The overconsolidation ratio considerably affects the physical and mechanical properties of soil as well as the interaction between structures and soil. Scale and consolidation time limitations render the preparation of overconsolidated soil for small-scale model tests difficult. Therefore, studying structure-soil interactions, especially the vertical bearing capacity of pile foundations in overconsolidated soil becomes challenging. Given the importance of reliable overconsolidated soil in physical model tests for studying soil-structure interactions, this study, based on the fundamental of the overconsolidation ratio, established a reliable method for preparing overconsolidated soil by altering centrifuge acceleration. Piezocone penetration tests were conducted to validate the accuracy of this method. Furthermore, vertical bearing capacity of pile foundations was evaluated in various overconsolidated soils. The vertical ultimate bearing capacity of pile foundations, cone penetration resistance, pore water pressure, and sleeve friction resistance were obtained in soils with various overconsolidation ratios. Based on the results of both tests, a formula was developed to calculate the vertical ultimate bearing capacity of pile foundations, taking into account the overconsolidation ratio of soil. This proposed method for evaluating vertical bearing capacity of pile foundations in overconsolidated soil can also be applied to study interactions between other marine structures and soil. The results of the study can provide technical support for designing the foundations of offshore oil and gas facilities, wind power, and other structures.

Static pile ended with cone apex angle is widely used in practical engineering. However, the corresponding penetration resistance is still impossible to be predicted accurately. To address this, the penetration process of static pile is simulated by using the coupled Eulerian-Lagrangian (CEL) method in this study. During the penetration process of static pile in clay, the effect of cone apex angle and soil rigidity index on pile-end resistance and the distribution of the plastic zone of the soil around the pile-end are analyzed. The corresponding results indicate that the pile-end resistance is positively correlated with the size of cone apex angle and soil rigidity index, and the pile-end resistance rises with the increase of penetration depth until reaching a certain depth. Besides, the expansion process of the plastic zone near the pile-end is characterized by the expansion of spherical cavity. Since the position of expansion cavity center is different from the traditional theory, the corresponding radius in the traditional theory of cavity expansion is modified according to the corresponding numerical results. Finally, a semi-empirical method, in which the effect of cone apex angle and the soil rigidity index are considered, is proposed to predict the ultimate pile-end resistance of static pile.

Bucket foundations are widely used in offshore fixed platforms, wind turbines, and floating structures. They are subjected to complex loads from the superstructure, among which the torsional load has a significant impact on foundation performance. Therefore, this study focuses on the bucket foundation under torsional load to address inaccurate calculations owing to the partial bearing phenomenon. First, the torsional bearing mechanisms of bucket foundations in normally consolidated and homogeneous soils are revealed through numerical simulations, and the limitations of the general equations for calculating the ultimate torsional capacity of bucket foundations are elaborated. Next, the torsional bearing characteristics under diversified conditions are determined considering the soil–bucket friction coefficient, bucket aspect ratio, and soil strength–heterogeneity ratio. A theoretical bucket foundation model under torsional loads is subsequently developed by summarising the observed torsional failure modes, and novel equations are derived to compute the ultimate torsional capacity of the bucket foundation accordingly. Finally, the effectiveness and accuracy of the proposed theoretical model are verified against the results of numerical simulations and its improved efficacy is demonstrated through comparison with the general equations.

Clarifying penetration characteristics and accurately predicting penetration resistance of bucket foundations is crucial to ensure their smooth penetration. This study performed large-scale model tests on nearshore seven-compartment (SC) bucket foundations and novel deep-sea five-connected (FC) bucket foundations to systematically explore the penetration attitude, development of soil plugs, flow rates, bucket-soil interactions, and required suction of these two structures in clay. The good penetrability was identified for the new FC bucket foundation. The development of soil plugs due to bucket wall replacement as well as the mechanism of drag reduction of the inner wall and bucket end were revealed. The experiments demonstrated that the penetration flow rate was almost equal to the volume of bucket body entering the soil and accounted for approximately 95% of the total flow rate. A formula for calculating penetration resistance in clay that considers the effect of suction on the reduction in resistance of the inner wall and bucket end was proposed and validated by field tests. The research results improve the safety of bucket foundation penetration in clay and provide significant guidance for the installation of deep-sea FC bucket foundations.

