Research on 3d elastoplastic numerical analysis of settlement joint of shield tunnel based on the interaction between soil and structure
Considering the effect on uneven settlement of tunnel longitudinal stratum, a 3d elastoplastic numerical model is established for the arrangement of settlement joint and the calculation of force and deformation of tunnel longitudinal structure based on the interaction between soil and structure. In the FEM calculation model, soil material is elastoplastic, the soil constitutive model selected Mohr Coulomb, the element type of soil choose a three-dimensional solid element, the element type of segment structure use space shell element, and settlement joint use three-dimensional linear elastic spring. Calculation shows that, this calculation model is able to fully consider the impact of tunnel the uneven settlement of all factors, and may better simulate the vertical force and deformation behavior of tunnel structure in complex ground formation conditions. Research conclusion gives the vertical force and deformation of the tunnel structure under the condition of different set of settlement joint, and has an important reference value for the future design and construction of the tunnel lining structure.
Experimental study on working parameters of earth pressure balance shield machine tunneling in soft ground
Deep sedimentary deposits of soft clays are widely distributed in coastal areas as well as many interior major cities in China. In order to study the stratum adaptability of earth pressure balance (EPB) shield machine tunneling in such types of soft ground, model tests of tunneling excavation, using the running tunnel of the Shanghai Metro Line M8 as a background, are carried out with different over burden ratios, opening rates of cutter head, driving speeds and rotation speeds of screw conveyor. Based on the test results, the interrelationships between chamber pressure and mucking efficiency, mucking rate and driving speed, thrust force and torque are obtained. The influences of tunnel depth, opening rate of cutter head and driving speed on thrust force and torque are revealed. Such findings can not only facilitate establishing relationships between shield working parameters and soil properties, but also serve as a guide for the design and construction of shield tunnel in soft ground.
Time and Heritage
As a historian studying what can be considered a form of intellectual history, I have slowly come to adopt Michel de Certeau’s observation made at the end of the 1980s that ‘objectifying the past, for the last three centuries, has undoubtedly left unconsidered time within a discipline that has continued to use it as a taxonomic instrument’. To a certain degree, time has become commonplace for the historian who has preserved or instrumentalized it. It is not considered because it is inconceivable, but because we do not think of it or, more simply, we do not think about it. As a historian attempting to pay attention to the time I’m living in, I have thus, like many others, noticed the swift development of the category of the present until it has become obvious that the present is omnipresent. This is what I refer to here as ‘presentism’.