Permafrost

70
Experimental Study on Solute Transport During Soil Freezing Process
Xiao-fei Chen 1,2 , Wei Ma 1 , You-sheng Deng 1 , Xue-zu Xu 3
(1. State Key Laboratory of Frozen Soil Engineering, Chinese Academy of Sciences, Lanzhou 730000, China;
2. College of Water Conservancy, Shenyang Agricultural University, Shenyang 110161,China;
3. Department of Civil Engineering, Shaoxing College of Arts and Sciences, Shaoxing 312000, China;)
Abstract: With the development and utilization of cold regions with high latitude or high
elevation, some special engineering problem appeared. For example, structure damage by frost
heave; ground and road subsidence due to the ablation of permafrost layer; the fracture, crash,
ponding, and base damage of road due to frost heave; the pull and rise of bridge pier by frost
heave and the foundation damage of runway and standing apron of airport. In addition, with the
development of modern technology construction, artificial freezing technology have been
widely used in mine shaft digging, tunnel excavation and subway construction, this respect
need us to know more about the frost soil as well.
In the aspect of agriculture and ecological environment: when the soil is frozen, the pore is
plugged by ice,the soil temperature is low, so not only the root of plant can’t growth, but also
the root can be damaged by pull of frost heave. In spring, after the top layer of frozen soil began
thawing, for the sub soil layer is still frozen, the permeability is very low, the thawed water
can’t infiltrate through it, the surface runoff will be easily formed, the soil loss and slop wash
will occur, especially because of the shearing strength of soil has been weaken by freezing and
thawing function, erodibility of soil is strong, therefore serious freeze-thaw erosion of soil will
appear. In the other hand, the solute will be carried by the transport of water from the lower
layer to the up layer during soil freezing, and take a secondarily rising to the soil surface due to
the strong water evaporation of surface soil in spring, so the secondary salinization or
alkalization will be caused by freeze-thaw action. In addition, the atmospheric change and
human activity make the very weak ecological environment change rapidly of the regions with
frost soil permanently, seasonally, or instantaneously, such as vegetation degeneration and
desertification. Consequently the existence, change of frost soil have important influence on the
living environment, productive activity and sustainable development of human being as a kind
of territory resources, low temperature environment of engineering foundation, and constructive
material.
In order to solve these problem related to frost soil, the mechanism of freeze and thaw of
soil must be studied in detail, and the heat, water and solute transport regularity during freezing
and thawing is a important content in it, because the frost heave or thawing subsidence problem
substantially belong to the heat and mass transport problem. The former researches are mainly
conducted about the normal solutes appeared in saline or alkaline soils. With the increase of the
amount of fertilizer used in agriculture, the study on the transport rule of plant nutrients during
freezing and thawing became necessary and important in frost soil field. Therefore, in this paper,
the transport rule of plant nutrients including (NH4)2SO4, KH2PO4 and KCl during freezing of
Brown soil is studied experimentally.
(1) For the specimens put with (NH4)2SO4 solution: the redistribution extent of NH4 + after
freeze is low, this suggested that the kept amount of it by brown soil is big. The NO3 - increase
from the cold side to the warm side obviously,reversing to the direction of water transport, this