季冻土路基永久变形现场监测与分析

利用光纤光栅开展了为期两年的季冻土路基永久变形现场监测，考虑了不同场地、不同时段、不同轴载组合对永久变形的影响。监测结果显示：（1）受气温影响，路基温度在正冻期和正融期随时间呈振荡线性变化，在一个冻融循环内，市区监测场地埋深30 cm和75 cm位置，地温变化范围分别为-9.0～14.4 ℃和-1.9～15.4 ℃，且随深度增加地温对气温的响应逐渐减弱，滞后性增强；（2）两个监测场地，当路基处于完全冻结状态时，车辆作用下的永久变形均较小，但在正融期，同样车重作用下路基永久变形增大，最大变形是冻结期的4.5倍，是融化期的4.2倍；（3）路基经历了两次冻融循环后，变形仍未稳定，在重载车辆作用下其永久变形仍不可忽视；（4）以轴重40 kN车辆引起的路基最大永久变形为基准，轴重80 kN及250 kN车辆引起的实测永久变形分别增大17倍及215倍，永久变形与轴重非线性关系明显；（5）冻融和重载叠加作用会产生最不利组合，放大路基永久变形，对此需特别关注。

In-situ monitoring and analysis of permanent subgrade deformation in seasonally frozen regions

Using the fiber Bragg grating sensors, a two-year in-situ monitoring for the subgrade permanent deformation in seasonally frozen regions was conducted. The combined effects of different sites, periods of a year, and different axial loads were considered. The results indicat that: 1) Affected by the air temperature, the subgrade’s temperature varies linearly but astatically with time in the freezing and melting periods. During a cycle of freezing and thawing, the range of ground temperature in the urban district at a depths of 30 cm and 75 cm are -9.0-14.4 ℃ and -1.9-15.4 ℃, respectively. The response of ground temperature to air temperature decreases and the hysteresis increases with the depth. 2) When the subgrade is fully frozen, the vehicle load-induced permanent deformation at both sites are small. However, when it is thawing, the deformation rises even under the same load. The maximum deformation is 4.5 and 4.2 times that of the frozen and normal period, respectively. 3) After two cycles of freezing and thawing, the subgrade has not reached a steady state. The permanent deformation under heavy vehicles can not be ignored. 4) Taking the maximum permanent subgrade deformation induced by a vehicle of 40 kN axial load as reference, the measured values caused by the 80 kN and 250 kN increase 17 and 215 times, respectively. There is a nonlinear relationship between the permanent deformation and axial load. 5) The combination of freezing and thawing cycles with heavy vehicle loading will produce the worst result, which can magnify the permanent subgrade deformation.