摘要:

Deep offshore geological surveys have been conducted on the Gabon continental shelf. A geological description of the area explored reveals the presence of seepage features and gas bubbles in the upper 50 m of sediments. Seafloor instabilities also occurred at quite low slope gradients. A laboratory study of the mechanical behavior of the sampled sediments helped verify that the ratio between undrained shear strength and preconsolidation pressure is very high at low confining pressures in terms of classical empirical regressions used mostly by geotechnicians. These experiments also lead to a mathematical model of undrained shear strength versus depth profile for some saturated and normally consolidated sediments. Hypotheses are developed concerning the undrained behavior of underconsolidated sediments. The eventuality of seepage forces in sediments leads to the calibration of safety factors under drained and undrained conditions. It is established that static infinite plane failure cannot be triggered at low slopes if the sediments are normally consolidated. Graphs are finally constructed in order to visualize the impact of water excess pore pressure on superficial sediments stability. A realistic physical interpretation is also given.

ISSN:1064-119X    

DOI:10.1080/10641199809379966

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Physical properties, undrained shear strength, and sound velocity of marine sediments (< 5 m below the seafloor) were measured in the laboratory on gravity and box cores taken in Eckernfoerde Bay, Baltic Sea. Shear wave velocity of surface marine sediments was estimated based on in‐situ measured profiles of shear modulus versus depth. Sediments at the study site are mainly soft silty clays, with high water content, high void ratio, high organic content, low bulk density, gas bubbles, low compressional and shear wave velocity, and low shear strength.

ISSN:1064-119X    

DOI:10.1080/10641199809379967

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The geotechnical properties of the fine‐grained sediments of the Tiber River prodelta slope are described. Laboratory investigations depict the overall physical and mechanical behavior of the sediments and give information regarding their in‐situ conditions due to gravitational campaction. In spite of relative homogeneity in terms of the basic geotechnical properties, noticeable differences between materials sampled at different water depths and at different depths below the seafloor can be detected. This variation is observed when in‐situ material properties are taken into account and can be explained if the different depositional and burial conditions of the sediments are considered. In particular, differences in compressibility and undrained behavior have been found between sediments sampled immediately underneath the seafloor and the underlying materials as well as between the entire present‐day prodelta clays and the “aged”; sediments of the delta front, which were originally deposited in a prodelta slope environment. These considerations can be generalized to other small marine deltas, which are not characterized by the exceptional depositional rates typical of the extensively studied large deltas but frequently occur worldwide and host offshore engineering activities.

ISSN:1064-119X    

DOI:10.1080/10641199809379968

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Seismic reflection methods have a wide range of applications in marine geologic and geotechnical applications. Mapping surfaces and subsurface features using analog seismic reflection data is a time‐consuming process because two‐way travel time values read from paper sections must be posted on a base map, and the volume of data involved is very large. In this article, a simple FORTRAN program to convert shot‐point numbers along a horizon or reflector in analog seismic data tox‐ycoordinates is presented. After conversion, thexandycoordinates with corresponding two‐way travel time values of the points along the horizon can be used for computer contouring, or the two‐way travel time values can be easily posted on the base map for hand contouring. Usage of the program is not limited to seismic reflection data; it can be used for any type of analog data measured along a track line.

ISSN:1064-119X    

DOI:10.1080/10641199809379969

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

ISSN:1064-119X    

DOI:10.1080/10641199809379965

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor