Study On The Mechanism And Effect Of Grouting Uplift In Underground Construction

There exists inevitable disturbing influence to the surrounding soil during the underground engineering construction.Excessive subsidence causes the deformation of adjacent structures,tunnellings,etc.,such as incline,differential settlement,and may affect the safety and normal use of them.Engineering practices show that grouting is one of the effective measures to strengthen soil,reduce subsidence and uplift structures.Considering of the characteristics for natural soil of layered,heterogeneity and environmental complexity,it is difficult to study the fundamental behavious of grouting by the field test.The indoor model test can study the influence of single factor.Under the specific test conditions,the grouting model test studies the effect of different factors on the grouting in order to study the fundamental behavious of grouting uplift.A series of laboratory grouting tests were conducted to research change rules of the long-term effectiveness of grouting uplift and study the fundamental behavious of grouting uplift under various grouting test conditions by using a set of grouting experimental setup.The results show that grouting in underconsolidated soil could effectively reduce the primary consolidation settlement compared with the corresponding condition without grouting,but had no influence on the secondary consolidation settlement.As the overconsolidation ratio increased,the final grouting efficiency in primary consolidation stage decreased for underconsolidated soil,dropping to the lowest value for normally consolidated soil and then increased for the overconsolidated soil,reaching a limit.Soil structure could effectively improve the long-term effectiveness of grouting uplift,shorten the time of primary consolidation,decrease the secondary consolidation settlement,but increase the peak grouting pressure.The peak grouting pressure was affected by the yield stress and the overlying pressure,and could be predicted with an empirical equation when the overlying pressure was less than the yield stress.For both artificial structured and overconsolidated reconstituted soils,the final grouting efficiency had a limit.The overconsolidated reconstituted soil had a lower yield stress reaching the limit of the final grouting efficiency than the artificial structured soil.Grouting efficiency decreased with the increase of overlying pressure.The grouting efficiency for continue grouting was better than regrouting when the overlying pressure was less than 100 kPa,and was inverse when the overlying pressure was greater than 100 kPa.For the layered soil,grouting in artificial structured soil layer was the most efficient.Moreover,discrete element method(PFC)was applied to simulate fracture grouting.Considering the difficulty of simulating the cracks initiation and development during the process of fracture grouting,a new particle flow model was established to simulate and gave a view of the whole process,which contained cracks initiation,slurry intrusion and development of cracks in the soil.The coupling between the soil particles and “domain” was developed to reflect the process of cracks initiation,and the filling of the particles was adopted to reflect the process of slurry intrusion in the model.The particle flow model was used to analysis and research the problem in fracture grouting uplift engineering.Finally,the project was to artificially uplifting an existing building by grouting under the condition of leakage for the construction of the Tianjin Metro Line 3.In-situ measured data and numerical simulation method were employed to analyze the grouting uplifting effect for existing building,when the tunnel was under the condition of leakage.Based on the numerical simulation,the effect of grouting uplifting and tunnel was analyzed under different grouting locations and time.