Modernized Vibratory Device for Deep Compaction of Sandy Soils

Deficiencies are noted for a vibratory device built by the All-Russian Scientific-Research Institute of Hydraulic and Sanitary Engineering for the deep compaction of a thick layer of sandy soil. A modernize vibratory device and comparative results of the experimental-production compaction of soil with the indicated devices are described.     

Estimating Relative Density of Sandy Soils

The applicability of three previous empirical correlations proposed for estimating relative density of sandy soils based on the SPT N-value, effective overburden stress and soil gradation characteristics was investigated in the present study by using a data base of relative density obtained from high quality undisturbed samples of fine to medium sand with F_c≦20%, D₅₀≦1.0 mm and D_max≦4.75 mm. All undisturbed samples were recovered by in-situ freezing method. The relative density estimated by Meyerhof's method (1957) was in the range of +15%~-45% of the measured values. Meyerhof's method (1957) was modified by Tokimatsu and Yoshimi (1983) by considering the effect of fines content on the SPT N-value. The relative density estimated by Tokimatsu and Yoshimi's method (1983) is in the range of +25%~-20% of the measured values. The underestimation of relative density of Meyerhof's method (1957) was modified. On the contrary, the overestimation of relative density is more significant than Meyerhof's method. The relative density estimated by the method proposed by Kokusho et al. (1983) is in the range of +20% to -35% of the measured values even for dense sand with a relative density larger than 60%. Meyerhof's method (1957) and the method proposed by Kokusho et al. (1983) have a common disadvantage that they will extremely underestimate the relative density of fine to medium sand for SPT N-value lower than about 8. The errors in estimation of relative density by these methods are large. A simple empirical correlation (Eq. (10)) was proposed in the present study to estimate the relative density of fine to medium sand based on the normalized SPT N-value, N₁. The relative density estimated by the proposed method is in the range of +15% to -30% of the measured values for N₁ in the range between 0 and 50. As a whole, the proposed method is less in errors for estimating relative density compared with those estimated by Meyerhof's method (1957) and the method proposed by Kokusho et al. (1983). Based on a data base of undisturbed samples with data of fines content obtained from the SPT spoon samples, the method proposed by the authors is again compared with the three previous methods. The relative density estimated by the proposed method based on the above data base is in the range of +15% to -10% of the measured values. Among four methods, as a whole, the proposed method shows the least errors in estimation of relative density. The proposed method was also modified (Eq. (16)) by taking into account of the effect of fines content of SPT samples. The relative density estimated by the modified method based on the fines content is almost in the range of +10% to -10% of the measured values. Two empirical correlations proposed in the present study are less in errors of estimating relative density compared with three previous methods. The range of relative density estimated by the proposed method is well consistent with the range of the measured values (40% to 90%). The empirical correlations proposed in the present study should be applied to fine to medium sand with F_c≦20%, D₅₀≦1.0 mm and D_max≦4.75 mm.     

砂土类地基中螺纹灌注桩竖向抗拔性能模型试验研究

依据模型试验相似理论,采用砂土模拟现场地基土层,通过室内模型试验得出:螺纹桩抗拔承载力是等直径直线型桩的1.34～1.92倍;同直径螺纹桩从螺纹间距100 mm加密到50 mm时抗拔承载力约为1.1倍。对等直径螺纹间距为100 mm、50 mm螺纹桩的轴力、侧摩阻力、桩周土压力进行对比分析,得出50 mm螺纹间距桩的抗拔承载能力的优越性。最后,依据试验参数提出合理螺纹间距设置公式,并推导出螺纹灌注桩基于砂土层的抗拔承载力公式。     

A Neuro-Fuzzy Logic for ATIS Stand-Alone Control Systems: Structure, Calibration, and Analyses

Abstract:   An Advanced Traveler Information System (ATIS) stand-alone operation scheme is formulated as a bi-level optimization problem. The scheme logic attempts to optimize the network overall travel time by adjusting the path proportions while guessing the signal phase split decisions. An approximate simulation-based optimization algorithm is devised as an example of the logic operating this scheme. The logic is then replicated by a fuzzy-logic control system. Neural nets are utilized to develop the knowledge base of the fuzzy system and to calibrate the fuzzy set parameters. The neural nets utilize data replicates generated by the approximate simulation-based optimization algorithm. The calibration and effectiveness results of the fuzzy control system are presented.     

