How to use geotextile in road construction project? This is frequently asked questions on the construction method of geotextile road fabric. You know, geotextile fabrics are the permeable geosynthetic materials used in civil engineering projects to improve soil characteristics. Among them, road construction is the important application field of geotextile fabric. Geotextile can make poor soils more suitable and reliable to improve road construction efficient and effective due to its special abilities to separate, filter, protect, drain and reinforce soils. This article tries to describe the hot topic – how to use geotextile in road construction project?
1. What Are Main Characteristics of Geotextile
1.1 Characteristics of geotextile
Geotextile fabric is applied to soil, and its raw materials include polypropylene, polyester, polywashing amine, etc. From the perspective of product types, it can be divided into two categories such as woven (spun) fabrics and non-woven fabrics. The so-called woven fabrics are fibers obtained from polymers, then spun into threads, and woven into regular fabrics on a loom. The so-called non-woven fabric is directly made of synthetic fibers by needle-punch bonding, thermal bonding and chemical bonding without going through the weaving process. Since the raw material of geotextile is chemical fiber products such as polypropylene, it has the advantages of strong chemical resistance, high melting point, and high strength. Compared with woven fabrics, non-woven fabrics have lower cost, simple process, high yield and no tensile strength. Significant directionality, so non-woven fabrics are currently widely used geotextiles in the world.
1.2 What Are The Main Functions and Applications of Geotextile Fabric
The functions of geotextiles as building materials are multifaceted. The following basic functions and applications have been recognized by experts, designers and manufacturers.
1.2.1 Separation
Geotextile fabric can effectively prevent the mixing of two kinds of soil materials with different particle sizes, so as to avoid mutual mixing or soil loss. This function is very useful for building road or railway foundations on soft soil. The economy shows that if there is no geotextile in some cases, it is actually impossible to build on such a foundation, because the filling material will directly sink into the subsoil. Therefore, the application of geotextile is an economical and effective solution.
1.2.2 Filtration
The use of geotextile as a filter layer is the same as the graded gravel layer. The geotextile can allow water to flow freely without almost any pressure, but it can also prevent the loss of soil fine particles, so as not to cause problems in certain projects. The geotextile fabric has the advantages of strong chemical resistance, high melting point, high strength, stability and anti erosion. For example, in hydraulic structures, rivers and lake banks are affected by wave impact or wave water level changes, which will reduce the stability due to soil erosion. A geotextile filter layer is laid between the river embankment and the retaining structure. It can prevent the erosion of the soil and prevent the river bank from collapsing.
1.2.3 Drainage function
The geotextile itself can form a drainage channel, collect the water in the soil in the fabric, slowly drain the soil along the fabric, and build roads in soft soil areas with high water content. Special machinery can be used to build roads in soft soil areas. The geotextile is inserted into the soil, and the groundwater flows out of the ground along the geotextile column and enters the permeable sand layer or geotextile to remove the roadbed.
1.2.4 Reinforcement
The geotextile is sandwiched in the aggregate-geotextile-soil foundation system, which can disperse the vehicle load to a larger area and reduce the pressure of the load on the soil foundation. Under the action of the load, the soft soil foundation will be deformed. Because the geotextile has a certain degree of toughness and elongation, the geotextile is deformed and embedded in the soil foundation, so that the entire system forms a continuous structure, improves the stability of the structure, and improves the bearing capacity of the soil foundation.
2 Precautions for Geotextile Construction
2.1 Surface preparation
First, clean the pavement so that there is no debris on it, preferably with water. Repair cracks larger than 0.6cm on the pavement. Asphalt concrete, asphalt sand, and cement concrete can be selected as the repair material according to the unused situation.
2.2 Spraying sticky layer oil
Spray the sticky layer oil on the pavement with a hot asphalt distributor. The amount of oil depends on the oil absorption rate of the pavement, and the general amount is between 0.9-1.2kg/㎡. It is generally better to use asphalt of 60 or more for the oil number.
If the method of sticking layer oil is adopted twice, the first time the amount is between 0.5-0.7kg/㎡, then the asphalt geotextile is laid, and the sticky layer oil is sprayed on the asphalt geotextile, and the amount is between 0.4-0.5kg/㎡.
2.3 Paving Surface
When laying the geotextile, make sure that the coiled material is at a certain height from the ground. When the geotextile is stretched and straightened, it is bonded with the sticky layer oil, smoothed with a brush and rolled with a steel roller.
