Liquefaction-Induced Ground Deformations Evaluation Based on Cone Penetration Tests (CPT)

The aim of this paper is to evaluate the liquefaction-induced ground deformations of sand-like soils based on Cone Penetration Tests (CPT) at Semani site, Fieri prefecture in Albania. These tests are performed during the process of investigation of this area, in which a Liquid Natural Gas Terminal-Power Plant was supposed to be built. This paper presents the assessment of the liquefaction and of the liquefaction-induced ground deformations such as lateral spreading displacement and post-liquefaction reconsolidation settlement. The liquefaction-induced lateral spreading and post-liquefaction reconsolidation settlement are estimated based on CPT data according to the method in MNO-12 “soil liquefaction during earthquake”, presented by Idriss and Boulanger (2008). This evaluation is very important and should be taken into consideration for the design of engineering structures that will be constructed in this area. All the calculation’s results are shown in graphs. At the end, there are highlighted some conclusions regarding the liquefaction-induced ground deformations in this site.

Regressive approach for predicting bearing capacity of bored piles from cone penetration test data

In this study, th e least sq u are su p p o rt v ecto r m achine （LSSVM） alg o rith m w as applied to predicting th ebearing capacity o f b ored piles e m b ed d ed in sand an d m ixed soils. Pile g eo m etry an d cone p e n e tra tio nte s t （CPT） resu lts w ere used as in p u t variables for pred ictio n o f pile bearin g capacity. The d ata u se d w erecollected from th e existing litera tu re an d consisted o f 50 case records. The application o f LSSVM w ascarried o u t by dividing th e d ata into th re e se ts： a train in g se t for learning th e pro b lem an d obtain in g arelationship b e tw e e n in p u t variables an d pile bearin g capacity, and testin g an d validation sets forevaluation o f th e predictive an d g en eralization ability o f th e o b tain ed relationship. The predictions o f pilebearing capacity by LSSVM w ere evaluated by com paring w ith ex p erim en tal d ata an d w ith th o se bytrad itio n al CPT-based m eth o d s and th e gene ex pression pro g ram m in g （GEP） m odel. It w as found th a t th eLSSVM perform s w ell w ith coefficient o f d eterm in atio n , m ean, an d sta n d ard dev iatio n equivalent to 0.99,1.03, an d 0.08, respectively, for th e testin g set, an d 1, 1.04, an d 0.11, respectively, for th e v alidation set. Thelow values o f th e calculated m ean squared e rro r an d m ean ab so lu te e rro r indicated th a t th e LSSVM w asaccurate in p redicting th e pile bearing capacity. The results o f com parison also show ed th a t th e p roposedalg o rith m p red icted th e pile bearin g capacity m ore accurately th a n th e trad itio n al m eth o d s including th eGEP m odel.

Fall cone tests considering water content, cone penetration index, and plasticity angle of fine-grained soils

This paper analyzed the consistency of some parameters of soils in the literature and experimental results from fall cone test and its application to soil plasticity classification.Over 500 data from both literatures and experiments using fall cone and Casagrande methods were compiled to assess the relationships among specified water content,cone penetration index ebT,and plasticity angle eaT of finegrained soils.The results indicate that no unique correlation exists among b,liquid limit of the fall cone test(LLc)and a.The water content at 1 mm cone penetration eC0T correlates well with b,plasticity ratio eRpT(i.e.the ratio of plastic limit to liquid limit),and a.Finally,the potential of using the btan a diagram to classify soil plasticity was also discussed.

