Big Chamber is located in the Power Waterway of Nam Theum 1 hydro power project (Laos PDR). The main dimensions of the Big Chamber are:Leng approximate 96m; Span from 11.5 to 16.4m; Height from 17.10–20.80m. Aim of paper are Analysis result of Lab test (UCS and Triaxial test), proposal parameters of sandstone with case different RMR indexs. The construction model anisotropic for rock mass. After that, apply anisotropic model for rockmass, simulation bolt, shortcrete, wire mess.


Nam Theun 1 hydropower project is in the Nam Kading river, a tributary of the Mekong River with a confluence approximately 30km downstream of the Nam Theun 1 dam site. The Nam Kading River flows from high mountains which reach a maximum altitude of close to 1,300m asl in the project area. Full reservoir capacity of 3,009 Mm3 with normal water level is +292m a.s.l. Headrace tunnel is a reinforced concrete lining component of 565m with EDL Shaft and 544m with EGAT Shaft, its water clearance cross section is in rounded shape with inner diameter D equal from 10m -:-4.50m. Maximum design incharge is 513.7 m3/s. Total installed capacity of power house is 650 Mw.

Big Chamber is located in the Power Waterway of Nam Theun 1 hydro power project, below the Pressure Shaft and extends to the bifurcation towards the fixpoints for EDL Shaft and EGAT Shaft. The design of Big Chamber showed in this Fig. 1, Fig. 3.

The main dimensions of the Big Chamber are:

  • Leng approximate 96m;

  • Span from 11.5 to 16.4m;

  • Height from 17.10–20.80m;

  • The overburden of the Big Chamber reaches approximate 150 m;

Geology and Geotechnical Interpretation

The Nam Theun basin will be located in central Laos in the Bolikahamxai province, which lies within the central area of the Asiatic Plate. The crystalline quarzitic schists and granites are reported to represent the oldest geological rocks forming the Nam Theun Basin. These basement rocks are overlain by Permian Limestone and by Mesozoic sediments, the youngest strata outcropping in the area. The Mesozoic sediments which cover most of the project area are referred to as J3K and K2 in the "Geological Map of Cambodia, Laos and Vietnam in scale of 1:1,000,000", Hanoi, 1991 (see Figure 31).

The Mesozoic sediments are formed by a terrigenous sequence which can be subdivided based on their lithology as follows:

  • – "Red Beds" (mudstone and shale with thin red sandstone beds).

  • – A sequence of thickly bedded, white quartz sandstone separated by thick mudstone beds.

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