- Email: [email protected]
Design Characteristics of Road Structure Reinforced with Cell Geosynthetic Materials with Account of Dynamic Load Impact
Available online at www.sciencedirect.com
ScienceDirect Procedia Engineering 189 (2017) 338 – 345
Transportation Geotechnics and Geoecology, TGG 2017, 17-19 May 2017, Saint Petersburg, Russia
Design characteristics of road structure reinforced with cell geosynthetic materials with account of dynamic load impact P. V. Ivanov a*ˈN.N. Belyaev aˈA.V. Petryaev b b
a Institute Stroyproekt, Dunaisky Prospekt 13/2A, St. Petersburg, Russia, 196158 Emperor Alexander I St. Petersburg State Transport University, Moskovsky Prospekt 9, St. Petersburg, Russia 190031
Abstract Modern highways are exposed to intensive transport loads, which require strengthening of the road structure and considering the dynamic load action on design characteristics of materials. The studies define quantitative changes of strength and strain characteristics of the road structure materials depending on amplitude of oscillations under dynamic loads. Subject to the road structure design and materials used, the strength of soil subgrade, for example, can decrease under vibration by 20-30% as compared to the design value defined without taking the vibration factor into account. The use of cell geosynthetic materials in the road structure allows improving its stress strain behaviour within the range of 5 % - 15 %. To that end, layers of less stiff material should not be placed above stiff layers reinforced with cell geosynthetic materials. © 2017 The Authors. Published by Elsevier Ltd. © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the scientific committee of the International conference on Transportation Geotechnics and (http://creativecommons.org/licenses/by-nc-nd/4.0/). Geoecology. Peer-review under responsibility of the scientific committee of the International conference on Transportation Geotechnics and Geoecology Keywords: cell geosynthetic materials, dynamic load, strength, deformability, oscillation amplitude
1. Introduction The design of motor road structures shall ensure the highest degree of reliability in terms of strength, stability and deformability under various external and internal loads and actions. One of the actions, which have not been *Corresponding author. Tel.: +7 (812) 331 0500 ext. 1637, +7 (921) 957 2472 fax +7(812) 331 0505 E-mail address: [email protected], [email protected]
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the International conference on Transportation Geotechnics and Geoecology
doi:10.1016/j.proeng.2017.05.054
339
P.V. Ivanov et al. / Procedia Engineering 189 (2017) 338 – 345
adequately considered in strength analyses of road structures, is vibration due to dynamic traffic load. To a certain extent, the vibration impacts all structural layers of the road pavement and subgrade. Its negative impact on the road structure can express differently. Firstly, it can be additional cycles of deformations in structural layers due to the road structure self-oscillations associated with dynamic traffic load. Secondly, it may be increased stress and strain amplitudes in structural layers due to vibration wave interference (or superposition). Thirdly, vibration action can result in significant deterioration of design strength and stress-strain properties of the materials. All together, these factors can increase actual load on the road structure and, at the same time, reduce its strength. Consequently, it results in a reduced reliability of the road structure designed without accounting for dynamic and vibration actions. The latest technical studies are focused on issues related to dynamic and vibration actions on the road subgrade [1,2,3]. That is why, the degree of possible dynamic and vibration impact on the road structure can be illustrated specifically by the example of road subgrade. In particular, this paper proves that design calculations of pavement for high class motor roads shall consider the influence of dynamic and vibration traffic loads on the road subgrade. Some provisions of this design method have been included in the road industry guidance «Recommendations to consider transport dynamic action in design analyses of road subgrade strength, stability and deformability» [4]. The traffic load impact on the road structure strength shall be more accurately considered as a dynamic action, which, in addition to static load, is distributed through and damped in the subgrade soil. It leads to reduction of design values for soil strength and stress-strain properties. Sensitivity of the subgrade and foundation soil mechanical properties to traffic dynamic loads can be taken into account with a reasonable accuracy through reduction of strength and stressstrain characteristics of soil. For the road subgrade soils, the dynamic action shall be measured using design amplitude of resultant oscillations generated by vehicles travelling at maximum admissible speed. The design resulting amplitude of subgrade soil oscillations across the pavement width at its bottom level, Ao, shall be calculated according to Table 1. Table 1 The design resulting amplitude of subgrade soil oscillations across the pavement width at its bottom level for calculation of subgrade stress-strain behaviour for motor road categories IA, IБ, IВ, II (characteristic load AK, load class 11.5 as to GOST R 52748-2007).
Weighted average of subgrade soil elasticity modulus, ܧ௩ , MPa 20 40 60 80 100 120
Design resulting amplitude of subgrade soil oscillations across the pavement width at its bottom level, ܣ , μm Thickness of road pavement, cm 70 80 90 100 110 120 89 86 77 69 73 60 56 50 43 56 46 41 37 33 45 38 36 31 28 38 33 32 26 24 34 28 27 23 21
Weighted average of subgrade soil elasticity modulus, Еave (MPa) is defined as:
ܧ௩ ൌ
ܧଵ ή ݄ଵ ܧଶ ή ݄ଶ ڮ ܧ ή ݄ ͵ǡͲ െ ݄
(1)
Where ܧଵ , ܧଶ , …ܧ – elasticity modulus of the existing non-uniform soil layers to the depth of 3 m from pavement top, MPa; ݄ଵ , ݄ଶ , …݄ – thickness of non-uniform soil layers to the depth of (3.0 – hrp) from the pavement bottom, m; hrp – thickness of the pavement, m; 3.0 m – the depth from the subgrade edge elevation that experiences dynamic actions.
