Then, the real displacement was transferred to the optical signal by using an optical ruler. The STS was connected to the grating ruler with the guide Enzalutamide line, and the optical signal was transformed to digital signal and then transferred to the DAS. The displacement data of the model was displayed and stored instantaneously. The high precision (1��m) GRDS can be used to measure the displacement in any direction as it can be bent at any angle. Figure 6Grating ruler multipoints displacement measuring system (GRDS). (1) Fixed end, (2) guding frame, (3) soft pipe, (4) flexible steel wire, (5) displacement transfer roller, (6) balance weight, (7) optical ruler, (8) STS, (9) DAS, (10) cable.The fiber bragg grating (FBG) was stuck to the analogical material blocks to make the grating strain sensor.
And it can be used to measure the strain in each direction inside the model (Figure 7).Figure 7Grating strain sensor measuring system.The FBG can measure the strain changing outside through the centre wavelength mobile. The relationship between the centre wavelength ��B and the effective refraction index neff of grating and the period of grating �� is��B=2neff��,(2)where ��B is centre wavelength of the Bragg grating; �� is the period of grating; neff is the effective refraction index.When the fiber is stretched, �� and neff will change, and then the centre wavelength ��B will drift. The wavelength gets larger when the fiber is stretched, while it gets smaller when the fiber is compressed. The linear relationship will be satisfied:����B=��B(1?Pe)��=Ke��,(3)where, ����B is the variation of wavelength; Pe is the effective optical coefficient (0.
22, generally); �� is the axial strain of fiber; Ke is the sensitivity of strain measuring.When the grating generates strain in the stress condition, the pitch of the grating will change to ����, which will make the wavelength change to ����, so the strain can be got:��=��ll=���˦�.(4)4. Construction of the ModelTo study the anchoring effect on zonal disintegration, a model was built and divided to two halves to make compassion: one half is anchored and the other half is nonanchoring. 4.1. Simulation Range of the ModelThe model size is limited by the reasonable size of the steel frame. Within the frame, if the similarity constant for the geometry CL is smaller than 1:50, then the model tunnel will be too small to be excavated.
If the CL is very large, then the relevant monitoring devices will Cilengitide be too difficult to install and the monitoring data will be inaccurate. Considering these prior factors, 100 is taken as the optimal similarity coefficient CL.The simulation range of the prototype is 30m �� 30m �� 30m. According to the geometry similar scale 1/50, the dimension of the model is determined to 0.6m �� 0.6m �� 0.