Centrifuge modeling of a large-scale surcharge on adjacent foundation

This study investigates the ground and structural response of adjacent raft foundations induced by largescale surcharge by ore in soft soil areas through a 130g centrifuge modeling test with an innovative layered loading device.The prototype of the test is a coastal iron ore yard with a natural foundation of deep soft soil.Therefore,it is necessary to adopt some measures to reduce the influence of the large-scale surcharge on the adjacent raft foundation,such as installing stone columns for foundation treatment.Under an acceleration of 130 g,the model conducts similar simulations of iron ore,stone columns,and raft foundation structures.The tested soil mass has dimensions of 900 mm×700 mm×300 mm(lengthwidthdepth),which is remodeled from the soil extracted from the drilling holes.The test conditions are consistent with the actual engineering conditions and the effects of four-level loading conditions on the composite foundation of stone columns,unreinforced zone,and raft foundations are studied.An automatic layer-by-layer loading device was innovatively developed to simulate the loading process of actual engineering more realistically.The composite foundation of stone columns had a large settlement after the loading,forming an obvious settlement trough and causing the surface of the unreinforced zone to rise.The 12 m surcharge loading causes a horizontal displacement of 13.19 cm and a vertical settlement of 1.37 m in the raft foundation.The stone columns located on both sides of the unreinforced zone suffered significant shear damage at the sand-mud interface.Due to the reinforcement effect of stone columns,the sand layer below the top of the stone columns moves less.Meanwhile,the horizontal earth pressure in the raft foundation zone increases slowly.The stone columns will form new drainage channels and accelerate the dissipation of excess pore pressure.

One-Step-Installation of Offshore Wind Turbine on Large-Scale Bucket-Top-Bearing Bucket Foundation

In 2010,the first offshore wind turbine with integrated installation was established in Qidong sea area of Jiangsu Province,China,which led to the implementation phase of one-step-installation technique based on the design and construction of large-scale bucket-top-bearing (LSBTB) bucket foundation.The critical technique of LSBTB bucket foundation included self-floating towing,penetration with adjustment of horizontal levelness,removability and one-step-installation.The process of one-step-installation included the prefabrication of LSBTB bucket foundation in onshore construction base,installation and debugging of wind power,overall water transportation of foundation and wind power system,and installation of foundation and offshore wind turbine on the appointed sea area.The cost of one-step-installation technique was about 5 000 Yuan/kW,which was 30%-50% lower than that of the existing technique.The prefabrication of LSBTB bucket foundation took about two months.During the one-step-installation process,the installation and debugging of wind power and overall water transportation need about one to two days in sea area within 35 m depth.After the proposed technique is industrialized,the cost will be further reduced,and the installation capacity is expected to be up to 500 wind turbines per year.

Simplified approach for design of raft foundations against fault rupture.Part II:soil-structure interaction

This is the second paper of two, which describe the results of an integrated research effort to develop a four-step simplified approach for design of raft foundations against dip-slip （normal and thrust） fault rupture. The first two steps dealing with fault rupture propagation in the free-field were presented in the companion paper. This paper develops an approximate analytical method to analyze soil-foundation-structure interaction （SFSI）, involving two additional phenomena： （i） fault rupture diversion （Step 3）; and （ii） modification of the vertical displacement profile （Step 4）. For the first phenomenon （Step 3）, an approximate energy-based approach is developed to estimate the diversion of a fault rupture due to presence of a raft foundation. The normalized critical load for complete diversion is shown to be a function of soil strength, coefficient of earth pressure at rest, bedrock depth, and the horizontal position of the foundation relative to the outcropping fault rupture. For the second phenomenon （Step 4）, a heuristic approach is proposed, which ＂scans＂ through possible equilibrium positions to detect the one that best satisfies force and moment equilibrium. Thus, we account for the strong geometric nonlinearities that govern this interaction, such as uplifting and second order （P-△） effects. Comparisons with centrifuge-validated finite element analyses demonstrate the efficacy of the method. Its simplicity makes possible its utilization for preliminary design.

