Combined tunnel consisting of four smooth left-turn/straight-going tunnels in shape of Bu (Chinese character)

The invention discloses a combined tunnel consisting of four smooth left-turn/straight-going tunnels in the shape of Bu (Chinese character). The combined tunnel is in a combined structure which is composed of four independent bifurcate tunnels and enables crossroads to be uncrowded. Each bifurcate tunnel has a straight-going tunnel and a left-turn tunnel, the left-turn tunnel is separated from the straight-going tunnel from the left-turn side thereof so as to form a bifurcate tunnel in the shape of Bu (a Chinese character), and four bifurcate tunnels are formed into four synclastically-bifurcate tunnels in the shape of Bu (a Chinese character); and two synclastically-bifurcate tunnels in the shape of Bu (a Chinese character) are formed into a branch combined tunnel, and the one-way sections of two straight-going tunnels of two branch combined tunnels are formed into a three-dimensional cross structure. The combined tunnel disclosed by the invention has the advantages that the degree of hazard (caused by local geological accidents) to the whole combined tunnel is reduced; and the left-turn tunnel can be used as a left-turn/right-turn shared tunnel and has a wider tunnel floor as a merged lane section, therefore, the situation of traffic congestion is not easily caused, and the vehicles can directly turn left without redundant detouring, so that a small crossroad of a dual 6-lane can be completely interchanged.