In-situ experimental and numerical investigation on the cooling effect of a multi-lane embankment with combined crushed-rock interlayer and ventilated ducts in permafrost regions

- Permafrost problem of multi-lane expressway embankment.
- A new cooling measure of combined crushed-rock and ventilated ducts.
- In-situ test validation of the new cooling measure.
- Numerical simulation of the long-term cooling effect.

For the multi-lane expressway embankment constructed in permafrost regions, the width is always over 20 m and asphalt-concrete pavement is adopted, both of which would largely increase the heat absorption of underlying permafrost compared with ordinary highway embankment. The increased heat absorption would result in more severe warming and thawing in underlying permafrost and threat the stability of the embankment. So, traditional cooling measures would not be effective enough to protect the underlying permafrost or to ensure the thermal stability of multi-lane expressway embankment. Based on this, a combined cooling measure composed of crushed-rock interlayer and ventilated ducts at its top was presented by the authors, the cooling mechanism of which was validated under laboratory condition. However, it is of necessity to further investigate the cooling effect of the new combined cooling measure under actual condition and its long-term cooling effect under global warming background. In this study, firstly, the observed temperature data from an in-situ test embankment of the new combined cooling measure were collected and analyzed. The observed data illustrated that the new cooling measure was effective in protecting underlying permafrost under actual condition of the Qinghai-Tibetan Plateau. Secondly, a numerical model was validated by the in-situ test data. Finally, the temperature distributions of ordinary multi-lane embankment, multi-lane embankment with crushed-rock interlayer and multi-lane embankment with combined crushed-rock interlayer and ventilated ducts after 20 years ofconstruction were numerically simulated under global warming background. According to the numerical study result, the long-term cooling effect of single crushed-rock in multi-lane embankment was limited. After the ventilated ducts were added at the top of the crushed-rock interlayer, the cooling effect was greatly enhanced and was effective enough to protect the underlying permafrost.