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Soil layers affect the vertical movement of moisture and salt, eventually resulting in land cover and land use pattern changes. This study explored the ability of ground penetrating radar (GPR) to detect soil layers in the modern Yellow River Delta of China and assessed its accuracy. It was found that soil moisture and salt had a strong dampening effect on the electromagnetic wave signal which resulted in blurred GPR images of the soil profile below 1 m. The cultivated soil layers of different crop types, such as rice, wheat, corn and cotton, were accurately identified in GPR images. To estimate an individual soil layer thickness, the propagation velocity of the electromagnetic wave was calculated using soil mass moisture content, and the propagation time was confirmed by comparing the GPR image with the amplitude–time plot of the soil profile. The estimated thickness was 1.02 times the thickness determined in the field and the average estimation error was 0.04 m, which was 24.09% of the soil layer thickness determined in the field. The second derivative value of envelope amplitude energy with time (SDEA) was used to describe the amplitude change in the soil layers. The SDEA has negative logarithmic and power function relationships with soil mass moisture content and electrical conductivity, respectively. The present results provide a reference database for future quantitative soil investigation in the sedimentary plain area using GPR. [ABSTRACT FROM AUTHOR]

Soil compaction resulted from mechanical rolling is one of the major problems in land reclamation. There are a lot of factors that influence soil compaction apart from soil properties, and also mechanical pressure, soil layer, and times of compaction etc. Based on the statistical theory, this article focused on a 2×5×4 mixed experimental design and established a simulation experimental area that employed a heavy punch to simulate the two compact machineries for respectively once, three times, five times, seven times, and nine times. Each fall depth for every compact punch on the soil would be measured. Afterwards, the soil compaction gauge was used to measure the soil compaction changes in different layers. At last, variance analysis in SPSS was conducted and a comparison of random pairs, with the intention of finding influential factors of soil density in the mechanical compaction process and the varied range and preconditions of each factor. The results derived were as follows: (1) A size increase of the compact machinery roller wheels can effectively reduce mechanical compaction on the soil. Since the ground contact area was relatively small when the wheel dumper ran, soil compaction was increasingly seriously affected in the land reclamation process. In the process of machinery compaction, soil fall depth reflects the soil compaction degree, to some extent, and can serve common farmland cultivation as one of the indicators for a preliminary judgment on soil compaction. (2) Compact machinery, soil layer, and times of compaction are all notable factors influencing soil compaction, all of whose contribution rate is highly above random error. The interactive effect, especially between the compact machinery and times of compaction, had a remarkable and profound effect on soil compaction. (3) Different compact machineries of varied weights and ground contact areas would lead to different compaction effects. The dump truck crushed down into 30cm on the upper layer and realized the maximum compaction after five times of compaction, while the crawler dozer needed seven times for the same outcome. (4) In the process of machinery compaction, the soil compaction in different layers did not remain the same. When the soil was less compacted, the upper layer would experience a skyrocketing soil compaction, and the compaction degree declines in a deeper layer. When times of compaction are increased, the soil compaction difference between each layer narrows. The mid-layer (>20-30cm) features a comparatively high compaction under upward and downward stress. (5) The times of machinery compaction had a remarkable effect on soil compaction. Five times of dump truck compaction and seven times of crawler dozer compaction generally achieve the same compaction degree in comparative soil. In addition, the physical property of soil was severely destroyed, which resulted in soil clay or hardening. Therefore, the type of construction machinery and times of compaction must be controlled in land reclamation. (6) Different compaction times had different depth influences and degrees on soil compaction. Initial compaction is most obvious on soil compaction. Single compaction effect on soil compaction will be gradually reduced when the times of compaction are increased in a certain range. A continuous increase of compaction times enforces lower layer compaction though, yet crawls slowly upward. Repeated single compaction of small pressure on soil indeed cannot be ignored. (7) Models were establish built on correlations between soil compaction and press, times of compaction, and soil layer to judge rough soil compaction under different conditions. In addition, improvement measures for land reclamation are defined as the next research focus. [ABSTRACT FROM AUTHOR]