Stability analysis of rock wedges with multiple sliding surfaces

Summary Although wedge and plane sliding stability analyses are well established in the geotechnical literature, certain geologic environments produce blocks which cannot be adequately modelled as either wedges or plane slides. An example is blocks forming in cylindrically folded sedimentary rocks, where the surface of sliding is neither a single plane nor a double plane but is curved. This type of block may be idealized as a prismatic block with multiple sliding planes, all with parallel lines of intersection. If the sliding planes number three or more, the distribution of normal forces, and hence the factor of safety, is indeterminate. A new analytical model for sliding stability analysis is described in which the distribution of normal forces on the contact planes is chosen to minimize the potential energy of the system. The classic wedge and plane solutions are shown to be special cases of this more general model, which allows determination of the safety factor for any shape of prismatic contact surface. An example from Tennessee concerning a block with a curved sliding surface is described and the factor of safety compared with the standard wedge analysis. It is shown that with three or more contact planes, the safety factor may be significantly lower than that calculated from the wedge model, which provides an upper limit on stability.     

Geochemical characteristics, Ar–Ar ages and original tectonic setting of the Band-e-Zeyarat/Dar Anar ophiolite, Makran accretionary prism, S.E. Iran

The Makran accretionary prism in southeastern Iran contains extensive Mesozoic zones of melange and large intact ophiolites, representing remnants of the Tethys oceanic crust that was subducted beneath Eurasia. To the north of the Makran accretionary prism lies the Jaz Murian depression which is a subduction-related back-arc basin. The Band-e-Zeyarat/Dar Anar ophiolite is one of the ophiolite complexes; it is located on the west side of the Makran accretionary prism and Jaz Murian depression, and is bounded by two major fault systems. The principal rock units of this complex are a gabbro sequence which includes low- and high-level gabbros, an extensive sheeted diabase dike sequence, late intrusive rocks which consist largely of trondhjemites and diorites, and volcanic rocks which are largely pillow basalts interbedded with pelagic sedimentary rocks, including radiolarian chert. Chondrite- and primitive-mantle-normalized incompatible trace element data and age-corrected Nd, Pb, and Sr isotopic data indicate that the Band-e-Zeyarat/Dar Anar ophiolite was derived from a midocean ridge basalt-like mantle source. The isotopic data also reveal that the source for basalts was Indian-Ocean-type mantle. Based on the rare earth element (REE) data and small isotopic range, all the rocks from the Band-e-Zeyarat/Dar Anar ophiolite are cogenetic and were derived by fractionation from melts with a composition similar to average E-MORB; fractionation was controlled by the removal of clinopyroxene, hornblende and plagioclase. Three ⁴⁰Ar–³⁹Ar plateau ages of 140.7±2.2, 142.9±3.5 and 141.7±1.0 Ma, and five previously published K–Ar ages ranging from 121±4 to 146±5 Ma for the hornblende gabbros suggest that rocks from this ophiolite were formed during the Late Jurassic–Early Cretaceous. Plate reconstructions suggest that the rocks of this complex appear to be approximately contemporaneous with the Masirah ophiolite which has crystallization age of (150 Ma). Like Masirah, the rocks from the Band-e-Zeyarat/Dar Anar ophiolite complex represent southern Tethyan ocean crust that was formed distinctly earlier than crust preserved in the 90–100 Ma Bitlis-Zagros ophiolites (including the Samail ophiolite).     

