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Surface sediment strength in bed-slope of northern South China Sea

  • October 2016
DOI:10.13544/j.cnki.jeg.2016.05.016
Authors:
Chaoqi Zhu at Ocean University of China
Chaoqi Zhu
Yonggang Jia at Ocean University of China
Yonggang Jia
Zhang Minsheng at Ocean University of China
Zhang Minsheng
Zhenhao Wang
Zhenhao Wang
Zhenhao Wang
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随着海洋开发活动由浅海走向深海，南海北部陆坡的沉积物强度特性逐渐成为关注热点。本文通过参与2015年与2016年共享航次计划，在南海北部莺琼陆坡、神狐陆坡、东沙陆坡、台湾浅滩陆坡进行沉积物重力取样与箱式取样，并现场剖样，用以进行沉积物强度测试。地质取样结果表明东沙陆坡砂含量相对较高并发现直径约22cm黑色气孔状碳酸盐结核。在神狐陆坡沉积物表层发现活体壳类生物，在110cm深度处发现壳类生物遗骸。十字板剪切试验与笔式贯入试验结果表明南海北部陆坡，沉积物强度差异较大。但总体而言，除东沙陆坡外，莺琼陆坡、神狐陆坡、台湾浅滩陆坡表层沉积物强度一般较低。0～20cm范围内，笔式贯入阻力一般小于0.1N，十字板剪切强度最大一般不超过10kPa。0～300cm深度范围内，沉积物强度沿深度方向大致呈递增趋势，个别站位递增趋势不明显。台湾浅滩陆坡等南海北部陆坡表层沉积物存在强度分层：分层界面以上，沉积物强度较低；分层界面处，沉积物强度骤增。该分层界面可能是海底滑坡的潜在滑动面。
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南海北部陆坡表层沉积物
强度特征研究.pdf
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... For instance, Liu (2017) performed CPTs at three sites in the SCS and derived the s u within 18m from the seafloor for each site. Zhu et al. (2016) utilized in-situ VST to obtain the s u of 16 sites in the SCS. The sampling methods for laboratory tests include gravity coring and box coring, and the laboratory tests mainly contain triaxial tests, laboratory VST, laboratory full-flow penetration test, etc. Hsu et al. (2018) used a modified gravity coring apparatus to take a 2m length seafloor soil sample in the Northeast of SCS, undrained triaxial tests were carried out to get s u while the γ was also measured. ...
Large-scale seismic seafloor stability analysis in the South China Sea
Article
Earthquakes are considered as the major trigger of submarine landslides. This study analyzes the large-scale seismic seafloor stability in the South China Sea (SCS), taking into consideration the earthquake probability and spatial distribution of seismicity and seafloor soil properties. For this cause, the geographical, seismic, and seafloor soil characteristics are first determined. The digital elevation model (DEM) of the study area is established using the geographic information system (GIS). Large-scale Peak Ground Acceleration (PGA) maps under different exceedance probabilities (EPs) are derived using the Chinese Probability Seismic Hazard Analysis (CPSHA) method. Three-dimension continuous models for seafloor soil properties are obtained using a proposed best-fit distribution-based Kriging method. With this information, the large-scale seafloor stability under different EPs is evaluated with an infinite slope model in the study area of the SCS. The proposed large-scale seismic seafloor stability is validated against recorded earthquake-induced submarine landslides. The analysis shows that the seafloor stability is found to be highly nonuniform, and the study area can be divided into three main parts based on their distinct seafloor stabilities. This study sheds new light on the large-scale seafloor stability, and can assist the development of ocean engineering projects in the SCS.
... * However, the research on deep-sea sediments in China is still not enough. Some scholars ( Zhu et al., 2016;Jiang et al., 2017;Nian et al., 2018) has carried out research on the sediment of the northern continental slope of the South China Sea, but it lacks a comprehensive quantitative description index. In this paper, the physical and mechanical characteristics of shallow surface sediments in Shenhu sea area were described quantitatively through the analysis results of sediment samples in the past four years, in order to provide support for geological disaster prediction and undersea ...
Physical and Mechanical Characteristics of Shallow Surface Sediments in the Shenhu Area, South China Sea
Article
  • Nov 2018
... The continental slope can be divided into upper, middle, and lower slopes depending on the depth of the water, and the slope characteristics are given in Table 1. The mechanical parameters of marine sediments at typical sampling positions on each slope are given in Table 2 [43]. ...
