Research On The Monitoring Of Expensive Soil’s Fissures Development Process Based On DFOS Technology

Expansive soil is a kind of special soil that is extremely sensitive to the warm and humidity of environment, with the ability of contraction, forming fissures and super-consolidation. It is widely distributed in our country and is the typical soil which harms the engineering safety. The main problems of highway engineering construction and slope project in expansive soil area are related closely with the fissures development. In that context, the development and evolution mechanism is significant to solve expensive soil engineering problems. However, we cannot observe the development of the inner fissures and strain of the soil in the water-loss shrinking process directly because of the restriction of tests technology, which influence mastering the development mechanism deeply.This paper applies the latest distributed optical fiber sensing technology (DFOS) to monitor and analyze the fissures and deformation of expansive soil due to dehydration. Around this issue, a series of research is conducted and the results are as follows:1. According to the mechanism and characteristics of expansive soil’s fissures development, the paper points out the weakness of the traditional monitoring techniques and analyzes the principle, characteristics and application of distributed optical fiber sensing technology. Meanwhile, the feasibility of applying distributed optical fiber sensor to the monitoring of expensive soil’s fissures development is discussed. 2. The spatial resolution, reproducibility and other indicators of the DSTS and NBX-6050A systems are tested. In the meanwhile, the strengths of these test technology above are analyzed and compared with BOTDR and FBG technology in theoretic ways and the subsequent experimental ways.3. Sensing coefficient of the new type Corning SMF-28e+single-mode fiber-optic sensor was standardized, Based on the research theme, three types of optical fibers with different diameter and surface material, including the new variable-diameter strain sensing cable、screw thread jacket sensing cable and a new FBG string with nylon-jacket are developed.4. One-dimension distributed optical fiber sensing model is used to measure the deformation and fissures during the expansive soil’s water-loss shrinking process. Results show that the distributed optical fiber sensing technology can precisely detect and locate the feature of unusual soil strain, according to which, newly generated fissures can be predicted.5. A two-dimension test model of expensive soil’s fissures development is designed. The result shows that:the two-dimension DFOS net can measure the dynamic strain distribution development process in expensive soil, as well as identify the fissures development. So the characters of the unusual strain areas can be detected.6. Through the above researches, we can locate and forecast the fissures development during the expansive soil’s water-loss shrinking process by using the sensing cable and FBG, coupled with high-spatial resolution DFOS technology.