Pullout testing and Particle Image Velocimetry (PIV) analysis of geogrid reinforcement embedded in granular drainage layers

The paper investigates the feasibility of using fine-grained soil as backfill material of geosynthetic-reinforced walls and slopes, through a laboratory study on pullout behavior of geogrids in granular layers. A series of pullout tests was carried out on an HDPE uniaxial geogrid in thin sand and gravel layers that were embedded in clay specimens.Aside from different soil arrangements, the influences of moisture content and overburden pressure on the geogrid pullout behavior is assessed and discussed. The tests were carried out at four different gravimetric water contents (GWC) on the dry and wet sides of the clay optimum moisture content (OMC), and overburden pressure values within the range σ_v = 25–100 kPa. Particle Image Velocimetry (PIV) was used to capture digital images during the tests, which were processed to help with the interpretation and improved understanding of the soil-geogrid interactions at different GWC values. Results show that embedding geogrid reinforcement in layers of sand or gravel can significantly increase the pullout resistance in an otherwise moist clay backfill, and this improved pullout efficiency is greater at higher overburden pressures. The improvement in pullout capacity was observed in clay specimens compacted at both the dry and wet sides of the OMC.     

Finite element limit analysis of load-bearing performance of reinforced slopes using a non-associated flow rule

This paper presents a numerical study on the load-bearing performance of reinforced slopes under footing load using a finite element limit analysis (FELA) method where a non-associated flow rule is assumed in the analysis. The method was validated against results from full-scale model tests and a limit equilibrium (LE) analytical method. A series of parametric analyses was subsequently carried out to examine the influences that the soil dilation angle, footing location, and reinforcement design (i.e. length, tensile strength, and vertical spacing) could have on the load-bearing performance of reinforced slopes. Results indicate that dilation angle has a significant influence on the predicted magnitudes of bearing capacity, slope deformation, and mobilized reinforcement load. The predicted values of bearing capacity using the FELA are smaller than those from the Meyerhof's analytical method for unreinforced semi-infinite foundation, especially for larger friction angle values. Additionally, the ultimate bearing capacity of the slope and its corresponding horizontal deformation increase with the reinforcement tensile strength. Finally, the slip planes under the applied footing load are found to be y-shaped and primarily occur in the upper half of the slope.     

Required strength of geosynthetics in a reinforced slope with tensile strength cut-off subjected to seepage effects

The Mohr-Coulomb (M-C) yield criterion is found to overestimate the tensile strength of cohesive soils. By introducing the concept of tensile strength cut-off, the M-C criterion is modified to reduce or eliminate the tensile strength from the criterion. In this study, a new approach is proposed to investigate the stability of geosynthetic-reinforced slopes in cohesive soils subjected to seepage effects by means of the kinematic approach of limit analysis. The distribution of pore-water pressure is obtained using the numerical modeling software package, FLAC3D. A kinematically admissible failure mechanism is discretized to incorporate the results from the numerical simulation. The strength of geosynthetics required for maintaining the slope stability is evaluated from the work-energy balance equation. An optimization routine is used to seek out the maximum value among all possible results. Design charts providing the normalized required reinforcement under different parameters are plotted for a parametric study and convenient use in engineering. The obtained results show that less reinforcement is required in the presence of soil cohesion, and that the inclusion of the effect of tensile strength cut-off leads to a more conservative solution, which is more obvious in the presence of seepage effects.     

含软弱夹层岩体边坡的突变模式分析

针对含软弱夹层岩体边坡失稳问题,考虑软弱夹层的应变弱化特性,运用突变理论方法,建立燕尾型突变模型。基于建立的突变模式,对含一层软弱夹层的岩体边坡定量分析滑坡演化过程中的突跳特性;对于含多层软弱夹层的岩体边坡,通过对燕尾突变模型得到的平衡曲面方程进行分析可知,其势函数最多可有4个极值点,3个控制变量的不同取值使系统处于不同的分叉点集区域,其势函数极值点的个数不同,形式也不同,相应地,系统也呈现出不同的性质,于是根据势函数极值点个数的不同,定性分析随着控制参量的变化,边坡失稳中突跳的可能性。     

Quantification of Tafel coefficients according to passive/active state of steel carbonation‐induced corrosion in concrete

