Design Principle of Shallow Earth Tunnel

由于日本主要人口区域的扩张，建设新的铁路系统变得必要。地下铁路的规划和建设越来越多地考虑到环境保护，特别是在商业区和住宅区。在地下铁路建设中，为了排水、通风和行车安全，以及方便乘客，从建设成本和维护成本的角度出发，最好让土层尽可能薄。由于日本主要城市位于宽阔的冲积平原上，软基和地下水位较高，隧道应安全施工，不会损坏邻近或上覆的建筑物、街道或公共设施。过去，这些城市隧道通常采用明挖掩护法或盾构法施工。近年来，砂质地面隧道越来越多地采用常规方法代替盾构法施工，大大降低了隧道施工成本。在薄覆盖层高地下水位条件下的隧道施工中，需要认真研究以下几个问题：1.隧道工作面及围岩的稳定性；2.与地下水有关的问题；3.地下水条件。隧道开挖对邻近或上覆结构和公共设施的影响。要解决这些问题，最重要的是了解隧道开挖过程中周围地面的实际行为，并建立一种能够尽可能准确地模拟这种行为的分析方法。本研究就是为了弄清这些问题，建立薄覆盖层高地下水位土质隧道的设计原则。

As a result of expansion of the major population regions in Japan, it has become necessary to construct new railway systems. It is becoming more common that underground railways are planned and constructed in consideration of the environment preservation especially in commercial and residential areas. In underground railway construction, it is better to leave the earth covering as thin as possible from the point of view of construction cost and maintenance cost for drainage, ventilation and traffic safety as well as the convenience of passengers. Since the major cities of Japan are located in wide alluvial plains where soft ground with a high groundwater table prevails, tunnel should be built safely without damaging adjacent or overlying buildings, streets or public utilities. In the past, these urban tunnels have usually been constructed by cut and cover method or shield method. In recent years, however, use of the conventional method has been increasingly implemented in sandy ground tunneling in lieu of the shield method and this has resulted in reduction of the tunneling cost to great extent.when tunneling through ground with a thin cover and high groundwater table, it is necessary to investigate the following problems carefully :1. the stability of tunnel face and surrounding ground,2. problems related to underground water conditions, and3. the effect of tunneling on adjacent or overlying structures and public utilities.To work out these problems, it is most important to understand the actual behavior of the surrounding ground during tunnel excavation and to establish an analytical method which can simulate the behavior as accurately as possible. This research has been carried out to make clear these problems and to establish the design principle for the construction of earth tunnels with thin cover and high groundwater table.