Spring constitutive model of rigid pile composite foundation and application in design of raft foundation

The simplified analysis method based on the static equilibrium is generally adopted for raft design. The secondary stress of superstructure due to the differential settlement of the foundation is neglected, which leads to larger support moments and longitudinal bending of raft compared with real values. The spring constitutive relation of composite foundation is obtained by the flat plate loading tests in Karst region. The interaction between the spring and the raft is equivalent to the interaction between the composite foundation and the raft. The model for superstructure-raft-composite foundation interaction analysis is thus established and the raft is designed. This method not only considers the nonlinear properties of composite foundation but also analyzes the influence of superstructure on bending moment and deformation of raft. Compared with the inverted floor method, the calculated values of moment become more reasonable and uneven settlements are considered. This can be references to the design of raft foundation in similar regions.

Settlement calculation for long-short composite piled raft foundation

The mechanism of long-short composite piled raft foundation was discussed. Assuming the relationship between shear stress and shear strain of the surrounding soil was elasto-plastic, shear displacement method was employed to establish the different explicit relational equations between the load and the displacement at the top of pile in either elastic or elasto-plastic period. Then Mylonakis & Gazetas model was introduced to simulate the interaction between two piles or between piles and soil. Considering the effect of cushion, the flexible coefficients of interaction were provided. With the addition of a relevant program, the settlement calculation for long-short composite piled raft foundation was developed which could be used to account for the interaction of piles, soil and cushion. Finally, the calculation method was used to analyze an engineering example. The calculated value of settlement is 10.2 mm, which is close to the observed value 8.8 mm.

Structural Behavior of Tall Building Raft Foundations in Earthquake Zones

The paper studies the behavior of reinforced concrete raft foundations for multi-story buildings. It also develops a reliability assessment tool for multi- story building raft foundations subjected to earthquake loading. Several multi-story buildings with various configurations, heights, and soil profiles, were subjected to several ACI code combinations of gravity and earthquake loads from different seismic zones. The reliability of the raft foundations of these buildings was assessed using the reliability index approach based on their resistance to the applied loads. Also, the responses of the multi-story buildings under these loading combinations were studied and analyzed in order to draw recommendations and guidelines for the preliminary design of structurally efficient and reliable raft foundations in earthquake zones.

Numerical Study of the Mechanical Behavior of a Foundation Raft under the Hydrodynamic Influence of the Mechanical Characteristics of Clay Soils

The clay soils of the city of Douala are constantly saturated with water, which permanently favors the hydrodynamic behavior of the soils (swelling or consolidation). This phenomenon can cause serious disturbances in the structure of buildings resulting in the appearance of cracks in structures (buildings, road bridge, viaduct, etc.). The foundation raft is a very important structure in the dimensioning of structures. Given the soil-structure interactions, its mechanical characteristics must be the subject of a special study linked to the building environment. In this article, we present a study of the mechanical behavior of a foundation raft anchored in a laminate floor. The aim is to highlight the influence of the mechanical properties of the foundation soil on the evolution of the mechanical behavior of the raft. The method used is a numerical simulation. A physical model taking into account a 5-storey building based in Douala in the Denver district is studied. The foundation on the raft foundation of this building follows an elastic constitutive law with Mazars damage, and rests on a laminated soil of plastic elastic model with Camclay plasticity criterion. The ground-raft and ground-ground interfaces are carried out with the finite elements joined to three nodes (JOI3), and obey the Coulomb model;it is an expansion joint model with Mohr-Coulomb type criterion and associated flow. The numerical resolution is carried out by the finite element method, and the numerical simulations via the Cast3M calculation code. The results from the simulations show that the mechanical characteristics of foundation soils, in this case the water content, the compactness, the state of consolidation, greatly influence the mechanical behavior of the foundation slab. There is indeed a significant settlement and a great deformation of the raft foundation when the water content of the soil layers increases, and when the states of consolidation and compactness are low. This article allows us to predict and control the evolution of the behavior of the ground-structure interface of a raft foundation and to adopt a new model appropriate for the sizing of civil engineering structures.