Adaptive sampling strategy for characterizing spatial distribution of soil liquefaction potential using cone penetration test

Characterizing spatial distribution of soil liquefaction potential is critical for assessing liquefactionrelated hazards(e.g.building damages caused by liquefaction-induced differential settlement).However,in engineering practice,soil liquefaction potential is usually measured at limited locations in a specific site using in situ tests,e.g.cone penetration tests(CPTs),due to the restrictions of time,cost and access to subsurface space.In these cases,liquefaction potential of soil at untested locations requires to be interpreted from limited measured data points using proper interpolation method,leading to remarkable statistical uncertainty in liquefaction assessment.This underlines an important question of how to optimize the locations of CPT soundings and determine the minimum number of CPTs for achieving a target reliability level of liquefaction assessment.To tackle this issue,this study proposes a smart sampling strategy for determining the minimum number of CPTs and their optimal locations in a selfadaptive and data-driven manner.The proposed sampling strategy leverages on information entropy and Bayesian compressive sampling(BCS).Both simulated and real CPT data are used to demonstrate the proposed method.Illustrative examples indicate that the proposed method can adaptively and sequentially select the required number and optimal locations of CPTs.

Seasonal influence on cone penetration test: An unsaturated soil site example

Interpretation of electric cone penetration test(CPT) based pore water pressure measurement(CPTu) is well established for soils with behavior that follows classical soil mechanics. The literature on the interpretation of these tests performed on unsaturated tropical soils is limited, and little is known about the influence of soil suction on in situ test data. In this context, the CPT data are presented and discussed to illustrate the seasonal variability in an unsaturated tropical soil site. The test data show that soil suction significantly influenced CPT data up to a depth of 4 m at the study site. It shows the importance of considering seasonal variability in unsaturated soil sites caused by soil suction, which was related to water content through a soil-water retention curve(SWRC). It is also important to consider this aspect in the interpretation of CPT data from these soils.

软基处理PST桩复合地基加固机理及CPTU验证

对于厂房、仓库、露天堆场等沿海软土地基加固处理工程,采用传统的软基处理方法如真空预压或堆载预压,其施工工期长、工后沉降大;采用水泥搅拌桩由于施工质量不易控制,桩体强度低、处理效果不佳;采用刚性桩复合地基存在地面堆载沉降不均匀等难题。“PST”复合地基处理方法采用预制桩与桩帽及厚褥垫层组合,将预制桩的高承载力转化为褥垫层均布承载力;地面均布荷载引起的变形应力传递到桩身而非其下的软土。以某大型地基处理工程为例,通过CPTU孔压静力触探技术评价PST桩地基处理加固效果与挤土效应,通过对打桩过程中,不同时期的超静孔隙水压力进行观测,掌握超静孔隙水压力消散和变化规律。通过打桩过程中的超孔压的变化情况,分析打桩顺序和速率对孔压的影响程度,了解PST桩施工对软土的扰动规律,以指导施工,降低PST桩施工对地基土的影响。

Application of artificial neural networks for predicting the impact of rolling dynamic compaction using dynamic cone penetrometer test results

Rolling dynamic compaction(RDC),which involves the towing of a noncircular module,is now widespread and accepted among many other soil compaction methods.However,to date,there is no accurate method for reliable prediction of the densification of soil and the extent of ground improvement by means of RDC.This study presents the application of artificial neural networks(ANNs) for a priori prediction of the effectiveness of RDC.The models are trained with in situ dynamic cone penetration(DCP) test data obtained from previous civil projects associated with the 4-sided impact roller.The predictions from the ANN models are in good agreement with the measured field data,as indicated by the model correlation coefficient of approximately 0.8.It is concluded that the ANN models developed in this study can be successfully employed to provide more accurate prediction of the performance of the RDC on a range of soil types.

基于CPTU的超深地连墙成槽土体扰动评价

地下连续墙成槽会引起邻近地层土体应力状态发生变化,导致土体受到扰动,进而影响土体的工程性质,因此,准确评价地连墙施工引起的土体扰动对工程设计与施工具有重要指导意义。以江阴靖江长江隧道工程为依托,在江北工作井的某幅地连墙成槽前后于槽段旁边开展了孔压静力触探(CPTU)测试,得到了成槽前后的CPTU参数,并基于修正的锥尖阻力q_(t)评价了地连墙成槽引起的土体扰动度。结果表明,地连墙成槽后,锥尖阻力、侧壁摩阻力及孔隙水压力总体上均有不同程度的降低,土体扰动度在30%以内。浅部扰动度高于深部,深度相近时砂土层扰动度高于软黏土层。

