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• • Cases and solutions ~m m '- c ~ u `m ca fig. 6 Sie~•~ ~.tnalysis of unconsolidated soils Table 2 Basic characteristics of unconsolidated soils in the study area Ground surface and Wit m 0 P2 Pt 5 ®P2-Pt (not scale) Fig. 7 The unconsolidated soil and travertine profile with hydrological conditions and pumping. It was ob- served that water level in the lake reached the E]ooding point in the period of April-M1lah 1996. Based on the data from Meteorology Station of Ni~de, annual average rain- fall is 341.76 mm between the years 19i1-199]. basic characteristics average resuhs specific gravity (Gs) 2.61 water content (w), % 34 unit weight (y„), kN/m~ 12.85 saturated unit weight (y,), kN/ms 14.71 physical properties of unconsolidated soils are given in Table 2. Typical unit weights in clay range from 1.5 to 2.0 Ivig/m', 'while they vary between 1.4 and 2.0 Mg/ma in sand (At- tawell and Farmer 1976). Average unit weight value in 'the unconsolidated soils around the Lake Dipsiz is found ito be too low (12.85 kN/ms=1.31 Mg/ma). If the Ter- Izaghi equation (1943) is applied to the region, each 1-m Sdro; of groundwater level in unconsolidated soils will kwuse a 7.947 kN/m~ increase in the effective stress above Rthe [ravertines (Table 3, Fig. 7). iroundwater Elow direction of unconfined aquifer is in a iWNW direction in the study area (Giilenbay 1972). (Hence, we believe that waters oEChe Akkaya Dam could ;not be affected from the solution-subsidence develop- ment. Topographic elevation of Lake Dipsiz is 1201 m Viand its water level is 1197 m. Groundwater level changes Karstic occurences in Lake Dipsiz and adjoining areas Karstic travertine with cavern porosity underlies the un- consolidated clayey and silty sand soils in the Lake Dip- siz and its surroundings. There exist organic soils and carbonated strata that have a thickness of about 5 cm in Lake Dipsiz and surroundings. It is assumed that Lake Dipsiz has been cohered by un- consolidated soils in the geological age. Groundwater lev- el has fluctuated due to aquifer recharges and discharges, dominated by runoff and groundwater in the study area. It was formed b)• the subsidence of unconsolidated soils as landslide into a karstic cave (Fig. 3). Excessive dratvdown has occurred as a result of excessive pumping (23 September 1995: 300 I/s) in Lake Dipsiz due [o the effect of human needs on groundwater. Excessive pumping has been cu[ down on the required groundwa- ter period (at least 3 months per year). Unconsolidated soils subsiding vertically to the voids of capes during the water table fluctuation resulted in solution subsidence. It is generally accepted that sinkholes induced by human Table 3 anon of effective stress due to groundwater depth (1=groundwater level at ground surface, I1=groundwater level 5 m deep travertine depth assumed 5 m below the ground surface) unconsolidated P, P„ P=(P,-PH) result soil kN/m' kN/m' kN/m' kN!m' thickness, m 5x14.71=73.55 5X9.807=49.035 73.55-49.035=24.515 Il-1= 5X12.85=6-1.25 0 6-1._'5-0=64.25 39.; i5~.5=7.9x7 Environmental Geology 36 13-4) Decemi!er 1998 ~ '- Springer-Verlag 1339 - Particle size (mm)