Seismic behavior of geosynthetic-reinforced retaining walls backfilled with cohesive soil

This study investigates the seismic performance of geosynthetic-reinforced modular block retaining walls backfilled with cohesive, fine grained clay-sand soil mixture. Shaking table tests were performed for three ½ scaled (wall height 190 cm) and ¼ scaled model walls to investigate the effects of backfill type, the influence of reinforcement length and reinforcement stiffness effects. The El Centro and Kobe earthquake records of varying amplitudes were used as base acceleration. Displacement of the front wall, accelerations at different locations, strains on the reinforcements, and the visual observations of the facing and the backfill surface were used to evaluate the seismic performance of model walls. The model walls were subjected to rigorous shaking and the walls did not exhibit any stability problems or signs of impending failure. The maximum deformations observed on the models with cohesive backfill was less than half of the deformation of the sand model. The load transfers between the geogrid and cohesive soil was comparable to that of sand and hence the needed reinforcement length was similar as well. As a result; the model walls with cohesive backfills performed within acceptable limits under seismic loading conditions when compared with granular backfilled counterparts.     

我国环境土壤中的重要超铀核素分布

Pu、Am、Np是3种重要的超铀核素，环境中的这些核素主要来源于人类的核活动，包括大气层核武器试验、核设施排放和核事故释放等。这些超铀核素不仅具有放射性，还兼具化学毒性。我国地域辽阔，环境土壤类型丰富，在当前核电事业蓬勃发展的背景下，建立和扩大我国环境土壤中这些重要超铀核素的“准本底”数据库是辐射环境安全评价的重要组成部分，也是公众关心的热点问题。近30多年来，研究人员对我国不同环境土壤中这几种超铀核素从不同科学角度开展了调查测量研究。本文对此进行整理和分析，对我国环境土壤中这些重要超铀核素（主要是Pu核素，还包括241Am和237Np）的来源、浓度水平和分布特征进行讨论和综述，为辐射环境安全评价奠定基础。     

多氢酸酸化反应特征及动力学

利用自制多氢酸液XS-1进行静态岩粉溶蚀与岩心流动实验,通过SEM、ICP等实验考察了多氢酸的缓速性与预防二次沉淀性能,并研究了多氢酸与岩心反应动力学特性。结果表明,XS-1多氢酸液具有良好的缓速与预防二次沉淀性能,反应后残酸的极限浓度为0.296 1 mol/L,酸液有效作用时间为6~7 h。在该多氢酸体系下岩心渗透率提高至4.15倍,在此条件下以酸岩反应动力学参数模型建立动力学方程,反应速率比同条件下普通酸液小,进一步证明多氢酸具有一定的缓速性。     

海水中134Cs、137Cs和60Co的联合分析

建立了小体积海水中¹³⁴Cs、¹³⁷Cs和⁶⁰Co的联合分析方法，确定了最佳实验条件。采用磷钼酸铵富集法对海水中放射性铯进行浓集后，其上清液利用氢氧化钴沉淀载带海水中的⁶⁰Co，用γ能谱仪进行测量。结果表明：该法对海水中放射性¹³⁴Cs、¹³⁷Cs和⁶⁰Co的回收率分别为87%~95%、87%~95%和89%~93%，检测限分别为0.048、0.051、0.046 Bq/L。另外，对2017年IAEA国际比对（IAEA-RML-2017-01）海水样品中的¹³⁴Cs、¹³⁷Cs和⁶⁰Co进行分析测量，核素分析结果的最终评价均为“通过”，验证了本实验室采用的¹³⁴Cs、¹³⁷Cs和⁶⁰Co联合分析方法的可行性和可靠性，为今后该方法在常规海洋环境放射性监测中的应用推广奠定了基础。     

Experimental investigations and constitutive modeling of cyclic interface shearing between HDPE geomembrane and sandy gravel

This paper presents the results of experimental investigations and constitutive modeling of cyclic interface shearing between HDPE geomembrane and cohesionless sandy gravel. A series of cyclic interface shear tests was performed using a large-scale cyclic shear apparatus with servo controlled system. Particular attention was paid to the influences of the amount of shear-displacement amplitude, number of cycles, shear rate and the normal pressure on the mechanical response. The experimental results show that the path of the shear stress against the cyclic shear displacement is strongly non-linear and forms a closed hysteresis loop, which is pressure dependent, but almost independent of the shear rate. For small shear-displacement amplitudes, the obtained damping ratio is significantly greater than zero, which is different to the behavior usually observed for cyclic soil to soil shearing. In order to describe the pressure dependency of the hysteresis loop using a single set of constitutive parameters, new approximation functions are put forward and embedded into the concept of the Masing rule. Further, a new empirical function is proposed for the damping ratios to capture the experimental data for both small and large cyclic shear-displacement amplitudes. The included model parameters are easy to calibrate and the new functions may also be useful in developing enhanced constitutive models for the simulation of the cyclic interface shear behavior between other geosynthetics and soils.     

