Study On Mechanical Properties And Quality Inspection Method Of The Composite Lining Of The Joint Construction Tunnel Using Shield And Mining Method

In order to investigate the influence of construction quality of composite lining on its performance in joint construction tunnel combining shield method and mining method,this study relies on section 1012-1B of Shenzhen Metro Line 10 to conduct the research.First,quality defects of each layer which will occur in construction procedure was discussed according to the construction technology of joint construction tunnel.Second,influence of the void on mechanical properties of composite lining and the shield machine thrust on the waterproof performance of composite lining were analyzed using theoretical analysis method and numerical simulation method.Finally,the construction quality of composite lining was tested by intelligent detection instrument and the quality control measures of composite lining were put forward.The major results of this study are summarized as follows:(1)The composite lining is composed of primary support,backfill layer and segment layer.In the construction of the primary support,over excavation and under excavation are easy to occur.Over excavation will affect the construction quality of the backfill layer,and under excavation will affect the construction process of the segment layer.During the construction of backfill layer,lots of construction quality problems will occur,such as uneven wrapping of pea gravel and slurry,no wrapping of pea gravel with slurry and so on.In addition,the backfill layer is also prone to exist single void or void area,which will affect the mechanical properties of composite lining.In the construction of segment layer,it is easy to cause insufficient compression of segment ring joint due to insufficient thrust of shield machine,which will affect the waterproof performance of composite lining.(2)When void area occurs at the top of backfill layer,the bending moment at the top of segment changes from positive to negative.With the increase of void area,the negative bending moment gradually increases.After the negative bending moment reaches the maximum value,it gradually decreases to zero.And the axial force at the top of segment decreases with the increase of void area.When a single void appears in the primary support and backfill layer,the maximum axial force and the maximum bending moment in the segment increase with the increase of the diameter of the void.when the same void appears in different positions,the influence area on the internal force of the segment is different.The void at the top of the segment and the right side of the segment have more influence on the internal force of segment than that between the top and the right side of the segment.(3)Under the 5000 kN thrust of shield machine,the compression of the rubber gasket is about 5.4 mm by using the linear elastic constitutive model in theoretical calculation,and about 5.1 mm by using the hyperplastic constitutive relationship in numerical simulation.The numerical simulation shows that when the amount of compression is small,the thrust is proportional to the amount of compression.However,when the amount of compression is greater than a certain value,the slope of the relationship curve increases.Under the 5000 kN thrust of shield machine,the rubber gasket can resist the water pressure of 0.37 MPa.The numerical simulation results show that under the condition of small compression,the waterproof performance is basically proportional to the compression.However,the slope of the relationship curve increases with the increase of compression.(4)The over and under excavation of the primary support is serious.All sections of 34 analysis sections have over excavation parts,with the maximum over excavation amount of 70 cm.14 sections have under excavation parts,with the maximum under excavation amount of 22 cm.The construction quality of backfill layer is good,and no single void or void area is found.(5)To improve the compactness of the backfill layer,secondary grouting in the process of shield propulsion can be adopted,so as to avoid the occurrence of single void and void areas.To increase the thrust of shield machine,pea gravel can be filled and jacks can be installed in front of the cutter head of the shield machine,which will increase the circumferential compactness of the segments and ensure the waterproof performance of composite lining.