When laying the geotextile in road construction, it should be as straight as possible to give a certain pulling force. When the bonded fabric has wrinkles larger than 1.27cm, it must be cut with a knife and overlapped in the laying direction. When laying the fabric at the turn of the road, it should be cut on the inner side of the fabric turn and overlapped along the laying direction. The overlap length between the cloth width and the cloth width is required to be 4-7.5cm.
2.4 Paving Stone Chips
After the fabric is fully combined with the sticky layer oil, sprinkle rubble on it. The rubble can generally be melon seeds or medium-coarse sand. The amount of rubble depends on the oil panning on the surface of the fabric, generally about 2m³/k㎡.
2.5 Laying geotextile for Large Area
The fixer includes a fixed nail and a fixed iron sheet. The fixing nails can be cement nails or shot nails, the nail length is about 8cm, and the iron sheet is fixed with iron strips with a thickness of 1mm and a width of 3cm. A hand hammer or a nail gun can be used to fix the nails, and a high-speed nail gun can be used in the case of relatively close rooms at the grassroots level.
At the same time, the geotextile should be kept dry. If it is exposed to rain, it should be dried before laying it. Do not smoke when laying geotextiles. When the asphalt used to bond the geotextile has cooled down, do the top layer. When the geotextile is in a saturated state, do not drive on it when the hot asphalt has not cooled down, and do not turn around and brake on the laid geotextile.
2.6 Geotextile Welding the in Road Construction
When welding and sewing, the top geotextile fabric should be overlapped over the lower geotextile by 2 to 2.5 inches. And the user’s manual or operating instructions on the web are helpful material for you.
The geotextile fabric surface should be flat, and proper allowance for deformation should be left. The installation of filament or short fiber geotextile usually uses several methods such as lap, stitch and welding. The width of stitching and welding is generally more than 0.1m, and the width of overlap is generally more than 0.2m. Geotextiles that may be exposed for a long time should be welded or stitched together. All stitching must be performed continuously (for example, spot stitching is not allowed). Before overlapping, the geotextile in road construction must overlap by 150mm less. The distance between the smaller needle and the selvedge (the exposed edge of the material) is at least 25mm. The seams of the sewn geotextile include one-line and chain stitch method. The thread used for stitching should be a resin material with a small tension exceeding 60N, and has the chemical resistance and ultraviolet resistance equal to or exceeding that of the geotextile. Any “drop stitches” on the sewn geotextile must be re-sewn in the affected area. Corresponding measures must be taken to prevent soil, particulate matter or foreign matter from entering the geotextile layer after installation. The cloth overlap can be divided into natural overlap, seam or welding according to the terrain and usage function. During construction, the geotextile on the geomembrane is naturally lapped, and the geotextile on the geomembrane is sewn or welded by hot air. Hot air welding is the first method of connecting filament geotextiles, that is, using a hot air blower to heat the connection of two pieces of cloth at a high temperature to make part of it reach a molten state, and immediately use a certain external force to make it firmly bonded together. When hot bonding is not possible in wet weather (rainy and snowy days), the geotextile should adopt another method—stitching connection method, which is to use a welding machine for double-line stitching and use chemical UV-resistant sutures.
2.7 Testing for Seam Strength
Refer to ASTM Standard Test Method for Strength of Sewn or Thermally Bonded Seams of Geotextiles, D4884-96. Conventional testing for seam strength of stitching or welding geotextiles includes a destructive shear test. Test Specimen needs to be at least 8-inches (200 mm) wide by 8-inches (200 mm) length. The Specimen width mush have 4-inches (100 mm) on either side of seam width.
3 Conclusion
Incorporating geotextile into road construction offers numerous benefits, such as enhanced stability, reduced potential for rutting and cracking, and improved overall performance over time. The specific application may vary based on project requirements and engineering specifications.
To ensure optimal results, it is crucial to adhere to the manufacturer’s guidelines, follow engineering recommendations, and comply with local regulations throughout the installation process. Consulting with experienced professionals in geotechnical engineering or road construction is highly recommended for specific project requirements and best practices.
By integrating geotextile effectively, you create a robust road structure that withstands the challenges of traffic loads, varying weather conditions, and subgrade soil movements. This proactive approach contributes to the longevity and durability of the road, providing a sustainable and cost-effective solution for infrastructure development.
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