Application of Geotextile in Road Engineering
The development history of modern geotextiles (geotextiles) is inseparable from the development of polymers and synthetic fibers. It has only been used in geotechnical engineering since the late 1950s, and gradually developed in the United States, Europe, and Japan from the late 1950s to the 1960s. promotion. Since the 1970s, geotextiles have been widely used in various fields such as highways, railways, water conservancy and port construction. , An ideal engineering material for extending the maintenance period. The research and application of geotextiles in my country started relatively late, and it has been applied in railway and water conservancy departments since the 1980s, and has achieved gratifying results, which has clearly demonstrated the superiority of this material. The use of geotextiles in engineering design has deepened the personnel of geotextiles. With the improvement of our understanding of the properties of this material and its application in practical engineering, and continuous summarization and communication, geotextiles will surely be widely used and valued.
1 Characteristics of geotextiles
1.1 Characteristics of geotextiles
Geotextile is a kind of chemical fiber product, and its raw materials are polypropylene (polypropylene), polyester (polyester), polyamine (polyester) and so on. From the perspective of product types, it can be divided into two categories: woven (woven) fabrics and non-woven fabrics. The so-called woven fabrics are obtained from polymers, and then spun into threads, which are woven into regular fabrics on a loom. The so-called non-woven fabric is directly made of synthetic fibers by needle punching, thermal bonding and chemical bonding without going through the textile process. Because the raw material of geotextile is polypropylene and other chemical fiber products, it has the advantages of strong chemical resistance, high melting point and high strength. Significant directionality, so non-woven fabrics are the most widely used geotextiles in the world.
1.2 Function and application of geotextile
The function of geotextile as a building material is multi-faceted. The following basic functions and applications have been recognized by experts, designers and manufacturers.
(1) Separation effect: The geotextile can effectively prevent the mixing of two kinds of soil materials with different particle sizes, so as to avoid mutual mixing or soil particle loss. This function is very useful for building road or railway foundations on soft soil layers. important. The economy shows that in some cases it is practically impossible to build on such foundations without geotextiles, as the fill material would sink directly into the subsoil. Therefore, the application of geotextiles is an economical and effective solution.
Filtration effect: The use of geotextiles as a filter layer is the same as that of a graded gravel layer. Geotextiles can allow water to flow freely without pressure, but can prevent the loss of soil fines, so as to avoid inconvenience in some projects. Stabilization and erosion, such as in hydraulic structures, river and lake bank embankments are affected by wave impact or wave water level changes, which will reduce stability due to soil erosion. It can prevent soil erosion and prevent river banks from collapsing.
(3) Drainage: make the geotextile itself form a drainage channel, collect the moisture in the soil into the fabric, slowly drain the soil along the fabric, build roads in soft soil areas with high water content, and use special machinery to drain the soil. 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 the geotextile to exclude the subgrade.
(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 load, the soft soil foundation is 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 whole system forms a continuous structure, improves the stability of the structure, and improves the bearing capacity of the soil foundation.
2 Construction precautions
2.1 Surface preparation
First, clean the road surface so that there is no debris on it, preferably with water. Repair the cracks larger than 0.6cm on the road surface. The repair materials can be selected from asphalt concrete, asphalt sand and cement concrete according to the situation.
2.2 Spray sticky oil
The sticky layer oil is sprayed on the road surface by the hot asphalt distributor. The amount of oil depends on the oil absorption rate of the road surface, and the general dosage is between 0.9-1.2kg/㎡. The oil number is generally better to use bitumen above 60.
If the method of sticky layer oil is adopted twice, the first dosage is between 0.5-0.7kg/㎡, then the asphalt geotextile is laid, and the sticky layer oil is sprinkled on the asphalt geotextile, and the dosage is between 0.4-0.5kg/㎡ between.
2.3 Paving surface
When laying geotextiles, it is necessary to ensure that the coils are at a certain height from the ground. When the geotextiles are stretched and straightened, they will be bonded with the sticky layer of oil, brushed flat with a brush and rolled with steel rollers.
When laying geotextile, try to make it as straight as possible to give a certain tension. When the bonded fabric has wrinkles larger than 1.27cm, it should be cut with a knife and overlapped along the laying direction. When laying fabric at road turns, it should be cut on the inside of the fabric turn and lapped along the laying direction. The overlapping length between the fabric and the fabric is required to be 4-7.5cm.
2.4 Stone paving chips
After the fabric is fully combined with the viscous oil, sprinkle gravel on it. The gravel can generally be used melon seed chips or medium-coarse sand. The amount of gravel depends on the oily condition of the fabric surface, generally about 2m³/K㎡ .
2.5 When laying geotextiles in a large area, at the horizontal lap joints of the fabrics, it can be considered to be fixed with a fixer according to the specific situation.
The fixer includes fixing nails and fixing iron sheets. Fixing nails can be used cement nails, shooting nails, nails are about 8cm long, and iron strips with a thickness of 1mm and a width of 3cm are used to fix the iron sheet. The nails can be fixed with a hand hammer or a nail gun, and a high-speed nail gun can be used in the case of a relatively closed room at the grassroots level.
At the same time, the geotextile should be kept dry. If it is exposed to rain, it should be completely dried before laying. When laying geotextiles, construction workers should not smoke. When the asphalt used to bond the geotextile cools down, do the top layer. Do not drive on the geotextile when the geotextile is saturated and the hot asphalt has not cooled down, and do not turn around and brake on the laid geotextile.