Research On Critical Failure Mode And Instability Criterion Of Underwater Cast-in-place Grouting Pad In Flooded Shaft

Due to complex hydrogeological conditions in the process of digging and building deep shaft,water inrush and flooding in the shaft often occur.The design and construction of underwater grouting pad is a common measure to control the water inrush in the shaft and repair the flooded shaft.For the flooded wellbore with deep water inrush point and filled with yellow mud and gravel at the bottom hole,it is expected that the underwater grouting pad made of microexpansible composite cement slurry can shorten the construction period and reduce the construction cost relatively.By means of theoretical analysis,laboratory test,model test,numerical simulation and application case analysis,this thesis carried out an in-depth study on the critical failure mode and instability criterion of underwater grouting pad,and mainly reached the following conclusions:(1)Based on the collection and analysis of engineering cases related to underwater grouting pad,the construction process of underwater grouting pad is put forward,which takes bottom hole filling → slurry selection → underwater pouring as the specific construction steps.The stress mode of underwater grouting pad is analyzed,and the failure mechanism of underwater grouting pad is explored by referring to Muttoni’s critical shear crack theory and hydraulic cracking method.The relevant formula for calculating the critical failure value of the stop pad is derived.(2)Orthogonal test method was used to select 16 groups of composite cement grout with mix ratio to carry out the compressive and shear strength test,free expansion rate test and grout anti-dispersion test of grout stone body.In order to ensure that the underwater grouting pad has a certain strength,good expansion and anti-dispersion.The composite cement grout with effluent cement ratio of 0.6,bentonite content of 6% and anti-dispersant content of 3% is selected as the material for the construction of underwater grouting pad.(3)The indoor physical model test system of grouting pad under current watering is designed and constructed by ourselves,including wellbore model,injection equipment,water pressure and strain monitoring system.The failure test process of water plugging caused by the failure of underwater grouting pad with different thicknesses under the action of stable and continuous water pressure was simulated,and the critical failure mode of underwater grouting pad was revealed: The first is that the body of the underwater stop grouting pad is damaged by punching and the second is that the boundary of the underwater stop grouting pad is broken by splitting.The analysis of the internal and boundary strain monitoring data of the grouting pad shows that using the composite cement grout with micro-expansion to construct the underwater grouting pad can improve the safety and economy of the flooded wellbore in the process of water damage control.(4)By analyzing the force model and punching failure criterion of underwater grouting pad,the critical punching failure formula of cylindrical underwater grouting pad was deduced,and verified by laboratory model test Based on the numerical simulation,the correlation between the thickness of the sealing pad and the compressive capacity of the sealing pad under the fracturing failure of the contact boundary between the sealing pad and the shaft wall was analyzed.Combined with the theory and the laboratory model test,the safety factor of the underwater sealing pad without splitting failure was 1.3.This thesis incudes 57 figures,16 tables and 86 references.