Construction technology of landscape greening in coastal saline-alkali land?

The following is the related content of landscaping construction technology of coastal saline-alkali land brought by Zhong Da Consulting for your reference.

Land salinization has always been the main factor affecting the urban landscaping construction in Weifang Binhai Economic Development Zone. Landscape engineering construction not only has the procedures and technical requirements of general landscape engineering construction, but also has the unique procedures and links of coastal saline-alkali land greening. Combined with many years' greening construction experience in saline-alkali land, this paper briefly introduces the general procedures, techniques and standards of landscape engineering construction in coastal saline-alkali land for discussion.

1, background overview

Weifang Binhai Economic Development Zone is located in the north of Weifang City and the south of Laizhou Bay in Bohai Sea. It belongs to the semi-humid climate in the continental monsoon region of warm temperate zone, with obvious seasonal changes and monsoon climate characteristics. The average annual sunshine hours over the years are 2762.9 hours; The annual cumulative average temperature is 12.5℃, the extreme maximum temperature is 4 1.3℃, the extreme minimum temperature is -20.8℃, and the annual average precipitation is 623.7mm, which is unevenly distributed, mainly in July and August. Dominant wind direction SSE throughout the year; The sunshine rate in winter is 64%; The initial freezing period is generally at the end of 1 1, and the final freezing period is in early April. The maximum depth of frozen soil over the years is 60cm. The elevation of this area is low, with some sections only 2-4m above sea level, shallow groundwater, annual variation of 1-3m, and high salt content. Most of the original land in the development zone is Yantian, with low-lying and gentle terrain, poor site conditions and serious alkali resistance, which brings great difficulties to greening. In order to achieve better greening effect, greening construction needs to take measures such as removing alkaline earth, laying alkali-discharging isolation layer and backfilling planting soil.

2. Preparation before construction

2. 1 The blue prints.the design

In order to carry out the construction smoothly, the construction personnel should carefully review the drawings, grasp the designer's creativity and construction objectives, specific green area, various engineering materials, earthwork filling and excavation, alkali drainage system setting, garden plant configuration, undulating terrain shaping, etc. , and understand other requirements of the construction unit or design unit for construction.

2.2 Field investigation

After understanding the meaning of the drawings and mastering the ideas of the engineering design and construction unit, the construction personnel should conduct on-site investigation, carefully investigate and analyze the topography and landforms of the construction site, as well as the above-ground and underground obstacles, and find out their position, depth, height and direction, so as to formulate the construction plan; Clearly understand the location of water source and power supply required for construction. Site investigation should be carefully and accurately mastered.

2.3 make a construction plan

Whether the construction scheme is detailed, scientific and reasonable is the key to the success or failure of the project construction, and it is also a necessary measure to ensure the timely and quality completion of the project. When making the construction progress plan, we should fully consider the difficulties, problems and solutions that may be encountered in the construction, such as land use coordination, construction difficulty, irresistible rainy days and other factors.

3, construction procedures and standards

3. 1 engineering lofting

Setting-out is the process of marking the position relationship of each element on the drawing to the site in proportion, and it is the key link to realize the design intention and the success or failure of construction. Pay-off requirements shall be carried out in strict accordance with the scale on the drawings and controlled within the allowable error range. The fixed-point lofting of garden plants must be carried out after the planting soil is formed.

3.2 Excavate saline-alkali land and level the site.

The green belts on both sides of some roads in the development zone used to be salt fields, and the salt content of the surface salt mud is basically saturated, so all the salt mud needs to be excavated and transported abroad.

For the construction section with salt mud, garbage and weeds on the surface, the table top should be cleaned first and transported to the designated place. The depth, width and flatness of saline-alkali soil excavation should meet the design requirements, and the excavation of saline-alkali soil must reach the end, edge and place, and the flatness of the bottom plane should reach the design error range.

3.3 Excavation of open drainage channels

The groundwater level in the development zone is on the high side, so it is necessary to excavate the open drainage channel outside the green belt, which is also used as a brine control ditch. Open drain excavation should reach the depth, width and slope designed in the drawings, especially the control of bottom elevation, and ensure the smooth drainage of surrounding salt fields and green belts; At the same time, the earthwork generated by the excavation of the open drainage channel can be used as a user, which is mainly used to build dams on both sides of the open drainage channel and backfill the sections with lower elevation in the green belt.

