Clay slides in the Målselv valley, northern Norway: Characteristics, occurrence, and triggering mechanisms

The distribution of a large number of clay slides in the Målselv valley, northern Norway, is analysed and put into context with the stratigraphic organization of the valley-fill sediments. About 32% of the landslides larger than 10⁴ m³ occur close to the valley margins, where mud is either exposed or at shallow depth. About 57% of the landslides occur mid-valley, where relatively thin (< 15 m) coarse-grained deltaic sediments overlay fine-grained marine and glaciomarine sediments, and about 11% of the landslides occur in front of ice-contact deposits. The slide-prone areas are all characterized by the occurrence of heterogeneous sediments (interbedded clay, silt and sand), in addition to the presence of steep slopes eroded by rivers. The heterogeneous nature of the sediments probably enhanced groundwater drainage and leaching of salts from the clay, increasing sensitivity. Thus, the distribution and organization of the valley-fill sediments and groundwater drainage probably controlled the position of the slide scars and sliding planes. Since deglaciation of the valley (11,500 BP–present), isostatic rebound has enhanced fluvial incision and the creation of steep slopes due to a fall in relative sea level of up to 80 m.Arcuate-shaped, ‘bottleneck’ landslide scars ranging from c. 10⁴ to 10⁷ m³ in size is the dominant morphological signature of the slides, typical for quick clay slides or earth flows involving fluid mud. Their most common triggering mechanism is probably erosion at the toe slopes by the river Målselv or its tributaries. River erosion close to the valley margin, where glaciomarine and marine sediments are present, seems to give the most severe slides. The overall valley-fill organization controls the distribution of clay slides, which may apply to other fjord valleys having similar sediment distribution.     

柴达木盆地北缘第三系碎屑岩储层特征

柴达木盆地北缘第三系有丰富的油气储集 ,主要存在于碎屑岩中 ,油气的储集明显与碎屑岩的沉积环境和成岩作用有关。对碎屑岩的储集空间和物性特征起直接的控制作用。通过分析碎屑岩的孔隙类型及在空间的分布特征 ,表明在早、晚成岩作用的转换带有大量的次生溶孔存在 ,是油气的有利富集区。储层物性与方解石成负相关 ,粘土矿物则有不同的变化趋势 ,伊利石的存在使物性变差。     

Ultimate lateral bearing capacity of tetrapod jacket foundation in clay

The tetrapod jacket foundations that are always used to support offshore wind turbines have been investigated primarily in laboratory experiments. In this study, the ultimate lateral soil resistance on this type of foundation was investigated using the finite element method and the analytical upper bound plasticity method. The numerical results show good agreement with the theoretical upper bound solutions under the same pile spacings (S) and soil-pile adhesion factors (α). Three distinct failure mechanisms (mechanisms A, B and C) were established in terms of different pile spacings. The ultimate lateral pressure was subsequently determined using numerical analyses with consideration of the loading direction. The most critical loading direction angles (θ) vary with the soil-pile adhesion factors, and are θ = 0 for α = 1 and θ = π/4 for α = 0. Selected empirical equations were proposed to predict the ultimate lateral bearing capacity for engineering practice, considering the pile spacing, soil-pile adhesion and loading direction.     

Review on Advances in Chemical Osmosis in Clayey Sediments

Osmotic phenomena refer to water and solute transport processes that occur when transport of solute molecules or ions is restricted by the porous medium relative to that of water molecules. Chemical osmosis and reverse osmosis/ultrafiltration are osmotic phenomena. The studies of “coupled flow” caused by chemical osmosis have been widely applied in many fields, such as earth science, environmental science and civil engineering. This paper provided a review of the considerable advances in the field of chemical osmosis and clay semipermeable membrane since the 1950s. We summarized the research progress of chemical osmosis in clayey sediments into three aspects: theoretical basis, experimental research and numerical model. In particular, the laboratory equipment and measurement methods of the chemico-osmotic efficiency coefficient σ were described,. The existing discontinuous models based on the ‘diffusive double layer’ theory were summerized, as well as the various control factors of σ. It increases with Cation Exchange Capacity (CEC), compaction pressure and decreases by the increasing of porosity and solution concentration. This paper also summerized the contimuum models based on non-equilibrium thermodynamics, which are used to explain and predict anomalies of hydraulic head pressure and salinity in clayey environments. For the future development of this discipline, it is critical to find a reliable method to confirm the σ value. It is also critical to emphasize the research on chemical osmosis in complex conditions and the influence of chemical osmosis on groundwater flow and solute transpotation. China has just stepped into this research area and more efforts should be made if significant progress is desired. This review will be helpful to further research on groundwater numerical simulation integrated with chemical osmosis in China.     

