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Zhang X.-H.,CAS Institute of Mechanics | Lu X.-B.,CAS Institute of Mechanics | Zhang L.-M.,Hong Kong University of Science and Technology | Wang S.-Y.,CAS Institute of Mechanics | Li Q.-P.,China Ocean Oil Co.
Acta Mechanica Sinica/Lixue Xuebao | Year: 2012

Mechanical properties of methane hydratebearing-sediments (MHBS) are basic parameters for safety analysis of hydrate exploration and exploitation. Young's modulus, cohesion, and internal friction angle of hydratebearing sediments synthesized in laboratory, are investigated using tri-axial tests. Stress-strain curves and strength parameters are obtained and discussed for different compositions and different hydrate saturation, followed by empirical expressions related to the cohesion, internal friction angle, and modulus of MHBS. Almost all tested MHBS samples exhibit plastic failure. With the increase of total saturation of ice and methane hydrate (MH), the specimens' internal friction angle decreases while the cohesion increases. © The Chinese Society of Theoretical and Applied Mechanics and Springer-Verlag Berlin Heidelberg 2012.


Jiao B.-T.,China Ocean Oil Co. | Shi Z.-M.,China Ocean Oil Co. | Lu X.-B.,CAS Institute of Mechanics | Zhang J.-H.,Tsinghua University
Gongcheng Lixue/Engineering Mechanics | Year: 2010

The centrifugal experiments are carried out to study the dynamic responses of suction buckets in fine silty sand under horizontal loading. The static bearing capacity after dynamic loading is investigated too. If there is a clay over-layer whose surface is at the same level with the bucket's top, the settlements of bucket and sand layer are bigger than that without an over-layer, but the increment of pore pressure is on the contrary. The static bearing capacity of the bucket increases after dynamic loading. With the increase of loading amplitude, the settlement of sand layer increases, but the affected zone with obvious deformation is limited (about one times the bucket's height)because of the filtering and decaying effects of the liquefaction zone on the vibration. The excess pore pressure decreases from the bucket's edge to the inside and from the surface of sand layer to the bottom. The complete liquefaction thickness of the sand layer increases with the increase of load amplitude whose maximum is about 40% of the bucket's height.


Zhang X.-H.,CAS Institute of Mechanics | Lu X.-B.,CAS Institute of Mechanics | Wang S.-Y.,CAS Institute of Mechanics | Li Q.-P.,China Ocean Oil Co.
Yantu Lixue/Rock and Soil Mechanics | Year: 2011

By using the integrated experimental apparatus for syntheses of gas hydrate sediment and triaxial tests, a series of static and dynamic tests are conducted on the tetrahydrofuran (THF) hydrate with fine sand and Mongolia sand as the skeleton. The stress-strain curves, strength and liquefaction characteristics of the sediments before and after hydrate dissociation are obtained. The mechanical properties of the two kinds of hydrate sediments with fine sand and Mongolia sand as the skeleton, as well as the liquefaction characteristics of the sediment after dissociation of hydrate and the corresponding saturated sand are compared. It is shown that the hydrate-bearing sediments all behave as plastic failure, strength of which the increases with the formation of hydrate and the confining pressure. The dissociation of hydrate can lead to the great decrease of the strength of the sediments. The liquefaction of the sediment after dissociation of hydrate needs shorter time relative to the corresponding saturated sand.


Lu X.,China Ocean. Oil. Co | Li Q.,CAS Institute of Mechanics | Wang L.,China Ocean. Oil. Co | Zhang X.H.,China Ocean. Oil. Co | And 2 more authors.
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2010

Numerical modeling is processed by using of the software ABQUAS to analyze the displacement's distribution and evolution of the pipes and surrounding seabed after dissociation of NGH. It is shown that dissociation scale, thickness of over-layer, elastic parameters of seabed before and after dissociation of NGH have crucial impacts on the deformation of pipes and seabed. In practical engineering design, the dissociation scale and the strength of seabed after dissociation of NGH should be controlled strictly to guarantee the safety of pipes and seabed. Copyright © 2010 by The International Society of Offshore and Polar Engineers (ISOPE).


Zhang X.,CAS Institute of Mechanics | Lu X.,CAS Institute of Mechanics | Li Q.,China Ocean Oil Co. | Yao H.,China Ocean Oil Co.
Science China: Physics, Mechanics and Astronomy | Year: 2010

Thermally induced evolution of phase transformations is a basic physical-chemical process in the dissociation of gas hydrate in sediment (GHS). Heat transfer leads to the weakening of the bed soil and the simultaneous establishment of a time varying stress field accompanied by seepage of fluids and deformation of the soil. As a consequence, ground failure could occur causing engineering damage or/and environmental disaster. This paper presents a simplified analysis of the thermal process by assuming that thermal conduction can be decoupled from the flow and deformation process. It is further assumed that phase transformations take place instantaneously. Analytical and numerical results are given for several examples of simplified geometry. Experiments using Tetra-hydro-furan hydrate sediments were carried out in our laboratory to check the theory. By comparison, the theoretical, numerical and experimental results on the evolution of dissociation fronts and temperature in the sediment are found to be in good agreement. © 2010 Science China Press and Springer-Verlag Berlin Heidelberg.


Zhang X.H.,CAS Institute of Mechanics | Lu X.B.,CAS Institute of Mechanics | Li Q.P.,China Ocean Oil Co.
Journal of Petroleum Science and Engineering | Year: 2011

Hydrate dissociation in marine sediments may cause large hazards. Two types of new hazard phenomena, outburst and layered fracture, are observed in laboratory experiments and the initiation mechanism is discussed. Experiments are carried out in a two-dimensional rectangular box and a one-dimensional cylinder, respectively. It is shown that layered fracture and outburst can appear after hydrate dissociation and are related closely to dissociation speed, permeability, strength of hydrate-bearing sediment and over-layered stratum. Outburst often occurs at low permeability, high strength of over layered stratum and high pore pressure, while layered fracture is just on the contrary. © 2011 Elsevier B.V.


Zhang X.-H.,CAS Institute of Mechanics | Wang S.-Y.,CAS Institute of Mechanics | Li Q.-P.,China Ocean Oil Co. | Zhao J.,CAS Institute of Mechanics | Wang A.-L.,CAS Institute of Mechanics
Yantu Lixue/Rock and Soil Mechanics | Year: 2010

With the integrated experiment apparatus of gas hydrate deposit syntheses and triaxial compression test, a series of ice, tetrahydrofuran(THF) hydrate, CO2 hydrate and methane hydrate(MH) in the skeleton of fine silty sand are synthesized; and then shear tests are carried out. The stress-strain and shear strength characteristics of these four kinds of deposits and the effects of gas hydrate and ice on the strength of deposit are analyzed and compared. It is shown that these four deposits behave as plastic failure. The larger the confined pressure is the higher the strength is. The deposits with the same saturation of gas hydrate have different strengths when the kinds of hydrates are different.

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