水质模糊综合评价模型的建立与应用

根据模糊数学的原理，建立了地表水环境质量模糊综合评价模型，利用该模型对江西省的乐安河进行了水质评价，介绍了模型应用于水质评价中的计算过程，证明该河流的主要污染物为有机物，为污染控制提供了科学依据。     

Evaluation of the Dynamic Stability of Unsaturated Sandy Soils

The potential for use of an energy criterion previously introduced by the authors - the amount of energy dissipated by the soil per unit volume, as determined from an experimental strain diagram in total stresses - is investigated for evaluation of the dynamic stability of unsaturated sands. A scheme is proposed for experimental evaluation of the dynamic instability of a soil mass on the basis of the energy approach.     

循环荷载作用下饱和砂土的液化破坏

本文探讨了循环荷载作用下饱和砂土的极限平衡条件和液化破坏过程,给出了一个可用于饱和砂层地震稳定性分析的广义库伦公式。提出了一种方法:根据一个砂土液化试验记录的分析,给出饱和砂土的动力有效应力抗剪强度。为了工程应用的目的,建议把循环荷载作用下饱和砂土的破坏过程分为两个阶段,并把这两个阶段的起点作为饱和砂土的破坏准则。此外,也给出了饱和砂土液化破坏时破坏面上循环剪应力与循环荷载次数间的一般关系。     

石灰土强度与最优施工含水率关系研究

为了研究石灰改良膨胀土得最优施工含水率与石灰土相关强度的关系,文中以某边坡膨胀土为研究对象,进行了直剪试验、CBR及无侧限抗压强度等相关强度的试验研究,研究了最优施工含水率、掺灰率与膨胀土强度的关系,试验结果表明石灰土的直剪、CBR值及无侧限抗压强度曲线与施工含水率的关系曲线类似于击实曲线,且最优施工含水率随着掺灰率的增大而线性增大,强度与掺灰率的关系曲线与击实曲线类似,存在最优掺灰率,这些结果的得出对现行石灰土路基施工控制参数的确定方法改进具有一定的指导作用。     

含水率对郴州煤系土邓肯-张模型参数的影响

以郴州地区典型煤系土为研究对象,制备了不同含水率的重塑煤系土试样进行三轴固结排水试验,计算得到了各含水率煤系土邓肯-张模型参数并分析了含水率对模型参数的影响。结果表明:试样均呈鼓胀破坏特征,无明显的峰值;试验初期,煤系土试样处于线弹性变形阶段,当应变达到3%~5%时,逐渐进入弹塑性变形阶段;含水率对煤系土邓肯-张模型各参数影响程度不同,其中c值受含水率影响显著,参数c、、Ei、K、Kb随含水率的增加而减小,参数m、n、Rf随含水率的增加而增大;试样含水率在15%-25%时,破坏比Rf值均在0.9以上,但并未发生剪切破坏,表明煤系土应力-应变关系呈硬化型特性。     

基于标贯的国内外砂土液化判别方法

砂土液化判别是场地岩土地震稳定性评价的重要组成部分。国内通常采用规范推荐的基于标准贯入试验的砂土液化判别方法;而欧美、非洲及东南亚大多采用Seed简化法。在对我国《建筑抗震设计规范》(GB 50011—2010)中砂土液化判别方法与国外修正的Seed简化法的原理、方法及参数进行分析的基础上,将这2种方法进行比较,进而讨论了2种方法判别结果的差异。对比分析发现:相对于规范法,Seed简化法对于表层地基土偏于安全;但对深层地基土判别,规范法更为保守。     

沙壤土直剪试验的离散元数值模拟

基于离散元法,用不同尺寸的球体代表土壤颗粒,添加平行粘连模型模拟颗粒间的相互作用,对沙土直剪试验进行数值研究;为了校正和验证数值模型和输入参数,将剪切结果与标准直剪试验所得的抗剪强度进行对比,结论表明离散元数值模型的仿真结果和试验能够很好吻合;还详细讨论了剪切过程中土壤颗粒的运动情况,以及剪切盒形状、剪切速度、法向载荷对剪切曲线和颗粒料床孔隙率的影响。     

级配缺失对砂土剪切力学特性的影响

为研究级配缺失对砂土剪切力学特性的影响,结合室内直剪试验和离散元模拟对其进行了分析。室内试验结果表明,颗粒级配的缺失会导致砂土抗剪强度出现不同程度的下降,其中缺失粗颗粒的土样强度下降程度最大。通过建立与室内试验结果相匹配的PFC2D数值模型,很好的弥补了室内试验在细观参数监测上的不足,主要对级配缺失后土样的力链形态、剪胀特性及孔隙率演变等情况进行了讨论,结果表明,在剪切过程中粗颗粒对土样的应力传递和局部应变起到主要的作用,而细颗粒的填充有助于提高砂土力链网络的稳定性。     

Response of Unsaturated Sandy Soils Under Constant Shear Stress Drained Condition

