Research On Karst Growth Law And Foundation Stability Of Some Airport In Lincang, Yunnan Province

The karst region area occupies one-third of China land. Limestone area in theentire southwest region including Yunnan province links a piece with a total area of550000km~2. The growth of karst depraves the project site geological conditions, andleads to the problem of building foundation subsidence, reservoir seepage, etc. Theproposed airport is located in the carbonate rock region where karst growth is in ahigh degree. Study karst growth law and its engineering effect are extremelyimportant to guide the construction of the airport.Based on fully understanding the predecessors karst study, this papersystematically researches the karst growth characteristic, law, mechanism and karstfoundation stability though the field large proportion engineering geological mapping,geophysical prospecting, drilling, geotechnical body physical and mechanicalexperiment, fuzzy comprehensive evaluation and numerical simulation use of theFLAC software. According to the research above, the main conclusions are asfollows:(1) The karst region locates in the position of north-south orientation tableland.Its shape is mainly vertical. Generally, the growth is in medium degree, but it’s strongin valley zone.(2) The geomorphology type in the southwest site is clint monadnock, and it isdissolution and erosion peak-cluster in the medium-northern site. In the mass, thekarst growth of the former is higher than the latter. The karst on surface registers asclint, solution groove and channel, karst funnel, sink hole, etc while the karst growthunder earth is karst cave, soil cave, strong corrosion belt, and so on. Solution grooveand channel, clint distribute in the whole site. There are69funnels and sink holes, andthe linear density is3-5/km. Karst cave is the main fissure type with encountered holes rate of23.59%and karst rate5.99%. Distribution of soil holes is sporadic.(3) In the plane, the karst growth is gradually reduced from southwest tonorthwest. Karst funnel and sink holes are often linear and beaded array. There areseven concentrated distribution areas which interval is300-500m. The strongcorrosion belt is SN-banded distribution in major.(4) In the vertical direction, the layered distribution feature of karst growth isremarkable. Karst funnel and sink holes are centralization growth near1780melevation. At the same times, karst cave and corrosion belt are focus on the1780-1810m elevation. Their growthes gradually decrease to both sides.(5) The growth of the karst is controlled by such factors: formation lithology,geological structure, neoteetonics, climate condition and karst water. Due to thesefactors, the karst growth is regular: dissolved form is uneven dissolution of thedolomitic limestone; karst shape mainly extend north-south and has the feature of"multi-layer","overlay" and "zoning"; geomorphology are zoned along the valley inthe plane; vertical karst dissolution is strong because of the position in groundwatervertical seepage zone.(6) The karst geomorphology expresses as the characteristic of multi-cyclesuperposition growth in the vertical. A karst period can be divided into six stages: theoriginal topography, solution crack and groove, peak-cluster, peak-forest, corrosionalhill and dissolution plain. The feature expresses as contemporaneousheterogeomorphics in the transverse, and it is significant difference.(7) Karst cave with the characteristics of narrow-shaped develops from solutioncrack, and it always grows along joint and level. The most important reason of soilcave growth is the dynamic change of the groundwater. Both critical level amplitudeand critical velocity are the major parameters of soil cave forming. The cave easilygrows in the soft-plastic soil. There are two types of karst funnel and sink holes fromthe causes: corrosion and subsidence. The former is the master.(8) Karst cave is in a more stable state with the result of fuzzy comprehensiveevaluation, and the rate is90%. The evaluation outcome of civilian airport surveyspecification is what karst caves are stable about70%. The calculation result isconservative because it doesn’t take into account of the filling degree of the cave. Thestable rate is91%after amending the specification, and it is consistent with the resultof fuzzy comprehensive evaluation.(9) By numerical simulation with the FLAC software, this paper obtains thefollowing conclusions: the surrounding rock of the cave which roof is buried in shallow and broken is prone to stress concentration, obvious plastic zone and largedisplacement; grouting treatment is better than the way of stepping over.