. The influence of sampling density on forecast accuracy is evaluated using a series of a simulated rainfall events generated with the same stochastic rainfall model. Sampling was conducted at five different network spatial densities. The results quantify the influence of sampling network density on real-time rainfall field forecasting. Statistical analyses of the rainfall field residuals illustrate improvement in one hour lead time forecasts at higher measurement densities.     

Earthquake Engineering and Engineering Vibration Aims And Scope

正This journal is established by the Institute of Engineering Mechanics(IEM),China Earthquake Administration,to promote scientific exchange between Chinese and foreign scientists and engineers so as to improve the theory and practice of earthquake hazards mitigation,preparedness,and recovery.To accomplish this purpose,the journal aims to attract a balanced number of papers between Chinese and     

Solute concentrations in the lower niger river and the source rock contribution

Water quality analyses for the Niger River for the 1980/81 hydrological year are presented. The samples were collected from the main river at Lokoja, and from two main tributaries, the Kaduna and the Benue Rivers. Different water types were distinguished by the concentrations of major ions. The type Ca > Na > Mg > K - HCO₃ > SO₄ > Cl was represented at all stations during at least part of the year. Chloride was found to dominate the sulphate ion in the Kaduna and Niger, while the Benue maintained a higher concentration of sulphate relative to chloride all year round. Distinct patterns of seasonal variation in the ion concentrations were observed, particularly for the samples collected at Lokoja. Low ion concentrations were prominent during periods of high discharge, while low flow periods coincided with high dissolved ion concentrations. The contribution of rainwater to the total dissolved solids in the river waters was assessed indirectly using rainwater chemistry data from the Gulf of Guinea. The estimated rainwater contribution to the Lower Niger amounts to 5.15 mg 1^?1. Geochemical weathering calculations involving reactions of the four major minerals of granitic rocks - anorthite, biotite, albite, and K-feldspar - with carbon dioxide and water, can account for the average water composition of the Lower Niger. The proportion of the ionic components was also related to the occurrence of the respective element in the minerals.     

Scenario predictions for potential near-field and far-field earthquakes affecting Hong Kong

Historical earthquakes noted in the written records of the South China region, including Hong Kong, are not well delineated along identified prominent fault sources. Despite the lack of any definitive, localised trend in the spatial distribution of seismic activity in the region, there does appear to be some major disparity in the seismic activity rates (especially for large magnitude earthquakes) between the near-field and the far-field regions of Hong Kong. Despite this observation, previous studies of the regional seismic activity and seismic ground motion hazard (the latter using a probabilistic seismic hazard assessment, PSHA) have considered very broad source zone regions, in which uniform levels of seismic activity have been assumed. The present paper further scrutinises this broad source zone (BSZ) approach by adopting a novel expanding circular disc (ECD) method to determine the rates of earthquake recurrence. Such a method is intended to counter-check previously developed models by determining earthquake scenario events in terms of magnitude–distance (M–R) pairs or combinations, having defined values of average return period. Unlike the BSZ approach, the ECD method specifically accounts for the supposed variations in the seismic activity rates between events in the near-field and the far-field of Hong Kong.The form of the developed method is particularly suited to the determination of design-level earthquake ground motions for bedrock sites, since it assumes a directionally-independent attenuation model as described in the companion paper. It is found that, whilst the BSZ approach may indicate the overall average levels of hazard that are representative of the South China region as a whole, it does not capture the large disparity in seismic activity rates between near-field and far-field events. This important feature is expected to have a significant impact upon engineering assessments of the seismic safety of structures in Hong Kong and elsewhere in the South China region. For example, it is found that for events with M≥6, the seismic activity rate (normalised by time and area) in the very far-field is around 3.5 times larger than in the near-field and medium-field of Hong Kong. The resulting design M-R combinations, covering a range of return periods from 70 to 2500 years, are limited, for very long return periods and for distant events, by the maximum credible earthquake (MCE) magnitude. Intensive research to determine this seismic hazard parameter is recommended, in order to refine further the results of the ECD analysis, which presently conservatively assumes the MCE to range between M=6 in the near-field of Hong Kong to M=8 in the very far-field, at distances greater than 280 km from Hong Kong.     

Depositional ages and characteristics of Middle–Upper Jurassic and Lower Cretaceous lacustrine deposits in southeastern Mongolia