Probability analysis of submarine landslides based on the Response Surface Method: A case study from the South China Sea
Article
... Marine engineering geology is mainly based on the actual project to study the seabed. This provides a variety of engineering geological parameters for the development of marine engineering (Zhu et al., 2016).This is an early job. The physical properties of the surface sediments collected by the box pattern can reflect some of the characteristics of the marine environment in the sea . ...
Surface Sediment Density and Moisture Content in North slope of South China Sea
Article
... China has a vast area of continental shelf and is very rich in marine resources, but because of the complex geological environment and frequent geological disasters, the utilization of marine resources and the construction of marine engineering are limited (Zhu et al., 2016). As the implementation of offshore construction must rely on the seabed soil, so it's important to identify the type of sediments, the engineering geological conditions and other unstable factors. ...
Liquid-plastic Limit of Surface Sediments in North Slope of South China Sea
Article
Susceptibility assessment of regional submarine landslides triggered by seismic actions
Article
Submarine landslide and even its evolution to high-speed sliding masses can seriously threaten the safety of ocean engineering. Earthquakes are the most frequent trigger factors for landslides, and thus, seismic instability evaluation of submarine slopes has become a hot topic. However, the mechanism of submarine slope failures triggered by earthquakes is enormously complex. Although certain satisfactory results have been achieved in specific slopes, submarine landslides are still difficult to monitor and control, meaning that prevention-oriented research remains the mainstream. Regional slide predictive analyses of vast submarine slopes should be emphasized , but relevant research is notably rare. In this paper, a regional assessment methodology for submarine slope instabilities under seismic loads is proposed, and susceptibility mapping of landslides is established. First, considering the quasi-static bidirectional seismic action and the marine soil strength-weakening effect, an infinite slope sliding mode is used to establish the stability evaluation formula for a multiple soil-layer slope. Second, according to water depth data and GIS techniques, slope gradients are investigated, and the safety factors of submarine slopes located at specific stations are acquired. Furthermore, discrete stations are taken as sample points, and susceptibility mapping of submarine landslides is achieved using the inverse distance weighted and GIS techniques. Finally, regional seismic instability assessments of submarine slopes are conducted in the northeastern South China Sea, and various factors that influence submarine landslides are briefly discussed. This study offers an important basis for the development of marine resources and the risk assessments in ocean engineering.
Large-scale seafloor stability evaluation of the northern continental slope of South China Sea
Article
  • Jul 2019
With the continuous expansion of energy demand, the deep-water continental slope in the northern South China Sea has become one of the significant offshore oil and gas exploration regions. The frequent occurrence of marine geological hazards in this region, especially submarine landslides, can cause serious damage to engineering facilities. However, there have been few studies on the stability of the northern continental slope of the South China Sea; these studies mainly focused on a specific submarine slope or small-range evaluation, resulting in a lack of large-scale and quantitative understanding. Hence, considering the variation in the physical and mechanical properties of marine soils with depth, formulas for calculating the safety factor of submarine slopes by an infinite sliding model are established, and the factors affecting slope stability such as soil properties, slope gradient and horizontal seismic action are systematically investigated. Using GIS techniques, the terrain slope gradients and a historical seismic database of the northern South China Sea are obtained. Combined with soil mechanical parameters, a regional stability evaluation of the northern continental slope is carried out. Furthermore, the distribution of risk zones is given. On the whole, under strong seismic action, large-scale submarine slope instability occurs and must be highly considered when assessing risk. This achievement is of great significance to engineering sites, route selection and engineering risk assessment.
Design and application of cone penetration test equipment in shoal water
Article
Full-text available
In order to provide the academic and industry with a cost-effective cone penetration test (CPT) equipment with particular emphasis on testing in shoal water, we designed the shoal-water CPT equipment. The buoyancy system distinguishes the shoal-water CPT equipment from others. Before the test, the shoal-water CPT equipment can be towed by a small boat with the buoyancy system charged. Having reached the scheduled site, we bleed the buoyancy system. The shoal-water CPT equipment sink to the seafloor with no enough buoyancy. We conducted a test at the Yellow River subaqueous delta, China. The CPT equipment works well. © 2018, National Institute of Science Communication and Information Resources (NISCAIR). All rights reserved.
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