1 Introduction
2 Influence of subgrade in design and performance of railroad track structures
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Reference [15] developed a methodology that prevents progressive shear failure and also excessive plastic deformation where the plastic strain (εp) and the cumulative deformation should be limited to 2% and 25 mm, respectively.
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Reference [31] presented a set of references for the design and maintenance of track substructure. According to [31], there are four soil quality classes: QS0 (unsuitable soils), QS1 (poor soils), QS2 (average soils) and QS3 (good soils). This concept will be explored further in this work. From the soils’ classification and thickness of the granular layers, the track is evaluated in three categories: P1, P2 and P3 (mediocre, average and good, respectively).
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British Rail Method and Network Rail Code defined recommendations related to the thickness of the trackbed layers [17].
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West Japan Railways defined a limit value for bearing capacity (288 kPa). Below this value, the improvement of the foundation is required. Thus, the bearing capacity of 288 kPa equates to a compressive strength σs of approximately 112 kPa assuming a cohesion model plastic solution to a simple strip footing where σb = 2.57σs.
3 Resilient modulus
3.1 Mechanistic-empirical modelling approach
3.1.1 Cohesive materials
Models | Expressions | Parameters | Authors |
---|---|---|---|
Bilinear | \({M}_{\mathrm{r}}={K}_{1}+{K}_{2}{\sigma }_{\mathrm{d}}\) when σd < σdi \({M}_{\mathrm{r}}={K}_{3}+{K}_{4}{\sigma }_{\mathrm{d}}\) when σd > σdi | K1, K2, K3 and K4 | Thompson and Robnett [46] |
Power | \({M}_{\mathrm{r}}=k{\sigma }_{\mathrm{d}}^{n}\) | k and n are parameters dependent on the type of soil and physical state; the parameter n usually has a negative value | Moossazadeh and Witczak [47] |
Power (with the influence of the confining stress for overconsolidated saturated soils) | \({M}_{\mathrm{r}}=k{\left(\frac{{\sigma }_{\mathrm{d}}}{{\sigma }_{3}^{{\prime}}}\right)}^{n}\) | \({\sigma }_{3}^{\prime}\) is the confining stress | Brown, Lashine [48] |
Semi-log | \({M}_{\mathrm{r}}={10}^{(k-n{\sigma }_{\mathrm{d}})}\) | k and n are empirical parameters | Fredlund, Bergan [49] |
Hyperbolic | \({M}_{\mathrm{r}}=\frac{k+n{\sigma }_{\mathrm{d}}}{{\sigma }_{\mathrm{d}}}\) | Mr in ksi and σd in psi | Drumm and Pierce [50] |
Octahedral | \({M}_{\mathrm{r}}=k\frac{{\sigma }_{\mathrm{oct}}^{n}}{{\tau }_{\mathrm{oct}}^{m}}\) | σoct and τoct are the shear and normal octahedral stresses | Shackel [51] |
3.1.2 Granular materials
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In each increment of calculus, a linear elastic behaviour is adopted.
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The shear and volumetric components of stress and strain are analysed independently.
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Better adjust to the experimental results, mostly when the solicitation presents a 3D character.
