Salt prevention and isolation process for airport runway engineering in salinized soil area

Abstract

The invention relates to the technical field of salinized soil roadbed construction, in particular to a salinized soil area airport runway engineering salt prevention and isolation process, which comprises the following steps of: cleaning the surface of a constructed runway surface influence area, determining the depth for removing salinized soil according to engineering geological conditions, removing the salinized soil, leveling a site, and carrying out salt prevention and salt isolation on the surface of the constructed runway surface influence area. The method comprises the following steps: performing dynamic compaction construction or dynamic compaction replacement construction according to the geological condition of a site, performing layered rolling and backfilling of natural sand gravels after compaction of a road base, backfilling to 45cm below the top surface of the road base so as to discharge construction water in time, symmetrically arranging drainage blind ditches and seepage wells along the center line of the road base, paving a composite geomembrane at a position 45cm below the top surface of the road base, and not paving the composite geomembrane at the blind ditches. A medium-coarse sand protective layer with the thickness of 5cm is arranged, and cement stabilized coarse-grained soil with the thickness of 40cm is arranged at the top of the road base. According to the technology, long-term effective salt prevention and salt isolation in the salinized soil area can be achieved, differential settlement of the foundation can be effectively reduced, and the overall stability of the pavement is improved.

Description

Technical Field

[0001] The invention relates to the technical field of saline soil roadbed construction, and in particular to a salt prevention and isolation process for airport runway engineering in saline soil areas. Background Art

[0002] Saline soil has the characteristics of salt swelling, dissolution and corrosion. As the salt in the soil changes with water and temperature, it constantly undergoes the process of crystallization-dissolution-transfer-moisture absorption. Its natural physical properties are extremely unstable, which can cause engineering diseases such as bulging, cracking, and a significant reduction in the strength of the foundation (roadbed, roadbed) of airports, roads, and buildings and structures. Various highway, railway, and civil aviation projects continue to penetrate into saline soil areas, making salt swelling, salt dissolution, and durability issues particularly prominent in engineering construction in saline soil areas.

[0003] There are many methods for treating saline soil, mainly including setting up isolation layers, replacement, raising the roadbed, water pre-dissolution, chemical treatment and overload loading. The roadbed raising method itself is limited by the terrain and the project cost is relatively high; water pre-dissolution is suitable for roadbed soil with a thick layer and a large permeability coefficient, such as gravel soil and silty saline soil. This method is more restricted and has certain adverse effects on the roadbed; the chemical treatment method is generally more expensive and may have a negative impact on the environment. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a salt prevention and isolation process for airport road engineering in saline soil areas, which reduces the influence of water and temperature on the roadbed, avoids uneven settlement of the roadbed and improves the overall stability of the roadbed.

[0005] The present invention provides a salt prevention and isolation process for airport runway engineering in saline soil areas, comprising the following steps:

[0006] S100, pavement clearing: clear the pavement affected area to remove surface garbage, organic residues and topsoil, and determine the thickness of the clearing according to engineering geological conditions;

[0007] S200, removing saline soil. After the surface clearing is completed, the depth of removing saline soil is determined according to engineering geological conditions and the saline soil is removed;

[0008] S300, leveling and rolling: after removing the saline soil, the site is leveled and rolled;

[0009] S400, roadbed compaction. When the roadbed soil type is gravel soil, sandy soil, low-saturation silty soil and clay-salt soil foundation, the strong compaction method is used for construction. When the roadbed soil type is highly saturated silty soil, the strong compaction replacement method is used for construction;

[0010] S500, backfill in layers. After the roadbed is compacted, it is leveled and rolled, and backfilled with natural sand and gravel to 45 cm below the top surface of the roadbed. The thickness and compaction of the backfill in layers are controlled according to the soil conditions.

[0011] S600, set up blind ditches and seepage wells, and set up blind ditches and seepage wells symmetrically along the center line of the roadbed;

[0012] S700, laying composite geomembrane, laying composite geomembrane 45cm below the top surface of the roadbed, not laying in the blind ditch, laying 5cm thick medium-coarse sand on the top of the composite geomembrane;

[0013] S800, laying cement-stabilized coarse-grained soil, lay 40cm thick cement-stabilized coarse-grained soil on the top of the roadbed.

[0014] Optionally, in step S400, the compaction depth of the roadbed is 3 to 7 m.

