With the increasing operational speed of high-speed train tunnels,tunnel aerodynamic effects and its side effects become prominent.A survey of domestic and international cases of sonic boom was first conducted.Afterwards,a set of full-scale tests were carried out in the test tunnel to investigate the basic variation laws of initial pressure gradient of the compression wave and amplitude of micro-pressure wave at the tunnel portal under three typical speeds at 200 km·h-1,250 km·h-1,and 300 km·h-1.A comparison was also made of the alleviation effects of auxiliary pressure relief under different conditions of inclined shaft.Research declares major findings as:1)Sonic boom mainly occurs in tunnels longer than 5.0 km.The peak value of the initial pressure gradient produced by the compression wave and the maximum value of micro-pressure wave are relatively smaller and increase slowly when the train speed is below 300 km/h,indicating that the compression wave has not been intensified,and no sonic boom was detected at the test tunnel portal.Once the train speed reaches 300 km·h-1 or above,the compression wave will be steepened.Peak values of the initial pressure gradient and micro-pressure wave exceed 90 kPa·s-1 and 150 Pa,respectively.In such condition,noise produced by the sonic boom is observed;2)For the same speed level,peak values of the initial pressure gradient and micro-pressure wave are different due to the train type.Measurements obtained from CRH380 high-speed train tests are found to be relatively lower than those derived from CR400 high-speed train tests;3)Peak values of the initial pressure gradient and micro-pressure wave can be reduced by opening the inclined shaft.Opening the inclined shaft can alleviate the wavefront gradient and the peak micro-pressure wave,but it is more effective to open the inclined shaft before the position where the peak pressure gradient reaches its maximum value.According to the test results,the maximum alleviation effect reaches 27.5％when the two inclined shafts at the tunnel entrance and exit are opened simultaneously.
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