Three-Dimensional Gravity Model Applied to Underwater Navigation

At present, new integrated navigation, which usesthe location function of reference gravity anomaly map to control the errors of the inertial navigation system (INS), has been developed in marine navigation. It is named the gravity-aided INS. Both the INS and real-time computation of gravity anomalies need a 3-D marine normal gravity model. Conventionally, a reduction method applied in geophysical survey is directiy introduced to observed data processing. This reduction does not separate anomaly from normal gravity in the observed data, so errors cannot be avoided. The 3-D marine normal gravity model was derived from the J2 gravity model, and is suitable for the region whose depth is less than 1000 m.     

Advanced Geostructural Survey Methods Applied to Rock Mass Characterization

The location and orientation of rock discontinuities, which are traditionally obtained from geological surveys with obvious drawbacks (safety, rock face accessibility, etc.), may also be derived from a detailed and accurate photogrammetric or laser scanning survey. Selecting from the point cloud determined on the rock face a set of points distributed on a particular discontinuity, location, dip, and dip direction can be computed from the least-squares estimate of the plane interpolating the set of points. Likewise, the normal vector to the surface may be computed from an interpolation or approximation of the surface by appropriate functions. To become a real alternative (both in terms of productivity as well as accuracy) to a traditional survey, interactive or automated software tools are necessary, to allow the efficient selection of the point sets on the discontinuities or the interpretation of the normal vector pattern. After introducing the two best technologies available today for data acquisition and their performance, the paper presents an approach, based on the random sample consensus (RANSAC) procedure, to the segmentation of the point cloud into subsets, each made of points measured on a discontinuity plane of the rock face. For each subset, the plane’s equations coefficients are first determined by robust estimation and then refined by least-squares estimation after outlier removal. The segmentation algorithm has been implemented in RockScan, a software tool developed to facilitate the interaction with the point cloud in the identification of the discontinuities; rather than using the three-dimensional (3D) data, selection of regions of interest is performed on oriented images of the rock face. Finally, application of RockScan to four different test sites is discussed and results presented. The sites differ in size (from tens to hundreds of meters), rock surface characteristics, and the technology used to produce the point cloud (in three cases photogrammetry, in the fourth laser scanning), giving the opportunity to test the methodology in different contexts. In the first and in the fourth site an extensive traditional survey has been performed, providing reference data to validate the RockScan results.     

Incorporating Parameter Variability in Rock Mechanics Analyses: Fuzzy Mathematics Applied to Underground Rock Spalling

Although fuzzy analysis has been widely developed, its use in rock mechanics and rock engineering is limited. Here, it has been used to evaluate the potential for underground rock spalling at the boundary of a circular excavation in terms of rock strength and in situ rock stress, given the uncertainty in both of these input parameters. Using standard techniques from fuzzy mathematics, we develop an expression for the fuzzy factor of safety, and extend this to form the crisp parameters Safety Certainty Value and its complement, the Failure Certainty Value. Plots of the Failure Certainty Value in terms of the in situ stress ratio and rock strength/stress ratio show the effect of uncertainty on the assessment of stability. From these plots, we illustrate how the relative importance of uncertainty in the input parameters can be assessed, with the associated ramifications for site investigation and subsequent engineering design.     

A Combined Three-Dimensional Geological-Geostatistical-Numerical Model of Underground Excavations in Rock

Summary. This paper exploits geological and borehole geotechnical data obtained in the exploratory phase of a tunneling project to investigate in a first place if the kriging interpolation scheme may effectively reproduce the spatial variability of rock mass quality (Rock Mass Rating, RMR) in the vicinity of tunnels. For this purpose a quick solver in Fortran has been developed that performs variography analysis of 3D spatial data, fast kriging estimations of RMR between borehole sampling locations at the centroids of the elements of the numerical model, and model validation. For the purpose of an integrated underground excavation design, a step further is made by incorporating into the 3D mechanical numerical model of the rock mass, the three-dimensional (3D) solid geological model, thus coupling the geology with the ground (geotechnical) model (i.e. each element of the numerical model is assigned a geological material). The mechanical properties of each finite difference cell (or Representative Elementary Volume) of the ground model were then prescribed according to its geological type, the spatial heterogeneity of the rock mass expressed quantitatively with the kriging model, and the upscaling calculations of the mechanical properties of the intact rocks determined in the laboratory, based on the size-effect (strength dependence on size) and Damage Theory. Furthermore, a preliminary numerical simulation of the advance of unsupported tunnels in the model of the heterogeneous rock mass was performed for illustration purposes.     