[0015] Optionally, the step S400 adopts the following method: three times of strong tamping are performed, and a tamping machine with a tamping energy of 150 t﹒ m is used for the first time of skip tamping, 15 consecutive tampings are performed at each tamping position, and the average tamping amount of the last two tampings is ≤3 cm, otherwise additional tamping is performed;

[0016] During the second round of construction, 12 consecutive strikes are made at each tamping position, and the average tamping amount of the last two strikes is ≤3cm, otherwise additional strikes are required;

[0017] The third strong compaction shall be carried out by using a compacting machine with a compaction energy of 100 t﹒ m. The third strong compaction shall be overlapped and tamped marks shall be overlapped by 1 / 3. Each mark shall be compacted three times continuously. The interval between each strong compaction construction shall be ≥14 days.

[0018] Optionally, the dynamic tamping replacement method in step S400 includes the following steps: cleaning and leveling the roadbed, and laying a sand and gravel construction cushion layer with a thickness of 1.0 to 2.0 m when the topsoil is soft;

[0019] Mark the location of the tamping points and measure the elevation of the roadbed;

[0020] The crane is in place and the tamping hammer is placed at the tamping point;

[0021] Measure the height of the hammer top before tamping;

[0022] Start tamping and record the depth of the tamping pit with each tamping. When the tamping pit is too deep and it is difficult to start the hammer, stop tamping and fill the pit until it is flush with the top of the pit. Record the amount of filler. Repeat this process until the specified tamping times and control standards are met. The tamping of a point pier is completed. When the soft soil around the tamping point is squeezed out and affects the construction, it can be cleaned at any time and gravel can be laid around the tamping point to continue construction.

[0023] Complete the construction of all tamping points in the order from inside to outside and skip every other row;

[0024] Level the construction roadbed, compact the loose soil on the surface of the roadbed with low-energy full tamping, and measure the elevation of the roadbed after tamping.

[0025] Optionally, the natural sand and gravel in step S500 has a salt content of ≤0.3%, is well graded, has a maximum particle size ≤2 / 3 of the thickness of the layered backfill, has a compaction degree of ≥98% within 45cm to 100cm below the top surface of the roadbed, has a compaction degree of ≥95% within 100cm to 400cm below the top surface of the roadbed, and has a compaction degree of ≥93% below 400cm below the top surface of the roadbed.

[0026] Optionally, the blind ditch in step S600 is 2m wide and 1m deep, 1m into the roadbed treatment boundary and extends 5m into the soil surface area, and the plane size of the infiltration well is 2m×2m and 3m deep;

[0027] The blind ditch and the seepage well are filled with gravel with a particle size of 3cm to 10cm, and the outside of the gravel in the blind ditch and the seepage well is wrapped with geotextiles. The specifications of the geotextiles are ≥300g / ㎡, the longitudinal and transverse breaking strengths are ≥15KN / m, the longitudinal and transverse standard strengths correspond to elongations of 40% to 80%, the CBR bursting strength is ≥2.9KN, the longitudinal and transverse tearing strengths are ≥0.42KN, and the equivalent pore size is 0.05mm to 0.2mm.

[0028] Optionally, the composite geomembrane in step S700 includes a geotextile and an impermeable membrane, the geotextile is made of polypropylene filament geotextile, the impermeable membrane is made of polyethylene geomembrane, and the overlap width is ≥20 cm.

[0029] Optionally, step S700 adopts the following method: before laying the composite geomembrane, a roller is used to statically press the surface of the roadbed to eliminate protrusions and sharp edges, the composite geomembrane is laid on the entire section, and it is laid flat and close to the underlying bearing layer. According to the longitudinal and transverse slopes of the roadbed, the lower joint is at the bottom and the higher joint is at the top. After the composite geomembrane is laid, 5 cm thick medium-coarse sand is spread on top of it.

[0030] Optionally, when loading the cement-stabilized coarse-grained soil in step S800, the material transport vehicle reverses to unload the material, the boundary of the cement-stabilized coarse-grained soil extends to 3m outside the edge of the road surface, the cement content of the cement-stabilized coarse-grained soil is 3%, the coarse-grained soil uses natural graded round gravel, the soluble salt content is less than 0.3%, the maximum particle size is ≤53cm, and the cement uses 42.5MPa ordinary Portland cement or slag Portland cement with an initial setting time of more than 3h and a final setting time of more than 6h.

