RU2824541C1 - Method for erection of motor road embankment with geotextile cage - Google Patents

Abstract

FIELD: road construction.

SUBSTANCE: invention relates to road construction and can be used in construction of roads and bases in complex engineering-geological conditions, in particular for the needs of oil and gas industry, both in summer and winter seasons. Method for erection of motor road embankment comprises laying geosynthetic material, dumping soil thereon, whereupon free edges of the material are brought over the soil and fixed to form a cage, on top of which the upper part of the embankment is filled. Soil used is a peat-sand mixture, the content of peat in which is 30–70 vol.%, before placing and fixation of free edges, the peat-sand mixture is compacted, with additional filling of the peat-sand mixture, if necessary.

EFFECT: reduced value of embankment settlement and provision of its stability.

8 cl, 1 dwg

Description

The invention relates to the field of road construction and can be used in the construction of roads, roadbeds and foundations in difficult natural-climatic and engineering-geological conditions, in particular for the needs of the oil and gas complex, both in summer and winter.

Distinctive features of the construction, maintenance and operation of oil and gas sector facilities are logistics issues related to the significant remoteness of such facilities from large cities, high requirements for the bearing capacity for the passage of heavy vehicles and industrial equipment, as well as the presence of difficult climatic conditions. The key to the reliability of road structures in such areas is the low degree of embankment settlement and high stability of embankments.

A method for constructing a road surface on peat and swampy soils is known, which includes spreading a layer of geotextile, laying rows of plastic strips or wooden boards on it, fastened together with transverse strips, and subsequent anchoring of the ends of the strips and laying on top of the ballast (GB2494402, published 13.03.2013, IPC: E01C11/02; E01C9/08). A common feature with the claimed technical solution is the use of geosynthetic material as part of the road surface.

The disadvantage of this method is its high labor intensity due to the large volume of manual labor, as well as the amount of settlement that exceeds the permissible norms.

A method for constructing a roadbed with a sleeper support collar on peat soils is known (RU2642601, published on 25.01.2018, IPC: E01C 3/06), in which, in order to freeze the peat soils of the base to the required thickness, snow is periodically cleared and the moss and grass cover is kneaded, a geocomposite material is laid on the frozen cleared surface with an overlap of adjacent strips by at least 1/3 of the roll width, a technological layer of sand is installed, logs are installed on the prepared technical layer in bundles in the longitudinal direction with an offset equal to half the length of the log, in order to ensure the cross-country ability of equipment on the sleeper flooring, an upper technical layer of sand is poured, a support collar is formed, for which the edges of the geocomposite material are brought to the top of the collar and the material is welded, to prevent mechanical damage to the geocomposite material involves backfilling a sand protective layer and constructing the upper part of the roadbed. A common feature with the claimed technical solution is the formation of a support collar.

The disadvantage of the known method is the high degree of subsidence of the roadbed base, which is especially pronounced on amorphous soils of soft-plastic consistency, since the filler of the casings is a heavy material (logs). In addition, there is a high risk of damage to the geocomposite material when laying logs and forming casings with the logs themselves, which subsequently reduces the bearing capacity of the roadbed erected in this way.

The closest in technical essence is the method of constructing an embankment of an inter-field automobile road in the 1st road-climatic zone (Fundamental schemes of design and technological solutions for the use of volumetric geogrids "Prudon-494" and examples of their implementation in transport structures - M .: OJSC "494 UNR", 2002), in which a layer of geosynthetic material (with a strength of 200 N / cm) is laid on a weak base (peat soil), a mixture of dried peat with expanded polystyrene (EPS) granules treated with liquid bitumen (to bind the EPS granules in the peat mass) is poured onto it, after which a geosynthetic soil collar is formed by bringing the edges of the geosynthetic material up with their subsequent fastening, a volumetric geogrid filled with slag rubble is laid on top of the collar, the roadbed is built from slag rubble, geosynthetic material is laid with a tensile strength of 150 N/cm and a geogrid filled with slag rubble.

The following features are common to the claimed solution:

- cutting of material for soil casings;

- the first (lower) layer is installed, for which a sheet of geotextile is laid and a frame is formed.

The disadvantage of the known method adopted as a prototype is the following. As a filler for soil casings, a mixture with EPS granules is used, which in themselves have a low specific gravity, but after processing with bitumen have a greater weight and increase the mass of the soil casing, and therefore the embankment as a whole. In addition, the use of crushed stone in the overlying layers also increases the weight of the embankment. As a result, the resulting embankment settles vertically even without a load and continues to settle vertically and "creep" horizontally beyond the projection of the roadway during active operation (when heavy equipment passes), which leads to embankment settlement by an amount significantly exceeding permissible standards, to a critical decrease in the stability of the embankment and the impossibility of using the road. In this case, the material of the collar is weak (strength 200 N/cm) and is not intended for reinforcement: under load, the material begins to stretch, which also contributes to the "creep" of the collar horizontally with subsequent loss of overall stability of the embankment. In addition, the construction of the road using the prototype method is unprofitable for economic and time reasons due to the need to use a large volume of imported material (granules of EPS and bitumen), the need to treat the said granules of EPS with liquid bitumen at the construction site (i.e. the need to use additional equipment), as well as the need to dry the peat used to fill the collars, which requires the construction of temporary peat piles, where it is drained, and the organization of protection of this peat from precipitation.