340
P.V. Ivanov et al. / Procedia Engineering 189 (2017) 338 – 345
The propagation of oscillations in the subgrade and beyond it takes place simultaneously in vertical and horizontal planes. The design amplitudes of soil oscillations in any point of the subgrade and its foundation are calculated using the formula as follows: ᇲ
ܣ௭௬ ൌ ܣ ή ݁ ௭ήఋభିሺ௬ሻήఋమି
ᇲ ሺ௬ሻήఋ ᇲᇲ ାఋ ή య మ
(2)
Where Azy – resultant amplitude of soil oscillations in a point at depth z (m) from the pavement bottom and at distance y (m) from subgrade axis, μm; Ao – resultant amplitude of soil oscillations under the pavement layer across pavement width, μm; ͻǡͲ ݕ ܾ ͻǡͲ ݂ሺݕሻ ൌ ቐ൫ ݕെ ܾˇˑ ൯ܾˇˑ ൏ ݕ ܾ ͻǡͲ Ͳ ݕ ܾ ൫ݕ െ ܾ ൯ܾ ൏ ݕ ݂ ᇱ ሺݕሻ ൌ ቊ Ͳ ݕ ܾ Ͳܽ ݕݐ Ͳǡͷ ή ܤ ݄ ൌ ቐሺ ݕെ Ͳǡͷ ή ܤሻ ή Ͳݐܽߙ݃ݐǡͷ ή ܤ൏ ݕ ܪ ή ߙ݃ݐ Ͳǡͷ ή ܤ Ͳܽ ݕݐ ܪ ή ߙ݃ݐ Ͳǡͷ ή ܤ
(3)
(4)
ܾ – half-width of the pavement on top, m; 9.0 – size of oscillation intensive decay zone in the direction perpendicular to the road axis, measured from the pavement edge, m; В – width of the subgrade top, m; ܪ – height of embankment/open cut slope; ߙ – slope angle of embankment/open cut as to its ratio; ߜଵ – oscillation damping factor in vertical plane, 1/m; ߜଶᇱ , ߜଶᇱᇱ – oscillation damping factor in horizontal plane, 1/m; ߜଷ – oscillation damping factor in the slope, 1/m is defined as: ߜଷ ൌ
݈݃ߜଵ ͳǡͷ ή ܿߙ݃ݐ
(5)
Oscillation damping factors are to be defined using Table 2. Table 2 - Oscillation damping factor in the soil of subgrade and outside the subgrade
Soil description
Liquidity index,
ܫ Sand Sandy loam Loam Clay
< 0,0 0-1.0 0-0.25 0.25– 0.50 0-0.25 0.25-0.50
Oscillation damping factors, 1/m horizontally vertically ߜଵ ᇱ open cut embankment ߜଶ ߜଶᇱᇱ 0.18- 0.21 0.22- 0.24 0.10 0.008 0.21– 0.24 0.23– 0.26 0.105 0.008 0.25– 0.36 0.27– 0.32 0.083 0.005 0.27– 0.31 0.30– 0.32 0.084 0.004 0.32– 0.33 0.33– 0.35 0.078 0.002 0.24– 0.27 0.26– 0.29 0.096 0.006 0.28– 0.30 0.30– 0.32 0.085 0.005
341
P.V. Ivanov et al. / Procedia Engineering 189 (2017) 338 – 345
Note: Higher factor values correspond to soils with higher moisture content ߜଵ . The factors for intermediate values of the liquidity index are determined by interpolation. The parameters characterizing shear resistance and soils stress-strain properties under dynamic loads subject to the design oscillation amplitude are determined with the following equations: ܥௗ ൌ ܥ௦ ൣሺͳ െ ܭ ሻ ܭ ή ݁ ିήሺିː ሻ ൧
(6)
߮ௗ ൌ ߮௦ ൣ൫ͳ െ ܭఝ ൯ ܭఝ ή ݁ ିή ൧
(7)
ି˖ܧௗ ൌ ି˖ܧ௦ ൣ൫ͳ െ ܭாି˖ ൯ ܭாି˖ ή ݁ ି
ᇲ ήሺି ሻ ː
൧
(8)
Where ܭ - maximum relative reduction of soil specific cohesion under traffic dynamic load action ; ܭఝ - maximum relative reduction of soil internal friction angle under traffic dynamic load action; ܭாʢ - maximum relative reduction of soil elastic modulus under traffic dynamic load action; ܥ௦ , ߮௦ , ି˖ܧ௦ - design values for soil specific cohesion, angle of internal friction and elastic modulus under static load; ܥௗ , ߮ௗ , ି˖ܧௗ - design values for soil specific cohesion, angle of internal friction and elasticity modulus under dynamic load; A is an oscillation amplitude (μm) defined by the formula (2); ܣː - oscillation amplitude which causes deterioration of soil mechanical properties for not more than 5 % (it is allowed to assume to be 10 μm for calculations); K, ܭᇱ - factors of destruction and deformation due to vibration during soil triaxial compression tests can be assumed according to tables 3-4. Table 3 – Factors of vibration destruction and deformation for clay soils
Soil description Parameters
Sandy loam with Loam with
ܬ
K
< 0.0 0.006
ܭᇱ
0.007
0.0-0.6 0.025 0.02
ܬ
Clay with
ܬ
0-0.15 0.006
0.16-0.45 0.011
>0.45 0.02
0-0.15 0.005
0.16-0.45 0.010
>0.45 0.015
0.008
0.012
0.015
0.010
0.012
0.018
Table 4 – Factors of vibration destruction and deformation for sand soils
Soil description Parameters
K
ܭᇱ
Coarse and medium gravel sand
Fine sand
Silty sand
ܵ Ͳǡͺ
ܵ Ͳǡͺ
ܵ Ͳǡͺ
0.006
0.012
0.019
0.005
0.013
0.022
342
P.V. Ivanov et al. / Procedia Engineering 189 (2017) 338 – 345
