The Experimental Study On Soil Crack Expansion Development And The Infiltration Characteristics Of Hefei Area

The largest proportion and change degree of urban rainfall is infiltration flow,especially the city of Hefei is located in the expansive soil which is the specialgeological conditions. It become expansion when under the influence of water,andfracture when loss water according to evaporative, this characteristics effect on thepermeability of soil, and make it different.With the expanding of the urbanization,more and more impervious underlying surface lead to some negative factors about theconvergence of rainfall. At present, urban rainfall mainly shunt for three aspects,accumulation, pipe drainage, water and soil infiltration. The phenomenon of theincreased urban hardening roads and road slope, greening, network factors may effecton the local water-logging,especially the heavy rainfall in the south just in the shorttime.At first, the paper takes advantage of the closely related between the uniqueexpansive soil infiltration properties and expansive, fracture in hefei area. Under theclearly condition of dry-wet circulation about expansive soil, understanding of soilmass crack growth rule and the influence on expansive soil permeability, prepare thesample specification standardized, using fixed-point digital cameras to take the fracturediagram, process vector quantization fissure diagram based on MATLAB, descripe itscrack changes quantitationly. Then, use the artificial rainfall simulator which is designby self and test standard before, complete the research of runoff and seepage about thetwo different underlaying surface which are the hardening of city impermeablepavement and naked expansive soil in front of the city development.Finally comparedthe runoff of the increase city hardening impervious facing the influence of surface.Analysis the whole process of the experiment and frequency of fracture which isobtained with MATLAB final disposal, we can get the conclusion that at the beginningof the fracture, before the paragraphs fissure formation throughout the body, the soilcan increase penetration when it suction, and maintain the water storage capacity, butwhen dry-wet cycles continue to increase, it will cause the soil increased internal formthrough cracks and crack width and length, resulting in loss of stability of soil and lost the ability of rain water. The alternate weather of dry-wet in summer, therefore,appropriately improve the moisture content of city of bare soil, green and etc. incontinuous sunny hot dry to can maintain its water storage capacity, it also can ease thesudden rainstorm runoff peak and forming time.The rainfall characteristics, raindrop size and uniformity of analysis are basicallymeet the demand of experiment research about the simplified laboratory smaller nozzle,spray slot under artificial rainfall simulator which is design and assemble by self.Compared impervious underlying surface with naked expansive soil runoffchange in city short time rainstorm cases, we found that impervious underlying surfacethat torrential rains in the early rain aquatic product flow time is shorter, faster,confluence time faster about form stable runoff, runoff quantity is larger, but after therain stopped,the cutting curve and naked expansive soil were similar, the change inrainfall intensity is relatively small or the slope slower, the reflect is more significant.Therefore, in certain extent, the urban impervious surface increasing caused local innercity under the heavy rainfall. Appropriate maintain the original state of soil or usingpermeable underlying surface in the appropriate area, it can be eased on the runoffdrainage pipe pressure in peak time and peak.This paper uses vector quantization to deal with the quantitative analysis of thesurface crack growth and the relationship between its stability co-efficient ofpermeability according to the map tools of MATLAB. We can know more clearlyabout the changes of soil permeability in the process of dry-wet circulation, andexploring runoff and infiltration capacity in different rainfall intensity, duration, soilinitial moisture content under the condition of expansive soil and imperviousunderlying surface combining with the development of simplified laboratory smallernozzle artificial rainfall simulator. Built coefficient relationship curve about a typicalarea of runoff, and analysis quantitatively for the expansive soil infiltration of rainfallinterception, it provides the basis of reducing drainage of drainage pipe networkpressure.