Methodology for Obtaining Optimal Sleeve Friction and Friction Ratio Estimates from CPT Data

Cone penetration testing (CPT) is a cost effective and popular tool for geotechnical site characterization. CPT consists of pushing at a constant rate an electronic penetrometer into penetrable soils and recording cone bearing (qc), sleeve friction (fc) and dynamic pore pressure (u) with depth. The measured qc, fs and u values are utilized to estimate soil type and associated soil properties. A popular method to estimate soil type from CPT measurements is the Soil Behavior Type (SBT) chart. The SBT plots cone resistance vs friction ratio, Rf [where: Rf = (fs/qc)100%]. There are distortions in the CPT measurements which can result in erroneous SBT plots. Cone bearing measurements at a specific depth are blurred or averaged due to qc values being strongly influenced by soils within 10 to 30 cone diameters from the cone tip. The qcHMM algorithm was developed to address the qc blurring/averaging limitation. This paper describes the distortions which occur when obtaining sleeve friction measurements which can in association with qc blurring result in significant errors in the calculated Rf values. This paper outlines a novel and highly effective algorithm for obtaining accurate sleeve friction and friction ratio estimates. The fc optimal filter estimation technique is referred to as the OSFE-IFM algorithm. The mathematical details of the OSFE-IFM algorithm are outlined in this paper along with the results from a challenging test bed simulation. The test bed simulation demonstrates that the OSFE-IFM algorithm derives accurate estimates of sleeve friction from measured values. Optimal estimates of cone bearing and sleeve friction result in accurate Rf values and subsequent accurate estimates of soil behavior type.

Technique for Estimating the Cone Bearing Smoothing Parameters

Cone penetration testing (CPT) is an extensively utilized and cost effective tool for geotechnical site characterization. CPT consists of pushing at a constant rate an electronic cone into penetrable soils and recording the resistance to the cone tip (qc value). The measured qc values (after correction for the pore water pressure) are utilized to estimate soil type and associated soil properties based predominantly on empirical correlations. The most common cone tips have associated areas of 10 cm2 and 15 cm2. Investigators also utilized significantly larger cone tips (33 cm2 and 40 cm2) so that gravelly soils can be penetrated. Small cone tips (2 cm2 and 5 cm2) are utilized for shallow soil investigations. The cone tip resistance measured at a particular depth is affected by the values above and below the depth of interest which results in a smoothing or blurring of the true bearing values. Extensive work has been carried out in mathematically modelling the smoothing function which results in the blurred cone bearing measurements. This paper outlines a technique which facilitates estimating the dominant parameters of the cone smoothing function from processing real cone bearing data sets. This cone calibration technique is referred to as the so-called CPSPE algorithm. The mathematical details of the CPSPE algorithm are outlined in this paper along with the results from a challenging test bed simulation.

现代数字式多功能CPTU与中国CPT对比试验研究

首先对国内外不同尺寸探头测试参数的对比研究现状进行综述,结合不同场地的孔压静力触探(CPTU)和静力触探(CPT)现场试验,总结江苏典型黏土场地上国际10cm2的CPTU探头和中国双桥15cm2的CPT探头试验结果,对2种尺寸探头的测试参数作了详细比较。在划分土层、判别土类方面,多功能CPTU具有较高的分辨率。针对不同土类,从实用角度建立CPTU测试指标与中国CPT测试指标的转化关系。研究成果奠定了我国工程实际中应用国际10cm2的CPTU探头基础,对推广应用国际标准的CPTU技术具有重要意义。

多功能孔压静力触探(CPTU)试验研究

孔压静力触探(CPTU)是20世纪80年代在国际上兴起的新型原位测试技术,因其诸多优点,特别适合于软土工程的勘察,目前在欧美诸国已得到广泛应用。本文首先对国内外静力触探(CPT)技术的发展作了简要的介绍,阐述了国外CPT的发展状况和我国CPT的现状。然后介绍了引进的美国多功能CPTU测试技术以及操作方法与技术要点,结合两个现场试验,对我国的原位测试技术与引进的多功能CPTU作了对比分析,最后得出了一些结论和建议。

