Qiongzhou Strait Submarine Cable Feasibility Study

The study of the Qiongzhou Strait(from the Nanling Village in Xuwen County of Guangdong Province to Yubaojiao of Hainan Province) Submarine Cable routing survey project is in the collection of survey conditions and the natural environment of the region surrounding geological conditions on the basis of historical information, and to conduct detailed environmental Road from District geological survey. According to the bathymetric and topographic method: we will use single beam,side scan sonar,sub-bottom profiler and other equipments, to carry out the sub-bottom profile survey, then analyzing and interpretation the data results of the survey. The aim of the survey is to preliminarily prospect the water depth, the seabed topographic features and the petrography of the sub-bottom profile, the geological structure, the adverse geological phenomena, etc; to preliminarily explore the specific location, scales, nature, occurrences of the various geological phenomena, and to evaluate their influence on the stability of the pipeline laying along the route. We believe that all these work can provide effective and reliable data or information for the engineering construction and the submarine pipeline laying and maintenance in the area.On feasibility study and evaluation of the Qiongzhou Strait Submarine Cable laying, we will mainly from the following comprehensive, multidisciplinary aspects to analysis and expound, and conclusions are drawn as follows:1,The three routes extend for approximately equal length and pass through basically identical geological and topographical units. In the 0-12.3km section of the route, the topography is slowly inclined, and except the moderately weathered basalt is buried at shallow depth in some local off-shore areas, the soft plastic to plastic sediments exceed 3m in thickness in most of the area, which is favorable for the burial construction and safe operation of submarine cable. In the 12.3-20.7km section (about 8.4km long) of the route, the water depth section takes the serrate form, the surface loose sediments are generally thin, basalts are buried shallow in protrusive relief, and locally coral reefs occur sporadically. Generally, landslip may easily occur in the north slope of the south uplifted zone, and the engineering geological conditions here are poor. In the 20.7-30.0km section (about 9.3km long) of the route, the topography is not remarkably undulating, here the plastic-hard plastic sediments are generally over 3m in thickness. Except the basalt is general buried at shallow depth nearby the coast lines, the engineering geological condition is favorable in general.2,Adverse geological phenomena mainly include active sand wave, steep slope topography, shallow-buried basalt and coral reefs, as well as the weak silt clay inter- layers occurring locally in the accumulation area in the north section of the route.3,CPT static force testing results indicate that possibility of liquefaction exists when sand bodies in the route area are subject to exogenic forces such as earthquake, etc., just the sand-liquefaction has little effect on the submarine cable, even more; the route area state will become more stable after the sand-liquefaction is occurred.4,In the terminal station areas around the two coasts, the anti-seismic fortified intensity is set at grade 7 on the Richter's scale, at a peak ground acceleration of 0.15g for a ground motion, and at an characteristic period of 0.35s on a ground motion response spectrum.5,Corrosive test results indicate that the sediments and sea water and in the route area are not strongly corrosive. However, in the sea area with a water depth of 4-10m in the 3-7km section of the north part of the route area, a great number of sulphate deoxidizing bacteria occur at a depth of <2m. Consequently, it is suggested that the cable in the section of 3-7km shall be buried at a depth of >2m.6,The theoretically possible maximum tidal current speed for the surface layer current in the route sea area is 286cm/s, while the theoretically maximum value for the bottom layer sea current is 198cm/s, which will has significant influence on the construction and safety maintenance of submarine cable.