Lower Cretaceous lacustrine oil shales are widely distributed in southeastern Mongolia. Due to the high organic carbon content of oil shale, many geochemical studies and petroleum exploration have been conducted. Although most of the oil shales are considered to be Early Cretaceous in age, a recent study reveals that some were deposited in the Middle Jurassic. The present study aims at establishing depositional ages and characteristics of the Jurassic and Cretaceous lacustrine deposits in Mongolia. The Lower Cretaceous Shinekhudag Formation is about 250 m thick and composed of alternating beds of shale and dolomite. The Middle Jurassic Eedemt Formation is about 150 m thick and composed of alternating beds of shale, dolomitic marl, and siltstone. The alternations of shale and dolomite in both formations were formed by lake level changes, reflecting precipitation changes. Shales were deposited in the center of a deep lake during highstand, while dolomites were formed by primary precipitation during lowstand. Based on the radiometric age dating, the Shinekhudag Formation was deposited between 123.8 ±2.0 Ma and 118.5 ±0.9 Ma of the early Aptian. The Eedemt Formation was deposited at around 165–158 Ma of Callovian–Oxfordian. The calculated sedimentation rate of the Shinekhudag Formation is between 4.7 ±2.6 cm/ky and 10.0 ±7.6 cm/ky. Shales in the Shinekhudag Formation show micrometer‐scale lamination, consisting of algal organic matter and detrital clay mineral couplets. Given the average thickness of micro‐laminae and calculated sedimentation rate, the micro‐lamination is most likely of varve origin. Both Middle–Upper Jurassic and Lower Cretaceous lacustrine oil shales were deposited in intracontinental basins in the paleo‐Asian continent. Tectonic processes and basin evolution basically controlled the deposition of these oil shales. In addition, enhanced precipitation under humid climate during the early Aptian and the Callovian–Oxfordian was another key factor inducing the widespread oil shale deposition in Mongolia.     

THEORETICAL APPROACH TO THE SOLUTION OF THE INFILTRATION PROBLEM

ABSTRACT

The one-dimensional transient downward entry of water in unsaturated soils is investigated theoretically. The mathematical equation describing the infiltration process is derived by combining Darcy's dynamic equation of motion with the continuity and thermodynamic state equations adjusted for the unsaturated flow conditions. The resulting equation together with the corresponding initial and boundary conditions constitues a mathematical initial boundary value problem requiring the solution of a nonlinear partial differential equation of the parabolic type. The volumetric water content is taken as the dependent variable and the time and the position along the vertical direction are taken as the independent variables. The governing equation is of such nature that a solution exists for t > 0 and is uniquely determined if two relationships are defined, together with the specified state of the system, at the initial time t = 0 and at the two boundaries. The two required relations are those of pressure versus permeability and pressure versus volumetric water content.

Since the partial differential equation has strong non-linear terms, a discrete solution is obtained by approximating the derivatives with finite-differences at discrete mesh points in the solution domain and integrated for the corresponding initial and boundary conditions. The use of an implicit difference scheme is employed in order to generate a system of simultaneous non-linear equations that has to be solved for each time increment. For n mesh points the two boundary conditions provide two equations and the repetition of the recurrence formula provides n—2 equations, the total being n equations for each time increment. The solution of the system is obtained by matrix inversion and particularly with a back-substitution technique. The FORTRAN statements used for obtaining the solution with an electronic digital computer (IBM 704) are presented together with the input data.

Analysis of the errors involved in the numerical solution is made and the stability and convergence of the solution of the approximate difference equation to that of the differential equation is investigated. The method applied is that of making a Fourier series expansion of a whole line of errors and then following the progress of the general term of the series expansion and also the behavior of each constituent harmonic. The errors (forming a continuous function of points in an abstract Banach space) are represented by vectors with the Fourier coefficients constituting a second Banach space. The amplification factor of the difference equation is shown to be always less than unity which guarantees the stability of the employed implicit recurrence scheme.

Experiments conducted on a vertical column packed uniformly with very fine sand, show a satisfactory agreement between the theoretically and experimentally obtained values. Many experimental results are shown in an attempt to explain the infiltration phenomenon with emphasis on the shape and movement of the wet front, and the effects of the degree of compaction, initial water content and deaired water on the infiltration rate.     

Late Permian post‐ophiolitic trondhjemites from Central Iran: a mark of subduction role in growth of Paleozoic continental crust

Late Permian trondhjemites in the Anarak area occur as stocks and dykes, which cross cut the Anarak ophiolite and its overlying metasedimentary rocks, and are exposed along the northern Anarak east–west main faults. These leucocratic intrusive bodies have enclaves of all ophiolitic units and metamorphic rocks. They are composed of amphibole, plagioclase (oligoclase), quartz, zircon and muscovite. Secondary minerals are chlorite (pycnochlorite), epidote, albite, magnetite and calcite. Whole‐rock major‐ and trace‐element analyses reveal that they are characterized by high SiO ₂ (67.8–71.0 wt%), Al ₂ O ₃ (14.9–17.1 wt%) and Na ₂ O (5.3–8.6 wt%), low K ₂ O (0.1–1.5 wt%; average: 0.8 wt%), low Rb/Sr ratio (0.01–0.40; average: 0.09), low Y (3–6 ppm), negative Ti, Nb and Ta anomalies, slightly negative or positive Eu anomaly, LREE enrichment and fractionated HREE. These rocks present 2 to 40 times enrichment in inclined chondrite‐normalized REE patterns. Geochemical characteristics of the Anarak trondhjemites all reflect melting of a mafic protolith at more than 10 kbar. The field evidence and whole‐rock chemistry reveal that these rocks have been crystallized from magmas derived from melting of subducted Anarak oceanic crust. This study reveals that melting of garnet amphibolite was an important element of continent formation in the study area.