Abstract: To investigate the calcium precipitation and change characteristics of water environment during pore infiltration into the shotcrete of tunnel primary support shotcrete, a test device is developed considering the tunnel drainage path and pressurized infiltration. A pressurized infiltration test is conducted on the shotcrete to determine the distribution of acidity and alkalinity under water infiltration into the surrounding rock. The change laws of the time course of the calcium ion concentration and water quality parameters of the primary support are determined and the results are verified by comparison with the literature to validate the reliability of the device. The following conclusions are drawn from the test results. (1) The developed test device comprises a watersealed pressure chamber placed in the surrounding rock, a specimen chamber placed in the shotcrete of the primary support, and a drain pipe as a return chamber. The device can simulate calcium precipitation and changes of water environment of the shotcrete of the primary support under 200kPa pressurized infiltration. (2) Lower the pH of the shotcrete in the seepage crosssection, leads to more severe calcium loss. The loss of calcium by precipitation deteriorates the shotcrete unevenly. (3) The primary support water under the action of shotcreting has high calciumion concentration (greater than 100 mg/L), high alkalinity (greater than 3 000 mg/L), high pH (greater than 11.5), and high total dissolved solids (greater than 8×10-6 mg/L); There are four stages in the development of the calcium ion concentration and water quality parameters: a rapid rise in the first four hours, shortterm stability during 4 to 18 h, fluctuating decline in 18 to 68 h, and stability after 68 h. The change characteristics of each stage are related to the start time of the experiment, the quantity of infiltrated water, and the precipitation of calciumion crystals.

Key words: tunnel engineering, test device, shotcrete, pressurized infiltration, calcium precipitation, water environment change