Analytical solutions for the restraint effect of isolation piles against tunneling-induced vertical ground displacements

This paper presents a simplified elastic continuum method for calculating the restraint effect of isolation piles on tunneling-induced vertical ground displacement,which can consider not only the relative sliding of the pile‒soil interface but also the pile rowesoil interaction.The proposed method is verified by comparisons with existing theoretical methods,including the boundary element method and the elastic foundation method.The results reveal the restraining mechanism of the isolation piles on vertical ground displacements due to tunneling,i.e.the positive and negative restraint effects exerted by the isolation piles jointly drive the ground vertical displacement along the depth direction from the original tunneling-induced nonlinear variation situation to a relatively uniform situation.The results also indicate that the stiffness of the pile‒soil interface,including the pile shaft‒surrounding soil interface and pile tip-supporting soil interface,describes the strength of the pile‒soil interaction.The pile rows can confine the vertical ground displacement caused by the tunnel excavation to the inner side of the isolation piles and effectively prevent the vertical ground displacement from expanding further toward the outer side of the isolation piles.

Modified image analytical solutions for ground displacement using nonuniform convergence model

Based on the image theory,the analytical solutions of tunneling-induced ground displacement were derived in conjunction with the nonuniform convergence model.The reasonable value of Poisson ratio in the analytical solution was discussed.The ground settlement width parameter which could reflect the ground condition was introduced to modify the analytical solutions proposed above,and new analytical solutions were presented.To evaluate the validity of the present solutions using the nonuniform convergence model,the results were compared with the observed values for four engineering projects,including 38 measured data of ground settlement.The agreement shows that the present solutions using the nonuniform convergence model are effective for evaluating the tunneling-induced ground displacements.

Prediction of ground surface displacement caused by grouting

Ground surface displacement caused by grouting was calculated with stochastic medium theory. Ground surface displacement was assumed to be caused by the cavity expansion of grouting, slurry seepage, and slurry contraction. A prediction method of ground surface displacement was developed. The reliability of the presented method was validated through a comparison between theoretical results and results from engineering practice. Results show that the present method is effective. The effect of parameters on uplift displacement was illustrated under different grouting conditions. Through analysis, it can be known that the ground surface uplift is mainly caused by osmosis of slurry and the primary influence angle of stratum β determines the influence range of surface uplift. Besides, the results show that ground surface uplift displacement decreases notably with increasing depth of the grouting cavity but it increases with increasing diffusion radius of grout and increasing grouting pressure.

Measuring ground deformations caused by 2015 Mw7.8 Nepal earthquake using high-rate GPS data

The April 25, 2015 Mw7.8 Nepal earthquake was successfully recorded by Crustal Movement Observation Network of China （CMONOC） and Nepal Geodetic Array （NGA）. We processed the high-rate GPS data （1 Hz and 5 Hz） by using relative kinematic positioning and derived dynamic ground motions caused by this large earthquake. The dynamic displacements time series clearly indicated the displacement amplitude of each station was related to the rupture directivity. The stations which located in the di- rection of rupture propagation had larger displacement amplitudes than others. Also dynamic ground displacement exceeding 5 cm was detected by the GPS station that was 2000 km away from the epicenter. Permanent coseismic displacements were resolved from the near-field high-rate GPS stations with wavelet decomposition-reconstruction method and P-wave arrivals were also detected with S transform method. The results of this study can be used for earthquake rupture process and Earthquake Early Warning studies.

A Model of Shield Jack Thrust to Shield Attitude

The attitude of the shield tunneling machine (or "shield" for short) during tunneling is important to tunnel excavation and construction quality, which results from a combination of jack thrust, ground displacement around the shield, and ground mechanics parameters, etc. A shield attitude model involving elements above was proposed. In this model, ground displacement was taken to calculate the load around the shield. Ground mechanics parameters were involved. Based on the shield load model, the needed jack thrust for shield desired attitude was derived. The proposed method is validated using engineering data, and lays reliable foundation for shield attitude control.

Numerical analysis on zone-divided deep excavation in soft clays using a new small strain elasto–plastic constitutive model

Accurate prediction of displacements associated with deep excavations is essential to ensure safety and stability of the excavation and to prevent any damage and distress to the adjoining infrastructures.This paper presents a numerical approach for prediction of ground displacements related to a zone-divided deep excavation construction executed in Shanghai soft clays based on a new elasto–plastic con-stitutive model(small-strain Shanghai model)that incorporates small strain stiffness.This model can describe the mechanical properties and structural and over-consolidated characteristics of natural clays.The model is implemented into a finite element analysis software.Numerical analysis on the deep excavation in Shanghai using zone-divided method is conducted.A comparison between monitored and simulated results of horizontal displacements along the diaphragm wall,the settlements in the surroundings,and the effects on the adjoin-ing metro tunnel due to excavation construction is carried out.Special attention is paid to the stiffness degradation of representative elements in the ground.The simulated displacements show a good agreement with the monitored data.Overall,this study provides an integrated solution for predicting displacements related to deep excavation in soft clays.