Analytical study on comprehensive behaviors of drag anchors in the seabed

Attributed to good performance in the seabed, drag anchors are adopted as an effective anchoring solution in deepwater mooring systems. This type of anchors is drag installed, companying with comprehensive behaviors during movement of the anchor in the seabed, which make the anchor trajectory and therefore the final embedment position difficult to be predicted. On the basis of the mechanical model and analytical procedure, an analytical method is proposed for exploring comprehensive behaviors of drag anchors in both clay and sand. The anchor behaviors are classified as keying, pulling out and diving. The bearing capacity and the trajectory of the anchor can be predicted through the combination of the three behaviors. By comparing analytical predictions with experimental data and other predictions, the efficiency and veracity of the theoretical model are validated. A parametric study is also performed to investigate the effects of different parameters, and to further understand the comprehensive anchor behaviors in the seabed. The present work provides an efficient theoretical tool for analyzing comprehensive behaviors of drag anchors in either clayey or sandy seabed.     

Vertical Variability of the Undrained Shear Strength of Golden Horn Clay

In this study, a stochastic method was applied to investigate if there exists a statistical correlation between values of undrained shear strength at various vertical distances along Golden Horn. Therefore, the undrained shear strength values measured by field vane shear tests at different depths were used to determine the depth dependent variation of the mean value and standard deviation. Futhermore, autocorrelation functions were defined to describe the correlation between values of c_u at different depths. The study showed that the applied method might provide a statistical range to estimate the undrained shear strength value at depths where no measurements are undertaken.     

油田开发后期储层岩石导电机理的实验研究

储层岩石中一般含有一定量的粘土成分.粘土与电解质溶液相接触时,在颗粒表面形成双电层,它是粘土导电的机理.当注水开发的油田到了后期,由于水的注入改变了粘土颗粒表面双电层的结构,从而有可能改变粘土的导电性能.本研究通过对实际岩芯样品进行的研究表明:由于水的注入,粘土导电性下降,从而导致整个储层电导率的降低.     

陕北晋西黄土滑塌灾害的初步研究以西气东输工程为例

黄土滑塌灾害是黄土高原北部地区的-种特殊斜坡变形破坏类型。由于其突发性和频繁发生的特点, 常造成大批窑洞、房屋倒塌和人员伤亡, 并给该区铁路、公路和长输管道建设造成严重危害。由于黄土滑塌灾害具有滑坡和崩塌两种机制和先滑后塌的变形破坏过程, 以往常把它们作为滑坡或崩塌来研究。作者通过陕西靖边县至山西蒲县间 30 0km黄土地质灾害的野外调查和室内的微观分析, 发现黄土滑塌灾害的发生主要受黄土粘粒含量的控制, 因此在空间上具有鲜明的地域性:0.0 0 5mm粘粒含量 10 %的砂黄土区是滑塌灾害严重发育区; 0.0 0 5mm粘粒含量在 10 %～ 2 0 %之间的典型黄土区是滑塌灾害弱发育区; 0.0 0 5mm粘粒含量 2 0 %的粘黄土区是滑塌灾害不发育区。作者在黄土滑塌灾害产生机理和形成条件研究的基础上提出了相应的工程对策。     

A general approach to model interfaces using existing soil constitutive models application to hypoplasticity

The modelling of interfaces is important for the holistic simulation of geotechnical structures (e.g. piles, tunnels and geogrids). For this reason, advanced constitutive interface models and numerical techniques are needed. There are few user-friendly models, and these are rarely implemented. In this paper, a new approach for advanced interface models is proposed. This is based on the assumption that the fully rough interface can be modelled considering simple-shear behaviour at the interface. A 3D soil model is used as a constitutive driver for a frictional subroutine. This minimises the effort required, and advanced interface models are available with less effort. Two different hypoplastic models are used with the new approach. The approach was verified for several aspects (e.g. mesh size dependence), and the volumetric behaviour was studied. The user-friendliness and absence of additional parameters led to more realistic simulation results. The proposed method can be extended to other modelling techniques and will improve the modelling of contacts in soil-structure interaction analysis.