地下连续墙泥浆槽的稳定性分析

本文论述泥浆槽(Slurry Trenches)在短槽挖掘时的稳定性问题。文中叙述了四个泥浆槽挖掘的典型实例,其中包括两个塌槽的例子,并用土拱理论进行了分析。当前的某些关于槽稳定性分析的方法,在预测土压力方面显得较为保守。本文重点讨论了泥浆槽在附加荷载(如产生于邻接基础和邻近基础的作用)很大的情况下的稳定性问题。针对这种荷载条件,提出了一种设计步骤,通过考虑在挖掘处邻近土壤中由于附加荷载引起的应力的重分布,以及建筑结构中的应力重分布,可避免在设计中出现过分保守的现象。     

柔性防护系统中钢丝绳锚杆性能试验研究

 在柔性防护系统中,钢丝绳锚杆受到的荷载作用方向与锚杆轴向存在一定的角度,而目前在钢丝绳锚杆的设计中,仅仅以轴向抗拔力作为设计依据,这并不能反映钢丝绳锚杆的实际工作状态。为此设计钢丝绳锚杆随不同方位荷载作用的试验,考察钢丝绳锚杆的孔径和荷载作用方位对其性能的影响,结果表明：在斜向荷载作用下,增大锚杆孔径或增大斜向荷载与锚杆水平方向夹角,能有效提高锚杆的性能,降低其在荷载作用下的位移。此外,当钢丝绳锚杆的锚固力由其自身能够承受的极限荷载确定时,需要局部加强鸡心环弯折部分的抗折能力,提高锚杆的整体受力性能。最后,提出柔性防护系统中钢丝绳锚杆的设计依据,供工程应用时参考。     

岩锚界面及其端部附近应力场奇异行为的弹性力学分析

预应力锚索的使用效果很大程度取决于锚杆和岩体的结合程度，而锚杆和岩体的结合界面不可避免地要受界面缺陷的影响。在锚索的设计和计算过程中，现有文献对岩锚界面的应力分布的描述有一定的误差。以锚索拔出为对象建立理论分析模型，对岩锚界面端部的断裂力学行为进行了研究。结果表明，剪应力和径向应力在界面的两个端部(内端部和外端部)都有较强的应力集中现象，应力集中可能直接引起端部的破坏，而平均应力法则忽略了这一现象。所得研究结果可以直接应用于工程施工和监测中，同时，对边坡预应力锚固设计也具有实际指导意义。     

不同埋深扩体锚杆竖向拉拔破坏模式试验研究

通过室内模型试验,研究砂土中竖直埋设的扩体锚杆在不同埋深条件下的竖向拉拔破坏模式。试验结果表明,扩体锚杆经过竖向拉拔,由于深径比的不同而存在3种破坏模式。浅埋扩体锚杆破坏体近似呈倒钟形并延伸至砂层表面,破坏模式属整体剪切破坏,在工程设计中应避免采用。深埋扩体锚杆破坏体在砂层表面以下一定深度内闭合成为"椭球形",砂层表面在扩体锚杆破坏后未产生变形,破坏模式属局部剪切破坏。因此,在工程设计中扩体锚杆应采用深埋形式。在浅埋与深埋扩体锚杆之间还存在一种过渡型锚杆,其破坏体形态兼具深埋与浅埋扩体锚杆破坏体的特征,但破坏模式趋近于浅埋锚杆,因此将其归类为浅埋锚杆破坏模式中。     

Investigations on pullout behavior of geogrid-granular trench using CANAsand constitutive model

Experimental and numerical investigations have been carried out on behavior of pullout resistance of embedded circular plate with and without geogrid reinforcement layers in stabilized loose and dense sands using a granular trench.Different parameters have been considered,such as the number of geogrid layers,embedment depth ratio,relative density of soil and height ratio of granular trench.Results showed that,without granular trench,the single layer of geogrid was more effective in enhancing the pullout capacity compared to the multilayer of geogrid reinforcement.Also,increasing the soil density and embedment depth ratio led to an increase in the uplift capacity.When soil was improved with the granular trench,the uplift force significantly increased.The granular trench improved the uplift load in dense sand more,as compared to the same symmetrical plate embedded in loose sand.Although it was observed that,in geogrid-reinforced granular trench condition,the ultimate pullout resistance at failure increased as the number of geogrid layers increased up to the third layer,and the fifth layer had a negligible effect in comparison with the third layer of reinforcement.Finite element analyses with hardening soil model for sand and CANAsand constitutive model for granular trench were conducted to investigate the failure mechanism and the associated rupture surfaces utilized.The response of granular material in the proposed model is an elastoplastic constitutive model derived from the CANAsand model,which uses a non-associated flow rule along with the concept of the state boundary surface possessing a critical and a compact state.It was observed that the granular trench might change the failure mechanism from deep plate to shallow plate as the failure surface can extend to the ground surface.The ultimate uplift capacity of anchor and the variation of surface deformation indicated a close agreement between the experiment and numerical model.     

