土钉支护结构极限支护深度的研究

土钉墙支护软弱地基基坑,只能适用于一定的开挖深度,即土钉基坑支护结构具有极限开挖深度。为此,提出了土钉支护结构极限开挖深度的确定方法,以淤泥类地层基坑作为研究对象,研究了土钉支护结构的极限开挖深度问题,以及研究了土钉墙墙面坡度、地面超载、土层物理力学性指标以及土钉直径等变化时对极限开挖深度的影响。对于位于淤泥类、淤泥质类土层中的基坑,其极限开挖深度可分别取为5.0 m和6.0 m。     

土钉墙在超软地基基坑支护中的应用

在论述宁波市区软弱地基特征及基坑支护结构现状的基础上,分析了采用土钉墙支护结构支护深度6.0 ~7.0 m软弱基坑的可行性。在镇海炼化工程的超软弱地基中,用土钉墙来支护深度为6.0 m的基坑,并获得成功,开辟了用土钉墙支护宁波软弱基坑的先例。由于宁波软弱地基的特殊性,应对土钉墙实施过程中可能出现的问题进行预测和预防。详细地介绍了土钉墙设计施工的经验和教训,并提出了适用于宁波软土基坑的土钉墙基坑支护型式。由于土钉墙基坑支护结构的经济合理性,可以在宁波市区的基坑支护中推广应用。     

鞍山东方大厦深基坑土钉支护技术

结合鞍山东方大厦工程实例介绍了土钉支护技术的设计和应用。实践证明，土钉支护技术在粉质粘土和粉土以及砂质土层中具有性能可靠、施工简便和造价低廉等优点。     

上海地区饱和粉土层中土钉墙支护的工程实践

通过虹祺花苑复合式土钉墙工程实例,阐述饱和粉土层中的土钉墙支护计算原理及现场施工要点,并总结了技术要点及注意事项以资推广。     

土钉支护结构的极限分析方法

土钉支护结构一般均按极限状态进行设计,其中稳定性验算为设计之重点。根据土钉支护结构的特点,从分析土钉支护结构的破坏模式入手,利用土坡的极限破坏理论和结构体的塑性极限分析方法,研究了土钉支护结构旋转滑动破坏的可能性,并依此来分析土钉支护结构的稳定性。研究表明,对位于软弱地基中的土钉支护结构,土钉结构本身的极限破坏的可能性很大,在工程设计中宜采用钢管击入土钉,以增强其抗弯能力。     

深基坑土钉墙支护的优化设计及工程应用

土钉墙支护是用于基坑开挖和边坡稳定的一种新的挡土技术.由于具有经济、可靠且施工快速简便的优点,该技术已在我国得到迅速推广和应用.在探讨土钉墙加固机理及钉土相互作用的基础上,结合具体的深基坑工程项日,优化设计和计算了土钉支护的几个主要参数.最后采用弹塑性有限元方法分析土钉施作后其应力一应变状况及其位移特征.数值模拟分析表明:这一优化设计是合理和经济的.     

土钉支护技术的发展应用与研究

土钉支护技术是用于基坑开挖和边坡稳定的一种新的挡土技术,由于经济、可靠且施工快速简便,已在我国得到迅速推广和应用.但土钉技术应用还处于凭经验和工程类比并结合一定计算分析的阶段,在工作机理和设计方法上还有待深入研究和不断完善.文章从土钉支护的国内外应用情况、特点与应用范围、施工设计等几个方面进行综述,以便更好的推广和应用.     

基坑土钉墙支护施工工艺探究

土钉墙作为一种比较实用的原位岩土加固技术,近年来在深基坑支护工程中得到了广泛的应用。本文简要阐述了基坑土钉墙支护施工的主要步骤及相关技术,分析了深基坑土钉墙支护主要施工工艺。     

广州市荟雅苑基坑支护及事故处理

广州市荟雅苑的基坑支护除北边采用土钉墙和桩锚联合支护外,另外三边均做放坡处理,施工过程中,发生了护壁一处土体被水掏空、土钉钢筋出露,基坑被水掩没的事故,事故原因：（１）土钉支护在软弱地层中有局限性;（２）土钉支护与北边排水沟渠湘同时施工,产生安全隐患,（３）天降暴雨;（４）临临应急排水措施不当,事帮经紧急处理,测量证明土钉支护仍然是成功的,但也提醒人们在基坑支护施工中,必须加强动态管理,注意信息化施工,重视水对基坑稳定所构成的影响。     

