Youhu Zhang

Bio: Youhu Zhang is an academic researcher from Norwegian Geotechnical Institute. The author has contributed to research in topics: Bearing capacity & Caisson. The author has an hindex of 1, co-authored 2 publications receiving 6 citations.

Bearing capacity of a side-rounded suction caisson foundation under general loading in clay

Abstract: A novel side-rounded suction caisson foundation is proposed in this study. Compared to a conventional circular shape in plan, it has a rectangular middle section inserted in between the two circular halves for increased moment capacity. This paper presents an investigation into the bearing performance of this novel foundation in clay under uniaxial and combined loading by means of an extensive finite element parametric analysis. It is found that by adopting a dimensionless equivalent embedment ratio and a dimensionless equivalent strength heterogeneity ratio, which account for the side-rounded shape of the proposed foundation, its design approach can be unified with an existing framework established for conventional skirted circular footings. The advantage of the proposed foundation and the application of the proposed design method is demonstrated through an example application.

Interpretation of the Torsional Resistance of Shallowly Embedded Hemiball Penetrometer

Abstract: The hemiball penetrometer is a geotechnical device developed to measure the property of surficial seabed sediments (<0.5 m), which is of most significance for pipeline design and for situa...

A computational study on the uncertainty quantification of failure of clays with a modified Cam-Clay yield criterion

Abstract: In this study, the quantitative effect of the random distribution of the soil material properties to the probability density functions of the failure load and displacements is presented. A modified Cam-Clay failure criterion is embedded into a stochastic finite element numerical tool for this purpose. Various assumptions for the random distribution of the compressibility factor $$\kappa$$ , of the constitutive relation, the critical state line inclination c of the soil, and the permeability k have been tested and assessed with Latin hypercube sampling followed by Monte Carlo simulation. It is confirmed that both failure load and displacements follow Gaussian normal distribution despite the nonlinearity of the problem. Moreover, as the soil depth increases the mean value of failure load decreases and the failure displacement increases. Consequently, failure mechanism of clays can be determined in this work within an acceptable variability, taking into account the soil depth and nonlinear constitutive relations which in the analytical solutions is not feasible as it is assumed the Meyerhoff theory which considers the elastic halfspace.

Finite element analyses of improved lateral performance of monopile when combined with bucket foundation for offshore wind turbines

Abstract: 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.

The wet-towing resistance of the composite bucket foundation for offshore wind turbines

Abstract: The composite bucket foundation (CBF) is a new and environmentally-friendly foundation for offshore wind turbines. This foundation can be prefabricated in batches onshore followed by integrated transport and installation at sea. The structure itself has a subdivision air cushion structure that enables the foundation to float stably on the water surface and realize long-distance towing of the foundation. The mechanism of this air-liquid-solid coupling towing process is complicated, and the influence of the bulkheads on the towing resistance is not clear. In this paper, the influence of the subdivision structure on the towing resistance of the CBF is compared with the tow test in hydrostatic water. The structural motion characteristics and the change of the cushion pressure are also analysed. Experiments are used to verify numerical calculation results. The flow field difference between the CBF with bulkheads, the CBF without bulkheads and the real floating structure was analysed. The dynamic pressure coefficient was used to analyze the force at surfaces of different CBF's. For the tow test and numerical calculation of multiple CBFs, the optimal multi-CBF tow distance and towage number are obtained through the calculation of energy consumption rate.

Shear and Interface Strength of Clay at Very Low Effective Stress

Abstract: Thin-specimen direct shear (TSDS) tests were conducted to measure the shearing strength of kaolinite, and interface strengths between kaolinite and acrylic plastic and anodized aluminum, at normal effective stresses from 1 to 2400 Pa (0.02 to 50 lb/ft 2 ). At the lowest effective normal stresses, curved strength envelopes fitted through the data exhibited no cohesion and high secant friction angles. Accurate information on the behavior of soil in this low-pressure range is needed to properly interpret the behavior of prototype foundations in laboratory-scale model tests.

Investigation of in situ thermomechanical behaviors of soil around an energy pile with flat dilatometer tests

Abstract: An energy pile alters the ground temperature fields around it, which may lead to uneven settlements and a higher risk of failure. The thermomechanical behaviors of soils have been studied extensively in laboratory experiments, while in situ investigations are rare. In this research, flat dilatometer tests (DMTs) are first employed to investigate the thermomechanical behaviors of soil under in situ conditions. The soils were heated by a full-scale precast high-strength concrete (PHC) energy pile, and a series of DMTs were conducted. The results show that temperature changes had a substantial impact on the DMT data of the silt and clay layers. The measured pressures p0 and p1 of the silt and clay layers decreased with increasing ground temperature, and the measured pressure p2 of the silt and clay layers decreased at the beginning and then increased with increasing ground temperature. Although the silt and clay layers have similar variations in the measured pressures, the clay layer has a greater thermal response than the silt layer. Finally, the critical state soil mechanics theory is used to analyze the pore water pressure and thermomechanical properties of in situ overconsolidated soil. The results indicate that the elastic region (yield surface) and mean effective stress of in situ soil decrease with increasing ground temperature, potentially resulting in more irreversible deformation and a higher probability of failure.