A numerical study on 2-D compressive wave propagation in rock masses with a set of joints along the radial direction normal to the joints

An explosion in a borehole or an accidental explosion in a tunnel will generate a two-dimensional (2-D) compressive wave that travels through the surrounding rock mass. For the problem of 2-D compressive wave propagation in a rock mass with parallel joints in the radial direction normal to the joints, parametric studies on the transmission ratio and the maximum rebound ratio are performed in universal distinct element code. The variation of the transmission ratio with the ratio of joint spacing to wavelength is generalized into a characteristic curve, which can be used as a prediction model for estimating the transmission ratio. The relationship between the maximum rebound ratio and the influence factors is obtained in charts. The charts can be used as a prediction model for estimating the maximum rebound ratio. The proposed prediction models for estimating the transmission ratio and the maximum rebound ratio are applied to a field explosion test, Mandai test in Singapore. The minimum possible values of peak particle velocity (PPV) at the monitoring points are estimated by using the proposed prediction model for estimating the transmission ratio along the radial direction normal to the joints. On the other hand, the maximum possible values of PPV are estimated by using the proposed prediction model for estimating the maximum rebound ratio along the same radial direction. The comparison shows a good agreement between the field-recorded PPVs and the estimated range of PPVs given by the minimum possible PPVs and the maximum possible PPVs at the monitoring points in Mandai test. The good agreement between the estimated and field-recorded values validates the proposed prediction models for estimating peak particle velocity in a rock mass with a set of joints due to application of a compressive wave at the boundary of a tunnel or a borehole.     

An 8.1Ma calcite record of Asian summer monsoon evolution on the Chinese central Loess Plateau

Carbonates in loess-red clay sequences consist mainly of calcite and dolomite. The EDTA analysis of carbonates in different size fractions and magnetic susceptibility reveal that calcite is a sensitive index of summer monsoon. The chemical analysis of carbonates and calcite from an 8.1 Ma loess-red clay sequence at Chaona on the Chinese central Loess Plateau shows that the evolution of the Asian summer monsoon experienced four stages, namely 8.1―5.5 Ma, 5.5―2.8 Ma, 2.8―1.5 Ma and 1.5―0 Ma, with increasing intensification and fluctuation, suggesting a possible combining impacts of uplift of the Tibetan Plateau and global changes on the Asian summer monsoon.     

云南水汞群体非均匀度异常与成组强震活动关系

阐述了一种前兆群体异常信息提取新方法前兆群体非均匀度的数学原理,并以云南水汞群体异常信息为例进行了具体计算。结果表明该方法以群体异常分布特征的变化为异常标准(ID≥1),达到异常即自动识别报警。该方法能克服个人经验的局限,易为他人进行检验,可成为本地区成组强震预测对应概率较高的新指标。     

TTI介质的相速度研究

推导了二维TTI介质的相速度表达式,并且依据推导出来的相速度表达式,模拟并分析了二维TTI介质相速度的传播快照以及TI介质相速度的传播快照;对比并分析了TTI介质和TI介质模型的相速度理论计算值的X分量特征的差异。TTI介质的相速度研究具有较高的理论研究价值和实际应用价值．     

准噶尔盆地陆西地区侏罗系西山窑组顶界不整合结构特征及其与油气关系

根据测井、录井资料,对陆西地区所有井的侏罗系西山窑组顶界不整合面上、下的岩性组合做了统计,并从中总结出7种具有代表性的不整合结构,对组成不整合结构的底砾岩、水解带、淋滤带的岩性特征、测井响应、孔渗特征做了系统的分析.通过研究7种不整合结构与油气的运聚关系认为,第Ⅰ种和第Ⅴ种不整合结构最易聚集成藏,第Ⅱ和Ⅲ种不整合结构较易聚集成藏,第Ⅳ种不整合结构也可以聚集成藏,第Ⅵ种和第Ⅶ种不整合结构不易成藏.最后指出,石南油田和石西油田之间未勘探区块是油气聚集的最有利地带.     