新型可视土工拉拔试验仪的研发与应用

研制了一台新型可视自动采集数据的土工拉拔试验装置,可用于多种土工材料和填料作用下的拉拔试验。该装置改进了加载系统和反力系统,实现了拉拔界面的可视与数据采集的自动化,并可量测土工材料不同嵌固长度处的位移,获取土工材料变形值,探索筋土作用过程中筋材受力机理及界面土体位移变化规律。使用新研制的试验装置开展了以砾类粗粒土为填料的格栅拉拔试验,结果表明:上覆荷载增大,土中格栅的应变变小,土体与格栅的界面摩擦和嵌固作用越显著;筋土界面处土体颗粒存在平移及转动两种运动模式,且界面处土体形成稳定的位移集中带。     

边坡工程中锚杆抗拔计算过程简化的研究

为节省边坡工程设计计算工作量,针对锚孔直径为90～150mm、锚筋直径为18～32mm、砂浆厚度为15～40mm、锚筋根数为1～3根的常规情况确定了可不做锚筋抗拔计算和可不做锚固体抗拔计算的锚杆范围。研究表明：当岩土层与砂浆极限粘结强度标准值小于460.8kPa时,锚杆设计可不做锚筋抗拔计算;当岩土层与砂浆极限粘结强度标准值大于1599.6kPa时,锚杆设计可不做锚固体抗拔计算。当岩土层与砂浆极限粘结强度标准值按相关规范取经验值时,锚固在土层与极软岩中的锚杆设计可不做锚筋抗拔计算,锚固在坚硬岩中的锚杆设计可不做锚固体抗拔计算。     

加筋土结构中加筋与土之间的摩擦性质研究

利用拉拔试验,对不同加筋材料,不同填料的加筋土的摩擦特性、抗拔位移的变化规律进行了研究,为今后的筋材拉拔试验及工程应用提供了参考.     

Investigation of masonry wall fixings subject to pullout load and torque

The experimental investigation into masonry wall fixings is carried out to develop an in-depth knowledge by investigating the factors which lead to a reduction in the effectiveness of scaffolding/brickwork anchors. Since the pullout test of fixings is currently not practical in construction site the research carried out to determine the potential use of torque test as an alternative. The information to assess how various parameters in anchor settings could affect the load bearing capacity of an individual anchor used in scaffolding/brickwork systems is presented in this paper. The correlation between the ultimate pullout load bearing capacity, the maximum torque values, the increments in anchor hole depths and diameters has also been determined. The method, which is described in this paper, can be used to estimate the in situ pullout strength of scaffolding/brickwork anchors by means of the calibration graph between torque and pullout load. The torque in practice can be applied by using a simple torque-meter like tool fits into the fixing and is clamped to it. Paper presents the results and draws conclusions.     

谈凯德MALL地下室抗浮设计

随着城市地下空间的开发利用,地下室抗浮成了工程师们不得不面对的问题。论文结合工程应用实例,对大兴凯德MALL商业建筑的地下室抗浮设计进行探讨,分析比较了抗浮锚杆与抗浮桩的优缺点。阐述了本工程中抗浮锚杆的设计思路和设计方法,并提出了抗浮锚杆设计中需要注意的问题。     

竖向浅埋锚锭板的侧向极限拉拔荷载

锚锭板是一种承受土体被动抗力的结构单元,常用于支挡结构、板桩锚固和管线转弯处的设计和施工。本文采用一种描述锚锭板极限拉拔荷载的统一表达式,根据砂土中锚锭板试验结果的统计分析、粘土中锚锭板有限单元上下限解结果和试验资料的整理,给出了锚锭板极限拉拔荷载统一表达式中相应参数的取值范围。该统一表达式可直接应用于锚锭板极限拉拔荷载的估算,也可进一步应用于其它地埋结构(如侧向受荷桩)的弹塑性分析。     

抗拔锚杆在某中心湖工程中的应用

设置抗拔锚杆是解决地下室、水池等结构抗浮问题的一个好途径。本文以某工程中心湖抗拔锚杆的设计为基础,分析了抗拔锚杆的设计思路,重点探讨了抗拔锚杆参数的设计、稳定性验算、群锚效应以及群锚效应对单根抗拔锚杆极限抗拔力的影响,为类似工程设计和施工提供了借鉴。     

The Mechanics of Inflatable Anchors in Cohesionless Soil

This paper describes an investigation into the performance and pullout capacity of an inflatable anchor system. The anchor system comprises a hydraulically inflated rubber membrane or packer that may be bored into place and then inflated to provide pullout resistance. A series of scaled physical model tests were used to study the anchor performance and pullout capacity. The model tests were done in a calibration chamber using cohesionless sand and anchors of various length, diameter, embedment depth and inflation pressure. The anchor behaviour during pullout is interpreted using finite element analysis that accounts for non-linear soil behaviour, inflation and subsequent deformation of the inflatable membrane, and anchor-soil interaction. The scaled model tests and interpretations assist with identifying the dominant mechanisms affecting the pullout capacity of inflatable anchor systems.     