Thus, the technical problem is to create a method for constructing a road embankment that is characterized by high stability during construction and operation.

The technical result consists in reducing the amount of embankment settlement and ensuring its stability.

The technical result is achieved by the fact that in the method of constructing a road embankment, in which geosynthetic material is laid, soil is poured onto it, after which the free edges of the material are brought over the soil and fixed, forming a collar, over which the upper part of the embankment is filled, according to the invention , a peat-sand mixture is used as soil, the peat content in which is 30-70 vol.%, before the introduction and fixation of the free edges, the peat-sand mixture is compacted, with additional peat-sand mixture being added if necessary.

The authors of the invention have experimentally established that the declared qualitative and quantitative composition of the mixture used in the soil shell and the features of the method stages are optimal for constructing an embankment with a low settlement degree in complex engineering and geological conditions and under high operational loads. The best method parameters were selected based on the results of full-scale tests, where design solutions were implemented using shells made of various geosynthetic materials filled with different types of soils, with varying degrees of compaction, using various construction equipment and operational construction sequences. Peat-sand mixtures with different peat and sand ratios were used to fill the shells. The degree of compaction was measured using the PDU-MG 4 "Udar" unit. The settlement value was assessed based on the analysis of the results of control drilling and geodetic surveys performed immediately after the end of construction, 1 month, 6 months and 12 months after the start of operation, taking into account the design settlement values. It was found that the minimum settlement value (and comparable with the design/calculated settlement value) is observed in embankment structures with a peat content of 30-70 vol.% in the filler mixture of the casing. In this case, the casings have the lowest specific gravity. The lowest specific gravity of the casings, in turn, with a sufficient degree of compaction necessary to impart rigidity to the entire embankment, is ensured by a peat content of 30-70 vol.% in the filler mixture of the casing, significantly exceeding the traditionally expected positive effect of using peat. A peat content of less than 30% leads to an increase in the percentage of sand, which leads to an increase in the embankment settlement value. A peat content of more than 70% leads to slippage of the equipment in use, and it also becomes difficult to distribute the peat-sand mixture over the surface. Varying the strength parameters of the material of the ferrules additionally contributes to achieving the technical result by eliminating the spread of the ferrules in the horizontal plane when used on very soft, amorphous soils.

The addition of peat-sand mixture is carried out in cases where the corresponding thickness of the shell (0.4-0.7 m) is not achieved as a result of compaction. The specified thickness has shown the greatest efficiency and, with the selected parameters, does not contribute to overconsumption of geosynthetic material.

When implementing the method, compaction of the peat-sand mixture is carried out until a shell thickness of 0.4-0.7 m is obtained.

When implementing the method, compaction of the peat-sand mixture is carried out until an elastic modulus of at least 50 MPa is obtained.

When implementing the method, a material with a tensile strength of 100-1000 kN/m is used as the material for the clamp.

When implementing the method, the first layer of the embankment is formed by laying sheets of geosynthetic material on the daylight surface.

When implementing the method, the geosynthetic material sheets are cut before laying.

When implementing the method, the upper part of the embankment may include the installation of a second layer of peat-sand mixture placed in a shell, laying a layer of sand or a layer of road surface.

When implementing the method, a geocomposite or geotextile material is used as a geosynthetic material.

The claimed invention is illustrated by drawings, where Fig. shows a cross-section of the embankment of a road constructed using the claimed method.

The method is carried out as follows.

The first embankment layer is formed by laying sheets 2 of geosynthetic material (for soil collars) on the day surface 1 without preliminary engineering preparation, overlapping each other, pre-cut to the required length depending on the design solution. Any reinforcing geosynthetic material that ensures the formation of a soil collar, such as woven geotextile fabric or composite fabric, can be used as the collar material. Depending on the initial data, the collar material used has a tensile strength in the longitudinal and transverse directions of 100-1000 kN/m. Then, peat-sand mixture 3 with a peat content of 30-70% by volume is poured by pushing it with a bulldozer with preliminary delivery of soil along the poured layer by dump trucks, in order to reduce the soil movement arm of the bulldozer. After this, compaction is performed by the vibrodynamic action of a roller (1-2 passes of a roller weighing 3-5 tons), the free edges of the geosynthetic material are brought over the compacted peat-sand mixture with some tension and fixed (with anchors), forming a closed or open collar. If necessary, additional peat-sand mixture 3 is added to obtain the design thickness of the collar (0.4-0.7 m) and an elastic modulus of at least 50 MPa during compaction with a roller. Next, the upper part 4 of the embankment is installed, which, depending on the design solution, may include the installation of a second layer of peat-sand mixture laid in the collar (using a technology similar to that described above), laying a layer of sand or a layer of road pavement at once.

