检索结果-南通市图书馆

Influence of principal stress rotation of unequal tensile and compressive stress amplitudes on characteristics of soft clay

在线全文

学校读者我要写书评

暂无评论

Journal of Mountain Science 2017年第2期14卷 369-381页

作者： SHEN Yang WANG Xin liu han-long DU Wen-han WANG Bao-guang XU Hai-dong Key Laboratory of Geomechanics and Embankment Engineering of Ministry of Education Hohai UniversityNanjing 210098China Jinan Rail Transit Group Co. LtdJinan 250100China School of Civil Engineering Chongqing UniversityChongqing 400044China

Soil behavior can reflect the characteristics of principal stress rotation under dynamic wave and traffic loads. Unequal amplitudes of tensile and compressive stresses applied to soils have complex effects on foundation soils in comparison with the pure principal stress rotation path. A series of undrained cyclic hollow torsional shear tests were performed on typical remolded soft clay from the Hexi area of Nanjing, China. The main control parameters were the tensile and compressive stress amplitude ratio(α) and the cyclic dynamic stress ratio(η). It was found that the critical η tended to remain constant at 0.13, when the value of the compressive stress amplitude was higher than the tensile stress amplitude. However, the influence of the tensile stress was limited by the dynamic stress level when α= *** obvious structural change in the soil, the corresponding numbers of cyclic vibration cycles were found to be independent of α at low stress levels and were only related to η. Finally, a new method for evaluating the failure of remolded soft clay was presented. It considers the influence of the tensile and compressive stresses which caused by complex stress paths of the principal stress rotation. This criterion can distinguish stable, critical, and destructive states based on the pore-water-pressure-strain coupling curve while also providing a range of failure strain and vibration cycles. These results provide the theoretical support for systematic studies of principal stress rotation using constitutive models.

关键词： Complex stress path Principal stress rotation Train loads Amplitude ratio Cyclic dynamic stress ratio Failure criterion

Study on the performance of the micropile-mechanically stabilized earth wall

在线全文

学校读者我要写书评

暂无评论

Journal of Mountain Science 2018年第4期15卷 825-844页

作者： ZhanG Zhi-chao Ronald Y.S.PAK CHEN Yu-min liu han-long Key Laboratory of Geohazard Prevention of Hilly Mountains Ministry of Land and Resources of China Department of Civil Environmental & Architectural Engineering University of Colorado College of Civil & Transportation Engineering Hohai University Key Laboratory of New Technology for Construction of Cities in Mountain Area Chongqing University

The Micropile-Mechanically Stabilized Earth(MSE) wall, specially designed for mountain roads, is proposed to improve the MSE wall local stability, global stability and impact resistance of roadside barriers. Model tests and the corresponding numerical modeling were conducted to validate the serviceability of the Micropile-MSE wall and the reliability of the numerical method. Then, a parametric study of the stress and deformation of Micropile-MSE wall based on the backfill strength and interfacial friction angle between backfill and backslope is conducted to evaluate its *** test results indicate that the surcharge-induced horizontal earth pressure, base pressure and lateral displacement of the wall panel of Micropile-MSE wall decrease. The corresponding numerical results are nearly equal to the measured values. The basic failure mode of MSE wall in steep terrain is the sliding of backfill along the backslope, while A-frame style micropiles are capable of preventing the sliding *** maximum resultant displacement can be decreased by 6.25% to 46.9% based on different interfacial friction angles, and the displacement canbe reduced by 6% ~ 56.1% based on different backfill strengths. Furthermore, the reduction increases when the interfacial friction angle and internal friction angle of backfill decrease. In addition, the lateral displacement of wall panel, the deformation of backfill decrease and the tension strain of geogrid obviously, which guarantees the MSE wall functions and provides good conditions for mountain roads.

关键词： Mechanically stabilized earth wall Model test Micropile Numerical simulation Stress and deformation behavior

A new adaptive fast motion estimation algorithm based on local motion similarity degree (LMSD)

在线全文

学校读者我要写书评

暂无评论

Progress in Natural Science:Materials International 2005年第12期15卷 1126-1134页

作者： liu long,han Chongzhao and BAI Yan School of Electronics & Information Engineering,Xi’an Jiaotong University,Xi’an 710049,China School of Electronics & Information Engineering Xi''an Jiaotong University Xi''an 710049 China

In the motion vector field adaptive search technique (MVFAST) and the predictive motion vector field adaptive search technique (PMVFAST),the size of the largest motion vector from the three adjacent blocks (left,top,top-right) is compared with the threshold to select different search *** a suitable search center and search pattern will not be selected in the adaptive search technique when the adjacent motion vectors are not coherent in local *** paper presents an efficient adaptive search *** motion vector variation degree (MVVD) is considered a reasonable factor for adaptive search *** the relationship between local motion similarity degree (LMSD) and the variation degree of motion vector (MVVD),the motion vectors are classified as three categories according to corresponding LMSD; then different proposed search schemes are adopted for motion *** experimental results show that the proposed algorithm has a significant computational speedup compared with MVFAST and PMVFAST algorithms,and offers a similar,even better performance.

