【作者】 朱正伟；

【导师】 刘东燕；

【作者基本信息】 重庆大学 ， 土木工程， 2011， 博士

【摘要】 不稳定边坡的危害几乎无处不在。据统计,近五年来我国共发生边坡失稳灾害17万余起,伤亡5000余人,直接经济损失近160亿元,而滑坡等地质灾害的成功预报仅2500多次,其比例为1.4%。分布式、实时、远程获知地质体内部力学信息,及时准确判断灾害前岩土体的异常状态,是有效监测边坡稳定的基本保证。地球物理方法、测斜仪技术、“3S”技术、时域反射技术、光时域反射技术、布里渊光时域反射技术、布里渊光时域分析技术等各有优点,但它们不能同时实现辅材价格低廉、分布式、实时、远程遥测、有较高的初始测量精度、以及判断滑坡运动方向的监测,而使得上述方法在边坡监测的应用受限。因此,为边坡位移监测提供新的监测方法非常重要和迫切。本文基于光纤传感原理和光时域反射技术,突破现有方法的局限,新设计了一种可同时实现上述指标的复合光纤装置,并系统研究了基于复合光纤装置的边坡监测方法、建立了复合光纤传感监测体系。取得的主要成果如下:①利用光纤弯曲时光线传输原理探讨了本文单模光纤不同纤芯直径和光透过率对应的曲率半径,建立了可以忽略光纤宏弯损耗临界曲率半径与波长的关系,确定了二次盘纤的最佳盘圈直径不宜小于200mm。②根据钢筋混凝土梁的空间架构理论,通过试验方案和试验结果改进、设计了成本低廉的复合光纤装置,对其进行了抗折、抗剪模型原理分析,并建立了抗折模型在线性和全截面断开阶段、以及单剪模型光纤伸长的理论公式。③开展了裸光纤抗拉、抗剪试验以及锯齿形套管光纤抗剪、光纤绕圆圈和光纤蝴蝶结等光纤装置弯曲损耗测定试验,提出了用蝴蝶结形光纤代替直光纤的设想,并通过以聚氯乙烯(PVC)普通塑料板和膨胀性聚酯乙烯(EPS)泡沫为基材、不同横截面尺寸的复合光纤装置的抗折试验,验证了设有蝴蝶结的复合光纤装置效果更好。④基于PVC塑料板和EPS泡沫基材、不同截面尺寸的复合光纤装置,以不同强度的水泥砂浆和砼为灌浆材料的灌浆体试件进行抗折试验、双剪试验和单剪试验,发现基于EPS基材的装置性能更佳,测得了不同装置的加载点竖向位移与光纤损耗、滑移的关系曲线,提出了试验中最优蝴蝶结宽度尺寸为30-32mm。⑤基于复合光纤装置开展了2次室内和1次现场模拟试验,结果表明该装置对剪切变形具有较高的初始测量精度,一定的测量行程和动态范围,可以判断荷载的运动方向;光纤的行程与模型的滑移量已呈明显的非线性关系,而且损耗具有更高的非线性关系。⑥对选定的工程应用场地按相关规范要求进行了现场直接剪切试验,对现场采集的岩样进行了天然单轴抗压和三轴试验,确定了现场土体的c=18.1kPa、Φ=21.28°,岩样的c=1.83MPa、Φ=37.5°,并结合破坏性监测边坡的实际确定了其综合内摩擦角Φ0=29.5°。⑦钻孔内灌浆材料是联系复合光纤装置与周边岩土体的中间纽带,是影响监测效果的关键要素之一。对特定的边坡,必须先尽可能多地确定岩土体的抗剪强度、摩擦角、压实系数、重度、含水率等参数,再选择匹配的钻孔尺寸、灌浆材料强度、复合光纤装置的基材形式及其尺寸和光纤保护方式,才能有效完成监测任务。⑧建立了可以实现分布式、实时、远程遥测的复合光纤装置法边坡监测体系,提出了该体系的技术指标和适用条件。将该体系运用于选定现场边坡的破坏性监测,结果验证了该体系的可行性,以及本文设计的复合光纤装置具有较高的初始测量精度、较大的运动行程和动态范围,可以判定滑坡运动方向。对选定的长期监测边坡,建立了边坡位移长期监测系统,并用测斜仪进行了对照监测。更多还原

