Disclosure of Invention
The invention provides a tunnel dynamic construction method based on a BP (back propagation) neural network, aiming at the problems that the mechanical parameters of a soil layer and a grouting body cannot be accurately identified in the construction process of the existing subway tunnel, the ground surface settlement is difficult to be well predicted, corresponding measures are taken and the like.
The method comprises the following steps:
s1: dividing the tunnel into a plurality of construction sections along the axial direction of the tunnel, and arranging ground surface settlement monitoring points in the middle of each construction section;
s2: carrying out geological drilling exploration in the area of the tunnel, extracting a soil body drill core and measuring mechanical parameters of the soil body drill core, layering the soil body according to the mechanical parameters, respectively measuring mechanical parameters of a grout pulse and the soil body within a grouting design range, and then solving the mechanical parameters of the equivalent grouting body according to an equivalent action principle;
s3: taking the mechanical parameters of each soil layer and the grouting body measured in the S2 as a reference set, generating output layer data by a Monte Carlo method, calculating by using a numerical simulation method to obtain a surface subsidence value as input layer data, and training to generate a BP neural network;
s4: performing pre-grouting reinforcement, excavation and support on the tunnel by adopting a multi-cycle mode, performing segmented construction and monitoring a surface subsidence value;
s5: inputting a ground surface settlement monitoring value caused by tunnel excavation into a BP neural network, and performing inversion to obtain mechanical parameters of each soil layer and grouting body;
s6: predicting the surface subsidence of the next construction section by using a numerical simulation method according to mechanical parameters of each soil layer and grouting body obtained by inversion in S5, and increasing the grouting range or grouting pressure when the maximum subsidence exceeds a surface subsidence control value; when the maximum sedimentation amount is less than 20% of the surface sedimentation control value, reducing the grouting range or grouting pressure; repeatedly adjusting, and optimizing grouting parameters;
s7: performing pre-grouting reinforcement by using the grouting parameters optimized by S6, excavating and supporting in time, and monitoring the surface subsidence value in real time;
s8: and repeating the steps from S5 to S7, and constructing forward section by section.
And in S1, the length of the construction section is 2-5 times of the tunnel diameter.
Ground surface settlement monitoring points are arranged on each construction section of the tunnel, and each row of ground surface settlement monitoring points in the S1 is 7-15 and is symmetrically distributed about the center of the tunnel.
Geological drilling holes are axially arranged in the tunnel at the front of construction and are subjected to geological exploration, geological drilling holes in S2 are axially arranged in the tunnel, the number of the drilling holes is not less than 3, and the hole bottoms of the geological drilling holes are positioned below 3 times of the hole diameter of the tunnel bottom plate.
The mechanical parameters in S2 include compression modulus, Poisson' S ratio, cohesion and internal friction angle.
And the mechanical parameters of each soil layer and the grouting body obtained by inversion in the S5 comprise elastic modulus, Poisson ratio, cohesive force and internal friction angle.
The technical scheme of the invention has the following beneficial effects:
in the scheme, based on the BP neural network, the mechanical parameters of the soil layer and the grouting body can be accurately obtained by inversion by utilizing the strong nonlinear mapping capability of the BP neural network, so that the precision of predicting the surface subsidence through numerical simulation is improved to a great extent; the dynamic construction method of real-time monitoring, advanced prediction, segmented construction and timely adjustment of grouting parameters is adopted, so that the method can better adapt to complicated and variable stratum conditions. The method can accurately identify the mechanical parameters of the soil layer and the grouting body, so that the accuracy of surface settlement prediction is improved to a certain extent, and the grouting parameters are adjusted in time and used for guiding tunnel construction of an unexcavated section.
Detailed Description
In order to make the technical problems, technical solutions and advantages of the present invention more apparent, the following detailed description is given with reference to the accompanying drawings and specific embodiments.
The invention provides a tunnel dynamic construction method based on a BP (back propagation) neural network, aiming at the problems that the mechanical parameters of a soil layer and a grouting body cannot be accurately identified in the construction process of the existing subway tunnel, the ground surface settlement is difficult to be well predicted, corresponding measures are taken and the like.
