Preliminary Research On Engineering Technology For Prevention And Control Of Secondary Disasters In Gully Land Consolidation Of Loess Hilly And Gully Regions

Since the gully land consolidation project was implemented in the hilly and gully region of the Loess Plateau in 2010,about 500,000 acres of land have been renovated,and the potential area for remediation is huge.The trench land consolidation project mainly uses waste silt dams or constructs retaining walls to form a barrier control project,and then cuts back trenches on both sides of the trench to quickly form high-quality cultivated land to ease the tension of land resources to ensure"Returning farmland to forest?grass?"achievements,"land security"and"food security".The mixed soil land formed by this land remediation method often blocks the original channel flow path,resulting in a significant increase in the soil water storage of the newly created land in the channel,resulting in uneven settlement of the new land,secondary salinization,and dam body Secondary disasters such as Guan Yong.Aiming at such disasters,this study took the infiltration characteristics of newly created soils in different situations as the starting point,combined with stormwater design standards and related specifications,studied the infiltration characteristics of mixed soils,and designed a method that uses gravel and blind ditch phases.Combined with the drainage method applicable to the newly constructed land,and its effectiveness was verified through later prototype monitoring,the following main conclusions were obtained:?1?Basic characteristics of newly-built soil:The mixed soil of newly-built land in the loess hilly and gully region is composed of Malan loess,loess soil,Heilu soil and ancient soil,and the proportion is about 2:5:2:1.In the depth range of 0?350 cm,the mechanical composition of the soil is about the same,the clay content is between 14.8%and 21.64%,the powder content is between 18.98%and 24.61%,and the sand content is between 54.87%and66.26%.The maximum infiltration rate of newly constructed soil is about 3.91×10^-1cm/min,and the stable infiltration rate is about 1.64×10^-2cm/min.The stable infiltration rate is lower than that of terraces in the same area,66.53%,orchard 65.11%and dam,respectively.57.95%.It explains that the newly-built land is mixed with Malan loess,ancient soil,with complex composition,low content of organic matter and agglomerates,poor water permeability,easy to accumulate water and leak,and induce secondary disasters.?2?Infiltration characteristics of newly-built soil:Under the experimental conditions,the maximum soil infiltration rate of the newly constructed soil increased from 1.2 g/cm³to1.5 g/cm³.The infiltration rate decreased from 2.16×10^-2cm/min to 1.13×10^-2cm/min.The infiltration stop time,the infiltration start time and end time of the same depth are extended with the increase of the bulk density of the soil upper layer.After infiltration,the soil moisture content and electrical conductivity both fluctuate and rise with increasing soil depth.In different areas of upper surface bulk density,soil moisture content decreases with increasing bulk density,and again stabilizes in the same area of lower bulk density,while The change of upper surface bulk density has little effect on the vertical distribution of soil electrical conductivity.Further soil column test fitting shows that the Horton infiltration model can reflect its infiltration law better than kostiakov,Philip and the general empirical infiltration model.?3?Newly-built site drainage design and secondary disaster prevention and control effect:Experiments and simulations show that the amount of precipitation recharge at different depths of the newly constructed land is exponentially negatively correlated with the soil depth.It is more appropriate to arrange the drainage works in the depth range of 1 m to 3m underground.According to the relevant specifications,taking the rainstorm of 1 hour and1 hour for 20 years in the Yangjuangou catchment of Yan'an as the design standard,the drainage facilities were designed for the land improvement of the Yangjuangou gully:the rectangular blind ditch in the form of gravel and three blind ditch lengths were respectively60 m,30 m,30 m,the size of the rectangular section is 1 m×0.5 m,and the slope is not less than 5%.The blind ditch is entirely filled with layered gravel with good particle size of 40?80 mm,controlling the porosity at about 50%,wrapped with non-woven geotextile,and overlapped.The overall depth of the blind ditch is between 0.7 m and 4.5 m.The soil seepage of the newly constructed land is collected by the blind ditch flow path and flows through the bottom of the dam.A"fully buried"water cellar is designed for collection and utilization behind the dam.The project was completed in August 2019.Sampling and monitoring found that,compared with the new construction of trenches without measures,the gravel blind ditch drainage project can reduce the increase in soil moisture content of the newly constructed land by 46.81%in response to a 54.2 mm secondary rainfall environment.,The absolute value of the maximum soil moisture content is reduced by1.53%;at the same time,the increase in the soil conductivity of the newly created land is relatively reduced by 3.61%,and the maximum soil conductivity is reduced by 15.41?s/cm;the gravel blind ditch drainage project can effectively reduce the soil caused by rainfall for a long time.The increasing trend of water content and electrical conductivity,thereby reducing the possibility of secondary disasters in the trench,and improving the capacity of the new trench construction.