Evaluation Of Reclaimed Soil Compaction And Project Quality Based On Ground Penetrating Radar

Coal is the primary energy in China even all over the world. The problems such as ground subsidence and surface crack due to the coal mining, lead to the reduction of cultivated area and ecological environment deterioration. Land and coal are two important, indispensable resources of human survival, and how to harmonize the contradiction between agricultural production and coal mining is an important subject to be resolved. Land reclamation is currently one of the main ways to increase the cultivated area and to relieve contradiction of population and land resources. To have scientific, effective assessment and monitoring of the land reclamation project has crucial significance of innovating reclamation technology, improving of land use pattern of reclamation and productivity of reclamation land.During the process of agricultural use of reclaimed soil, soil compaction has become the main factor influencing the quality of reclaimed land. In the quality inspection of reclamation land, the soil thickness is part of the important test projects in farming, animal husbandry, and forestry. Moreover, the anti-seepage performance of irrigation channels and the stability and bearing capacity of the field road are also the important contents of quality test for the reclamation project.At present, traditional methods are typically used for the measurement of reclamation land quality and project quality. While the accuracy is higher, it is time-consuming and laborious, cannot fully reflect the overall situation of the reclamation district. In addition, the methods are certainly destructive to the channel and the road, thus large area detection is not suitable. It is essential to explore fast, reliable and simple test methods. Taking this as the breakthrough point, on the basis of summarizing the predecessors’ research, the paper innovated the project designs, research methods and research contents, taked ground penetrating radar(GPR) as detection means, tested nondestructively the quality of reclamated soil and project on land reclamation area, moreover studied deeply the key technologies during the process of testing, including the theories and methods involved.The main work and achievements are as follows:(1)The variation of soil density under different reclamation process and their influential factors was proved. Based on the statistical theory, the author established simulation experimental area by 2×5×4mixed experimental design and compacted different times(1, 3, 5, 7, 9) to soil simulating the common compact machineries. Through the variance analysises and multiple comparisons to soil compaction dataes of different layers in each combination, the paper intended to find the variation of soil density and their influential factors. Experimental results indicate that compaction machinery, compacting times and soil thickness are all the significant factors affecting soil compactness in the process of land reclamation(each contribution rate is more than 97%). Different compaction machinery, quality and grounding area will produce different compaction effect. The upper layer realizes the maximum compaction after 5 times of compaction by dump truck while the crawler dozer needs 7 times for the same outcome. The greater the depth, the smaller the soil compactness; and with the increase of compaction times, the soil thickness differences between soil compactness are decreasing, while intermediate levels(10~30cm) of soil has high density relatively. Too much compaction will harden the soil before it’s broken and has severe compact. Research results above provide the basis for reclamation techniques innovation. For the purpose of reducing soil compaction, on the one hand, choosing the machinery of smaller mass, bearing wheel with a larger area is helpful to soil compaction; on another hand, so multiple rolling compaction with the smaller single pressure for soil compaction is not permitted to ignore, so repeated rolling to same soil must be prohibited as possible and the number should be controlled within 5 ~ 7 times.(2)Relational model between compaction index and soil dielectric constant was built. Taking soil bulk density as soil compaction index, it was confirmed by correlation analysis that the soil dielectric constant and soil compaction indexes have good correlation and the absolute value of the correlation coefficients are greater than 0.89, which can characterize soil compaction situation. To obtain soil dielectric constant value calculation on the basis of existing complex dielectric constant model, to obtain soil dielectric constants on the basis of ground penetrating radar, there are different levels of error(21.85% ~ 138.80%) but the correlation between the two is better(the correlation coefficients are greater than 0.99). The composite dielectric constant model was modified through the correlation equation. The results showed that the accuracy of soil bulk density obtained by modified model was high(error range is between 0.79% ~ 0.98%), but also it had been proved by field experiment that the revised model has good generality.(3)The spatiotemporal variability of soil compaction among different land use types and reclamation period was revealed. Reclamation experimental areas of three land use types were selected that had been completed in different period. The paper monitored the soil quality of each reclamation experimental area and obtained the value of soil bulk density for the fourth successive year by using ground penetrating radar. Through the statistical analysis of soil bulk density values, the spatiotemporal variability of soil compaction status and its influencing factors were revealed which belonged to different land use types and reclamation period. Research showed that along with the increase of reclamation years, soil bulk density presents a downward trend on the whole and each has different descenging law. After 8 years, the soil bulk density of cultivated land reclamation reaches the lowest(1.30g/cm3). Respectively after 12 years and 15 years, the soil bulk density of grassland(1.46g/cm3) and forest(1.39g/cm3) achieves the original basic geomorphic soil condition after the reclamation. At the same time the soil bulk density of cultivated land is minimum, then grassland, and forest has the highest soil bulk density. Under the influence of human activities and plant roots, the variation of soil bulk density in different soil layers of three land use types is different. In general, reclamation years and land use type are factors that cause significant differences of soil bulk density, in which the land use type is the main source of variation of soil bulk density(contribution rate lies between 72.4%~97.7%). The proportion of variation caused by reclamation years decreased gradually with the extension of time. Soil bulk density of different land use types is changing in different time scales. The influence degree of the land use types on bulk density is also changing with the change of reclamation years. It has positive significance on soil compaction improved to take different use patterns at reclamation medium-term(contribution rate lies between 82.3% ~ 95%).The above research results, on the one hand, provide the basis for the effective utilization of reclaimed soil, as well as making measures for soil improvement, on the other hand, achieve the long-term dynamic monitoring of the quality of reclaimed soil.(4)The key technologies of ground penetrating radar that detect the reclamation engineering quality were demonstrated. The thickness of covering soil, pavement and channel lining were selected as the testing indicators of reclamation engineering quality, the paper obtained the profile images of medium by ground penetrating radar, and achieved the nondestructive testing of the above indexes. In addition, some key technologies such as ground position location, calibration of electromagnetic wave propagation velocity and reflector picking were emphatically analyzed. Comparing with traditional detection data, the accuracy and its reasons of the detection based on ground penetrating radar is analyzed. Results showed that the thickness of covering soil in project area is slightly insufficient(mean thickness is 48cm) but the variation degree is low(variable coefficient is 9.375%); Pavement thickness fluctuates obviously(variable coefficient is 27.94%) and the design standards in some areas are lower; the thickness of canal lining meets the design standards(mean thickness is 15.57cm) and the variation is small(variable coefficient is 12.86%)。The position of the first peak in waveform is closest to the ground, and the Hilbert transform can solve the difficult identification problem well caused by various factors. Meanwile the work model of ground penetrating radar is extremely important to the accuracy of the test results. Because of the complexity of soil structure, there are many influencing factors in the use of ground penetrating radar. It should be paied attention to that weakens the attenuation effect of underground media on the electromagnetic wave in data processing.To sum up, on the one hand, on the premise of obtaining soil dielectric constant by means of ground penetrating radar, the nondestructive testing of soil compaction is implemented on the basis of the modification of dielectric constant model, on the other hand, on the premise of obtaining profile images of medium by means of ground penetrating radar, the nondestructive testing of reclamation engineering quality is implemented through the processing to some key technologies such as ground position location, calibration of electromagnetic wave propagation velocity and reflector picking. Besides, the spatiotemporal variability of soil compaction is analysed as well as its influencing factors. Research results enrich the application technology of ground penetrating radar in the field of soil reclamation, provide the theoretical basis and technological means for nondestructive testing of reclamation quality, and possess reference meaning in the innovation of reclamation process, effective use of reclaimed soil and improving.measures of reclaimed soil.