A note on the physical properties of the chalk

The Chalk is one of the most extensively distributed series in England. It is essentially a soft limestone principally consisting of the remains of marine organisms, deposited in shallow water.The Upper Chalk of Kent, in particular, is characterized by a high porosity and relatively low dry density. The porosity and dry density of the Lower Chalk of Yorkshire and the Middle Chalk of Norfolk are lower and higher respectively, because of the higher content of interstitial secondary calcite. Porosity is not a significant factor as far as the gross permeability of the Chalk is concerned.The Upper Chalk of Kent is moderately weak, when tested in unconfined compression, whilst the Lower and Middle Chalk are moderately strong. All three groups of Chalk suffer a substantial reduction in strength when saturated, in the case of the Upper Chalk the loss in strength is dramatic. The indirect tensile strength is usually less than one twentieth that of the unconfined compressive strength. When subjected to undrained triaxial tests the Upper Chalk first underwent brittle failure at lower confining pressures but above 4.9 MN/m² significant plastic deformation occurred leading to barrel-shaped failures.Young's modulus is not a simple constant but varies with stress, increasing somewhat with increasing stress in the Chalk from Yorkshire and Norfolk. This did not happen in the Upper Chalk since plastic deformation began much earlier.     

非饱和白垩压缩变形依时特性的研究

工程实践和室内试验都表明，非饱和的油田白垩同一般岩土材料一样具有不可忽视的依时性态，为此，在试验和理论研究的基础上为非饱和白垩建立了一个修正剑桥模型，该模型可同时反映时间、应力吸力对非饱和白垩强度及变形特性的影响，为进一步深入了解吸入对非饱和白垩依时性态的影响及其机理提供了一定的参考。     

Notes on the Sinian Glaciation in the Upper Nanpankiang Valley,E.Yunnan

正 The Sinian Glaciation as revealed by the occurrence of tillite in eastern Yunnan was first recognized in Chenkiang by Prof. P. Misch.' During a reconnaissance survey. along the Sufu-Kunming Railway Line from Kunming to Chutsin last year, I had the opportunity to visit this tillite locality in Chen     

砂岩类脆性无序介质连续破坏过程的细观模拟

为了分析砂岩类无序介质在各种荷载作用下的连续破坏过程,本文提出了梁-颗粒细观模型。在此模型中,介质被离散为一系列的颗粒单元,这些颗粒单元均由弹脆性的梁单元联结。颗粒的力学行为由离散单元法和有限单元法确定。当某个梁单元所受应力超过其强度时,就随即将它从计算网络中剔除,以模拟介质的破坏行为。为了验证数值模型的可靠性,分别从破坏模式和荷载-位移曲线两方面与物理模型实验进行了对比,结果表明两者基本一致。此外,探讨了无序性对介质裂纹分布形式的影响,并用分维表述了裂纹分布与荷载强度之间的内在联系。      

Mechanical behaviour of Lixhe chalk partly saturated by oil and water: experiment and modelling

Two or more different fluids generally saturate chalk in oil reservoir, and therefore its behaviour can be very complicated. In this paper, a constitutive law is proposed for modelling the mechanical behaviour of a chalk saturated by two non‐miscible fluids, water and oil. The effects of the capillary pressure or suction are taken into account. They are considered as an independent variable, as in the Barcelona's basic model developed for unsaturated soils. On the other hand, internal friction and pore collapse are modelled as independent mechanisms. The determination of the parameters is based on triaxial and oedometer tests. Finally, in order to validate the model, predictions are compared with experimental results of water‐flooding test. Copyright © 2002 John Wiley & Sons, Ltd.     

A 2.5 G.a. reworked sialic crust: Rb-Sr ages and isotopic geochemistry of late archaean volcanic and plutonic rocks from E. Finland

In east-central Finland, Archaean terrains present three main lithologic units: a) gneissic basement, emplaced from 2.86 G.a. to 2.62 G.a., b) greenstone belt (2.65 G.a.) and c) calc-alkaline magmatism (2.50 G.a. to 2.40 G.a). Twenty three rocks of the calc-alkaline suite have been chosen for geochronologic and Rb-Sr isotopic studies. These rocks are subdivided into three groups: 1) acid volcanics from Luoma, 2) augen gneiss from Arola, and 3) post kinematik pink leucogranite from Arola. The 2.50±0.10 G.a. age of the Luoma volcanics indicates that they represent the upper part of a greenstone belt composed of a single sequence of volcanic rocks. The ages, initial ⁸⁷Sr/⁸⁶Sr (I_Sr) and major element compositions of the augen gneisses of Arola and Suomussalmi indicate that these rocks are the plutonic equivalents of the Luoma acid volcanics. The Arola pink leucogranite marks the terminal phase of Archaean magmatic activity (from 2.86 G.a. to 2.41 G.a.). This was followed by at least 0.40 G.a. of quiescence. The I_Sr and major element compositions suggest that the genesis of the calc-alkaline magmatic rocks involved crustal materials, but all their geochemical features cannot be explained without the participation of mafic greenstone belt materials. The first crustal components had low I and low K₂O/ Na₂O ratios while the younger ones (calc-alkaline magmas) had medium to high I_Sr and high K₂O/Na₂O ratios. Thus the petrogenetic processes have changed with time from ensimatic to ensialic, implying major reworking of preexisting crustal materials. This evolution leads to the accretion of the continental crust from the mantle.