Determination distance between two transport tunnels is very important problem and has influence on the stability calculation and tunnel designations. However, nowadays in Viet Nam this problem has many disadvantages. This paper introduces the studying on determination of optimal distance between two transport tunnels when consideration to shape changes base on numerical method in Viet Nam's geological conditions.

1. Introduction

Vietnam is one of the most beautiful countries located in the South East Asia (figure.1). In the North, Vietnam shares the long borderline with China. In the East, Vietnam is bordered by the Gulf of Tonkin, in the East and South by the South China Sea, in the South West by the Gulf of Thailand, and in the West by Cambodia and Laos. Owning to stretching the length of the Indochinese Peninsula, Vietnam boasts a unique shape of an elongated S and a long coastline of 3,260 km with a lot of wonderful sites. Although Vietnam lies entirely within the tropics, the Vietnam's climate surprisingly varies from region to region with the annual average temperature from 22°C to 27°C because of its topography. The mountainous people of Sapa in the north might be seeking shelter from snow while the urban dwellers of Ho Chi Minh City in the south seek refuge from mid-day heat. Although it is a small country with the area of 329,560km2, there are up to 54 different ethnic groups inhabiting in Vietnam, of which Kinh (Viet) people accounts for nearly 86% of the whole population, and the others are ethnic minority groups that represent about 14%.

To develop industry in Viet Nam in the future we need building many hydroelectric power plants, thermal power plants, atom power plants and other energies to develop country, which can be listed as following:

Hoa Binh Hydropower plant (figure 2a) was built from 1979 to 1994 with 8 machines provides 1920MW- 1/3 productivity of Vietnam. It is not only an important industrial construction but also an attractive sightseeing for visitors. Many valuable items such as: Ho Chi Minh statue on Tuong hill with 18m height, the traditional area keeping letters, memorial Vietnamese and Soviet experts sacrifice to built hydropower projects. Along with the functions of social, economic, Hoa Binh hydroelectric becomes an exciting destination for visitors.

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