岩体的加、卸载状态与能量的分配关系

岩体是流变体,在高地应力的长时间作用下其内部非均匀应力随着时间自我松弛,逐渐趋向于静水压力状态。在这样的状态下,虽然其体积仍维持弹性,但丧失了进一步抵抗剪切变形的能力,处于流动的状态,其能量储存具有体积的特征。采用平面压缩模型,研究岩石在不同应力水平长期作用下的变形性状及能量分配关系,给出在快速卸荷条件下发生自持续动力断裂破坏条件,以期揭示深部岩体初始地应力水平（能量在体变及形变上的分配关系）对卸荷条件下岩体运动过程中表现的惯性、黏性及弹塑性变形的影响规律,为建立深部岩体加卸荷本构关系打下基础。     

Grain size and transport characteristics of non-uniform sand in aeolian saltation

Size frequency distributions of sediment particles in a wind tunnel containing a bed of non-uniform sand are investigated by re-interpreting existing experimental data using particle-size analysis. Each particle sample is classified into one of eight groups according to its size grading. The analysis reveals that the modal shape of the particle-size frequency distributions of the saltating sand at different elevations or longitudinal distances is similar to that of the mixed sand in the bed once the boundary layer is fully developed. The standard deviation of the grain-size frequency distribution increases with increasing elevation above the bed then stays constant, whereas its skewness decreases. The mean grain size decays exponentially with elevation. The aeolian sand mass flux is determined for each size grading at different vertical and horizontal measurement locations. The vertical profile of aeolian horizontal mass flux depends on the size grading. The distribution of the sand transport rate according to the mean grain size in each grading fits the normal distribution. A parameter w_i is defined to reflect the likelihood of saltation for sand particles of the i-th size grading, and the mean sand size corresponding to the maximum value of w_i is found to be 0.2 mm. In addition, wind velocity strongly influences the magnitudes of the particle-size distribution and the sand mass flux distribution in both vertical and longitudinal directions.     

中小体质指数患者腹部能谱CT血管成像双低扫描方案优化

目的:探讨腹部能谱CT血管成像双低扫描方案的可行性和应用价值。方法:前瞻性收集疑腹部病变需行全腹血管CT成像BMI≤25的患者367例。首先按照首诊时间分实验组和对照组,再根据体质指数(BMI)分成两个亚组,BMI≤22为实验1组或对照1组,22vol,对比剂碘含量及肾动脉图像质量评分。结果:腹主动脉CT值:实验1组、实验2组分别为(601.75±67.11)HU和(459.87±49.17)HU,对照1组、对照2组分别为(436.55±84.12)HU和(432.15±87.68)HU,实验1组>对照1组,差异具有统计学意义(P值<0.05)。CNR:实验1组、实验2组分别为(19.01±2.66)和(15.24±2.52),对照1组、对照2组分别为(12.42±2.68)和(10.24±2.22),实验1组>对照1组,实验2组>对照2组,差异均有统计学意义(P<0.05)。FOM:实验1组、实验2组分别为(69.72±29.75)和(33.44±8.87),对照1组、对照2组分别为(20.08±8.05)和(15.21±10.12),实验1组>对照1组,实验2组>对照2组,差异均有统计学意义(P值<0.05)。CTDI_vol:实验1组、实验2组为(5.41±1.38)mGy和(6.98±1.49)mGy,对照1组、对照2组为(9.87±2.97)mGy和(12.02±5.21)mGy,实验1组较对照1组降低45.19%(4.46/9.87)、实验2组较对照2组降低41.93%(5.04/12.02)。实验组、对照组的碘对比剂浓度分别为270mgI/mL和350mgI/mL,实验组降低22.86%(80/350)。肾动脉血管评分:实验1组、实验2组分别为(4.61±0.47)和(4.22±0.59),对照1组、对照2组分别为(3.73±0.72)和(3.93±0.66),实验1组>对照1组,差异具有统计学意义(P<0.05);实验2组与对照2组间差异无统计学意义(P值>0.05)。结论:针对中小体质指数患者,双低扫描方案腹部能谱CT血管成像在保证图像质量的同时可以大幅度地降低辐射剂量和碘对比剂含量,适于推广临床应用。      