关键词： motion estimation motion vector video coding local motion

Vertical vibration of a large diameter pipe pile considering transverse inertia effect of pile

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Journal of Central South University 2016年第4期23卷 891-897页

作者：郑长杰刘汉龙丁选明周航 Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University) Chongqing 400045 China

Considering the transverse inertia effect of pile, the vertical soil layer is studied. The wave propagations in the outer and inner soil dynamic response of a large diameter pipe pile in viscoelastic are simulated by three-dimensional elastodynamic theory and those in the pile are simulated by Rayleigh-Love rod theory. The vertical and radial displacements of the outer and inner soil are obtained by utilizing Laplace transform technique and differentiation on the governing equations of soils. Then, based on the continuous conditions between the pile and soils, the displacements of the pile are derived. The frequency domain velocity admittance and time domain velocity response of the pile top are also presented. The solution is compared to a classical rod model solution to verify the validity. The influences of the radii and Poisson ratio of pile on the transverse inertia effect of pile are analyzed. The parametric study shows that Poisson ratio and outer radius of pile have significant influence on the transverse inertia effect of large diameter pipe piles, while the inner radius has little effect.

关键词： large diameter pipe pile vertical vibration Rayleigh-Love rod transverse inertia effect

Numerical investigation of piled raft foundation in mitigating embankment vibrations induced by high-speed trains

在线全文

学校读者我要写书评

暂无评论

Journal of Central South University 2015年第11期22卷 4434-4444页

作者：付强刘汉龙丁选明郑长杰 College of Civil and Transportation Engineering Hohai University Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering

A three-dimensional dynamic finite element model of track-ballast-embankment and piled raft foundation system is established. Dynamic response of a railway embankment to a high-speed train is simulated for two cases: soft ground improved by piled raft foundation, and untreated soft ground. The obtained results are compared both in time domain and frequency domain to evaluate the effectiveness of the ground improvement in mitigating the embankment vibrations induced by high-speed trains. The results show that ground improving methods can significantly reduce the embankment vibrations at all considered train speeds(36-432 km/h). The ground response to a moving load is dictated largely by the relationship between load speed and characteristic value of wave velocities of the ground medium. At low speeds, the ground response from a moving load is essentially quasi-static. That is, the displacements fields are essential the static fields under the load simply moving with it. For the soft ground, the displacement on the ballast surface is large at all observed train speeds. For the model case where the ground is improved by piled raft foundation, the peak displacement is reduced at all considered train speeds compared with the case without ground improvement. Based on the effect of energy-dissipating of ballast-embankment-ground system with damping, the train-induced vibration waves moving in ballast and embankment are trapped and dissipated, and thus the vibration amplitudes of dynamic displacement outside the embankment are significantly reduced. But for the vibration amplitude of dynamic velocity, the vibration waves in embankment are absorbed or reflected back, and the velocity amplitudes at the ballast and embankment surface are enhanced. For the change of the vibration character of embankment and ballast, the bearing capacity and dynamic character are improved. Therefore, both of the static and dynamic displacements are reduced by ground improvement; the dynamic velo

关键词： finite element simulation track-ballast-embankment

在线全文

学校读者我要写书评

暂无评论

桩承式加筋路堤的现场试验及数值分析

岩土力学 2009年第4期30卷 1004-1012页

作者：费康刘汉龙扬州大学岩土工程研究所江苏扬州225009 河海大学岩土工程科学研究所南京210098

对一桩体面积置换率为8.7%的低置换率桩承式加筋路堤进行了现场试验及三维有限元分析。现场主要进行了桩、土荷载分担,孔压、沉降及侧向水平变形等内容的观测。将观测数据与常规设计方法及三维有限元分析结果进行了对比研究,在此基础上... 详细信息