The main parameters showing the sensitivity of the subgrade and foundation soil mechanical properties to the action of traffic dynamic loads are: - Maximum relative reduction of soil specific cohesion under traffic dynamic load action, େ ; - Maximum relative reduction of soil internal friction angle under traffic dynamic load action, ܭఝ ; - Maximum relative reduction of soil elasticity modulus under traffic dynamic load action, ܭாʢ . As a rule, these parameters should be determined based on laboratory soil test data using the formulas:
ܭ ൌ
ܥ௦ି െ ܥௗ ܥ௦ି
(9)
ܭఝ ൌ
߮௦ି െ ߮ௗ ߮௦ି
(10)
ܭாʢ ൌ
ି˖ܧ௦ି െ ି˖ܧௗ
ି˖ܧ௦ି
(11)
Where ܥ௦ି , ߮௦ି , ି˖ܧ௦ି – characteristic values of soil specific cohesion, internal friction angle and elasticity modulus under static load tests performed according to GOST 12248-2010; - minimum values for soil specific cohesion, internal friction angle and elasticity modulus ܥௗ , ߮ௗ , ି˖ܧௗ determined under vibration dynamic load.
For preliminary calculations and in case experimental data is absent or insufficient, it is allowed to use parameters ܭ , ܭఝ , ܭா and ܭாʢ , shown in Tables 5 and 6. Table 5 – Parameters of the sensitivity of clay soil mechanical properties to dynamic load
Soil description Parameters
Sandy loam with ܬ
Loam with ܬ
Clay with ܬ
ܭ
< 0.0 0.10
0.0-0.6 0.60
0-0.15 0.20
0.16-0.45 0.50
>0.45 0.15
0-0.15 0.15
0.16-0.45 0.55
>0.45 0.13
ܭఝ
0.07
0.40
0.10
0.40
0.08
0.09
0.45
0.10
ܭாʢ
0.15
0.35
0.15
0.25
0.20
0.12
0.24
0.18
Table 6 - Indicators of the sensitivity of the mechanical properties of sand soil to dynamic load
343
P.V. Ivanov et al. / Procedia Engineering 189 (2017) 338 – 345
Soil description Coarse and medium gravel sand
Fine sand
Silty sand
ܵ ͲǤͺ
ܵ ͲǤͺ
ܵ ͲǤͺ
ܭ
0.10
0.20
0.30
ܭఝ
0.15
0.18
0.20
ܭாʢ
0.10
0.18
0.25
Indicators
The results of analyses performed using the above methodology, i.e. taking into account dynamic action on the subgrade soil, show the influence of dynamic action factor on the results of pavement strength calculations. The road structure [4] taken as an example is shown in Table 7. Table 7 - Exemplary structure of road pavement on the subgrade consisting of two geological elements
Layer number
Layer material
Layer depth (h), cm
Elasticity modulus for elastic deflection calculation, Е, MPa
1
Dense asphalt concrete based on road bitumen grade 60/90
4
3200
2
Porous asphalt concrete based on road bitumen grade 60/90
8
2000
3
Highly porous asphalt concrete based on road bitumen grade 60/90
22
2000
4
26 90
420
5
Reinforced crushed stone gravel sand mix Silty sandy loam Wo = 0.7WТ
6
Light clay loam Wo = 0.75WТ
-
46 34
According to ODN (Industry Road Codes) 218.046-01 [5] the required total elasticity modulus of the road pavement at ∑Nр = 7.15 mln units should be Еtot = 326 MPa at the required strength coefficient as per elastic deflection criteria Кrst = 1.3. The strength calculation for the given road structure according to the standard method of ODN 218.046-01 with the design soil elasticity modulus Е = 46 MPa results in the value К st = 1.61 > 1.3. This, formally, means that the analysed road structure has sufficient strength reserve. Meanwhile, more precise determination of the design elasticity modulus of the subsoil taking into account the dynamic action and the depth of dynamic impact propagation shows that the design elasticity modulus is actually 33 MPa, not 46 MPa. As a result, the predicted strength coefficient of the road pavement is only Кst= 1.28 < 1.3. This indicates a completely opposite result - insufficient strength reserve of the road pavement! Thus, taking only the subgrade soil as example, we can see how important it is to take into account the dynamic and vibration impacts on the actual pavement strength when performing pavement strength calculations. However, vibration also affects other structural layers of the road pavement. That includes sand base layers, crushed stone beds, base layers from rock materials and soils reinforced with binding compounds, and asphalt-concrete road surface [6, 7, 8, 9, 10, 11, 12, 13]. That is why the next step in increasing the accuracy of road pavement strength calculations should be to consider the vibration impact not only on soil design characteristics but also on other road construction materials.
