SHEAR MODULUS (Gmax): A COMPARATIVE STUDY BETWEEN GEOTECHNICAL ENGINEERING AND GEOPHYSICAL OVERVIEWS, ON A LIQUEFIED NATURAL GAS PLANT AREA AT DAMIETTA PORT, EGYPT.

Abstract

Liquefied Natural Gas Plant (LNG) area is located at Damietta Port, EGYPT. The plant consists of different strategic structures. The area of the plant is approximately 1,200,000 m2 in plan and is bounded by latitudes 30o 00\ & 31o 30\ N and longitudes 31o 30\ & 32o 00\ E. A geotechnical investigations campaign has been carried out for the study area. Five boreholes were drilled, four of them were 34.00 m deep and the fifth one was only 30.00 m. Standard Penetration Tests (SPT) were accomplished in the field. Different laboratory tests were executed on some extracted soil samples to determine the physical and mechanical properties of the soil. In-situ seismic (P & S-waves) down-hole investigations campaign has been performed for the study area every 1.0 meter depth intervals at five carefully selected locations coincided with the five drilled boreholes. The geotechnical and the in-situ seismic down-hole investigations illustrate that, the ideal lithologic section can describe the occurrence of surface and subsurface layers in the study area, that consist of three main rock types: sand, clay and sand layers. The corrected field measured SPT blowcount (N1)60, the seismic SPT values, the geotechnical shear modulus (for low amplitudes of strain) and the maximum shear seismic modulus (Gmax) were determined and plotted versus depth through the five boreholes. The interpretation displays that, there is a consistency between the SPT values, the shear modulus (Gmax) values and the plots, which can be divided into three zones coincided with the typical soil section of the area. Some of the discrepancy between the Gmax values from field and laboratory tests could be explained by release of confining pressure, change of temperature and wettability, absence of fissures and cracks in labouratory specimens, time effects, and that the NG could be used to correct the Gmax values from laboratory tests to better representation of the actual in-situ conditions.