Construction of a connecting road between ‘Russia’ M-10 route (Moscow to Saint Petersburg) and Moscow-St. Petersburg highway near Zelenograd town
The design institute Soyuzdorproject OAO has specified the application of a reinforcement geoplatform in a troubleshooting area of weak soils (very soft, grey-coloured, pocket-shaped clayey silt of 5m to 15m relative depth, E = 0.45 MPa).
The geoplatform has included a Geospan GCP 30/20 volumetric geogrid encased by Geospan GT PP-80 high-strength woven geotextile. An analysis of the troubleshooting area and the soil reinforcement geoplatform technical and economic viability has been carried out by our engineers assisted by PLAXIS geotechnical design program (weak-based reinforced embankment design modelling by the finite element method).
The soil-reinforced embankment calculations have shown:
- reduction of settlement values as compared to a nonreinforced embankment settlement by 56 cm (54%), as well as a lower deformation variation;
- higher slope stability factor of K=1.18 to K=1.72 with K=1.3 required. The Geospan geoplatform use has ensured the soil-reinforced embankment stability margin of 35%;
- consolidation time has shortened by 44%.
Saint Petersburg to Belarus M-20 federal motorway renovation via construction of Gatchina bypass in Leningrad region
The elaboration of detailed design by Geo-Project institute has revealed a troubleshooting area. In the area base there have been found some fibric peat and mud-peat, wet and 3 to 4.1 m water-saturated, inapplicable as a motorway embankment foot, and a cushion layer of soft plastic clay loam with a soil modulus equal to 4 MPa.
The troubleshooting area design analysis has been conducted by Gexa engineers and VAD AO’s design department. Based on design analysis of the embankment settlement, consolidation period and the foundation stability, there has been a decision taken to reinforce the embankment base with Geospan GT PP-80 woven geotextile fabrics to be laid crosswise as a closed 1 m high casing, including full replacement of peat down to 4 m.
As a result of the design decision taken, the embankment lower part stiffness has increased, deformation variations caused by the geotechnical profile nonuniformity have reduced, and the consolidation period has shortened.
Materials marketed as Geospan are used in road structure reinforcement, with 500 regional and municipal projects and over 60 federal projects in Gexa’s track record. It should be noted that in some regions such road arrangements have been adopted as standardized solutions that have proved their effectiveness during the decade of operation.
In order to solve various tasks associated with weak-soil embankment construction and justify soil reinforcement solutions, our engineers calculate the embankment subgrade stability, the embankment settlement, deformation and consolidation period, including those requiring full or partial soil replacement. Based on the calculation results, an optimal way of reinforcement and the methods of carrying out the job are defined, for example:
- Replacement of weak soil of insufficient bearing capacity;
- Casing or geoplatform types of embankment bottom reinforcement;
- Preloading to prevent embankment settlement;
- Vertical drainage installation (pressing of vertical draining elements in swamp soil;
- Piled embankments with flexible geosynthetic capping;
- Reinforcement of slopes with steepness of over 1:1, soil reinforcement installations, retaining walls.
Such engineering approach provides confidence in correct application of armoring geomaterials and obtaining of an economic benefit based on lower conventional roadbuilding material consumption and increased road structure operability and service life.
Let’s consider some successful examples of reinforcement geomaterial use under complicated geotechnical conditions.
Belgorod – Pavlovsk motorway renovation in Belgorod region
The renovation design documentation has provided for arrangement of the motorway subgrade in weak-based problem areas (soil with deformation modulus of under 5 MPa), i.e. soft sandy loam and soft plastic or viscous clay loams of various strength with deformation modulus in soaked condition equal to 1.4 MPa. Also, the geotechnical profile has been complicated by high ground water elevation and water evacuation problems causing the embankment sub-soil and surface waterlogging. It has ben additionally required to ensure the embankment stability considering the presence of a weakened zone where the existing subgrade contacts the would-be subgrade, calling for the zone reinforcement to avoid possible deformation.
