Design Of FBG Detection System For Seasonal Frozen Subgrade's Strain

With the rapid development of the times, the transportation has become the focus that each country wants to develop. Especially the ambitious expansion of roads, bridges, tunnels, etc., transportation network dotted the landscape,promoted the development of social economy greatly. Both the frozen area and non-frozen area have been covered by the traffic network. According related data,the frozen area almost occupies half of the world's total land area. Affected by the bad climatic conditions, the construction and maintenance of transport infrastructure in frozen regions face a severe test. And the distribution of transportation network in seasonal frozen regions is more widely than in permafrost regions. As a kind of concealed project, the measurement of physical and mechanical properties of the subgrade has been a problem, so it is the safety assessment of the roads. And this work is important to the roads condition's evaluation and transportation safety. Take the subgrade's strains as the test object,and choose the Fiber Bragg Grating(FBG) as method, this paper tends to explore the adaptability of FBG on the detection of this particular medium's strain of seasonal frozen subgrade.This article presents the current status of the application of FBG testing technology, the detection technology for frozen soil subgrade's strain, the FBG sensing properties and the demodulation technique. Based on the relevant characteristics of the test object, the package and laying method for FBG are designed. The main works are shown as follows:(1) The embedded-beam method which is based on the FBG testing techniques is proposed. Two kinds of sensors' packaging and layout methods are introduced taking account of the difference of the test objects, namely the shallow-setting semi-flexible probe for short distance and the deep-setting semi-rigid probe for long distance.(2) Two sites of seasonally frozen subgrade are chosen and a one year observation is conducted.(3) Testing results showed that FBG has a high survival rate within the temperature range from-20 ? to 30 ?, and it has a high sensitivity and reliability.(4) In view of the feasibility of the test plan, the hardware circuit implementation scheme used for the detection of the subgrade's strain which is based on the FBG is presented. The scheme chooses the FPGA + NIOS II architecture, and the requirements of the hardware system were analyzed. Finally,the key realization methods for the hardware circuit are put forward.(5)Revealing the potential significance of the project. The test system provides a set of new technical means for testing the physical indicators of the concealed works.