Numerical simulation of hydrodynamic characteristics during the diversion closure in a horizontal tunnel

Based on water inrush accident of 1841 working face of Desheng Coal Mine in Wu'an, Hebei province, China, an evaluation model of hydrodynamic characteristics of the project is set up and simulated using Matlab. It is assumed that the pipe flow would transform into seepage flow when the aggregates are plugged into the water inrush channel and the seepage flow would disappear along with grouting process. The simulation results show that the flow velocity will increase with an increase in height of aggregates accumulation body during the aggregates filling process; the maximum seepage velocity occurs on the top of plugging zone; and the water flow decreases with increasing plugging height of water inrush channel. Finally, the field construction results show that the water inrush channel can be plugged effectively by the compacted body prepared with aggregate and cement slurry.

A practical ANN model for predicting the excavation-induced tunnel horizontal displacement in soft soils

The objective of this study is to propose an artificial neural network(ANN)model to predict the excavation-induced tunnel horizontal displacement in soft soils.For this purpose,a series of finite element data sets from rigorously verified numerical models were collected to be utilized for the development of the ANN model.The excavation width,the excavation depth,the retaining wall thickness,the ratio of the average shear strength to the vertical effective stress,the ratio of the average unloading/reloading Young’s modulus to the vertical effective stress,the horizontal distance between the tunnel and retaining wall,and the ratio of the buried depth of the tunnel crown to the excavation depth were chosen as the input variables,while the excavation-induced tunnel horizontal displacement was considered as an output variable.The results demonstrated the feasibility of the developed ANN model to predict the excavation-induced tunnel horizontal displacement.The proposed ANN model in this study can be applied to predict the excavation-induced tunnel horizontal displacement in soft soils for practical risk assessment and mitigation decision.

Influence of adjacent shield tunneling construction on existing tunnel settlement: field monitoring and intelligent prediction

Urban subway tunnel construction inevitably disturbs the surrounding rock and causes the deformation of existing subway structures. Dynamic predictions of the tunnel horizontal displacement, tunnel ballast settlement, and tunnel differential settlement are important for ensuring the safety of buildings and tunnels. First, based on the Hangzhou Metro project, we analyzed the influence of construction on the deformation of existing subway structures and the difficulties and key points in monitoring. Then, a deformation prediction model, based on a back propagation(BP) neural network, was established with massive monitoring data. In particular, we analyzed the influence of four structures of the BP neural network on prediction performance, i.e., single input–single hidden layer–single output, multiple inputs–single hidden layer–single output, single input–double hidden layers–single output, and multiple inputs–double hidden layers–single output, and verified them using measured data.

Air-core characteristics in a swirling tunnel flow

A cost-effective technique to dissipate the energy in hydropower systems is the formation of a swirling flow within a tunnel.In such flows,an air core with a significant cross section usually occurs.To reveal the air-core features in the horizontal tunnel of a high-head shaft spillway,laboratory tests,numerical modeling,and prototype observations are performed,to examine issues such as the formation of the air core,the interjacent air motion,the air-carrying capacity,and the scale effects.It is shown that the shape of the air core varies greatly in the axial and radial directions along the tunnel and that the center of the core deviates from the axis of the tunnel.The motion of the air within the core is caused by the combined action of the water entrainment on the inner surface of the swirling flow and the axial pressure difference in the air core.The aeration process can be divided into five processes with respect to the changes of the gate openings.A theoretical expression is established for the air-carrying capacity of the swirling flow.The vacuum degree is the similarity condition of the air-carrying capacity of the swirling flow between the model and prototype tests based on the Froude law of the similitude,and this similarity condition is verified by both the model and prototype results.This work provides a reference for the application of the swirling flows in horizontal hydropower tunnels.

Behaviours of existing shield tunnels due to tunnelling underneath considering asymmetric ground settlements

New tunnelling underneath could influence existing shield tunnels in underground spaces.The evaluation of the influences of tunnelling-induced ground movements on existing tunnels has been a major concern during urban construction.This paper presents a two-stage analytical method that considers the asymmetric ground settlement for investigating the longitudinal tunnel responses to new tunnelling.An improved semi-analytical solution considering the horizontal movement of the new tunnel is established for evaluating the tunnelling-induced asymmetric greenfield settlement.The proposed method is verified with field measurement data from a case study.A parametric analysis is conducted to study the influences of the input parameters on the tunnel responses.Results indicate that the horizontal movement of the new tunnel due to bias loading or asymmetric construction may lead to asymmetric responses of the existing tunnel.With increasing tunnel horizontal movement,the asymmetry of the tunnel responses becomes more obvious.An increase in the pillar depth and decreases in the tunnel horizontal movement and skew angle lower the internal forces induced by new tunnelling.