Abstract: Surrounding rock loose circle support theory has been widely recognized and accepted by engineers, how accurate and fast detection loose circle depth better for engineering services become all issues of concern, the new Lan-xin railway girder tunnel based on field test, the test section of surrounding rock loose circle depth by single-hole sonic test method, the ground penetration radar(GPR) for detection and combining with the ground stress and physical and mechanical parameters of rock mass according to the result of the benchmark for the numerical simulation analysis shows that with single span acoustic test results for reference, GPR test results and acoustic method test results are basically the same, in the surrounding rock water area test results in some deviation, geological radar emit electromagnetic fields to water area is relatively sensitive, transmit and receive interference is bigger, but the geological radar as a rapid and nondestructive detection method should be strongly applied: Due to the numerical calculation of surrounding rock loose blasting without considering the influence of the circle, the calculation results are slightly smaller that ones obtained by the acoustic detection, but the trend is basically consistent. Numerical calculation should be based on the physico-mechanical parameters of rock mass stress and according to the test results, so as to make the results of calculation more real and better for the decision of project service.

Key words: tunnel, surrounding rock loose circle, detection technology, geostress field, numerical simulation