Experimental Study of Pore Pressure and Deformation of Suction Bucket Foundations Under Horizontal Dynamic Loading

Centrifuge experiments are carried out to investigate the responses of suction bucket foundations under horizontal dynamic loading. The effects of loading amplitude, the size of the bucket and the structural weight on the dynamic responses are investigated. It is shown that, when the loading amplitude is over a critical value, the sand at the upper part around the bucket softens or even liquefies. The liquefactio...

The Response of Bucket Foundation under Horizontal Dynamic Loading

The experimental investigation of the response of suction bucket foundation in fine sand layer under horizontal dynamic loading has been carried out. The developments of settlement and excess pore pressure of sand foundation have been mainly studied. It is shown that the sand surrounding the bucket softens or even liquefies at the first stage if the loading amplitude is over a critical value, at later stage, the bucket settles and the sand layer consolidates gradually. With the solidification of the liquefied sand layer and the settlement of the bucket, the movement of the sand layer and the bucket reach a stable state.

Refractive index and thickness analysis of natural silicon dioxide film growing on silicon with variable-angle spectroscopic ellipsometry

The refractive index and thickness of SiO2 thin films naturally grown on Si substrates were determined simultaneously within the wavelength range of 220-1100 nm with variable-angle spectroscopic ellipsometry. Different angles of incidence and wavelength ranges were chosen to enhance the analysis sensitivity for more accurate results. Several optical models describing the practical SiO2-Si system were investigated, and best results were obtained with the optical model, including an interface layer between SiO2 and Si, which proved the existence of the interface layer in this work as described in other publications.

Centrifugal experimental study of suction bucket foundations under dynamic loading

Centrifugal experiments were carried out to investigate the responses of suction bucket foundations under horizontal and vertical dynamic loading. It is shown that when the loading amplitude is over a critical value, the sand at the upper part around the bucket is softened or even liquefied. The excess pore pressure decreases from the upper part to the lower part of the sand layer in the vertical direction and decreases radially from the bucket's side wall in the horizontal direction. Large settlements of the bucket and the sand layer around the bucket are induced by dynamic loading. The dynamic responses of the bucket with smaller height (the same diameter) are heavier.

Centrifuge modeling of suction bucket foundations for platforms under ice-sheet-induced cyclic lateral loadings

This paper presents the results of a series of centrifuge model tests performed to study the behavior of suction bucket foundations for a tension leg platform in the Bohai Bay, China. The target lateral loadings were from ice-sheet-induced structural vibrations at a frequency of 0.8-1.0 Hz. The results indicate that excess pore water pressures reach the highest values within a depth of 1.0-1.5 in below the mud line. The pore pressures and the induced settlement and lateral displacement increase with the amplitude of the cyclic loading. Two failure modes were observed: liquefaction in early excitations and settlement-induced problems after long-term excitations. (c) 2006 Elsevier Ltd. All rights reserved.

On the Bearing Capacity of Suction Bucket Foundations in Saturated Sand

Abstract: The static bearing capacity of suction caisson with single-and four-caissons in saturated sand foundation is studied by experiments. The characteristics of bearing capacity under vertical and horizontal loadings are obtained ex- perimentally. The effects of loading direction on the bearing capacity of four-caissons are studied under horizontal load- ing. The comparison of the bearing capacity of single-caisson and four-caisson foundation, the sealed condition of cais- son’s top and loading rate are analyzed.

Study on the Capacity Degradation of Bucket Foundation in Liquefied Sand Layer under Cyclic Loads

The capacity degradation of bucket foundation in liquefied sand layer under cyclic loads such as equivalent dynamic ice-induced loads is studied. A simplified numerical model of liquefied sand layer has been presented based on the dynamic centrifuge experiment results. The ice-induced dynamic loads are modeled as equivalent sine cyclic loads, the liquefaction degree in different position of sand layer and effects of main factors are investigated. Subsequently, the sand resistance is represented by uncoupled, non-linear sand springs which describe the sub-failure behavior of the local sand resistance as well as the peak capacity of bucket foundation under some failure criterion. The capacity of bucket foundation is determined in liquefied sand layer and the rule of capacity degradation is analyzed. The capacity degradation in liquefied sand layer is analyzed comparing with that in non-liquefied sand layer. The results show that the liquefaction degree is 0.9 at the top and is only 0.06 at the bottom of liquefied sand layer. The numerical results are agreement well with the centrifugal experimental results. The value of the degradation of bucket capacity is 12% in numerical simulating whereas it is 17% in centrifugal experiments.

