Experimental Study On Layout And Data Processing Of Tunnel Plane Control Network

In order to test the optimal layouts of the control network in the tunnel,and to find out the effect of different distance error calculation methods and the influence of distance angle matching on the control network adjustment,a control survey network was established to simulating an 8km long tunnel.The method of GNSS measurement is used to establish the reference point.The total station measurement method is used to measure the left and right cross-traverse network,the diamond-shaped cross-traverse network and the middle free-standing intersection network.Some useful conclusions are obtained through data test calculation and analysis:The influence of different distance error calculation methods on the transverse error of the straight traverse network is very small.The results of Helmert variance component estimation will make the region of the adjustment result consistent and close to the true value.Robust estimation can automatically recognize and deal with the gross error,which is the result of the adjustment more reliable.The applying of the combination of the two methods improves the lateral accuracy of the experimental network.The gyro azimuth can correct the direction of the underground control network where the azimuth deviation occurs,and improve the tunneling lateral accuracy significantly.In the tunnel,the left and right cross-traverse net and the middle free-standing intersection network can effectively weaken the influence of the refraction of the line of sight near the wall of the tunnel.The latter also avoids the effects of instrumental misalignment,which is currently the best network layout for control measurements in tunnels.The systematic error of the control network can be detected by checking the the size and sign of the angular closure error of all the least number of closed loops in the control network and the discrepancies between the measured distances and calculated ones.