随着筒型基础逐渐成为海上风电基础的常用形式,其在循环荷载作用下的倾角长期发展规律备受关注.基于模型试验与原型无量纲量等效的缩比尺原则,开展了不同工况风-浪荷载耦合作用下筒型基础模型试验,得到了筒型基础在循环荷载作用下的累积倾角发展规律.试验结果表明:影响筒型基础倾角累积速率的参数随着无量纲荷载幅值的增加而增加并与荷载的非对称性无关,部分双向非对称的风-浪耦合加载工况会导致筒型基础产生更为严重的累积倾角.当循环次数和循环荷载幅值一定时,累积倾角与表征荷载非对称性的无量纲参数呈近似线性关系.根据试验数据,建立了预测不同循环荷载条件下筒型基础累积倾角的经验公式.

The composite bucket shallow foundation proposed by Tianjin University can be better adapted to the soft geological conditions in China for offshore wind engineering. The offshore wind turbines are generally subjected to relatively large horizontal load induced by waves, currents and ice loading. Therefore, calculating the horizontal bearing capacity is an important part of the design for the composite bucket shallow foundation. In this paper, according to the numerical simulation, considering the constraint of bucket foundation on internal soil in different degrees firstly, the horizontal soil damage rate is introduced into the formula as a new empirical parameter Next, upper-bound solution of the horizontal bearing capacity of a composite bucket shallow foundation is derived in sand. Fianally, the calculation method is validated by the bucket model tests with different height-diameter ratios in sand under horizontal loading.

Bearing the large moment that is generated by the wind load that acts on the upper structure of offshore wind turbines is an important feature of their foundations that is different from other offshore structures. A composite bucket shallow foundation (CBSF) has been proposed by Tianjin University to address the soft geological conditions in the offshore regions of China for wind turbines. The CBSF is a new type of foundation and is effective against large moments. The soil deformation test of a CBSF and the numerical simulation study under the same working conditions are carried out to determine the failure mechanism of a CBSF under moment loading. The resisting soil compression rate η m is defined as a new empirical parameter that indicates the ability of the soil inside the bucket to resist moment loading. The upper limit of the resisting moment bearing capacity of the bucket foundation is derived through the upper bound theorem of classical plasticity theory based on the failure mechanism. The calculation method is validated by tests of bucket models with different height-diameter ratios in sand under moment loading.

The soil plug is a common problem in the installation of bucket foundations for offshore wind turbines (OWTs), but there is little research about the influence of the soil plug on the bearing performance of bucket foundations. In this paper, the range of soil plug height is firstly determined according to the recordings of engineering cases and geotechnical tests in the published literature. Then the finite element models of bucket foundations with different soil plugs are established to investigate the influence of the soil plug on uniaxial and combined bearing capacities under different soil properties and embedment ratios. Based on the numerical results, a bearing capacity calculation method of bucket foundations considering the effect of soil plug is proposed. The proposed equivalent method can be used to evaluate the influence of the soil plug on the bearing capacities of bucket foundations.

重组竹作为一种新兴的绿色建筑材料,以其绿色环保、轻质高强、耐腐蚀和易加工装配等优点成为广大学者的研究重点,以重组竹作为结构承重构件的项目不断落地.针对村镇建筑低荷载和低层数的特点,提出一种以重组竹为材料,适用于上部结构形式为竹木结构的格栅式条形基础,并对其开展结构选型和优化设计.开展了砂土地基中基础底面开孔率为 0 和 24%的格栅式条形基础的土工离心机模型试验,揭示了基础底面开孔对地基极限承载力、基底压力和土体附加应力的影响规律.试验结果表明,基础底面开孔对极限承载力和基底压力的分布影响显著,但对土体附加应力的分布无明显影响.通过有限元计算方法模拟了砂土中格栅式条形基础的竖向承载特性,并且有限元计算得到的荷载-位移曲线和基底压力分布规律与离心机模型试验值结果吻合良好,证明了有限元方法的正确性.采用经验证的有限元方法对不同开孔率下格栅式条形基础的承载性能进行了系统研究,计算得到了不同密实度砂土地基中不同开孔率的格栅式条形基础的地基极限承载力,并与太沙基极限承载力计算结果进行了对比,引入开孔率概念,得到考虑开孔影响的格栅式条形基础的地基极限承载力计算方法.

