GEOTECHNICAL HAZARDS

Since ancient times, Man has taken the soil or ground that is to be used for the construction of various works such as roads, bridges (Fig. 1), buildings, water dams (Fig. 2), ports and mines into serious consideration.

Engineering Geology is a scientific branch of earth sciences which evaluates the behaviour of the soil and rock where a construction will be built. It evaluates the stability conditions of any rock mass or soil which may create hazard or have any potential damage to existing constructions or infrastructure near or around the building.

The knowledge of the characteristics of the ground is achieved through a geotechnical investigation, which is divided into site and laboratory investigations. 

The aim of the site investigation is to understand the character of the geological material. The composition and structure of the geological formations, their thickness and side variations, the main mechanical properties of the ground and the hydrogeology of the area are the data obtained by the evaluation.

The laboratory investigations include a number of tests (Fig. 3) and analyses on samples collected during the site investigation. The aim of the laboratory test is to gain the physical and mechanical properties of the ground as well as its chemical and hydraulic characteristics.

The main geotechnical problems that occur in Cyprus are: slope failures and landslides (Fig. 4); rock falls (Fig. 5); and, foundation settlements (Fig. 6, Photo M4). Slope failures (Photo M2, M3, M5) may originate from the structural, mineralogical and hydrogeological conditions of the rock or soil. This phenomenon has been observed at the dumping sites of mining areas in Cyprus due to their physical properties and lack of proper design practices of the dumped material. Rock falls are observed mainly in the mountainous areas of Cyprus and in natural and manmade slopes. They are mainly related to geological, topographical and rainfall conditions.

Marls, clays and gypsum are the main soil types in Cyprus that are related to foundation settlements.

Foundation settlements or subsidence of civil structures can also be caused by the development of void spaces or caves in the ground called sinkholes (Photo M1).  The foundation settlements are highly related to the geological conditions and mechanical properties of the ground in the built-up areas. 

Limestone is another rock type that sinkholes or caves can be developed in due to its dissolution by water.  In Cyprus, the dissolution of limestones appears to be rather limited, forming small, irregular surface caves or complex underground voids and drainage systems leading to the development of karstic springs. Underground dissolution voids are difficult to identify from the surface and constitute a serious potential problem in the stability of civil structures.