A model of the generation of electromagnetic emissions detected prior to earthquakes     

《Physics and Chemistry of the Earth》2015

Recent satellite and ground-based observations prove that during the formative period of earthquakes VLF/LF and ULF electromagnetic emissions are observed in seismogenic areas. This work offers an original model of self-generated electromagnetic oscillations of local segments of the lithospheric origins of the emissions. In the paper, the seismogenic area is considered to be an oscillatory-distributed system. This model simplifies physical analyses of the nonlinear effects and qualitatively explains the mechanisms that generate very low frequency electromagnetic waves in the period prior to an earthquake.  相似文献   

Analysis Procedure of the Cyclic Bearing Capacity for Suction Anchors in Soft Clays     

Jianhua Wang  Shuzhao Li 《Marine Georesources & Geotechnology》2013,31(6):546-555

This article presents a procedure to calculate the bearing capacity of suction anchors subjected to inclined average and cyclic loads at the optimal load attachment point using the undrained cyclic shear strength of soft clays based on the failure model of anchors proposed by Andersen et al. The constant average shear stress of each failure zone around an anchor is assumed and determined based on the static equilibrium condition for the procedure. The cyclic shear strength of each failure zone is determined based on the average shear stress. The cyclic bearing capacity is finally determined by limiting equilibrium analyses. Thirty-six model tests of suction anchors subjected to inclined average and cyclic loads were conducted, which include vertical and lateral failure modes. Model test results were predicted using the procedure to verify its feasibility. The average relative error between predicted and test results is 1.7%, which shows that the procedure can be used to calculate the cyclic bearing capacity of anchors with optimal loading. Test results also showed that the anchor was still in vertical failure mode under combined average and cyclic loads if an anchor was in vertical failure mode under static loads. The anchor failure would depend on the vertical resistance degradation under cyclic loads if an anchor was in lateral failure mode under static loads. Cyclic bearing capacities associated with the number of load cycles to failure of 1000 were about 75% and 80% of the static bearing capacity for vertical failure anchors and lateral failure anchors, respectively.  相似文献   

Calculation of side friction resistance between the formation and conductor during the jetting process in deepwater drilling     

Yunjin Xu  Jin Yang  Wei Meng  He Deng 《Marine Georesources & Geotechnology》2013,31(4):409-416

ABSTRACT

The purpose of this paper is to develop a method for calculating side friction resistance during the jetting process to improve drilling efficiency. Side friction dynamics in length of time was determined by means of dynamic force analysis of the conductor during the jetting process by experiment, and the real-time calculation model of side friction between the formation and conductor was developed. In particular, 3-1/2″, 5-1/2″, and 9-5/8″ conductors were used to simulate actual field operation. The calculated values match well with the true values. Simulation experiments were performed in the central fishing harbor of Bohai Sea, Tianjin Province, China.  相似文献   

Bearing capacity of strip and circular footings in sand using finite elements     

D. Loukidis  R. Salgado 《Computers and Geotechnics》2009

Design of shallow foundations relies on bearing capacity values calculated using procedures that are based in part on solutions obtained using the method of characteristics, which assumes a soil following an associated flow rule. In this paper, we use the finite element method to determine the vertical bearing capacity of strip and circular footings resting on a sand layer. Analyses were performed using an elastic–perfectly plastic Mohr–Coulomb constitutive model. To investigate the effect of dilatancy angle on the footing bearing capacity, two series of analyses were performed, one using an associated flow rule and one using a non-associated flow rule. The study focuses on the values of the bearing capacity factors N_q and N_γ and of the shape factors s_q and s_γ for circular footings. Relationships for these factors that are valid for realistic pairs of friction angle and dilatancy angle values are also proposed.  相似文献   

地基载荷试验的原理与应用     

黄清华 《华南地震》1996,16(4):80-84

介绍了地基载荷试验的方法及原理，讨论了如何应用该方法来检测地基的承载力及压缩特性，并结合工程实例，对存在不同程度缺陷的地基试验曲线进行了分析。  相似文献   

旁压试验确定上海软土地区的单桩承载力   总被引：1，自引：0，他引：1  

杨石飞  顾国荣  董建国 《上海国土资源》2002,(4):41-46

该文搜集上海地区三十多项旁压试验资料工程，以及近133组静载荷试验，经过分析、统计、比较，得出根据旁压试验确定单桩竖向极限承载力的公式，表明该公式的普遍适用性，是对静载试验方法的有益补充。同时对379组分别采用旁压和静探试验估算的单桩承载力的比较，表明采用旁压试验方法估算的单桩承载力与静探方法基本吻合。  相似文献   

Climate change and extreme weather events: can developing countries adapt?     

M.Monirul Qader Mirza 《Climate Policy》2003,3(3):233-248

Developing countries are vulnerable to extremes of normal climatic variability, and climate change is likely to increase the frequency and magnitude of some extreme weather events and disasters. Adaptation to climate change is dependent on current adaptive capacity and the development models that are being pursued by developing countries. Various frameworks are available for vulnerability and adaptation (V&A) assessments, and they have both advantages and limitations. Investments in developing countries are more focused on recovery from a disaster than on the creation of adaptive capacity. Extreme climatic events create a spiral of debt burden on developing countries. Increased capacity to manage extreme weather events can reduce the magnitude of economic, social and human damage and eventually, investments, in terms of borrowing money from the lending agencies. Vulnerability to extreme weather events, disaster management and adaptation must be part of long-term sustainable development planning in developing countries. Lending agencies and donors need to reform their investment policies in developing countries to focus more on capacity building instead of just investing in recovery operations and infrastructure development.  相似文献   

波形拟合法在人工挖孔扩底桩承载力测试中的应用          下载免费PDF全文

吕芝全  潘纪顺  刘长来  海蕊  王碧辉  孙方宇 《地震工程学报》2002,24(1):78-84

从人工挖孔扩底桩的工作机理和波形拟合法的基本原理出发 ,结合工程实例阐述了波形拟合法在确定人工挖孔扩底桩承载力中的应用特点及可行性 .  相似文献   

地基承载力动测的附加质量法   总被引：7，自引：2，他引：7  

李丕武 《地球物理学报》1993,36(5):683-687

本文介绍的方法是将地基的振动问题等效为质量弹簧体系,并在该体系上附加一级或多级质量块,测出该体系的动刚度及地基土的参振质量;再通过动静关系求得地基承载力。从理论及方法上摆脱了土动力学中求地基土动刚度及参振质量的困扰。  相似文献   

Upper bound limit analysis for finding interference effect of two nearby strip footings on sand     

Jyant Kumar  Priyanka Ghosh 《Geotechnical and Geological Engineering》2007,25(5):499-507

The ultimate bearing capacity of two closely spaced strip footings, placed on a cohesionless medium and loaded simultaneously to failure at the same magnitude of failure load, was determined by using an upper bound limit analysis. A logarithmic spiral radial shear zone, comprising of a number of triangular rigid blocks, was assumed to exist around each footing edge. The equations of the logarithmic spiral arcs were based on angles φ_L and φ_R rather than soil friction angle φ; the values of φ_L and φ_R were gradually varied in between 0 and φ. The ultimate bearing capacity was found to become maximum corresponding to a certain critical spacing between the footings. For spacing greater than the critical, the bearing capacity was found to decrease continuously with increase in the spacing. The extent of the spacing corresponding to which the ultimate bearing capacity becomes either maximum or equal to that of a single isolated footing increases with increase in φ. The results compare reasonably well with the available theoretical and experimental data.  相似文献