344
P.V. Ivanov et al. / Procedia Engineering 189 (2017) 338 – 345
Therefore, the study of the vibration behaviour of reinforced road structures is of special theoretical and practical interest. This especially concerns soil and discrete layers, reinforced with three-dimensional geogrids. The reason is that such reinforcement radically changes the stiffness not only of the reinforced layers, but the road structure as a whole. Previous experimental research showed that the use of cell geosynthetic materials in the road structure allows changing its stress strain behaviour within the range of 5 % - 15 % [14]. First, this improves the performance conditions of the layers located below the reinforced layer, which serves as some kind of a screen protecting them from traffic load action. This is the result of the reinforced layer stiffness increase. In addition, the effect of the stiffness is evident not only directly in this layer which is 10-20 cm thick, but extends to the adjacent pavement structural layers or the subgrade soil. As a result, the thickness of a more rigid layer within the road structure can be 20-30 % more than the nominal height of the three-dimensional geogrid. However, the new more rigid layer within the road structure can lead to undesirable consequences. Thus, according to the research carried out by Prof. A. Smirnov, S. Illiopolov et al [15], the presence of such a layer can result in a change of amplitude - frequency characteristics (AFC) of road structures and occurrence of resonance phenomena in the overlying structural layers. That, in turn, can result in deterioration of the stress-strain state of the pavement upper layers, or in reduction of the design strength characteristics of the materials used in these layers due to more intense vibration. Therefore, when designing progressive reinforced road structures, a balance of positive (for lower layers) and negative (for upper layers) effects of reinforcement should be considered in the most comprehensive way. This issue requires further study of the vibration behaviour of the road structures, including reinforced ones. 2. Conclusions The studies should be continued to design roads with account for: - impact of dynamic load on design characteristics not only of soils, but also other road construction materials, such as sand, crushed stone, asphalt concrete, etc. - impact of soil reinforcement on amplitude-frequency characteristics of road structures, including the subgrade. References [1] Manual for the design of subgrade for motor roads on soft soil, М., 2004 (approved by RF Ministry of Transport Directive No. ОС-1067-р of 03.12.2003). [2] А. V. Petryaev, I.V. Prokudin, V.P. Velikotniy, Ye.V. Berezantceva. Study of physical and mechanical and strength properties of filled soil under vibro-dynamic action. Scientific technical report, theme 313, Leningrad, 1984, 10 pages [3] А. V. Petryaev. Distribution of oscillations in the subgrade soil during thawing. Interacademic collection of scientific papers Geotechnics in transport construction, Dnepropetrovsk, 1988, 5 pages [4] Draft (first draft) of ODM (road industry guidance) Recommendations to consider transport dynamic action in design of road subgrade strength, stability and deformability (Federal Road Agency of RF Ministry of Transport, 2016). [5] ODN (Industry Road Codes) 218.046-01 Design of flexible road pavement. [6] Wichtmann T., Niemunis A., Triantafyllidis T. Validation and calibration of a high-cycle accumulation model based on cyclic triaxial tests on eight sands // Soils and Foundations. 2009. Vol. 49. №5. Pp. 711-728. [7] Leng J. Characteristics and Behavior of Geogrid-Reinforced Aggregate under Cyclic Load: PhD thesis. North Carolina State University, Raleigh, USA. 2002. [8] Francken L., Clauwaert C. Characterization and structural assessment of bound materials for flexible road structures // Proceedings of the 6-th International Conference on Asphalt Pavements. Ann Arbor. Michigan. 1987. Pp. 130-140. [9] Theyse H.L. The development of mechanistic-empirical permanent deformation design models for unbound pavement materials from laboratory accelerated pavement // Proceedings of the 5-th International symposium on unbound aggregates in road. Nottingham. 2000. Pp. 285293. [10] Tseng K. H., Lytton R. L. Prediction of permanent deformation in flexible pavement materials. Implication of Aggregates in the Design, Construction and Performance of Flexible Pavements // ASTM. 1989. Vol. STP 1016. Pp. 154-172. [11] Brecciaroli F., Kolisoja P. Deformation behavior of railway embankment materials under repeated loading. Literature review. Helsinki, 2006. 201 p. [12] Numrich R. Modellierung des nichtlinear-elastischen verformungsverhaltens von tragschichten ohne bindemittel (Modelling of non-liner elastic deformation behavior of unbound granular materials): PhD thesis University of Tecchnology, Dresden, Germany. 2003. [13] E. V. Uglova. Theoretical and methodological principles for assessment of residual fatigue life of road asphalt pavements. Extended abstract of PhD theses, Volgograd, 2009, P. 38. [14] Principal schemes of structural and process solutions on application of volume geogrids PRUDON-494 and examples of their implementation in transport facilities. FGUP SOYUZDORNII, 2002
P.V. Ivanov et al. / Procedia Engineering 189 (2017) 338 – 345
[15] A.V. Smirnov, S.K. Illiopolov, A.S. Aleksandrov Dynamic stability and analysis of road structures. Study guide - Omsk, SibADI, 2003, 52 pages.
