面向山洪预警的水雨情监测站网布设方法研究

山洪灾害是中国高频发、高死亡率的自然灾害之一。水雨情站网的合理布设及优化,有利于捕获区域暴雨、洪水情势变化的时空异质性,可显著提高中小流域山洪预警的精度,增强山洪灾害防御能力。本文以山洪灾害高发的福建省顺昌县为例,提出了面向山洪预警的水雨情站网布设方法。县内现状雨量和水位站网监测密度分别为37 km²/站和76 km²/站,主要分布在平原主干河流地区,山洪灾害重点防治区内站网布设不足,小流域暴雨山洪监测和预警能力较弱。针对上述问题,综合分析流域降雨时空特征、历史山洪灾害与山洪灾害预警预报需求,对研究区水雨情站网进行了合理性分析和布设研究,建议增设雨量站3座、水位站3座,其中一座水位站同时监测降雨过程,调整后县内雨量站和水位站的监测密度达到34 km²/站和68 km²/站。本文研究对山洪灾害高发区的水雨情站网布设具有参考和指导意义。     

自由落体式球形贯入仪在硬-软黏土中的贯入响应

自由落体贯入仪（free falling penetrometer,简称FFP）通过自由下落贯入土层中,由于其高效便捷的特性,越来越广泛地被应用于海底浅层土体原位勘察。采用耦合欧拉-拉格朗日（Coupled Eulerian Lagrangian,简称CEL）方法,进行了球形FFP在硬-软双层黏土中贯入的大变形有限元分析,考虑了土体的应变率和应变软化效应。与离心机试验、现场试验和数值模拟结果进行了对比,验证了模型的可靠性。分析了成层土对贯入过程的影响,发现FFP在贯入过程中上部硬黏土层形成空腔,且底部会伴随着土塞。通过广泛的变参数分析结果,拟合了球形FFP最终贯入深度与总能量之间的归一化表达式,建立了土体不排水抗剪强度、FFP直径和贯入速度与FFP在硬-软黏土层中最终贯入深度的关系。     

ND-CPT测量非均质地层密度剖面的研究

同位素密度静力触探仪（ND-CPT）是一种把同位素密度仪并入到静力触探仪的探头中,同时测量锥尖阻力、侧壁摩阻力、孔隙水压力和密度的新型原位测试仪器。根据ND-CPT测量的密度为 射线源和检测器之间回转椭球体内土体的平均密度 的原理,首先建立了可以计算回转椭球体内土体的平均密度 的后向散射模型和平均值模型,然后调查了ND-CPT贯入各种非均质地层时的测量密度 剖面与实际密度 剖面的区别,结果表明在地层分界处附近的测量密度 与实际密度 有较大差别,最后对ND-CPT在实际工程中测量的有明海底泥的测量密度 剖面进行了理解,得到了海底泥的实际密度 剖面。研究结果可为利用ND-CPT准确划分地层提供依据。     

Assessment of direct CPT and CPTU methods for predicting the ultimate bearing capacity of single piles

Twelve methods to determine axial pile capacity directly based on cone penetration test (CPT) and piezocone penetration test (CPTU) data are presented, compared and evaluated. Analyses and evaluation were conducted on three types of piles of different size and length. All the tested piles have failed at the end of static load test. Both the CPT methods and the CPTU methods were used to estimate the load bearing capacities of the investigated piles (Q_p). The static load test was performed to determine the measured load bearing capacities (Q_m). The pile capacities determined through different methods were compared with the measured values obtained from the static load tests. Two criteria were selected as bases of evaluation: the best fit line for Q_p versus Q_m and the arithmetic mean and standard deviation for the ratio Q_p/Q_m. Results of the analyses showed that the best methods for determining pile capacity are the two CPTU methods. Furthermore, the CPTU method is simple, easy to apply, and not influenced by the subjective judgements of operating staff. Therefore, it is quite suitable for the application in pile engineering practice.     

Modelling the Cone Penetration Test in sand using Cavity Expansion and Arbitrary Lagrangian Eulerian Finite Element Methods

The paper considers two techniques to model the Cone Penetration Test (CPT) end resistance, q_c in a dense sand deposit using commercial finite element programmes. In the first approach, Plaxis was used to perform spherical cavity expansion analyses at multiple depths. Two soil models, namely; the Mohr–Coulomb (MC) and Hardening Soil (HS) models were utilized. When calibrated using simple laboratory element tests, the HS model was found to provide good estimates of q_c. However, at shallow depths, where the over-consolidation ratio of the sand was highest, the relatively large horizontal stresses developed prevented the full development of the failure zone resulting in under-estimation of the q_c value. The second approach involved direct simulation of cone penetration using a large-strain analysis implemented in Abaqus/Explicit. The Arbitrary Lagrangian Eulerian (ALE) technique was used to prevent excessive mesh deformation. Although the Druker–Prager soil model used was not as sophisticated as the HS model, excellent agreement was achieved between the predicted and measured q_c profiles.     