3.2 Models dependent on the physical state—suction and degree of saturation
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net confining stress: σ3−ua;
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deviatoric stress: σ1−σ3;
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suction matrix: ψm = ua−uw,
3.3 Main differences of the resilient modulus formulation—analysis and comparison
4 Permanent deformation
5 Geomechanics classification and the rating
5.1 Resilient modulus: parametric study
Refs. | Models |
---|---|
\({M}_{\mathrm{r}}={k}_{1}{\left(\theta \right)}^{{k}_{2}}\) | |
[56] | \({M}_{\text{r}}={k}_{1}{p}_{0}{\left(\frac{\theta }{{p}_{0}}\right)}^{{k}_{2}}{\left(\frac{q}{{p}_{0}}\right)}^{{k}_{3}}\) |
[79] | \({E}_{\mathrm{v}}=C{{\sigma }_{\text{v}}^{^{\prime}}}^{m}\) |
[59] | \({M}_{\text{r}}={k}_{1}{p}_{0}{\left(\frac{\theta }{{p}_{0}}\right)}^{{k}_{2}}{\left(\frac{{\tau }_{\text{oct}}}{{p}_{0}}+1\right)}^{{k}_{3}}\) |
No. | UIC and ASTM classification | Materials | Properties | Observations |
---|---|---|---|---|
1 | QS3 GW | Well-graded gravel | Cu = 27; Cc = 2 (PImin = NP; PImax = 6) WL;máx = 25 W = 6.3% WOMC = 6.8% | Granular material used as based and sub-base in the flexible pavement sections; |
2 | QS2/QS3 SW/SM-ML | Sand | Cu = 20; Cc = 0.8–1.1 (PImin = NP; PImax = 6) WL;máx = 25 W = 7.7% WOMC = 7.7% | The target moisture content and densities were selected based on AASHTO T99 test results and field-measured values [80] |
Models | Material classification | Parameters | Regression analysis R2 |
---|---|---|---|
\({M}_{\mathrm{r}}={k}_{1}{\theta }^{{k}_{2}}\) | Well-graded gravel QS3-GW | k1 = 5176 k2 = 0.64 | 0.997 |
Sand QS2/QS3-SW/SM-ML | k1 = 36,942 k2 = 0.32 | 0.933 | |
\({M}_{\mathrm{r}}={k}_{1}{p}_{0}{\left(\frac{\theta }{{p}_{0}}\right)}^{{k}_{2}}{\left(\frac{q}{{p}_{0}}\right)}^{{k}_{3}}\) | Well-graded gravel QS3-GW | k1 = 5306 k2 = 0.59 k3 = 0.05 | 0.998 |
Sand QS2/QS3-SW/SM-ML | k1 = 34,336 k2 = 0.45 k3 =-0.15 | 0.942 | |
\({M}_{\mathrm{r}}={k}_{1}{p}_{0}{\left(\frac{\theta }{{p}_{0}}\right)}^{{k}_{2}}{\left(\frac{{\tau }_{\mathrm{oct}}}{{p}_{0}}+1\right)}^{{k}_{3}}\) | Well-graded gravel QS3-GW | k1 = 1.02 k2 = 0.62 k3 =-0.01 | 0.997 |
\({E}_{\mathrm{v}}=C{{\sigma }_{\text{v}}^{^{\prime}}}^{m}\) | Well-graded gravel QS3-GW | C = 6768 m = 0.65 | 0.988 |
Models | Material classification | Resilient modulus (MPa) |
---|---|---|
\({M}_{\mathrm{r}}={k}_{1}{\theta }^{{k}_{2}}\) | Well-graded gravel QS3-GW | 156 |
Sand QS2/QS3-SW/SM-ML | 109 | |
\({M}_{\mathrm{r}}={k}_{1}{p}_{0}{\left(\frac{\theta }{{p}_{0}}\right)}^{{k}_{2}}{\left(\frac{q}{{p}_{0}}\right)}^{{k}_{3}}\) | Well-graded gravel QS3-GW | 143 |
Sand QS2/QS3-SW/SM-ML | 131 | |