Deep Foundation Pit Excavations Adjacent to Disconnected Piled Rafts: A Review on Risk Control Practice

Foundation pit excavation engineering is an old subject full of decision making. Yet, it still deserves further research due to the associated high failure cost and the complexity of the geological conditions and/or the surrounding existing infrastructure around it. This article overviews the risk control practice of foundation pit excavation projects in close proximity to existing disconnected piled raft. More focus is given to geotechnical aspects. The review begins with achievements to ensure excavation performance requirements, and follows to discuss the complex soil structure interaction involved among the fundamental components: the retaining wall, mat, piles, cushion, and the soil. After bringing consensus points to practicing engineers and decision makers, it then suggests possible future research directions.

Settlement mechanism of piled-raft foundation due to cyclic train loads and its countermeasure

In this paper, numerical simulation with soil-water coupling finite element-finite difference（FE-FD） analysis is conducted to investigate the settlement and the excess pore water pressure（EPWP） of a piled-raft foundation due to cyclic high-speed（speed： 300km/h） train loading. To demonstrate the performance of this numerical simulation, the settlement and EPWP in the ground under the train loading within one month was calculated and confirmed by monitoring data, which shows that the change of the settlement and EPWP can be simulated well on the whole. In order to ensure the safety of train operation, countermeasure by the fracturing grouting is proposed. Two cases are analyzed, namely, grouting in No-4 softest layer and No-9 pile bearing layer respectively. It is found that fracturing grouting in the pile bearing layer（No-9 layer） has better effect on reducing the settlement.

关于Staad Foundation在筏板基础设计中的运用

分别介绍了Staad Foundation软件的设计模式,界面各区域功能及数据输入方式,以某厂房筏板基础设计为例,对该软件在筏板基础设计中的运用进行了论述,着重阐述了操作步骤及操作过程中应注意事项,为今后同类筏板基础设计提供了借鉴。

Estimation of Settlement under Shallow Foundation for Different Regions in Iraq Using SAFE Software

Foundation design must satisfy limited values of settlement. Settlement is an essential criterion in the design process of shallow foundations. To calculate the settlement under different types of shallow foundations, 79 samples were taken from twenty-three sites distributed in three regions: Mosul, Baghdad and Basrah in the northern, central and southern parts of Iraq. Field and laboratory tests were performed to obtain the strength parameters to calculate the bearing capacity. The results obtained for the bearing capacity were used in SAFE software. The software was used to design and analyze the foundation and to calculate the settlements under two types of foundations (raft and continuous) for the three regions. Average and minimum values of bearing capacity were used. The software used subgrade reaction modules values for the design and analysis. According to the results, the suitable, safe and economical type of foundation to be used in Mosul, Baghdad and Basrah regions for the average value of bearing capacity is the continuous type for the first two regions while the raft type is recommended for Basrah region. In case that the minimum bearing capacity values are used, raft foundation is recommended for Mosul and Baghdad. While deep foundation is the suitable type of foundation for Basrah region.

3D-Analysis of Soil-Foundation-Structure Interaction in Layered Soil

The analysis of building structure in contact with soil involves an interactive process of stresses and strains developed within the structure and the soil field. The response of Piled-Raft Foundation system to the structure is very challenging because there is an important interplay between the component of building structure and the soil field. Herein, soil-foundation-structure interaction of buildings founded on Piled-Raft Foundation is evaluated through 3D-Nonlinear Finite Element Analyses using PLAXIS3D FOUNDATION code. The soil settlements and forces demand of the high-rise building structures and foundation is computed. The parametric study affecting the soil-foundation-structure response has been carried out. The parameters such as construction phasing, sequential loading, building aspect ratios, soil failure models and thickness proportion of soil field stiff layer, are considered. It is concluded that the interaction of building foundation-soil field and super-structure has remarkable effect on the structure.

