Experimental Study On Action Mechanism Of Uplift On The Underground Structure In Beijing

The development of the underground space of city makes the foundation ofthe building buried deeply constantly. It also brings about lots of groundwaterquestions. The dynamic change of the groundwater is restricting the securityoperation of the underground project strongly , the uplift and lateral pressurecreated by which are particularly remarkable on the underground structures.Because the stratum of different areas change greatly, and the type , structure andfoundation of a building have nothing in common with each other, the groundwaterstoring and seepage state impacting on foundation works seriously. Although thedesigner has already paid enough attention to the buoyancy question at present,there is no better methods on the design and evaluation about anti-floating problemfor lacking of theoretical foundation , practical design methods and gist obtainingfrom in-site survey. Therefore it is still difficult to confirm the exact value of theuplift load impacting on the underground structure. So it either causes the potentialsafety hazard in the design of underground structure , or causes wasting in economy.In view of this, this text relies on the anti-floating and optimization question ofunderground structure about skyscraper and large-scale public service in Beijing ,and study the action mechanism between groundwater and the undergroundstructure . It also put forward new methods to calculate the uplift load impacting onthe motherboard of the underground structure and to confirm the anti-floating waterlevel in reason .In addition , it can save project invest effectively base on thepremise of safety . First of all, this text systematically analyse the characteristic of typical stratum,hydrogeological characteristic and engineering geological condition in main urbanarea of Beijing , study the storing, transporting , and seepage of groundwater , andanalyse the factor that influences the dynamic law of groundwater. In addition, bycombining the typical underground structural characteristic in Beijing area, the textgeneralize the hydrogeological conceptual model reflecting the action mechanismbetween groundwater and the underground structure. Secondly, on the basis of thegeological conceptual model that is set up, the model experimental devices about'study of the uplift acting on underground structure 'have been developed. fivekinds of experimental operating modes have been designed to study the transferringregulation of pore water pressure and the transformation of the uplift acting onmodel motherboard under different strata and water bearing bed condition , andunder different supply way of groundwater .And then the text analysed thefunction mechanism of the uplift. Moreover, the in-site experiment has been carriedout depend on the practical project, and through monitoring pore water pressure fora long time in construction site, the distribution law of pore water pressure andcorresponding relation of theory quiet water pressure strength has been found out.And the hydrogeological contact law among different water bearing bed has beenanalysed to further study the function mechanism of the underground structuraluplift. Finally, according to the research results obtained from the modelexperiment and the in-site test, and combining regional weather andhydrogeological data, through ARMA the groundwater level in building site hasbeen predicted to discuss how to compute the uplift acting on motherboard ofbasement and solve the practical problem directly. So the reliable experimentalbasis and theory can be offered for the anti-floating design of undergroundstructure.