Revisiting the methods for gas permeability measurement in tight porous medium

Permeability is a key parameter to describe fluid transport properties of porous medium; however, the permeability measurement is extremely difficult for tight porous medium, e.g. fine-grained rock or dense soil. In this paper, three methods for gas permeability measurement, i.e. steady state method, pulse decay method(PDM) and pressure oscillation method(POM), are first reviewed and then their advantages and drawbacks are discussed. Both analytical and numerical solutions of gas permeability are presented for the tight porous medium. The results show that the analytical method is relatively simple but only valid under certain conditions, whilst the numerical method is more robust and generic, which can take into account several factors such as porosity, saturation, gas leakage, and unconventional boundary conditions. The influence of the effective porosity on the permeability determination is further analyzed using the proposed numerical method. In this study, new pressure data interpretation procedures for PDM and POM are proposed, and the obtained results can serve as a guidance to define a proper method for permeability measurement of the tight porous medium.

Three-Dimensional Collapse Analysis for a Shallow Cavity in Layered Strata Based on Upper Bound Theorem

Layered rock strata are observed to be common during the excavation of tunnels or cavities,and may significantly affect the deformation and failure characteristics of surrounding rock masses due to various complex forms and mechanical properties.In this paper,we propose a three-dimensional axisymmetric velocity field for roof collapse of shallow cavities in multi rock layers,by considering the influences of roof cross-section shapes,supporting pressure,ground overload,etc.The internal energy dissipation rate and work rates of external forces corresponding to the velocity field are computed by employing the Hoek-Brown strength criterion and its associated flow rule.Further,the equations of the collapse surfaces and the corresponding weight of collapsing rock masses are derived on the basis of upper bound theorem.Furthermore,we validate the proposed method by comparing the results of numerical calculations and existing research findings.The change laws of the collapse range under varying parameters are obtained for the presence of rectangular and spherical cavities.We also find that the three-dimensional mechanism is relatively safer for engineering designing actually,compared with the traditional two-dimensional mechanism.All these conclusions may provide workable guidelines for the support design of shallow cavities in layered rock strata practically.

Oblique impact breakage unification of nonspherical particles using discrete element method

Particle breakage commonly occurs during processing of particulate materials,but a mechanistic model of particle impact breakage is not fully established.This article presents oblique impact breakage characteristics of nonspherical particles using discrete element method(DEM)simulations.Three different particle shapes,i.e.spherical,cuboidal and cylindrical,are investigated.Constituent spheres are agglomerated with bridging bonds to model the breakage characteristics under impact conditions.The effect of agglomerate shapes on the breakage pattern,damage ratio,and fragment size distribution is fully investigated.By using a newly proposed oblique impact model,unified breakage master surfaces are theoretically constructed for all the particle shapes under oblique impact conditions.The developed approach can be applied to modelling particulate processes where nonspherical particles and oblique impact breakage are prevailing.

食管癌新辅助治疗参与保存器官的研究进展

食管鳞状细胞癌是我国常见的恶性肿瘤类型之一。局部晚期食管鳞状细胞癌是一种复杂的异质性疾病,治疗方法不断发展。目前,放化疗及手术等多学科综合治疗为其主要手段。然而,由于食管所处的特殊解剖部位,手术切除对患者的生理功能影响较大。在不影响患者整体疗效的基础上,采用保存食管的非手术治疗方法,对于改善患者生命质量等具有重要的意义。新辅助治疗作为一种非侵入性肿瘤治疗手段,在保存食管的综合治疗中扮演重要角色。近年来,陆续有新辅助治疗参与保存食管的食管癌综合治疗策略的研究,对这些研究进展的认识将为食管癌的综合治疗提供参考价值。

Analysis of mobilization of inorganic ions in soil by electrokinetic remediation

Saline soil has imposed a serious threat on many expressway engineering and agricultural areas.This paper describes the performance of saline soil treatment using electrokinetic remediation technology.Comparison study involving sample soil and in situ soil is carried out.Two different electric fields,i.e.,uniform and non-uniform are utilized to promote the migration of inorganic ions contained in the soil toward the electrode area.The effects of different electric field types and potential gradient ion migration rate in soil are investigated.The test result reveals that a uniform electric field of a constant potential gradient of 1 V/cm drives the Cl-through the sample soil at a rate of 1.36 cm/h.Moreover,larger potential gradients could make ions migrate faster,but more electrical energy is consumed in such a way.Compared with uniform electric field,the non-uniform process maintains the soil pH values more effectively and consumes less electrical energy.A desirable result of removing Na+in soil is expected using electrokinetic remediation technology under four-times scaling up of soil volume.