铷原子频标小型化发展现状     

曹远洪  蒲晓华  刘勇军  杜伦宇  杨林 《时间频率学报》2007,30(2):132-137

铷原子频标使用最广泛,小型化是其最重要的发展趋势。微波腔小型化、电子线路数字化以及附加特殊功能是铷原子频标小型化的主要技术手段。相干布居囚禁(CPT)频标是一种可以做到芯片级的新型原子频标。目前相干布居囚禁频标的技术方案有:传统方案,物理系统采用MEMS(micro-electro-mechanical system)[0]技术的方案和整机采用MEMS[0]技术的方案。实现小型化后的原子频标将会迎来蓬勃发展的前景。  相似文献   

Automated facies identification by Direct Push-based sensing methods (CPT,HPT) and multivariate linear discriminant analysis to decipher geomorphological changes and storm surge impact on a medieval coastal landscape     

Hanna Hadler  Andreas Vött  Timo Willershäuser  Dennis Wilken  Ruth Blankenfeldt  Claus von Carnap-Bornheim  Kurt Emde  Peter Fischer  Ulf Ickerodt  Stefanie Klooß  Bente Majchczack  Lea Obrocki  Wolfgang Rabbel 《地球表面变化过程与地形》2021,46(15):3228-3251

In ad 1362, a major storm surge drowned wide areas of cultivated medieval marshland along the north-western coast of Germany and turned them into tidal flats. This study presents a new methodological approach for the reconstruction of changing coastal landscapes developed from a study site in the Wadden Sea of North Frisia. Initially, we deciphered long-term as well as event-related short-term geomorphological changes, using a geoscientific standard approach of vibracoring, analyses of sedimentary, geochemical and microfaunal palaeoenvironmental parameters and radiocarbon dating. In a next step, Direct Push (DP)-based Cone Penetration Testing (CPT) and the Hydraulic Profiling Tool (HPT) were applied at vibracore locations to obtain in situ high-resolution stratigraphic data. In a last step, multivariate linear discriminant analysis (LDA) was successfully applied to efficiently identify different sedimentary facies (e.g., fossil marsh or tidal flat deposits) from the CPT and HPT test dataset, to map the facies' lateral distribution, also in comparison to reflection seismic measurements and test their potential to interpolate the borehole and CPT/HPT data. The training dataset acquired for the key site from coring and DP sensing finally allows an automated facies classification of CPT/HPT data obtained elsewhere within the study area. The new methodological approach allowed a detailed reconstruction of the local coastal landscape development in the interplay of natural marsh formation, medieval land reclamation and storm surge-related land losses.  相似文献   

The Fourth James K. Mitchell Lecture: The CPT in offshore soil investigations - a historic perspective     

《Geomechanics and Geoengineering》2013,8(2):75-101

For the last 40 years, the CPT has played a key role in offshore soil investigations, mainly in connection with oil and gas development, but also for other purposes. The offshore application of CPT has been an important factor with regards to development of equipment, data processing and interpretation. Each of the following aspects are discussed in terms of historic development, present status and future challenges:

- Deployment method and equipment.

- Penetrometer design and construction.

- Data acquisition, processing and quality control.

- Standards and guidelines.

- Interpretation of results and application in foundation design.

It is shown that these developments have greatly enhanced the reliability and applicability of the use of the CPT in soil investigations and design. However, there are still important challenges to be faced in the future  相似文献   

A performance-based framework for assessing liquefaction potential based on CPT data     

《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2013,7(3):177-187

This article describes a new performance-based approach for evaluating the return period of seismic soil liquefaction based on standard penetration test (SPT) and cone penetration test (CPT) data. The conventional liquefaction evaluation methods consider a single acceleration level and magnitude and these approaches fail to take into account the uncertainty in earthquake loading. The seismic hazard analysis based on the probabilistic method clearly shows that a particular acceleration value is being contributed by different magnitudes with varying probability. In the new method presented in this article, the entire range of ground shaking and the entire range of earthquake magnitude are considered and the liquefaction return period is evaluated based on the SPT and CPT data. This article explains the performance-based methodology for the liquefaction analysis – starting from probabilistic seismic hazard analysis (PSHA) for the evaluation of seismic hazard and the performance-based method to evaluate the liquefaction return period. A case study has been done for Bangalore, India, based on SPT data and converted CPT values. The comparison of results obtained from both the methods have been presented. In an area of 220 km² in Bangalore city, the site class was assessed based on large number of borehole data and 58 Multi-channel analysis of surface wave survey. Using the site class and peak acceleration at rock depth from PSHA, the peak ground acceleration at the ground surface was estimated using probabilistic approach. The liquefaction analysis was done based on 450 borehole data obtained in the study area. The results of CPT match well with the results obtained from similar analysis with SPT data.  相似文献   

基于流变仪测试海底浅表层软黏土不排水强度研究     

缪栋杰  宋丙辉  宋玉鹏  孙永福  苏志明  刘绍文 《海洋工程》2022,40(6):97-104

鉴于海底浅表层软黏土强度测试精细化程度不足的现状,引入流体测试中的流变仪,对青岛海域海底浅表层软黏土开展多组原状和重塑试样的不排水剪切强度试验,通过对比静力触探和微型十字板测试结果,验证了流变仪测试方法的有效性。基于流变仪试验结果,揭示了海底软黏土原状和重塑状态下不排水剪切破坏模式,探讨了海底软黏土不排水剪切强度和灵敏度随埋深及液性指数的发展演变趋势,评价了软黏土的结构性特征。最后,引入含水率与液限之比对海底浅表层软黏土重塑不排水剪切强度进行了归一化分析,为近海海洋开发活动提供技术支撑。  相似文献   