土层扩大头锚杆设计理论研究

基于地层扩大锚杆的原位实测资料,作者研究分析了土层扩大锚杆的设计理论,包括其抗拔力、抗拔力与变位关系等问题,提出了土层扩大锚杆抗拔力计算公式以及抗拔力-变位计算方法。通过实例分析比较,验证了本方法的正确性。     

喷锚支护在市政沟槽跨越地下管线中的应用

介绍了成都三环路五段A标成黄路口市政深沟槽横穿已埋地下管线,采用窄槽边坡加固用喷锚网支护的设计与施工技术方法,通过沟槽边坡变形监测反馈于设计并指导施工获得了成功,为市政深沟槽跨越类似管线积累了丰富的设计与施工经验。     

中风化花岗岩中抗浮锚杆的试验研究

 抗浮锚杆已经在我国许多地区得到广泛应用。但是不同规范推荐采用的锚杆设计参数变化范围较大,并且未考虑不同地区岩石的差异性,实际应用中不利于设计参数的选取。在青岛大剧院工程场地上对设置测力元件的抗浮锚杆进行破坏性拉拔试验,重点测试锚杆杆体的轴力、杆体与注浆体之间的剪应力变化规律,结果显示内力沿锚杆长度不均匀分布并且超过一定长度后不再受力,进而确定出该地区中风化花岗岩中抗浮锚杆的极限抗拔力和有效的锚固段长度,为抗浮锚杆设计、施工提供了依据。     

Experimental study on the L-shaped anchorage capacity of the geogrid by the pullout test

The soil reinforcement by geosynthetics has been extensively applied in covers and liners of landfills. The stability of this structure is especially dependent on the effectiveness of the anchorages holding the geosynthetic sheets. The simple run-out and L-shaped anchorages are the two most commonly used approaches. For increasing the available knowledge of the anchorage system behavior, experimental studies have been conducted. This paper shows the results of the experimental analysis that are based on the results of large-scale pullout apparatus on geogrid embedded in simple run-out and L-shaped anchorage in two modes (fixed length and fixed space). The influence of different geometric parameters of the trench on the behavior of the geogrid is also examined. Based on the results, the values of pullout force were approximately 69% and 196% higher in the case of the fixed length mode and the fixed space mode, in the respective order, compared to the simple run-out anchorage. In the L-shaped anchorage, it is observed that for the initial length (L) constant, the mode is optimized with a small value of the geogrid rear heel length (B) and a greater value of the depth of the buried geogrid (D) when D+B is constant.     

Geotechnical design considerations for geomembrane lined slopes: Slope stability

The design of geomembrane lined containment systems is a multi-faceted problem requiring the combined talents of many diverse disciplines. One of these disciplines is that of geotechnical engineering, within which falls the topic of soil slope stability. Since the integrity of the liner is dependent on this support system its proper design is of obvious importance. This paper addresses various approaches of soil slope stability and also includes the stability of cover soils which are often placed above the geomembrane for its protection. Related topics of anchor trench design at the top of the slope and of post-construction stability problems will be treated in subsequent papers.     

预应力锚索作用机理研究中的几个问题

根据作者的相关研究成果,系统地论述了与预应力锚索作用机理相关的几个关键问题,即预应力锚索破裂面形状、锚固段极限侧阻力及极限抗拔力、锚固段侧阻力分布规律、锚固段荷载变位特性、群锚效应、长期荷载下预应力损失以及新型灌浆材料的研制、灌浆压力的影响等问题,并得出了相关的结论。上述成果对于认识预应力锚索作用机理,改进设计有一定的指导意义。     

Engineering geology investigations of a hazardous-waste landfill in West Central Illinois,USA

Faster-than-predicted pollutant migration at a state-licensed, hazardous-waste landfill was investigated 3 years after its operation was ceased by court order. At that time, the operator of the landfill discovered organic chemicals in a monitoring well during routine sampling, suggesting laekage from the trenches at a rate of 100 to 1000 times faster than predicted by the laboratory tests made for the initial landfill design. To determine the causes for this rapid pollutant migration, investigators studied site geology and stratigraphy, mine subsidence, hydrogeology, condition of waste containers, trench covers, and soil properties. Organic chemical probably leaked when meteoric waters drained freely through the trench covers, flushing liquid wastes from the burial trenches into the permeable, fracture ablation till. Interpretation of aerial photographs was used to find depressions and surface impediments in covers through which the drainage occurred. Pipe-type depressions in covers were probably caused by highly erodible (dispersive) soils. Surface impediments, such as roads and erosion-control dikes, caused runoff to pool over the trench covers. In an attempt to eliminate these problems, the following studies are proposed: geologic studies in exploration and design, field hydrogeologic tests, laboratory tests for highly erodible soils, and postclosure monitoring by photointerpretation and remote sensing.