Estimation of Undrained Bearing Capacity for Offshore Soft Foundations with Cyclic Load

The degradation strength of soils under cyclic loading is studied and a method for deter-mining the cyclic degradation strength with cyclic triaxial tests is given in the paper.Furthermore,a dum-my static method for estimating the undrained bearing capacity for offshore soft foundation under waveloads is developed.It can consider the effect of the difference of cyclic stress for different parts of the foun-dation on both the degradation strength of the foundation soil and the bearing capacity so that the esti-mated result can better reflect the real condition of foundation under cyclic loading.The method can be ap-plied to plane and space problem.     

塑料排水板在海岸工程水下软基处理中的应用

通过综合分析工程建设区域的自然条件和地质条件,对比选取塑料排水板排水固结法加固护岸工程的水下软土地基。系统介绍了塑料排水板的加固机理、排水板的选型、施工工艺、质量控制要点。经过对处理后地基的沉降、位移的长期跟踪观测,结果表明:采用排水板排水加固水下软土地基,取得了理想效果,具有一定的工程指导意义。     

Settlement and Stability Analysis on Soft Clay Under Cyclic Loading

The results of undrained cyclic triaxial tests on three types of clays are collected and a relationship among the accumulated strain, the initial stress state, cyclic stress in the soil, as well as the number of cycles is established based on the experimental data. With this relationship, a procedure is proposed for subsidence and stability analysis on soft clay under the action of cyclic loads.     

考虑蠕变特性的斜坡堤软土地基变形数值分析

目前在防波堤设计和施工中,较少考虑软粘土的蠕变特性对软土地基长期变形的影响.为准确预测斜坡堤软土地基的变形水平,研究采用Plaxis二维有限元程序,利用不考虑蠕变的摩尔-库仑模型和能反映土体时间效应的软土蠕变模型,模拟某斜坡堤地基软土层施工期和工后的地基变形过程,对比分析了两种不同模型的计算结果,表明由软土蠕变模型得到...     

Calculation of Hydro-Dynamic Stability of the Soil Inside Bucket in the Process of Bucket Foundation Penetration

—The offshore platform with bucket foundations is a new type of offshore platform that distin-guishes from traditional template platforms by replacing driven piles with bucket foundations.The suctionpenentration of bucket foundation is a complicated hydro-dynamic process.The key of this process is theseepage field caused by the difference of pressure applied on purpose inside and outside the bucket.The ap-pearance and developement of seepage field has a decisive influence on the suction penetration process.Inthis study,the finite element analysis method is applied to the dynamic simulation of the seepage field ofsuction penetration of bucket foundation.A criterion is suggested to distinguish the hydro-dynamic stabili-ty of the soil inside the bucket according to the critical hydraulic gradient method.The reliability of themodel and its applicability to engineering practice have been proved through comparison between the re-sults of model test and finite element calculation.     

高真空击密法在软地基处理中的应用

姑合工程实践,介绍快速“高真空击密法”软地基处理方法的施工原理、施工工艺及质量控制等,并简单阐述“高真空击密法”在进行软地基处理中的优点。     

海上风机吸力式桶形基础承载特性研究综述

风机基础作为海上风机整体结构的重要组成部分,承受着上部风机所受到的风浪流荷载,并且对风机的安全性及可靠性至关重要。吸力式桶形基础由于其安装简单和可重复利用等优点,在海洋平台基础中得到了广泛应用,并逐步应用于海上风机基础中。但由于海上风机与海洋平台在海洋环境中的荷载工况有一定的差别,仍需要通过对其承载特性研究现状进行全面认识,以实现吸力式桶形基础在海上风机基础中的可靠应用。文中通过总结和评价现有研究对桶形基础在不同土体条件以及荷载条件下进行试验及数值模拟分析得到的研究结果,综述了静荷载和循环荷载作用下砂土和黏土中的吸力式桶形基础的承载特性研究现状,以及海上风机吸力式桶形基础的相关研究。文章展望了目前应用于海上风机基础的桶形基础仍缺乏的研究,为海上风机吸力式桶形基础的可靠应用及后续研究提供重要参考。     

黄河三角洲海上风机新型吸力锚基础型式分析

海上风力发电是未来风电产业的主要趋势,黄河三角洲沿海滩涂地带风能蕴藏量丰富,多为风能富集型,具有很大的开发潜力。但水下黄河三角洲地域条件复杂,广泛发育着不稳定地形地貌,加上波浪荷载和风荷载的联合作用,极易引起海床土体侵蚀液化,直接影响海上风机基础的安全稳定性。在分析了现有海上风电风机基础的优缺点后,针对现有风机基础存在的弊端,提出了一种新型伞式吸力锚基础,并对其结构优势和安装方法做了说明,该新型吸力锚基础独特的结构设计在黄河三角洲地区风电开发中具有一定的应用前景。     

