Dong-Mei Zhang

A new hybrid real-coded genetic algorithm and its application to parameters identification of soils

Abstract Inverse analysis using an optimization method based on a genetic algorithm (GA) is a useful tool for obtaining soil parameters in geotechnical fields. However, the performance of the optimization in identifying soil parameters mainly depends on the search ability of the GA used. This study aims to develop a new efficient hybrid real-coded genetic algorithm (RCGA) being applied to identify parameters of soils. In this new RCGA, a new hybrid strategy is proposed by adopting two crossovers with outstanding ability, namely the Simulated Binary Crossover and the simplex crossover. In order to increase the convergence speed, a chaotic local search technique is used conditionally. The performance of the proposed RCGA is first validated by optimizing mathematical benchmark functions. The results demonstrate that the RCGA has an outstanding search ability and faster convergence speed compared to other hybrid RCGAs. The proposed new hybrid RCGA is then further evaluated by identifying soil parameters based on both laboratory tests and field tests, for different soil models. All the comparisons demonstrate that the proposed RCGA has an excellent performance of inverse analysis in identifying soil parameters, and is thus recommended for use based on all the evaluations carried out in this paper.

UNIFIED MODELING OF THE MONOTONIC AND CYCLIC BEHAVIORS OF SAND AND CLAY

In this study, we aim to investigate a unified modeling method for the monotonic and cyclic behaviors of sand and clay. A simple double-yield-surface model, with plastic hardening modulus and dilatancy relation being dependent on density state unlike in existing approaches, is developed by considering the location of the critical state line. The model is used to simulate the drained and undrained tests of various sands and clays under monotonic and cyclic loadings. Prediction results are compared with experimental results, which show that the proposed approach is capable of modeling the monotonie and cyclic behaviors of sand and clay.

Numerical Study on the Effect of Grouting on Long-Term Settlement of Tunnels in Clay

The long-term settlements over tunnels can be rather significant, particularly when tunnels are embedded in soft and compressible soils. The influence of grouting on the evolution of long-term surface settlement, as well as ground loss, is simulated by imposing prescribed volumetric strain on the disturbed area around the tunnel due to shield tunneling. The volumetric strain could be detected from the grouting ratio of grouting volume and the volume of the physical gap of shield tunnel. Finally, some conclusions are drawn from the numerical simulations.

Micromechanical modelling of phase transformation behaviour of a transitional soil

Experiments show that silts and silty soils exhibit contraction followed by dilation during shearing and the slope of failure line decreases at large strains, termed as phase transformation behaviour. This paper is to develop a new micromechanical stress-strain model that accounts for the phase transformation behaviour by explicitly employing the phase transformation line and its related friction angles. The overall strain includes plastic sliding and plastic compression among grains. The internal-friction angle at the phase transformation state and the void state variable are employed to describe the phase transformation behaviour. The model is examined by simulating undrained and drained triaxial compression tests performed on Pitea silts. The local stress-strain behaviour for contact planes is also investigated.

A Coupled Hydro-Mechanical Modeling of Tunnel Leakage in Sand Layer

The tunnel leakage in sand layer plays an important role in the evolution of the lining stresses and the ground movement. The phenomenon of internal erosion occurs when underground water leaks into the tunnel from the damaged joints or the cracks of the linings. Fines in sand are pulled off by seepage forces and transported throughout the soil matrix into the tunnel. The loss of fines due to seepage flow affects the mechanical behavior of the soil around the tunnel. Conversely, the change of porosity influences the permeability of the soil and, therefore, its hydraulic conductivity. In this study, the effect of tunnel leakage in sand layer is investigated numerically with a coupled hydro-mechanical approach, considering the internal erosion phenomenon induced by the local flows of underground water, using the continuous porous medium theory and a critical-state based constitutive model. Simulation results show that the loss of fines as well as the leakage locations have significant impacts on the tunnel lining and the ground movement.

