The typical plot in the project area is surrounded by the final fixed field project, which is the basic unit of field operation, crop rotation, project construction and management. Its scale and layout directly affect farmland production management, yield increase, layout of field roads and irrigation and drainage projects, and also affect land use and transportation efficiency. The length of the field is directly related to the field operation efficiency of agricultural machinery, and the width directly determines the spacing of the last fixed drainage ditch, thus affecting whether the drainage ditch can effectively eliminate floods and reduce the groundwater level in time. On the basis of soliciting opinions and suggestions from local experts in land, agriculture, water conservancy and other departments and the masses in the project area, it is finally determined that the design site is mainly arranged in the north-south direction, and the typical site layout is as follows:

The site layout of the project area is mainly dry land, so the site layout is mainly sloping land. Dry land consolidation is based on terraces, and the width of the field is determined by topography and soil quality. The greater the slope of the ground, the narrower the width of the field, the higher the ridge height and the smaller the slope outside the ridge. Generally, the width of terraced fields is 5 ~10m, and the local height difference should be between10 ~15cm, and there is a slope of 1/300 ~ 1/500 in the long direction of the field to facilitate drainage. The lateral slope of the ridge is 55 ~ 80; The slope in the ridge can be 50 ~ 60; The width of the ridge is generally 0.3 ~ 0.4m See table 10-8 for the profile parameters of terraced fields.

Table 10-8 Parameter Table of Horizontal Terrace Profile

In the process of land leveling, the damaged land slope is changed into a step with four grades, and the cultivated land with a slope of 5 ~ 10 is leveled into a slope of 8. The planned field width is 4.2m, the ridge height is 0.7m, and the ridge width is 0.4m: 10 ~ 15 cultivated land leveling 13. The planned land width is 3.5m, the ridge height 1m, the ridge width is 0.4m: 15 ~ 20 cultivated land leveling 18, the planned ground width is 2.22m, and the ridge height 1.2m, the ridge. ..

In land leveling, dry land consolidation is carried out in three gradient grades, mainly 13, 18, and 23, all of which use soil ridges. The clear width, ridge height and ridge width of the field surface are consistent with the slope corresponding to the damaged land slope.

(2) Land leveling zoning

Land leveling is an important content of land consolidation and reclamation projects. The accuracy of land leveling not only affects the quality of reclaimed land, but also relates to the size and benefit of investment. The central task of land leveling is to level the field and make the land more suitable for crop planting. In the design of land leveling project, on the basis of meeting the requirements of irrigation and drainage, the earthwork should be rationally allocated, and the balance of excavation and filling should be achieved as far as possible, and at the same time, it should be combined with soil and water conservation and soil improvement. Land leveling should be based on natural topography and landforms as far as possible, and the elevation should be designed reasonably. According to the principle of basic balance of excavation and fill in the project area, the excavation and fill in the site should also be basically balanced, so as to minimize the excavation and fill and meet the requirements of mechanical operation, irrigation and crop planting.

The purpose of land leveling is to meet the requirements of farmland cultivation by leveling land, cutting high and filling low; By leveling field land and improving irrigation conditions, the fundamental purpose of improving land use quality and building high and stable yield farmland is achieved.

There are two kinds of land leveling: complete leveling and local leveling. According to the field investigation, the local slope of the project area drops and the terrain changes greatly, which is not suitable for large-scale leveling, so the design adopts local leveling.

According to the topographical features of the project area, land use direction, farmland cultivation, irrigation and drainage, soil erosion prevention and control, etc., the land leveling engineering design of this project mainly includes the following contents.

1. Turn the damaged land into a ladder.

In the project area, it is planned to change the slope of the damaged land to 824.94 mu, and the ground slope less than 25 is suitable for reclamation. The design of changing the damaged slope into a ladder is the same as that of changing the ladder into a dry land. The construction procedure is the same as that of changing the dry land slope into a ladder, except that rubble and sand are removed first. The focus of this disaster-stricken land reclamation is to change the slope of the disaster-stricken land into a ladder.

The construction from slope to ladder is divided into five procedures:

(1) Remove the stones covered by mudslides and landslides on the surface of cultivated land, and pile up the usable stones in an orderly manner.

(2) Topsoil stripping. Before changing the slope into a ladder, peel off the cultivated layer of the original sloping farmland to a thickness of 0.30 meters, and backfill the topsoil after leveling to facilitate farming; Topsoil stripping mainly adopts the method of stacking soil in horizontal middle zone combined with vertical frame stacking soil to reduce the engineering quantity.