Underwater Explosion Treatment of Marine Soft Foundation

The consolidation of soft foundation is a problem that commonly appears in harbor construction engineering on muddy coast. Introduced in this paper is the experimental study on underwater explosion treatment of soft foundation, including the regulations of explosion hollow development and medium movement, the law of similarity of densification and settlement of filled stone mass by shock wave pressure and explosion energy and their construction technologies, etc. A number of projects have been completed by applying this new technique, and the technique itself has been proved practicable.     

振冲挤密法加固砂类土地基在海岸工程中的应用

为了有效控制软土地基上海岸建筑物的工后沉降和不均匀沉降,各种软基处理方法在海岸工程建设中得到了越来越广泛的应用。结合海岸工程软土地基处理实例,对振冲挤密法的地基加固机理、加固砂类土地基时的设计参数、施工及加固后地基的检测等进行了探讨,结果表明,振冲挤密处理砂类土地基是行之有效的,并对今后的施工和设计提出了一些参考性建议。     

湛江某海上风电桩基局部冲刷特征研究

海上风电场桩基局部冲刷是工程设计与运行阶段的重要参数之一。基于湛江某海上风电场桩基3次现场局部冲刷实测数据,进行冲刷坑最大深度、冲刷坑半径和冲淤变化特征的分析与研究;根据桩基局部冲刷经验公式,采用工程海域实测海洋水文动力学数据进行最大冲刷深度与冲刷半径的计算,并进行公式计算值的对比与分 析。结果表明:桩基础在防冲刷设施的保护下,3次实测最大冲刷深度基本稳定为4.0 m,最大冲刷深度与桩径之比为0.57。而经验公式的最大冲刷深度与桩径之比均超过了1.1,说明桩基防冲刷设施取得了一定的效果,冲刷坑半径的计算值与现场实测值吻合较好。建议海上风电场在运行阶段进一步加强桩基冲刷坑监测与防护。     

Test and Numerical Analysis of the Constitutive Relation of a Diatomaceous Soft Rock

A kind of diatomaceous soft rock and its constitutive model are studied in this article. Based on Yin and Graham's (1999) 3-D elastic viscoplastic constitutive model, the formulation under a triaxial stress state is established, and it is used to simulate the time-dependent stress-strain behavior and effective stress path of consolidated undrained triaxial tests of both normally consolidated and overconsolidated soft rock. The comparison between the model predictions and measured results shows that their agreement is good. This demonstrates that the constitutive equation established here can be used to simulate the time-dependent stress-strain behavior of the soft rock under triaxial stress condition.     

Test and Numerical Analysis of the Constitutive Relation of a Diatomaceous Soft Rock

A kind of diatomaceous soft rock and its constitutive model are studied in this article. Based on Yin and Graham's (1999) 3-D elastic viscoplastic constitutive model, the formulation under a triaxial stress state is established, and it is used to simulate the time-dependent stress-strain behavior and effective stress path of consolidated undrained triaxial tests of both normally consolidated and overconsolidated soft rock. The comparison between the model predictions and measured results shows that their agreement is good. This demonstrates that the constitutive equation established here can be used to simulate the time-dependent stress-strain behavior of the soft rock under triaxial stress condition.     

Reinforcement of Soft Foundation with Geotextile and Observation for Sea Dike Project of Zhapu Port

1 .IntroductionTheZhapuPortissituatedonthenorthbankoftheHangzhouBay ,nearZhapuTowninPinghuCity ,Zhejiangprovince .Asthefirststepofconstruction ,reclamationwasaccomplishedinthehinter landoftheharbor.Theborderdikeofafulllengthof 1 2 71mislocatedinthetidalregionoftheHangzhouBay .ThepreliminarydesignofthisprojectwascompletedinJune 1 986 ,anditsconstructionbeganinJuly 1 986 ,andwascompletedinMarch 1 991 .TheseadikewasbuiltontheQ4marinedepositofsaturatedsoftclaywithathicknessofabout2 7mandgeo…     

Stability Analysis of Bohai Oil-Drilling Ship No. 6 Under Static and Cyclic Loads

- This paper presents a procedure to calculate the safety factor against sliding of a marine gravity structure subjected to a combination of static and cyclic loads. This procedure claculates the stress at the sliding surface by the finite element method (FEM) and takes the dynamic properties of clay into account. With this procedure, the stability of a Bohai oil-drilling ship is analyzed. The calculated safety factor is much smaller than 1, indicating that this oil-drilling ship would fail just as what had happened to it.     

