(1) Key technologies of land reclamation in non-stagnant land

(1) For the land with slight subsidence, uneven surface, small fluctuation and large area, the land shall be leveled by means of leveling, cutting high and filling low. Terraces can be built according to local conditions for those with large ground slopes.

(2) For the land with deep subsidence and no accumulated water on the surface, the topsoil should be peeled off first, then the depression should be filled with filler, and finally the topsoil should be covered to restore to the same elevation as the surrounding surface.

(3) In the case of reclamation into cultivated land, garden land, woodland and grassland, which requires high soil fertility, green manure, organic manure, microbial technology and chemical fertilizer can be used to improve the physical and chemical properties of soil and increase soil fertility after reclamation.

(4) When reclaimed as forest land, suitable tree species should be selected to build soil and water conservation forest according to the collapse degree and ground slope. For the subsided land with strong three-dimensional reclamation project, measures such as paving turf or planting economic grass and shrubs can be taken to protect the slope on the ridge or slope. Farmland shelterbelts should be arranged when reclaimed as cultivated land.

(5) The road system should be rationally laid out, and the original water source in the reclaimed area should be fully utilized and a perfect irrigation and drainage system should be laid.

(6) In hilly areas, projects such as ponds, weirs, horizontal ditches, fish scale pits and grain farms should be built to improve the capacity of intercepting and storing surface runoff.

(7) In the plain area, the ground slope of reclaimed farmland should not exceed 15, and the field height difference should be controlled within 5 cm; When reclaimed as garden, woodland and grassland, the slope should not exceed 25. When the hilly area is reclaimed as cultivated land, the slope should not exceed 25, and the field height difference should be controlled within 1 cm; When reclaimed as garden, woodland and grassland, the slope should not exceed 35.

(8) The field scale should be adapted to local conditions, and the length and width of the flat area should be 2-5m and 1-2m respectively. For terraced fields, the length of terraced fields should be 1-2m and the width should be 2-5m. The terraced rate in hilly areas should be no less than 9%.

(II) Key technologies of land reclamation in seasonal waterlogging subsidence areas

(1) Seasonal waterlogging areas with large ground fluctuation should be transformed into horizontal terraces or paddy fields by cutting high and filling low according to the terrain fluctuation or inclination after subsidence. For seasonal water accumulation areas with small ground fluctuation, it can be reclaimed directly after appropriate leveling according to local conditions.

(2) Fill the collapsed low-lying areas and cracks with silt, construction waste and landslide deposits, and then cover the foreign soil with a certain thickness to restore the surface to a usable state.

(3) plant varieties with nitrogen fixation, rapid growth, drought tolerance and strong pollution resistance are preferred for vegetation restoration, and farmland shelterbelt construction should be carried out when cultivated land is reclaimed. Reclaimed for forest land, trees and shrubs can be mixed, and deep-rooted and shallow-rooted tree species can be mixed for afforestation. Grass can be planted for soil and water conservation in unstable seasonal stagnant water subsidence areas.

(4) The road system should be rationally laid out, and the mining area or the original water source should be fully utilized when reclaimed as cultivated land, and a perfect irrigation and drainage system should be laid out.

(5) Ponds, dams and weirs can be built according to local conditions in combination with the collapsed terrain, so as to improve the capacity of intercepting surface runoff and develop irrigation water sources.

(6) When reclaimed as cultivated land, the ground slope should not exceed 15, and the field height difference should be controlled within 5 cm; When reclaimed as garden, woodland and grassland, the slope should not exceed 25.

(7) The field scale and terraced rate have been described before, so they are not introduced here.

(3) Key technologies of land reclamation in waterlogged subsidence areas

(1) For perennial waterlogged areas with severe subsidence, the reclamation method is to dig deep and cushion shallow, and reclaim them into aquaculture water surfaces or artificial lakes. The method is to combine land reclamation with pond digging, dig the deep subsidence area with digging machinery (such as bulldozers and hydraulic pond digging units) to form a water (fish) pond, and take out earthwork to fill the shallow subsidence area and reclaim it into cultivated land, so as to achieve the goal of aquaculture and agricultural planting simultaneously. The key of "deep excavation and shallow cushion" reclamation technology is to strip and backfill topsoil and optimize the sequence of new excavation and filling: ① Increase the process of stripping and backfilling topsoil in the area to be reclaimed (i.e. shallow cushion area): Step 1, before reclamation, strip topsoil from the reclamation area with bulldozer, the thickness of which is generally 2 ~ 3cm, and pile it in order, and special attention should be paid to soil and water conservation and fertilizer conservation measures to prevent topsoil loss and impoverishment; Step 2: After leveling, backfill the topsoil to the reclaimed land to form a high-quality mature soil layer, which is conducive to restoring crop yield as soon as possible. ② Optimization of excavation sequence and filling position: the current excavation process and filling position lead to the mixing of upper and lower soil layers in the excavation depth area or the lower soil layer covering the upper soil layer. The "deep excavation area" is not easy to peel off the topsoil like the "shallow cushion area" because of accumulated water or high water content. Therefore, it is appropriate to adopt a method similar to the open-pit mining and reclamation process of inverted pile method, so as to keep the soil layer order of reclaimed soil basically unchanged. Figure 6-5 shows the method of soil reconstruction, which includes the following specific steps: a. Divide the "deep excavation area" and "shallow cushion area" into several sections (according to topography and earthwork volume), and set up small soil (field) ridges at the boundaries of the sections divided in the "shallow cushion area" to facilitate filling. B. Divide the soil layer in the "deep excavation area" into upper soil (generally 3-5cm) and lower soil (generally more than 3cm or 5cm), and excavate and fill it in the following order: firstly, cover the upper soil of one section in the deep excavation area on the "first filling block section", then fill the lower soil of one section on the 1' section in the shallow cushion area, and then cover the upper soil of two sections on the 1. So that the structure of 1' block is "2 blocks of topsoil+1 block of subsoil", and so on, a new soil structure can be constructed, which can be expressed as follows:

i' block soil structure = "I+1 block of topsoil+I block of subsoil"

where I = 1,2, ...

(3) Combining with the collapsed terrain, we should build ponds and weirs according to local conditions to improve the capacity of intercepting surface runoff and develop irrigation water sources.

(4) Rational layout of road system and construction of flood control and drainage system.

(5) When shallow reclamation is used for fishing land, the area and depth of pond (pond) should be moderate, generally, the area should be .3 ~ .7 hectares and the depth should be 2.5 ~ 3. meters. The requirements of fishery water quality meet the Standards for Fishery Water Quality (GB 1167-89).

(6) When constructing soil and water conservation forest, the slope of reclaimed forest land and grassland should not exceed 25.

figure 6-5 schematic diagram of excavation sequence and filling position of reclamation process (according to Hu Zhenqi, 1997)