Because of its irregular shape, it is inaccurate to calculate the bearing capacity of the A-shaped mat foundation by a conventional method, which may have potential safety hazards. In this paper, the vertical bearing capacity of the mat is obtained by using the equivalent calculation method (ECM) and the finite element method respectively, and compared with the centrifuge test results. A correction method based on the ECM is proposed. Influences of foundation dimensional parameters on the H, M and H-M combined bearing capacity are studied. Expressions of H-M failure envelopes related to the dimensional parameters are established. A new form of V-H-M envelope expression for mats is suggested according to the effect of vertical load on H-M capacity. The modified ECM and the V-H-M envelope proposed in the paper can be used to quickly evaluate the vertical bearing capacity of the A-shaped mat and its stability under coupling loads.

With the increasing of current installed capacity of offshore wind power, super-large diameter steel pipe pile foundation has been widely used. The increase of pile diameter changes the pile-soil interaction mode, thus the applicability of the method for calculating inner frictional resistance of steel pipe piles in the current code is open to question. In this study, centrifugal model tests are carried out to reveal the behavior of earth pressure and internal frictional resistance in clay with different pile diameters by using double-walled pile and pipe pile models. By using finite element numerical analysis method, the factors influencing the inner frictional resistance are analyzed, and a method for calculation of inner frictional resistance of steel pipe piles is developed. The proposed method is verified by comparison with the centrifuge test results. The results show that, with the increase of pile diameter, the inner wall earth pressure increases, and the inner frictional resistance also increases. The inner frictional resistance is exponentially distributed along the pile depth, and it is available within 5 times the pile diameter from the pile tip. The proposed calculation method of inner wall frictional resistance is found to be in good agreement with centrifuge test results.

Pile-bucket foundation, which attaches a wide-shallow bucket to the head of monopile, has been proposed for offshore wind turbines to improve the bearing performance of monopile foundation. In this paper, model tests were firstly conducted to investigate the lateral bearing capacities of monopile, mono-bucket and pile-bucket foundations, as well as providing a validation to finite element (FE) analysis. The results show that the bucket can effectively enhance the lateral bearing performance of the monopile foundation. Next, according to a series of finite element analysis, p-y curves in both reinforced section and non-reinforced section of pile component in pile-bucket foundation are modified considering the influence of the bucket component. The moment and lateral resistance provided by bucket component are calculated by limit equilibrium method. Consequently, by regarding the contribution of bucket as a restoring moment and lateral load, the pile-bucket is converted to a pile with external moment and lateral load acting on the pile head. A theoretical calculation method of pile-bucket foundation subjected to lateral loads is put forward based on modified p-y curves. This method is validated by FE results and can provide estimations of lateral loads and deflections for pile-bucket foundations under lateral loading in engineering design.

新时代以碳中和为目标的能源结构转型,对高校新兴专业人才培养提出了迫切的需求,尤其体现在毕业生的动手实践与创新能力方面.天津大学结合社会对人才的需求,新设了风能工程专业,快速设计并建立了双校区双平台开放运行的风电基础综合实验教学平台,以满足本科生及研究生的实验课程教学及科研使用需求.单个该平台可同时进行四种不同土/水质模型试验,且具有向上的扩展性.平台配备有同时进行竖向荷载(V)、水平荷载(H)、弯矩荷载(M)及扭矩荷载(T)加载的装置.平台运行多年以来,师生均认为平台设计合理、功能齐全、操作便捷,该平台能够满足风电基础实验的各项功能需求,一直处于满负荷状态.

新时代对新工科人才培养提出以"立德树人"为根本的高素质专业型人才目标要求,天津大学水利水电教研室对专业实验课程展开教学改革,历经常规线下教学、疫情封校期远程线上教学、复课后线上线下组合式教学和新工科课程思政融合式教学四个典型阶段的实验教学改革及总结,探讨新时代新工科背景下专业实验类课程改革的最佳方案.近几年,水利水电专业实验课程教学改革取得良好的效果,充分发挥前期在线学习的预习作用、中期虚仿平台操作的问题前置作用及后期现场实操的再次强化作用,同时将思政元素融入到实验教学课堂中起到很好的"德育为先"的教育作用.新工科课程思政融合式实验教学积极引导学生建立起"建设祖国永远向前进,家国情怀一生来践行"的人生追求,实现以学生为主题+问题导向的实验课程授课方式,达到为祖国培养新时代新工科卓越人才的培养目标.

