Information in Brief

○By the end of 1991, there have beenaltogether 479 cities in mainland China, anincrease of 12 over the previous year. Theurban population in the mainland was343.97 million (including the agriculturalpopulation in cities), accounting for 30.12%of the total population, an increase of0.74% over 1990. The non-agricultural     

Development of Human Settlements in China in 1980s

During 1980s, China experienced an unprecedented settlement development which wastriggered by a major change of policies. lmplication of this development in the overall nationalsocio-economic development has been profound and lasting. It is no exaggeration to say that thesuccess of this settlement development has been playing an incomparable role in keeping the so-cial, political and economic stability of our country in the past volatile decade. The author of this paper has an intention to present readers with essentialmatter-of-facts about this development through the use of statistics and figures; to dis-cuss the reasons or momemturns including reforms and innovations that promoted therealization of this development; to explore issues relating to further development.     

至in玩物

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至in玩物

杰克逊版iPod网上开拍；皮革版ThinkPad笔记本；超小禄莱数码双反相机登场；     

Social in SoHo

这块地方曾经是基督教会的成员——科学家们进行礼拜的场所．现在却成为了那些墨水爱好者的祭坛。SoHo的伍斯特街社交俱乐部（WoosterStreetSocialClub）不仅从事纹身的业务．而且还是OriginalMedia拍摄其电视真人秀节目”NYInk（纽约墨水）”的现场。OriginalMedia的执行总裁查理·考尔文（CharlieCorwin）说．他曾经设想过这样一个”当代的工厂．工厂里一些富有创意的人们和项目能够通过展览、剧本阅读和现场表演来实现不同品种之间的相互影响和借鉴。”     

Challenge in Protecting Famous Historic and Cultural Cities in New Situation and Some Issues in Understanding

China is now in a period of fast economic growth withlarge-scale construction.Especially since 1992 some statelevel famous historic and cultural cities are undergoing aprocess of land leasing and transferring the the land userights,trying to attract domestic and foreign fund for devel-opment of their old city propers.Therefore, it has becomeextremely urgent as to how to handle properly the relation-ship between conservation of these cities and their econom-ic development and construction. It is well known that China is a country with an an-cient civilization.Its rich historic remains and cultural heri-tage are appreciated by the whole world. The protectionand preservation of this heritage is an issue of concern notonly for all the decendents of the Chinese nation but alsofor other countries and peoples,for this heritage is an essen-tial part of the cultural heritage of the whole mankind.Tenitems from China have been included in the list of the worldnatural and cultural heritages under protection publish     

Evaluation of rock strength criteria for wellbore stability analysis

Polyaxial strength test data of five rocks are used to examine the Mohr–Coulomb, Drucker–Prager, modified Lade, Mogi–Coulomb and three-dimensional (3D) Hoek–Brown criteria regarding their ability, with parameters determined based on the triaxial compression test data, to represent the rock behavior under polyaxial stress states. Then the five strength criteria, with parameters determined based on the triaxial compression test data, are used to analyze wellbore stability of both vertical and inclined boreholes. The results show that the Mohr–Coulomb criterion under-predicts the polyaxial strength and estimates the highest minimum mud pressure required for wellbore stability while the Drucker–Prager criterion over-predicts the polyaxial strength and estimates the lowest minimum mud pressure. The modified Lade, Mogi–Coulomb and 3D Hoek–Brown criteria, with parameters based on triaxial test data, can either over-predict or under-predict the polyaxial strength. The over-prediction of the modified Lade criterion can be very large, and thus it may be unsafe to use it to estimate the minimum mud pressure. Both the over-prediction and under-prediction are relatively small for the 3D Hoek–Brown and Mogi–Coulomb criteria. Therefore, the 3D Hoek–Brown and Mogi–Coulomb criteria are recommended for wellbore stability analysis.     

Stability analysis of vertical boreholes using the Mogi–Coulomb failure criterion

A main aspect of wellbore stability analysis is the selection of an appropriate rock failure criterion. The most commonly used criterion for brittle failure of rocks is the Mohr–Coulomb criterion. This criterion involves only the maximum and minimum principal stresses, σ₁ and σ₃, and therefore assumes that the intermediate stress σ₂ has no influence on rock strength. As the Mohr–Coulomb criterion ignores the strengthening effect of the intermediate stress, it is expected to be too conservative in estimating the critical mud weight required to maintain wellbore stability. Recently, Al-Ajmi and Zimmerman [Relationship between the parameters of the Mogi and Coulomb failure criterion. Int J Rock Mech Min Sci 2005;42(3):431–39.] developed the Mogi–Coulomb failure criterion, and showed that it is reasonably accurate in modelling polyaxial failure data from a variety of rocks. We then develop a model for the stability of vertical boreholes, using linear elasticity theory to calculate the stresses, and the fully-polyaxial Mogi–Coulomb criterion to predict failure. Our model leads to easily computed expressions for the critical mud weight required to maintain wellbore stability.     

