Research purposes:The design of a railway tunnel project in a foreign country have faced several engineering problems such as standardizing the pressure calculation and the design basis of tunnel reinforcement measures for the surrounding rock pressure within volcanic ash layer and the swelling soil stratum,standardizing the seismic design basis of tunnel within high intensive seismic area,optimizing the selection method of service gallery under short construction period.The main purpose of the study is how to adopt China design standards as design basis and adjust details with local conditions to formulate appropriate technical standards and engineering countermeasures.Research conclusions:(1) Plastic design theory was adopted to determine the surrounding rock pressure around tunnel within volcanic ash layer.Forecast on swelling force shall refer to the ratio of displacement and stress relief during tunnel excavation.(2) Comprehensive measures were used to pre-reinforce the tunnel within weak stratum formed by volcanic ash,by applying chemical churning piles,dewatering and discharging measures in both inside and outside tunnel.(3) Response displacement method and Level Ⅰ,Ⅱ performance-based design method was applied on seismic performance verification of tunnel structure.The region that requires seismic precaution was determined based on overburden depth and local geological structure,with corresponding precaution measures applied such as ground grouting,structure reinforcement and joints optimizing.(4) Scheme comparison was used to optimize the form of service gallery,by considering technology,economy issues and applicability.(5) The research results can provide guidance for other overseas tunnel design projects or within soft soil stratum and high intensive seismic area.%研究目的:某国外铁路隧道工程设计面临火山堆积软土及膨胀性围岩的压力计算标准和加固设计措施、高烈度软弱围岩抗震设计方法及技术标准、短工期隧道施工辅助坑道选择等设计问题,如何以我国技术体系为基础,因地制宜针对性地制定适宜的设计技术标准和工程对策是研究的主要目的.研究结论:(1)火山灰土层隧道围岩压力设计可按塑性区设计理念进行,膨胀力可参照位移发展开挖释放力的比率来预测;(2)火山灰软土隧道预加固可综合采用地表、洞内的旋喷桩预加固和地表降水、洞内泄水等措施;(3)可采用反应位移法及Ⅰ、Ⅱ级性能目标进行抗震验算,通过埋深、地质构造等设定抗震设防的区段和采取注浆、配筋及设缝等构造措施;(4)通过技术经济和本地适宜性比选确定辅助坑道形式;(5)该研究成果可为其他类似海外项目或软土层高烈度地震区隧道设计项目提供借鉴.
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