基于紧凑存储的任意四边形网格有限元法地震波场数值模拟

采用有限元法精确模拟复杂介质条件下的地震波场,一般采用三角单元,但在节点数相同的情况下,三角单元的计算精度不如矩形单元高,采用三角单元模拟复杂界面时,编制确定结构刚度矩阵非零元素位置的程序也较为麻烦。采用矩形单元离散含有倾斜或起伏界面的地质模型时,无法避免绕射噪声,若加密网格又会增加计算量。为此,本文基于任意四边形单元模拟声波的传播,在倾斜或起伏界面条件下,可以有效避免因离散引起的“阶梯状”界面,在不增加计算量以及内存占用的前提下,有效地消除离散绕射噪声。采用对角的集中质量矩阵代替一致质量矩阵,避免矩阵的求逆运算,从而提高显式有限元法的计算效率;对结构刚度矩阵采用紧凑存储格式,每一行需要存储的元素最多为5个,同时零元素不参与运算,既减少内存的占用,又极大地提高计算效率。      

黑洞大型古地下洞室群工程地质条件及岩体稳定性分析

位于浙江天台县蟹山山体内的黑洞洞室群, 以其优越的工程地质条件和完整的岩体结构, 自隋朝以来成为大型古地下采石场。洞室群包括总面积达24 000 m²的21个洞室, 其长轴方向基本沿两组主要地质结构面走向展布。研究显示:总体采石层系上白垩统塘上组(K₂t)第6层灰白色含玻屑熔结凝灰岩;岩体质量指标Q值计算结果为53(I级)。按现代地下洞室设计理念, 其长期稳定最大跨度应不大于50 m, 但实际上5号洞最大跨度达81 m, 可望成为地下人工岩石单洞跨度之最。现场调查发现, 古人在蟹山山脚残留多处地质探洞。古代工匠在洞室开挖过程中遇到断层破碎带时, 采用了近垂直、小断面、高台阶穿越技术方法, 有效保证了不良地质体中无支护开采的安全性和长期稳定性, 这对现代地下工程具有借鉴和工程类比意义。     

Geochemical behavior during mineralization and alteration events in the Baiyinchang volcanic-hosted massive sulfide deposits,Gansu Province,China

The Zheyaoshan deposit is the largest within the Baiyinchang (BYC) volcanic-hosted massive sulfide (VHMS) district, located in the northern Qilian orogenic belt of North China. The deposit is hosted by quartz keratophyre tuffs, with wall-rock alteration mainly comprising chlorite, sericite, quartz, pyrite and epidote. Mineral assemblages within the altered host rocks can be divided into a sericite-quartz-dominant assemblage (sericite-silicified zone), a chlorite-dominant assemblage (chlorite-dominant zone) and a pyrite-dominant assemblage (mineralized zone) based on geochemical analysis and alteration characteristics. We have conducted detailed processing and critical analysis of the geochemical data of both the altered and least-altered host rocks in order to investigate the problem of closure in the geochemical dataset to eliminate the influence that each component has on the other in terms of mass change, and have applied the standardized method of the mass change calculation to analyze this data. The results show that: (1) the sericite-silicified zone formed along fissures due to the ingress of hydrothermal fluids, with MnO₂, Na₂O and CaO being mobilized into the hydrothermal fluids leached and MgO, Fe₂O₃, SiO₂, K₂O, BaO deposited. Additionally, Ag, Cu and chalcophile elements (Ag, As and Bi) were enriched while Pb, Zn and large ion lithophile elements (LILEs) (Cs, Sr, Eu, Be) were mobilized into hydrothermal fluids; (2) the physiochemical conditions and pH levels of the hydrothermal fluids changed during sericitization, with MgO, Fe₂O₃, BaO being further enriched and MnO, Na₂O, CaO further depleted, leading to formation of chlorite and the initial precipitation of metallogenic the (Cu, Zn, Pb) and chalcophile elements (Ag, As, Bi); (3) the negative Eu anomaly was mainly due to its strong activity when Eu is mobilized into the hydrothermal fluids during since plagioclase break-down during the sericite-silicification process; (4) AI and CCPI values gradually increase towards the orebody. The chlorite-dominant assemblage and sericite-quartz-dominant assemblage on the periphery of the chlorite-dominant zone can all be used as vectors towards the volcanic massive sulfide orebody and for regional-scale mineral exploration. Either leached elements or enriched elements can be considered as significant indicator elements and as prospective indicators for geochemical exploration within the BYC district. The Eu anomaly may be especially useful as an indicator for distinguishing the least-altered rocks which has great significance for exploration on the regional scale.     

