The severe engineering hazards connected with rock swelling were encountered in the construction of many countries such as U.S., 3SSR, Japan, Brazil, Ghana, and so on. A lot of researches in the fields of soil mechanics and rock mechanics have been done in the recent years. According to the preliminary study and information collected by the author there exists the engineering geological problem related to rock swelling in many construction sites, including some adits of coal mines, in China.

This paper presents an example of the engineering damage caused by rock swelling in an underground excavation. Following the deformation phenomenon, this Paper deals with the study of the origin of the failure, especially the influence of the dehydration during drying in air on the engineering properties of the swelling rocks. On the basis of above-mentioned study. Some suggestions were made for attention in the underground construction.

Due to the lack of comprehensive knowledge on the properties of swelling rocks some engineering hazards appeared causing mentual and material damage. However, on the other hand, some dam sites were changed just because of the presence of bentonite which may have no serious influence on the dam construction. The swelling rocks are defined here as the rocks which can yield swelling deformation due to increasing of water content.


The studied site is located in the Yanshan Mountain Region which belongs to the continental semi-arid zone in the climatic aspect. The preciptation is concentrated in autumn. The rock system on the construction site presents a series of siliceous limestone, dolomitic limestone and dolomite of Wumi Mountain group, Sinian System, which composes a gentle fold striking in NE direction. At middle Jura-sic time there appeared intrusion of andesite-porphyry along the tension fractures of NW direction, forming a series of viens and dykes. The maximum width of such igneous bodies exposed by excavation is about 70 m.(Fig. 1.)

(Figure in full paper)

The igneous bodies usually contact the surrounding rocks with crushed zone. The boundary is clear and thermal baked phenomena can be observed.

The experiences of the underground excavation show, that all the openings subjected to severe damage are of surrounding rocks in andesite-porphyry. The contour of damaged area coincides with the area of distribution of andesite-porphyry. (Fig. 1).

The width of the openings is of 4–8 m, and traditional type of separated wall was used as support without using the shotcrete bolt system. The thickness of concrete arch is about 30–40 cm. The prefabricated blocks are used for the side walls of height about 3.1–5.3 m. The excavation started in 1972,and the construction was completed in 1977. There was heavy rain in autumn that year, and the intensive heave of bottom was observed in the excavation tunnels No. 27 and No.33 with length about 260 m. The height of heave is 1.0 m, and maximum height reached 1.5 m. The andesite-porphyry on the location of bottom heave become into a state of highly plastic mud.

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