Preparation of peat-sand mixture 3 of the required quantitative composition is carried out within the framework of preparatory work based on the percentage ratio of sand (30-70%) and peat (30-70%) from the volume in the mixture. The percentage ratio of the components varies depending on the availability of materials (peat, sand) in the construction area. For this purpose, the required amount of peat (local material) and sand (imported) are stored on a separate site, and mixed with a bulldozer until a visually uniformly mixed mixture is obtained.

Example 1

As a result of engineering and geological surveys during the construction of an access road to the oil field development site, it was established that the road section, with an embankment height of 2 m, runs through a highly swamped area with peat, mainly type 1B, with a thickness of 3 m. Based on this, a technical solution was developed, including the use of one reinforcing layer - a collar made of geocomposite material with a tensile strength of 300/300 kN/m, a thickness of 0.6 m and an elastic modulus of 55 MPa. In this case, the collars were filled with a mixture of local peat (60%) and imported sand (40%) of fraction 2-2.5 mm. The design value of settlement is 1.45 m. The actual value of settlement after 4 months of operation is 1.30 m.

Example 2

As a result of engineering and geological surveys during the construction of an access road to the oil field development site, it was established that the road section, with an embankment height of 5 m, runs through a highly swamped area with peat, mainly type 1A, with a thickness of 2.5 m. Based on this, a technical solution was developed that included the use of one reinforcing layer - a layer of geotextile material clips with a tensile strength of 200/200 kN/m, a thickness of 0.6 m and an elastic modulus of 65 MPa. In this case, the geotextile clips were filled with a mixture of local peat (60%) and imported sand (40%) of fraction 2-2.5 mm. The design value of settlement is 1.20 m. The actual value of settlement after 4 months of operation is 1.15 m.

Example 3

As a result of engineering and geological surveys during the construction of an access road to the oil field development site, it was established that the road section, with an embankment height of 4 m, runs through a highly swamped area with peat, mainly type 2, with a thickness of 7 m. Based on this, a technical solution was developed, including the use of two layers of geotextile material casings with a tensile strength of 200/200 kN/m, a thickness of 0.7 m and an elastic modulus of 53 MPa. In this case, the geotextile casings were filled with a mixture of local peat (70%) and imported sand (30%) of fraction 2-2.5 mm. The design value of settlement is 4.60 m. The actual value of settlement after 4 months of operation is 4.48 m.

Example 4

As a result of engineering and geological surveys during the construction of an access road to the oil field development site, it was established that the road section, with an embankment height of 3 m, runs through a highly swamped area with peat, mainly type 3, with a thickness of 5 m. Based on this, a technical solution was developed, including the use of two layers of geocomposite material casings with a tensile strength of 400/400 kN/m, a thickness of 0.55 m and an elastic modulus of 56 MPa. In this case, the geotextile casings were filled with a mixture of local peat (30%) and imported sand (70%) of fraction 2-2.5 mm. The design value of settlement is 3.50 m. The actual value of settlement after 4 months of operation is 3.23 m.

Thus, the claimed method of constructing embankments for motorways allows to reduce the amount of settlement during operation and to increase its stability, which ensures the production of an embankment that is stable during construction and operation.

Claims (8)

1. A method for constructing a road embankment, in which geosynthetic material is laid, soil is poured onto it, after which the free edges of the material are brought over the soil and fixed, forming a collar, on top of which the upper part of the embankment is filled, while a peat-sand mixture is used as soil, the peat content of which is 30-70 vol.%, before bringing in and fixing the free edges, the peat-sand mixture is compacted, with additional peat-sand mixture being added if necessary. 2. The method according to item 1, characterized in that the compaction of the peat-sand mixture is carried out until a shell thickness of 0.4-0.7 m is obtained. 3. The method according to paragraph 1, characterized in that the compaction of the peat-sand mixture is carried out until the elastic modulus value is obtained to be at least 50 MPa. 4. The method according to item 1, characterized in that the material used for the collar is a material with a tensile strength of 100-1000 kN/m. 5. The method according to item 1, characterized in that the first layer of the embankment is formed by laying sheets of geosynthetic material on the daylight surface. 6. The method according to item 1, characterized in that the sheets of geosynthetic material are cut before laying. 7. The method according to item 1, characterized in that the upper part of the embankment includes the construction of a second layer of peat-sand mixture placed in a shell, laying a layer of sand or a layer of road surface. 8. The method according to paragraph 1, characterized in that a geocomposite or geotextile material is used as the geosynthetic material.