Abstract: In order to investigate the mechanical and deformation characteristics or action effects caused by vehicles and impacts on important parts of bridge or tunnel connecting sections under weak surrounding rocks especially grade Ⅳ or Ⅴ surrounding rocks, systematical indoor model tests have been carried out. The relationship among physical quantities and the similarity indexes have been worked out under the dimensional analysis method of the similarity theorem considering the characteristics of bridge and tunnel connecting projects. The model test methods such as test contents, working conditions, test equipments and instruments etc., have been systematically analyzed and elaborated. Through analyzing the test phenomena and results, some conclusions are drawn as follows: the vehicle loads with impact actions during post operation stage cause harmful mechanical effects or structure damages on some key parts of bridge or tunnel, such as oversize displacement on bridge mid-span and lap joint tip or oversize settlement of tunnel bottom, or lower stability of surrounding rocks nearby tunnel entrance etc. Consequently, for bridge and tunnel connecting projects under Ⅳ or Ⅴ surrounding rocks, some key parts of bridge, tunnel lining and surrounding rocks nearby the entrance should be strengthened in order to avoid damages or diseases .

Key words: weak surrounding rocks, bridge and tunnel connected section, indoor model tests, test methods, vehicle impact, mechanical behaviors, action effects