Statistical quantification of Tafel coefficients is investigated in this study for isolated steel rebar embedded in concrete. The survey is supported by a wide experimental campaign carried out earlier to characterize the passive and active states of carbonation‐induced corrosion of steel. Electrochemical measurements (polarization resistance, corrosion potential, Tafel coefficients) and gravimetric estimations of iron loss were regularly conducted over 417 days on 108 concrete specimens. The statistical analysis reveals that the mean value of Tafel coefficients, both cathodic and anodic, is higher under active corrosion, which seems to contradict the general tendency found for chloride‐induced corrosion, while their coefficient of variation is smaller. The statistical inference was based on the first step of distributions fitting the experimental data and then on the second step of goodness‐of‐fit tests. The most suitable of the distributions proposed were the Burr, Rayleigh, and Gamma distributions. A similar analysis was made for the corrosion potential and polarization resistance. The findings of the study will be valuable for probabilistic approaches to corrosion where probabilistic distributions are required.     

裂隙水压力作用下锚杆加固岩石边坡稳定性分析

裂隙中的渗流是岩石边坡失稳的重要因素之一。渗流对岩石裂隙存在静水压力和动水力,特别是暴雨会引起裂隙中的渗流压力迅速增大,造成滑坡等地质灾害。锚杆作为岩土工程的重要支护手段,被广泛应用于岩土加固工程中。基于岩土塑性极限平衡理论,从塑性功角度首先探讨了岩土边坡能量安全系数的取值,进而对岩体裂隙中存在静水压力和动水力情况下,锚杆加固岩体边坡的稳定性进行了研究,建立了相应的计算方法和公式。结合工程算例,重点分析了渗透压力作用对岩体边坡稳定性的影响以及锚杆的加固作用。分析表明,渗透压力对岩体边坡稳定性的影响是不可忽略的。     

自调整模糊PID策略的异步电机软启动器设计

通过分析常用软启动控制方式中存在的问题以及传统PID控制存在的不足,介绍了1种将异步电机转矩斜坡控制和模糊自调整PID结合的控制方式,控制策略根据误差大小在模糊控制和PID控制间切换,使系统具有更好的动、静态性能,并基于PIC单片机设计了控制器。利用MATLAB进行了仿真,仿真结果表明该软启动控制方式不仅可以很好地控制启动电流,同时可以有效地控制输出转矩来减小对系统的冲击,启动过程平缓。     

水电岩质边坡稳定性预测的支持向量机方法

以我国水电工程区典型岩质边坡为例,选择边坡岩体质量系数、结构面方位系数、结构面类型修正系数、坡高系数及施工方法修正系数6个边坡稳定性复合指标作为评价因子,建立了水电岩质边坡稳定性预测的支持向量机方法,并将其与传统统计判别方法（如距离判别方法和Bayes判别方法）进行了比较。分析结果表明,支持向量机方法的预测精度较高,且高于传统数理统计判别方法的预测精度。     

基于粗糙集理论的岩体边坡稳定性模糊综合评判

将粗糙集理论与模糊集理论相结合,应用于边坡稳定性问题中,利用粗糙集理论中的知识约简方法挖掘评价指标。把权重问题转成粗糙集理论中的属性重要性问题,建立了关于边坡稳定性分级评价的关系数据模型。评价结果表明:预测等级比较客观地反映了边坡稳定性的复杂状况,且该方法操作简单,结果可信。     

Electrokinetic geosynthetics in hydraulic applications

In use most geosynthetics play a passive role. New applications for geosynthetics have been identified if they can provide an active role, initiating biological, chemical or physical change to the matrix in which it is installed as well as providing the established functions. This can be achieved by combining the electrokinetic phenomena of electro-osmosis, electrophoresis and associated electrokinetic functions such as electrolysis with the traditional functions of geosynthetics of drainage, filtration, containment and reinforcement to form electokinetic geosynthetics (EKG). Electrokinetic geosynthetics can be made singly or from combinations of woven, non-woven, needle punched knitted, extruded or laminated materials and can be formed in any 2D or 3D shape.The majority of the uses of EKG are in hydraulic applications or applications with a significant hydraulic component. These can be grouped in separate engineering categories such as civil, mining, and water engineering. The concept of electrokinetic geosynthetics is described and details of applications and case studies are provided in the paper.