Analytical solutions for the stresses and deformations of deep tunnels in an elastic-brittle-plastic rock mass considering the damaged zone

The excavation impact (e.g. due to blasting, TBM drilling, etc.) induces an excavation damaged or disturbed zone around a tunnel. In this regard, in drill and blast method, the damage to the rock mass is more significant. In this zone, the stiffness and strength parameters of the surrounding rock mass are different. The real effect of a damage zone developed by an excavation impact around a tunnel, and its influence on the overall response of the tunnel is of interest to be quantified. In this paper, a fully analytical solution is proposed, for stresses and displacements around a tunnel, excavated in an elastic–brittle–plastic rock material compatible with linear Mohr–Coulomb criterion or a nonlinear Hoek–Brown failure criterion considering the effect of the damaged zone induced by the excavation impact. The initial stress state is assumed to be hydrostatic, and the damaged zone is assumed to have a cylindrical shape with varied parameters; thus, the problem is considered axial-symmetric. The proposed solution is used to explain the behavior of tunnels under different damage conditions. Illustrative examples are given to demonstrate the performance of the proposed method, and also to examine the effect of the damaged zone induced by the excavation impact. The results obtained by the proposed solution indicate that, the effects of the alteration of rock mass properties in the damaged zone may be considerable.     

Mechanical characteristics of the exponential strength criterion under conventional triaxial stresses

The minor principal stress is the key factor influencing the mechanical property of rock, and the strength criterion of conventional triaxial stresses is the basis of any true triaxial criterion. This paper examines the Coulomb criterion, Hoek–Brown criterion, the generalized Hoek–Brown criterion, and the exponential criterion proposed by the author. The procedure to determine the parameters in criteria is studied. Parameters in the generalized Hoek–Brown criterion are sensitive to the power n, thus Coulomb criterion with n=1.0 and the original form of Hoek–Brown criterion with n=0.5, especially that determined by linear regression, are not the best choice for the fitting solution of test data. The exponential criterion determined on the least absolute deviation will approximate a great number of normal test data, and expose the oddity data. It can describe the relation between strength and confining pressure in the entire stress range, with low misfit. The uniaxial compressive strengths predicted by the exponential criterion are nearly the same as the real magnitudes for all rocks. The deviator of strengths under conventional triaxial extension and compression is larger than half of the maximum strength increase from the intermediate principal stress. Therefore, the parameters in the exponential criterion may be completely determined from the strengths under conventional triaxial compression and extension.     

Determination of safe mud window considering time-dependent variations of temperature and pore pressure:Analytical and numerical approaches

Wellbore stability is a key to have a successful drilling operation.Induced stresses are the main factors affecting wellbore instability and associated problems in drilling operations.These stresses are significantly impacted by pore pressure variation and thermal stresses in the field.In order to address wellbore instability problems,it is important to investigate the mechanisms of rockefluid interaction with respect to thermal and mechanical aspects.In order to understand the induced stresses,different mathematical models have been developed.In this study,the field equations governing the problem have been derived based on the thermo-poroelastic theory and solved analytically in Laplace domain.The results are transferred to time domain using Fourier inverse method.Finite difference method is also utilized to validate the results.Pore pressure and temperature distributions around the wellbore have been focused and simulated.Next,induced radial and tangential stresses for different cases of cooling and heating of formation are compared.In addition,the differences between thermo-poroelastic and poroelastic models in situation of permeable and impermeable wellbores are described.It is observed that cooling and pore pressure distribution reinforce the induced radial stress.Whereas cooling can be a tool to control and reduce tangential stress induced due to invasion of drilling fluid.In the next step,safe mud window is obtained using Mohr-Coulomb,Mogi-Coulomb,and modified Lade failure criteria for different inclinations.Temperature and pore pressure distributions do not change the minimum allowable wellbore pressure significantly.However,upper limit of mud window is sensitive to induced stresses and it seems vital to consider changes in temperature and pore pressure to avoid any failures.The widest and narrowest mud windows are proposed by modified Lade and Mohr-Coulomb failure criteria,respectively.     

Numerical investigations of rock bridge effect on open pit slope stability

In this study, the effect of rock bridges on rock slope stability was investigated by incorporating non-persistent joint networks in numerical models, and the critical profiles of an open pit mine were analysed. Parallel deterministic networks of infinite and finite lengths, ubiquitous joint network model and Veneziano joint network model were used in order to simulate the rock fractures. Materials were modelled based on the generalised Hoek―Brown and equivalent Mohr–Coulomb failure criteria. The parallel deterministic infinite and the ubiquitous joint network models produced lower safety factors. The introduction of rock bridges along discontinuity planes in the parallel deterministic network and Veneziano joint network models significantly contributed to the stability and strain distribution, which should be considered in stability analysis of rock mass in open pit by rock slope practitioners. The results show the significance of joints in hard rock behaviour and the joints should be included in order to attain practical and realistic simulations.     