Hybrid finite-discrete element modelling of dynamic fracture and resultant fragment casting and muck-piling by rock blast

A state-of-the-art review is conducted to highlight the fracture mechanism in rock blast and advantages and limitations of various methods in modelling it. A hybrid finite-discrete element method (FEM-DEM) is implemented to simulate rock fracture and resultant fragment muck-piling in various blasting scenarios. The modelled crushed, cracked and long radial crack zones are compared with those in literatures to calibrate the hybrid FEM-DEM. Moreover, the hybrid modelling reproduces the rock fragmentation process during blasting. It is concluded that the hybrid FEM-DEM is superior to continuous and discontinuous methods in terms of modelling dynamic fracture of rock under blast-induced impact load.     

“Transverse Action” – A model benchmark exercise for numerical analysis of the Callovo-Oxfordian claystone hydromechanical response to excavation operations

The Callovo-Oxfordian claystone (COx) is considered as a potential geological formation to host an industrial radioactive waste repository in France. A detailed understanding of the thermo-hydro-mechanical (THM) behavior of the COx is a key issue for design of different repository structures and the safety calculations of the project. More particularly, numerical modeling of induced fracture networks around drifts excavated at the main level of the Andra’s Meuse/Haut-Marne Underground Research Laboratory (M/HM URL) and short and long term behavior of the COx around these drifts are of great interest. Several constitutive models have been developed/used in the framework of the R&D and simulation programs of Andra. A model benchmark exercise has been launched since 2012 to provide an overall view of the developed models regarding the in situ observations. In this view, two series of test cases, respectively at material point scale and at drift excavation scale are defined. Different kinds of constitutive models based on the elasto-visco-plasticity concept, continuum damage mechanics, the rigid block spring method and two-scale computational homogenized model (CHM) are used within this exercise. The obtained results show that accounting for material anisotropy and strain localization treatment techniques can improve the obtained results when elasto-visco-plastic models are used. Damage mechanics based approaches and methods accounting for discontinuities through discrete elements provide also interesting insights especially when fracturing processes must be modeled. However, more efforts are necessary to improve the robustness of these kinds of approaches in the complex context of COx response to excavation works.     

Numerical 3D modeling of the effects of strain rate and confining pressure on the compressive behavior of Kuru granite

This paper deals with numerical modeling of the compressive behavior of granite rock under high strain rate dynamic loading and wide range of confining pressure. For this end, a constitutive model based on damage mechanics and viscoplasticity for rock is formulated and implemented in explicit dynamics FEM. The viscoplastic part is based on a simple power law type yield criterion that incorporates the rate-dependency with a linear viscosity term. Moreover, a Rankine type of tensile cut-off is employed. The damage part of the model is formulated with separate scalar damage variables in tension and compression. The model is calibrated for Kuru granite and validated with the experimental data from dynamic compression tests at the strain rate of 600 1/s up to 225 MPa of confining pressure. The numerical simulations demonstrate that, despite the underlying continuum modeling approach, the model captures the correct experimental failure modes, including the transition from single-to-multiple fragmentation, as well as the dynamic compressive strengths at different confining pressures.