粉土中筒型基础贯入阻力的研究
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摘要
筒型基础在海洋工程中应用广泛,贯入阻力的准确计算是筒型基础成功应用的关键。在海洋工程中,粉土是介于砂土与黏土间的特殊土,现有计算方法中将粉土等同于砂土,忽略了黏聚力c对贯入阻力的影响。开展了粉土中筒型基础的现场贯入试验,观测了自重下沉阶段与负压贯入阶段筒型基础贯入阻力与贯入深度的关系,提出了粉土中计算沉贯阻力的方法,并对不同筒端形式的减阻效果进行了深入分析。研究结果表明,采用现有规范方法计算粉土中筒型基础的贯入阻力值较实测值偏小20%,提出的两种方法不仅适用于计算粉土中筒型基础的贯入阻力,而且能够反映负压贯入阶段的减阻效果;尖筒端可使筒端阻力减少50%,减阻环可使筒侧摩阻力减少50%,但减阻环会破坏筒壁周围土体,形成渗流通道,导致负压失效。
Bucket foundations are widely used in ocean engineering. The determination of the penetration resistance is a key to the successful application of this type of foundation. In ocean engineering, the properties of silt is largely different from sand and clay.But the existing calculation method of penetration resistance of bucket foundation is generally for sandy soil, which neglects the influence of the cohesion c on the penetration resistance. In this paper, three bucket foundations with different types of tip are penetrated by dead-weight and suction pressure. The relations between penetration resistance and penetration depth are measured in the different penetration stages by dead-weight and by suction. Two methods for calculating the penetration resistance of bucket foundation in silt were derived. The effect of drag reduction in different tips were analyzed. Studies have shown that the calculation value of the penetration resistance of bucket foundation by specification in slit is 20% smaller than measured value. Two methods proposed in this paper that can not only accurately calculate the penetration resistance, but also can reflect the drag reduction effect caused by suction. The sharp-tip can reduce the half of the tip resistance and the anti-drag ring reduce the half friction resistance.However, the anti-drag ring will destroy the soil around the wall and formed a seepage channel, which fail to provide the penetration force.
Bucket foundations are widely used in ocean engineering. The determination of the penetration resistance is a key to the successful application of this type of foundation. In ocean engineering, the properties of silt is largely different from sand and clay.But the existing calculation method of penetration resistance of bucket foundation is generally for sandy soil, which neglects the influence of the cohesion c on the penetration resistance. In this paper, three bucket foundations with different types of tip are penetrated by dead-weight and suction pressure. The relations between penetration resistance and penetration depth are measured in the different penetration stages by dead-weight and by suction. Two methods for calculating the penetration resistance of bucket foundation in silt were derived. The effect of drag reduction in different tips were analyzed. Studies have shown that the calculation value of the penetration resistance of bucket foundation by specification in slit is 20% smaller than measured value. Two methods proposed in this paper that can not only accurately calculate the penetration resistance, but also can reflect the drag reduction effect caused by suction. The sharp-tip can reduce the half of the tip resistance and the anti-drag ring reduce the half friction resistance.However, the anti-drag ring will destroy the soil around the wall and formed a seepage channel, which fail to provide the penetration force.
引文
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[2]LIAN J,SUN L Q,ZHANG J F.Bearing capacity and technical advantages of composite bucket foundation of offshore wind turbines[J].Transactions of Tianjin University,2011,17(2):132-137.
[3]乐丛欢,丁红岩,张浦阳.分舱板对海上风机混凝土筒型基础承载模式的影响[J].工程力学,2013,30(4):429-434.LE Cong-huan,DING Hong-yan,ZHANG Pu-yang.Influences of bulkheads on the bearing mode of concrete bucket foundation for offshore wind turbine[J].Engineering Mechanics,2013,30(4):429-434.
[4]练继建,陈飞,杨旭,等.海上风机复合筒型基础负压沉放调平[J].天津大学学报(自然科学与工程技术版),2014,47(11):987-993.LIAN Ji-jian,CHEN Fei,YANG Xu,et al.Suction installation and leveling of composite bucket foundation for offshore wind turbines[J].Journal of Tianjin University(Science and Technology),2014,47(11):987-993.
[5]ANDERSEN K H,MURFF J D,RANDOLPH M F,et al.Suction anchors for deepwater applications[C]//Proceedings of International Symposium on Frontiersin Offshore Geotechnics IS-FOG.Perth,Australia:[s.n.],2005:3-30.
[6]LEBLANC C B.The monopod bucket foundation[R].[S.l.]:Dong Energy,2009.
[7]API RP 2GEO.ISO 19901-4:2003 Petrolem and natural gas industries specific requirements for offshore structures part4:geotechnical and foundation design considerations[R].1st Ed.[S.l.]:European Standards,2003.
[8]DNV-CN-30-4.Foundations,Classification Note 30.4[S].[S.l.]:Det Norske Veritas,1992.
[9]HOULSBY G T,BYRNE B W.Design procedures for installation of suction caissons in sand[J].Proceedings of the ICE-Geotechnical Engineering,2005,158(3):135-144.
[10]SENDERS M,RANDOLPH M F.CPT-based method for the installation of suction caissons in sand[J].Journal of Geotechnical and Geoenvironmental Engineering,2009,135(1):14-25.
[11]CAO J,PHILLIPS R,POPESCU R,et al.Penetration resistance of suction caissons in clay[C]//Proceedings of the 12th International Offshore and Polar Engineering Conference.[S.l.]:[s.n.],2002:800-806.
[12]HOULSBY G T,BYRNE B W.Design procedures for installation of suction caissons in clay and other materials[J].Geotechnical Engineering,2005,158(2):75-82.
[13]曹耀峰.粉土地基下桶形基础沉贯试验研究及工程应用[J].海洋科学进展,2000,18(4):6-11.CAO Yao-feng.Bucket foundation penetration test study and its application in the engineering[J].Advances in Marine Science,2000,18(4):6-11.
[14]朱斌,孔德琼,童建国,等.粉土中吸力式桶形基础沉贯及抗拔特性试验研究[J].岩土工程学报,2011,33(7):1045-1053.ZHU Bin,KONG De-qiong,TONG Jian-guo,et al.Model tests on penetration and pullout of suction caissons in silt[J].Chinese Journal of Geotechnical Engineering,2011,33(7):1045-1053.
[15]祁越,刘润,练继建.无黏性土中筒型基础负压下沉模型试验[J].岩土力学,2018,39(1):139-150.QI Yue,LIU Run,LIAN Ji-jian.Model test of bucket foundation suction installation in cohesionless soil[J].Rock and Soil Mechanics,2018,39(1):139-150.
[16]天津港湾工程研究所.JTJ-250-98港口工程地基规范[S].北京:人民交通出版社,1998.National Standard of the People's Republic of China.JTJ-250-98 Foundation Code for Port Engineering[S].Beijing:China Communications Press,1998.