| The development of karst has an directly impact on the construction and operation safety of tunnel engineering in Southwest of China.It is of theoretical and practical significance to study the corrosion characteristics and influencing factors of the tunnel.This research was supported by Nation Science Foundation Project:Study On Chemical Dynamics And Fractal Characteristics Of Groundwater In Karst Tunnel（No.41372334）,Selected a typical tunnel of karst area in Southwest China,which called Wulong tunnel.The karst development place of the tunnel engineering area was investigated in detail,and the key development areas of karst were determined.The corrosion law of the tunnel rock under different environmental conditions had been studied by experiments.Numerical simulation was used to forecast the karst corrosion in the next100 years.Finally,combined with field investigation,experiments and numerical simulation,the corrosion characteristics of the key development karst areas of the tunnel were discussed,for providing advice of tunnel protection.The research results were as follows:1.Based on the investigation of the development karst characteristics of ground and underground in Wulong tunnel,it was determined that the most developed area of tunnel karst is the middle section of the tunnel（3892m5276m）,which has two subterranean rivers（2#,3#subterranean river）below the tunnel area and the significant karst phenomenon-karst funnel above the tunnel area.2.According to the environment conditions of the study area,four kind of flow rates（0ml/min、0.05ml/min、0.1ml/min、0.2ml/min）,five kind of temperatures（15℃、25℃、35℃、45℃、55℃）,and three kind of pH values（5.5,7,8.5）,a total of 22 kind of experiment conditions were set in the experiments of A and B samples in different parts of karst key development area of Wulong tunnel.The results were as follows:（1）The influence of pH on the corrosion of rock samples was more significant than that of temperature and flow rates.The corrosion ratio and Ca2+concentration of the karst key development area’s rock samples under acidic conditions（pH=5.5）were more higher than those in neutral（pH=7.0）and alkaline（pH=8.5）conditions（25℃,0ml/min）.Comparatively,the corrosion ratio and Ca2+concentration under the neutral condition（pH=7.0）had very less difference with the alkaline condition（pH=8.5）.（2）The influence of the flow rates on the corrosion of rock samples was more significant than the temperature.The maximum corrosion rate difference of the karst key development area’s rock samples at different flow rates were 5.96.0 times than that of the maximum corrosion ratio at different temperatures respectively.During the rainy season（June to August）,the corrosion rate was about 3 times higher than the dry season（December to next year’s February）in the middle section of the tunnel’s key development karst areas.（3）The corrosion law of tunnel rock was affected by rock’s physical and chemical properties.The chemical properties of rock sample A,B are basically same,but the rock sample A is more denser than rock sample B,led to rock sample B was more easier to be corroded,which is in loose structures.（4）The corrosion characteristics of the rock samples（sampling rock from the tunnel karst development area）under the field conditions near the tunnel engineering were discussed by the field experiment.Within the first three quarters,the corrosion ratio of the buried rock samples in the field increased with time,and the corrosion of rock samples in rainy season was faster than that in dry season.3.The main karst fissures in tunnel vault of krast most developed part in the tunnel middle section,which was above the two subterranean rivers（2#,3#subterranean rivers）and under the Yang aotuo karst funnel,was studies by numerical simulation within 100years.The results were as follows:（1）Within the set conditions of this study,the influence of temperature and permeability on the development corrosion range was not obvious,while the flow rates has a great influence on the corrosion range.The extent of corrosion range increased very fast with the flow rates.Under different flow rates（weak hydrodynamic conditions,normal hydrodynamic conditions and strong hydrodynamic conditions）,the intensity and range of corrosion had great differences,the intensity and range of corrosion were:weak hydrodynamic conditions﹤normal hydrodynamic conditions﹤strong hydrodynamic conditions.The karst fissures under different permeability conditions（low permeability,medium permeability,high permeability）and different temperature conditions（10℃,20℃,35℃）,the corrosion range had less difference from each other.（2）In the same time period,the corrosion ratio were positive correlation to the temperature,flow rates,porosity and permeability.The karst fissures in tunnel had the fastest corrosion rates under the condition of 35℃,strong hydrodynamic conditions and high permeability.（3）The corrosion parts of the tunnel fissure were different under different environmental conditions.The main corrosion parts of high permeability condition was the core part and the middle part of the fissure,while the main part of the corrosion was the core part and the upper part of the fissure under the low permeability condition.Strong hydrodynamic conditions’s corrosion parts of the tunnel fissure was mainly the core and the lower part of the fissure.The corrosion place of the tunnel fissure under the weak hydrodynamic conditions were the core and the upper part of the fissure.（4）The porosity and permeability of fissures had secondary effects on the corrosion of fissures.The higher the initial permeability and porosity,the faster the corrosion rates.At the same time,after the corrosion,the greater the permeability and porosity increment,in turn,that accelerated the corrosion again. |
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