345
ScienceDirect Procedia Engineering 189 (2017) 338 – 345
Transportation Geotechnics and Geoecology, TGG 2017, 17-19 May 2017, Saint Petersburg, Russia
Design characteristics of road structure reinforced with cell geosynthetic materials with account of dynamic load impact P. V. Ivanov a*ˈN.N. Belyaev aˈA.V. Petryaev b b
a Institute Stroyproekt, Dunaisky Prospekt 13/2A, St. Petersburg, Russia, 196158 Emperor Alexander I St. Petersburg State Transport University, Moskovsky Prospekt 9, St. Petersburg, Russia 190031
Abstract Modern highways are exposed to intensive transport loads, which require strengthening of the road structure and considering the dynamic load action on design characteristics of materials. The studies define quantitative changes of strength and strain characteristics of the road structure materials depending on amplitude of oscillations under dynamic loads. Subject to the road structure design and materials used, the strength of soil subgrade, for example, can decrease under vibration by 20-30% as compared to the design value defined without taking the vibration factor into account. The use of cell geosynthetic materials in the road structure allows improving its stress strain behaviour within the range of 5 % - 15 %. To that end, layers of less stiff material should not be placed above stiff layers reinforced with cell geosynthetic materials. © 2017 The Authors. Published by Elsevier Ltd. © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the scientific committee of the International conference on Transportation Geotechnics and (http://creativecommons.org/licenses/by-nc-nd/4.0/). Geoecology. Peer-review under responsibility of the scientific committee of the International conference on Transportation Geotechnics and Geoecology Keywords: cell geosynthetic materials, dynamic load, strength, deformability, oscillation amplitude
1. Introduction The design of motor road structures shall ensure the highest degree of reliability in terms of strength, stability and deformability under various external and internal loads and actions. One of the actions, which have not been *Corresponding author. Tel.: +7 (812) 331 0500 ext. 1637, +7 (921) 957 2472 fax +7(812) 331 0505 E-mail address: [email protected], [email protected]
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the International conference on Transportation Geotechnics and Geoecology
doi:10.1016/j.proeng.2017.05.054
339
P.V. Ivanov et al. / Procedia Engineering 189 (2017) 338 – 345
adequately considered in strength analyses of road structures, is vibration due to dynamic traffic load. To a certain extent, the vibration impacts all structural layers of the road pavement and subgrade. Its negative impact on the road structure can express differently. Firstly, it can be additional cycles of deformations in structural layers due to the road structure self-oscillations associated with dynamic traffic load. Secondly, it may be increased stress and strain amplitudes in structural layers due to vibration wave interference (or superposition). Thirdly, vibration action can result in significant deterioration of design strength and stress-strain properties of the materials. All together, these factors can increase actual load on the road structure and, at the same time, reduce its strength. Consequently, it results in a reduced reliability of the road structure designed without accounting for dynamic and vibration actions. The latest technical studies are focused on issues related to dynamic and vibration actions on the road subgrade [1,2,3]. That is why, the degree of possible dynamic and vibration impact on the road structure can be illustrated specifically by the example of road subgrade. In particular, this paper proves that design calculations of pavement for high class motor roads shall consider the influence of dynamic and vibration traffic loads on the road subgrade. Some provisions of this design method have been included in the road industry guidance «Recommendations to consider transport dynamic action in design analyses of road subgrade strength, stability and deformability» [4]. The traffic load impact on the road structure strength shall be more accurately considered as a dynamic action, which, in addition to static load, is distributed through and damped in the subgrade soil. It leads to reduction of design values for soil strength and stress-strain properties. Sensitivity of the subgrade and foundation soil mechanical properties to traffic dynamic loads can be taken into account with a reasonable accuracy through reduction of strength and stressstrain characteristics of soil. For the road subgrade soils, the dynamic action shall be measured using design amplitude of resultant oscillations generated by vehicles travelling at maximum admissible speed. The design resulting amplitude of subgrade soil oscillations across the pavement width at its bottom level, Ao, shall be calculated according to Table 1. Table 1 The design resulting amplitude of subgrade soil oscillations across the pavement width at its bottom level for calculation of subgrade stress-strain behaviour for motor road categories IA, IБ, IВ, II (characteristic load AK, load class 11.5 as to GOST R 52748-2007).
Weighted average of subgrade soil elasticity modulus, ܧ௩ , MPa 20 40 60 80 100 120
Design resulting amplitude of subgrade soil oscillations across the pavement width at its bottom level, ܣ , μm Thickness of road pavement, cm 70 80 90 100 110 120 89 86 77 69 73 60 56 50 43 56 46 41 37 33 45 38 36 31 28 38 33 32 26 24 34 28 27 23 21
Weighted average of subgrade soil elasticity modulus, Еave (MPa) is defined as:
ܧ௩ ൌ
ܧଵ ή ݄ଵ ܧଶ ή ݄ଶ ڮ ܧ ή ݄ ͵ǡͲ െ ݄
(1)
Where ܧଵ , ܧଶ , …ܧ – elasticity modulus of the existing non-uniform soil layers to the depth of 3 m from pavement top, MPa; ݄ଵ , ݄ଶ , …݄ – thickness of non-uniform soil layers to the depth of (3.0 – hrp) from the pavement bottom, m; hrp – thickness of the pavement, m; 3.0 m – the depth from the subgrade edge elevation that experiences dynamic actions.