Analytical Solution of Underneath Tunnelling-Induced Deformation of Existing Tunnel

Tunnelling underneath the existing tunnels are very common these days. It is obvious that the under-crossing tunnelling will affect and even damage the existing tunnels. An analytical method is proposed in this paper to better understand the effects of the under-crossing tunnelling on the existing tunnel. The existing tunnel is modeled as a Timoshenko beam lying on a Kerr foundation. The validity of the analytical solution is verified by a series of centrifuge tests. The parametric study is then carried out to well understand the effect of under-crossing tunneling on the deformation of existing tunnel. The results indicate that the pattern and the magnitude of the deformation of the existing tunnel dependent on the longitudinal shear stiffness, volume loss and the vertical clearance between newly built and existing tunnels.

Dynamic Response of Tunnel Lining to Resonance Rubblization Induced Vibration in Pavement Renewal

The resonance rubblization technology can be adopted to reconstruct old concrete pavement and eradicate reflection cracking. This method fractures pavement into fragments quickly and directly casts asphalt on fractures, shortening time cost of reconstruction. Previous studies about this technology mainly concentrated on asphalt-casting methods, and the quality, stiffness, and flatness of reconstructed pavement. Few studies concerned about the resonance rubblization-induced tunnel response. Based on a rock tunnel in China, 3D numerical simulation and field tests were conducted. Acceleration-time history curves of tunnel lining was monitored during field tests, and it was used to validate the numerical model. Then the resonance rubblization caused additional internal stress of tunnel was investigated using the validated numerical model. Results show that the peak additional Mises stress in inverted arch and tunnel lining is about 2 MPa and 1.5 MPa respectively, and it reduces significantly along transverse, longitudinal and vertical directions on tunnel. The effects of isolation trenches were also discussed, and outcomes show that isolation trenches can help reduce the peak additional Mises stress in inverted arch and tunnel lining by 31.7% and 16.0% respectively, demonstrating the effects of isolation trenches.

Shearing Behavior of Segmental Joints of Large-Diameter Shield Tunnel

Segments floating is often encountered during the large-diameter shield tunneling. Shearing resistance of circumferential joints is of great importance for resisting the tunnel floating. The shearing resistance in terms of circumferential joint dislocation is studied using 3D numerical simulation. The influences of bolt types, gaskets, transmission cushions, and longitude bolt pre-force on the shearing resistance are investigated, respectively. The simulation results indicate that the dislocation process of circumferential joint can be divided into three stages, and the friction force between transmission cushion and concrete mainly determines the shear resistance of segment joint in the first stage, then in the last two stages, bolts contact the bolt holes and perform shear ability which varies from the bolt type. Based on the results, the safety and durability of circumferential joint are discussed. Some suggestions of shearing resistance design of lining structure are presented.

In-situ Experimental Analysis of Acceleration Response of Mountain Tunnel Lining to Rubblization-Induced Vibrations

Resonant rubblization technology is often utilized to rehabilitate deteriorated concrete pavements. Vibrations induced by a resonant breaker would produce detrimental effects on lining structures in tunnel during rubblization construction. The in-situ experiments were carried out in Yangjiao Mountain Tunnel in Zhejiang Province, China. First, the characteristics of rubblization-induced vibration are analyzed in time and frequency domains. Then effects of different testing points and pavement breaking positions on lining dynamic response in several frequency bands are taken into consideration to investigate vibration propagation rules. Later, the amplitudes of acceleration, vibration acceleration level (Val) and velocity in the examined cross section are presented to evaluate the dynamic response of lining structure in the procedure of resonant rubblization. The results show that the acceleration peak (3.52 g) appears on the lining arch foot while the maximum of Val (132.6 dB) and velocity (17.2 mm/s) show on the arch side. The presented data and results can be useful for design and safety assessment of resonant rubblization construction in mountain tunnel.

Identifying Soil Parameters from Excavation Using MOOP

In this paper, a framework that combines the stochastic multi-objective optimization (MOOP) and the observed field data for identifying soil parameters is presented. For conducting the parameter identification, a multi-objective differential evolution algorithm is employed. Then, an elastoplastic soil model accounting for the small-strain stiffness and anisotropic elasticity behaviors of clays is developed and adopted. Finally, the proposed procedure is applied to a well-instrumented deep excavation. The observed wall deflection and ground settlement are used as objective in the optimization. The results demonstrate that the anisotropy of elasticity and small strain stiffness are two important factors influencing the ground settlement and wall deflection in the excavation. All the comparisons demonstrate that the proposed framework is effective and efficient for identifying soil parameters from excavation.