Inception Point and Air Concentration in Flows on Stepped Chutes Lined with Wedge-Shaped Concrete Blocks

Stepped channels lined with wedge-shaped concrete blocks are a promising solution to provide overtopping protection for embankment dams if the discharge capacity of existing spillways is not adequate. The paper addresses the characteristics of the two-phase transition and skimming flows in stepped channels lined with this type of block. An experimental setup was developed with two flumes designed with a relative scale of 1:2.5. Air concentration was measured with an optical probe in several cross sections of both flumes. The scale effects are analyzed. An expression for the location of the inception point is proposed. The vertical air concentration profiles and their longitudinal variation are studied, considering data and models proposed by other researchers. The establishment of the uniform flow regime is analyzed.     

基于逆向扩散和分层赋权的黄河堤防工程安全评价

针对黄河堤防工程安全的评价问题，首先基于后果逆向扩散法，构建了多层次半结构性的评价指标体系；基于分层赋权思路，对多层次的黄河堤防评价体系进行赋权。第1层（输入层）通过计算熵值权向量来确定指标的数学权向量，第2层（准则层）采用熵值权向量、等权重和经验赋权法3种权向量，利用模糊评价模型进行计算对比。选择黄河下游6个典型堤段进行实例计算，第2层采用了3种权重进行计算，第1种为熵值权向量（0.394,0.606）；第2种为等权重（0.500,0.500）；第3种为主观权重（0.600,0.400）。根据评价结果可知，综合评价值趋势和走向基本一致。工程因素子系统最优的是堤防1、3、4，非工程因素子系统最优的是堤防5、6，熵值权向量和等权重评价结果均为堤防5黄河北岸陶城铺段堤防最优；主观权重评价为堤防3黄河南岸东平湖段堤防最优。后果逆向扩散法可以快速全面的确定安全影响因子，分层赋权可以有效的克服人为权重的影响，从而保证获得客观合理的安全评价值，并能根据评价结果找到堤防工程安全相对薄弱的因素，为黄河堤防的安全运用提供数据支撑。     

Bearing capacity of geocell reinforcement in embankment engineering

Soil reinforcement using geocells has been utilized in many areas of geotechnical engineering. In this paper, a model and a simple bearing capacity calculation method for the geocell-supported embankment on the soft subgrade were proposed based on the study of the reinforcement functions of a geocell layer in a road embankment. The model and calculation procedures considered both the “vertical stress dispersion effect” and “membrane effect” of geocell reinforcement. They were verified by a laboratory experiment and compared with Koerner's method. The results indicated that the calculated results obtained from the present method were much closer to the experimental results than those from Koerner's method when the foundation settlement is large. The study also indicated that the installation of the geocell onto the crushed stone cushion significantly increased the bearing capacity of the soft subgrade.     

Improvement in seismic resistance using replacement/counterweight fill method for existing high embankments on inclined ground constructed with various embankment materials

The seismic resistance of existing embankments has become a significant issue as embankments fail frequently because of earthquakes. However, there are only a limited number of methods that can improve the seismicity of these existing embankments. In this study, a new improvement method, called the “replacement/counterweight fill method”, is proposed to improve seismic resistance. Two high embankments, of different materials, were constructed on an inclined ground and the replacement/counterweight fill method was applied to them. A seismic response analysis was performed to investigate the effectiveness of the improvement in seismicity. It was found that the replacement/counterweight fill method reduced the area of shear strain by more than 30%, suppressed the deformation of the embankments, and improved the seismic resistance. Along with the increase in the height of the counterweight fill, the effectiveness of this method increased and the seismic resistance was improved even further. Applying the replacement/counterweight fill method contributed to the improvement in seismic resistance by increasing the mean effective stress inside the embankments, decreasing the specific volume, decreasing the stress ratio (q/p’), and reducing the plastic deformation caused by the increase in the overconsolidation ratio due to unloading during the earthquake. Increasing the height of the counterweight fill was seen to be more effective for suppressing embankment deformation than increasing its width because increasing the height meant that the area of the reinforcement effect would be expanded.     