基于CPTU测试的桩基承载力预测新方法

首先回顾了基于静力触探试验(CPT)和孔压静力触探试验(CPTU)预测桩基承载力的方法。根据连盐高速和宁常高速公路工程中的PTC、CFG和PHC桩的CPTU试验资料,提出了基于CPTU预测桩基承载力的折线法。以静载荷和高应变试验得到的桩基承载力作为参考值,评估了各种预测桩基承载力方法的有效性。结果表明,折线法比其余三种方法在预测桩基承载力方面具有更高的可靠性,具有简单、快速、多参数的优点,并且不依赖于操作者主观性的影响,值得在桩基工程中推广应用。

基于台湾集集地震数据的CPT与SPT液化判别方法比较

利用集集地震静力触探试验(CPT)数据,对基于CPT测试的Robertson液化判别方法和Olsen方法进行了检验,两个方法对液化点判别成功率分别为82.61%和80.43%,对非液化点判别成功率分别为31.82%和44.32%。CPT液化判别方法对液化点判别基本可靠,但对非液化点判别准确性较差。对集集地震标准贯入试验(SPT)数据,美国地震工程研究中心(NCEER)推荐的SPT液化判别方法对液化点和非液化点判别成功率分别达到92.41%和94.35%。SPT方法判别成功率非常高,整体准确性远高于CPT方法。另一方面,CPT的土分类图可以同时反映土的种类与强度,甚至可以对集集地震液化土与非液化土进行区分。对于细粒土的液化初判,CPT土分类图也优于SPT方法中的黏粒含量指标。因此,土分类图是CPT的优势所在。

适用于新疆巴楚地区的CPT液化判别新方法

以2003年新疆巴楚—伽师地区Ms6.8级地震大规模砂土液化为背景,通过对地震液化场地的详细勘察,获取了39个场地的静力触探勘察数据,根据现有国内外静力触探液化判别方法均不适合于新疆巴楚地区的情况,依据实测数据建立了含锥尖阻力基准值、地下水位、砂层埋深、地震烈度等常规参数的液化判别新公式。建立的液化判别方法分为初判和复判两部分,初判条件以特征深度表示;复判公式对液化场地和非液化场地的回判别成功率均在95%左右,可靠度较高。提出的公式形式与中国工程上最常用的液化判别公式一致,可为新疆地区液化判别及相关地区性规范制订提供技术支持。

国内外静力触探液化判别方法对比检验

静力触探试验(cone penetration test,简称CPT)具有独特优势,使其成为了海上风电工程的主要勘察方法。海上风电工程位于液化易发区,因此研究基于CPT液化判别方法的适用性和可靠性就成为亟待解决的突出问题。详细介绍了4种国内外具有代表性的CPT液化判别方法,并采用理论分析及大量CPT液化实测数据检验,对现行的美国国家地震工程研究中心(National Center for Earthquake Engineering Research,简称NCEER)方法、《岩土工程勘察规范》(GB50021-2001)方法(岩规法)、《软土地区岩土工程勘察规程》(JGJ 83-2011)方法(软土规程法)和《建筑工程抗震性态设计通则》(CES 160:2004)方法(通则法)等4种方法进行对比检验,提出了4种主要方法的评价结果。结果表明:NCEER法液化判别临界线在低烈度区存在不合理的回弯现象,在高烈度区存在临界值增大过快的问题,在Ⅶ度区深层偏于危险,在Ⅸ度区深层明显偏于保守,在Ⅶ、Ⅸ度区浅层和Ⅷ度区判别结果较好;岩规法液化判别临界线存在很大的问题,液化判别临界线随深度递减,液化判别时在Ⅶ度区浅层偏于危险,在深层明显偏于危险,在Ⅷ、Ⅸ度区浅层偏于保守,在深层偏于危险;软土规程法液化判别临界线在土层深度约6 m处存在不合理的回弯现象,在Ⅶ度区浅层判别较好,在Ⅸ度区浅层偏于保守,在不同烈度区深层均偏于危险;通则法液化判别临界线是符合目前认知的,在不同烈度区和深度下的判别效果是最好的。研究成果可为相关规范修订和工程应用提供参考与支持。

