Abstract: On the basis of the existing research on the pot cover effect, the law of the water accumulation caused by the pot cover effect is studied for the road surface and runway, which have a structure of cover layer (equivalent to "pot cover"), gravel layer, and clay layer from top to bottom in actual engineering. Through carrying out indoor tests to simulate the road foundation structure of the actual project, the law of the water accumulation in soil, under the two conditions of open and closed, was analyzed respectively. The test results show that there is a phenomenon of water vapor circulation of the pot cover effect under the two test conditions, and the peak values of the water head circulation of the two tests are different. The internal mechanism of water vapor circulation was explained by the calculation of the water heads value. Calculating the circulating water volume of the closed system verified that the circulating water volume generated by the two tests in half of the cycle is approximately equal. It is found that the law of the water accumulation caused by the pot cover effect is related to whether the bottom of the gravel layer is flat. If the bottom of the gravel layer is not flat, the water in the gravel layer will keep accumulating. If the bottom of the gravel layer is flat, the water in the gravel layer just increases to a certain amount, the water volume will no longer increase, and a certain amount of water circulates in the form of water vapor in the gravel layer. Favorable road foundation structure should be designed in the project to prevent massive water accumulation under the road surface.

Key words: pot cover effect, water vapor circulation, pavement structure, law of increasing water