Study On Back Analysis Of M-values Of Foundation Soils And The Application Of Optical Fiber Sensing In Deep-excavation

Uncertainty, multifactor and time domain are the characteristics of the retaining structure of deep excavation. The design of the retaining structure is dynamic. The next stage response of the retaining structure is pre-estimated according to the properties of soil strata got by the method of back-analysis on the base of the measured data at this stage. In respond to the predicted response, measures could be taken, such as reinforcing the retaining structures, revising the formerly design or other necessary operations. So this is the course of dynamic design and information construction by the method of back-analysis. The elastic foundation beam method has some merits such as easy calculation pattern and definite model and m-method is fit to practical situation, so m-value is calculated by back-analysis method using the measured data of deep foundation pit. This paper introduces the history and the status in quo of the back-analysis method, and the means to use back-analysis method in deep foundation pit. The influences of /n-value and the elements of retaining structures on the displacement of retaining structures are studied with the m-method back-analysis programme. And the variation of optimized values caused by the numbers of different inversion parameters is also analyzed, and a conclusion is drawn that a propriety parameter numbers should be in use of back-analysis. And the combination of optimal points is ascertained through the analysis sensitivity of parameters. At last, according to the measured data, the m-value of soil strata in a foundation pit is analyzed. So it is necessary and feasible to use back-analysis method in deep foundation pit.Brillouin Optical Time Domain Reflectometer (BOTDR) is a state-of-the-art sensing technology in recent years. The research about the application of BOTDR to civil engineering and hydraulic engineering is at the beginning. The principle of the distributed sensing technology based on spontaneous Brillouin backscattering is introduced in detail. Some relevant issues, such as the layout methods and the installation techniques of the sensing fiber for real structures, the temperature compensation methods for strain measurement purpose, are discussed systematically. BOTDR is applied to the system of foundation pit monitoring for the first time, which BOTDR is used to get the soil deep-seated displacement. This paper introduces the layout methods and the installation techniques of the sensing fiber in foundation pit and converts the optical strain to the displacement of the deep-seated soil, which is carried out in a foundation pit in Nanjing and expands the application of BOTDR and is a significative experiment for the application of BOTDR.