According to Point 7.44 of Company’s Standard 34.113330.2012, calculation-based special measures should be taken to allow construction of weak-based embankments, i.e. the embankment reinforcement with woven geosynthetics. Calculations have been made for every area under review in terms of the subgrade overall stability, the embankment settlement, deformation and consolidation period, including partial soil replacement and preloading to avoid the embankment subsequent settlement. The calculations have been made by analytical methods in Credo Slope, Settlement and GEO-5 programs, as well as by finite-element quantitative analysis in Plaxis program. The type and brand of geosynthetic material for soil reinforcement structures have been selected based on the required strength calculations with reference to performance-impairing factors, such as damageability, creep, resistance to frost, UV rays and chemical impact.
Based on the calculation results, the following optimal reinforcement variants, geomaterial strength properties and construction procedures have been selected.
- The embankment bed reinforcement, without any weak soil replacement, through casing-type soil armoring with Geospan GT PP-80 woven polypropylene geotextile serving the combined function of reinforcement and separation. This has allowed increasing the embankment lower part stiffness and reducing settlement variation along the axis and the edge of the embankment cross section to shorten its consolidation period (the embankment consolidation time to reach the extent of 0.9xUTP has taken 6 months);
- Reinforcement of 1:1.5 to 1:1 steep slopes of the embankment body, in order to ensure the required slope stability factor of 1.3, through layers of Geospan PET-300 high-strength polyester geotextile with tensile strength of 300 kN/m lengthwise.
“Sibir” R-255 Novosibirsk-Kemerovo-Irkutsk motorway 1375th km to 1379th km section overhaul
This weak-bed material borrow area was characterized by the existing subgrade deformation. This caused surface cracking and early destruction. MK Indoor ZAO design company in Irkutsk prescribed soil replacement and paving for the weak-soil material borrow area. The encased-soil-type of replacement was carried out by placement of rocks to a depth of 1 meter from the pavement bottom. Geospan GT PP-80 woven geotextile was selected as the reinforced soil casing material. Construction at this site was performed by Bratskdorstroy ZAO in June 2014.
The soil reinforcement casing use allowed an increase in the structure rated strength values to further allow the widening of inter-repair spans.
Construction of ‘Don’ M-4 route’s 517th km to 544th km section bypassing Novaya Usman and Rogachevka and 633rd km to 715th km section bypassing Losevo and Pavlosk of Voronezh region
The design institute of Giprodornii OAO’s Voronezh branch prescribed installation of protection and reinforcement interlayer of Geospan GT PP-40 woven polypropylene geotextile or a similar material between macadam and sand underlying layers of the road pavement. The road pavement design, meeting RIN 218.046.-01 requirements as confirmed by Credo Radon program assisted calculations, contained an asphaltic concrete layer of 5+6+12 cm, a C-6 mixture base of 40 cm, a Geospan GT PP-40 (GT PP-50) protection and reinforcement interlayer, a sub-base of medium sized sand of 50 cm and a subgrade of fine sand.
Construction of 197th km to 215th km section of “Sortavala’ A-121 route connecting Saint Petersburg and R-21 ‘Kola” in Karelia
Geospan GT PP-50 woven geotextile was used as a protection and reinforcement interlayer for enhancing the road pavement bearing capacity along the whole section length with installation between the underlying layer of sand and the bearing layer of macadam and sand mixture. Construction was carried out by VAD AO.
Sayanogorsk – Mainskaya Hydro Power Station – Cheryomushki motorway renovation
Sayanogorsk – Mainskaya Hydro Power Station – Cheryomushki motorway renovation is one of the standing out projects of 2011 as it enabled unrestrained and safe passage of heavy loads (up to 300 t) to Sayano-Shushenskaya HPP for post-accident restoration of its main equipment. Dozens of variants of the road pavement advanced-material-based design were considered by the project engineer.
As a result of discussions, a protection and reinforcement interlayer of Geospan GT PP-50 woven geotextile was applied at the border of the subgrade and the aggregate layer to increase the bearing capacity. After Sayano-Shushenskaya HPP recommissioning and three-year operation, the motorway pavement condition was reviewed to have confirmed the correctness of the decision taken.