3.4 laying alkali isolation layer

This is a special technical measure of saline-alkali land greening project in development zone. The purpose is to prevent the original salt at the bottom of the green belt from rising by laying an isolation layer. The materials used in the isolation layer are stones, stone chips, grass curtains, etc. Stones are blocky and granular, and should not be too broken. The particle size is generally 0.5-2.0cm, the impurity content should not be too much, and the mud content should be less than 3%. The thickness of stone isolation layer is 20cm, and the thickness error range is generally 65438±0cm. The stone isolation layer is covered with a straw curtain made of wheat straw and other materials, and the thickness after compaction is 4cm. During construction, earth-moving vehicles cannot directly enter the green belt to avoid the isolation layer.

3.5 Isolation around the Green Belt

Before backfilling the planting soil for greening, isolate the green belt from the surrounding alkaline earth with plastic sheets to prevent the salt in the surrounding alkaline earth from infiltrating into the green belt. During construction, the bottom of the plastic sheet is closely combined with the isolation layer, and the top is about 20cm higher than the surface of the green belt. It is compacted with stones to prevent it from slipping when backfilling the green planting soil. Because the green space is longer and the plastic sheets are shorter in a week, the overlapping size should be large enough, not less than 50cm.

3.6 laying alkali discharge pipe

3.6. 1 function of alkali discharge pipe

This is a special technology of coastal saline-alkali land greening project based on the law of water and salt movement. The laying of alkali drainage pipe is generally combined with isolation layer. When the water in the green planting soil penetrates into the isolation layer, it will slowly penetrate downward (because the original soil layer is hard). If there is too much accumulated water or accumulated water due to long-term rain, the alkali drainage pipe can discharge the excess water in time. The salt in the alkaline earth at the bottom of the green belt can rise along the soil capillaries, and when it reaches the plane of the alkali drainage pipe, the capillaries are destroyed. At the same time, the medium sand around the alkali discharge pipe has strong water permeability, which can collect water into the alkali discharge pipe and discharge it in time, so as to control the groundwater level below the critical depth and achieve the purpose of soil desalination and prevention of secondary salinization.

3.6.2 Types of alkali discharge pipes

The types of alkali drainage pipes are sand-free cement pipes, PVC pipes, plain concrete pipes and PVC double-arm striped drainage pipes. Among them, sand-free cement pipes and PVC double-arm striped drainage pipes are the most widely used. The former has good alkali discharging effect, but it is easy to break down and has high cost. The latter is originally a drainage pipe laid on the golf course, which has good use effect, simple operation and low cost. Now our community uses PVC double-arm striped drainage pipes.

3.6.3 Laying density and gradient of alkali drainage pipe

The laying density and slope of alkali drainage pipes are affected by green space area, surrounding environment (groundwater level), road drainage elevation and planting soil depth. But there are no clear standards for density and slope. In actual operation, the distance between large areas is generally 10m, but the minimum distance is generally not less than 5m, and its slope is generally not less than 0.3%. If conditions permit, the slope can be increased appropriately. However, the slope is limited, generally not exceeding 0.8%. If it exceeds 0.8%, the drainage effect is good, but it brings a lot of inconvenience to the watering of green space. In general, the inspection wells for alkali drainage should be set at the intersection of alkali drainage pipes and other pipeline facilities, and the spacing of inspection wells should be set according to needs, generally about 25m.

