Undrained monotonic shear behavior of marine soft clay after long-term cyclic loading     

Lin Guo  Hongxu Jin  Li Shi 《Marine Georesources & Geotechnology》2020,38(7):854-866

Abstract

In the coastal area, nearshore and offshore structures have been or will be built in marine soft clay deposits that have experienced long-term cyclic loads. Therefore, the mechanical behavior of marine clay after long-term cyclic loading needs to be investigated. In this research, a series of monotonic and cyclic triaxial tests were carried out to investigate the postcyclic mechanical behavior of the marine soft clay. The postcyclic water pore pressure, shear strength and secant stiffness are discussed by comparing the results with the standard monotonic test (without cyclic loading). It is very interesting that the postcyclic behavior of marine soft clay specimen is similar to the behavior of overconsolidated specimen, that is, the specimen shows apparent overconsolidation behavior after long-term cyclic loading. Then relationship between the overconsolidation ratio and the apparent overconsolidation ratio is established on the basis of the theory of equivalent overconsolidation. Finally, a validation formula is proposed which can predict the postcyclic undrained shear strength of marine soft clay.  相似文献   

Orbital control on cyclical organic matter accumulation in Early Silurian Longmaxi Formation shales     

Siding Jin  Hucheng Deng  Xing Zhu  Yan Liu  Sibing Liu  Meiyan Fu 《地学前缘(英文版)》2020,(2):533-545

High resolution(939 samples)total organic carbon content(TOC)analyses were conducted on the Shuanghe Section of^152.6 m in the Changning area,Sichuan Basin.The sampling section was divided into two units considering the distinct-different deposit environment and sediments accumulation rate.The lower part(Unit 1)and the peer part(Unit 2)with high resolution sample spacing(0.08–0.4 m)enables the identification of the precession cycle in two sedimentary sequences with distinct different sedimentary accumulation rate.MTM Power spectral analyses on untuned TOC series reveals significant peaks exceeding above the 95%confidence level and shows that both Unit 1 and Unit 2 have recorded Milankovitch cycles of 405 kyr long eccentricity,short eccentricity,obliquity and precession.The floating astronomical time scale(ATS)was constructed on the Shuanghe Section in the Early Silurian(~439.673–444.681 Ma),and which was calibrated by 405 kyr long eccentricity cycles.The total duration of the Wufeng and Longmaxi shales is 5.01 Myr.The floating ATS used for estimating the duration of the graptolite zones and each stage in the study interval.Finally,we postulated two models that could verify the linkage between orbital cycle and organic accumulation.To make sure whether productivity or preservation is the main factor that under long eccentricity control,the phase correlation between the obtained filtered signal and the theoretical orbital solution should be made clear in the further research.  相似文献   

钛同位素地球化学综述     

赵新苗  唐索寒  李津  朱祥坤  王辉  李志汉  张宏福 《地学前缘》2020,27(3):68-77

随着分析技术的进步,非传统稳定同位素体系在地球化学、天体化学和生物地球化学等研究领域的应用日益广泛。钛(Ti)是一个非常重要的过渡族金属元素,在地球和其他类地球行星中广泛存在。但是由于Ti是一种难熔的、流体不活动性元素,高温地质过程中Ti同位素分馏很小。人们对Ti同位素体系的地球化学应用的关注相对其他非传统稳定同位非常有限。而近年来,随着化学纯化方案的优化以及双稀释剂方法的改进和仪器质谱性能的提高,Ti同位素组成的高精度测试已经能够实现。天然样品中Ti同位素组成的变化随之得以发现,使得学者们能够利用这一新的稳定同位素体系来解决与高温和低温地球化学相关的问题。很快Ti同位素体系地球化学研究成为当前国际地质学界的前沿研究课题和新的发展方向之一。本文首先在简要介绍Ti元素和Ti同位素体地球化学性质的基础上,介绍了Ti元素化学分离和Ti同位素分析方法。随后笔者总结了已有的不同类型球粒陨石和地球样品的质量相关Ti同位素组成研究结果,对硅酸盐地球的Ti同位素组成做了初步评估。前人对高温地质样品的Ti同位素组成研究初步探明Ti同位素在岩浆演化过程,例如部分熔融和结晶分异等重要地质过程中的分馏行为。笔者在此基础上探讨了结晶分异过程中引起Ti同位素分馏的主要控制因素,指出Ti同位素是潜在的研究岩浆演化过程的新工具。最后笔者探讨了Ti同位素地球化学未来的发展方向,以加速我国在Ti同位素地球化学方面的应用研究。  相似文献   

