Influence Of Tunnel Construction On Soil Quality In Karst Valley Of Zhongliang Mountain Chongqing

With the rapid development of China's economy,roads and railway tunnels have emerged as the link between the connected regions.The construction and operation of highways and railway tunnels have strengthened exchanges and contacts between various regions,which has facilitated people's travel and brought huge social and economic benefits,and inevitably produced a series of ecological and environmental problems.Especially in the karst area where soil erosion is serious,the tunnel has a greater impact on the soil ecological environment of the tunnel area.In this paper,the soil physical properties?soil water content,soil bulk density,soil porosity,soil mechanical composition,soil temperature,soil CO₂?and soil chemical properties?nutrient content and its loss?in the tunnel affected area and non-tunnel affected area are constructed in the karst trough valley of Zhongliang mountain chongqing.The response process and change mechanism of soil physical properties and chemical properties to tunnel construction after tunnel construction are discussed,in order to make scientific and rational use of land,improve land productivity,maintain soil fertility and preventing soil erosion,provide a theoretical basis for residents in the study area.The main results of this study are as follows:?1?Compared with the non-tunnel affected area,the soil water content,bulk density,soil organic matter,total nitrogen,total phosphorus,total potassium,available nitrogen,available potassium,and available phosphorus decreased by 22.58%,10.28%,44.85%,36.38%,22.58%,26.12%,28.21%,19.67%,37.69%;while soil porosity,pH,Ca,Mg increased:11.6%,10.25%,17.24%,and 145.9%;In terms of soil mechanical composition,the sand content of1-0.05 mm in the tunnel affected area and the coarse powder content of 0.05-0.01 mm are higher;while the fine powder of 0.01-0.001 mm and the content of<0.001 mm of the clay are lower.?2?As the tunnel construction destroys the surface vegetation,the surface vegetation coverage rate in the tunnel affected area is low.Regardless of the depth of different soil layers or different land types,the soil temperature in the tunnel affected area is slightly higher than that in the non-tunnel area,while the soil moisture and soil CO₂ concentration are lower than those non-tunnel affected area.Correlation analysis showed that soil CO₂ concentration was significantly positively correlated with temperature,15cm temperature,30cm temperature,45cm temperature,15cm moisture,30cm moisture,45cm moisture,soil organic matter,total nitrogen and available nitrogen;The total porosity and pH of the soil is negatively correlated.Principal component analysis showed that the first main component had higher load:15cm temperature,30cm temperature,45cm temperature,15cm moisture,30cm moisture,45cm moisture;the second principal component had higher load:soil organic matter,total nitrogen,available nitrogen,pH and porosity.The multivariate regression analysis model showed that soil CO₂ concentration was affected by soil temperature,soil moisture,organic matter,pH and porosity.Soil temperature and moisture were the main factors affecting soil CO₂concentration,and the interpretation rate of soil CO₂ concentration was 66.3%-86%.Correlation analysis showed that the correlation between soil temperature and soil CO₂concentration was lower than soil moisture.?3?Using soil nutrient index to evaluate soil nutrient content,the results showed that the soil nutrient content in the tunnel affected area was significantly lower than that in the non-tunnel affect area.The soil fertility index of Nemero indicates that the soil fertility of different land types in the tunnel affected area is moderate,while the non-tunnel affected areas are relatively fertile.The mean P value is:non-tunnel affected area?1.97?>tunnel affected area?1.42?.?4?The soil nutrient loss concentration in the study area is:Ca²⁺,Mg²⁺and HCO₃^-ion concentration are all tunnel affected zone>non-tunnel affected area,while K⁺,Na⁺,Si⁴⁺,Al³⁺,SO₄^2-,NO₃^-,PO₄^3-and Cl^-ion concentration is:tunnel affected area<non-tunnel affected area.The total loss of nutrients such as Ca²⁺,Mg²⁺,HCO₃^-,K⁺,Na⁺,Si⁴⁺,Al³⁺,SO₄^2-,NO₃^-,PO₄^3-and Cl^-in the study area is the tunnel affected area>non-tunnel affected area,from different soil layers in depth,the total annual loss of soil nutrients is:15cm>30cm>45cm.From the perspective of different land types,the total annual loss of soil nutrients in the three types of land is:cultivated land>wild grassland>forest land.Total annual loss of soil nutrients:tunnel affected area>non-tunnel affected area.?5?In summary,the impact mechanism of tunnel construction on soil quality in the study area is:due to the construction of the tunnel,the underground aquifer is exposed,the groundwater is drained,the groundwater level is lowered,the soil is dried,the soil water content is reduced,and the vegetation cover Degree drops.The soil bulk density is reduced,the porosity is increased,and the soil erosion resistance is weakened,which aggravates the loss of SOM,TN,TP,TK,AN,AP,AK and other nutrients in the soil,resulting in a decrease in soil fertility and a decrease in soil quality.