| Karst geomorphology has great influence to the stability of foundation, which is always a big issue plaguing the construction. Therefore, it is significant to research the development law of Karst geomorphology, and find effective treatment. This paper sets underground cave of Luguhu Airport Platform as the research object. Basing on site investigation and geological survey, focusing on the growth feature and foundation stability analysis, this research finds out the stability of Karst foundation under external load conditions. Qualitative analysis, quantitative analysis and numerical simulation method were used in this study. Major contents and suggestions are as follows:1. The karst status on surface are as follows in research district: clint, melting groove, melting tank, karst dolines, sinkholes and so on, while the karst growth under earth are concealed district,melting groove, dissolution pore,dissolved fissure , and karst cave etc. Karst collapse and dolines have their own growth characteristic, which grow stronger in the folded axis area nearby, and the central part grows stronger than north and south. The underground karst cave in research area is mainly the round, oval cave, and multi-cavity basing on these two types. Horizontal multi-cavity grows on concentrated parts. The underground Karst caves always fold in core parts on the point of distribution in plane, while develop strong under earth. It often presents big caves in large diameter, along with thin roof.2. Karst growth is effected by many factors in research areas. Firstly, Lithology, joints and fractures control its development degree, which lead to crystalline limestone and fractured longitudinal. Completely crystallized crystalline limestone in northeast grow weak, and the same with siliceous limestone in southwest. However, the bioclastic limestone and fine-grained limestone in central part grow very well. Secondly, geological structure effects its development trends. Karst cave on surface and underground always grow fast along the folded axis, and has its own direction. Karst depressions and karst major funnel axis is consistent with the structural alignment. Underground cave grows mainly on the folded line. Thirdly, the water also influent the development of karst cave. Karst collapse and dolines grows strong in centralized location of surface water.3. Collapse problems in research district are caused by earth dissolving and roof broking. As the crystalline limestone and the fracture of axis of fold lines grows in different degree, surface water varies, the collapse develop uneven. Northeast and southwest are mainly the melting groove on surface and a small amount of funnel with no growth. The central part is mainly the dissolves funnel, soil cave and sinkholes, which are in large scale, bead-like and well developed.4. There are many factors influencing the stability of karst base: joints distribution, strength of rock, altitude of bed, cave style,burial conditions, load form and size, groundwater, filling in cave and so on . Those factors push different effects on the base stability. According to drilling profile, this study promotes a better roof thickNess basing on the most representative cave , common plane loads, building Load and other factors. This paper also sets qualitative evaluation system, and gave sound evaluation to the stability of the karst base. The results are consistent with the semi-quantitative evaluation,which suggests this qualitative evaluation system is practical and credible.5. On the basis of karst cave distortion conceptualism,this study evaluates kast cave with a variety of mechanical semi-quantitative calculation and finds out the stability status of karst cave under outside pressure in research areas. That is ,the stability of karst cave roof in research district are in good condition. There are only 79 caves unstable. Comparing the 275 caves in this study, unstable caves accounts to 33.5% in total.6. ABAQUS software is used by Moore Coulomb elastic plastic model and numerical modeling methods in the research area, focusing on single typical cave and stability of multi-layer caves. The results are consistent with the semi-quantitative evaluation,which suggests the semi-quantitative conclusions can give good guidance in study.7. This paper also presents relative methods for collapse problems, stability of karst cave in research district. Treatment of collapse could be combining backfill, compaction and grouting basing on good drainage. Concrete Filling is also practical. For lower caves in deep extension, reinforced concrete beam is recommended for overlapping the cave. |
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