8.

Summary and conclusions

This study focused on the mechanism of process of ice lensing.

The

formation of ice lenses is recognized as a necessary condition for frost heave and also
occurs in many porous media.

The importance of studying soil freezing associatedwith ice lensing was described in chapter 1.
Numerical studies on ice lensing have been carried out.

The main factors

involved in soil freezing and ice lensing, and the models and theories for ice lensing
were summarized in chapter 2.
ice lensing.

Then, it presented two main problems for considering

One is to clarify the microstructure near the freezing front, which has been

dealt with like a black box.

The other is to explain the dynamic mechanism of ice

lensing, in which the generation and growth of an ice lens is repeated to form
intermittent layers.
Soil is heterogeneous in terms of texture, particle shape, electrical charge, andchemical composition.

Ice lensing is a complex crystal growth phenomenon that iscaused by various water and heat-related factors.

Observing the microstructure andclarifying the mechanism are difficult because of the non-uniformity and the complexity.
Therefore, we observed ice lensing in actual soil and in porous media consisting of
uniform glass particles using an unidirectional freezing apparatus that can control
temperature gradient and freezing rate independently.

And based on the experimentalresults, we proposed a model to simulate ice lensing in water-saturated porous media.
The characteristics of the samples we used and the unidirectional detail offreezing apparatus were described in chapter 3.

The relationship of temperature,

specific surface area, solute type and its concentration to unfrozen water amount in theporous media was also shown in this chapter.

- 119 -The details of unidirectional freezing experiments were described in chapter 46, then, following results were obtained. (1) Ice lensing in soil and porous media
consisting of fine particles were microscopically observed.
modeling can be made using uniform sized glass beads.

Ideal ice lenses for

The growth of ice lens isdependent on supercooling of the growth surface.

The freezing rate influences the icelens growth more than temperature gradient.

It is suggested that freezing rate,

supercooling degree at growth surface of ice lens and particle condition near growing
ice lens were important factors for considering ice lensing model.

(2) From theobservation of ice interface in water with dispersed glass particles, the criteria forexclusion and encapsulation of particles during ice formation with respect to particle
size and freezing rate was shown.

The relationship between particle size and criticalfreezing rate was explained by Köber’s theory.

It is suggested that the critical freezing

rate was important for the generation of ice lens.

(3) Microstructure in the vicinity ofice lens is observed using Raman spectroscopy.

No ice was found in any pore warmer

than the warmest ice lens in the porous media and the ice lens grew without penetrating
the warmer pores.
Based on the experimental results, a model for simulating the formation of ice
lenses during freezing of unconfined uniform porous media was presented in chapter 7.
This model is based on the freezing rate, the temperature at the growth surface of the icelens, and the change in the critical freezing rate due to the change in the number ofparticles near the growing ice.

The simulating location, growth, and formation of anintermittent layer of ice lenses using this model were good agreement with experimentalresults.
As mentioned above, we clarified the microstructure near the freezing front inwater-saturated porous media experimentally and made a model, which can explain theformation of intermittent layers of ice lenses.

- 120 -