The Deformation Monitoring For The Toroidal Secondary Lining In A Circular Tunnel Based On The Distributed Strain Measurement

Excessive deformation,sometimes with crack,in the secondary lining has been seen as one of the major diseases in the operating period of a tunnel.It can weaken the safety,durability and usability of the tunnel,which can finally result in the reduction of the whole service life of the tunnel.However,some traditional methods,which can only measure the deformation on a few preset points,cannot satisfy the requirements including comprehensiveness,accuracy and stability for the secondary lining monitoring.Therefore,this thesis proposes to indirectly obtain the deformation of the secondary lining in tunnel by means of distributed strain measurements.This thesis focused on the deformation monitoring for the toroidal secondary lining in a circular tunnel.By separating the hoop strain of the secondary lining,this thesis puts forward methods of the deformation calculation when the secondary lining in mountain tunnel is fixed supported or elastic supported which provides displacements at the end of secondary lining.Finally,a finite element simulation and a laboratory test are conducted to verify the effectiveness of the proposed method.The main contents are shown as follows:(a)The applicability of the deformation calculation for the secondary lining has been analysis in this thesis based on various design model of mountain tunnel.Then a simplified calculation model of the secondary lining is proposed considering the common sections of secondary lining and load forms.(b)The deformation of any point on the cross section of the secondary lining can be decomposed into bending deformation and circumferential compression deformation.The hoop strain of the point can also be decomposed into bending strain and circumferential compression strain.The relationship between the circumferential compression strain and its deformation function is different from the bending strain and its deformation function,and the sensor can only measure the average strain,therefore,the metrical data of strain is separated firstly in this thesis.(c)Based on the conclusion of study(b),this thesis demonstrates the relationships between the bending strain and radial displacement when the secondary lining in mountain tunnel is fixed supported by combined the theory of curve beam with traditional conjugate beam method.In addition,the relationship of compressive strain and the displacement of the secondary lining are established using the knowledge of mechanics.(d)On the basis of study(c),this thesis puts forward the strain-displacement algorithm when the secondary lining in mountain tunnel is elastic supported which provides the subsidence displacement,horizontal displacement and slope at the end of secondary lining.(e)The feasibility of monitoring algorithm that proposed in study(c)and(d)is verified by a laboratory test,in which,the radial deformation of several key points and strain distribution on the circumference of secondary lining are measured when the concrete scale model of secondary lining are under loading.The results show that the most of the radial displacement which calculated by the data of the strain distribution are within 10%compared with the displacement of actual monitoring,and the error of a few measuring point is slightly larger,but also within 15%.It is implied that the deformation monitoring for the toroidal secondary lining in a circular tunnel based on the distributed strain measurement has a good accuracy and can be applied to the deformation monitoring of cross section in actual mountain tunnel.