Geosynthetics in highway increasingly wide range of applications, in dealing with weak foundations, drainage, embankment slope protection, reinforced retaining walls, extraordinary Bump in the area of governance has been very successful applications. The greatest feature is the completion of geotechnical engineering in a variety of conventional methods difficult to deal with difficult issues, such as Bump, soft ground subsidence, Frothing, landslides and so on. Practice proved Geocell compared with other geo-synthetic material is a novel, and has more advantages, practical, affordable, the application works well for road construction and new materials.
Key words: Geocell Expressway soft foundation treatment Bump Applications

Geocell as a new type of synthetic material, in the late eighties early nineties, Europe and the United States and other countries began a great deal of research and development work, and confirmed by the tests and field applications in improving the general fill to withstand dynamic loads as well as the subgrade protection area, a big effect. China in the early nineties the basis of absorbing foreign advanced experience, began the development of Geocell research and treatment of defects in the road-based bed and fixed a loose application of the medium has made a major breakthrough. As the people geocell characteristics of a better understanding of have been found to have other geotechnical materials, irreplaceable advantages so unique in many fields of application.

The characteristics of a Geogrid

Geogrid is a kind of high-strength polyethylene sheet, through methods such as ultrasonic welding connection, was the commencement of the three-dimensional honeycomb-like grid structure materials, belong to special geosynthetics. Project in the rock and soil, sand and stone as the filler is composed of different cohesion, different reinforced strength, different depths cushion. The cushion can be placed in accordance with the engineering requirements of the position required for strengthening the road subgrade, slope protection, construction of retaining walls. Its biggest feature is to be completed in the conventional methods of rock engineering difficult to deal with a variety of difficult issues, such as Bump, soft ground subsidence, Frothing, landslides and so on. Has a material light, resistant to abrasion resistance, aging resistance, chemical corrosion, suitable temperature range, tensile strength, rigidity, toughness is good, strong impact, size is relatively stable and easy transportation and so on. Connecting is simple in construction, the construction method is simple, thus simplifying the construction process, improve the construction speed; and can be repeatedly used many times.

Two basic principles of Geocell

Geocell been the reason why the effectiveness of engineering with outstanding concerns, but also from its start with the basic principles. Foreign literature, when describing his theory called "a honeycomb-like three-dimensional limit system, you can significantly improve within a wide range of general fill material in bearing and worm-eaten in the performance of control applications." It is a key principle of three-dimensional limit . We all know that, when the vehicle traveling in the desert, they will squeeze two deep tire tracks were pressed part of the deep subsidence, the rut will be high on both sides of uplift. If the vehicles behind and continue along the track to move forward, sink part of it will sink further, some further uplift uplift until the swell part of the rubs up against the car chassis, subsidence of the rut buried more than half of the wheel, and then can not go forward. This is so because when the external load acting on the ground surface, based on theory and the Taylor theory Pulangteer can see: In the role of concentrated load, the active area a pressure sink, and will power to pass on both sides of decomposition transition zone 2, zone 2 has to pass over the passive zone 3, a passive zone deformation will occur without restriction and uplift. In other words, once the load acting on the embankment, in the load from the bottom of the deed will be shaped to form the active region, it squeezed through the transition region, so that the passive region has uplift. In other words, by the shear force along the slip-line and mobile initiatives, transition, passive three regions to decide the foundation bearing capacity. Not only in the ground can be very obvious Chaki experience the true principles of the above process, the soft base on the road will be to find such a model, but its formation rate than the change in the sand on the slower Bale. Even better roadbed materials are also still unable to avoid its lateral movement. Highway embankment are generally several meters above the ground, water-absorbent Frothing do not readily, but the long-term settlement still exists. The reason for rainwater infiltration, material loss, the base is one of the sinking part of the reason the road embankment in the long-term rolling wheel load and vibration under the action of forces, materials, on both sides of the embankment cross-section transverse displacement can not be denied is another very important reasons. To all levels of roads throughout the province as an example, there is the main road in the driveway can clearly feel the road has been pressed out of an "S"-type groove-shaped belt. Part of the highway is no exception, cars driving in the driveway clear of the bumps in the road in overtaking bring a strong sense of connection segment is particularly evident in the bridge. This settlement is a groove-like roadbed roadbed materials, the typical horizontal slip.