Assessment of liquefaction evaluation procedures and severity index frameworks at Christchurch strong motion stations     

《Soil Dynamics and Earthquake Engineering》2015

The objective of the study presented herein is to assess three commonly used CPT-based liquefaction evaluation procedures and three liquefaction severity index frameworks using data from the 2010–2011 Canterbury earthquake sequence. Specifically, post-event field observations, ground motion recordings, and results from a recently completed extensive geotechnical site investigation programme at selected strong motion stations (SMSs) in the city of Christchurch and surrounding towns are used herein. Unlike similar studies that used data from free-field sites, accelerogram characteristics at the SMS locations can be used to assess the performance of liquefaction evaluation procedures prior to their use in the computation of surficial manifestation severity indices. Results from this study indicate that for cases with evidence of liquefaction triggering in the accelerograms, the majority of liquefaction evaluation procedures yielded correct predictions, regardless of whether surficial manifestation of liquefaction was evident or not. For cases with no evidence of liquefaction in the accelerograms (and no observed surficial evidence of liquefaction triggering), the majority of liquefaction evaluation procedures predicted liquefaction was triggered. When all cases are used to assess the performance of liquefaction severity index frameworks, a poor correlation is shown between the observed severity of liquefaction surface manifestation and the calculated severity indices. However, only using those cases where the liquefaction evaluation procedures yielded correct predictions, there is an improvement in the correlation, with the Liquefaction Severity Number (LSN) being the best performing of the frameworks investigated herein. However scatter in the relationship between the observed and calculated surficial manifestation still remains for all liquefaction severity index frameworks.  相似文献   

Predicting standard penetration test N-value from cone penetration test data using artificial neural networks     

Bashar Tarawneh 《地学前缘(英文版)》2017,8(1):199-204

Standard Penetration Test(SPT) and Cone Penetration Test(CPT) are the most frequently used field tests to estimate soil parameters for geotechnical analysis and design.Numerous soil parameters are related to the SPT N-value.In contrast,CPT is becoming more popular for site investigation and geotechnical design.Correlation of CPT data with SPT N-value is very beneficial since most of the field parameters are related to SPT N-values.A back-propagation artificial neural network(ANN) model was developed to predict the N6o-value from CPT data.Data used in this study consisted of 109 CPT-SPT pairs for sand,sandy silt,and silty sand soils.The ANN model input variables are:CPT tip resistance(q_c),effective vertical stress(σ'_v),and CPT sleeve friction(f_s).A different set of SPT-CPT data was used to check the reliability of the developed ANN model.It was shown that ANN model either under-predicted the N_(60)-value by 7-16%or over-predicted it by 7-20%.It is concluded that back-propagation neural networks is a good tool to predict N_(60)-value from CPT data with acceptable accuracy.  相似文献   

Failure analysis of CPT-based direct methods for axial capacity of driven piles in sand     

S. Moshfeghi 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2019,13(1):1-19

Due to variety of current pile bearing capacity methods based on cone penetration test (CPT) measurements, there is always a need for evaluating performance of existing methods to make proper choices of methods as well as safety factors for optimum design. In this regard, geotechnical databases are known as useful tools which facilitate evaluation of existing methods. This paper deals with axial bearing capacity of driven piles in sand using CPT-based methods. A database of seventy-six records is employed to analyze different criteria of interpreting static pile load test results to select the most consistent approach with the CPT-based methods. Then, performance of nine commonly used direct CPT-based methods was evaluated. Finally, via a failure probability and cost optimisation approach, optimum safety factors are presented and discussed. Analysis of different failure criteria shows that the Hansen 80% criterion leads to more consistent results with the CPT-based methods. In addition, almost all of the investigated methods showed promising performance. The attained safety factors range from 1.6 to 3.1 for all records, 1.4 to 3.1 for piles in compression, and 1.4 to 2.2 for the piles in tension. Then, efficiency of methods was evaluated and the methods with higher efficiency are introduced.  相似文献   

旁压试验确定上海软土地区的单桩承载力   总被引：1，自引：0，他引：1  

杨石飞  顾国荣  董建国 《上海国土资源》2002,(4):41-46

该文搜集上海地区三十多项旁压试验资料工程，以及近133组静载荷试验，经过分析、统计、比较，得出根据旁压试验确定单桩竖向极限承载力的公式，表明该公式的普遍适用性，是对静载试验方法的有益补充。同时对379组分别采用旁压和静探试验估算的单桩承载力的比较，表明采用旁压试验方法估算的单桩承载力与静探方法基本吻合。  相似文献   

基于双桥静力触探的饱和砂土液化判别方法刍议     

孙君  韩琪 《地质灾害与环境保护》2020,(1):87-92

饱和砂土液化是地震引发地基变形失稳、建筑受损破坏的主因之一,合理判定液化可能性是勘察实践和理论研究的重大课题。国内规范要求砂土液化判别仍以标准贯入试验为主,静力触探等原位测试方法为辅,静力触探较其他原位测试手段,在操作便利性、数据采集连续性、测试成本和抗干扰能力等方面更具优势。针对国内规范常用静力触探砂土液化判别方法进行了分析研究,并结合勘察实例进行了计算和对比,探讨了静力触探判别液化方法的土层适用性,并提出有关改进建议。  相似文献