The infiltration characteristics of soil under the action of heavy rainfall is an important part to study the developing process of landslide debris flow and soil landslide. A soil cylinder experimental facility for infiltration test under artificial rainfall is prepared to do infiltration test for strongly weathered mudstone under six rainfall intensities

i.e. 10

20

30

40

50 and 60 mm/h

and the longest rainfall duration is 105 minutes. Three conclusions are drawn as follow. Firstly

the infiltration process can be divided into non-compressive infiltration

compressive infiltration

and saturated infiltration stages. Meanwhile

the infiltration rate will close to be a constant along the rainfall duration in the non-compressive infiltration and saturated infiltration stages

and it will reduce quickly in compressive infiltration stage. Secondly

the infiltration interface in the soil is defined as infiltration front

and it contains original infiltration interface and final infiltration interface. Then

the relation is discussed between the depth of infiltration front and rainfall intensity

the bigger the rainfall intensity is

the bigger the amplitude between two infiltration interfaces is. Thirdly

a rainfall infiltration formula is built to express the infiltration process of Jurassic strong weathering mudstone in Chongqing city. The results have positive effect for the study of constructing the forecasting model of rainfall-induced type landslide and slope debris flow in Chongqing city.