Analysis On Land Subsidence Evolution Based On Time-varying Parameters And Non-engineering Subsidence Control

In recent years,land subsidence disaster and its secondary disasters have brought immeasurable losses to social and economic construction.Land subsidence is caused by the continuous movement and recombination of soil particles.Due to the complexity of stratum structure and the variability of land subsidence occurrence process,the physical parameters change dynamically with the compression deformation of soil.At the same time,there has always been a contradiction between groundwater exploitation and geological disasters.How to realize the utilizability and regulation of groundwater resources under the premise of ensuring the land subsidence rate within the control allowable range is a very key problem.Based on the above problems,this paper analyzes the variation rules of various physical parameters in the consolidation and compression process of soil,and constructs a numerical model of land subsidence based on the time-varying parameters.Taking Mudan District,Heze City,Shandong Province as the engineering background,the development trend prediction of land subsidence in this area and the suitability of non-engineering subsidence control measures are studied.The main work and conclusions of this paper are as follows:1.The trend characteristics of various parameters of soil layer during the development of land subsidence are analyzed in detail,a numerical model of land subsidence considering the dynamic changes of parameters is built.The development trend of land subsidence and the dynamic evolution of physical parameters before and after considering the dynamic changes of parameters were analyzed by establishing a multi-strata model with single pumping well.It can be found that the maximum subsidence with the dynamic change of parameters considered is bigger than that without consideration.After stoping exploiting,the latter will immediately rebound,while the former will have a temporary subsidence lag.The calculation gap caused by neglecting the dynamic change of parameters is smaller in the early subsidence period and larger in the middle and late subsidence period.2.Through collects and analyses the hydrogeologic and engineering geology,drilling data and predecessors’ studying results,the scope of the study area is determined,the strata structure is divided.Combining with the groundwater exploitation in the study area,the groundwater flow field dynamic information and the ground subsidence monitoring data information,the present situation and characteristics of land subsidence disasters in this area are systematically summarized and analyzed.It can be found that the land subsidence in Mudan District is increasing year by year,which tends to form a large regional land subsidence funnel.3.Based on the comprehensive application of multidisciplinary knowledge and considering the characteristics of dynamic changes of strata parameters,the three-dimensional combined numerical model of groundwater seepage and land subsidence is established and verified based on reasonable strata constitutive relationship.The evolution trend of land subsidence under different groundwater exploitation conditions,such as maintaining the present groundwater exploitation,planning to stop groundwater exploitation in batches and reducing groundwater exploitation,is predicted and analyzed.The maximum land subsidence in 2029 would be about 3.4 times that of 2019 if groundwater exploitation remained constant.With the gradual closure of wells,the cumulative land subsidence decreases to 182.14 mm in 2027,and the subsidence funnel area in the whole study area also decreases,and shows a rebound trend.When the reduction of exploitation is more than 10%,the decreasing range of subsidence affected area increases obviously.4.Through simulation prediction spatiotemporal dynamic evolution process of land subsidence in the future,the influence of various non-engineering subsidence control measures on land subsidence is quantified,the effect of subsidence control measures are evaluated from two aspects of cumulative subsidence and subsidence trap area,and the appropriate non-engineering subsidence control measures are demonstrated.The results show that the land subsidence does not slow down linearly with the decrease of groundwater exploitation.With the decrease of exploitation,the cumulative land subsidence at the subsidence funnel decreases significantly,but with the continuous decrease of exploitation,the decreasing trend of cumulative land subsidence slows down gradually.Considering the actual groundwater demand of Mudan District,the land subsidence decreases most significantly when the groundwater reduction amount is between 10%and 30%,which is also suitable for mitigating the land subsidence disaster.