高层建筑迫降法纠倾方案研究

建筑物因勘察、设计、施工或环境等不良因素影响,导致不均匀沉降,从而产生超过规范允许范围的倾斜。而高层建筑纠倾工程技术难度大、风险高。结合工程实例,通过对现有技术资料分析得出倾斜的原因,并根据工程实际情况,提出桩侧射水扰动迫降纠倾方案,对迫降法的原理、方案设计和施工工艺流程进行了介绍,可为类似工程提供参考。

某高层剪力墙结构不均匀沉降分析及处理

无新增荷载情况下的持续不均匀沉降常常发生在地基有缺陷的高层建筑中,该类沉降产生的破坏是缓慢持续的。地基不均匀沉降会导致建筑物开裂、倾斜,进一步发生结构安全事故。依据某高层剪力墙结构以及不均匀沉降监测数据,采用ABAQUS建立该高层剪力墙结构三维有限元计算模型,分析不均匀沉降工况下上部结构的内力分布及整体变形发展规律。结果显示,有限元计算得到的模型内力增大位置与实际外墙主要开裂位置相吻合,整体沉降变形发展规律与现场实测数据基本一致,证明上部结构三维有限元模型的可行性。进一步建立剪力墙结构-桩筏基础-地基耦合计算模型,开展不同筏板厚度对整体结构不均匀沉降的影响分析。同时结合实际案例制定“增设筏板+补桩”处理方法,加固完成后监测数据显示房屋处于稳定状态,变形与裂缝均无发展。

基于钢筋实际应力状态的基础不均匀沉降地下车库加固方法

某地下车库在降水作业时,将勘探孔改为降水井,引发突涌现象,导致基础底部脱空,筏板产生不均匀沉降,上部结构开裂严重。通过ABAQUS建立地下车库的实体模型,模拟承重结构的变形和损伤,探明地基不均匀沉降对承重结构的影响。结合现场实测结果、数值模拟结果及《混凝土结构设计规范》(GB 50010-2010)推荐公式,获取承重构件受力钢筋的实际应力状态,为结构加固设计提供依据。最后,采取加大截面、粘贴碳纤维布等方法对该车库承重构件进行了加固处理,加固方法可为类似工程提供借鉴。

秦望广场塔楼沉降后浇带提前封闭技术研究

研究目的:带超高层物业开发的大型地下综合体,为了不影响裙房和地下室提前投入使用,需要研究超高层建筑沉降后浇带提前封闭可行性,通过杭州富阳秦望广场通道工程实际项目,采用有限元整体建模分析,提出了残余沉降差计算方法,利用试桩静载试验P-S曲线确定了桩基线刚度参数,推导出沉降后浇带提前封闭楼层,通过实际监测数据,对理论计算结果进行对比验证。研究结论:(1)试桩线刚度与单桩承载力特征值比值在76~119之间,与传统经验值100倍单桩承载力特征值相比,试桩结果离散性较大;(2)塔楼总沉降量与楼层数关系不大,与桩基线刚度取值关系较大;(3)塔楼桩基采用相同线刚度,楼层数与总沉降量成正比;(4)塔楼沉降呈线性发展趋势,理论计算与监测数据基本一致,因成桩工艺控制不稳定,导致工程桩线刚度有离散性,理论计算沉降速率与监测相比均偏小,导致后浇带提前封闭楼层判断有误差;(5)本研究成果可为超高层建筑提前封闭沉降后浇带设计提供参考。

某筏板基础居民楼顶升纠偏方案设计与实践

通过PLC顶升系统,对一倾斜量达16‰的6层砖混结构纠倾。该工程由于地基土层受到多次侵蚀,导致建筑基础发生不均匀沉降。根据现场实际情况,决定采用新增桩基作为反力系统对原建筑进行顶升,最终成功将建筑纠正。

建筑工程中筏板基础大体积混凝土温度裂缝计算及施工技术

该文以某高层建筑为例,探究筏板基础大体积混凝土温度裂缝的计算方法及混凝土施工技术。分别计算各龄期混凝土的收缩变形值、弹性模量、温度应力等参数,然后求解抗裂安全系数。计算结果显示,大体积混凝土各龄期的抗裂安全系数均大于1.0,满足抗裂要求。在大体积混凝土施工中,重点加强物料质量检验与配合比设计,以及混凝土浇筑、养护等环节的施工管理,把握施工技术要点,才能提高筏板基础的施工质量。在混凝土养护结束后进行温度测控,结果表明大体积混凝土内外温差较小,不存在温度裂缝的风险。