\({M}_{\mathrm{r}}={k}_{1}{p}_{0}{\left(\frac{\theta }{{p}_{0}}\right)}^{{k}_{2}}{\left(\frac{{\tau }_{\mathrm{oct}}}{{p}_{0}}+1\right)}^{{k}_{3}}\) | Well-graded gravel QS3-GW | 159 |
\({E}_{\mathrm{v}}=C{{\sigma }_{\text{v}}^{^{\prime}}}^{m}\) | Well-graded gravel QS3-GW | 118 |
Refs. | Models |
---|---|
[59] | \({M}_{\mathrm{r}}={k}_{1}{p}_{0}{\left(\frac{\theta }{{p}_{0}}\right)}^{{k}_{2}}{\left(\frac{{\tau }_{\mathrm{oct}}}{{p}_{0}}+1\right)}^{{k}_{3}}\) |
[35] | \({M}_{\mathrm{r}}={k}_{1}{({\sigma }_{\mathrm{d}}+\chi {\psi }_{\mathrm{m}})}^{{k}_{2}}\) |
[9] | \({M}_{\mathrm{r}}={k}_{1}{p}_{\mathrm{a}}{\left(\frac{\theta +\chi {\psi }_{\mathrm{m}}}{{p}_{\mathrm{a}}}\right)}^{{k}_{2}}{\left(\frac{{\tau }_{\mathrm{oct}}}{{p}_{\mathrm{a}}}+1\right)}^{{k}_{3}}\) |
[81] | \({E}_{\mathrm{r}}=A+B{p{^{\prime}}}_{0}+C{q}_{\mathrm{r}}\) |
No. | UIC and ASTM classification | Materials | Properties | Observations |
---|---|---|---|---|
1 | QS1-CL Low plasticity | Lean clay | WL = 30.8% WP = 18.4%; IP = 12.3%; | The effect of the matric suction will be included in the effective stress |
2 | QS1-CL-ML Low plasticity | Silt-lean clay | WL = 27.8%; WP = 19.8%; IP = 8%; | The triaxial tests following the AASHTO T307-99 procedure were conducted on both materials |
Models | Material classification | Parameters | Regression analysis R2 |
---|---|---|---|
\({M}_{\mathrm{r}}={k}_{1}{p}_{0}{\left(\frac{\theta }{{p}_{0}}\right)}^{{k}_{2}}{\left(\frac{{\uptau }_{\mathrm{oct}}}{{p}_{0}}+1\right)}^{{k}_{3}}\) | QS1-CL Low plasticity opt | k1 = 0.55 k2 = 0.15 k3 = -1.82 | 0.98 |
QS1-CL Low plasticity opt + 2% | k1 = 0.35 k2 = 0.14 k3 = -1.61 | 0.90 | |
QS1-CL-ML Low plasticity Opt | k1 = 0.97 k2 = -0.17 k3 = -1.97 | 0.96 | |
QS1-CL-ML Low plasticity opt + 2% | k1 = 0.68 k2 = -0.10 k3 = -1.13 | 0.87 | |
\({M}_{\mathrm{r}}={k}_{1}{({\sigma }_{\mathrm{d}}+\chi {\psi }_{\mathrm{m}})}^{{k}_{2}}\) | QS1-CL Low plasticity | k1 = 5.45 k2 = 0.36 | Difficult adjustment |
QS1-CL-ML Low plasticity | k1 = 72.11 k2 = -0.04 | Difficult adjustment | |
\({M}_{\mathrm{r}}={k}_{1}{p}_{\mathrm{a}}{\left(\frac{\theta +\chi {\psi }_{\mathrm{m}}}{{p}_{\mathrm{a}}}\right)}^{{k}_{2}}{\left(\frac{{\tau }_{\mathrm{oct}}}{{p}_{\mathrm{a}}}+1\right)}^{{k}_{3}}\) | QS1-CL Low plasticity | k1 = 0.24 k2 = 0.85 k3 = -2.29 | 0.62 |
QS1-CL-ML Low plasticity | k1 = 0.78 k2 = 0.13 k3 = -2.01 | 0.61 | |
\({E}_{r}=A+B{p{^{\prime}}}_{0}-C{q}_{\mathrm{r}}\) | QS1-CL Low plasticity | A = 3499.51 B = 261.25 C = -190.78 | 0.91 |
QS1-CL-ML Low plasticity | A = 60,443.76 B = -167.96 C = -474.39 | 0.69 |
Models | Material classification | Resilient modulus (MPa) |
---|---|---|
\({M}_{\mathrm{r}}={k}_{1}{p}_{0}{\left(\frac{\theta }{{p}_{0}}\right)}^{{k}_{2}}{\left(\frac{{\tau }_{\mathrm{oct}}}{{p}_{0}}+1\right)}^{{k}_{3}}\) | QS1-CL Low plasticity | 50 (opt) 33 (opt + 2%) |
QS1-CL-ML Low plasticity | 70 (opt) 56 (opt + 2%) | |