Numerical Simulation of Liquefaction Deformation of Sand Layer around Bucket Foundations under Dynamic Loadings

Bucket Foundations under Dynamic Loadings The liquefaction deformation of sand layer around a bucket foundation is simulated under equivalent dynamic ice-induced loadings. A simplified numerical model is presented by taking the bucket-soil interaction into consideration. The development of vertical and horizontal liquefaction deformations are computed under equivalent dynamic ice-induced loadings. Firstly, the numerical model and results are proved to be reliable by comparing them with the centrifuge testing results. Secondly, the factors and the development characteristics of liquefaction deformation are analyzed. Finally, the following numerical simulation results are obtained: the liquefaction deformation of sand layer increases with the increase of loading amplitude and with the decrease of loading frequency and sand skeleton’s strength. The maximum vertical deformation is located on the sand layer surface and 1/4 times of the bucket’s height apart from the bucket’s side wall (loading boundary). The maximum horizontal deformation occurs at the loading boundary. When the dynamic loadings is applied for more than 5 hours, the vertical deformation on the sand layer surface reaches 3 times that at the bottom, and the horizontal deformation at 2.0 times of the bucket height apart from the loading boundary is 3.3% of which on the loading boundary.

Responses of saturated sand surrounding a bucket foundations under horizontal vibration loading

In this paper we investigated the responses of saturated sand under horizontal vibration loading induced by a bucket foundation. It is shown that the saturated sand liquefies gradually since the vibration loading is applied on. The maximum displacement on the surface of sand layer occurs near the loading end and in this zone the sand is compressed and moves upwards. The liquefaction zone is developed from the upper part near the loading side and stopped gradually.

Experimental Study on the Responses of Bucket Foundations in Calcareous Sand under Vertical Dynamic Loading

Abstract: Experiments to determine the vertical static bearing capacity are carried out first in laboratory which is taken as a reference for choosing the amplitudes of vertical dynamic loading. Then a series of experiments are carried out to study the influences of factors, such as the scales of bucket, the amplitude and frequency of loading, the density of soils etc.. According to the experimental results, the responses of bucket foundations in calcareous sand under vertical dynamic loadings are analyzed. It is shown that there exists a limited effected zone under vertical dynamic loading. The scale of this zone is about one times of the bucket’s height. In this zone, the density of soil layer, the deformation and the pore pressure change obviously.

Response of the Bucket Foundation in Calcareous Sand under Horizontal Dynamic Load

Abstract: Experiments to determine the horizontal static bearing capacity are carried out first. The static bearing capacity is a reference for choosing the amplitudes of dynamic load. Then a series of experiments under dynamic horizontal load are carried out in laboratory to study the influences of factors, such as the scales of bucket, the amplitude and frequency of load, the density of soils etc.. The responses of bucket foundations in calcareous sand under horizontal dynamic load are analyzed according to the experimental results. The displacements of bucket and sand layer are analyzed.

Dimensionless Analysis of the Simulation of Bucket Foundations under Dynamic Load

Firstly, the main factors are obtained by use of dimensionless analysis. Secondly, the time scaling factors in centrifuge modeling of bucket foundations under dynamic load are analyzed based on dimensionless analysis and control- ling equation. A simplified method for dealing with the conflict of scaling factors of the inertial and the percolation in sand foundation is presented. The presented method is that the material for experiments is not changed while the effects are modified by perturbation method. Thirdly, the characteristic time of liquefaction state and the characteristic scale of affected zone are analyzed.

Negative refractive index in a four-level atomic system

We propose a scheme for realizing negative refractive index in a four-level atomic system. It is shown that such a system can simultaneously exhibit negative permittivity and negative permeability in an optical frequency range. Furthermore, by analysing the dispersion property of the left-handed material, we find that the probe beam can be controlled from superluminal to subluminal or vice versa via choosing appropriate parameters.

Phase control of switching from positive to negative index material in a four-level atomic system

Electric and magnetic responses of the medium to the probe field are analysed in a four-level loop atomic system by taking into account the relative phase of the applied fields. An interesting phenomenon is found: under suitable conditions, a change of the refractive index from positive to negative can occur by modulating the relative phase of the applied fields. Then the medium can be switched from a positive index material to a negative index material in our scheme. In addition, a negative index material can be realized in different frequency regions by adjusting the relative phase. It may give us a convenient way to obtain the desired material with positive or negative index.