340
P.V. Ivanov et al. / Procedia Engineering 189 (2017) 338 – 345
The propagation of oscillations in the subgrade and beyond it takes place simultaneously in vertical and horizontal planes. The design amplitudes of soil oscillations in any point of the subgrade and its foundation are calculated using the formula as follows: ᇲ
ܣ௭௬ ൌ ܣ ή ݁ ௭ήఋభିሺ௬ሻήఋమି
ᇲ ሺ௬ሻήఋ ᇲᇲ ାఋ ή య మ
(2)
Where Azy – resultant amplitude of soil oscillations in a point at depth z (m) from the pavement bottom and at distance y (m) from subgrade axis, μm; Ao – resultant amplitude of soil oscillations under the pavement layer across pavement width, μm; ͻǡͲ ݕ ܾ ͻǡͲ ݂ሺݕሻ ൌ ቐ൫ ݕെ ܾˇˑ ൯ܾˇˑ ൏ ݕ ܾ ͻǡͲ Ͳ ݕ ܾ ൫ݕ െ ܾ ൯ܾ ൏ ݕ ݂ ᇱ ሺݕሻ ൌ ቊ Ͳ ݕ ܾ Ͳܽ ݕݐ Ͳǡͷ ή ܤ ݄ ൌ ቐሺ ݕെ Ͳǡͷ ή ܤሻ ή Ͳݐܽߙ݃ݐǡͷ ή ܤ൏ ݕ ܪ ή ߙ݃ݐ Ͳǡͷ ή ܤ Ͳܽ ݕݐ ܪ ή ߙ݃ݐ Ͳǡͷ ή ܤ
(3)
(4)
ܾ – half-width of the pavement on top, m; 9.0 – size of oscillation intensive decay zone in the direction perpendicular to the road axis, measured from the pavement edge, m; В – width of the subgrade top, m; ܪ – height of embankment/open cut slope; ߙ – slope angle of embankment/open cut as to its ratio; ߜଵ – oscillation damping factor in vertical plane, 1/m; ߜଶᇱ , ߜଶᇱᇱ – oscillation damping factor in horizontal plane, 1/m; ߜଷ – oscillation damping factor in the slope, 1/m is defined as: ߜଷ ൌ
݈݃ߜଵ ͳǡͷ ή ܿߙ݃ݐ
(5)
Oscillation damping factors are to be defined using Table 2. Table 2 - Oscillation damping factor in the soil of subgrade and outside the subgrade
Soil description
Liquidity index,
ܫ Sand Sandy loam Loam Clay
< 0,0 0-1.0 0-0.25 0.25– 0.50 0-0.25 0.25-0.50
Oscillation damping factors, 1/m horizontally vertically ߜଵ ᇱ open cut embankment ߜଶ ߜଶᇱᇱ 0.18- 0.21 0.22- 0.24 0.10 0.008 0.21– 0.24 0.23– 0.26 0.105 0.008 0.25– 0.36 0.27– 0.32 0.083 0.005 0.27– 0.31 0.30– 0.32 0.084 0.004 0.32– 0.33 0.33– 0.35 0.078 0.002 0.24– 0.27 0.26– 0.29 0.096 0.006 0.28– 0.30 0.30– 0.32 0.085 0.005
341
P.V. Ivanov et al. / Procedia Engineering 189 (2017) 338 – 345
Note: Higher factor values correspond to soils with higher moisture content ߜଵ . The factors for intermediate values of the liquidity index are determined by interpolation. The parameters characterizing shear resistance and soils stress-strain properties under dynamic loads subject to the design oscillation amplitude are determined with the following equations: ܥௗ ൌ ܥ௦ ൣሺͳ െ ܭ ሻ ܭ ή ݁ ିήሺିː ሻ ൧
(6)
߮ௗ ൌ ߮௦ ൣ൫ͳ െ ܭఝ ൯ ܭఝ ή ݁ ିή ൧
(7)
ି˖ܧௗ ൌ ି˖ܧ௦ ൣ൫ͳ െ ܭாି˖ ൯ ܭாି˖ ή ݁ ି
ᇲ ήሺି ሻ ː
൧
(8)
Where ܭ - maximum relative reduction of soil specific cohesion under traffic dynamic load action ; ܭఝ - maximum relative reduction of soil internal friction angle under traffic dynamic load action; ܭாʢ - maximum relative reduction of soil elastic modulus under traffic dynamic load action; ܥ௦ , ߮௦ , ି˖ܧ௦ - design values for soil specific cohesion, angle of internal friction and elastic modulus under static load; ܥௗ , ߮ௗ , ି˖ܧௗ - design values for soil specific cohesion, angle of internal friction and elasticity modulus under dynamic load; A is an oscillation amplitude (μm) defined by the formula (2); ܣː - oscillation amplitude which causes deterioration of soil mechanical properties for not more than 5 % (it is allowed to assume to be 10 μm for calculations); K, ܭᇱ - factors of destruction and deformation due to vibration during soil triaxial compression tests can be assumed according to tables 3-4. Table 3 – Factors of vibration destruction and deformation for clay soils
Soil description Parameters
Sandy loam with Loam with
ܬ
K
< 0.0 0.006
ܭᇱ
0.007
0.0-0.6 0.025 0.02
ܬ
Clay with
ܬ
0-0.15 0.006
0.16-0.45 0.011
>0.45 0.02
0-0.15 0.005
0.16-0.45 0.010
>0.45 0.015
0.008
0.012
0.015
0.010
0.012
0.018
Table 4 – Factors of vibration destruction and deformation for sand soils
Soil description Parameters
K
ܭᇱ
Coarse and medium gravel sand
Fine sand
Silty sand
ܵ Ͳǡͺ
ܵ Ͳǡͺ
ܵ Ͳǡͺ
0.006
0.012
0.019
0.005
0.013
0.022
342
P.V. Ivanov et al. / Procedia Engineering 189 (2017) 338 – 345