2020年云南省巧家县M_S 5.0地震强震动记录初步分析     

赵昆  林国良  杨黎薇  崔建文 《地震地磁观测与研究》2020,41(3):200-208

2020年5月18日云南省巧家县发生M_S5.0地震,中国数字强震动台网的13个强震台站和昭通简易烈度计示范项目建设的43个烈度计台站,共接收168条强震动记录,经常规处理,绘制震区加速度峰值等值线图,并与云南地区常用地震动衰减关系进行对比,分析加速度峰值较大的几个台站频谱特性,计算地震动能量持时,讨论中小地震中高加速度峰值/低震害现象的成因,得到以下结论:(1) PGA等值线图形状较为平滑,其长轴呈NW—SE向展布;(2)云南地区常用地震动衰减关系预测值总体衰减趋势与观测值一致,但在近场(0—30 km)时,预测值基本偏小;(3)加速度峰值较大的几个台站记录主频集中在1—5 Hz;(4)小河镇台记录的能量持时较短,说明能量衰减较快,属脉冲型记录,不会对建筑物造成较大破坏。  相似文献   

土石混合体分形几何特征与强度演化特征     

曾晋 《地质与勘探》2020,56(3):590-596

针对土石混合体的结构性特点,以含石量为20%、30%、40%、50%、60%的土石混合体为研究对象,基于多重分形原理研究多重分形特征,研究分形维数与强度之间的关系。研究表明,土石混合体具有双重分形特征,不同尺度条件下具有不同分形指标,包括块石粒度、土体粒度以及平均粒度等分形维数,与含石量相关。单轴压缩试验表明,抗压强度随含石量增加呈现先增大后减小的趋势,根据单维分形特征,确定最优含石量约为40%。建立了含石量、不同分形维数指标与抗压强度之间的关系,分析了双重因素综合影响下抗压强度的变化特征,确定了含石量与分形维数之间存在最优区域。  相似文献   

Enhancement of backtracking search algorithm for identifying soil parameters     

Yin-Fu Jin  Zhen-Yu Yin 《国际地质力学数值与分析法杂志》2020,44(9):1239-1261

In this paper, an enhanced backtracking search algorithm (so-called MBSA-LS) for parameter identification is proposed with two modifications: (a) modifying the mutation of original backtracking search algorithm (BSA) considering the contribution of current best individual for accelerating convergence speed and (b) novelly incorporating an efficient differential evolution (DE) as local search for improving the quality of population. The proposed MBSA-LS is first validated with better performance than the original BSA and some other typical state-of-the-art optimization algorithms on a benchmark of soil parameter identification in terms of effectiveness, efficiency, and robustness. Then, the efficiency of the MBSA-LS is further illustrated by two representative cases: identifying soil parameters from both laboratory tests and field measurements. All comparisons demonstrate that the proposed MBSA-LS algorithm can give accurate results in a short time. Finally, to conveniently solve the problems of parameter identification, a practical tool ErosOpt for parameter identification is developed by integrating the proposed MBSA-LS and some other efficient algorithms for readers to conduct the parameter identification using optimisation algorithms.  相似文献   

