This paper aims to study the effects of the non-stationary soil property on the horizontal bearing capacity of three-dimensional monopile in spatially variable soils. The soil undrained shear strength is assumed to obey lognormal distribution and is simulated as non-stationary random fields. The mean value of the undrained shear strength linearly increases with depth, while the standard deviation keeps constant. The random finite-element method is applied to analyze the reliability of the bearing capacity. The influence of the correlations and non-stationary property on the mean and coefficient of variation of the bearing capacity are discussed. It is found that the correlation distance has no obvious effect on the bearing capacity and the bearing capacity increases with the increase of non-stationary coefficient. The results can guide the reliability-based design of horizontally loaded piles embedded in spatially variable soil.

通过建立考虑土与结构相互作用的海上风机支撑结构三维有限元分析模型,结合泥面处固定连接和不同的地基土性质,研究了风浪荷载联合作用下海上风机TMD的减振效果,分析了土与结构相互作用对TMD减振效果的影响.结果表明,若将泥面处简化为固定连接,会严重低估风机结构的动力响应;土与结构相互作用会放大风机结构的动力响应,且降低TMD的减振效果,与泥面处固定连接相比控制率降低约4％;在其他条件都相同的前提下,风机结构的动力响应随地基土弹性模量的增大而减小,且土体工程性质越好,TMD的减振效果越好.

现行相关规范采用的立方体劈裂抗拉强度计算公式未考虑试件形状和加载条件的影响.分别建立立方体试件劈裂抗拉试验的三维弹性模型和考虑材料塑性损伤属性的数值模型,模拟研究了立方体试件的应力状态,结合Griffith强度准则分析了木质垫条宽度和材料弹塑性的影响.结果表明,随着垫条宽度的增大,试件劈裂面上的等效应力最大值逐渐减小,起裂点的位置逐渐向试件端面中心移动.考虑材料的塑性损伤属性后,试件的初始起裂点位置与材料强度无关,且皆不位于试件端面中心.由于试件初始起裂点对应的竖向荷载并不是试件破坏时的峰值荷载,所以采用基于三维弹性数值模拟结果确定试件劈裂抗拉强度是不准确的,而采用规范公式计算出的劈裂抗拉强度值则偏小.建议垫条宽度宜在25mm左右.

The soil parameters may obey different types of distribution. However, the lognormal distribution is generally chosen in the probability analysis of pile foundations. The undrained strength of soil is taken as the random variable, and it is assumed to obey Lognormal distribution, Beta distribution and Gamma distribution, respectively. Then the bearing behavior of single pile foundation under vertical and horizontal loads is simulated by stochastic finite element method, in which the different coefficient of variation and correlation distance are considered. The mean value and standard deviation of bearing capacity of single pile are analyzed. The results show that the average vertical bearing capacity of single pile is not affected by the distribution of soil strength. The average horizontal bearing capacity of single pile is the largest when the lognormal distribution is adopted, while the bearing capacity is the smallest when random field obeys the Beta distribution. The standard deviation of bearing capacity obtained by Beta distribution under vertical and horizontal loads is the largest. It is recommended to use Beta distribution to determine the bearing capacity of single pile foundation when the spatial distribution of soil strength is unknown.

单桩基础是海上风电的主要基础形式,其主要受水平荷载作用.为了提高海上风机单桩基础的水平承载力,针对3种不同的地基条件,通过数值方法研究了水平荷载作用下单桩的承载特性,进而提出了提高单桩水平承载力的加固措施,并进行了加固效果分析.结果表明,单桩水平承载力随着桩径的增大而呈线性增大;由于桩端的嵌固作用,单桩水平承载力随桩长的增大而先增大后趋于不变;与均质地基相比,上差下好地基中的单桩水平承载力显著下降,下降幅度达30％以上.可采用水泥搅拌法对桩周浅层土体进行加固,加固后的单桩水平承载力可提高1倍以上.实际工程中,可结合桩径和浅层地基土性质,采取水泥搅拌法加固以提高单桩基础的水平承载力.