现代多功能孔压静力触探及在软土地区测试要点

简要分析了我国CPT技术与国际CPT技术的差距,介绍了现代多功能CPTU测试系统、应用于CPT的传感器技术的发展、现代多功能CPTU技术的优势及SCPTU、RCPTU、VisCPT技术的新应用。同时,分析了软土地区多功能CPTU测试技术要点,包括测试计划的制定、孔压系统的饱和与标定、测试精度的保证、负值的分析及探头的保养等问题。     

利用qc,D50评价砂土地震液化势研究

本文根据国内外地震液化调查资料，建立了利用双桥静力触探锥头阻力ｑｃ和平均粒径Ｄ５０判别地震液化势的半经验性方法。这种方法对评价地震液化势是颇为有效的。     

1976年唐山大地震CPT液化数据库检验

1976年唐山大地震引发了范围广、灾害重的液化震害。铁道部科学研究院等单位于1977、1978年对液化场地进行了单桥静力触探测试。但单桥静力触探在数据指标方面存在缺陷,与国际标准不接轨。中国地震局工程力学研究所与东南大学等单位于2007年对上述唐山地区部分测点再次进行了孔压静力触探（CPTU）测试。本文通过对比2次静力触探数据,利用Robertson土质分类图,进行新孔压静力触探数据土类分层检验,将土类检验结果与单桥静力触探测试时钻孔柱状图进行对比,发现大部分测点土层土类均能较好对应,现场测试力学指标沿深度变化趋势较相符,仅剔除了错误点T2、T3。对所有测点选定液化层,分别建立基于单桥静力触探测试比贯入阻力p_s和基于孔压静力触探测试锥尖阻力q_c的液化数据库。利用基于静力触探测试（CPT）的我国规范液化判别方法检验了2个数据库,发现对单桥静力触探测试的数据库液化判别效果好,而对孔压静力触探测试的数据库液化判别效果较差,说明经过30年的时间,土层液化可能已发生较大改变。因此,基于孔压静力触探测试的液化数据库可靠性较低,基于该数据库对液化判别方法进行改进意义较小。     

The intensification of the East Asian winter monsoon contributed to the disappearance of Cedrus (Pinaceae) in southwestern China

Climate change during the Quaternary played an important role in the distribution of extant plants. Herein, cone scales of Cedrus (Pinaceae) were uncovered from the Upper Pliocene Sanying Formation, Longmen Village, Yongping County of Yunnan Province in southwestern China. Detailed comparisons show that these fossils all belong to the genus Cedrus (Pinaceae), and a new species is proposed, Cedrus angusta sp. nov. This find expands the known distribution of Cedrus during the Late Pliocene to Yunnan, where the genus no longer exists in natural forests. Based on the analysis of reconstructed Neogene climate data, we suggest that the intensification of the East Asian winter monsoon during the Quaternary may have dramatically increased seasonality and given rise to a much drier winter in Yunnan. Combined with information on Cedrus fossil records and its seed physiology, we conclude that the intensification of a drier climate after the Late Pliocene may have prevented the survival of Cedrus seedlings, leading to the eventual disappearance of Cedrus in western Yunnan. This study indicates that the topography in southwestern China acted as a vital refuge for many plants during the Quaternary, but that other species gradually disappeared due to the intensification of the monsoonal climate.     

DEM modelling of cone penetration tests in a double-porosity crushable granular material

A three-dimensional discrete element model is used to investigate the effect of grain crushing on the tip resistance measured by cone penetration tests (CPT) in calibration chambers. To do that a discrete analogue of pumice sand, a very crushable microporous granular material, is created. The particles of the discrete model are endowed with size-dependent internal porosity and crushing resistance. A simplified Hertz–Mindlin elasto-frictional model is used for contact interaction. The model has 6 material parameters that are calibrated using one oedometer test and analogies with similar geomaterials. The calibration is validated reproducing other element tests. To fill a calibration chamber capable of containing a realistic sized CPT the discrete analogue is up-scaled by a factor of 25. CPT is then performed at two different densities and three different confinement pressures. Cone tip resistance in the crushable material is practically insensitive to initial density, as had been observed in previous physical experiments. The same CPT series is repeated but now particle crushing is disabled. The ratios of cone tip resistance between the two types of simulation are in good agreement with previous experimental comparisons of hard and crushable soils. Microscale exploration of the models indicates that crushing disrupts the buttressing effect of chamber walls on the cone.