基于可拓学理论的围岩分级方法在变质软岩隧道中的应用

对可拓学中物元、可拓集合的概念进行了阐述,并以火车岭隧道为例,结合影响变质软岩区隧道稳定性的岩性、结构面、地下水等主要因素,选取钻孔岩芯质量、隧道埋深、地下水流量、饱和单轴抗压强度、结构面间距作为评价指标,同时选择3个典型岩段,建立相应的待评物元模型;对各评价指标及各围岩级别的关联度指标进行了计算,据此对3个岩段进行分级的结果表明,绿泥钠长石英片岩岩段为Ⅲ级,与原设计相符;绢云母石英片岩岩段为Ⅱ级,比原设计低一级;白云钠长石英片岩岩段为Ⅳ级,比原设计高一级.该分级方法与RMR法、Q法及公路隧道规范分级方法的对比结果表明,传统方法与现场条件存在较大误差,证明基于可拓学理论的围岩分级方法能较好地满足该围岩条件的要求,同时分析了传统围岩分级方法在该地质条件下应用的缺陷.     

冻土蠕变的渐进屈服准则

基于冻土蠕变的现象分析表明，冻土蠕变的破坏是由于冻土中非弹性变形积累的结果，在冻土的任何变形阶段都存在着非弹性变形。非弹性变形的积累在一定条件下导致了冻土渐进屈服的出现，渐进屈服反过来又促进了冻土蠕变的进一步增加。     

Three-Dimensional Numerical Investigation of the Interaction Between Twin Tunnels

Geotechnical and Geological Engineering - The construction of twin tunnels is a mandatory guideline and a prevailing practice in either conventional or mechanized tunneling. Nevertheless, most of...     

粘弹-塑性岩体中衬砌与围岩的共同作用问题

在许多类型的岩层中(比如粘土质的沉积岩、岩盐以及其他较软弱的岩质等)地下洞室在开挖完成之后,其围岩的变形特性,强度特性以及整体的稳定性有明显的时间效应.因此,近年来在国内外的研究工作中已有不少人致力于时间因素对围岩稳定性影响的研究.     

A型岩套的分类、判别标志和成因

以新近在粤北开展A型岩套研究所获得的新数据，结合国内外文献中已发表的数据(17个岩体，124件样品)，讨论了A型岩套亚类型划分的必要性和亚类型之间的判别方法。将A型岩套分为两亚类型三组。A1类型主要以似长石正长岩、碱性正长岩和响岩为主(AS组)，SiO2不饱和、准铝、过碱-碱性岩石，通常含似长石，如方钠石、霞石、白榴石和钠沸石等为特征。A2亚类型为SiO2过饱和、碱质-亚碱质岩石。该亚类型又包括铝质A型花岗岩(AU她组)(弱过铝质、亚碱质岩石)和碱性花岗岩(AAG组)(准铝质、碱质-亚碱质岩石)；后者通常含少量钠钙质和钠质辉石和角闪石。在地球化学特征上，A1亚型具低SiO2，高ALK和NK／A值，相对富氯低氟，低R1和高R2，低Y／Nb比(具OIB源区特征)，高Nb／Ta，Zr／Hf，Eu／Eu*，LREE／HREE和锆石饱和温度等。A2亚型中，以AAG组为例，其许多地球化学特征与Al亚型相悖，如高SiO2，较低ALK，相对贫氯富氟，高R1和低R2，高10^4Ga／Al和Y／Nb(具IAB源区特征)，低Nb／Ta，Eu／Eu*和LREE／HREE，以及高的锆石饱和温度等。A2亚型中ALAG组除铝过饱和外，其他地球化学特征很相似于．AAG组。利用R1-R2，Yb／Nb-Yb／Ta，Nb-Y-Ce，Nb／Ta-Nb等图解可有效地区分和判别A型岩套中Al和A2两种亚型。利用A1和A2亚型Sr，Nd同位素组成，以亏损地幔-全壳两端员混合模拟计算A2亚型花岗岩物质来源得出结论，其源区物质主要是以地幔端员占优势，地幔组分占68％～78％(7个岩体)，只有Namibia的碱流岩为下地壳成因，其地幔组分仅占30%。A1亚型碱性正长岩(3个岩体)以亏损地幔-富集地幔两端员混合模拟计算表明，其源区物质中富集地幔端员所占比例较低，为4％～17％，表明A型岩套两亚型其源区物质组成有明显不同。     

基于三维激光点云技术的岩体结构面智能解译

准确、高效、全面获取岩体结构面信息,对岩体的稳定性分析有着重要的意义.采用三维激光扫描设备进行岩体数据采集,基于岩体点云模型提出了结构面自动识别方法.通过对Ransac算法进行改进,引入了新的采样方法和评分准则,大大提升了Ransac算法的计算效率和提取精度,使之更好地适应粗糙不平的岩体点云数据;基于改进的Graham...     

