THE STABILITY OF SANDY SOILS AND ITS DEPENDENCE ON HUMIFICATION DEGREE AND CONTENT OF ORGANIC-MATTER

The influence of organic matter on the strength parameters cohesion and friction angle was investigated with mixtures of a fine sand and 0-8 % peat of different humification degrees - determined by using a thermobalance - and under different soil water suction. The results show that the strength parameters cohesion and friction angle increase with increasing organic matter content, but the increase is greater with lower humification degree. Especially if the organic matter content is lower than 5 %, cohesion and friction angle depend on soil water suction and have a maximum in the range of about 50 hPa soil water suction. A simplified model based on the capillary theory for the calculation of cohesion was proposed to explain the influence of content and humification degree of organic matter on cohesion. One possible reason for the lower cohesion with higher humification degree is its lower wettability. The dependence of friction angle on soil water suction and humification degree of organic matter needs further examinations.