Applicability of existing empirical shear wave velocity correlations to seismic cone penetration test data in Christchurch New Zealand

Seismic piezocone (SCPTu) data compiled from 86 sites in the greater Christchurch, New Zealand area are used to evaluate several existing empirical correlations for predicting shear wave velocity from cone penetration test (CPT) data. It is shown that all the considered prediction models are biased towards overestimation of the shear wave velocity of the Christchurch soil deposits, demonstrating the need for a Christchurch-specific shear wave velocity prediction model (McGann et al., 2014) [1]. It is hypothesized that the unique depositional environment of the considered soils and the potential loss of soil ageing effects brought about by the 2010–2011 Canterbury earthquake sequence are the primary source of the observed prediction bias.     

用静力触探资料估算单桩竖向极限承载力标准值的几点体会

本文通过实例,用静力触探资料进行了单桩竖向极限承载力标准值的估算,并把估算结果和传统的经验参数法估算结果进行了对比,同时,又用单桩静力载荷试验资料进行了验证,从而说明该方法在不断积累经验后,在本地区是可以推广应用的。     

土性参数相关距离的计算研究和统计分析

通过大量计算,对求相关距离的各种方法进行了对比研究,对太原和杭州地区典型土层的相关距离进行李统计分析,还结合某一工程实例讨论了相关距离估计的贝叶斯方法。     

静力触探在复合地基质量检测中的应用

论述了静力触探 ( CPT)技术在黄土地区对人工复合地基承载力的确定 ,以及静力触探曲线特征与灰土挤密桩挤密效果的对应关系。     

Downhole CPT海底基座液压自动调平系统研究

井下式(Downhole)海底CPT贯入设备中的海底基座需要为探头和探杆竖直贯入海底土体时产生的地层阻力提供支撑反力,然而当海底基座坐落于倾斜的海床面时会对触探数据的真实性造成影响,严重时甚至造成作业事故。文中针对前期方案中球铰被动式调平装置存在的问题,提出了球铰液压式自动调平方案,从机械结构、液压原理、控制策略等方面进行了详细论述,可为今后海底CPT系统的进一步完善和海底钻探取样设备的研制提供借鉴。     

Non-stationary realisation of CPT data: considering lithological and inherent heterogeneity

ABSTRACT

The main sources of uncertainty in the soil specification and mechanical behaviour consist of the lithological and heterogeneous randomness of soil deposits. It is quite obvious that the cone penetration testing (CPT) data and the variation of soil characteristics are not stationary. Hence, this paper investigates a new approach to realise a CPT data, taking both sources of uncertainty into consideration. In this regard, the first part of this study illustrates a simple approach to stratify the CPT data, using the Eslami–Fellenius chart of classification. In the second part, the non-stationary algorithm of generating random field is introduced to generate a multi-layer random field. This algorithm takes account of each layer’s statistical properties (i.e. standard deviation, mean, and the trend value), separately. To validate the proposed approach, 41 case histories from different worldwide sites, have been regenerated by considering both the stationary and non-stationary algorithms. The correlation coefficient between real and realised CPT data has been employed to show that the proposed non-stationary algorithm can simulate the CPT data more accurately in comparison with the stationary algorithm.     

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.     

静力触探在水合物勘探中的应用

水合物的勘探方法主要有地球物理方法、地球化学方法、微生物方法和地质学方法等,三维地震为主要而且也是最重要的手段。含有游离天然气和天然气水合物的海底沉积物在物理性质上存在明显差异,三维地震利用这些差异性可以确定天然气水合物的分布,但有些沉积物如碳酸盐岩也可以表现出类似的异常。对于精确确定海底沉积物物性及沉积物类型,静力触探具有非常突出的优势。静力触探可以开展土力学测试、土体摄像、定点地质取样、波速测试、热力学测试、磁力观测、电导率测试、放射性同位素测试和化学分析测试等,调查范围非常广泛。用CPT配合其他方法来联合勘探水合物是精确计算水合物分布及储量的非常有前景的方法。     

海床CPT和井下CPT在砂土中贯入机理差异研究

海洋石油建设中的一个关键环节是对有关海域的工程地质条件作出准确评价。海上原位静力触探(CPT)是主要的原位勘察手段,与陆地CPT不同,其贯入方式主要有Seabed和Downhole两种形式。这两种CPT由于贯入方式不同,所得到的锥端阻力存在一定的差异。采用有限元方法对这两种形式的CPT锥端阻力和贯入模式进行计算分析。研究显示,CPT入土过程中,周围土体存在两种不同位移状态,即滑动状态和排挤状态。在入土初期,土体以滑动状态为主,土体中竖向应力随贯入深度的增加而递增。在入土一定深度以后,土体的排挤状态占主导地位,竖向应力变化趋于平稳。这两种位移状态的相互转化解释了Seabed CPT和Downhole CPT实测数据之间的差异。在贯入深度较大时,Seabed CPT受排挤状态控制,而Downhole CPT仍然受滑动状态的影响。     

启东某场地自升式平台插桩可行性试验研究

桩靴接触应力是影响插桩深度的主要因素之一,桩靴的锥尖型式可能会影响接触应力的大小及分布。以江苏省启东市某插桩试验项目为例,针对不同的桩靴端部型式基于桩靴接触应力现场实测数据,分别采用国内外规范方法及数值计算方法对插桩深度开展预测分析,揭示桩靴端部型式对插桩深度的影响规律。结果表明：在插桩过程中不同锥端类型桩靴的接触应力呈现出中央大周边小的分布特征,表明现场桩靴为柔性结构类型;采用不考虑桩靴端部形状的规范方法进行桩靴插深预测,得出的预测结果同现场实测结果基本吻合;采用小变形有限元数值方法进行插深预测也可以得出令人满意的结果,研究结果可为类似工程实践提供参考。