【Abstract】 The danger of unstable slope is omnipresent. According to statistics of recent five years, over 170 thousand hazards out of slope unstability occurred in China’s mainland, leading to casualties of more than 5 thousand and direct economic loss of nearly RMB 16 billion yuan; while only over 2,500 of them were forecasted, accounting for only 1.4% of the total. Acquisition of mechanics information inside the geologic body in a distributed, real-time, and remote manner to conclude a prompt and accurate judgment of abnormal conditions of the rock and soil mass before hazards are the basic guarantee for effective landslide monitoring. In spite of their respective advantages, geophysical method, clinometers,“3S”technology, time domain reflectormetry technology (TDR), optic time domain reflectormetry technology (OTDR), Brillouin optical time domain reflectometry technology (BOTDR), and Brillouin optical time domain analysis technology (BOTDA), etc. are limitedly applied in landslide monitoring, for they fail to meet the requirements of low-cost auxiliary materials, distributed, real-time, and remote telemetry, high initial measurement accuracy, and judgment of landslide movement direction at the same time. Therefore, it is of utmost importance and urgency to explore a new method for slope stability monitoring.Based on optical fiber sensing theory and OTDR technology, and rid of constraints of existing methods, the author presents a combined optical fiber sensor simultaneously meeting the above requirements, conducts systematic researches on slope monitoring method based on the sensor, and establishes a combined optical fiber sensing & monitoring system. The main results are as follows:a. Curvature radiuses corresponding to different core diameter and transmissivity of the single mode fiber (SMF) are discussed based on the theory of ray transmission when the optical fiber is bended, a relation between the critical curvature radius and the wave length, of which the optical fiber microbending loss can be ignored, is established, and the optimal diameter for the optical fiber second coiling is determined to be not less than 200mm.b. Based on the spatial architecture theory of reinforced concrete beam, and according to the test program and results, the low-cost combined optical fiber sensor is improved and designed, whose bending and shearing resistance model principle analysis is conducted, finally contributing to the establishment of theoretical formulas of the bending resistance model at the linear and total cross-section disconnection phases as well as optical fiber stretching of the simple shear model.c. Pulling and shearing resistance tests of bare optical fibers, as well as determination tests on shearing resistance of indented cased optical fiber and bending losses of circle-type and optical fiber sensors with bowknot, are conducted, an assumption of replacing straight optical fiber with optical fiber with bowknot is promoted, and the better effect of the sensor is verified through bending test of the combined optical fiber sensors of different cross sectional dimensions with the base materials of ordinary polyvinyl chloride (PVC) plastic plate and expansile polyester ethylene (EPS) cystosepiment.d. Through bending, shearing, and simple shear tests on the combined optical fiber sensor of different cross sectional dimensions with the base materials of ordinary PVC plastic plate and EPS cystosepiment, where grout with cement plaster and concrete of different strength as the agents are employed, it is found that the sensor with EPS as the base material shows better performance; the vertical load point displacement, as well as relation curve between optical fiber loss and slide of different sensors, are measured, and the optimal bowknot width in the test is provided to be 30-32mm.e. Two indoor and one in-situ simulation tests are conducted targeting the combined optical fiber sensors. The results show that the sensor is of high initial measurement accuracy, maximum sliding distance and dynamic range on the shearing deformation, as well as judgment of the load movement direction; the optical fiber sliding distance and the model movment show significant nonlinear relation, and the loss shows more significant one.f. In-situ direct shear test of the selected project site is conducted as per requirements in relevant codes, accompanied by natural homotaxial compression resistance and triaxial test of the rock sample collected in-situ, whereby c andΦvalues of the in-situ soil mass and rock sample are determined, that is c=18.1kPa,Φ=21.28°representative the soil mass and c=1.83MPa,Φ=37.5°representative the rock sample. The comprehensive internal friction angle is also determined according to the actual condition of the field destructiveness monitoring slope, and its value isΦ0=29.5°.g. Grouting material inside the boreholes is the link between the combined optical fiber sensor and the surrounding rock or soil mass and is one of the key factors influencing the monitoring effect. For effective monitoring of specific slope, the parameters, including the shear strength, friction angle, compacting factor, unit weight, and moisture content, etc. of the rock and soil mass shall be determined first as much as possible, then followed by the selection of matched borehole size, grouting material strength, type and size of base material of the combined optical fiber sensor, and the protection mode of optical fiber.h. A landslide sensing & monitoring system based on the combined optical fiber sensor is established for distributed, real-time, and remote telemetry. The Specification and suitable condition were also introduced. The system was utilized to the field destructive slope monitoring. Results showed that the system is feasible, and the sensor is of high initial measurement accuracy, maximum sliding distance and dynamic range, as well as judgment of the load movement direction. A long-term slope stability field monitoring system based on the combined optical fiber sensor is established for the selected in-situ slope, where the clinometer is employed for contrast monitoring.更多还原