In order to understand the mechanism and conditions leading to failure of sandy slopes due to the infiltration of rainwater, constant shear stress drained triaxial tests were conducted on three sets of soil samples-normal sand, gravelly sand and silty sand-taken from natural slopes where large-scale landslides have occurred in the past. Water was infiltrated from the bottom of an initially unsaturated soil specimen under constant shear stress drained condition until failure occurred. Such a loading pattern simulated the stress path followed by a soil element on a potential failure plane on a slope subjected to rainwater infiltration. The effects of various parameters reflecting the initial condition, such as relative density, principal stress ratio, degree of saturation and infiltration rate, on the development of deformation during the infiltration process were investigated. The test results confirmed that the development of pore water pressure within the soil is the main reason for the failure of slopes during heavy rainfall. The results obtained can serve as guidelines in developing warning systems against impending rainfall-induced slope failures.     

一种新的结构性土损伤模型

从结构性土体的基本性质出发,放弃了将结构性土体视为结构性土和重塑土的复合体的传统思路,而将结构性土看作是重塑土富含有土体结构,损伤直接导致土体结构的丧失,与重塑土部分无关。在此基础上,提出了一种适用于结构性土的新型损伤模型,该模型是修正剑桥模型的推广,当结构性的参数取为0时,该模型退化为修正剑桥模型。结合显式有限差分程序FLAC3D的主要计算思路,使用VC++.NET平台开发了该模型的FLAC3D接口程序,并编译成动态链接库DLL文件。并与结构性黏土不同围压下的三轴排水剪切试验进行对比,表明所建立的模型可以较好的描述结构性土的变形特性。     

饮用水生物稳定性的评价体系

AOC和温度对饮用水中微生物的生长繁殖具有重要影响。通过试验的方法对不同AOC含量、不同温度条件下静止存放的饮用水(自来水和瓶装水)的生物稳定性进行了研究，建立了AOC-TDWMS评价体系，弥补了用AOC单项指标评价饮用水生物稳定性的不足，更科学、可靠，且更具适用性。     

砂卵石地层桩锚支护结构现场实测与研究

对成都市某楼的深基坑桩锚支护结构进行现场监测,研究分析了砂卵石地层条件下深基坑开挖过程中土压力、桩身内力、锚杆拉力的分布和变化规律。研究表明:桩侧静止土压力约占理论静止土压力的1/6～1/10,开挖过程对冠梁与底板附近的土压力影响较小;桩体钢筋应力仅发挥了钢筋设计强度的16.8%;预应力锚杆只出现了前期预应力损失等,为今后成都地区的桩锚支护结构的研究提供了较好的参考价值。     

砂土液化预测的人工神经网络模型

本文根据人工神经网络的一典型模型-反向传播模型,以及地震荷载下的各项土的物理-力学参数,建立了土液化类型的神经网络数学模型。研究表明,人工神经网络方法性能良好,可望成为砂土液化预测的有效手段。     

Fuzzy Logic Model for Determining Minimum Bid Markup

Abstract:   Many construction markets exhibit severe price competition where contractors have to cut their bids to compete, giving priority to winning enough contracts to sustain normal operation, and it is common to see a winning bid close to the expected project cost. While cutting bids not only gives up profits but also undoubtedly increases the risk of making a loss, the behavior of contractors in intense competition is difficult to explain by existing models. A fuzzy-logic-based model is proposed for determining the minimum bid markup with assessments of chance of winning and loss risk. The model incorporates the position of a decision maker in the fuzzy rules according to his/her attitude toward risk and degree of need for the job. Two illustrative examples, one hypothetical and one real, are provided, in which differences in priorities are simulated by four sets of fuzzy rules for a comparison of the effects. The results show that the model is sensitive enough to differentiate a decision maker's position on bidding and suggest bid-cutting limits consistently, thereby remedying some shortcomings of existing models.     

砂卵石地层基坑开挖土体本构模型辨识研究

随着基坑工程分布的广泛性,施工过程中会遇到各种复杂的地质条件,其中砂卵石就是一种广泛分布的特殊地层。为了解砂卵石地层中基坑开挖的变形特征,探究砂卵石土体的本构模型,该文首先详细介绍了Harding-Soil模型的理论基础,然后采用均匀设计(UD)与有限元(FEM)计算相结合的方法对本构模型的未知参数进行辨识,均匀设计可以减少计算量并保证试验方案的科学性、准确性,最后结合长沙地区某在建砂卵石地铁深基坑工程进行实例验证Harding-Soil模型描述砂卵石地层开挖行为的适用性。有限元计算结果表明Harding-Soil模型能较准确的描述砂卵石基坑的变形特征,且利用均匀设计(UD)与有限元(FEM)计算相结合的方法对本构模型的未知参数进行辨识是可行的。