Embankment project conventional treatment method does not need to repeat, the purpose is to increase the shear strength of foundation materials, and friction, reduce or delay the loading of the foundation material under pressure or vibration occurs ability to move and thus works against the material requirements necessary There are many harsh restrictions, if not close to obtaining the required materials, you need to acquire these materials, purchase of materials and transportation costs accounted for much of the cost of the entire project. The use of Geocell can be drawn locally or nearby, or even used in normal circumstances can not use the materials, thereby drastically reducing the acquisition cost of materials and transportation costs. Why is it so? Geocell load of hands: In the concentrated load, the force is still an active area will suffer force transmission to the transition zone 2, but because of cell wall of the lateral limits of the reaction chamber and adjacent cells, as well as the filler and the cell wall formed by lateral friction resistance, inhibit the transition zone 2 and zone 3, lateral movement passive tendencies, so that the subgrade bearing capacity can be improved. After testing, limited room in Georgia under the action of the dense sand, the apparent cohesion can be increased 30 times. Obviously, if the subgrade material can increase the shear force or suppress the three regional mobile can obtain the effect of raising the foundation bearing capacity, which is limited geocell principles.

Most of the interior filled with gravel or crushed stone cells and other non-sticky material, therefore, Geogrid reinforcement layer is a level of drainage channel, to accelerate the consolidation process in the saturated soil pore pressure dissipation rate, thus accelerating soil consolidation . In short, Geocell has a cushion, reinforcement, drainage, regulation of stress and deformation, improve the comprehensive capacity of soil permeability effect.

3 Geocell construction method

Geocell as a new type of geosynthetics. Construction of fast, convenient, labor-saving, the entire flat construction site to remove debris. Laying and compaction of construction cushion, and then laying Geocell, the laying of the tensioner as far as possible, without褟wrinkles. Promptly filled with the filler cell interior, and compaction, while observing the deformation and check the room grid density. Last revised completion slope.

4 Geocell application in highway construction

4.1 Application of the desert road

As early as 1994, the Xi'an Highway Institute and the Huabei Petroleum Management Bureau of road construction companies, the use of Huabei Petroleum Management Bureau of rubber-cum-anti-corrosion technology, developed by the Institute geocell conducted a desert road applied research focuses on the Geo-grid room filled with the Taklimakan Desert of the main design parameters of road ------ compression modulus. The results confirmed that the compressive resilience model obtained amounted to 190 ∽ 210MPa, fully meet the design requirements for roadbed and filling with sand geocell structure layer structure than the natural sand and gravel layer thinning is about 10cm, can be close drawn. In 1995 to study the application of the Tarim Desert Highway permanent master of the oil tower 4 ∽ Minfeng lines on the southern section of 10Km full use of Geocell France to build a roadbed and filling with sand cushion. The measured road surface deflection value of 49 ∽ 64, were less than promised deflection value, resilience modulus of 206.19 ∽ 273.97MPa, average 239.58MPa, said Minge room sand-fixation obtained significantly greater than the overall strength of Graded gravel layer strength, and all strata of the compaction test are met specifications. The savings in conventional roadbed material costs and transportation costs, so that road construction costs by 50 percent, the use of shorter duration than conventional methods of 60%.