3.6.4 Construction of alkali drainage pipe.

One is to check the drawings and set out at a fixed point. Firstly, according to the design drawings, check the design elevation and spacing of relevant pipelines in detail, especially the elevation of the joint between the alkali drainage inspection well and the sewage well or rainwater well. After verification, pay-off will be carried out in strict accordance with the design requirements. Second, the alkali discharge pipe is slotted. After pay-off, a groove is made along the pay-off position, and its depth varies with the distance and slope of the alkali discharge pipe. The general principle is shallow at one end and deep at the other, and the slope of the trough is strictly controlled. Take a control point every 3-5m and measure the elevation at any time. Grooving should be straight and not bent, otherwise it will affect the effect of alkali drainage. The third is to lay the alkali discharge pipe. Before laying the alkali drainage pipe, wrap the alkali drainage pipe with non-woven fabric to prevent the soil from blocking the gap of the alkali drainage pipe and affecting its water permeability. Generally, non-woven fabrics are wrapped in three layers and tied tightly with hemp rope to prevent falling off. When laying pipes, the alkali discharge pipe should be laid straight. The fourth is to backfill medium sand. The purpose of sand filling is to increase its water permeability and enhance the effect of alkali discharge. After the laying of the alkali drainage pipe is qualified, the medium sand shall be backfilled in time, and the soil on both sides shall not be mixed into the sand when backfilling. Fill it with medium sand to the top of the isolation layer, and backfill the green planting soil after acceptance. The sixth is to build an inspection well for discharging alkali to test the effect of discharging alkali. After the backfilling of green planting soil is completed, an alkali drainage inspection well will be built to check the effect of the alkali drainage pipe in time. Generally, the inspection wells for alkali drainage are built with red machine bricks with an inner diameter of 700mm and a wall thickness of 240, and M7.5 cement mortar is used, and its height varies with the elevation of alkali drainage pipes. The bottom is c10-C20-C20 plain concrete with a thickness of 100mm, and the inside and outside are plastered with 12 cement mortar. The manhole cover is made of plain concrete or cast iron. After completion, inject water from the top to see if the water can be discharged from the bottom and test the alkali discharge effect.

In the process of construction, we should also pay attention to the following problems: first, the slope of the trough is inconsistent, the elevation is inconsistent, the width is not enough, and it is not straight; Second, the thickness and width of plain concrete can not meet the design requirements; Third, the non-woven fabric is not tightly wrapped; Fourth, the thickness and width of sand in the overburden can not meet the design requirements, and it is mixed with foreign soil; Fifth, the plastering of manhole is not sufficient, especially the part below the foreign soil is easy to be ignored, which is easy to cause water seepage.

3.7 Backfilling greening planting soil

This is the key link of coastal saline-alkali land greening. Green planting soil samples must be inspected by relevant technicians before use. Backfilling of planting soil is carried out by back pressure on one side. In order to ensure that the alkali drainage pipe and isolation layer are not damaged, the planting soil cannot be directly transferred to the green belt, and it needs to be transported twice or more by excavator or loader. When the excavator enters the filling range, the crawler of the excavator cannot press on the alkali drainage pipeline, and the distance is greater than 1 m; The loader can't work directly on the alkali drainage system, and it can only enter when the upper layer of the alkali drainage system is covered with 1m thickness. At the same time, the plastic sheets for isolation around the green space should not fall off, so as not to mix the planting soil with the surrounding alkaline earth.

In order to prevent salt accumulation at high water level, the backfill elevation of planting soil should be raised to a certain height, and the groundwater level will be relatively reduced after raising the ground. On the one hand, it is difficult for the water and salt in the lower layer to rise to the surface by capillary action, on the other hand, it is conducive to the downward movement of soil moisture, and the soil is not prone to secondary salinization, and the saline-alkali soil in the lower layer will gradually fade [2].

3.8 Application of organic fertilizer

Chen Enfeng, a famous soil scientist in China, believes that the transformation of organic matter is closely related to soil desalination and alkali removal. In addition to water, organic matter is also an important substance for improving saline-alkali land [1]. Organic fertilizer can not only improve the soil structure, provide all kinds of nutrients needed for plant growth, but also produce acidic substances to neutralize saline-alkali in the process of organic fertilizer decay, so that the site conditions of plants can be improved to some extent. After the topographical layout of the green belt meets the design requirements, humic acid organic fertilizer with the dosage of 0.5kg/㎡ is spread in the green belt, and the rotary tiller is used for rotary tillage twice. The content of nitrogen, phosphorus and potassium in humic acid organic fertilizer is more than 10%, the content of organic matter is more than 20%, and the content of humic acid is more than 30%.

