APPLICATION OF GEOSYNTHETICS IN THE PERMAFROST ZONE
Geosynthetics are most widely used when working with soft soils and in areas with severe climatic conditions, particularly in the permafrost zone. They are used in the oil and gas industry in the improvement of oil and gas fields, as well as in the construction of roads and railways. There, geosynthetics have practically no alternative substitutes.
Construction of SMG Bovanenkovo-Ukhta with the use of PRESTORUS three-dimensional reinforced geocell
The permafrost zone includes the tundra and forest-tundra area. Most of these areas are swampy. In this regard, the aggressiveness of the waters and the nature of the peat content of the construction area have a significant impact during the construction of any industrial facilities or roads.
Moreover, low negative ground temperatures are often observed here. In addition, the loss of strength and subsidence of permafrost soils during thawing are important problems. Many regions of the permafrost zone face another common challenge: the lack of soil that would be suitable for the construction of an embankment.
To keep the roadbed in a frozen state, it is best to carry out all the necessary excavation work in the winter. The embankment should be located in such a way that the upper permafrost horizon rises into the body of the embankment or is at a certain depth that is calculated, making allowances for the permissible subsidence of the base. All this must be taken into account when designing an object and drawing up a work plan.
Geosynthetics and Their Purpose
The range of works in which geosynthetic materials are involved in the permafrost zone is as follows:
- construction of technological roads
- protection of pipelines from hazardous geological processes
- ballasting of pipelines
In implementing these works, geosynthetics solve the main problem: reinforcement of the subgrade and structural layers of road pavements.
For the implementation of the last point, geosynthetics have been used since the 1980s—at first, non-woven geotextiles, and starting from 2000, three-dimensional geocells. This made it possible to structure the soil, placed in the cells, and practically exclude its shifts by redistributing the load on the underlying layers.
3D geocells are used to reinforce the subgrade: both the body of the embankment and its base. In this case, geosynthetics significantly extend the service life of technological lines and, in general, contribute to the acceleration of the process of laying roads. This is often a determining factor in construction at extremely low temperatures. PRESTORUS suggests using the GEOCORD® reinforced geocell for such works. Synthetic threads in its composition provide high strength, which retains stable geometric characteristics for many years. Temperature drops do not cause deformation. The geocell easily handles continuous static, dynamic and cyclic loads and is resistant to freezing and thawing and the effects of ultraviolet radiation.
A road built with the GEOCORD® reinforced geocell (6 months later)
However, GEOCORD® is most often used for constructing structural layers of road pavements.
In the permafrost zone, road pavements are laid in 2 stages:
- temporary. The period of operation of the route until the end of the subsidence of the subgrade.
- final. After the end of the subsidence process.
At both stages, the 3D geocell with filler material (crushed stone, sand) is used as a transitional type coating and in the form of a base under an improved layer.
Three-dimensional geocells with filler materials are also used for strengthening the surface of the slope. It helps protect the structure against weathering and erosion.
Weld-free geocell GEOSTEP® from PRESTORUS is perfect for slope reinforcement (laying angle from 30 to 60 degrees). It is made of high-quality polyethylene, and its service life exceeds 100 years. GEOSTEP® is resistant to repeated freezing and thawing, capable of withstanding temperature fluctuations from -65 to 70 С without deformation. It also endures the effects of aggressive soil media, both acidic and alkaline.
Flexible concrete slab GEOSOTY® is suitable for the protection and ballasting of pipelines in the permafrost zone. Its structure is reinforced with three-dimensional geocells. A reliable and flexible plate is resistant to water, ice, strong currents, frost heaving, and mechanical damage. GEOSOTY® are also highly seismic resistant. They are also environmentally friendly. The use of flexible concrete slabs minimizes the need to repair and reconstruct oil and gas pipelines.
Advantages of Using Geosynthetics in Extremely Low Temperatures
Geosynthetic materials easily solve the problems of construction and operation of industrial facilities and roads in the permafrost zone. Thanks to them, the amount of subsidence is reduced, and the soil bulging is prevented.
However, it is necessary to carry out a number of calculations for their successful application, including thermophysical and strength calculations. It is also important to consider the effect of surface water.
The GEOSOTY® flexible concrete slabs have become an excellent solution for strengthening water passages through the Zapolyarnoye-Urengoy gas pipeline. The constructed structure reliably protects the gas pipeline from floating and exposing the pipe, reducing the risk of emergencies.
- overall cost reduction
- high reliability and durability
- high speed of construction
- pipeline surcharge
Strengthening the water passage through the Zapolyarnoye-Urengoy gas pipeline using GEOSOTY®
Geosynthetics are a versatile solution to a wide range of problems. Completely non-toxic, durable, and reliable in terms of their parameters and characteristics, they are in no way inferior and often superior to bulky concrete structures. At the same time, geosynthetics are easy to install and easy to use. They do not require any special equipment for delivery to the construction site. The combination of these features can significantly reduce the cost of construction and achieve the final result much faster.