土层锚杆、土钉受力分析及土钉加固土体作用

随着工程建设的推动出现一些土钉支护设计软件,为设计者节省很多时间。但对于淤泥土层和二种土层CФ值相差较大时软件计算结果失真度较大。分析原因,认为主要是土钉、土锚的力学模型建立方面值得进一步研究。本文对土锚、土钉的力学模型在前人基础上提出初浅分析,同时对土钉加固土体作用也进行了探讨。     

碳纤维塑料筋锚杆界面粘结强度试验研究

研制开发了适用于碳纤维塑料(CFRP)筋锚杆的夹片式锚具.在此基础上,通过48个试件的拉拔试验,在国内首次对碳纤维塑料筋锚杆与多种粘结介质之间的界面粘结强度进行了研究.研究表明:碳纤维塑料筋锚杆具有较高的界面粘结强度;碳纤维塑料筋的直径对锚杆粘结强度的影响不明显;当滑移值为0.3~0.4 mm时,碳纤维塑料筋锚杆的粘结应力达到最大,相比之下,钢绞线锚杆的粘结应力最大值发生在滑移值为20 mm左右时.此研究结论为碳纤维塑料筋锚杆在岩土锚固工程中的应用提供了依据和参考.     

锚–土界面剪切蠕变试验及其经验模型研究

为了研究土层灌浆锚杆锚–土界面剪切蠕变特性,提出了一种新颖的锚–土界面蠕变试验方法,并设计制作了相应的试验装置。通过分级加载蠕变试验,得到了锚–土界面剪切蠕变曲线,采用"陈氏加载法"将分级加载曲线转化为分别加载曲线。分析试验结果发现,锚–土界面衰减蠕变阶段的位移–应力关系采用幂函数、位移–时间关系采用改进双曲线函数拟合效果最好。由此建立了适合锚–土界面衰减蠕变阶段的经验蠕变模型,该模型可更好地拟合并预测衰减蠕变曲线。同时,在该衰减蠕变模型基础上,引入Kachanov损伤因子考虑加速蠕变损伤,建立了适合锚–土界面加速蠕变阶段的加速(损伤)蠕变模型。     

锚杆布置对岩石锚固体承载力影响的数值试验

在探讨岩石锚固机理和计算模型基础上,提出了锚固岩石的承载力的三维数值试验方法,采用速度边界控制加载,进行了不同密度、不同数量、不同布置方向的锚杆的条件下岩石承载力的数值试验,并得出了承载力变化规律。     

风积沙中扩体锚杆承载特性试验研究

针对我国西北地区昼夜温差大且多为软弱砂层地质导致锚杆承载能力衰退现象,研究风积沙中扩体锚杆承载特性以及冻融循环的影响。基于12个模型试验组得到6种锚固端头类型在不同冻融循环周期下的锚杆极限承载力、荷载-位移关系、土层内应力以及破坏形式的变化。结果表明：扩体锚杆在风积沙中处于高围压(深埋)情况下,极限承载力有更大的增长潜力。锚固端头体积的增大能有效提高扩体锚杆在风积沙中的极限承载力,且存在锚固端头最优设计比。随着冻融循环周期增长,加速了荷载-位移曲线拐点和极限承载力的出现。土层内应力发生突变,衰减增快,破坏时变形增大。     

