What Is Soil Nailing?

Charge soil is also known as change soil. Engineering measures such as excavating the soft soil at the base of the embankment and replacing the cohesive or sandy pebbles with higher strength. It can fundamentally improve the nature of the foundation, leaving no further problems. It is suitable for soft soil layer on the ground, thin soil layer and easy drainage construction. It can be excavated by manual, mechanical or blasting methods. Soil replacement depth is generally within 3m.

Charge soil is also known as change soil. Engineering measures such as excavating the soft soil at the base of the embankment and replacing the cohesive or sandy pebbles with higher strength. It can fundamentally improve the nature of the foundation, leaving no further problems. It is suitable for soft soil layer on the ground, thin soil layer and easy drainage construction. It can be excavated by manual, mechanical or blasting methods. Soil replacement depth is generally within 3m ^[1]

"Four degrees" should be well controlled during soil replacement, that is, the thickness of the paving, flatness, compaction, and height of the soil foundation (elevation) must meet the requirements of the specification during soil replacement. Specifically do the following.

1. Handle the original ground well before changing soil

(1) For the base of the station floor, the original turf, plant soil and other debris must be completely removed, and its depth can be determined according to specific conditions. If the soil thickness of other parts exceeds 60cm, the turf will not be removed, but the grass will be cut.

(2) Ditch ponds, pits, and wells should be handled well so as not to accumulate water and affect large-area soil replacement operations.

2. Measure the pay-off ^[1]

1. Preliminary leveling. Each layer of soil replacement (excavation when necessary) is evenly leveled by mechanical or human work, and then compacted, so that the moisture in the soil has not evaporated, which is conducive to compaction, especially during construction in rainy areas. Hazard of soil compaction and rework caused by excessive soil change.

2. Finally flatten. The last fill level of the fill surface or excavation site. After the preliminary leveling and compaction of the earthwork, there will still be local small undulations, and a leveling and trimming will be performed for the last time until it meets the quality requirements of flatness, compaction and elevation. The final leveling is a very meticulous work. It is necessary to master the virtual height. Generally, piles are added to cross the line every 5m or leveling is used for trimming, and the combination of new and old soil layers must be paid attention. Wet, or loosen the topsoil about 5cm, then change the soil, and finally use 6t ~ 8t two-wheel road roller to flatten and compact to prevent shelling and ensure good filling and bonding.

Finally, after leveling and passing the measurement and inspection, they should be protected to control the passage of machinery and vehicles; personnel are prohibited from passing on rainy days.

1. Optimal water content

At the construction site, the moisture content of the soil before rolling must be well grasped, and it should generally be controlled within the range of ± 2% of the optimal moisture content. The commonly used soil method for determining the water content is: take a handful of soil by hand, and if it can be kneaded into a mass, the soil will spread out after free fall. Such a water content is generally suitable. The soil cannot be lumped into groups, which means that the soil is too dry. After the soil is lumped into groups, the soil will not fall apart or become cakes, indicating that the water content is too large. Soils that are too dry or too wet cannot meet the compaction requirements.

2. The thickness of the soil layer should be appropriate

The layer thickness of soil replacement is related to the number of compaction passes, the compaction requirements, the type of soil, the size of the water content, and the performance of the compaction machinery. The earth change at the station floor is usually 25cm ~ 30cm, the soil texture is 30cm, and the artificial compaction is 20cm.

3.Rolling method

(1) From low to high, from side to middle, overlap appropriately. When rolling on a single-sided slope, the roller should gradually roll from low to high. Double-sided slope sections should be rolled from the two sides to the middle. This rolling method can prevent the soil from moving and sliding outward during the rolling process, and is conducive to drainage. In order to prevent pressure leakage, the main wheel of the roller should overlap properly when rolling back and forth, and the overlap is generally 10cm ~ 15cm.

(2) Light first and then heavy, with appropriate speed. When rolling, it can be pre-compressed with a 6t ~ 8t roller to improve the compaction of the upper part of the compaction layer, and then rolled with a 10t ~ 15t roller. If it is rolled with a heavy roller at the beginning, it will easily cause unevenness , Affecting the rolling effect. In order to ensure the uniformity of rolling, the rolling speed should not be too fast, and the general driving speed should be controlled within 2km / h.

(3) The number of rolling passes. It should be determined on the premise that the compactness requirements are met, according to the nature of the soil, water content, loose paving thickness, compaction coefficient, and compaction machinery. During construction, the approximate number of control passes and the wheel track of the roller should be determined based on past experience and field tests. The roller hand can ask the site laboratory staff to check the compaction in time according to the number of passes, and decide whether to continue rolling.

(4) The length of the rolling operation section should not be greater than 100m. At the stubble of the two working sections, the overlapping range of the main wheels should not be less than 5m. The earthwork for that day should be finished that day and must not be overnight. In the rainy season, pay attention to the weather changes at any time, the rolling should be timely, and the length of the operation section can be shortened appropriately.

During the rolling process, if any unevenness is found, it should be leveled in time. After compacting to the specified number of passes, a compaction test is performed. After passing the approval, the earthwork can be filled. All corners that are difficult to be crushed by machinery should be compacted by manual tamping. The compaction test shall be recorded, indicating the sampling location, pile number, soil replacement layer, soil type, test results, etc., so as to check and sort out the completed data.

(5) The main factors affecting the compaction effect are generally water content, soil type, and compaction function. At the construction site, because there is already standard compaction, the type of soil replacement and the standard filler are basically the same, so the factor affecting the compaction effect is mainly the water content. According to on-site construction experience, it is best to measure the actual moisture content of the filler before compaction. Experience has shown that the actual moisture content of the soil is best when it is crushed by plus or minus 2% -5% of the optimal moisture content. If the water content of the filler is too large, the number of rolling passes cannot reach the standard. Therefore, based on the measured water content, if the water content is too large, you should consider rolling and drying the soil until it is close to the optimal water content, and then rolling, otherwise there will be rolling failures due to excessive water content. Soft bullet phenomenon. The simple way to measure the water content on site is to use the alcohol combustion method, which is easy to do and suitable for construction site operations. If there is no time to dry because of the construction period, you can consider the method of mixing lime to reduce the moisture content of the soil, or you can solve the problem by appropriately reducing the thickness of the filling. However, both of these methods increase costs, and the consent of the supervision engineer should be sought to obtain appropriate compensation.