Dynamic Response of Foundations during Startup of High-Frequency Tunnel Equipment

The specialized equipment utilized in long-line tunnel engineering is evolving towards large-scale,multifunctional,and complex orientations.The vibration caused by the high-frequency units during regular operation is supported by the foundation of the units,and the magnitude of vibration and the operating frequency fluctuate in different engineering contexts,leading to variations in the dynamic response of the foundation.The high-frequency units yield significantly diverse outcomes under different startup conditions and times,resulting in failure to meet operational requirements,influencing the normal function of the tunnel,and causing harm to the foundation structure,personnel,and property in severe cases.This article formulates a finite element numerical computation model for solid elements using three-dimensional elastic body theory and integrates field measurements to substantiate and ascertain the crucial parameter configurations of the finite element model.By proposing a comprehensive startup timing function for high-frequency dynamic machines under different startup conditions,simulating the frequency andmagnitude variations during the startup process,and suggesting functions for changes in frequency and magnitude,a simulated startup schedule function for high-frequency machines is created through coupling.Taking into account the selection of the transient dynamic analysis step length,the dynamic response results for the lower dynamic foundation during its fundamental frequency crossing process are obtained.The validation checks if the structural magnitude surpasses the safety threshold during the critical phase of unit startup traversing the structural resonance region.The design recommendations for high-frequency units’dynamic foundations are provided,taking into account the startup process of the machine and ensuring the safe operation of the tunnel.

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.

Settlement characteristics of large-diameter shield excavation below existing subway in close vicinity

A case of Qinghuayuan tunnel excavation below the existing Beijing Subway Line 10 is presented.The new Qinghuayuan tunnel,part of the Beijing-Zhangjiakou High-speed Railway,was excavated by a shield machine with an outer diameter of 12.2 m.The existing subway was excavated by shallow tunnelling method.The project layout,geological conditions,reinforcement measures,operational parameters of shield machine and monitoring results of the project are introduced.During the Qinghuayuan tunnel excavation below the existing subway,total thrust,shield driving speed,cutterhead rotation speed and torque were manually controlled below the average values obtained from the previous monitoring of this project,which could effectively reduce the disturbance of the surrounding soil induced by shield excavation.The Gaussian fitting function can appropriately fit both the ground and the existing subway settlements.The trough width is influenced not only by the excavation overburden depth,but also by the forepoling reinforcement and tail void grouting measures.

Toward an Ecological Civilization:China’s Progress as Documented by the Second National General Survey of Pollution Sources

The relationship between environmental quality and economic growth has been a hot topic for decades.After years of rapid industrialization and urbanization,China’s environmental challenges are approaching a turning point.Following the principles of ecological civilization construction,China is on its way to maintaining high-quality and green economic development.On 10 June 2020,the Chinese Government reported the key findings of the Second National General Survey of Pollution Sources(fiscal year 2017),which provides strong quantitative evidence of progress toward ecological civilization.In terms of our comparison between the two National General Surveys in 2007 and 2017,it was found that environmental pollution,measured in terms of many wastewater and air emission pollutant discharges,is decreasing despite the steady growth in economic activities—and at a noticeably fast pace.Other national and local governments can adopt some of China’s ecological civilization practices,within their own individual contexts.

Prediction of ground settlements induced by twin shield tunnelling in rock and soil--A case study

Ground movements caused by the construction of tunnels and excavation are inevitable.Estimation of such movements is a very important for risk management in tunnel design.This paper presents a case study of ground settlements induced by twin shield tunnelling in Copenhagen using analytical and numerical methods and their predictions.The predictions are compared with the monitored settlements.The comparison shows that the predictions are sufficiently conservative.

Investigation on thermo-mechanical behavior of reinforced concrete energy pile with large cross-section in saturated sandy soil by model experiments

Energy piles are a new type of heat exchange systems with buried pipes in a pile foundation,which optimize a ground source heat pump system for the utilization of shallow geothermal energy.In this study,based on the principle of similarity,the thermo-mechanical behavior of the model energy pile with a large cross-section in saturated sandy soil was experimentally evaluated.The pre-cast model concrete pile with a diameter of 0.2 m and length of 1.5 m was buried in saturated sand in a steel box with dimensions of 2.5 m×2.5 m×2.0 m(length×width×height).The pile was heated using water in the polyethylene(PE)pipe,which was connected to a water cycle temperature controller.At a constant inlet water temperature of 55℃,three thermal cycles were carried out with the same heating and cooling periods and different water flow rates.The temperature distributions in the pile and soil,in addition to the pore pressure,soil pressure,and displacement of the pile,were monitored to clarify the thermo-mechanical behavior of the pile and soil.The heat transfer efficiency was analyzed based on the temperature difference and water flow rates.The measured strain at different locations in the pile under cyclic thermal loading revealed that the uneven strain that developed in a pile body should be considered for its long-term application.Furthermore,focus should be directed toward the long-term unrecoverable displacement of the energy pile due to the thermal plastic strain and thermal consolidation of the soil.

A continuum method for granular collapse with μ(I)-rheology-based dynamic earth pressure coefficient

In this paper,a continuum model with dynamic earth pressure coefficient is established to describe the granular slump process by introducingμ(I)rheology.This rheology is adopted to quantify the normal stresses in our proposed model rather than shear stresses in classical models.The constitutive laws of different depth-averaged continuum approaches including the hydrodynamic,Savage–Hutter and proposed models are comparatively investigated in terms of the rheological effects on the spread of a granular column.The simulation results indicate that the proposed dynamic model captures some significant features during granular slump on inclined planes with different inclination angles(for example,the runout distance,runout time,and final profile).The proposed model can also reproduce the inner static sided axisymmetric region observed in tests when the granular column's initial aspect ratio(ratio of height to radii)is small.

Theoretical prediction of ground settlements due to shield tunneling in multi-layered soils considering process parameters

This paper conducts a theoretical analysis of ground settlements due to shield tunneling in multi-layered soils which are usually encountered in urban areas.The proposed theoretical solution which is based on the general form of the Mindlin’s solution and Loganathan-Poulos formula can comprehensively consider the in-process tunneling parameters including:unbalanced face pressure,shield-soil friction,unbalanced tail grouting pressure,unbalanced secondary grouting pressure,overloading during tunneling and the ground volume loss.The method is verified by comparing with the field data from the Qinghuayuan Tunnel Project in terms of the ground surface settlements along the longitudinal and transverse direction.Due to the local settlement or heave caused by the certain tunneling parameters,the ground surface settlements calculated using current solution along the longitudinal direction presents an irregular S-shaped curve instead of the traditional S-shaped curve.Results also find that the effect of the unbalanced secondary grouting pressure and the overloading during tunneling cannot be ignored.