预应力锚杆拉拔力学特性及临界锚固长度研究

相较于非预应力锚杆而言,预应力锚杆在受到拉拔作用后呈现出特殊的支护力学特性。为深入探明预应力锚杆的这一特点,采用足尺室内实验和理论分析的方法研究预应力锚杆在受载后的力学响应情况,掌握预应力锚杆的支护力学特点及其机制,进一步丰富和扩展了预应力锚杆的主动支护理论,并从锚固系统支护效果最优化的角度出发,基于二次开发手段提出一种预应力树脂锚杆临界锚固长度的数值计算方法。结果表明：(1)预应力施加后锚杆的荷载–位移曲线形态发生了明显变化,在前期支护刚度增加,同时出现荷载突变点,且随着预应力施加量值的增加,突变点处荷载从17.3 kN增加至54.6 kN;(2)预应力锚杆在受载后呈现出“先刚后强”的支护力学特性,在支护前期能够迅速达到较大的承载力,有效提高锚杆控制围岩变形的能力;(3)建立的数值分析模型很好地再现了锚固系统在受到拉拔荷载时的力学响应情况,基于该模型分析了不同锚固长度条件下锚固系统的承载能力峰值,确定了该实验条件下树脂锚杆的临界锚固长度为44 cm。相关研究成果对认识预应力锚固系统的支护力学特性和参数设计具有指导意义。     

土层锚杆拉拔界面松动破坏分析

根据界面黏滑本构模型假定和剪切位移法基本原理,推导了土层锚杆拉拔临界松动荷载理论公式和锚杆拉拔荷载与松动长度内在关系表达式。界面黏滑特性致使锚杆剪应力重新分配,引起荷载进一步往里端传递,加剧里端锚固体损伤劣化。依据界面抗剪强度与残余强度之间大小关系将土层锚杆拉拔松动破坏类型划分为渐进式和突发式两种形式,并给出了破坏类型定量判别标准及其所对应的锚杆拉拔极限荷载理论解。最后,结合已有的锚杆拉拔试验资料,通过计算对比分析,验证了方法的可行性。     

锚-土界面力学分析及拉拔试验研究

基于弹塑性状态下锚固体与周围土体之间的变形协调,建立围压条件下土层锚杆荷载传递机理模型,推导外荷载与锚固土层塑性半径及锚杆极限拉拔力之间的理论计算式。通过拉拔试验,分析锚固体所处应力状态、粗颗粒含量及土样含水率对土层锚杆极限拉拔力的影响。结果表明：在一定范围内改善土层锚杆所处的应力状态,有利于防止土层锚杆瞬间从土层中拔出;土样粗颗粒含量为60%时,试样较为密实,拉拔过程中土颗粒间的应力分布相对均匀,锚杆的承载力相对较大;在相同围压条件下,土层锚杆的极限拉拔力随着含水量的增加呈现出先增大后减少的趋势;试样极限拉拔力理论计算值与室内试验结果吻合较好,验证了理论模型的有效性。     

拉力型土工布加筋复合锚杆锚固界面应力传递试验分析

土工布复合锚杆是一种可应用于松散地层锚固工程的新型锚锭结构。以某滑坡治理工程为平台,开展了拉力型土工布加筋复合锚杆锚固体与破碎岩土体界面间应力传递规律的实测研究。现场试验结果表明,土工布的加筋鼓胀作用调整了锚固体与破碎岩土体接触界面的应力分布,土工布加筋复合锚杆锚固段近端存在稍长的应力协调缓冲段,随着荷载增大,黏结应力峰值向锚固段深部转移的现象不明显;实测破碎岩土体中拉力型土工布加筋复合锚杆主要抗力区域分布在3.0~13.0 m之间,即有效锚固体长度以不超过15 m为宜,过长的锚固长度对提高锚杆抗拔力意义不大;在松散破碎岩土体中应用土工布加筋复合锚杆技术能起到提高锚固力与节约成本的双重作用。     

土工格栅 黏性土界面特性的拉拔试验分析

筋土界面特性是影响加筋土结构性能的重要因素之一,利用中型拉拔模型试验分析了界面正应力和黏性土含水量对格栅黏性土界面相互作用特性的影响,试验结果表明黏性土含水量对格栅极限抗拔力、界面黏聚力和摩擦系数影响明显。不同界面正应力下格栅极限抗拔力在含水量较小时差别显著,随着黏性土含水量增加,格栅极限抗拔力和界面摩擦系数呈现减少趋势,而筋土界面间黏聚力先增大后减小,且当含水量达到塑限含水量时,三者均趋于稳定。格栅抗拔力位移曲线均经历线性和非线性增加以及拉拔极限阶段,并随含水量增加,抗拔力位移曲线由线性增长向极限状态发展的中间阶段逐渐缩短。在拉拔最大载荷下持续一段时间后卸载,发现格栅的横肋应变有增大的趋势,而纵肋应变呈现减小的趋势。     