芙蓉锡矿田骑田岭花岗岩黑云母矿物化学组成及其对锡成矿的指示意义

芙蓉锡矿田骑田岭复式岩体主要由早阶段角闪石黑云母花岗岩和晚阶段黑云母花岗岩组成.电子探针分析结果表明角闪石黑云母花岗岩中的黑云母属于铁黑云母,黑云母花岗岩中的黑云母属于铁叶云母.相对于黑云母花岗岩,角闪石黑云母花岗岩中黑云母的MgO、TiO2含量偏高,Al2O3含量偏低.矿物化学研究结果显示,角闪石黑云母花岗岩中黑云母的结晶温度、氧逸度(logfO2)分别为680℃～740℃、-16.00～-15.31,黑云母花岗岩中黑云母的结晶温度、氧逸度分别为530℃～650℃、-19.20～-17.50.从角闪石黑云母花岗岩到黑云母花岗岩,岩浆结晶温度和氧逸度逐渐降低.与花岗岩有关的共存流体性质的研究发现,与角闪石黑云母花岗岩共存的热液流体log(fH2O/fHF)fluid,log(fH2O/fHCl)fluid,log(fHF/fHCl)fiuid值分别为4.22～4.39,2.78～3.24,-1.82～-1.73,而与黑云母花岗岩共存的热液流体log(fH2O/fHF)fluid,log(fH2OfHCl)fluid,log(fHF/fHCl)fluid值分别为3.27～3.53,2.85～3.22,-0.75～-0.22,可见与两种岩石类型共存热液流体的性质存在明显差异,且热液中Cl、Sn含量变化与岩浆结晶分异指数呈正相关关系.骑田岭岩体从角闪石黑云母花岗岩到黑云母花岗岩,随着岩浆的演化.岩浆结晶期后分异出的热液流体向富Cl和Sn方向演化.芙蓉锡矿田的成矿流体应主要来源于黑云母花岗岩岩浆结晶期后分异出的岩浆热液.     

城市公共饮用水应急水源勘查及其意义——以浙江长兴雉城镇应急水源勘查为例

通过浙江长兴雉城镇公共饮用水应急水源勘查实例,认为充分利用原有地下水供水井,并在地下水资源较为丰富、人口较为集中的社区选择施工供水深井作为公共饮用水应急水源是科学的、经济的、可行的.作为公益性市政基础建设,政府有责任落实到位,以尽快建立城市公共饮用水危机应急供水预案并采取措施.     

论河流水能资源过度开发的地质生态环境问题

水能是清洁安全的能源。但如果对水能资源进行竭泽而渔地过度开发,必将引起地质生态环境方面的负面影响,甚至引发生态灾难。文章列举了岷江上游流域水能开发中的大量事例,呼吁应科学、合理、有序地开发利用河流水能资源,岷江上游流域水能资源的开发现状,应给人们以警醒和反思。     

北京市地面沉降发展及对城市建设的影响

地面沉降是北京市平原区主要地质灾害之一,最早在1935年发现于西单至东单一带,到目前为止已经形成了多个地面沉降中心,到2005年底,累计沉降量大于50mm的沉降区达4114 km~2,大于100mm的沉降区达2815km~2。地面沉降已经对城市基础设施造成一定程度的破坏,并且已经对奥运场馆、规划新城、CBD等重要区域构成潜在威胁,所以必须及时制定完善的防治措施来降低地面沉降的危害。     

Cold Air Activities in July 2004 and Its Impact on Intense Rainfalls over Southwest China

The severe rainfall events in the mid-summer of July 2004 and the roles of cold air in the forma- tion of heavy precipitation are investigated by using daily observational precipitation data of China and NCEP/NCAR reanalysis.The results show that the severe rainfalls in Southwest China are closely related to the cold air activities from the mid-high latitudes,and the events take place under the cooperative effects of mid-high latitude circulation and low latitude synoptic regimes.It is the merging of a cold vortex over mid-latitudes with the northward landing typhoon and eastward Southwest China Vortex,as well as the abrupt transformation from a transversal trough into an upright one that causes three large alterations of mid-high atmospheric circulation respectively in the early and middle ten days of this month.Then,the amplitude of long waves soon magnifies,leading to the unusual intrusion of cold air to low-latitude areas in the mid-summer.Meanwhile,the warm and humid southwest summer monsoon is quite active.The strong interactions of cold air and summer monsoon over Southwest China result in the large-scale convective rain- falls on the southern side of cold air. With regard to the activities of cold air,it can influence rainfalls in three prominent ways.Firstly,the incursion of upper-level cold air is often accompanied by partial southerly upper-level jet.The ascending branch of the corresponding secondary circulation,which is on the left front side of the jet center,provides the favorite dynamic upward motion for the rainfalls.Secondly,the southward movement of cold air contributes to the establishment of atmospheric baroclinic structure,which would lead to baroclinic disturbances.The atmospheric disturbances associated with the intrusion of cold air can destroy the potential instability strat- ification,release the convective available potential energy(CAPE)and finally cause convective activities.In addition,the advection processes of dry and cold air at the upper level along with the advection of humid and warm air at the lower level are rather significant for the reestablishment of potential instability in the precipitation area,which is one of the crucial factors contributing to persistent rainfalls.