(3) Land leveling. The principle of leveling is to balance excavation and filling; The leveling method is to remove the slope soil, dig high and fill low, so as to meet the requirements of terrace leveling.

(4) ridging and topsoil backfilling. Ridge setting: The ridges below the gradient ladder 10 are all ridges; 10 ~ 15 adopts 40% stone ridge and 60% earth ridge; 5 ~ 20, except for some small areas with 80% stone ridges and 20% soil ridges, the rest are all stone ridges; 20 ~ 25 are all stone ridges. The ridge top is 40 cm wide, 20 cm higher than the field surface, and the outer slope is 1: 0.4. Ridges are formed according to the width of fields with different slopes. Ridges are vertically arranged every 100 meters along the ridge, with back ditches at the foot of the downstream slope, and drainage facilities, hardening and dripping facilities at the upstream and downstream ridges.

(5) plow the fields. The main function is to loosen the plough layer, which is beneficial to rainwater storage, promote nutrient transformation and crop root extension, improve the quality of soil preparation and sowing, and inhibit the growth and reproduction of diseases, insects and weeds.

2. Reclamation of homestead

There are 1 1. 19 mu of abandoned homestead in the project area with reclamation potential, and the effective cultivated land area can be increased through reclamation. To reclaim the abandoned homestead, first remove the bricks and rubble tiles, push down the earth wall with a bulldozer and flatten it, and then plow off the 60 cm thick soil layer.

3. Dry land consolidation

Through the consolidation of 329.92 mu of dry land in the project area, the slope less than 25 can effectively increase the cultivated land area. All dry land consolidation uses soil ridges, and the construction is divided into four processes: topsoil stripping, land leveling, ridging, topsoil backfilling and ploughing. Its specific method is similar to the reclamation of the affected land.

4. Blasting

After the disaster, there were many deposits in the collapsed houses, and those that were difficult to remove were removed with blasting stones.

(3) Earthwork calculation

The calculation section of earthwork volume for changing slope to ladder is shown in figure 10-3.

Figure 10-3 Schematic Diagram of Earthwork Calculation Section of Horizontal Terrace

The relationship between elements is:

Bm=(H+b)ctgθ ( 10-7)

bn =(H+b)ctgβ+α+bctgα( 10-8)

b = Bm-Bn =(H+b)(ctgθ-ctgβ)-α-bctgα( 10-9)

Where: θ-original ground slope, ();

β —— the slope of the outside of the ridge, where the ridge is 1: 0.4 and the ridge is1:0.6;

α —— the slope of the inside of the terrace ridge, ();

H—— height of roof, m;

B—— the net width of the site, m;

Bn-ridge area m;

Bm—— The surface of the site is wide, m;

α —— The width of the top of the ridge is 40cm, and it is also used as a sidewalk.

The excavation and filling are basically balanced, and the excavation volume per mu v is calculated as follows:

Reclaim land destroyed by disasters

Where: v-earthwork volume, cubic meters;

L-field length, m, ridge length per mu l = 666.67/BM.

According to the Rules for Investigation of Land Use Status, four typical slopes are selected in the project area, and the excavation and fill quantities of 6 ~ 10,1~15, 13 and 16 are calculated respectively. The land leveling in the project area is based on the field, and the leveling amount is calculated by the cross-section method. The main process is as follows: First, select typical fields; According to the topographic map, the site to be calculated takes several parallel cross sections along the land leveling area, and the division principle is vertical contour line or vertical main building side length, and the cross section spacing is 50 meters; Calculate the average leveling elevation of the site, and determine the leveled ground elevation line according to the average leveling elevation and the natural slope of the site; After the contour lines of natural ground and design ground of each cross-sectional drawing are drawn in proportion by computer-aided design software (AutoCAD), the area of excavated (filled) section is calculated by using the function of area calculation of software. According to the distance between two adjacent sections, the earthwork quantity between two adjacent sections is calculated; Finally, the excavation and filling of the whole site are summarized respectively.

According to the requirements of Construction Standard of Land Development and Consolidation Project in Sichuan Province and the characteristics of land leveling and zoning in the project area, representative typical plots are selected in each district, and the area of typical plots is not less than 2 times of the newly-added cultivated land area.