长昆客运专线湖南段经过湘中低山丘陵区、湘中中低山区及云贵高原东缘高山区，项目桥隧工程多，工程设计难度大、施工风险高。为解决项目在复杂山区困难条件下的桥隧相连、大量隧道洞口偏压高陡，部分隧道洞口段穿越岩堆或顺层等不良地质等造成的诸多设计施工难题，针对高速铁路隧道工程的特点，通过研究复杂条件下桥隧相连工程的相对关系，将复杂山区的桥隧相连工程划分为隧桥串接、隧桥对接和隧桥毗连（短路基）3种衔接方式分别系统处理，首次开发并应用高速铁路分离式隧桥串接洞门，用于解决桥隧相连情况下的隧桥串接洞门设计； 通过研究偏压、高陡洞口地形、地质，对困难条件下的隧道洞口提出采取“耳墙+护拱+反压回填”暗挖进洞技术、锚固桩正面防护技术及基底桩基托板技术等工程方案解决了进洞困难、洞口不良地质、隧底软硬不均或部分悬空、安全施工等难题。

As passing through the hilly areas and the midlow mountain areas of Hunan province and the high mountains on the eastern margin of YunnanGuizhou Plateau, a large number of bridges and tunnels are necessary in Hunan section of ChangshaKunming Passenger Dedicated Line, which increases design difficulties and construction risks. In order to solve the problems of design and construction caused by bridgestunnels connection in complex mountainous regions, many high and steep portals with unsymmetrical load, and poor geological conditions such as rock piles or bedding in some tunnel portals, the bridgestunnels connection projects in complex mountainous regions are divided into three connecting types, i.e. overlapping bridges structure and linings of tunnel portal, separating abutment and tunnel portal structure, closing abutment and tunnel portal structure (with short subgrade), based on the characteristics of high speed railway tunnel and the relationship of bridgestunnels connection projects under complex conditions. In addition, the method of connecting tunnel and bridge by overlapping bridges structure and linings of tunnel portal with separating beating structure is developed and applied in highspeed railways to solve the design difficulties of connecting bridge and tunnel portal in bridgestunnels connection projects. By studying the topography and geology conditions of high and steep portals with unsymmetrical load, some schemes, i.e. "ear wall + arch protection + back pressure backfilling" technology for underground excavation, frontal protection technology for anchor piles, and supporting technology for base piles and pallets, are proposed for tunnel portal construction to solve problems of difficulty in entering the hole, bad geology of the portal, hard and soft stratum or partial suspension of tunnel bottom, and construction risks, etc.