乌东德坝区拱座岩体三维裂隙连通率特征

裂隙连通率是进行岩体稳定性评价不可或缺的参数,合理确定三维裂隙连通率的大小一直是岩体力学中的难题之一.结合金沙江乌东德水电站工程,采用投影法对乌东德坝区850m高程的拱座岩体进行了三维连通率研究.根据研究区域的工程地质条件,确定了拱座岩体的潜在滑动边界;采用逆建模方法建立拱座岩体的裂隙网络模型;在裂隙网络模型中设置不同大小、不同位置和不同方位的投影面进行三维连通率求解,探讨三维连通率的尺寸效应、分布特征和空间变化规律.研究结果表明:侧滑面连通率尺寸效应显著而底滑面连通率尺寸效应不明显;侧滑面连通率近似呈正态分布,左岸侧滑面连通率均值为3.9%,右岸侧滑面连通率均值为8.1%;侧滑面连通率随空间方位产生明显变化,投影面倾角越大,侧滑面连通率越小.这为乌东德坝区拱座岩体的稳定性评价提供了重要的参数依据.     

软岩立井井壁与流变岩体相互作用的实验分析

利用流变介质模型，分析软岩立并并壁与粘弹塑性围岩的相互作用。根据现场实测结果及围岩压力与时间的关系，得到围岩应力、位移随时间的变化规律和粘塑性区的扩展规律。     

Stereological and Other Methods Applied to Rock Joint Size Estimation—Does Crofton''s Theorem Apply?

A number of authors concerned with the analysis of rock jointing have used the idea that the joint areal or diametral distribution can be linked to the trace length distribution through a theorem attributed to Crofton. This brief paper seeks to demonstrate why Crofton's theorem need not be used to link moments of the trace length distribution captured by scan line or areal mapping to the moments of the diametral distribution of joints represented as disks and that it is incorrect to do so. The valid relationships for areal or scan line mapping between all the moments of the trace length distribution and those of the joint size distribution for joints modeled as disks are recalled and compared with those that might be applied were Crofton's theorem assumed to apply. For areal mapping, the relationship is fortuitously correct but incorrect for scan line mapping.     

Numerical Observation of Three-Dimensional Wing Cracking of Cracked Chevron Notched Brazilian Disc Rock Specimen Subjected to Mixed Mode Loading

The cracked chevron notched Brazilian disc (CCNBD) specimen has been suggested by International Society for Rock Mechanics for measuring mode I fracture toughness of rocks. Subsequently, this specimen geometry has been widely extended to conduct mixed mode fracture tests on rocks as well. A straight through crack front during the fracturing process upon the root of the chevron notch is assumed in the testing principle, but has never been thoroughly evaluated before. In this study, for the first time, the progressive rock fracture mechanism of the CCNBD rock specimen under mixed mode loading is numerically simulated. Specimens under representative mixed mode loading angles are modelled; and the assumption of the straight through crack front growth is critically assessed. The results show that not only the notch tip but also the saw-cut chevron notch cracks during the experiments, yielding a prominent twisted front, far from being straight. The crack front never grows up to the root of the notch ligament and the straight through crack front assumption is never satisfied in the realistic rock fracture progress of this chevron notched specimen subjected to mixed mode loads. In contrast, the fracture progress features typical three-dimensional wing cracking towards the loading ends. The numerically observed progressive fracture mechanism reveals that the measuring principle of mixed mode fracture tests employing CCNBD specimens is significantly violated and the measures of both modes I and II fracture toughness are uncertain.     

粘弹性体力学模型的判别准则及在岩石试验中的应用

从粘弹性介质的蠕变柔量出发，推导出粘弹性体力学模型的判别准则。并通过单轴压缩条件下４种岩石的蠕变试验，讨论了判别准则实用化中的两个问题，解的存在条件问题，多解性及解的唯一性问题。     

Stereological and Other Methods Applied to Rock Joint Size Estimation—Does Crofton's Theorem Apply?

A number of authors concerned with the analysis of rock jointing have used the idea that the joint areal or diametral distribution can be linked to the trace length distribution through a theorem attributed to Crofton. This brief paper seeks to demonstrate why Crofton's theorem need not be used to link moments of the trace length distribution captured by scan line or areal mapping to the moments of the diametral distribution of joints represented as disks and that it is incorrect to do so. The valid relationships for areal or scan line mapping between all the moments of the trace length distribution and those of the joint size distribution for joints modeled as disks are recalled and compared with those that might be applied were Crofton's theorem assumed to apply. For areal mapping, the relationship is fortuitously correct but incorrect for scan line mapping.