对一桩体面积置换率为8.7%的低置换率桩承式加筋路堤进行了现场试验及三维有限元分析。现场主要进行了桩、土荷载分担,孔压、沉降及侧向水平变形等内容的观测。将观测数据与常规设计方法及三维有限元分析结果进行了对比研究,在此基础上对设计方法的适用性进行了分析。研究结果表明,路堤填土的土拱效应造成荷载向桩体转移,这种荷载转移大幅度减小了在软土层中产生的超孔隙水压力。当填土高度大于2.5m时,土拱效应的应力折减系数可用Russell和Pierpoint或Hewlett和Randolph提出的土拱效应分析方法进行计算,其结果与三维有限元分析也较相符,但在路堤高度较小时,只有Russell和Pierpoint方法与实测结果相接近。路堤施工过程中,实测的水平变形与沉降之比仅为0.2左右,这表明采用桩承式加筋路堤不仅可减小沉降,而且可减小水平向的变形,提高路堤的稳定性。

关键词：桩承式加筋路堤土拱效应现场试验三维有限元分析

在线全文

学校读者我要写书评

暂无评论

土石坝动力分析的改进二次加速度积分法

岩土力学 2009年第5期30卷 1497-1503页

作者：杨贵刘汉龙河海大学岩土力学与堤坝工程教育部重点试验室南京210098 河海大学岩土工程科学研究所南京210098

土石坝动力分析常用的是Wilson-θ积分方法,但该方法用于分析高频问题和大步长问题时精度较低。针对该缺点提出一种改进的二次加速度积分法,该算法与一步二次加速度积分法相比,计算精度不变、稳定性要求容易满足,计算用时大大减少。对... 详细信息

土石坝动力分析常用的是Wilson-θ积分方法,但该方法用于分析高频问题和大步长问题时精度较低。针对该缺点提出一种改进的二次加速度积分法,该算法与一步二次加速度积分法相比,计算精度不变、稳定性要求容易满足,计算用时大大减少。对算法的基本原理、稳定性及精度进行了分析,并给出一个土石坝动力分析的算例,验证了该算法的可行性。与常用的Wilson-θ法、Newmark法和中心差分法进行了数值比较。计算结果表明:该算法在分析高频问题和大步长问题时,计算精度较高。

关键词：土石坝逐步积分法改进的二次加速度积分法

现浇薄壁管桩在低应变瞬态集中荷载作用下的动力响应解析解

在线全文

学校读者我要写书评

暂无评论

岩土工程学报 2007年第11期29卷 1611-1617页

作者：刘汉龙丁选明河海大学岩土工程水利部重点实验室

管桩低应变检测时,平截面假定并不满足,应力波的传播不能简单地用一维波动方程描述。对于薄壁的大直径管桩,桩顶各点的动力响应沿径向变化不大,因此,可以假定各物理量沿径向无变化而建立只含有变量z,θ,t的波动方程。采用分离变量法和... 详细信息

管桩低应变检测时,平截面假定并不满足,应力波的传播不能简单地用一维波动方程描述。对于薄壁的大直径管桩,桩顶各点的动力响应沿径向变化不大,因此,可以假定各物理量沿径向无变化而建立只含有变量z,θ,t的波动方程。采用分离变量法和常数变易法求得了该波动方程的解析解,并对一个算例进行了计算分析,探讨了桩顶的动力响应和平截面假定的影响深度问题,并把计算结果与一维波动理论以及三维有限元的结果进行了对比分析。

关键词：管桩低应变检测动力响应解析解三维效应

轴对称均匀黏弹性地基中现浇薄壁管桩竖向动力响应简化解析方法

在线全文

学校读者我要写书评

暂无评论

岩土力学 2008年第12期29卷 3353-3359页

作者：丁选明刘汉龙河海大学岩土力学与堤坝工程教育部重点实验室南京210098 河海大学岩土工程科学研究所南京210098

考虑土体材料的黏性阻尼和桩-土纵向耦合振动,建立了轴对称均匀黏弹性地基中现浇薄壁管桩管桩纵向振动的定解问题,采用Laplace变换的方法求得了解析解。对一算例进行了分析,将计算结果与实测波形和有限元进行了对比,三者吻合较好。进一... 详细信息

考虑土体材料的黏性阻尼和桩-土纵向耦合振动,建立了轴对称均匀黏弹性地基中现浇薄壁管桩管桩纵向振动的定解问题,采用Laplace变换的方法求得了解析解。对一算例进行了分析,将计算结果与实测波形和有限元进行了对比,三者吻合较好。进一步分析了桩周土和桩芯土黏性阻尼系数对桩顶速度导纳和复动刚度的影响以及桩底土阻尼系数对桩顶速度导纳的影响,得到了各参数对桩纵向振动特性影响的规律。

关键词：现浇薄壁管桩动力响应解析解动刚度黏弹性地基