浅海桶形基础平台水平承载力与抗滑稳定分析

平台在海上受风、浪、流、冰等水平载荷作用产生滑移,而土壤粘结力、摩擦力和土抗力是平台的抗滑力,桶基平台应满足抗滑稳定的要求,以保证平台的整体稳定性.介绍了浅海桶形基础平台受水平力作用时桶形基础的破坏模式及其计算方法,并阐述了抗滑稳定计算方法.     

正压冲固平台结构分析中基础边界条件的影响

正压冲固平台是一种采用短桩加固基础的新型海洋采油平台,对于这种新型的平台结构,在结构分析和构件强度校核中必须考虑其有限元模型的基础边界条件处理问题。本文提出了正压冲固平台有限元计算模型中基础边界条件的一种简化方法,将两个水平方向的扭转自由度简化为扭转弹簧边界元,其余自由度简化为固定约束。通过计算分析得到了不同的边界约束刚度系数的取值对平台总体位移和强度校核应力的影响及变化趋势。结论是,平台结构对约束刚度系数K的反应在10^4～10^4之间时比较明显,对K的敏感度最为强烈：在此范围之外,平台反应分别接近于简支约束情况和刚性约束情况。尤其对于接近约束边界的单元,其应力变化最敏感。     

浅海桶形基础平台抗拔力与抗倾稳定分析

平台在海上受风、浪、流、冰等水平载荷作用产生倾斜 ,而土壤粘接力、摩擦力和土抗力是平台的抗拔和抗倾力 ,桶基平台应满足抗拔、抗倾稳定的要求 ,以保证平台的整体稳定性。讨论了桶基平台受水平力作用时 ,桶形基础的破坏模式及其计算方法 ,阐述了抗倾稳定计算方法     

黄河三角洲北部地区软土工程地质特性及空间分布

软土作为一种不良土体,在黄河三角洲分布比较广泛,其工程特性一般表现为含水量高、强度低、压缩性大以及渗透性低等,易发生不良工程地质问题。黄河三角洲北部区域的河口区,软土的工程特性及空间分布目前尚未有系统分析研究。基于最新的较系统的工程地质钻孔数据资料,对河口区软土的工程地质特性参数进行了统计分析,研究了软土物理力学性质各指标的概率分布模型及参数间的相关性,就黄河三角洲地区软土的成因、厚度、埋藏条件、空间分布规律进行了分析总结,并对其主要工程地质问题及措施提出了建议。黄河三角洲北部河口地区的软土具有典型的软土特征：高含水量、高压缩性、低抗剪强度等,其软土的物理力学性质指标变异系数较小,概率分布基本符合正态分布,研究区85%的面积范围内发育软土层,软土层由近饱和或饱和的黏性土、淤泥及淤泥质粉土组成,属滨海相与三角洲相软土。该地区地基处理宜采用桩基法、排淤换填法、堆载预压法、电化学加固法等方法。     

多层砂土地基扩底桩单桩抗压模型试验及颗粒流模拟研究

利用室内半模试验和颗粒流数值模拟,揭示多层砂土地基扩底桩单桩抗压承载特性及变形特征。结果表明,通过对比分析极限承载力与H_h/D(持力层厚度与扩大头直径之比)的关系可以看出,单桩的抗压极限承载力随H_h/D逐渐增加,当H_h/D超过2.0时,极限承载力基本不再增加,此时的单桩抗压极限承载力稳定在300.01~303.25 N,是H_h/D=0.5时极限承载力(183.83 N)的1.65倍。扩大头下部土体发生局部压缩-剪切破坏,破坏面从扩大头底面边缘向斜下方扩展,在水平方向影响范围达到最大后逐渐向桩内侧收缩;荷载作用越大,地基破坏区域越大,相应的极限抗压承载力也越大;持力层厚度增加,扩大头分担的荷载比例增大,分担的荷载达到稳定需要的桩顶位移也越大,H_h=0.5 D试验扩大头分担的荷载比例稳定时为60%,对应的桩顶位移约为29 mm;桩顶位移达到33 mm后,H_h=1.0~3.0 D试验稳定在63%~65%之间;通过细观颗粒流理论对砂土移动特性的研究发现,持力层厚度从0.5 D增大至2.0 D,破坏面的起始扩展角度从31°增大至42°。数值模拟研究结果与模型试验数据吻合效果良好,证明该方法分析多层砂土地基扩底桩单桩抗压荷载传递机理是可行的。