Northern Shaanxi The Homestead Slope Of Casualties Loess Collapse Formation Mechanism And Prevention Programs

The Formation Mechanism And The Prevention-cureProgramme Of The Casualty Loess Landfalls On TheHouse Side-slope In The Northern ShaanxiAbstractThe main contents of this dissertation include four parts as follows:1. Based on data and information from field investigation and laboratory experiments for the physical and mechanical properties of loess, the regional geological setting and physical-mechanical environment of the landfall are generalized. Furtherly, according to their state in suffering force and their modes of initial motion, the casualty loess landfalls on the house side-slope are classified into two types of tension-sliding loess landfall and collapsed earth cave dwelling. The warning signs (such as the fissures on the slope, frequent fall of earth block, and abnormal phenomena of animal, etc.) and distribution characters of the landfall are summed up. Grounded on analysis of the interior factors (such as valley-side slope structure, stratum structure, fissure without displacement, loess microstructure and shearing strength , etc.) and exterior factors such as rainfall, earthquake and so on, it is proved that human's cutting a terrace of building houses in the loess slope is the main factor of inducement of the landfall. On the basis of the geomechanical model for slope deformation and destruction, the developmental process of this landfall is divided into four stages, which are valley-side margin ripping, margin slope creeping, the short slip belt being formed and pierced, and the landfall befallen.2. Taking five representative casualty loess landfalls on the house side-slope as examples, applying the method of limit analysis of soil plasticity and the ultimate equity method, the equation of the stability and gradient of the landfall is derived. The results indicate that the stability of the landfall reduces with the increase of gradient of it. Furthermore, the landfall is only stable when its gradient is no bigger than its natural gradient (40皛45?.3. By means of the finite element inverse analysis, based on stress-strain theoretical equations of the elastoplasticity and viscoelasticity-viscoplasticity, the change of the valley-side margin stress distribution during original state, the condition of human cutting a terrace of building houses in the loess slope, and the condition of cutting the top of loess slope is elucidated. It is testified that the landfall happens because of the increase in shearing stress and tensile stress. The mechanism and main prevention-cure measure of cutting the top of loess slope according to its nature gradient for the landfall are quantitatively reformed and simulated.4. The prevention-cure measure for the landfall is put forward. The prevention measures emphasizes on monitoring and choosing site, combining with scientificpublication for enhancing people's consciousness of preventing from this disaster. The cure measures are mainly to cut the top of loess slope, to drain terrene water, and so on.There are two main innovate ideas in the dissertation. (1) Supported by the results from the method of limit analysis of soil plasticity and the ultimate equity method, the author proposes the criterion of judging of stability of slope of foundation of a building. It's that the gradient of the valley-side margin is no more than its natural gradient. (2 ) The finite element is used to analyze the stress field change of the valley-side margin during original state, the condition of human's cutting a terrace of building houses in the loess slope, and the condition of cutting the top of loess slope, then the dynamic mechanism for forming of the landfall is probed. It is scientific reference to prevention-cure and control the valley-side margin.