填土中锚固体–土接触面剪切特性研究

自行研发了一种锚固体–土接触面剪切装置,该装置能够充分考虑锚杆的实际形状特征和剪切方向,并具有能够保证剪切过程中接触面面积不变等特点,并为研究锚杆锚固体–土剪切特性提供一种新方法。利用该装置,共完成了35个不同条件下的锚固体–土剪切试验,深入研究了法向压力、土样压实度和土样含水率等因素对锚固体–土接触面剪切特性的影响。研究结果表明:压实度相同情况下,土体含水率w大小,对锚杆抗拔力取值具有重要的影响,越接近最优含水率,越有利于接触面剪应力的发挥;土体压实度对接触面剪应力的影响十分明显,压实度越大,接触面剪切参数越大,但始终小于土体的剪切参数。     

大型三维土与结构接触面试验机的研制与应用

已有的土与结构接触面试验研究集中在二维加载条件下的接触面力学特性,而实际工程中接触面的受载条件大多为三维的,即接触面的剪应力方向在剪切过程中是不断变化的。针对粗粒土与较粗糙结构面的大型三维接触面的试验手段目前较为缺乏,自主设计研制了一台用于土与结构接触面特性试测的大型三维加载试验机。该试验机具有高加载能力,提供大试样截面,能够进行较大粒径土体与较粗糙接触面在较大应力变化范围内的单调和循环加载试验;采用液压伺服控制系统,法向可提供应力、常位移、常刚度等边界条件;切向两个方向均可按应力或位移控制,能够实现接触面上单向往返、十字、圆形、椭圆等不同的任意设定的加载路径。试验表明,该试验机能够很好地再现粗粒土与结构接触面在上述的复杂加载条件下的力学响应,为接触面的三维力学特性的研究提供了基础。     

Unsaturated soil-geotextile interface behavior

The behavior of mechanically stabilized earth (MSE) structures under seasonal climatic variations, i.e. wetting and drying, is not well understood. Stability and serviceability of MSE walls and embankments can significantly depend on the soil-reinforcement (e.g., geosynthetics) interface shearing behavior in unsaturated conditions. This is especially true for reinforced soil slopes and embankments that have significant fines contents. This paper presents results of a laboratory study on the mechanical behavior of unsaturated soil-geotextile interfaces using a specially modified direct shear apparatus. Several suction-controlled laboratory tests were conducted to investigate the effect of soil suction on the soil-geotextile interface. Results of the study indicate that the peak shear strength of the soil-geotextile interface increases nonlinearly with the soil suction. On the other hand, while inconclusive, the effect of suction on the post-peak shear strength of the interface was negligible in some cases. An elastoplastic constitutive model was used to simulate the laboratory results. This study demonstrates that the constitutive model is capable of capturing the mechanical behavior of the unsaturated soil-geotextile interface subjected to constant suction. Both shearing and volume change responses were reasonably simulated by the model.     

从本构模型研究到试验和光纤监测技术研发

为研究土的基本性质,验证土的本构关系,监测建筑岩土结构,进行了以下5方面的研究:①土的次弹性本构模型和弹黏塑模型;②一维应变黏性土沉降计算;③一维应变下黏性土非线性蠕变和压缩;④双室三轴装置、真三轴加载装置、非饱和土-结构界面直剪装置和土钉抗拔箱等试验技术的研发;⑤岩土结构光纤监测技术研发.研究结果表明:①次弹型模型较...     

