Discrete Element Modeling of Strength Properties of Johnson Space Center (JSC-1A) Lunar Regolith Simulant

This paper simulates the three-dimensional axisymmetric triaxial compression of JSC-1A lunar regolith simulant under lunar and terrestrial gravity environments under a wide range of confining pressures and relative densities. To accomplish this, the discrete element method (DEM), using Particle Flow Code In Three-Dimensional (PFC3D) software, was employed. The paper focuses on the peak and the critical state (CS) friction angles, which were predicted in the ranges of 35.4°–82.7° and 31.2°–79.8°, respectively, depending on the specimen density and confining pressure. A significant increase in peak and CS friction angles was predicted at near-zero confining pressure. The DEM results validated an empirical model that relates the peak friction angle with the CS friction angle, relative density, and mean effective stress at the CS. Comparison of DEM results with lunar in situ measurements of friction angle, from Apollo missions and other extraterrestrial laboratory experiments under a microgravity environment, shows a favorable agreement.     

Dynamic notched semi-circle bend(NSCB) method for measuring fracture properties of rocks:Fundamentals and applications

Rocks are increasingly used in extreme environments characterised by high loading rates and high confining pressures.Thus the fracture properties of rocks under dynamic loading and confinements are critical in various rock mechanics and rock engineering problems.Due to the transient nature of dynamic loading,the dynamic fracture tests of rocks are much more challenging than their static counterparts.Understanding the dynamic fracture behaviour of geomaterials relies significantly on suitable and reliable dynamic fracture testing methods.One of such methods is the notched semi-circle bend(NSCB) test combined with the advanced split Hopkinson pressure bar(SHPB) system,which has been recommended by the International Society for Rock Mechanics and Rock Engineering(ISRM) as the standard method for the determination of dynamic fracture toughness.The dynamic NSCB-SHPB method can provide detailed insights into dynamic fracture properties including initiation fracture toughness,fracture energy,propagation fracture toughness and fracture velocity.This review aims to fully describe the detailed principles and state-of-the-art applications of dynamic NSCB-SHPB techniques.The history and principles of dynamic NSCB-SHPB tests for rocks are outlined,and then the applications of dynanic NSCB-SHPB method(including the measurements of initiation and propagation fracture toughnesses and the limiting fracture velocity,the size effect and the digital image correlation(DIC) experiments) are discussed.Further,other applications of dynamic NSCB-SHPB techniques(i.e.the thermal,moisture and anisotropy effects on the dynamic fracture properties of geomaterials,and dynamic fracture toughness of geomaterials under pre-loading and hydrostatic pressures) are presented.     

Effect of Rock Trenching Vibrations on Nearby Structures

Trenching to install deep gravity sewers and drains in medium-to high-strength rock requires large and heavy rock trenchers that produce high levels of vibrations that may affect the structural integrity of nearby utilities and buildings. Although not every vibration causes damage, owners often believe that their structures have been harmed by rock excavation. The resulting disputes can waste a great deal of time and money. In an effort to reduce structural damage and associated disputes, this paper provides guidelines for the safe distance between rock trenchers and nearby buildings and underground structures. Vibration data at different distances from the trencher centerline were collected from five trenching projects in Northwest Ohio. The data analysis suggests a moderate relationship between the vibration level and the distance from the source of vibration. In addition, the risk of damage to nearby structures dissipates significantly and quickly as the distance from the point of excavation increases. Rock trenching should not take place closer than 1.50?m for buried structures and 1.00?m for residential buildings. Beyond this safe distance, damage to nearby structures should not take place.     

中国地热能源开发的机遇与挑战

作为低碳新能源家族的一员,地热能源开发已经被提到国家应对气候变化和防治雾霾的议事日程.本文回顾了地热资源开发历史,分析了我国地热能源开发落后的原因,认为要切实改变当前的落后局面,不仅需要产业界克服工程技术方面的障碍,而且需要地热学界重新评估我国包括水热系统和干热岩在内的地热资源分布格局,更需要政府主管部门调整目前偏重西部边远地区而轻视能源需求旺盛的东部地区的地热能源开发指导方针.