| In recent years, the extreme climate events frequently happen, which bring a huge life and property loss to the state and the society. In order to improve the anti-disaster ability of our country’s important linear engineering in extreme weather conditions, and fill in the blank of the field related to our country’s unsaturated soil engineering dealing with extreme climate events design and construction level, this article, based on the science and technology research project(KJ120407)of Board of Education in Chongqing city, takes the observed meteorological data of Chongqing as the boundary conditions, the field sampling soil geotechnical test results as the parameters reference, adopts the numerical simulation method to entirely couple the extreme climate with the unsaturated soil subgrade slope, explores the response of the unsaturated soil subgrade slope to the extreme climate, and analyzes the change of physical and mechanical parameters of the unsaturated soil. The main conclusions are as follows:1. Based on the meteorological data from 1950 to 2013 in Chongqing area, it adopts the percentile method to determine the threshold value of extreme climate in Chongqing area, extract the index of extreme climate, analyze the intensity and frequency characteristics of various extreme climates, and predict the future trend according to the interannual oscillation cycle. The results show that:①In Chongqing area in latest 64 years, the annual mean temperature value presents a slightly rising trend and the precipitation grows in a weak trend, and the interannual trend shows the characteristics of obvious alternation of drought and flood;②Except that the days of extreme low temperature in the extreme low temperature index presents a declining trend, the rest of the extreme low temperature index and extreme high temperature index and extreme precipitation index show a rising trend;③In a future period, the happening frequency of extreme high temperature and extreme precipitation and other extreme climate events in Chongqing will increase;2. Based on the statistics of the happening frequency of landslide, collapse, debris flow, ground collapse and ground crack five kinds of geological disasters from 1300 to 2013 in Chongqing; it analyzes the time domain characteristics of the temperature fluctuation and the geological disaster occurrence frequency in different time scales and the influence of extreme climate on geological disasters. The results show that:①In hundred interannual and interdecadal time series, the disaster frequency and temperature fluctuations in Chongqing area present a synchronization in the same time domain, that is, high(low)-incidence season geological disasters corresponds with the rising(lowing) temperature period of the climate;②The interannual superimposed effect of the extreme high temperature events and extreme precipitation events aggravates the occurrence of geological disasters in the following year, and the in-year superimposed effect of the extreme low temperature events and extreme precipitation events inhibits the occurrence of geological disasters in the same year, and the interannual and in-year superimposed effect of extreme high temperature and extreme drought inhibits the occurrence of geological hazards;③The extreme precipitation in a relatively short period urges the happening of geological disasters, and the extreme temperature inhibits or promotes the occurrence of geological hazards in a larger time scale.3.Taking the threshold value of the extreme climate in Chongqing area from 1950 to 2013 as the boundary conditions and the indoor geotechnical experiment data as the parameters, it adopts Geo- Studio geotechnical analysis software to make a damp- heat- physical three fields coupling numerical simulation for the unsaturated soil roadbed physical mechanics under the action of the extreme climate, and analyzes the parameters change rule of physical mechanics of the unsaturated soil body under the action of extreme climate. The results show that:① Under the action of evaporation of extreme high temperature, the soil temperature of the unsaturated soil presents a rule that it increases with rise of temperature and it decreases with the increase of the depth; Among them, the diurnal variation of soil temperature and the change of day air temperature present an approximate same trend; the seasonal variation of soil temperature shows a different seasonal characteristic, in summer, it gradually cools down with the increase of the depth. In winter, it gradually warms with the increase of the depth. In spring and autumn, it appears a thermosphere in a certain depth of soil, and it gradually decreases from this layer to the surface and deep of the soil body;②Under the influence of different temperature, the shear strength of unsaturated soil raise with the increase of temperature and hold time of temperature. When the temperature was from 10% to 50%, the cohesion did not change significantly, and when the temperature was from 10% to 50%, the cohesion linear increase from 0h to 48 h. After seven days, the basically reached stability, the growth rate is about 20%; the friction angle of the soil showed a linear increase at the 0h~12h and at any temperature. There was no obvious change after 12h;③The shear strength of unsaturated soil continued to decline on the whole with the increase of rainfall intensity, and the fall rate is different with the different rainfall intensities.The fall rate of the shear strength of soil with the rainfall intensity in the range of 50mm/d~120mm/d is higher than it with the rainfall intensity in the range of 120mm/d~180mm/d;④Under different rainfall intensity, the subgrade slope safety factor of unsaturated soil decreased with the increase of rainfall intensity, but in different range of rainfall intensity showing decreases first and then increases. When the rainfall intensity was from 50mm/d to 280mm/d range, the safety factor shows the phenomenon of falling features and violent shocks in the local, and when the rainfall intensity was from 280mm/d to 360mm/d range it shows small amplitude growth;⑤The safety factor of unsaturated soil subgrade slope has a downward trend with the increase of the seepage holding, but in the different flow duration range it showed first decreased, then increased, stabled and lowed finally. In the 1d~3d time domain with seepage action, the slope surface soil is from unsaturated soil into saturated soil with affected by the slope surface runoff, the saturation water level is transferred from the surface of the slope to depth over time, The underground water level of the foot of slope gradually rising, the safety factor decreased linearly; In the 4d~7d time domain with seepage action, the slope surface soil is from saturated soil into unsaturated soil with affected by the seepage function inside the slope body, the safety factor small amplitude increased; In the 8d ~ 56 d time domain with seepage action, The safety factor decreases slowly with the linear trend, tending towards stability after 57d;⑥Under the conditions of single dry-wet cycle, the mutual restriction between rainfall and evaporation, the influence range of subgrade soil is about 1.2m; Under the conditions of repeated dry-wet cycle, rainfall and evaporation promote each other, The influence of subgrade soil is deeper, The influence depth is steadily at 6.3m after 5 times of cyclic;⑦Under the vertical pressure at the same level, the shear strength of unsaturated soil increases with the increase of the matrix suction, and weaken with the increase of the dry-wet cycles, stabilized after repeated the cycles by 5 times, The attenuation range of cohesion is about 40% ~ 61%, The attenuation range of effective friction angle is about 12% ~ 18%;⑧Under suction with the same matrix, the shear strength of saturated soil weaken with the increase of the dry-wet cycle times, and related to the circular path, the shear strength with desorption path is lower than it with absorption path, The mechanical property of unsaturated soil after repeated dry-wet cycles will produce irreversible changes. |
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