Fiber Bragg grating-based performance monitoring of a slope model subjected to seepage

Hong-Hu Zhu1, Bin Shi1, Jun-Fan Yan1, Jie Zhang2,

Cheng-Cheng Zhang1 and Bao-Jun Wang1

1 School of Earth Sciences and Engineering, Nanjing University, Nanjing 210046, People’s Republic of China

2 Department of Geotechnical Engineering, Tongji University, Shanghai 200092, People’s Republic of China

Smart Mater. Struct. 23 (2014) 095027 (12pp)


In the past few years, fiber optic sensing technologies have played an increasingly important role in the health monitoring of civil infrastructures. These innovative sensing technologies have recently been successfully applied to the performance monitoring of a series of geotechnical structures. Fiber optic sensors have shown many unique advantages in comparison with conventional sensors, including immunity to electrical noise, higher precision and improved durability and embedding capabilities; fiber optic sensors are also smaller in size and lighter in weight. In order to explore the mechanism of seepage-induced slope instability, a small-scale 1 g model test of the soil slope has been performed in the laboratory. During the model’s construction, specially fabricated sensing fibers containing nine fiber Bragg grating (FBG) strain sensors connected in a series were horizontally and vertically embedded into the soil mass. The surcharge load was applied on the slope crest, and the groundwater level inside of the slope was subsequently varied using two water chambers installed besides the slope model. The fiber optic sensing data of the vertical and horizontal strains within the slope model were automatically recorded by an FBG interrogator and a computer during the test. The test results are presented and interpreted in detail. It is found that the gradually accumulated deformation of the slope model subjected to seepage can be accurately captured by the quasi-distributed FBG strain sensors. The test results also demonstrate that the slope stability is significantly affected by ground water seepage, which fits well with the results that were calculated using finite element and limit equilibrium methods. The relationship between the strain measurements and the safety factors is further analyzed, together with a discussion on the residual strains. The performance evaluation of a soil slope using fiber optic strain sensors is proved to be a potentially effective approach.

Keywords: fiber optic sensor, fiber Bragg grating (FBG), slope stability, geotechnical monitoring, model test, soil strain measurement

1. Introduction

Seepage-induced slope failure is a frequently encountered geo-environmental hazard for mountainous areas. According to the literature, almost 90% of slope instability issues have a close relationship with groundwater activities [1]. There are two main aspects regarding these influences. First, the physical and chemical effects of flowing ground water on soil and rocks result in significant strength reduction of the slope slip surface. Second, the pore water pressure and seepage force acting on the slope mass substantially affects the slope stability condition. In recent years, large numbers of reservoirs and dams have been built in developing countries. The construction and operation of these reservoirs and dams have led to a variation of localized groundwater levels, which is considered

a triggering factor for slope failures along the reservoir banks [2–5]. In particular, the frequency of landslides occurring during water level drawdowns is found to be higher than when water levels are rising. However, there are many uncertainties in the existing long-term field monitoring data, which cannot fully support the above conclusions [6]. The mechanism of reservoir-induced slope failure is still not yet well understood...

2. Working principle of FBG sensing technology

2.1. FBG sensing technology

2.2. Temperature compensation

3. Model test of a soil slope

3.1. Test chamber and model materials

3.2. Model construction

3.3. Instrumentation

4. Design of the test conditions

4.1. Test procedure

4.2. Numerical simulation of water seepage

4.3. Slope stability analysis

5. Test results and analysis

6. Conclusions


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