渭河盆地地温场分布规律及其控制因素     

任战利  刘润川  任文波  祁凯  杨桂林  崔军平  杨鹏  张园园 《地质学报》2020,94(7):1938-1949

本文以渭河盆地地温场为研究对象,在收集补充新地热井资料及分析测试样品的基础上,通过盆地深部结构、构造特征、地温场特征、热储层特征、地热资源量等分析,建立了盆地不同岩性岩石热导率与深度关系图版,确定了盆地地温场变化规律及地热田控制因素,提出了渭河盆地地热田形成模式。评价了盆地地热资源有利区,为盆地后续的开发利用提供了理论支持。研究认为渭河盆地热地温梯度分布在2.34～5.85℃/100m之间,平均地温梯度为3.50℃/100m,代表性大地热流68.33mw/m~2,地温梯度及不同深度地层温度具有东高西低、南高北低的特点。热导率总体上具有随深度的增加,逐渐增大的规律,热导率随深度增加主要受压实程度增强控制。相同深度条件下泥岩热导率最低,砂岩热导率居中、白云岩热导率最高。渭河盆地主要为层状地热田,盆地内地热通过热传导及热对流两种方式进行传递,以热传导为主。渭河盆地地热资源丰富,热储层可分为三种类型:①新生界砂岩孔隙型;②下古生界碳酸盐岩岩溶型;③断裂型。渭河盆地地热资源有利区主要分布于西安凹陷、固市凹陷。盆地地温场及地热田分布与莫霍面、软流圈上隆、岩石圈厚度减薄的深部背景密切相关,主要受地热传导和深大断裂热对流控制,是岩石圈深部结构、盆地构造、基底岩性、储盖组合等多因素共同作用下形成的。最后结合当前渭河盆地地热资源开发利用现状及存在问题,提出了地热开发利用建议。  相似文献   

基于层次分析法和模糊数学相结合的甘肃东乡八丹沟泥石流易发性评价          下载免费PDF全文

崔志超  王俊豪  崔传峰  潘国营 《中国地质灾害与防治学报》2020,31(1):44-50

八丹沟位于甘肃东乡县,近年来多次发生泥石流,对流域内居民生命财产造成了巨大的威胁,因此对八丹沟泥石流易发性评价是非常必要的。本文在详细分析八丹沟流域特征和动力学特征的基础上,选取了11个评价因子作为八丹沟泥石流易发性评价的指标,利用层次分析法对各个因子赋予权重,并且构建模糊数学综合评价模型对八丹沟泥石流进行易发性评价。结果表明:八丹沟泥石流爆发频率20年、50年、100年的的易发性为中易发,应加强防范并采取合理的防治措施,保证当地居民的生命财产安全。  相似文献   

海南典型热带海草床4种代表性鱼类的生长特征及其对海草资源量变化的响应     

陈启明  刘松林  张弛  崔黎军  江志坚  吴云超  黄小平 《热带海洋学报》2020,39(5):62-70

文章以海南岛新村湾、黎安港和潭门港海草床为研究区域, 选取褐篮子鱼(Siganus fuscessens)、点斑篮子鱼(Siganus guttatus)、四带牙鯻(Pelates quadrilineatus)和细鳞鯻(Terapon jarbua) 4种代表性鱼类为研究对象, 分析其体长与体质量的关系, 并探讨4种鱼类对海草资源量变化的响应。结果表明, 除栖息于潭门港海草床的4种鱼为负异速生长, 其他区域海草床的鱼类均为正异速或等速生长; 4种鱼的体质量生长速率(即异速生长因子b)和肥满度呈现黎安港>新村湾>潭门港的趋势, 并与3个海草床的海草覆盖率、密度和生物量的变化趋势一致; 推测海草资源量下降可能增加鱼类的被捕食压力和减少食物来源, 从而导致生活于海草床的代表性鱼类生长速率下降。  相似文献   

Flexural performances of prestressed high strength concrete piles reinforced with hybrid GFRP and steel bars     

Ping Wu  Yang Guo  Dayong Zhu  Weiliang Jin  Zhenhua Zhang  Rongzhu Liang 《Marine Georesources & Geotechnology》2020,38(5):518-526

Abstract

This study developed prestressed high-strength concrete (PHC) piles reinforced with high-strength materials (glass fiber-reinforced polymer (GFRP) bars) for flexural performance enhancement. Flexural strengths and behaviors of PHC piles reinforced with hybrid GFRP and steel bars were experimentally investigated, respectively. Large-scale specimens with total lengths of 12,000?mm and diameters of 600?mm were constructed and tested under bending, accompanied by evaluation of effects of non-prestressed reinforcement type and longitudinal reinforcement ratio. J-factors were calculated to evaluate deformability of all the specimens. PHC piles reinforced with GFRP bars were demonstrated to have much higher flexural capacity than those reinforced with steel bars. Moreover, strains at the midspans of cross sections of all the specimens basically conformed to the assumption of plane section. Failure of PHC piles reinforced with GFRP bars was attributable to gradual concrete crushing, while that of PHC piles reinforced with steel bars resulted from steel yielding. Results of this study were expected to provide theoretical basis for wide engineering applications of PHC piles reinforced with hybrid GFRP bars and steel bars in marine structures.  相似文献