吹填珊瑚礁砂地基处理方法适用性与加固效果应用研究

Applicability and quality evaluation of foundation treatment method for backfilled coral sand site

珊瑚礁砂是珊瑚礁、贝壳等经侵蚀、破碎后沉积在近岸环境中的一种生物碎屑,吹填珊瑚礁砂作为地基土可就地取材、大幅降低工程造价、缩短施工时间。然而,吹填珊瑚礁砂地基处理工程实践中一般采用基于陆源砂的地基处理与加固效果评价方法,具有很大的不确定性。本文在苏丹、沙特、南海某试验区分别采用振动碾压、强夯、振冲法对吹填珊瑚礁砂场地进行地基加固处理,依据载荷试验、标准贯入、动力触探、静力触探等原位测试对珊瑚礁砂场地进行加固效果与有效深度评价,采用平板载荷试验获取珊瑚礁砂场地处理后的地基承载力,结果表明:(1)珊瑚礁砂场地振动碾压法的有效加固深度约1.0 m,加固深度十分有限;(2)500~3000 kN·m夯击能下强夯法的有效加固深度2.0~4.0 m,明显低于相同条件下陆源砂的有效加固深度;(3)珊瑚礁砂场地振冲后可达到中密、密实状态,132 kW振冲的最大有效加固深度为8.0~10.0 m;(4)平板载荷试验获取的珊瑚礁砂承载力特征值与动力触探击数存在良好的经验关系,地基承载力特征值多数超过500 kPa,最高可达2000 kPa,与陆源砂的承载力特性存在显著差别,珊瑚礁砂具有“珊瑚礁砂变形大、高压缩性”的特点易出现于高应力情况下,加固后的珊瑚礁砂地基在常压应力下,往往具备较高的强度与承载能力。

Coral reef sand is a kind of biological debris deposited in the coastal environment after erosion and fragmentation of coral reef and shell.The hydraulic filling coral reef sand can be used as the foundation soil,which can greatly reduce the project cost and shorten the construction time.Nevertheless,it is uncertain that the method of foundation treatment and its quality evaluation,derived from quartz sand engineering practice,is applied to coral sand.In this paper,vibration compaction,dynamic compaction and vibro-flotation were used to reinforce the foundation of backfilled coral sand in Sudan,Saudi Arabia and South China Sea.The quality and reinforcement depth of the backfilled coral sand site are evaluated according to the in-situ tests such as load plate test,standard penetration test,dynamic penetration test and cone penetration test,and the foundation bearing capacity of the treated coral sand site was obtained by plate load test.Results indicate that:(1)the effective reinforcement depth of vibration compaction method for coral sand site is about 1.0m,which is very shallow.(2)the effective reinforcement depth of dynamic compaction under 500 kN·m~3000 kN·m energy is 2.0 m~4.0 m,which is obviously lower than that of quartz sand under the same energy compaction.(3)the coral sand site can reach the state of medium density after vibro-flotation,and the maximum reinforcement depth using 132kW vibrator is 8.0 m~10.0 m.(4)There is a good empirical relationship between the bearing capacity of coral sand obtained by plate load test and the blow count of dynamic penetration test.The allowable bearing capacity of coral sand site after treatment mostly exceeds 500kPa and can reaches the maximum of 2000kPa,which is significantly different from that of quartz sand.Coral reef sand is characterized by“large deformation and high pressure shrinkage”,which is easy to occur under high stress.While the reinforced coral reef sand foundation often has higher strength and bearing capacity under normal stress.