Numerical verification of the continuous calculation method for tip stress during the driving process of the dynamic penetration test

This paper presents a calculation method for obtaining the continuous variation in stress between the tip and the soil during dynamic penetration tests, particularly in the case of using the Panda 3® penetration testing device. The originality of the method is that the tip stress can be computed continuously throughout the driving process. For each impact of the hammer on the penetrometer, data are recorded by sensors located at the top of the apparatus. Then, the stress at the tip and the displacement of the apparatus are calculated with a method based on the propagation of waves in the device. A three-dimensional numerical model of the penetration test, based on the Panda 3® specifications and using the discrete element method (DEM), is proposed in this paper. The purpose of the simulations is to validate the calculation method by comparing the curves of the tip stress versus the penetration distance obtained in two different ways, the first being the distance directly observed at the tip and the second being the distance calculated from the data recorded at the top of the penetrometer, as with the experimental device. The entire apparatus is represented, including the hammer, the rod, and the tip, and is driven into the model soil. The calculation method is applied, and the results are compared to the actual response of the soil to the driving of the penetrometer directly at the tip, which can be obtained with the numerical model. The responses are found to be very similar, confirming the theoretical framework and its underlying assumptions. This method is applied to dynamic penetration tests and provides the opportunity to obtain mechanical parameters other than the tip resistance from the tests.     

基于组合双向拍卖的云资源调度方法

针对跨数据中心的资源调度问题，提出了一种基于组合双向拍卖（PCDA）的资源调度方案。首先，将云资源拍卖分为三个部分：云用户代理报价、云资源提供商要价、拍卖代理组织拍卖；其次，在定义用户的优先级及任务紧迫度的基础上，在拍卖过程中估算每一个工作发生的服务等级协议（SLA）违规并以此计算云提供商的收益，同时每轮竞拍允许成交多项交易；最终达到根据用户等级合理分配云资源调度的效果。仿真实验结果表明该算法保证了竞拍成功率，与传统一次拍卖成交一项的组合双向拍卖方案相比，PCDA在竞拍时间段产生的能耗降低了35.00%，拍卖云提供商的利润提高了约38.84%。     

高低温循环及对称冲击耦合加载下 炸药的安全性研究

基于一级轻气炮加载装置，研究了高低温循环及对称冲击耦合加载下某黑索今(RDX)基含Al炸药的安全性，计算了缺陷处的内能等参数。结果表明:高低温循环后，炸药试样出现可见的孔隙。对称碰撞加载后，不经高低温循环的试样未发生点火，应力加载峰值为835 MPa，加载时间为35 μs；而经历高低温循环的试样出现点火，点火前应力为242 MPa，加载时间11 μs。高低温循环所产生的缺陷是导致炸药点火的重要原因。     

圆柱形带壳推进剂装药枪击响应特性

为研究某圆柱形带壳推进剂装药的枪击响应特性,设计了一种12.7 mm子弹撞击试验。利用高速摄影机记录带壳装药在子弹撞击下的响应过程,并测试不同距离、方位处的空气超压及壳体破片速度,同时进行带壳装药在理想爆轰条件下的数值计算,得到了带壳装药的能量释放率。一共开展了四次圆柱形带壳装药的枪击试验,前三次装药发生了爆燃反应,第四次几乎无反应。结果表明:子弹撞击位置对圆柱形带壳装药的反应和能量释放率有较大影响,当子弹垂直入射带壳装药轴线后,推进剂发生点火、冒烟、熄火和低压燃烧的时序响应,其相对能量释放率为1.146%;而当子弹撞击位置偏离轴线一定距离时,推进剂几乎无反应,其相对能量释放率仅为0.473%;推进剂的反应对壳体破片有加速效应,带壳装药发生爆燃反应时的破片速度可达428.6 m·s~(-1),而几乎无反应时的最高破片速度仅有70.1 m·s~(-1)。