[0031] Compared with the prior art, the technical solution provided by the embodiment of the present invention has the following beneficial effects:

[0032] The embodiment of the present invention provides a salt prevention and salt isolation process for airport road engineering in saline soil areas. After clearing the surface and removing the saline soil, the saline soil roadbed is directly subjected to strong tamping construction or strong tamping replacement construction, thereby effectively reducing the porosity of the soil body, improving the density of the soil body and the reinforcement effect. The compacted roadbed is backfilled in layers and the backfilled gravel is rolled, thereby effectively improving the bearing capacity and stability of the roadbed, reducing foundation settlement and deformation, and improving the safety and reliability of the project. By symmetrically arranging two groups of blind ditches and infiltration wells along the center line of the roadbed, the external water brought by precipitation in the road trough can be discharged in time, the water content of the roadbed and its groundwater level can be reduced, water accumulation can be prevented, the infiltration of external water can be reduced, and the problem of groundwater carrying salt upward caused by capillary action can be reduced. By 45 An anti-seepage composite geomembrane is laid at 1 cm, and 5 cm thick medium-coarse sand is laid on it to eliminate the frost heave problem of the soil foundation caused by the infiltration of precipitation and snow water. At the same time, it can prevent the infiltration of upper water and directly prevent the capillary water from rising, thereby reducing the adverse effects of the capillary water rise on the foundation. The geotextile can protect the anti-seepage membrane and at the same time play a certain role as a drainage layer, which can discharge the infiltrated water or pore water above and below the anti-seepage membrane, and can increase the friction coefficient with the contact surface of soil, gravel, etc. By spreading cement on the medium-coarse sand to stabilize the coarse-grained soil, the strength, stability and durability of the roadbed are further enhanced. This process can achieve long-term and effective salt prevention and isolation in saline soil areas, effectively reduce the adverse effects of water and temperature on the roadbed, avoid uneven settlement of the foundation, and improve the stability of the road surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0035] Figure 1 This is a construction drawing for preventing and isolating salt from an airport runway project in a saline soil area as described in an embodiment of the present invention.

[0036] Among them, 1. original ground; 2. cleared ground; 3. ground after rolling; 4. composite geomembrane; 5. medium-coarse sand; 6. cement-stabilized coarse-grained soil; 7. water-stabilizing layer; 8. concrete pavement surface layer; 9. blind ditch; 10. infiltration well; 11. center line of roadbed; 12. edge line of pavement; 13. edge line of roadbed treatment. DETAILED DESCRIPTION

[0037] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0038] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all of the embodiments.

[0039] Reference Figure 1 As shown, this embodiment provides a salt prevention and isolation process for airport runway engineering in saline soil areas, including the following steps:

[0040] S100, pavement clearing, clear the pavement affected area of ​​the construction, that is, Figure 1 The original ground 1 in the middle is cleaned, and the surface garbage, organic residues and topsoil are removed until the silt is exposed. According to the engineering geological conditions, the surface cleaning thickness is determined to be 0.7m. After the surface is cleaned, the road surface is Figure 1 Clear surface ground 2;

[0041] S200, remove saline soil. After the surface is cleared, the depth of removing saline soil is determined according to the engineering geological conditions and the saline soil is removed. That is, after the surface is cleared, the silt is continued to be excavated until the gravel is exposed. The depth of removing saline soil is 1.05m. The saline soil is removed to facilitate replacement with soil and stone that meet the design requirements. The replacement depth should be ≥45cm;

[0042] S300, leveling and rolling. After removing the saline soil, use a loader and grader to level and roll the site. If there are pits, holes, graves, etc., they should be properly handled;

[0043] S400, roadbed compaction. When the roadbed soil type is gravel soil, sandy soil, low-saturation silty soil and clayey saline soil foundation, the strong compaction method is used for construction. When the roadbed soil type is highly saturated silty soil, the strong compaction replacement method is used for construction. Strong compaction construction and strong compaction replacement construction can directly treat saline soil roadbeds with a treatment depth of 3 to 7 meters, which can effectively reduce the porosity of the soil, effectively improve the density of the soil, and have a good reinforcement effect;

