Evaluation of the structural response of two in-service thin flexible pavements under heavy vehicle loading during different seasons by built-in sensors

Figures & data

Figure 1. Illustration of the pavement instrumentation procedure (a) excavation procedure in plan-view, (b) excavation procedure in cross-section-view, (c) installation positions for the sensors, and (d) completed installation.

Figure 2. Pictures taken during the installation of the sensors used for the instrumentation procedure (a) ASGs – Asphalt Strain Gauges, (b) SPC – Soil Pressure Cell, and (c) ϵMU coil – Strain Measuring Unit coil.

Figure 3. The layer and sensor configurations for the (a) Lv373 cross-section, and (b) Lv515 cross-section.

Figure 4. Recorded values at Lv373 for (a) the daily average AC temperature and (b) the moisture content variation of the unbound granular layers.

Figure 5. Recorded values at Lv515 for (a) the daily average AC temperature and (b) the moisture content variation of the unbound granular layers.

Figure 6. Cross-sectional temperature variation and frost depth corresponding to the 0°C isotherm for Lv373 from 01 October 2018 to 30 June 2019. The dotted line represents the two dates when response measurements were made.

Figure 7. Cross-sectional temperature variation and frost depth corresponding to the 0°C isotherm for Lv515 from 01 October 2018 to 30 June 2019. The dotted line represents the two dates when response measurements were made.

Figure 8. Flowchart illustrating the backcalculation procedure used in the study.

Figure 9. Deflection bowls under 50kN FWD loading compared to MLET calculations for the campaign (a) August 2018, (b) May 2019, (c) June 2019, and (d) August 2019.

Figure 10. Adjusted values of AC stiffness according to temperature and stiffness of granular layers according to the degree of saturation.

Table 1. Backcalculated stiffness values at each measurement date for Lv373. Out. and In. represent the value sets outside and inside the trench.

Layer	Thickness	Stiffness (MPa)
		29 August 2018		8 May 2019		12 June 2019		21 August 2019
	(cm)	Out.	In.	Out.	In.	Out.	In.	Out.	In.
1. Asphalt Concrete	10	6107	6107	10,756	10,756	4464	4464	5764	5764
2. Base Course	12	383	341	376	336	331	296	380	329
3. Subbase	26	266	197	259	191	256	187	248	177
4. Base Course	12	169	118	166	116	147	102	154	103
5. Tarmac	13	149	138	232	201	158	152	188	182
6. Subbase	30	148	88	143	84	169	101	161	97
7. Sandy Clay	15	129	76	117	71	133	79	131	77
8. Subgrade (dfrost)	42	64	51	2800	2800	49	39	47	37
9. Subgrade (dfrost)	45	74	74	2800	2800	2800	2800	68	68
10. Subgrade Unfrozen	∞	75	75	105	105	72	72	76	76

Table 2. Backcalculated stiffness values at each measurement date for Lv515. Out. and In. represent the value sets outside and inside the trench.

Layer	Thickness	Stiffness (MPa)
		30 August 2018		9 May 2019		13 June 2019		22 August 2019
	(cm)	Out.	In.	Out.	In.	Out.	In.	Out.	In.
1. Asphalt Concrete	4	5160	5160	10,421	10,421	4605	4605	6138	6138
2. UGM Base	15	180	145	150	135	195	160	185	155
3. SG Sub.1 (TDR1)	37	93	76	90	74	100	82	97	78
4. SG Sub.2 (TDR2)	40	94	78	91	76	106	86	98	82
5. SG Sub.3 (TDR3)	40	85	73	78	69	95	80	89	75
6. SG Sub.4(TDR4,dfrost)	14	77	67	2800	2800	83	73	77	67
7. SG Sub.5 (dfrost,June)	10	85	85	2800	2800	2800	2800	87	87
8. SG Sub.6	16	95	95	2800	2800	2800	2800	97	97
9. SG Sub.7 (TDR5,dfrost)	84	107	107	2800	2800	2800	2800	108	108
10. SG Sub.8 (Natural SG)	∞	107	107	95	95	96	96	108	108

Figure 11. The LHV2 used for the response measurements. The axles are shown according to the used naming convention.

Figure 12. Half-axle and tyre configuration, spacing, and IDs for the LHVs used in this study. All distances in cm.

Table 3. Measured axle loads F and tyre pressures p for the three LHVs used in the study. Type S and D represent single vs. dual tyres respectively.

Axle	LHV1			LHV2			LHV3
ID	Type	p	F	Type	p	F	Type	p	F
(–)	(–)	(kPa)	(kN)	(–)	(kPa)	(kN)	(–)	(kPa)	(kN)
A1-1	S	840	83.36	S	850	74.53	S	890	93.16
A2-1	D	750	83.85	D	700	93.65	D	700	114.25
A2-2	D	750	82.38	D	700	91.20	S	920	67.67
A2-3	S	840	65.70	–	–	–	–	–	–
A3-1	D	850	87.77	D	900	91.20	S	870	94.14
A3-2	D	850	90.22	D	900	89.73	S	860	95.61
A4-1	D	850	78.45	D	900	101.50	S	870	69.14
A4-2	D	850	79.43	D	900	100.03	S	890	72.08
A4-3	D	850	80.41	–	–	–	S	890	74.53
ΣF			731.58			641.85			680.58

Figure 13. Longitudinal horizontal strain ϵ_xx response registrations from ASG compared to MLET calculations at Lv373 under LHV1 for (a) August 2018, (b) May 2019, (c) June 2019, and (d) August 2019.

Figure 14. Transversal horizontal strain ϵ_yy response registrations from ASG compared to MLET calculations at Lv373 under LHV2 for (a) August 2018, (b) May 2019, (c) June 2019, and (d) August 2019.

Figure 15. Vertical stress σ_zz response registrations from SPC at 35 cm depth compared to MLET calculations at Lv373 under LHV3 for (a) August 2018, (b) May 2019, (c) June 2019, and (d) August 2019.

Figure 16. Longitudinal horizontal strain ϵ_xx response registrations from ASG compared to MLET calculations at Lv515 under LHV1 for (a) August 2018, (b) May 2019, (c) June 2019, and (d) August 2019.

Figure 17. Transversal horizontal strain ϵ_yy response registrations from ASG compared to MLET calculations at Lv515 under LHV2 for (a) August 2018, (b) May 2019, (c) June 2019, and (d) August 2019.

Figure 18. Vertical stress σ_zz response registrations from SPC at 38 cm depth compared to MLET calculations at Lv515 under LHV3 for (a) August 2018, (b) May 2019, (c) June 2019, and (d) August 2019.

Figure 19. Vertical strain ϵ_zz response registrations from ϵMU coil at 84 cm depth compared to MLET calculations at Lv515 under LHV1 for (a) August 2018, (b) May 2019, (c) June 2019, and (d) August 2019.

Figure 20. Comparison between measured responses, linear elastic modelling (LE), viscoelastic modelling (VE), and nonlinear k-theta modelling (k-theta) for (a) longitudinal asphalt strain gauge ASG, and (b) soil pressure cell SPC under LHV1 in measurements in August 2018.

Figure 21. Validation of calculations against measurements for (a) longitudinal ASGs, (b) transversal ASGs, (c) SPCs, and (d) EMUs for all four measurements campaigns.