Investigation of effects of temperature cycles on soil-concrete interface behavior using direct shear tests

The intermittent operation of the ground source heat pump connected to thermo-active geo-structures (e.g. energy piles) results in cyclic thermal loading on the soil-structure interface. To investigate the effects of cyclic thermal loading on soil-structure interface properties, a conventional direct shear device was modified by replacing the bottom shear box with a concrete plate (with smooth and rough surfaces) that has embedded aluminum tubes to heat and cool the interface. A series of tests were performed with interface temperatures of 4.5, 22.5, and 42.5 °C, respectively. The constant normal stresses of the direct shear tests were 27.6, 41.4, and 100 kPa. The tests were conducted both under cooling and heating conditions with thermal cycle numbers of 0.5 and 10.5. The tests were conducted at a shearing rate of 3 mm/min. The effects of water content changes on the shear strength of soil-concrete interface was also investigated by performing tests with soil water content ranging from 15% to 19%. The responses of soil-concrete interface subjected to temperature change and cycles and different water contents are presented in this paper.     

一种土与结构接触面模型的建立及其应用

在进行了一系列接触面单剪试验的基础上，分析和探讨了接触面剪切破坏和变形的机理，提出了错动位移、剪切位移以及接触面“剪切错动带”的概念。在此基础上，建立了一种新的接触面模型，并给出了确定模型参数的方法。有限元计算结果表明，该模型能够较合理地反映接触面上剪应力的传递及相对位移的发展，它比常规接触面模型有较明显的改进。     

Numerical simulation of the flow in the interface of a composite bottom liner

This paper focuses on the quantification of flow rates at interfaces in composite liners using numerical simulations that explicitly take into account of the non-uniformity of the interface thickness. A new methodology is presented to obtain the accurate spatial distribution of interfaces in laboratory tests, in a 1-m-diameter device where flow was previously measured. The method is based on a multi-molding protocol, adopted from studies on fracture aperture measurements in rocks. The interface aperture data is been used to numerically simulate the flow in interfaces. Comparison of the numerical and experimental results shows that the simulated flow in the interface of a composite liner has similar hydrodynamic features to those observed. The analysis of fluid displacement in the interface shows that a flow channelling phenomena, caused by the existence of connected apertures linking the defect in the geomembrane to the boundary, is a key mechanism for leakage in composite liners consisting of a geomembrane and a compacted clay liner. The influence of the defect location vis-à-vis distribution of interface apertures on the flow rate is demonstrated.     

新拌混凝土成分快速测定新技术原理及应用

基于体积平衡原理和密度测定法,分析了日本圆井公司单位水量测定仪的工作原理,探讨了新拌混凝土成分快速测定技术的关键问题.利用该技术对某在建长江公路大桥施工现场新拌混凝土组成成分进行了监控,并结合检测结果对现场施工工艺进行了调整.结果表明:该方法具有快速简便、准确度高、与传统28 d强度评定方法相关性好等特点,对加强混凝土质量预控具有重要意义.     

An integrated laboratory experiment of realistic diagenesis,perforation and sand production using a large artificial sandstone specimen

Sand production is,a challenging issue in petroleum industry,mainly associated with weak unconsolidated formations.A novel testing procedure and a new apparatus were developed to conduct an integrated experiment of diagenesis,perforation and sand production on a single large cylindrical artificial sandstone specimen,where solid and fluid pressures can be independently controlled such that realistic reservoir historical conditions can be well simulated in the laboratory.Fluid injection can be performed in both radial and vertical directions,where both single-and two-phase flows can be implemented for study of sand production behaviors at different reservoir’s maturity stages.The equipment consists of an intensive instrumentation system to monitor pressures,displacements and material states continuously.The produced sand particles were filtered and monitored in real-time for the study of time-dependent phenomena.The experimental results showed similar patterns to that observed in the field and provided valuable insight for the development of prediction methods for sand production of similar materials.