Experimental Research On Envelope Monitor Of Deep Foundation Pit

With the development of economic construction in our nation,the construction of infrastructure in our country is at the continuous raising speed.During this course,lots of deep foundation pit engineering appear.Deep foundation pit engineering is a very complex system engineering,involved with various interdisciplinaries,such as,geotechnical engineering, structural engineering and construction technology.And each factor has cross influence on others.As for the foundation pit envelope,it has great influence on foundation construction safety.Therefore, support engineering of deep foundation pit is much more emphasized. However,many problems exist in foundation support structure,such as strength,deformation,stability and interaction between soil and support structures.As the same time,complexity and uncertainty of civil engineering properties and difference between calculation model in soil mechanics and actual situation make much more complex and uncertainty to calculation and analysis of deep foundation support struction.So there are many problems of deep foundation support engineering in engineering practice of excavation.Therefore,it's very important of construction safety of deep foundation pit to monitor the support engineering during the construction period.At present,monitor during the construction period is carried out in most deep foundation pit engineering.By setting the control value of monitoring projects, related units are warned to take countermeasures when the monitoring value is more than the control value.Monitor plays a very important pole in making sure the safety of foundation construction and surrounding environment.But most monitoring units pay attention to instrument installation,data acquisition,data analysis and feedback.And it can only settle for data collection,data report submission,easy analysis and giving alarm judging by whether monitoring value is more than the control value.What's more, sufficient and further theoretical analysis of monitoring results can not be carried out combined with construction and geological condition.It has serious shortages in data prediction,especially.Therefore,most foundation monitoring work plays simple feedback effect.These cause that monitoring work,costing lots of human and material resources,can't be made full use of to carry out optimized design and timely feedback to lead construction.Meanwhile,in practical monitoring work,foundation construction has great influence on monitoring work.Monitoring work has complex programs,and failure or error can't be avoided.It can lead to error datas,and even gross errors when the influence is great.Therefore,it has great research significance of how to use advanced mathematical means to identify and check monitoring datas and reject accidental errors,in order to improve the accuracy and stability of monitoring datas.According to the features of deep foundation pit envelope,monitoring content of envelope is determined and monitoring scheme is also made.Early warning technology of deep foundation envelope is discussed,and the monitoring datas are deeply analyzed.By using the basic principle of grey theory,monitoring prediction model of envelope called GM(1,1) is established.Finally,relying on deep foundation pit project for Chang Chun rail station comprehensive traffic passage transfer center in northern plaza,monitoring technology of deep foundation envelope and data prediction model formed in this paper are used in pratical project and verified.Main research work is carried out as follows:1.Deep foundation pit and envelope are analyzed,and monitoring content of deep foundation envelope is determined basis on theoretical analysis results and corresponding standard.Based on advanced test methods and test instruments,detailed monitoring methods of each test content are made.Tranverse survey is used to make the monitoring scheme of horizontal displacement on pile top;Based on measuring principle of vibration string concrete strain meter,monitoring scheme of strain in fender piles is made;Based on the basic theory of wheatstone bridge,anchor meters are self made to monitor the internal force in anchors.accurately.2.Staring with theoretical analysis and engineering practice,referencing to the standard,early warning scheme of deep foundation envelope is made.According to the changes of external environment,monitoring dates are analyzed comprehensively.Basis on comprehensive analysis of monitoring datas and prediction scheme,force condition of foundation envelope is deeply analyzed,furthermore the stability of the whole foundation is judged.3.Basic principle of grey prediction theory is introduced.Solving theory of the grey model is discussed,and basic calculation is formed for model GM (1 ,1) to carry out prediction of envelope.Under the situation of original datas of prediction model increasing dynamically,strain of fender piles and internal force of anchors are predicted by using model GM (1 ,1).And it can obtain good prediction results.