为了完善现有轻质土用发泡剂性能评价体系,开展了9种自制发泡剂和3种市售发泡剂的发泡试验,基于试验数据讨论了外在条件对发泡剂评价结果的影响,对比分析了1h消泡占比、1h泌水量、1h沉降距和气泡群密度等评价指标的优缺点.研究表明:在相同的发泡方式、稀释倍数、水温和室温条件下测定的发泡剂性能指标才具有可比性;1h泌水量指标难以准确评价发泡剂的稳泡能力和综合性能;《气泡混合轻质土填筑工程技术规程》(CJJ/T 177-2012)建议的方法难以准确测得1h沉降距,且其对于气泡群密度的规定略显严格;提出了综合指标P=n(1-m)来评价发泡剂的综合性能,其中n为发泡剂的发泡倍数,m为发泡剂的1h消泡占比,P值越大,发泡剂的综合性能越好.

Spatial variability is the inherent nature of soil, which needs to be considered when calculating the bearing capacity of piles. Different coefficients of variation and correlation distance will be considered. Based on the numerical method, the existing simulation method of random field will be used to generate soil parameters so as to study the effect of spatial variability of soil strength on the horizontal bearing capacity of a single pile. The results show that after considering the spatial variability of soil strength, the average value of the single pile horizontal bearing capacity is significantly less than that obtained by the deterministic analysis, and the single pile foundation designed by the standard method is still possible to fail; the correlation distance has no significant effect on the average value of the single pile horizontal bearing capacity, but the standard deviation of bearing capacity increases with the increase of the correlation distance; with the increase of the coefficient of variation, the average value of the horizontal bearing capacity of the pile foundation decreases, while the standard deviation of the bearing capacity increases. The distribution law of horizontal bearing capacity of the pile foundation considering the spatial variability can fit log-normal distribution. According to this law, the failure probability of the pile foundation under any load can be obtained.

制备了不同密度的气泡混合轻质土试样,研究了硫酸钠环境下气泡混合轻质土的抗干湿循环性能,重点分析了气泡混合轻质土的体积、密度和强度随浸泡时间和干湿循环次数的变化规律.试验结果表明,气泡混合轻质土在硫酸钠溶液和干湿循环共同作用下,硫酸钠晶体的析出和溶解以及钙矾石等物质所致的试样膨胀与表层剥落,均会对试样的体积产生显著的影响,较高的初始强度和孔隙率对于试样体积稳定性是有利的;试样在膨胀、剥落前的密度随干湿循环次数变化曲线相互平行乃至重合,试样在膨胀、剥落后的密度变化曲线相互交错;硫酸钠侵蚀试样生成钙矾石等物质,致使试样在干湿循环作用下更易产生裂缝,选用较高初始强度和较低水泥用量的试样可有效控制这一影响.

采用有限元软件ABAQUS建立三维土质边坡模型,基于强度折减法研究了边坡稳定性与坡转角的关系,以及坡转角对边坡稳定性与坡高、坡角和边坡长度关系的影响.结果表明,边坡安全系数随着坡转角的增大会逐渐降低;坡转角对边坡安全系数与坡高、坡角关系的影响较小,但对于边坡安全系数与边坡长度关系的影响较大,且当坡角较大时,坡转角对安全系数与边坡长度的关系的影响就较小;当坡角较小时,坡转角对安全系数与边坡长度的关系的影响就较大.

为了研究主应力轴连续旋转下软黏土的轴向纯压循环变形特性,基于空心圆柱扭剪仪(HCA)模拟了交通等类似荷载作用下的圆形应力路径,开展了不同围压和不同循环应力比(CSR)下循环次数达5 000次的主应力轴连续旋转试验.研究了饱和软黏土试样的应变累积、应力-应变滞回曲线、模量软化等特性,得到了不同循环应力比和不同围压条件下主应力轴连续旋转引起的变形规律.试验结果表明:随着循环次数的不断增加,土体的应力-应变滞回曲线有明显的差异,土体剪切模量不断降低.相同有效围压时,随着循环应力比的增大,土体的软化指数逐渐减小;相同循环应力比时,随着有效围压的增大,试样受到的侧向约束增大,土体的软化指数减小.

In the strict framework of limit analysis, an analytical approach is derived to obtain the upper bound solutions for three-dimensional inhomogeneous slopes in clays under undrained conditions. Undrained strength profiles increasing linearly with depth below the crest of the slope and below the outline surface of the slope are assumed representative of cut slopes and natural slopes, respectively. Stability charts are produced for the cut slopes and the natural slopes under both static and pseudostatic seismic loading conditions. The presented charts are convenient to assess the preliminary and short-term stability for 3D slopes in practical applications, such as rapid excavation or buildup of embankments and slopes subjected to earthquakes. Compared with the available results from the finite element limit analysis method, a better estimate of the slope safety is obtained from the analytical approach.