[0044] Specifically, the dynamic tamping method in step S400 specifically includes the following steps: construct three times of dynamic tamping, use a tamping machine with a tamping energy of 150t﹒m to construct the first time of skip tamping, 15 consecutive tampings for each tamping position, and the average tamping settlement of the last two strikes is ≤3cm, otherwise, additional strikes are made; construct the second time of skip tamping, 12 consecutive strikes for each tamping position, and the average tamping settlement of the last two strikes is ≤3cm, otherwise, additional strikes are made; use a tamping machine with a tamping energy of 100t﹒m to construct the third time of dynamic tamping, the third time of dynamic tamping is overlapping tamping, the tamping marks are overlapped by 1 / 3, 3 consecutive tampings are made for each mark, the interval time between each time of dynamic tamping is ≥14 days, and when the third time of tamping is completed, the surface is rolled with a 22t vibratory roller, and the compaction degree is ≥90%. Then carry out layered backfilling with a thickness of 30cm, an optimum moisture content of 5.1%, a salt content of natural sand and gravel ≤0.3%, good grading, a maximum particle size ≤2 / 3 of the thickness of the layered backfilling, a compaction degree of ≥98% within 45cm to 100cm below the top surface of the roadbed, a compaction degree of ≥95% within 100cm to 400cm below the top surface of the roadbed, and a compaction degree of ≥93% below 400cm below the top surface of the roadbed.

[0045] The dynamic tamping replacement construction specifically includes the following steps: cleaning and leveling the roadbed, laying a 1.0-2.0m thick gravel construction cushion layer when the topsoil is soft; marking the tamping point position and measuring the roadbed elevation; putting the crane in place and placing the tamping hammer at the tamping point position; measuring the elevation of the hammer top before tamping; starting tamping and recording the depth of the tamping pit with each hit, stopping tamping when the tamping pit is too deep and it is difficult to start the hammer, filling the pit until it is flush with the pit top, recording the amount of filling, repeating this process until the specified number of tamping times and control standards are met, completing the tamping of a pier body at a point, and when the soft soil around the tamping point is squeezed out and affects the construction, it can be cleaned at any time and gravel can be laid around the tamping point to continue construction; completing the construction of all tamping points in order from the inside to the outside, following the principle of skipping every other row; leveling the construction roadbed, compacting the loose soil on the surface of the roadbed with low-energy full tamping, and measuring the elevation of the roadbed after tamping.

[0046] S500, backfill in layers, after the roadbed is compacted, level and roll the roadbed. Figure 1 After rolling the ground 3, backfill with natural gravel to 45cm below the top surface of the roadbed, and control the thickness and compaction of the layered backfill according to the soil conditions. Layered backfill can effectively improve the bearing capacity and stability of the foundation, reduce foundation settlement and deformation, and improve the safety and reliability of the project;

[0047] S600, blind ditches 9 and seepage wells 10 are set symmetrically along the center line 11 of the roadbed. By setting the blind ditches 9 and the seepage wells 10, it is possible to ensure that the external water brought by precipitation in the road channel is discharged in time, reduce the water content of the roadbed and its groundwater level, prevent water accumulation, reduce the infiltration of external water, and reduce the problem of salt accumulation in groundwater caused by capillary action;

[0048] Specifically, a blind ditch 9 and an infiltration well 10 are respectively arranged at intervals of 250m on both sides of the roadbed centerline 11. The blind ditch 9 is 2m wide and 1m deep, enters the roadbed treatment edgeline 13 by 1m and extends 5m to the soil surface area. The plane size of the infiltration well 10 is 2m×2m and the depth is 3m. The blind ditch 9 and the infiltration well 10 are filled with gravel with a particle size of 3cm to 10cm, and the outside of the gravel in the blind ditch 9 and the infiltration well 10 is wrapped with geotextiles. The geotextiles are made of polyester long-fiber non-woven fabrics. The specifications of the geotextiles are ≥300g / ㎡, the longitudinal and transverse breaking strengths are ≥15KN / m, the longitudinal and transverse standard strengths correspond to elongations of 40% to 80%, the CBR bursting strength is ≥2.9KN, the longitudinal and transverse tearing strengths are ≥0.42KN, and the equivalent pore size is 0.05mm to 0.2mm.