土钉墙面层土压力的计算分析

在目前的土钉墙设计中,面层通常被当作构造处理而不参与计算,墙后的主动土压力全部由土钉承担。实际上,土钉墙面层承受一部分土（水）压力。文中把土钉墙面层看作是弹性地基上的有限长梁,基于试验,推导了成层地基上土钉墙面层在土钉拉力作用下的挠曲线、转角、弯矩和剪力方程,并与实测数据进行了比较分析,验证了模型的合理性,得到的解析解基本上可以反映土钉墙面层土压力的分布。在此基础上,探讨了不同土性土层中土钉墙面层土压力的分布。面层土压力在土层的分界面上,位移连续,土压力发生突变;软弱土层分布的面层土压力较硬土层为大;上软下硬型较上硬下软的土层分布更能使面层土压力得到充分发挥,同时计算了面层土压力换算成荷载与土钉拉力的比值,其值随着开挖深度的增加越来越大,面层对于土压力的作用随着深度的增加表现得愈加明显,并提出针对不同地区、不同深度和不同土性条件下应给出比值的建议值,以使土钉墙的设计更符合其真实的作用机制,得到的结论和上述比值的计算方法对于进一步研究土钉墙的作用机制及设计中如何充分发挥面层的作用等具有重要的理论意义和实际应用价值。     

离子土壤固化剂改性膨胀土的试验研究

利用离子土壤固化剂（ionic soil stabilizer,简称ISS）对河南安阳地区膨胀土进行化学改性试验研究,通过不同配比的自由膨胀率试验结果,结合施工成本,得出ISS溶液改良膨胀土的最优配合比为1:350。对ISS溶液最优配合比改性后土体进行收缩试验、膨胀性试验、固结快剪、高压固结及水浸泡试验。试验结果表明,改性土线缩率减小,膨胀性指标降低,抗剪强度增大,土体由亲水性变成憎水性,且能达到较好的水稳定性,即膨胀土经化学改性为非膨胀土。ISS改性膨胀土的机制可解释为,通过ISS溶液与土粒离子进行强烈的交换作用,打开土粒与水分子之间的“电化键”,降低土颗粒表面吸附水膜厚度,包裹在黏粒颗粒表面的疏水基团覆盖膜使土对水的敏感性减弱,从根本上减少了土体吸水性和膨胀性。     

侧向土体耦合作用对土层地震反应的影响

把侧向土体耦合作用简化为一个弹性系数为k的弹簧和一个阻尼系数为η的线性阻尼器并联作用，建立了考虑耦合作用静止边界－一维土层地震反应波动方程，并给出了其完全解析解，为进一步分析侧向土体耦合作用对土层地震反应的影响，土层密度统一取1900kg/m^3，针对不同的土层厚度：10，20，30米，不同的剪切模量：42．75MPa(剪切波速150m/s)，118．75MPa(剪切波速250m/s),232.75MPa(剪切波速350m/s),k,η分别取不同的数值，进行土层地震反应计算，计算结果表明，k,η对地震动位移峰值，速度峰值影响较小，k对地震动加速峰值影响较大，k减少加速度峰值增大，k增大加速度峰值减少，最大影响程度可达15％以上，η对地震动加速度峰值影响较大，η减少加速度峰值增大；η增大加速度峰值减小，最大影响程度可达25％以上。     

Laboratory tests on soil conditioning of clayey soil

Tunnelling in difficult and challenging conditions such as soft soils in urban areas is increasing. In this condition, it is important to minimise the possible negative effect of the tunnel excavation, such as settlement or, in the worst case, collapses. To achieve this result, earth pressure balance machines are commonly used. One of the key parameters that must be considered for an optimal management of the EPB-TBM excavation is soil conditioning since the excavated muck must properly transmit the pressure to the tunnel face. Soil conditioning is also necessary to reduce the effect of the problems, such as clogging in clay layers, that can occur during the excavation and that can affect the performance of the tools and of the entire tunnelling process. For this reason, in the last decade, much research has been carried out to understand how to deal with and reduce the effects of clogging and stickiness, using different conditioning additives. These studies have proposed several different test procedures to evaluate the effect of the conditioning on the adhesion of the soil on the metallic parts of the machines. The present research has been carried out with the aim of proposing a new approach and new devices to study clay conditioning with laboratory tests, and the results of many tests carried out with the proposed device are presented and discussed.     