The dynamic response of a double infinite beam system connected by a viscoelastic foundation under the harmonic line load is studied. The double infinite beam system consists of two identical and parallel beams, and the two beams are infinite elastic homogeneous and isotropic. A viscoelastic layer connects the two beams continuously. To decouple the two coupled equations governing the response of the double infinite beam system, a variable substitution method is introduced. The frequency domain solutions of the decoupled equations are obtained by using Fourier transforms as well as Laplace transforms successively. The time domain solution in the generalized integral form are then obtained by employing the corresponding inverse transforms, i.e. Fourier transform and inverse Laplace transform. The solution is verified by numerical examples, and the effects of parameters on the response are also investigated.

Geotechnical materials are products of the nature, and their properties have great spatial variability. Based on the existing research results of soil random field simulation methods, considering the variability coefficients of soil strength parameters and correlation distance, the influences of soil spatial variability on the vertical bearing capacity of the pile foundation under vertical loading is investigated by the numerical method. The analysis results show that the median value of the bearing capacity of the pile foundation is smaller than that obtained by deterministic analysis, considering the spatial variability of soil. With the increase of coefficient of variation and the correlation distance, the uncertainty of the bearing capacity of the pile foundation becomes more and more. It is necessary to pay attention to the large variability of the soil parameters in practical engineering. The distribution law of the vertical bearing capacity of the pile foundation considering the spatial variability of soil strength parameters can be described by lognormal distribution curves. When the number of samples is enough, the totality can be inferred from the samples, and the failure probability of the pile foundation under any load can be obtained accordingly.

Abstract The prevailing problems in countryside, such as excessive use of chemical fertilizer and large amounts of livestock manure, need to be addressed urgently. In order to optimize the amount of applied organic fertilizer, the experiment was carried out in the planting-breeding combined circular agricultural area of Huang-Huai plain and the effects of pig manure fertilizer amounts on lettuces yields, quality and nitrate/phosphorus utilization efficiency were investigated. It was found that the replacement of chemical fertilizer with organic fertilizer had no significant effects on the N and P content of lettuces when treated with the same amounts of fertilizer. However, it could improve its yield, quality, and nitrogen/phosphorus utilization efficiency. When the ratio of organic fertilizer replacement was 25%∼75%, the nitrate and nitrite content of lettuces were reduced by 19.41% and 73.33% compared with the chemical fertilizer treatment. The nitrogen and phosphorus utilization efficiency in the 75% organic fertilizer replacement were highest, which were 30.4%/44.9% higher than that of chemical fertilizer respectively. Above all, the 75% organic fertilizer with 25% fertilizer group had the best effect on the yield of lettuces, improving the quality and utilization efficiency of nitrogen and phosphorus fertilizer. The results could provide an important scientific basis for determination of regional vegetable planting fertilizer and reduce the non-point source pollution risk.

It is important to be fully aware of the dynamic characteristics of saturated soft clays under complex loading conditions in practice. In this paper, a series of undrained tests for soft clay consolidated with different initial major principal stress direction ξ were conducted by a hollow cylinder apparatus (HCA). The clay samples were subjected to pure principal stress rotation as the magnitudes of the mean total stress p, intermediate principal stress coefficient b, and deviator stress q were all maintained constant. The influences of intermediate principal stress coefficient and initial major principal stress direction on the variation of strain components, generation of pore water pressure, cyclic degradation and non-coaxiality were investigated. The experimental observations indicated that the strain components of specimen were affected by both intermediate principal stress coefficient and initial major principal stress direction. The generation of the pore water pressure was significantly influenced by intermediate principal stress coefficient. However, the generation of pore water pressure was merely influenced by initial major principal stress direction when b = 0.5. It was also noted that the torsional stress–strain relationships were affected by the number of cycles, and the effect of intermediate principal stress coefficient and initial major principal stress direction on the torsional stress–strain loops were also significant. Stiffness degradation occur under pure principal stress rotation. Anisotropic behavior resulting from the process of inclined consolidation have considerable effects on the strain components and non-coaxial behavior of soft clay.