Offshore wind energy is one of the most important clean energy sources developing in China in recent years. As a new type of offshore wind turbine foundation, the wide-shallow bucket foundation with large diameter has a good ability to withstand moments. It is thus suitable for offshore region in China with soft clay deposits. Moreover, this type of foundation has advantages of onshore prefabrication, foundation-tower-turbine integrated floating transportation and suction installation, resulting in a good benefit for cost reduction. To better understand the bearing capacity of the wide-shallow bucket foundation in clay, numerical analyses are conducted to study the monotonic ultimate bearing behavior. The horizontal and moment ultimate bearing capacities and corresponding failure mechanisms are obtained. By building the velocity field based on the failure mechanisms of the bucket foundations, combined with the virtual work equation and the internal energy loss rate function, the upper bound solutions for the horizontal and moment ultimate bearing capacities of the bucket foundations are established and programmed using mathematical software. The results of the upper bound limit analysis have a good agreement with the calculation of the numerical analyses.

The accurate estimation of penetration resistance of the bucket foundation is the key step for its installation, and the core part of the estimation of the penetration resistance is the exact prediction of the drag reduction effect due to suction. Therefore, in the present paper, the change regularity of the excess porewater pressure along the bucket wall and at the tip is analyzed by combining the model test and finite element analysis method, along with the soil pressure of the bucket foundation during the suction penetration process in sand. The results showed that, during the suction penetration process of the bucket foundation, the soil pressure and excess porewater pressure change approximately linearly with the depth of the bucket wall, and the reduction degree of lateral resistance due to seepage increases in a power function growth trend. Based on the effective stress principle of soil and basic theory of seepage and considering the effect of seepage on penetration resistance, the change regularity of the effective stress of soil along the bucket wall during the penetration process is obtained. Besides, the calculation method for penetration resistance and required suction of bucket foundation in sand soil is established, and the effectiveness of the present method is verified by comparing with the model test and engineering case, which can provide theoretical basis for engineering design and construction of bucket foundation.

由于宽浅式筒型基础具有不同于传统筒型基础的超大直径(D≥30 m)和较浅入土深度(d≤15 m),因此其竖向承载模式和极限承载力计算方法有待研究.通过数值分析得到宽浅式筒型基础在达到竖向极限承载力时的破坏模式,引入承载力极限分析理论,构建宽浅式筒型基础竖向极限承载的地基破坏机动场;结合虚功方程采用Matlab求解宽浅式筒型基础竖向极限承载力的上限解,计算结果与数值分析结果和离心试验结果吻合良好.

A wide-shallow bucket is connected to a monopile for offshore wind turbines to withstand the severe loading conditions in marine environments and this innovative pile-bucket foundation has not been investigated comprehensively. In this paper, a monopile, wide shallow mono-bucket and pile-bucket were firstly tested under lateral loading via geotechnical centrifuge to examine the performance of the hybrid foundation. The results of the centrifuge tests and extensive finite element analyses with dimensions of an actual wind turbine foundation show that the addition of the bucket significantly enhances the lateral bearing capacity and stiffness of the monopile in both sand and soft clay. The load transfer mechanism, failure mode and bearing behavior are illustrated to study how the bucket and pile component contribute to the performance of the foundation system and the interactions of the pile-soil-bucket. Finally, parametric studies about the loading eccentricity and geometry of the bucket are carried out to provide references for the engineering practice.

As ocean engineering has developed towards the deep sea, a precise instrument is urgently needed to accurately measure the in situ strength of soft clay at the shallow strata of the deep sea and thus to evaluate the bearing capacity of the foundation. In this paper, a new type of probe - the strip probe - is introduced. The soft clay failure modes, including the shallow penetration and deep penetration of the strip probe, were analysed by a centrifugal model test and the mesh-to-mesh solution mapping (MMSM) finite element method. Based on limit analysis, the upper-bound solutions between the soft clay strength and the strip probe penetration resistance were established under non-full-flow and full-flow modes. Through an in site penetration test, the upper-bound solutions were proven rational, and the strip probe was appropriate for detecting the strength of abyssal soft clay.

面向新时代和新工科的发展要求,天津大学水利工程专业对水工建筑物实验教学课程进行了改革,应用乌东德大型水工模型综合实验代替传统常规小型模型实验.3年来,取得了良好的教学效果,加强了科研与本科教学的深度融合,有效挖掘和利用了实验室中的优质教学资源,提升了本科生的实验能力和综合创新能力.