原特提斯洋的俯冲、增生及闭合:阿尔金-祁连-柴北缘造山系早古生代增生/碰撞造山作用

分布在青藏高原北缘的阿尔金-祁连-柴北缘早古生代造山系被认为是原特提斯构造域最北部的构造拼合体。与其北侧具有长期增生历史的中亚造山系相比,特提斯造山拼合体被认为是各种来自冈瓦纳大陆北部大陆块体相互碰撞的产物。然而,与典型的阿尔卑斯和喜马拉雅碰撞造山带相比,阿尔金-祁连-柴北缘早古生代造山系包括有大量蛇绿岩、弧岩浆杂岩、俯冲-增生杂岩等,因此一些学者认为青藏高原北部的早古生代造山系为沿塔里木和华北克拉通边界向南逐渐增生的增生型造山带。但是,增生造山模式又很难解释南阿尔金-柴北缘地区普遍存在的与大陆俯冲有关的UHP变质岩、广泛分布的巴罗式变质作用和相关的岩浆作用,以及与碰撞造山有关的变形构造等。在本文中,通过对已有研究资料的综合总结,结合一些新的研究资料,我们提出在青藏高原东北缘的阿尔金-祁连-柴北缘造山系中,早古生代时期存在两种不同类型的造山作用,即增生和碰撞造山作用,其主要标志是北祁连-北阿尔金的HP/LT变质带、蛇绿混杂岩及与洋壳俯冲有关的构造岩浆作用,以及分布在柴北缘-南阿尔金与大陆俯冲和陆陆碰撞有关的UHP变质带、区域巴罗式变质作用、深熔作用、相关的岩浆活动及伸展垮塌作用等,并建立了一个反映原特提斯洋俯冲、增生、闭合及碰撞造山作用的构造模式。     

Modification of strain wedge method for lateral soil-pile interaction in sandEI北大核心CSCD

A modified strain wedge (SW) method for analyzing the behavior of laterally loaded single piles in sand is proposed. The modified model assumes that the lateral displacements of a pile behind the three-dimensional passive soil wedge are nonlinear, which makes the horizontal soil strain variable with depths instead of a constant value in the original strain wedge model, and also employs two different hyperbolic models, one for describing horizontal stress increment-strain behavior of soil in the wedge, and the other for describing the shear stress-displacement property at the interface between soil and pile shafts. An example is analyzed to demonstrate the effectiveness of the modified method, and a good agreement is obtained. Finally, the effects of modifications on the lateral bearing capacity of pile shafts are discussed. The results show that the problem of overestimating the lateral bearing capacity of piles with strain wedge method can be ameliorated by introducing the assumption of nonlinear lateral displacements of piles. It makes the SW method more convenient and effective in analyzing the behavior of laterally loaded piles by introducing the new relationships of horizontal stress increment-strain and shear stress-displacement.     

既有建筑地基基础加固劈裂注浆法在青纸汽运办公楼的应用

青纸汽运办公由于部分基础座落在松散的杂填土层上，产生不均匀沉降破坏，通过劈裂注浆加固，建筑物停止沉降，地基土承载力标准值提高了4倍，效果显著。加固劈裂注浆法是治理既有建筑地基基础沉降灾害的有效方法之一。     

The Recognition of the Chuxiong Foreland Basin System in Yunnan, China

THE RECOGNITION OF THE CHUXIONG FORELAND BASIN SYSTEM IN YUNNAN,CHINA     

高压超高压变质岩抬升—剥露的一种动力学机制分析

综述了高压超高压变质岩带的基本构造特征，认为运用体粘滞性流变学理论可以很好地解释高压超高压变质岩的发育过程及其抬升－剥露动力学机制。     

Climate and material controls on periglacial soil processes: Toward improving periglacial climate indicators

One of the distinguished efforts of A.L. Washburn was to reconstruct mean annual air temperature using periglacial features as climate indicators. This paper reviews existing periglacial indicators and proposes a strategy to improve their thermal resolution based on recent periglacial process studies, with a focus on solifluction and thermal contraction cracking and associated landforms/structures. Landforms resulting from solifluction reflect both the depth subjected to freeze-thaw and the thickness of frost-susceptible soils. The thickness of a solifluction structure can be used to infer the dominant freeze-thaw regime and minimum seasonal frost depth. Ice-wedge pseudomorphs have limited potential as a climate indicator because (1) they mainly reflect extreme winter temperatures, (2) their thermal thresholds depend on the host material, and (3) they need to be distinguished from frost wedges of other origin produced under different thermal and/or material conditions. Monitoring studies of currently active ice wedges suggest that ice-wedge cracking requires a combination of low temperature and large temperature gradients in the frozen active layer. Further field monitoring of periglacial processes and their controlling factors under various climate conditions and in various materials are needed, however, to improve the resolution of periglacial paleoclimate indicators.