[0049] S700. Lay the composite geomembrane 4. Lay the composite geomembrane 4 45 cm below the top surface of the roadbed. Do not lay the blind ditch 9. Lay 5 cm thick medium-coarse sand 5 on the top of the composite geomembrane 4. The medium-coarse sand 5 is the protective layer of the composite geomembrane 4. After laying the composite geomembrane 4, the protective layer should be constructed as soon as possible to avoid it from being exposed to the sun for a long time. The medium-coarse sand 5 can effectively ensure the integrity of the composite geomembrane 4 and ensure that its function is not damaged. It can eliminate the frost heave problem of the soil foundation caused by the infiltration of precipitation and snow water, effectively prevent the infiltration of upper water, and can directly prevent the capillary water from rising, thereby reducing the adverse effects of the capillary water rising on the foundation. At the same time, when the medium-coarse sand 5 is spread, if the composite geomembrane 4 is found to be damaged, the damaged part should be repaired in time. The geosynthetics that can prevent water leakage are used for reinforcement. The composite geomembrane 4 includes a geotextile and an impermeable membrane. The composite geomembrane 4 in this embodiment can be two cloths and one membrane or three cloths and two membranes. The geotextile adopts polypropylene filament geotextile, and the impermeable membrane adopts polyethylene geomembrane. The overlap width is ≥20cm. Before laying, the surface of the roadbed should be statically pressed by a roller to eliminate protrusions and sharp edges. The composite geomembrane 4 is laid on the whole section and laid flat and close to the underlying layer. According to the longitudinal and transverse slopes of the roadbed, a joint at a low position is at the bottom and a joint at a high position is at the top. The geotextile can protect the impermeable membrane and play a certain role as a drainage layer. It can discharge the infiltrated water or pore water above and below the impermeable membrane and increase the friction coefficient with the contact surface of soil, gravel, etc.

[0050] S800. Lay cement-stabilized coarse-grained soil 6. Lay 40cm thick cement-stabilized coarse-grained soil 6 on the top of the roadbed in two layers. When laying cement-stabilized coarse-grained soil 6, the material transport vehicle should reverse to unload the material. The cement content of cement-stabilized coarse-grained soil 6 is 3%. The coarse-grained soil uses natural graded round gravel with a soluble salt content of less than 0.3% and a maximum particle size of ≤53cm. The layered paving and compaction thickness is 20cm. A 22t vibratory roller is used for rolling. The optimal moisture content is 5.6% and the compaction degree is ≥98%. The boundary of cement-stabilized coarse-grained soil 6 extends to 3m outside the edge line 12 of the road surface. The cement uses 42.5MPa ordinary Portland cement or slag Portland cement with an initial setting time of more than 3h and a final setting time of more than 6h. Quick-hardening cement and early-strength cement should not be used. When the setting time does not meet the requirements during construction, a retarder can be added. The installation of cement-stabilized coarse-grained soil 6 can further enhance the strength, stability and durability of the roadbed.

[0051] After laying cement stabilized coarse-grained soil 6, water-stabilizing layer 7 is constructed. First, the flatness and elevation of the roadbed surface after laying cement stabilized coarse-grained soil 6 are tested to ensure that the flatness and density of the roadbed surface meet the requirements. After all the requirements are met, the mixture is mixed. The crushed stone, slag, lime and other raw materials are proportioned according to the design requirements, and are fully mixed by a mixer to make various raw materials fully mixed and uniform. Subsequently, construction layout is carried out. Specifically, when the paver is paving, layout is carried out in each construction operation area, and reference line piles are driven. The longitudinal spacing of the reference line piles is 6.5m. When paving the first line, double-line type is arranged, and when paving the rest, single-line type is arranged. The other side is directly controlled by sliding shoes on the adjacent water-stabilizing layer 7 that has been pressed and formed. After the reference line piles are driven, the reference line is laid first. The reference line is a steel strand, and the tensioner is fixed. The elevation and horizontal position of the cutout position of the reference line horizontal drag rod on each reference line pile are measured, and the tensioner at the operating end tightens the reference line. Then hang the reference line in the hanging line cut of each reference line horizontal tow bar, transport the cement stabilized mixture to the site, use the paver to continuously spread the mixture, sprinkle water on the top surface of the lower layer before paving the upper layer, when the moisture content of the mixture reaches the optimum moisture content, it should be immediately rolled with a light two-wheel roller and a roller of more than 18t within the full width of the structure layer. When rolling, the wheel width should be overlapped by 1 / 2, and the rear wheel should exceed the joint of the two sections. When the rear wheel rolls the full width of the road surface, it is considered one pass. Generally, 6 to 8 times of compaction are required until the required density is reached. The compaction speed of the roller should be 1.5 to 1.7 km / h for the first two times, and then gradually increase to 2.0 to 2.5 km / h. In order to ensure that the surface of the water-stabilizing layer 7 is not damaged, it is strictly forbidden for the roller to turn around or brake suddenly in the completed or rolling section. During the rolling process, if there are "spring", looseness, peeling and other phenomena, they should be dug out and supplemented with newly mixed mixture to achieve compaction to meet the quality requirements. When using a paver to spread the mixture, it should not be interrupted. If the interruption time exceeds 2 hours for some reason, a transverse joint should be set. When setting the transverse joint, the paver should drive away from the end of the mixture, and the section should be laid forward for a distance. After the section is rolled, the excess mixture is removed by manual laying. The distance left should be able to ensure that the elevation and flatness of the project entity meet the requirements. Before re-paving the mixture, clean up the surroundings. The longitudinal and transverse joints must be connected vertically. The longitudinal joints should be trimmed after the previous section is rolled. The trimming must be cut flush with the line. The cutting range is 10 to 20 cm depending on the compaction situation. The subbase and base joints must be staggered. After the construction of the water-stable layer 7 is completed, it needs to be maintained. Specifically, when carrying out layered construction, it is advisable to lay the base after the subbase has been maintained for no less than 7 days. The maintenance adopts wet treatment maintenance, the surface is covered with geotextile and kept moist, and heavy vehicles should be restricted from driving on the base during the maintenance period.