基于CPTU测试的K_0固结黏土中静压桩时变承载力研究

基于空间滑动面(SMP)准则改进的K_0固结各向异性修正剑桥模型,考虑K_0固结饱和黏土初始应力各向异性、应力历史及应力诱发各向异性对土体三维力学特性的影响,推导了静压沉桩柱孔扩张问题的弹塑性解析解。在此基础上,根据桩侧土体应力状态与单剪试验中试样应力状态的相似性,结合桩周土轴对称固结理论提出采用孔压静力触探仪(CPTU)锥尖阻力、锥肩孔隙水压力及相应孔压消散数据预测静压桩时变承载力的理论方法。通过离心机模型试验实测结果和理论预测值的对比,验证了理论方法的有效性,研究了静压桩承载力随时间的变化规律。研究结果表明,本文理论预测方法避免了土体基本参数测定等繁琐过程,且可以较为合理地预测静压桩时变承载力;静压桩沉桩结束后其承载力在短时间内迅速增加,之后承载力增加幅度变缓且逐渐趋于稳定值;静压桩桩径越大,沉桩结束后承载力增加的速度越慢,承载力达到稳定值的时间越长。

CPT土分类方法在地基检测中的应用对比

在地基处理设计中，针对相应的工程场地，采用合理的CPT土分类法进行砂性土和黏性土的准确划分对地基处理检测验收极为重要。通过搜集卡塔尔多哈地区200个CPT原住测试孔和邻近位置的SPT钻孔取样与室内土工试验，对比分析4种基于CPT的土分类方法，发现不同的土层分类法在颗粒级配上具有较为明显的分区，但在区分砂性土和黏性土上，Robertson（1990）最为准确，Robertson（1986）次之；而Schmertmann法和Douglas法砂性土划分范围较宽，均将细颗粒含量高达35％～55％黏性土划分为砂性土。

基于CPTU的三亚新机场海洋软土工程特性评价

三亚新机场项目为中国海南省计划,拟于三亚市红塘湾建成的一座总面积达28平方公里的大型海上机场项目。项目的建设对于海南省发挥作为"海上丝绸之路"战略支点的重大作用,推动海南省经济高速发展具有重要意义。项目填海造岛工程的现场勘测采用海洋CPTU技术。CPTU技术作为国内外普遍使用的原位测试手段,能够有效评价土体的工程特性,但其在国内海洋工程方面仍缺乏使用经验。本文利用自主研发的CPTU设备,对三亚新机场填海造岛工程进行海上CPTU试验。结合该地区相关现场勘察及室内土工试验数据对实验结果进行分析,认为CPTU技术作为一种较为成熟的海洋原位测试技术,能够较好地应用于海洋工程实践,且具有很好的指导意义。

基于CPTU孔压消散试验的欠固结土OCR计算方法

利用CPTU孔压消散试验数据对欠固结土的欠固结状态进行定量评价,并在此基础上提出基于固结状态参数的欠固结土超固结比计算方法.结合现场CPTU孔压消散试验及室内固结试验对崇启大桥北接线工程沿线③1层软土应力历史进行了研究.结果表明:消散时间足够长时,CPTU孔压消散实验曲线的末端无限逼近原位初始孔压,且消散曲线尾端的实测孔压与时间平方根倒数成线性相关性,提出采用时间平方根倒数外推法计算原位初始孔压.当所计算的原位初始孔压大于静水压力时,则判定软土处于欠固结状态,进而建议采用固结状态参数对软土的欠固结程度进行定量评价,固结状态参数越小,说明欠固结程度越高.根据CPTU孔压消散试验计算了沿线软土③1层(淤泥质粉质黏土)的欠固结程度,然后利用室内固结试验成果验证了其合理性.基于OCR传统计算公式中系数与固结状态参数间定量关系,提出了考虑固结程度的欠固结土OCR计算公式.