Hexavalent chromium (Cr6+)-contaminated soil samples were obtained from an electroplating workshop in Jingjiang, China. Then, the Cr6+-contaminated soil was processed using reduction and stabilization methods. Six reducing agents with different remediation abilities with respect to Cr6+ contamination (iron, SSL, FeSO4, Na2HSO3, Na2S2O3, and Na2S) were tested. The most efficient reducing stabilizing agent was FeSO4; which efficiency varied with the pH, with the optimum pH being neutral or near neutral. Lastly, the effects of acidified ferrous sulfate as a reducing agent, cement as a curing agent, and the combined use of dyeing were tested. Increases in the cement content and curing age led to a marked improvement in the curing effect on the Cr6+-contaminated soil.

Soft silty soils are widespread on floodplains and have a high natural water content, void ratio, weak permeability (10-10 cm/s), high strength, and low compressive engineering characteristics. Therefore, taking necessary action in areas where these soils are present is vital because they pose tremendous risks to the reliability of engineering. In this paper, the intensity variation rule of cement pile mixing in soft soil on the Wicheng Road, in the city of Wuxi, China, was studied under various unconfirmed compression strength tests, and with different stabilizer mixing agents and ages. For convenience to application to solidified soil engineering, we also confirmed a 28 day predictive model for the strength of solidified soil when different quantities were added, by date fitting using MATLAB. Our experimental results provide a reference for design of soft soil foundations, and show that cement content exerts a large influence on the strength of soft silt soil. The strength of a solidified soil increases linearly as cement content increases. Under conditions where there is a fixed amount of cement, incorporation of fly ash, lime, triethanolamine, sodium chloride, and sand, have different raising effects on the curing strength of silt soil. Indeed, it is important that these additives are mixed in optimal dosages, as too much or too little can augment the impact strength of a stabilized soil.

In consequence of froth breaking, there is a caved problem about air-foam treated lightweight soil after casting indoor and in-site. To analyze and solve the problem, a series of samples preparation experiments on sand were conducted on air-foam treated lightweight soil with three specific densities under different conditions, i.e., temperature, humidity and sand mixing or not. Meanwhile, the height and strength of samples were measured. Based on the thermodynamics theory, the effects of three factors on the preparation and strength of the samples were analyzed using experimental data. The results show that temperature difference is the decisive factor affecting the shrinkage and expansion of air-foam treated lightweight soil. The temperature difference impact greatly in sample of high bubble content. Humidity and sand mixing barely affect sample preparation while the mold unloading time of samples will be extended and the integrity of samples will be affected when ambient humidity becomes higher. Early strength of samples is influenced by temperature and temperature difference. temperature difference mainly affects the density of samples, and the temperature mainly affects the rate of hydration reaction of cement. The results of this study provide reference for the preparation and construction time of air-foam treated lightweight soil.

In view of the effect of freeze-thaw cycles on air-foam treated lightweight soil applied in cold areas,its volume,density and pore structure are studied in laboratory under freeze-thaw cycles based on 0.6 g/cm3samples. The results show that the rate of volume change of air-foam treated lightweight soil is not exceeding 1.5% under freeze-thaw cycles. The original water content has great effects on the change of the density of air-foam treated lightweight soil under freeze-thaw cycles.When the original water content is low,its density increases with cycle times going up and ends up with a stable value. The rule is opposite when the original water content is high. As cycle times increase,the superficial structure of air-foam treated lightweight soil is broken to some extent,resulting in that the pores inside gets amplified,and the surface starts peeling off.

Based on the application background of the suction caisson foundation in bridge engineering, a numerical simulation method is used to investigate the bearing performance of the combined suction caisson foundation,and the number and spacings of caissons are considered. The effort is focused on the difference of bearing performance between the combined foundation and the single foundation, and on the contributions of connecting roofs to the bearing capacity of foundation.The analysis results show that the load?displacement curves of the combined caisson foundation are the same as those of the single caisson foundation. Similar to the pile group effect,the vertical bearing capacity of the caisson cannot be fully utilized in the combined foundation. Due to the contribution of the connecting roof between caissons, the vertical bearing capacity of the combined foundation will be greater than the sum of the corresponding numbers of the single suction foundation under a large caisson spacing, and it increases with the increasing caisson spacing. The lateral bearing capacity of the combined foundation is greater than the sum of the corresponding numbers of single suction foundation,and the contribution of connection roof can be neglected.