The main parameters showing the sensitivity of the subgrade and foundation soil mechanical properties to the action of traffic dynamic loads are: - Maximum relative reduction of soil specific cohesion under traffic dynamic load action, େ ; - Maximum relative reduction of soil internal friction angle under traffic dynamic load action, ܭఝ ; - Maximum relative reduction of soil elasticity modulus under traffic dynamic load action, ܭாʢ . As a rule, these parameters should be determined based on laboratory soil test data using the formulas:
ܭ ൌ
ܥ௦ି െ ܥௗ ܥ௦ି
(9)
ܭఝ ൌ
߮௦ି െ ߮ௗ ߮௦ି
(10)
ܭாʢ ൌ
ି˖ܧ௦ି െ ି˖ܧௗ
ି˖ܧ௦ି
(11)
Where ܥ௦ି , ߮௦ି , ି˖ܧ௦ି – characteristic values of soil specific cohesion, internal friction angle and elasticity modulus under static load tests performed according to GOST 12248-2010; - minimum values for soil specific cohesion, internal friction angle and elasticity modulus ܥௗ , ߮ௗ , ି˖ܧௗ determined under vibration dynamic load.
For preliminary calculations and in case experimental data is absent or insufficient, it is allowed to use parameters ܭ , ܭఝ , ܭா and ܭாʢ , shown in Tables 5 and 6. Table 5 – Parameters of the sensitivity of clay soil mechanical properties to dynamic load
Soil description Parameters
Sandy loam with ܬ
Loam with ܬ
Clay with ܬ
ܭ
< 0.0 0.10
0.0-0.6 0.60
0-0.15 0.20
0.16-0.45 0.50
>0.45 0.15
0-0.15 0.15
0.16-0.45 0.55
>0.45 0.13
ܭఝ
0.07
0.40
0.10
0.40
0.08
0.09
0.45
0.10
ܭாʢ
0.15
0.35
0.15
0.25
0.20
0.12
0.24
0.18
Table 6 - Indicators of the sensitivity of the mechanical properties of sand soil to dynamic load
343
P.V. Ivanov et al. / Procedia Engineering 189 (2017) 338 – 345
Soil description Coarse and medium gravel sand
Fine sand
Silty sand
ܵ ͲǤͺ
ܵ ͲǤͺ
ܵ ͲǤͺ
ܭ
0.10
0.20
0.30
ܭఝ
0.15
0.18
0.20
ܭாʢ
0.10
0.18
0.25
Indicators
The results of analyses performed using the above methodology, i.e. taking into account dynamic action on the subgrade soil, show the influence of dynamic action factor on the results of pavement strength calculations. The road structure [4] taken as an example is shown in Table 7. Table 7 - Exemplary structure of road pavement on the subgrade consisting of two geological elements
Layer number
Layer material
Layer depth (h), cm
Elasticity modulus for elastic deflection calculation, Е, MPa
1
Dense asphalt concrete based on road bitumen grade 60/90
4
3200
2
Porous asphalt concrete based on road bitumen grade 60/90
8
2000
3
Highly porous asphalt concrete based on road bitumen grade 60/90
22
2000
4
26 90
420
5
Reinforced crushed stone gravel sand mix Silty sandy loam Wo = 0.7WТ
6
Light clay loam Wo = 0.75WТ
-
46 34
According to ODN (Industry Road Codes) 218.046-01 [5] the required total elasticity modulus of the road pavement at ∑Nр = 7.15 mln units should be Еtot = 326 MPa at the required strength coefficient as per elastic deflection criteria Кrst = 1.3. The strength calculation for the given road structure according to the standard method of ODN 218.046-01 with the design soil elasticity modulus Е = 46 MPa results in the value К st = 1.61 > 1.3. This, formally, means that the analysed road structure has sufficient strength reserve. Meanwhile, more precise determination of the design elasticity modulus of the subsoil taking into account the dynamic action and the depth of dynamic impact propagation shows that the design elasticity modulus is actually 33 MPa, not 46 MPa. As a result, the predicted strength coefficient of the road pavement is only Кst= 1.28 < 1.3. This indicates a completely opposite result - insufficient strength reserve of the road pavement! Thus, taking only the subgrade soil as example, we can see how important it is to take into account the dynamic and vibration impacts on the actual pavement strength when performing pavement strength calculations. However, vibration also affects other structural layers of the road pavement. That includes sand base layers, crushed stone beds, base layers from rock materials and soils reinforced with binding compounds, and asphalt-concrete road surface [6, 7, 8, 9, 10, 11, 12, 13]. That is why the next step in increasing the accuracy of road pavement strength calculations should be to consider the vibration impact not only on soil design characteristics but also on other road construction materials.
