Chongqing where the Jialing River joins the Chang(Yangtze) River, is a mountainous city, with an altitude about 200–400m above the mean sea level the air temperature and humidity are high with abundant rainfall, and scarcely any snow or ice all year round. It is typical of the so-called Sichuan basin subtropic climate. The prevailing regional wind direction is north-northeast, with rather high frequency and low velocity.
The outcropping layer in Chongqing area is of the Jurassic system sediment, which consists mainly of mudstones, sandy mudstones: and clayey sandstones. As the later Cretaceous system and Tertiary system strata were lacuna owing to epeirogeny, the vertical terrestrial stress of which is rather small, and induration inadequate. At the Yenshan movement stage, the Jurassic system layer was subject to largescale level terrestrial stress, and the present Eastern Sichuan arcuate belt of folded strata was thus formed.
The broad distributive features of the Chongqing area out cropping is weak rock alternating with hard ones, with mudstones - sandstones interstratified. Its topographic features are as follows. Due to epeirogenesis, under the deep downcut dissection by surface water, vast number of valley systems and scarps came into being and slope failures often take place under certain conditions.
Basing on investigations and studies of Chongqing area, failure of weak rock slopes can be divided into three main types, i.e., crumbling and spalling, rockfall and landslides and creep.
Crumbling and spalling due to weathering chiefly takes place on thick weak rocklayer slope such as mudstone or clayey sandstone layer slopes in Chongqing area, which has low strength and easy to be weathered under the subtropic climate conditions. The mudstone on the sunny side mayscale off 5 to 15 cm annually. Open-cut pit rock banks freshly excavated may crumble or small on their outer part through 24 hours' exposure. Typical chemical analyses may be shown as follows:
(Equation in full paper)
Chemical analysis data of the sizing material show the chief elements, with few materials dissolvabe in water. The element compositions of Chongqing mudstones before and after crumbling and spalling are exactly the same. Thus we may conclude that it is not the chemical factors that caused the weathering of mudstones.
To reveal the mechanism of the defecting factors of Chongqing mudstones due to physical weathering, comparison tests had been run with rock specimens of two tppes: one extracted from above and the other below the ground water table. Each type consists of a number of groups, each group consists of about ten specimens. The main conclusions are as follows:
Rock specimens taken from below the ground water table:
Tests were made in 3groups:1st group, exposed outdoors in open air; 2nd group, soaked in still water; 3rd group, soaked in water heater, where the temperature varied from 18° to 65°C at random. Observation showed the first group specimens began to breakdown in 3 days, and collapsed to crumbles in 10 days, while specimens of the other two groups remained intact After 40 days.
