OAO GIPRODORNII’s Voronezh design branch specified installation of protection and reinforcement interlayer from Geospan GT PP 40 woven polypropylene geotextile, or equivalent, at the interface of macadam and sand base layers in the road pavement structure. The road pavement structure (asphaltic concrete of 5+6+12 cm, base of macadam and sand mixture of 40 cm, Geospan GT PP 40 protection and reinforcement interlayer, sub-base of mid-sized sand of 50 cm, subgrade of fine sand) was compliant with RIN 218.046-01 criteria at the accepted design data, that was confirmed by CREDO RADON-assisted calculations of the road pavement.
The reinforcement effect was calculated with reinforcement coefficients introduced as per Company Standard 18603495.008-2013 ‘Geospan GT PP woven geotextile. Recommendations for use in road construction’ developed jointly with the federal agency ROSDORNII’s specialists. Checking calculations conducted by Soyuzdorproject OAO as per RIM 218.5-002-2008 confirmed the compliance of the accepted structure with the practices of the road pavement design in federal road projects.
While selecting geosynthetics type and brand, a comparative analysis of various materials installed in the road pavement base lower layers as protection and reinforcement interlayers was performed (the table below).
| Sl.No. | Geomaterial | Canvalan IP-250 nonwoven geotextile | Geospan GT PP 40 woven geotextile | SD 40 type geogrid |
| 1 | Raw material | Polypropylene | Polypropylene | Polypropylene |
| 2 | Geomaterial purpose and function per RIM 218.2.046-2014 (R — reinforcement S — separation) | Protection interlayer (S) | Protection and Reinforcement interlayer (R + S) | Reinforcement interlayer (R) |
| 3 | Reinforcement effect, possibility to optimize road pavement lower part thickness | None | Defined by calculation | Defined by calculation |
| 4 | Strength parameters: Tensile strengthTensile strain | 14 kN/m ≥100% | 40 kN/m ≤15% | 40 kN/m ≤15% |
| 5 | Strength requirements per road standards Tensile strengthTensile strain | GOST R 56419 | GOST R 56338 ≥30 кН/м ≤20% | GOST R 56338 ≥30 кН/м ≤20% |
| 6 | Technique (installation with vehicle passing over fabrics) | Not allowed | Allowed | Probably |
Geosynthetics performing the combined function of reinforcement and separation are recommended as a protection and reinforcement interlayer at the interface of macadam, sand and gravel mix with fractions of up to 40 mm and the sub-base of sand in the road pavement base. Geogrids without an additional underlayer of nonwoven geotextile will not ensure an effective separation of layers in this case.
The requirements to the main quality parameters of a protection and reinforcement interlayer are specified by the following valid standards:
- GOST R 56338-2015 ‘Public automobile roads. Geosynthetics for reinforcement of the road pavement base lower layers. Technical requirements’.
- Company Standard 34.13330.2012 (Table D.2 – recommended geosynthetics performance depending on application).
Transstroymekhnizatsia OOO was performing the civil works for installation of the road pavement layers at 517th km to 544th km section during June 2014 till 2016, and at 633rd km to 715th km section during 2018 to 2019. The total volume of Geospan GT PP 40 and Geospan GT PP 50 geosynthetics supplied and laid amounts to over 2,000,000 m2.
The entry quality control of Geospan geosynthetics supplied to the project was carried out in accordance with Company Standard with regard to roll marking, quality certificate and laboratory test report of every batch verifying its compliance with the project documentation requirements (samples of quality certificate and test report are enclosed in Appendix D).