[0052] To ensure the construction quality, the concrete pavement surface layer 8, the water-stabilizing layer 7 and the cement-stabilized coarse-grained soil 6 are constructed in a stepped manner from top to bottom, so as to protect the stability of the superstructure, improve the construction quality of the superstructure, and provide the necessary working space for the superstructure construction.

[0053] It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0054] The above description is only a specific embodiment of the present invention, so that those skilled in the art can understand or implement the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments described herein, but should conform to the widest scope consistent with the principles and novel features invented herein.

Claims

1. A process for preventing and isolating salt in airport runway engineering in saline soil areas, characterized in that: The following steps are involved: S100, pavement clearing: clear the pavement affected area to remove surface garbage, organic residues and topsoil, and determine the thickness of the clearing according to engineering geological conditions; S200, removing saline soil. After the surface clearing is completed, the depth of removing saline soil is determined according to engineering geological conditions and the saline soil is removed; S300, leveling and rolling: after removing the saline soil, the site is leveled and rolled; S400, roadbed compaction. When the roadbed soil type is gravel soil, sandy soil, low-saturation silty soil and clay-salt soil foundation, the strong compaction method is used for construction. When the roadbed soil type is highly saturated silty soil, the strong compaction replacement method is used for construction; S500, backfill in layers. After the roadbed is compacted, it is leveled and rolled, and backfilled with natural sand and gravel to 45 cm below the top surface of the roadbed. The thickness and compaction of the backfill in layers are controlled according to the soil conditions. S600, setting a blind ditch (9) and a seepage well (10), and setting the blind ditch (9) and the seepage well (10) symmetrically along the center line (11) of the roadbed; S700, laying the composite geomembrane (4), laying the composite geomembrane (4) 45 cm below the top surface of the roadbed, not laying the composite geomembrane at the blind ditch (9), and laying 5 cm thick medium-coarse sand (5) on the top of the composite geomembrane (4); S800, laying cement-stabilized coarse-grained soil (6), laying 40 cm thick cement-stabilized coarse-grained soil (6) on the top of the roadbed.

2. The process for preventing and isolating salt from airport runway engineering in saline soil areas according to claim 1 is characterized in that: The compaction depth of the roadbed in step S400 is 3 to 7 m.

3. The process for preventing and isolating salt from airport runway engineering in saline soil areas according to claim 1 is characterized in that: The dynamic tamping method in step S400 includes the following steps: performing three dynamic tamping operations, using a tamping machine with a tamping energy of 150 t﹒ m to perform the first jump tamping operation, tamping 15 times in each tamping position, and the average tamping amount of the last two tampings is ≤3 cm, otherwise additional tamping is performed; During the second round of construction, 12 consecutive strikes are made at each tamping position, and the average tamping amount of the last two strikes is ≤3cm, otherwise additional strikes are required; The third strong compaction shall be carried out by using a compacting machine with a compaction energy of 100 t﹒ m. The third strong compaction shall be overlapped and tamped marks shall be overlapped by 1 / 3. Each mark shall be compacted three times continuously. The interval between each strong compaction construction shall be ≥14 days.