Shear strength criteria for rock,rock joints,rockfill and rock masses: Problems and some solutions

Although many intact rock types can be very strong, a critical confining pressure can eventually be reached in triaxial testing, such that the Mohr shear strength envelope becomes horizontal. This critical state has recently been better defined, and correct curvature or correct deviation from linear Mohr–Coulomb (M-C) has finally been found. Standard shear testing procedures for rock joints, using multiple testing of the same sample, in case of insufficient samples, can be shown to exaggerate apparent cohesion. Even rough joints do not have any cohesion, but instead have very high friction angles at low stress, due to strong dilation. Rock masses, implying problems of large-scale interaction with engineering structures, may have both cohesive and frictional strength components. However, it is not correct to add these, following linear M-C or nonlinear Hoek–Brown (H-B) standard routines. Cohesion is broken at small strain, while friction is mobilized at larger strain and remains to the end of the shear deformation. The criterion ‘c then σ_n tan φ’ should replace ‘c plus σ_ntan φ’ for improved fit to reality. Transformation of principal stresses to a shear plane seems to ignore mobilized dilation, and caused great experimental difficulties until understood. There seems to be plenty of room for continued research, so that errors of judgement of the last 50 years can be corrected.     

单参数的正则抛物线准则

 线性的Coulomb 准则并不能完全描述岩石强度特征,有多种改进形式。剪切破坏的Mohr准则表现为应力圆的包络线,其待定参数难以从常规三轴压缩试验结果直接确定而研究较少。主应力形式的强度准则可分为显式和隐式,后者常以最大剪应力和平均主应力构造,且具有较高的相关系数和较小的拟合偏差。实际上显式和隐式准则的力学背景相同,可通过坐标系旋转互换。砂岩、大理岩等强度源于颗粒间黏结和摩擦,单参数的正则抛物线准则拟合强度与围压关系的精度优于两参数的Coulomb准则,而与Hoek-Brown准则相当。以正则抛物线准则拟合高围压下强度能够得到完整岩石的理想单轴压缩强度,进而与实际数值对比可确定岩石的初始损伤。     

A fracture sliding potential index for wellbore stability analysis

Sliding failure along the fractures intersecting a wellbore is one of the major wellbore instability mechanisms. This kind of failure is similar to the slope instabilities, a well-known phenomenon in mining and civil engineering. During drilling operations the drilling fluid can penetrate through fractures and lead to fracture reactivation and wellbore instability. The rock engineering systems (RES), initially introduced in the mining- and civil-related geomechanics problems, is an approach to analyze the interrelationship between the parameters affecting rock engineering activities. In this study, after discussing the sliding mechanism along a fracture in a wellbore during drilling, and identifying all the effective parameters, an interaction matrix is introduced to study the sliding failure mechanism. Thereafter, the interaction intensity and dominance of each parameter in the system is determined to classify these parameters. A systematic approach was used to determine the relative interactive intensity and value of each contributing parameter in the fracture sliding mechanism. As a result, an index is presented to estimate the fracture sliding potential. The results indicate the ability of this method to analyse wellbore instability due to fracture reactivation mechanism. This will assist in finding a better engineering action to mitigate or eliminate potential fracture sliding during drilling. The results show a good agreement with those obtained using Mohr–Coulomb failure analysis and field observations.     

Modification of rock mass strength assessment methods and their application in geotechnical engineering

Due to complicated structures and discontinuities in surrounding rock mass, existing empirical failure criteria cannot meet the requirements of engineering practice such as tunnels. To improve estimation accuracy on the strength of rock mass with joints, a modified chart of the Geological Strength Index using Hoek–Brown criteria was further tested to estimate rock mass strength [Lin et al. (2014) Bull Eng Geol Environ 4(73):1245–1258], and, in this paper, new strength estimation equations for jointed rock mass were then modified based on a large dataset obtained from Chinese projects. Here, standard drilling time is first introduced and described in this study, and then used as a parameter to estimate rock strength. Different empirical formulas based on joint density, rock mass classification, Hoek–Brown criteria, and elastic wave velocity are thus used to estimate rock mass strength by using data from the Jiubao tunnel. The results estimated based on different empirical formulas were similar, indicating that the modified assessment method presented in this paper can be used to estimate rock mass strength under certain circumstances. Cross-correlation of different empirical methods provides significant confidence in predicted rock mass strength calculations.