Investigation for frost penetration depth using the GPR

Abstract

We have a problem that frost heaves by ice lenses sometimes damage buried constructions and pavements of road surface in the northern part of Japan in winter. Especially on the expressway, a bumpy road surface caused by frost heaves leads some serious traffic accidents.
Generally, we estimate the frost heaves distribution by means of the roughness measurements at the road surface. But this method can not give us the frost penetration depth. If we estimate the frost heaves distribution with the frost penetration depth, we can plan the method to reduce the damage by the frost heaves, for example replacement method for non-heaving soil.
We attempted a new nondestructive prospecting method for the frost penetration depth by the ground penetrating radar (GPR). One nanosecond monocycle pulse was used for transmitting waves of the GPR to obtain high resolution data.
The time lapse measurements by the GPR were conducted in autumn before frost heave appearance (first stage) and in winter while frost heaves appearing (second stage) at Doutou expressway in Hokkaido prefecture. The obtained GPR profile in the first stage was different from the GPR profile in the second stage obviously.
We conducted the common mid-point (CMP) gathers two times and confirmed the electromagnetic wave (EMW) became faster in the second stage than that in the first stage because of the frost soil.
We carried out boring and excavation tests based on the GPR data and confirmed that the ice lenses existed where the GPR profiles and the EMW velocities between two stages were different. The frost penetration depth could be estimated from the differences of the two GPR profiles.
The frost heaves can be easily produced in cutting sections due to much underground water, and hardly produced in banking sections due to lack of underground water. The estimated frost heaves areas from the GPR distributed in cutting sections showed consistent with mentioned above.
The time lapse GPR, one of the nondestructive testing methods, shows the effectiveness for the estimation of the frost penetration depth.