4. The process for preventing and isolating salt from airport runway engineering in saline soil areas according to claim 1 is characterized in that: The dynamic tamping replacement method in step S400 includes the following steps: cleaning and leveling the roadbed, and laying a sand and gravel construction cushion layer with a thickness of 1.0 to 2.0 m when the topsoil is soft; Mark the location of the tamping points and measure the elevation of the roadbed; The crane is in place and the tamping hammer is placed at the tamping point; Measure the height of the hammer top before tamping; Start tamping and record the depth of the tamping pit with each tamping. When the tamping pit is too deep and it is difficult to start the hammer, stop tamping and fill the pit until it is flush with the top of the pit. Record the amount of filler. Repeat this process until the specified tamping times and control standards are met. The tamping of a point pier is completed. When the soft soil around the tamping point is squeezed out and affects the construction, it can be cleaned at any time and gravel can be laid around the tamping point to continue construction. Complete the construction of all tamping points in the order from inside to outside and skip every other row; Level the construction roadbed, compact the loose soil on the surface of the roadbed with low-energy full tamping, and measure the elevation of the roadbed after tamping.

5. The process for preventing and isolating salt from airport runway engineering in saline soil areas according to claim 1 is characterized in that: The natural sand and gravel in step S500 has a salt content of ≤0.3%, good gradation, a maximum particle size ≤2 / 3 of the thickness of the layered backfill, a compaction degree of ≥98% within 45cm to 100cm below the top surface of the roadbed, a compaction degree of ≥95% within 100cm to 400cm below the top surface of the roadbed, and a compaction degree of ≥93% below 400cm below the top surface of the roadbed.

6. The process for preventing and isolating salt from airport runway engineering in saline soil areas according to claim 1 is characterized in that: The blind ditch (9) in step S600 is 2m wide and 1m deep, 1m into the range of the roadbed treatment edge line (13) and extends 5m into the soil surface area, and the plane size of the infiltration well (10) is 2m×2m and 3m deep; The blind ditch (9) and the infiltration well (10) are filled with gravel with a particle size of 3 cm to 10 cm, and the outside of the gravel in the blind ditch (9) and the infiltration well (10) is wrapped with geotextiles, the specifications of the geotextiles are ≥300g / ㎡, the longitudinal and transverse breaking strengths are ≥15KN / m, the longitudinal and transverse standard strengths correspond to elongations of 40% to 80%, the CBR bursting strength is ≥2.9KN, the longitudinal and transverse tearing strengths are ≥0.42KN, and the equivalent pore size is 0.05mm to 0.2mm.

7. The process for preventing and isolating salt from airport runway engineering in saline soil areas according to claim 1 is characterized in that: The composite geomembrane (4) in step S700 comprises a geotextile and an impermeable membrane, wherein the geotextile is made of polypropylene filament geotextile and the impermeable membrane is made of polyethylene geomembrane, and the overlap width is ≥20 cm.

8. The process for preventing and isolating salt from airport runway engineering in saline soil areas according to claim 1 is characterized in that: The step S700 adopts the following method: before laying the composite geomembrane (4), a roller is used to statically press the surface of the roadbed to eliminate protrusions and sharp edges and corners, and the composite geomembrane (4) is laid on the entire section and laid flat and close to the underlying layer. According to the longitudinal and transverse slopes of the roadbed, the lower joint is at the bottom and the higher joint is at the top. After the composite geomembrane (4) is laid, 5 cm thick medium-coarse sand (5) is spread on top.

9. The process for preventing and isolating salt from airport runway engineering in saline soil areas according to claim 1, characterized in that: When the cement-stabilized coarse-grained soil (6) in step S800 is loaded, the material transport vehicle reverses to unload the material, the boundary of the cement-stabilized coarse-grained soil (6) extends to 3m outside the road surface edge line (12), the cement content of the cement-stabilized coarse-grained soil (6) is 3%, the coarse-grained soil uses natural graded round gravel, the soluble salt content is less than 0.3%, the maximum particle size is ≤53cm, and the cement uses 42.5MPa ordinary silicate cement or slag silicate cement with an initial setting time of more than 3h and a final setting time of more than 6h.

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