Surface history of lunar soil and soil columns

Measurements of cosmic ray track densities are presented for soil samples from Apollo 15, 16 and 17. Median track densities are used to infer total effective exposure times within ~15 cm of the lunar surface. Minimum track densities are used to derive the time of the last impact-produced rearrangement of soil grains. For samples from near various craters ages are derived of 40 m.y. for St. George, 6 (±3) m.y. for S. Ray, 25–90 m.y. for Plum, and 20–35 m.y. for Shorty. The material of 15003. the Apollo 15 deep core at depths of 120–160 cm, is inferred to have been deposited at an average rate of ≥0.35 cm/m.y. The Apollo 16 core at 41–47 cm depths. 60007, appears to be well mixed and was covered up by deposition at 0.3 cm/m.y. for the next few m.y. after its deposition.     

月壤及模拟月壤微观结构的研究

为了对比研究月壤与模拟月壤的微观结构,介绍了月壤的形成作用过程和5种基本颗粒类型;通过真实月壤照片,对月壤微观结构进行了分析;利用火山灰为模拟月壤主体材料,对其成分进行了检测;对模拟月壤的火山灰颗粒进行了显微图像分析试验。结果表明,月壤存在胶结物微观颗粒,胶结物颗粒具有分支的组织形态和封闭的气泡,并且有金属铁珠存在;火山灰所含的主要成分及含量与月壤相似,经过粉碎的火山灰试样棱角较为明显,其纵横比峰值略小,稍显长条状,但与月壤比较相近,而复杂度因子则略有欠缺,说明颗粒还不够粗糙和多棱     

水泥基土壤固化剂固化土的物理化学作用

采用击实试验、液塑限联合测定界限含水率试验、蜡封法测定干密度试验、二氧化碳气量法、交换性钠离子百分比试验等方法,结合黏土矿物组成与结构特点,研究了水泥基土壤固化剂固化土的物理化学作用。试验结果表明：随着固化剂剂量的增加,混合料的最大干密度增大,最优含水率降低;固化土混合料经过养护后,塑性指数降低,干密度增大,碳酸盐含量增加,交换性钠离子百分比升高;黏土矿物在强碱性和钙离子作用下被激活,形成各种水化硅酸盐和铝酸盐。研究认为：在土-固化剂-水-气系统中通过液相和气相向固相的转变以及各类水化产物的填充、挤密、胶结等作用,混合料逐渐形成较致密的整体;离子交换反应对土体的加固作用在后期起负效应;铝硅酸盐黏土矿物在强碱性和钙离子存在条件下被分解,参与水化硅酸盐和铝酸盐的反应。     

Volume-based soil particle fractal relation with soil erodibility in a small watershed of purple soil

The particle size distribution in small watershed changes under different land uses and affects soil erodibility. The aims of this study were (1) to investigate the volume fractal dimension of particle size distribution under different land uses in a typical small watershed of purple soil, (2) to estimate soil erodibilities of various land uses utilizing the Erosion-Productivity Impact Calculator (EPIC) model and the nomogram (NOMO) model, and (3) to relate volume fractal dimension with the soil erodibility used in the Universal Soil Loss Equation (USLE) in purple soil areas. Laser diffractions and double-logarithmic model were used to measure and calculate volume fractal dimension values. The results show that soil volume fractal dimensions were well linearly fitted to the double-logarithmic model with high correlation coefficients of 0.902–0.936 under six land uses in the small watershed. The averaged volume fractal dimension values under different land uses, from high to low were in the order of Zea mays L, Ipomoea batatas, Citrus reticulata Blanco, Setaria viridis, Robinia pseudoacacia L, Pinus massoniana Lamb. The volume fractal dimension was positively correlated to clay particle fraction (R = 0.933). The average soil erodibility values under different land uses from high to low were in the order of Setaria viridis, Citrus reticulata Blanco, Pinus massoniana Lamb, Zea mays L, Ipomoea batatas, Robinia pseudoacacia L while average soil erodibilities from high to low values were in the order of Setaria viridis, Citrus reticulata Blanco, Zea mays L, Ipomoea batatas, Pinus massoniana Lamb, Robinia pseudoacacia L. The soil erodibilities calculated by the two models were similar, and positively correlated (R = 0.630–0.877). The volume fractal dimension values of six land uses were negatively correlated to both soil erodibility estimated by EPIC and by NOMO models. Moreover, the correlations of the volume fractal dimension values of Zea mays L, Ipomoea batatas and Citrus reticulata Blanco estimated by EPIC or NOMO were lower than those of Pinus massoniana Lamb, Robinia pseudoacacia L and Setaria viridis. Further research is needed to determine the influence of volume fractal dimension on the soil erodibility under different land use and managements.     

