The Basic Character And Formation Mechanism Of Geological Disasters For Haiyuan County

Haiyuan county is located in the mountainous area of southern Ningxia hui autonomous region. Its stratigraphic region is located at the strata of QinglingQilian-Kunlunshan. Mainly by Quaternary loess hilly loess cover the Paleogene-Neogene bedrock, Loess hilly mainly covered with the quaternary loess in the paleogene system- neogene bedrock,after water cutting and soil erosion,and modern combination of ravines and so on,the geological effects,Mainly for the Loess Plateau、Loess Mountain Ridge;Mountain squeezed by crustal deformation and tectonic uplift in the fold 、 breakage, power late geological weathering,erosion substandard renovation.Loess wide covered in the Paleogene-Neogene and Cretaceous Red River-lake facies clastic rock above. After the cutting and eroding of the river, e.g. Qingshui River, Zuli River, the cutting effect given by Haiyuan county is enhanced. The landscape including grider undulation and ravines horizon is eventually formed.Due to the unique geopolitical conditions, Haiyuan county is become to be an region that geologic disaster happened frequently. By a profound research of distribution rule, development characteristics, and forming condition for geological disasters, e.g. landslide, collapse, unstable slopes, mud, this paper has made progress which is given as follows.一、There are water system development, ravines horizon, tattered landform in Haiyuan county. Furthermore the Loess Plateau grider is the chief geography type in Haiyuan county. Its geological environmental condition is quite fragile, which leads to serious loss of water and soil. There have happened several devastating earthquake due to the development of fault structure. In general, the environment engineering geology of Haiyuan county is very poor. It is the region of geologic disaster happened frequently.二、The main geological disasters happened in Haiyuan county are distributed as banded in the banks slope of river’s branches. Those disasters mainly happen in the shade slops in which the depth of loess is larger. In addition, it also usually occurs on the linear slope and convex slope. In term of time, it shows that the landslides and collapse generally happened in the Holocene Age during geological history period. For human history period, the landslides and collapse mainly happen in the age that intensive human activities are occurred. Furthermore, the landslides and collapse mostly appeared between July and September during one year. The landslides and collapse also mainly occurred in tectonic activity, e.g. Haiyuan great earthquake in 1920.三、Geological disasters, e.g. landslides, collapse and unstable slope, have features of large number, concentrated distribution generally. Most of landslide planes present a whole morphologic. Furthermore, due to the small thickness, it is easy to resurrect under the influence of rain. The volume of collapse is small but harmful. The width of unstable slope is large. Convex slope and linear slope is the main slope type of unstable slope. The damage of potential landslides is serious.四、The control factors of landslides happened are lithology of strata, geologic structures of slope and shape of slope. The affecting factors of landslides happened are groundwater and rain. The main trigger of landslides happened is earthquake. The human engineering activity and rain may touch off landslides. The thickness and intensity of loess as well as the outcropping altitude of mudstone determine the intensity and damage mode of slope deformation which has obvious control effect on the frequency and risk of landslides. The formation conditions of landslides are created by shear strength of rock, bulk density of rock, pore water pressure of rock, uplift force of rock, which affected by atmospheric rainfall. The surface water, in form of current, erodes the free surface conditions of landslides which created by rock. The activities of groundwater decrease the intensity of loess and change slope stress status by lubrication and softening. And then it accelerates the destruction of deformation of rock. Earthquake is the main inducing factor to landslides. The resurrection of old landslide is caused by rain. The damage of forming landslides is exacerbated by human unreasonable engineering activity.