\({M}_{\mathrm{r}}={k}_{1}{({\sigma }_{\mathrm{d}}+\chi {\psi }_{\mathrm{m}})}^{{k}_{2}}\) | QS1-CL Low plasticity | Difficult adjustment |
QS1-CL-ML Low plasticity | Difficult adjustment | |
\({M}_{\mathrm{r}}={k}_{1}{p}_{\mathrm{a}}{\left(\frac{\theta +\chi {\psi }_{\mathrm{m}}}{{p}_{\mathrm{a}}}\right)}^{{k}_{2}}{\left(\frac{{\tau }_{\mathrm{oct}}}{{p}_{\mathrm{a}}}+1\right)}^{{k}_{3}}\) | QS1-CL Low plasticity | 53 (opt) 47 (opt + 2%) |
QS1-CL-ML Low plasticity | 73 (opt) 72 (opt + 2%) | |
\({E}_{r}=A+B{p{^{\prime}}}_{0}-C{q}_{\mathrm{r}}\) | QS1-CL Low plasticity | 83 (opt) 76 (opt + 2%) |
QS1-CL-ML Low plasticity | 80 (opt) 71 (opt + 2%) |
5.2 Permanent deformation: parametric study
Refs | Soils | ASTM classification | UIC classification | Observations |
---|---|---|---|---|
[76] | Sand | SP | QS2 | Compacted at field conditions and saturated |
Silt | CL-ML | QS1 | Compacted at field conditions and saturated | |
Silty sand (42.2% fines) | SM | QS1 | Compacted at optimum compaction—standard proctor | |
Silty sand (27.4% fines) | SM | QS1 | Compacted at optimum compaction —standard proctor | |
[83] | Well-graded Sand | SP | QS2 | Compacted at optimum compaction—standard proctor |
Poor-graded Sand | SW | QS3 | Compacted at optimum compaction—standard Proctor |
Material Properties | C. Bruynweg [83] | Crusher [83] | Silty clay (42.2% fines content) [82] | Silty clay (27.4% fines content) [66] | Silt [76] | Coarse sand [76] |
---|---|---|---|---|---|---|
Cu | 2.100 | 10.50 | 28.0 | 33.0 | 2.51 | 4.68 |
Cc | 1.050 | 1.250 | 0.54 | 0.75 | 1.32 | 0.62 |
D10 | 0.148 | 0.217 | – | – | – | – |
D30 | 0.219 | 0.784 | – | – | – | – |
D50 | 0.280 | 1.722 | – | – | – | – |
D60 | 0.310 | 2.280 | – | – | – | – |
CBR (%) | 22.00 | 15.70 | – | – | – | – |
Material properties | C. Bruynweg [83] | Crusher [83] | Silty clay (42.2% fines content) [82] | Silty clay (27.4% fines content) [66] | Silt [76] | Coarse sand [76] |
---|---|---|---|---|---|---|
γdry;max (kg/m3) | 1723 | 1755 | 1998 | 2070 | 1620 | 2110 |
Wopt (%) | 12.5 | 10.5 | 10.1 | 7.6 | – | – |
γwet (kg/m3) | 1942 | 1937 | – | – | – | – |
Liquid limit (%) | Non-plastic | Non-plastic | Non-plastic | Non-plastic | 35 | Non-plastic |
Plastic limit | Non-plastic | Non-plastic | Non-plastic | Non-plastic | 24 | Non-plastic |
Material properties | C. Bruynweg [83] | Crusher [83] | Silty clay (42.2% fines content) [82] | Silty clay (27.4% fines content) [66] | Silt [76] | Coarse sand [76] |
---|---|---|---|---|---|---|
ϕ (o) | 48.2 | 50.20 | 36.18 | 45.66 | 11.7* | 0.00* |
c (kPa) | 5.60 | 8.680 | 15.82 | 10.43 | 16.4* | 33.0* |
s (kPa)** | 9.90 | 14.90 | 31.80 | 19.10 | 24.8 | 0.00 |
m** | 1.98 | 2.070 | 1.470 | 1.880 | 0.62 | 1.33 |
6 Geomechanical classification
