平面应力型动态断裂韧度的一种测试方法

1 引言由于试验技术及动态断裂分析上的困难,材料动态断裂韧度的表征与测试方法至今仍然很不成熟,尤其对于弹塑性材料,进展更为缓慢.早期的动态断裂韧度测试多半是在落锤式试验机上进行的,且用表征和测量准静态断裂韧度的方法来处理试验数据。

混凝土构件内Ⅰ型裂纹的一种断裂分析方法

本文在文^[1]的基础上采用裂纹线方法，从平衡方程和混凝土材料的破坏准则出发，对有限宽混凝土构件内受单向拉伸的1型微裂纹进行弹脆性断裂分析，分析过程中认为已扩展的脆断区应变能完全释放，得出了单向位应力的大小与微裂纹脆断区长度之间的关系。

Ground movement mechanism in tectonic stress metal mines with steep structure planes

When mining metal mines with steep structure planes by the caving method,there is a mechanical model in which the horizontal stress on the rock mass is simplified as a column before surface subsidence.The model is used to deduce critical support load and limiting column length for a given horizontal stress and support pressure.Considering the impact of the column effect,a method is proposed to determine the movement of the ground and caving area in a mine.After surface subsidence,the horizontal stress on a surrounding rock mass can be simplified to a cantilever beam mechanical model.Expressions for its bending fracture length are deduced,and a method is given to determine its stability.On this basis,an explanation for the large ground movement and subsidence scope was given.A case study shows that the damage effect of column and cantilever beam is significant for ground movement in metal-ore mine,and an appropriate correction value should be applied when designing for its angle of ground movements.

Improved slope safety analysis by new Druker-Prager type criterion

Based on Mohr-Coulomb （M-C） criterion, the parameters of Druker-Prager （D-P） criterion for geomaterial were determined under non-associated flow rule, and thus a new D-P type criterion was presented. Two assumptions were employed during the derivation： 1） principal strains by M-C model and D-P model are equal, and 2） the material is under plane strain condition. Based on the analysis of the surface on rt plane, it is found that the proposed D-P type criterion is better than the D-P criterion with M-C circumscribed circle or M-C inscribed circle, and is applicable for stress Lode angle less than zero. By comparing the predicted results with the test data of sand under plane strain condition and other D-P criteria, the proposed criterion is verified and agrees well with the test data, which is further proved to be better than other D--P type criteria in certain range of Lode angle. The criterion was compiled into a finite difference package FLAC3D by user-subroutine, and was used to analyze the stability of a slope by strength reduction method. The predicted slope safety factor from the proposed criterion agrees well with that by Spencer method, and it is more accurate than that from classic D-P criteria.

Experimental evaluation on well pattern adaptability of ultra-low permeability reservoir using sandstone flat model

As for ultra-low permeability reservoir,the adaptability of common nine-spot well pattern is studied through large-scale flat models made by micro-fractured natural sandstone outcrops.Combined with non-linear porous flow characteristics,the concept of dimensionless pressure sweep efficiency and deliverability index are put forward to evaluate the physical models' well pattern adaptability.Through experiments,the models' pressure distribution is measured and on which basis,the pressure gradient fields are drawn and the porous flow regions of these models are divided into dead oil region,non-linear porous flow region,and quasi-linear porous flow region with the help of twin-core non-linear porous flow curve.The results indicate that rectangular well pattern in fracture reservoirs has the best adaptability,while the worst is inverted nine-spot equilateral well pattern.With the increase of drawdown pressure,dead oil region decreases,pressure sweep efficiency and deliverability index increase; meantime,the deliverability index of rectangular well pattern has much more rational increase.Under the same drawdown pressure,the rectangular well pattern has the largest pressure sweep efficiency.

A Simple Model for Earthquake Instability

Based on the heterogeneity of fault plane strength,the macro rupture process of a fault plane can be treated as the rupture accumulation process of local micro-elements in the fault surface.Assuming that the strength of the local micro-elements follows the Weibull probability distribution,the macro-fault constitutive relationship of the complete load-deformation process is derived from a statistical mechanics viewpoint.Applying a one-dimensional earthquake mechanics model and using far-field displacement a as the control variable,the problem of earthquake instability is investigated by employing the stability theory.The results show that the system stiffness ratio(stiffness ratio of fault to surroun-ding rock) β is the important parameter that affects the occurrence of earthquakes.Earthquake instability occurs only when β < 1,and the sudden stress jump appears at the displacement turning point of the equilibrium path curve.The expression of three important parameters for earthquakes(fault half-dislocation distance after earthquake,earthquake stress drop and elastic energy release) is also given.When β≥1,the earthquake does not occur and the fault only slips slowly without an earthquake.