Experimental study on the mechanical behavior of shored mechanically stabilized earth walls for widening existing reinforced embankments

Shored mechanically stabilized earth (SMSE) walls have been increasingly applied in embankment widening projects because of their good mechanical performance, simple construction, low cost, and low site requirements. In this paper, several large-scale model tests were conducted to explore the mechanical behavior of the composite structures with different connection forms and relative densities, and the wall deformation, earth pressure, reinforcement strain, potential failure surface and the effects of the connection forms behind SMSE walls were also analyzed. The results show that the deformation of SMSE walls is mainly concentrated on the upper middle part, showing a “bulging” failure trend. The deformation of the SMSE walls can be effectively controlled by improving the relative density and adopting a “sandwich” connection behind the walls. The horizontal earth pressure against the SMSE wall facing shows a “K”-shaped distribution, and the vertical earth pressure is large in the upper part and small in the lower part. The potential failure surface originated at the junction of the old and new retaining walls, forming a “double-line” failure surface. For a “sandwich” connection, the failure surface moves forward and occurs where the primary and secondary reinforcements overlap, and this connection form is recommended in engineering practice.     

土石坝坝基接触段静压灌浆工艺研究

针对坝体(或防渗体)与坝基帷幕灌浆相互衔接及施工控制问题,本文通过工程实例对接触段进行静灌处理的试验研究,提出先行对坝体与坝基接触段进行独立静灌处理,以其作为坝基帷幕灌浆的“压浆板”;对接触段进行独立静灌时,需根据接触段埋深来确定灌浆压力.坝基岩体帷幕灌浆需在接触段静灌1.5～3 d后进行.     

防洪堤振动沉管灌注桩施工质量控制

振动沉管灌注桩是一种广泛运用的桩型。但其施工工艺较复杂，稍有疏忽就容易导致施工质量问题。如出现断桩、缩颈、管内进泥水、吊脚桩等。在施工中应对出现的问题及时进行分析，并提出相应的防范方法和质量控制措施，才能保证振动沉管灌注桩的施工质量。     

Displacements of column-supported embankments over soft clay after widening considering soil consolidation and column layout: Numerical analysis

The common challenges for constructing embankments on soft clay include low bearing capacity, large total and differential settlements, and slope instability. Different techniques have been adopted to improve soft clay, such as the use of foundation columns including stone columns, deep mixed columns, and vibro-concrete columns, etc. Due to increased traffic volume, column-supported embankments may be widened to accommodate the traffic capacity need. Adding a new embankment to an existing embankment generates additional stresses and deformations under not only the widened portion but also the existing embankment. Differential settlements between and within the existing embankment and the widened portion may cause pavement distresses. Limited research has been conducted so far to investigate widening of column-supported embankments. In this study, a two-dimensional finite difference numerical method was adopted. This numerical method was first verified against field data and then used for the analysis of widened column-supported embankments over soft clay. The modified Cam-Clay model was used to model the soil under the existing embankment and the widened portion. Mechanically and hydraulically coupled numerical models were created to consider the consolidation of the foundation soil under the existing embankment and the widened portion. Different layouts of foundation columns under the existing embankment and the widened portion were investigated. The numerical results presented in this paper include the vertical and horizontal displacements, the maximum settlements, the transverse gradient changes, and the stress concentration ratios, which depended on column spacing. The columns installed under the connection side slope were most effective in reducing the total and differential settlements, horizontal displacement, and transverse gradient change of the widened embankment.     

路基土的力学性状试验研究与分析

通过应力控制仪,对高含水率土进行路基填筑过程模拟试验,研究路基下土的力学性状变化规律。通过试验分析得出:路基填筑速度对第一填筑过程影响较小,在相同的时间内不同的路基填筑速度下,路基下土的变形、孔隙水压力增长以及应力路径的变化不明显;但由于在停载排水固结过程中,快速填筑造成土中孔隙水压力消散过慢,使得从第二阶段路基填筑开始,孔隙水压力较高并且消散过慢,使得路基下土的变形量过大,在较短时间内难以获得较高的固结度。因此,对于含水率较高、渗透系数较大的软土路基填筑来说,需要合理选择路基填筑速度,从而缩短路基下土的排水固结时间,保证工程安全迅速的进行。     

THE DEVELOPMENT OF A KNOWLEDGE-BASED EXPERT SYSTEM FOR UTILIZATION OF COAL COMBUSTION BY-PRODUCT IN HIGHWAY EMBANKMENT

The study in this paper introduces the development of a knowledge-based expert system that helps to determine the suitability of FGD by-product in embankment construction. The expert system shell Personal Consultant Plus was used for this purpose. The knowledge base in the Embankment Construction Expert System (ECES) consists of a root frame and four subframes, and accommodates the production rules obtained from laboratory tests as well as an extensive literature review. An external program to calculate the embankment settlement was integrated into the system. A case study is presented to demonstrate the use of ECES. This study provides the embankment designer with a useful tool for making decisions on FGD by-product application as an embankment material.