3.9 Seedling Planting and Maintenance

The greening of coastal saline-alkali land, if the management can't keep up, the investment is large and the labor consumption is large, it is difficult to achieve the expected effect. Therefore, in addition to the technology of discharging alkali and controlling brine, we should also strengthen a series of planting techniques and maintenance management links such as seedling raising, transportation, planting, pruning and irrigation.

3.9. 1 Pay-off positioning.

First of all, on the whole green space, according to the construction drawing, the positions of various seedlings and modules are released and marked with gray.

3.9.2 Tree hole excavation.

Before planting seedlings, you should dig holes in the trees in advance. The size of the tree hole is determined according to the requirements of technical specifications. If there are buried objects, pipes or hard rocks at the bottom of the tree hole, the size of the tree hole should be determined according to the site conditions. The diameter of tree holes can generally be 30-40 cm larger than the diameter of roots or soil balls.

3.9.3 Buy seedlings.

First of all, the selection of seedlings must meet the design requirements of DBH, with height, crown width, good growth and beautiful appearance. There shall be no residual branches, skin scraping, wind, frost, freezing injury or other damage, and no pests and diseases.

Seedling raising and transportation. We must pay attention to the protection of root system and the particularity of coastal saline-alkali land greening when raising seedlings. When raising seedlings, soil balls of corresponding size should be brought according to the specifications, and the soil balls should be strictly guaranteed to be in good condition. When loading, transporting and unloading trees, it is necessary to ensure that the roots and soil balls of trees are in good condition, to prevent the main tips and branches of trees from breaking, and not to scratch the bark. Seedlings should be planted immediately after unloading, and seedlings that cannot be planted within 24 hours should be buried in the heel to protect the roots. Long-distance transportation should be covered with tarpaulin (spray water if necessary), protect roots, branches and crowns according to weather conditions, and reduce water evaporation.

3.9.4 Seedling planting.

When planting, the virtual soil should be backfilled in the original dug tree hole according to the situation, then the seedlings should be put vertically, and the soil should be cultivated after righting. When backfilling seedlings, they should be compacted, and the planting depth of seedlings should be kept at the original depth, and the deepest covering soil should not exceed the original planting depth of 5 cm; After planting, it will be trimmed by professional technicians, the wound will be wrapped with hemp rope, and the incision will be painted. The wind in the development zone is very strong. In order to ensure the survival rate of seedlings, hard support should be set up in time after planting is completed. Water immediately after planting, the second time the next day, the third time in 3-5 days, and then turn to normal maintenance after one week. Evergreen trees and trees planted out of season should be sprayed with water at least 2-3 times a day to reduce the evaporation of water from trees and improve the survival rate. After the first watering, the skewed trees should be righted and supported in time, and some trees with serious skew should be replanted.

3.9.5 Seedling maintenance.

The most important task of coastal saline-alkali land greening is post-maintenance, which requires higher standards and longer period than ordinary green land. The quality of maintenance management directly affects the greening effect. Therefore, after seedling planting, measures such as timely management of each link, loosening soil, increasing application of organic fertilizer and timely and appropriate irrigation can reduce the salt content to a certain extent. In winter, the wind is strong and the temperature is low, so it is necessary to pour enough frozen water before freezing to ensure the safe overwintering of seedlings. Because the resistance of trees to pests and diseases decreases under salt stress, it is necessary to strengthen the prevention and control of pests and diseases.

4. Conclusion and discussion

4. 1 Practice has proved that although the landscaping of coastal saline-alkali land cities is very difficult, it can be achieved by following the law of water and salt movement and adopting reasonable engineering and technical measures and scientific management means.

4.2 After years of efforts, Weifang Binhai Economic Development Zone has made great achievements in saline-alkali land greening and accumulated a lot of valuable experience. Through greening practice, the construction technology, procedures and standards of greening earthwork in coastal saline-alkali land were explored, and suitable saline-alkali tolerant varieties were selected, which accelerated the greening work of saline-alkali land.

4.3 How to reduce the cost of landscaping under the premise of ensuring good landscaping effect and high speed is a problem being studied at present. With the development of modern science and technology, landscaping and natural conditions form a virtuous circle, ensuring the sustainable development of landscaping in coastal saline-alkali land will greatly promote the in-depth development of this work.

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