Permafrost

consists of 14 ultrasonic sensors working at a frequency of 400 kHz. Each sensor can serve as
either a transmitter or a receiver. The ultrasonic scanning process starts by initiating a P-wave
pulse from one ultrasonic senor serving as a transmitter and using the remaining 13 sensors as
receivers. The scanning continues with one transmitter at a time until all 14 sensors are covered
and a total of 14x13 = 182 ray paths are tested. The signal first arrival times are determined and
the average sonic wave velocity for each ray path is computed. A sonic velocity tomogram is
then generated by a computer program and displayed in color contour maps.
In the study, a frost heave test model is constructed with a 50 mm pipe buried in fully
saturated artificial soil, as shown in Figure 1. Fourteen ultrasonic sensors are buried in the soil
in circular pattern surrounding the chilled pipe to observe the frost bulb and freezing front
development, and LVDT’s are placed on top of the model to measure the frost heave. The test
model is placed in a cold room with the temperature set at 2°C and chilled liquid with a
temperature of -10°C is circulated through the buried pipe. Ultrasonic scans are conducted at
preset time intervals and a P-wave velocity tomogram is constructed for each scanning. The
dynamic process of frost bulb development and the freezing front movement are clearly
observed in the experiments. The experiments are also conducted under various loading
conditions to observe the relationship between loading pressure and the frost bulb and freezing
front growing. Analyses are conducted to determine the dependency of frost bulb and frost
heave development on various parameters.
Key words: Laboratory observation, dynamic frost bulb and frost heave, computerized
ultrasonic tomography
30
General Systematics of Engineering Cryolithology
I.E. Guryanov
(Melnikov Permafrost Institute SB RAS, Yakutsk, Russia)
Abstract: The paper presents the systematics of engineering cryolithology, a discipline dealing
with the development of mechanical properties of perennially frozen ground. The focus of
investigation is on perennially frozen, primarily sedimentary, materials of the lithosphere
represented at various structural levels by rocks, genetic types of sediments and cryogenic
formations. The latter are viewed as the result of cryolithogenesis in its specific varieties
corresponding to the combined effect of various environmental factors. Three types of the
factors – thermal, climatic and tectonic – in various combinations reproduce all possible kinds
of lithogenesis and cryolithogenesis.
The concept ground is used following V.A. Obruchev’s definition to designate any earth
material with certain engineering properties which allows us to approach the development of
various features of the ground as a single engineering superstratum at all structural levels of
sediments, such as rocks, genetic types and cryogenic formations. At the level of rocks, mineral
disintegration of rocks and universalization of grain size distribution and structure of the ground
occurs. At the level of genetic types, cryogenic factors smooth the structure of the ground,