4.2 Soft Foundation Treatment

In 1997, the Liaohe Oil Field Survey and Design Institute Ocean Engineering Research Institute, in the inter-tidal beach roads with a clinical exploration of the road geocell test further confirmed the geocell unique in addressing the effectiveness of the settlement area. Yellow elevation in the region for more than 1m high tide water depth of nearly 1m, the foundation bearing capacity is only 110MPa, there are more than 10cm of mud. They used rubber products in North China Petroleum Management Bureau of production-cum-anti-corrosion Technology Institute 20cm high Geogrid layers, with the basal layer of geotextile for road, lower cell interior to fill grit, gravel, fill, within the upper slag, with mountains on both sides of tiles for shoulder. After soaking the tide of natural subsidence after the rolling can walk without a large heavy tipper. After more than four months, nearly a hundred trips per day, reflecting the cell room, slag pavement structure, high strength, overall good, strong ability to spread load evenly features. From their position at the trial made by geocell mountain road with the conventional use of two kinds of tiles road reclamation program analysis, we can see economic and social benefits: the use of mountain tiles cost per kilometer of road in the 400 ∽ 500 million the duration of 30 ∽ 40 days, per kilometer of transport units needed 3600 classes, each covers an area of 200,000 km m2. The use Geocell road construction, a construction cost of 100 ∽ 130 million, about 7 days duration, each 310 km transport units classes per km covering nearly 7000m2. Large gap between the two is impressive. Vehicles to reduce pollution, reduce the amount of stone to reduce the fill of marine pollution, the extraordinary price of beach is a breeding area, its environmental and economic benefits are even more impressive.

4.3 collapsible loess areas, high fill embankment excavation and filling connection segment

Compared with other regions, the application of the highways in our province of new materials, new technology is relatively backward. The good news is in 2000 at the company Huo Guo Tao greedy Blue Highway, State Road 109 lines Prynne highway construction, in order to overcome the high fill embankment loess consolidation settlement which led to the conjunction of excavation and filling cracks and take in the excavation and filling with the Department of tamping paved geocell treatment measures to address the Watian connection subgrade layers of different rates of subsidence problem of articulation. After practice, confirmed that the effect is obvious. In 2002, Lan Pro highway, Yin Expressway are pink soil, drought and water shortage, therefore, are used in the road sub-base or sub-base under the cushion paved geocell deal Watian connecting segment, half-dug half-filled segment of differential settlement, the effect clearly. Can be seen in the Highway geocell a wide range of applications, application a good prospect.

4.4 deal with Bump

In 2001, the province Department of Transportation Road and Chang'an University, College of Arts and the completion of research projects at the company Huo Guo Road Gulang to Yongchang highway bridges across the board are used geocell produce differential settlement transition section, specialized treatment "Bump," a common problem. As the full range of silt, sand soils are mostly used 10cm (high) × 40cm Geocell, each bridge 600 ∽ 800m2 covering an area of need, ranging cost per square meter for the 26 ∽ 30 Yuan. Geocell eliminated, the use of a large number of dust, project total cost with conventional approaches to cost quite a Bump, but the effect and service life doubled and redoubled.

4.5 Control of the application of erosion: berm, dam

These examples cited above are mostly used to improve the carrying capacity Geocell. In fact, Geocell Another important role is to control erosion, but also in foreign countries using Geogrid erosion control applications just as much as the amount of load applied. The most widely used are slope, dams, retaining walls, breakwater shore and so on. Its principle is to increase liquidity and reduce hair ditch erosion, to prevent pressure build-up, eliminating concentrated erosion. Honeycomb structure can be fixed limit filling material, limiting its on the water pressure, thereby improving mobility. Cell wall so that the normal drainage can be, but it controls the flow rate inside the nest. Like thousands of micro-dams, will focus on the water dispersed into a uniform, ease the sheet flow.

5. Conclusion

Today, the building of National Highway is still peak period, the geological conditions vary through the region needed a lot of Watian segment convergence, there are a lot of bridge connections. These are all the more difficult to deal with highway construction problems, although previously there are many treatment methods, but the result is not satisfactory, especially the bridge junctions, "Bump" issues and roadbed material under the action of lateral loads, squeeze a problem that seriously affects the life and safety of highways. There are protective slope, whether it is traditional Jiang Qi, dry or cement concrete puzzle grid can not stop the rain of their following the devastating soil erosion, resulting in increased highway maintenance costs. If the use of Geocell slope, with well-developed root system of grass seed, either solid earth slope, but also green, protect the ecological environment, in full compliance with the national emphasis on environmental protection and construction of green channel requirements. Even if the initial project cost slightly more than traditional methods, but to extend the road life, reduce maintenance costs, as well as environmental protection, ecological aspects of the overall economic efficiency is power in the contemporary era will benefit future generations.