Information | UIC and ASTM classification | Materials | Properties | Observations |
---|---|---|---|---|
[50] | QS1-CL | – | WL = 28.5%; WP = 19.2%; IP = 9.3%; Gs = 2.73; Clay content 20.0%; Passing #200 73.0%; Maximum dry density 17.36 kN/m3 | – |
From the resilient modulus parametric study | QS1 Low plasticity CL | Lean clay | WL = 30.8%; WP = 18.4%; IP = 12.3% | The effect of the matric suction will be included in the effective stress; the triaxial tests following the AASHTO T307-99 procedure were conducted on both materials |
[84] | QS1 Lean clay (CL) | Silty clay | WL = 28.19%; Gs = 2.63; IP = 12.55% (low plasticity); Passing #200 80%; Maximum dry density 17.10 kN/m3; Wopt = 17.11%; c = 60 kPa; ϕ = 18o | Compacted at optimum compaction—standard proctor |
From the permanent deformation parametric study | QS1 CL-ML | Silt | WL = 35%; WP = 24%; IP = 11% (low to medium plasticity); Gs = 2.67; Cu = 2.51;Cc = 1.32; Maximum dry density 15.89 kN/m3; Hydraulic permeability 5.3 × 10–7 m/s; c’ = 11.7 kPa; ϕ’ = 16.4° | Compacted at field conditions and saturated |
From the resilient modulus parametric study | QS1 Low plasticity CL-ML | Silt-lean clay | WL = 27.8%; WP = 19.8%; IP = 8% | The effect of the matric suction will be included in the effective stress; The triaxial tests following the AASHTO T307-99 procedure were conducted on both materials |
From the permanent deformation parametric study | QS1 SM | Silty sand (42.2% fines) | Cu \(\approx\) 28; Cc \(\approx\) 0.54; Gs = 2.68; Wopt = 10.1%; Fines content = 42.2%; Maximum dry density 19.6 kN/m3 | Compacted at optimum compaction—standard proctor |
From the permanent deformation parametric study | QS1 SM | Silty sand (27.4% fines) | Cu \(\approx\) 33; Cc \(\approx\) 0.75; Gs = 2.67; Wopt = 7.6% Fines content = 27.4%; Maximum dry density 20.3 kN/m3 | Compacted at optimum compaction—standard proctor |
[84] | QS1 Silt (SM) | Silty clayed sand | WL = 16.70%; Gs = 2.70; IP = 7.50% (low plasticity); Passing #200 38%; Maximum dry unit weight 16.9 kN/m3; Wopt = 19.3%; c = 103 kPa; ϕ = 35o | Compacted at optimum compaction—standard proctor |
From the permanent deformation parametric study | QS2 SP | Well-graded sand | Cu = 2.10; Cc = 1.05; Maximum dry density 16.90 kN/m3; Wopt = 12.5%; c = 5.60 kPa; ϕ = 48.2° | Compacted at optimum compaction—standard proctor |
[58] | QS2 SP | Poorly graded Sand | Gs = 2.74; Cu≈2.0; Cc≈1.04 | – |
[83] | QS2 SP | Poorly graded Sand | Cu≈1.88; Cc≈1.04; Maximum dry density 16.56 kN/m3; Wopt = 14.0%; c = 6.34 kPa; ϕ = 41.8° | Standard proctor |
From the permanent deformation parametric study | QS2 SP | Sand | Gs = 2.66; Cu = 4.8; Cc = 0.62; Maximum dry density 20.69 kN/m3; Minimum dry density 15.89 kN/m3; Hydraulic permeability 3.2 × 10−5 m/s; c’ = 0 kPa; ϕ’ = 33° | Compacted at field conditions and saturated |
