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海洋石油建设中的一个关键环节是对有关海域的工程地质条件作出准确评价。海上原位静力触探(CPT)是主要的原位勘察手段,与陆地CPT不同,其贯入方式主要有Seabed和Downhole两种形式。这两种CPT由于贯入方式不同,所得到的锥端阻力存在一定的差异。采用有限元方法对这两种形式的CPT锥端阻力和贯入模式进行计算分析。研究显示,CPT入土过程中,周围土体存在两种不同位移状态,即滑动状态和排挤状态。在入土初期,土体以滑动状态为主,土体中竖向应力随贯入深度的增加而递增。在入土一定深度以后,土体的排挤状态占主导地位,竖向应力变化趋于平稳。这两种位移状态的相互转化解释了Seabed CPT和Downhole CPT实测数据之间的差异。在贯入深度较大时,Seabed CPT受排挤状态控制,而Downhole CPT仍然受滑动状态的影响。
A key link in the construction of offshore oil is the accurate assessment of engineering geological conditions in the sea area concerned. In situ CPT is the main method of in situ exploration. Unlike the terrestrial CPT, the CPT mainly has Seabed and Downhole modes. The two CPT due to different ways of penetration, cone resistance obtained by the end there are some differences. The finite element method was used to calculate and analyze the CPT cone tip resistance and penetration modes of these two forms. The results show that there are two different displacements in the soil around the CPT, that is, sliding state and crowding state. In the initial period of soil entry, the soil was mainly in the sliding state, and the vertical stress in the soil increased with the penetration depth. After entering a certain depth, the displacement state of soil dominates, and the vertical stress changes tend to be stable. The interconversion of these two displacement states explains the difference between the measured data of Seabed CPT and Downhole CPT. Seabed CPT is controlled by the crowding state when the penetration depth is large, while the Downhole CPT is still affected by the sliding state.