344
P.V. Ivanov et al. / Procedia Engineering 189 (2017) 338 – 345
Therefore, the study of the vibration behaviour of reinforced road structures is of special theoretical and practical interest. This especially concerns soil and discrete layers, reinforced with three-dimensional geogrids. The reason is that such reinforcement radically changes the stiffness not only of the reinforced layers, but the road structure as a whole. Previous experimental research showed that the use of cell geosynthetic materials in the road structure allows changing its stress strain behaviour within the range of 5 % - 15 % [14]. First, this improves the performance conditions of the layers located below the reinforced layer, which serves as some kind of a screen protecting them from traffic load action. This is the result of the reinforced layer stiffness increase. In addition, the effect of the stiffness is evident not only directly in this layer which is 10-20 cm thick, but extends to the adjacent pavement structural layers or the subgrade soil. As a result, the thickness of a more rigid layer within the road structure can be 20-30 % more than the nominal height of the three-dimensional geogrid. However, the new more rigid layer within the road structure can lead to undesirable consequences. Thus, according to the research carried out by Prof. A. Smirnov, S. Illiopolov et al [15], the presence of such a layer can result in a change of amplitude - frequency characteristics (AFC) of road structures and occurrence of resonance phenomena in the overlying structural layers. That, in turn, can result in deterioration of the stress-strain state of the pavement upper layers, or in reduction of the design strength characteristics of the materials used in these layers due to more intense vibration. Therefore, when designing progressive reinforced road structures, a balance of positive (for lower layers) and negative (for upper layers) effects of reinforcement should be considered in the most comprehensive way. This issue requires further study of the vibration behaviour of the road structures, including reinforced ones. 2. Conclusions The studies should be continued to design roads with account for: - impact of dynamic load on design characteristics not only of soils, but also other road construction materials, such as sand, crushed stone, asphalt concrete, etc. - impact of soil reinforcement on amplitude-frequency characteristics of road structures, including the subgrade. References [1] Manual for the design of subgrade for motor roads on soft soil, М., 2004 (approved by RF Ministry of Transport Directive No. ОС-1067-р of 03.12.2003). [2] А. V. Petryaev, I.V. Prokudin, V.P. Velikotniy, Ye.V. Berezantceva. Study of physical and mechanical and strength properties of filled soil under vibro-dynamic action. Scientific technical report, theme 313, Leningrad, 1984, 10 pages [3] А. V. Petryaev. Distribution of oscillations in the subgrade soil during thawing. Interacademic collection of scientific papers Geotechnics in transport construction, Dnepropetrovsk, 1988, 5 pages [4] Draft (first draft) of ODM (road industry guidance) Recommendations to consider transport dynamic action in design of road subgrade strength, stability and deformability (Federal Road Agency of RF Ministry of Transport, 2016). [5] ODN (Industry Road Codes) 218.046-01 Design of flexible road pavement. [6] Wichtmann T., Niemunis A., Triantafyllidis T. Validation and calibration of a high-cycle accumulation model based on cyclic triaxial tests on eight sands // Soils and Foundations. 2009. Vol. 49. №5. Pp. 711-728. [7] Leng J. Characteristics and Behavior of Geogrid-Reinforced Aggregate under Cyclic Load: PhD thesis. North Carolina State University, Raleigh, USA. 2002. [8] Francken L., Clauwaert C. Characterization and structural assessment of bound materials for flexible road structures // Proceedings of the 6-th International Conference on Asphalt Pavements. Ann Arbor. Michigan. 1987. Pp. 130-140. [9] Theyse H.L. The development of mechanistic-empirical permanent deformation design models for unbound pavement materials from laboratory accelerated pavement // Proceedings of the 5-th International symposium on unbound aggregates in road. Nottingham. 2000. Pp. 285293. [10] Tseng K. H., Lytton R. L. Prediction of permanent deformation in flexible pavement materials. Implication of Aggregates in the Design, Construction and Performance of Flexible Pavements // ASTM. 1989. Vol. STP 1016. Pp. 154-172. [11] Brecciaroli F., Kolisoja P. Deformation behavior of railway embankment materials under repeated loading. Literature review. Helsinki, 2006. 201 p. [12] Numrich R. Modellierung des nichtlinear-elastischen verformungsverhaltens von tragschichten ohne bindemittel (Modelling of non-liner elastic deformation behavior of unbound granular materials): PhD thesis University of Tecchnology, Dresden, Germany. 2003. [13] E. V. Uglova. Theoretical and methodological principles for assessment of residual fatigue life of road asphalt pavements. Extended abstract of PhD theses, Volgograd, 2009, P. 38. [14] Principal schemes of structural and process solutions on application of volume geogrids PRUDON-494 and examples of their implementation in transport facilities. FGUP SOYUZDORNII, 2002
P.V. Ivanov et al. / Procedia Engineering 189 (2017) 338 – 345
[15] A.V. Smirnov, S.K. Illiopolov, A.S. Aleksandrov Dynamic stability and analysis of road structures. Study guide - Omsk, SibADI, 2003, 52 pages.
345