Generating Relations Between Geological Disaster And Engineering Properties Of Metamorphic Rocks In Duhe River Basin

Duhe River is the largest tributary of the Hanjiang River.The tectonic fault develops in the Duhe River Basin,so there are many high and steep mountains and crossed valleies.The lithology of the strata is complex and the fractures and joints develop there.The water system with serious side erosion develops,which provides favorable geological and environmental conditions for the geological disasters such as landslide,collapse and debris flow.The Duhe River Basin has become one of the mountainous areas with much geological disasters in Hubei Province.Since the 21 st century,with the implementation of the National Western Development Strategy,the social and economic in the mountainous areas developed.At the same time,human beings’ demand from nature was expanding and the frequency of human activities raised,especially the unreasonable production activities and engineering activities.The destruction of the geological environment in the Duhe River Basin results harmful geological disasters with higher frequency and larger scale.The frequent geological disasters not only poses a serious threat to the life and property of local people,but also restricts the sustainable development of economic society.The geological disasters in the Duhe River Basin are mainly distributed in the metamorphic rocks areas which are mainly composed of schist,slate and phyllite.In order to prevent and reduce the geological disasters and lessen the losses caused by geological disasters,it is necessary to explore the distribution and development of geological hazards and the engineering characteristics of metamorphic rocks.The intrinsic relationship between the engineering characteristics of metamorphic rocks and the generation of geological disasters should be revealed so that to put forward reasonable countermeasures.In view of this,based on the full collection of data in the Duhe River Basin,the geological environment condition and the geological disaster comprehensive investigation in typical area are researched in this paper,revealing the environmental conditions for the breeding of disasters and the spatial and temporal distribution rule of the geological disaster in the study area.On this basis,this paper mainly focuses on the types of geological disasters,morphological characteristics and failure modes of the metamorphic rock and the causative effect of some influencing factors.Then,the engineering characteristics of metamorphic rocks,including the microscopic properties,physical properties,mechanical properties and water properties,were researched through the field and laboratory tests on the metamorphic rock samples from different geological hazards.Afterwards,two typical metamorphic rock landslide disasters with different lithology and failure modes were selected and researched.The mechanism of the metamorphic rock was studied.Finally,based on the research above,the relationship between the engineering characteristics of metamorphic rock and geological disasters is revealed.This paper has made the following achievements and conclusions:(1)Based on the investigation of the geological environment in the Duhe River Basin,combined with relevant data in this district,the geological and environmental conditions of the Duhe River Basin are summarized.According to the analysis of the geological hazard,some useful conclusions about the influencing factors and the disaster effect are obtained.The terrain and geomorphologic conditions in the Duhe River Basin are complex.The tectonic movement is active.The lithology of the strata is complex and variable.The intensely weathered rock mass and weak fragmentation provides the basic conditions for the generation of geological disasters.Moreover,the intensive and concentrated rainfall and large scale human engineering activities lead to a wide distribution of geological disasters with high frequency.(2)By means of the statistical analysis of the geological hazard survey data in the study area,the temporal and spatial distribution of geological disasters is summarized.The geological disasters mainly break out in rainy season,especially in the rainstorm season.The geological disasters mainly occur in the soft metamorphic area,such as tectonic rupture,valley terrace and both sides of the trunk line.On this basis,the development characteristics of the geological disaster in metamorphic rock area are mainly studied in this paper.The plane shapes of these landslides are mainly longitudinal tongue and semicircular.And the profile shapes are stepped and convex.But the collapse plane is always irregular.Most of the slopes are straight lines.The landslide and the collapse are mainly in small scale.With the increase of the disaster scale,the number of the disasters is gradually reduced.And the large scaled disasters are always concentrated in some specific zones.There are mainly two failure modes of the landslides with metamorphic rocks,layer slide failure mode and cutting slide failure mode.Collapse mainly consists of slip collapse,falling collapse,dumping collapse and peeling collapse.(3)Microscopic properties of metamorphic rocks with different lithologies were tested.The metamorphic rocks were found to contain a large amount of soft and easily weathered flake minerals,such as mica,chlorite and illite.Most of the minerals have multi-layered texture and epidoblastic texture.The micro-fissure develops in flaky structure,plate structure,phyllite structure and foliation structure.The porosity of the metamorphic rock is large.The wave velocity in the foliation tangentially is much larger than the wave velocity orthogonally.And the wave velocity is affected by the weathering intensity of rocks.According to the field needle penetration test and the point load test,most of the severely weathered metamorphic rocks belong to soft rock or very soft rock which are easily softening.The mechanical parameters such as compressive strength,tensile strength,elastic modulus,Poisson’s ratio and failure modes of metamorphic rocks were measured by indoor uniaxial compression acoustic emission test,Brazil splitting test and uniaxial compression numerical test.These parameters are related to the inclination of the inner foliation in the metamorphic rock,showing obvious anisotropic characteristics.By analyzing the water properties of metamorphic rocks,the hydrolysability of the foliations in metamorphic rocks is strong as it could absorb a large scale of water rapidly.It is easily swelling and softening,resulting poor resistance to disintegration.The hydrochemical properties of metamorphic rocks are mainly due to the fact that the development of foliations provide good access for water to enter into the rock.Chlorite,mica,illite and other clay minerals are soft and easy to weather.It’s easily to absorb water and swell.So metamorphic rocks are rapidly weathered in natural conditions.(4)Based on the mechanism study of typical landslides with metamorphic rocks,the mechanism of layer slide failure mode is obtained.The foliations in metamorphic rocks are flat and smooth,so there is low shear strength between the foliations.And the foliations are easy to weather,soften and expand.When the slope of landslide is steeper than the foliation angle in the metamorphic rocks,self-weight and the sliding force of the landslide will increase on the condition of rainfall.Foliations are easy to weather and crack,so the rock mass will slide along foliations.The mechanics of cutting slide failure mode are also researched.Metamorphic rocks are easily weathered and cracked,cutting the rock mass into layers.When the slop of the landslide reverse to the rock foliations,the foot of the slop is eroded,forming an empty surface.Then the rock mass is cut off layer by layer from the bottom to the top of the rock mass under the action of self-weight or any other external forces,gradually forming a continuous weak surface.The broken rock body slides along the weak surface under the action of earthquakes or rainfall.(5)The relationship between the engineering characteristics of metamorphic rocks and the geological disasters in the Duhe River Basin can be summarized as follows: 1)the special mineral composition,the microtexture and the structure of metamorphic rocks constitute the basic weathering condition for metamorphic rocks.And the properties of water absorption,softening,expansion and poor resistance to disintegration increase the weathering speed.At the same time,the tectonic structure is active in this area,breaking the rock and developing fissures.In the alternating natural conditions of hot and cold,dry and wet,as well as freeze and thaw,local metamorphic rocks are seriously weathered.A large number of loose and broken rocks are formed there.Consequently,slope is accumulated by these loose weathered rocks,which provides a rich material basis for the geological disasters.2)In the Duhe River Basin,a lot of smooth foliations are concentrated in metamorphic rocks,which are slippery,less resistant to water,and easy to soften in water condition.So there are a lot of landslides,including rock landslide,soil landslide and rock-soil landslide,sliding along the smooth foliation surface,showing a phenomenon of the heavier rain,the larger scale of landslide.3)The main reason of rocky landslides and rocky collapse is the low strength of loose,broken and easily softened metamorphic rock in the Duhe River Basin.4)The distribution of foliations in metamorphic rocks affects the failure mode of geological disaster.The relationship between the foliation and the slope of landslide as well as the combination features of the foliation with other joint fissures induce different failure modes of the landslides and collapse with metamorphic rocks.