[84] | QS2 SP | Poorly graded sand | WL = 26.40%; Gs = 2.71%; Passing #200 0.70%; Cu = 1.79; Cc = 0.89; Maximum dry unit weight 15.70 kN/m3; Wopt = 13.70%; c = 20 kPa; ϕ = 42° | Compacted at optimum compaction—standard proctor |
[85] | QS2-QS3 | – | LA = 22; MED = 15; Fines content = 10% | Modified proctor |
From the resilient modulus parametric study | QS2/QS3 SW/SM-ML | Sand | Cu = 20; Cc = 0.8–1.1; (PImin = NP; PImax = 6) WL;máx = 25; W = 7.7%; WOMC = 7.7% | Granular material used as base and sub-base in the flexible pavement sections; The target moisture content and densities were selected based on AASHTO T99 test results and field-measured values [80] |
From the permanent deformation parametric study | QS3 SW | Poor-graded sand | Cu = 10.5; Cc = 1.25; Maximum dry density 17.21 kN/m3; Wopt = 10.5%; c = 8.68 kPa; ϕ = 50.2° | Compacted at optimum compaction—standard proctor |
From the resilient modulus parametric study | QS3 GW | Well-graded gravel | Cu = 27; Cc = 2; (PImin = NP; PImax = 6) WL;máx = 25; W = 6.3%; WOMC = 6.8% | Granular material used as base and sub-base in the flexible pavement sections; The target moisture content and densities were selected based on AASHTO T99 test results and field-measured values [80] |
[58] | QS3 GW | Well-graded gravel | Gs = 2.69;Cu≈61; Cc≈2.11 | – |
Information | Materials classification | Resilient modulus (Mpa) | Permanent deformation εp (%) |
---|---|---|---|
[50] | QS1-CL | 37 | – |
From the resilient modulus parametric study | QS1-CL Low plasticity | 50 | – |
[84] | QS1-CL | – | 0.01864 |
From the permanent deformation parametric study | QS1-CL/ML Silt | – | 0.03126 |
From the resilient modulus parametric study | QS1-CL-ML Low plasticity | 70 | – |
From the permanent deformation parametric study | Silty sand (42.2% fines) QS1-SM | 258 | 0.01385 |
From the permanent deformation parametric study | Silty sand (27.4% fines) QS1-SM | 294 | 0.01251 |
[84] | QS1-SM | 511 | 0.00658 |
From the permanent deformation parametric study | Well-graded sand QS2-SP | 509 | 0.00003 |
[58] | QS2-SP | 673 | – |
[83] | QS2-SP | – | 9.85 × 10–10 |
From the permanent deformation parametric study | Sand QS2-SP | – | 0.01170 |
[84] | QS2-SP | 172 | 0.01873 |
[85] | QS2-QS3 | – | 0.0002 |
From the resilient modulus parametric study | Sand QS2/QS-SW/SM-ML | 131 | – |
From the permanent deformation parametric study | Poor-graded sand QS3-SW | 178 | 0.00084 |
From the resilient modulus parametric study | Well-graded gravel QS3-GW | 159 | 0.00320 |
[58] | QS3-GW | 862 | – |
Clay | Wopt (%) | ϕ (°) | c (kPa) | Liquid limit (%) | Plasticity index (%) | Maximum dry unit weight (kN/m3) |
---|---|---|---|---|---|---|
Optimum | 17.11 | 18 | 60 | 28.19 | 12.55 | 17.10 |
Dry of optimum | 11.10 | 8 | 152 | – | – | – |
Wet of optimum | 21.50 | 16 | 42 | – | – | – |