影响标准贯入（SPT）击数因素浅析

通过分析某涉外跨海大桥工程地质勘察中的标贯SPT击数差异问题，发现钻孔直径、钻探工艺、标贯头刃口尺寸和泥浆浓度的差异等显著影响砂性地层中的SPT击数。特别是小口径套管下到钻孔底部限制了土体的变形，进而影响了SPT测试结果；泥浆浓度过低将不足以将孔底残渣特别是颗粒较大的砂砾携带出钻孔等。这些因素的累计导致了两家勘察公司N值出现了较大的差异。文中对跨海大桥的勘察管理提出了一些建议，通过采取有效措施，使同一土层的N值基本一致，对加强勘察资料的可信度和实用性具有参考价值。

Analysis on Influencing Factor of N Value of SPT

Based on the analysis of Standard Penetration Test differences during a marine bridge crossing project engineering geological exploration, find the diameter of borehole, boring technology, boring tool and the mud density significantly affect the N value of SPT. Especially the small-caliber casing drilling down to the borehole bottom to limit the deformation of soil, so that the N value of SPT is affected. The mud density is too watery to take the residue or coarse grain out of borehole bottom, the differences of the N value between two investigation companies are caused by several influencing factors. This paper gives some suggestions for survey management of Crossing Sea Bridge. Through taking effective measures to enable the N value at the same soil layer is basically the same, It has reference value for enhancing the credibility and usefulness of survey data.