Tropical residual soil as compacted soil liners

A series of laboratory tests was conducted on a tropical residual soil, which is widespread and readily available over a considerable part of Peninsular Malaysia, to assess whether it could be compacted as hydraulic barriers in waste disposal landfills. Index properties, swelling potential, cation exchange capacity (CEC), compaction characteristics, and hydraulic conductivity of the soil indicate that it is inorganic, very plastic, inactive (activity <0.75), moderately expansive (modified free swell index is about 3.06), and of fair attenuation capacity (for inorganic contaminants). For hydraulic conductivity measurement, the soil was compacted in rigid-wall permeameter moulds at a variety of water contents and compactive efforts and then permeated with de-aired tap water. The results of hydraulic conductivity tests illustrate that hydraulic conductivity lower than 1×10^–7 cm/s can be achieved using a broad range of water contents and compactive efforts, including water contents dry of optimum. Its shrinkage and strength properties show that it has minimal potential to shrinkage and has adequate strength to support the overburden pressure imposes by the waste body. These findings suggest that the residual soil can be potentially utilized as compacted soil liner material.     

土壤酶对碘离子在土壤中吸附行为的影响

以批式试验法研究了微生物、葡萄糖氧化酶、脲酶、纤维素酶及其催化底物葡萄糖、尿素和纤维素对Ⅰ-在土壤中吸附的影响,结果表明微生物能显著提高Ⅰ-吸附量,但葡萄糖氧化酶、脲酶、纤维素酶及葡萄糖、尿素和纤维素对Ⅰ-吸附并无促进作用.葡萄糖氧化酶及葡萄糖含量在小于100 mg/L时对Ⅰ-吸附无影响,1000 mg/L时与Ⅰ-呈竞争吸附;脲酶及尿素随浓度增大,对Ⅰ-吸附的抑制作用变得明显;1～1000 mg/L范围内,纤维素酶和纤维素对Ⅰ-吸附没有影响;但葡萄糖氧化酶和葡萄糖生成的中间产物可促进土壤对Ⅰ-的吸附.平衡液中溶解性有机碳(DOC)含量随时间增加而逐渐降低,有机质浓度越大,降低趋势越明显.     

Simulation of liquefaction of unsaturated soil using critical state soil model

Several researchers have reported that the mean effective stress of unsaturated soils having a relatively high degree of saturation gradually decreases under fully undrained cyclic loading conditions, and such soils can be finally liquefied like saturated soils. This paper describes a series of simulations of fully undrained cyclic loading on unsaturated soils, conducted using an elastoplastic model for unsaturated soils. This model is a critical state soil model formulated using effective stress tensor for unsaturated soils, which incorporates the following concepts: (a) the volumetric movement of the state boundary surface containing the critical state line owing to the variation in the degree of saturation; (b) the soil water characteristic curve considering the effects of specific volume and hydraulic hysteresis; and (c) the subloading surface concept for considering the effect of density. Void air is assumed to be an ideal gas obeying Boyle's law. The proposed model is validated through comparisons with past results. The simulation results show that the proposed model properly describes the fully undrained cyclic behavior of unsaturated soils, such as liquefaction, compression, and an increase in the degree of saturation. Finally, the effects of the degree of saturation, void ratio, and confining pressure on the cyclic strength of unsaturated soils are described by the simulation results. The liquefaction resistance of unsaturated soils increases as the degree of saturation and the void ratio decrease, and as the confining pressure increases. Furthermore, the degree of saturation has a greater effect on the liquefaction resistance than the confining pressure and void ratio. Copyright © 2017 John Wiley & Sons, Ltd.