As shown in fig. 1, the method comprises the steps of:
s1: dividing the tunnel into a plurality of construction sections along the axial direction of the tunnel, and arranging ground surface settlement monitoring points in the middle of each construction section;
s2: carrying out geological drilling exploration in the area of the tunnel, extracting a soil body drill core and measuring mechanical parameters of the soil body drill core, layering the soil body according to the mechanical parameters, respectively measuring mechanical parameters of a grout pulse and the soil body within a grouting design range, and then solving the mechanical parameters of the equivalent grouting body according to an equivalent action principle;
s3: taking the mechanical parameters of each soil layer and the grouting body measured in the S2 as a reference set, generating output layer data by a Monte Carlo method, calculating by using a numerical simulation method to obtain a surface subsidence value as input layer data, and training to generate a BP neural network;
s4: performing pre-grouting reinforcement, excavation and support on the tunnel by adopting a multi-cycle mode, performing segmented construction and monitoring a surface subsidence value;
s5: inputting a ground surface settlement monitoring value caused by tunnel excavation into a BP neural network, and performing inversion to obtain mechanical parameters of each soil layer and grouting body;
s6: predicting the surface subsidence of the next construction section by using a numerical simulation method according to mechanical parameters of each soil layer and grouting body obtained by inversion in S5, and increasing the grouting range or grouting pressure when the maximum subsidence exceeds a surface subsidence control value; when the maximum sedimentation amount is less than 20% of the surface sedimentation control value, reducing the grouting range or grouting pressure; repeatedly adjusting, and optimizing grouting parameters;
s7: performing pre-grouting reinforcement by using the grouting parameters optimized by S6, excavating and supporting in time, and monitoring the surface subsidence value in real time;
s8: and repeating the steps from S5 to S7, and constructing forward section by section.
The following description is given with reference to specific examples.
In the concrete construction, the process mainly comprises the following steps:
s1: dividing the tunnel 3 into a plurality of construction sections along the axial direction of the tunnel, and arranging a ground surface settlement monitoring point 1 in the middle of each construction section; as shown in FIG. 2;
s2: carrying out geological drilling exploration in the area of the tunnel 3, extracting a soil body drill core, measuring mechanical parameters of the soil body drill core, and layering the soil body according to mechanical characteristics;
s3: taking the measured mechanical parameters of each soil layer 6 and the grouting body 2 as a reference set, generating output layer data by a Monte Carlo method, calculating by using a numerical simulation method to obtain a surface subsidence value as input layer data, and training to generate a BP neural network;
s4: pre-grouting reinforcement, excavation and supporting are carried out on the tunnel 3 in a multi-cycle mode, wherein the excavation adopts an upper step method and a lower step method, the supporting structure 4 adopts a steel grating and net-sprayed concrete, the construction is carried out in sections, and the surface subsidence value is monitored; as shown in fig. 3;
s5: inputting a ground surface settlement monitoring value caused by excavation of the tunnel 3 into a BP neural network, and performing inversion to obtain mechanical parameters of each soil layer and the grouting body 2;
s6: predicting the surface subsidence of the next construction section by using a numerical simulation method according to the mechanical parameters of each soil layer 6 and the grouting body 2 obtained by inversion in the S5, and increasing the grouting range or the grouting pressure when the maximum subsidence exceeds a surface subsidence control value; when the maximum sedimentation amount is less than 20% of the surface sedimentation control value, reducing the grouting range or grouting pressure; repeatedly adjusting, and optimizing grouting parameters;
s7: performing pre-grouting reinforcement by using the grouting parameters optimized in the S6, excavating and supporting in time, and monitoring the surface subsidence value in real time;
s8: and repeating the steps from S5 to S7, and constructing forward section by section.
And (3) adopting a dynamic construction method based on the BP neural network, and controlling the length of the segments of the tunnel 3 to be 2-5 times of the tunnel diameter when the tunnel 3 is segmented.
As shown in fig. 4, ground surface settlement monitoring points 1 are arranged at each construction section of the tunnel 3, and the number of the ground surface settlement monitoring points in each row is 7-15, and the ground surface settlement monitoring points are symmetrically distributed around the center of the tunnel.
Mechanical parameters of the soil layer 6 and the grouting body 2 involved in the measurement comprise compression modulus, Poisson ratio, cohesive force and internal friction angle; soil layer 6 and grouting force 2 optical parameters involved in inversion comprise elastic modulus, Poisson ratio, cohesive force and internal friction angle.
As shown in fig. 5, geological boreholes 5 are axially arranged in the tunnel at the front of the construction and geological exploration is performed, wherein the number of the geological boreholes 5 is not less than 3, and the bottoms of the geological boreholes 5 are located below 3 times the hole diameter of the tunnel bottom plate.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.