2 Volumes Final Proceedings - Washington 1984.pdf - IARC Research

CURRENT DEVELOPMENTS IN CHINA ON FROST-HEAVE PROCESSES IN SOILChen XiaobaiInstitute of Glaciology and Cryopedology, Academia SinicaLanzhou, People's Republic of ChinaINTRODUCTIONUp to now, because frost heave and Ice segregationare still important problem in civil engineeringconstruction in northeast and northwestChina, the mechanism of frost heave and water migrationand how to protect structures from frostdamage have been studied in the last few years.There has been good progress in the frostsusceptibilitycriterion of coarse-grained soils;the effect of penetration rate, surcharge stress,and depth to groundwater on frost heave; the basiccharacteristics of tangential, normal, and horizontalfrost heave forces; the effect of allowabledeformation of foundation and rheology of frozensoil on heaving force, the variation of normalheaving force under various foundation areas, andthe application value of the three heaving forces.In the last two years, the energy theory forunsaturated soil has been used to establish a modelof water migration and ice segregation in soilduring freezing, and research experiments are beingperformed both in the laboratory and in thefield.Frost heave is one of the main problems forcivil engineering and road construction in permafrostand seasonally frozen regions, t&peciallyfor hydraulic structures, which usually sufferfrost damage. In recent years, many investigatorshave studied the cryogenic process, frost heave,and the frost heave force, with special attentiongiven to field observations. The author has prepareda general review of the problem in this paper.ACTION OF FROST HEAVEBecause of the needs of engineering construction,the main factors affecting frost-heave processes,such as particle size, frost penetrationrate, effective surcharge stress, and groundwatertable, have been investigated. It is well knownthat, in saturated sand or gravel, water migrationis mainly in response to a pressure gradient.However, for clayey soil, it results from thegradient of soil water potential. The current developmentsare described below.Particle Size and GradingAccording to the current frost susceptibilitycriteria for railway construction, a frozen coarsegrainedsoil in which the content of silt-clayeyparticles is Less than 15% of the total weight doesnot consolidate during thawing. It is the author'sexperience, however, that because permafrost wasformed over a geological period, the. thawing settlementcoefficient of a frozen gravel, whose contentof silt-clayey particles is less than 2.5% ofthe total weight, is more than 12%. In an opensystem (Chen et al. 19SZ), if a saturated sandygravel with uniform grading contains more than 6%siltrclayey particles, its heave ratio will exceed1%; if the silt-clayey particle content is morethan 8-lo%, then its heave ratio will be more than2%. If the sand or gravel has a non-uniform grading,corresponding with above heave ratio, thesilt-clayey particle content is 3-4% and 6-7% oftotal, respectively, Wang (1983) indicated thatIf a coarse-grained soil contains 5% silt-clayeyparticles in open system, its average heave ratiois 1.8%.In the current "Norm of Base and FoundationDesign for Industrial and Civil Engineering Construction"(1975), fine sand Is included in thenon- or weakly frost-susceptible soil category.According to Wang's (1983) results, however, theabove criterion is not complete. Compared withthe content of 0.05-0.005 mm (X,) and 0.1-0.25 mm(X,), Wang Zhengqiu (1980) indicated that the sizeless than 0.005 mm (XI) is the most important factorinfluencing the heave ratio n of fine sand.'Ihe relationship can be expressed byn - 4.48 + 0.62X1 + 0.07X2 - 0.04X1,in which the content of 0.05-0.1 mm particles (X,)does not affect the heave ratio.me results of field observations by the Low-Temperature Construction Institute, HeilongjiangProvince, show that when a clayey soil containsmore than 50% clay particles by weight, Its permeabilityis very low and it might be classified aea weakly frost-suaceptible soil.Penetration RateThe results of Chen et al. (1981) show thatthe penetration rate strongly affects the heaveratio. When the penetration rate is less than thefirst critical limit Vfl, the ratio of frostheave I-, is very large and ice lenses are stronglysegregated. After the penetration rate exceedsthe second critical limit Vf2, however, there isalmost no water migration during freezing, and onlyin-situ pore water freezes. The relation mightbe expressed as follows:when Vfk Vf2, then 11 =segregation;when Vf2 2 Vf2 V fl,= const.; i.e. no icethen n if n' = lo + An [(1/6 - l /G)/(l/fi- 1/4q3]~; i.e. a little ice segregation;55