| Under the background of the strategy of building a strong traffic country,Chinese highway construction has entered a stage of rapid development,and the focus of construction has gradually shifted to the western region.In recent years,complex geology emerges one after another in the process of highway tunnel construction in China.The Tertiary water-rich semi-diagenetic sandstone stratum is one of the extremely complex strata encountered in tunnel construction.This stratum has the engineering characteristics of low diagenesis intensity,poor cementation ability and water softening,which has become a major problem in tunnel construction.This paper takes the Tertiary water-rich semi-diagenetic sandstone section of Wangjiazhai Tunnel on Linqing Expressway as the research object,and demonstrates the applicability of horizontal high pressure jet grouting pile in the Tertiary water-rich semi-diagenetic sandstone tunnel.Through shear strength test of sandy soil under different moisture content and tunnel construction characteristics,the main engineering characteristics of Tertiary semi-diagenetic sandstone tunnel are summarized.Combined with theoretical analysis,numerical simulation and field monitoring,the reinforcement mechanism of horizontal high pressure jet grouting pile and the influence of different design parameters on the reinforcement effect of horizontal high pressure jet grouting pile are expounded.The design parameters of horizontal high pressure jet grouting pile suitable for the water-rich and semi-diagenetic sandstone tunnel of Tertiary system are proposed,and the optimization design method of steel pipe composite structure of horizontal high pressure jet grouting pile is proposed.The main research contents and results are as follows :(1)According to the engineering geological conditions of the Tertiary water-rich and semi-diagenetic sandstone section of Wangjiazhai tunnel,the main technical problems and engineering geological disasters of this kind of geology are summarized.By comparing the advantages,disadvantages and applicability of different advanced reinforcement measures of the tunnel,it is suggested that the horizontal high pressure jet grouting pile should be used for advanced reinforcement of the Tertiary water-rich and semi-diagenetic sandstone tunnel.(2)Through field sampling and laboratory tests,the physical and mechanical properties of sandy soil disturbed by Tertiary water-rich semi-diagenetic sandstone in Wangjiazhai Tunnel are analyzed,and the main engineering characteristics of sandy soil disturbed by Tertiary semi-diagenetic sandstone are summarized.Through the direct shear test under different water contents,the variation law of shear strength of disturbed sandy soil with water content was obtained.The results showed that fine sand accounted for 8.167%(0.075～0.25mm),clay content accounted for 2.033%(18%).The cohesion of sandy soil changes significantly with the change of water content.When the water content of sandstone is greater than 18%(close to saturation),the cohesion of sandy soil decreases sharply.(3)The reinforcement mechanism of horizontal high pressure jet grouting pile in tunnel is expounded,including slurry action and overall reinforcement mechanism.The stress and deformation of surrounding rock before and after the reinforcement of horizontal high pressure jet grouting pile in the Tertiary semi-diagenetic sandstone section of Wangjiazhai tunnel are studied by numerical simulation.The results show that the advanced reinforcement of horizontal high pressure jet grouting pile can effectively limit the stress of surrounding rock and the deformation and settlement of tunnel.The limit water pressure(about 30 m water pressure)of horizontal high pressure jet grouting pile under the conditions of 60 cm pile diameter,10 m pile length,25 cm occlusal thickness and 3m lap length is determined.(4)By establishing the calculation model of horizontal high pressure jet grouting pile with different diameter,length,occlusal thickness and lap length,the stress and deformation of surrounding rock and the change of pile stress under different design parameters are analyzed.The results show that under the condition that the rotary jet grouting pile can withstand the surrounding rock and water pressure,the change of design parameters of rotary jet grouting pile has little influence on the stress and deformation of surrounding rock,and the influence on the reinforcement effect is mainly reflected in the obvious change of pile stress.When the diameter and thickness of rotary jet grouting pile exceed a certain value,the influence on reinforcement effect is limited;if the pile length is too long,the ultimate stress of the pile will increase significantly,and the lap length has little effect.Therefore,the appropriate design value should be selected according to the actual situation.(5)In view of the poor bending and shear capacity of horizontal high pressure jet grouting pile,it is proposed to insert steel pipe before the jet grouting pile is not condensed to form a steel pipe composite structure to improve the bearing capacity of the structure.The numerical simulation proves that the composite structure of jet grouting pile and steel pipe can improve the stress of pile body and give full play to the mechanical advantages of pile body and steel.By studying the stress distribution law of the rotary spray arch shed,the stress of the rotary spray arch shed structure is divided into three main regions : vault(0°～30°),arch shoulder(30°～45°)and side wall(45°～90°).The reasonable arrangement of steel pipes in different regions is proposed.The number of steel pipes is optimized,and the safety of the composite structure is ensured.There is no pipe or less pipe at the side wall.The arch shoulder of the vault should be arranged with an interval of one pipe.When the water pressure increases,it can be appropriately encrypted.(6)Through the field monitoring of the reinforcement section of the horizontal high pressure jet grouting pile,the variation law of the surrounding rock deformation and support force of the tunnel after the reinforcement of the horizontal high pressure jet grouting pile is analyzed.By comparing the field monitoring results with the numerical simulation results,the measured values are slightly larger than the numerical simulation values,but the changing trends of the two are basically the same,indicating the reliability of the numerical simulation.Horizontal high pressure jet grouting pile can play a good reinforcement effect.Under the influence of the beam arch effect of the jet grouting arch shed(transverse arch and longitudinal beam),the surrounding rock pressure of the tunnel,the force of the steel arch and the settlement deformation are effectively controlled.Horizontal high pressure jet grouting pile has good applicability in Tertiary water-rich semi-diagenetic sandstone formation,which can play a good role in sealing groundwater and bearing the load.(7)The application conditions of horizontal high pressure jet grouting pile in Tertiary water-rich semi-diagenetic sandstone tunnel are proposed,including:(1)It is suggested that the groundwater pressure of horizontal high pressure jet grouting pile(plain pile)should not exceed 30m(pile diameter 60 cm,pile length 10 m,occlusal thickness 25 cm,lap length 3m)in Tertiary water-rich semi-diagenetic sandstone tunnel;(2)When the water pressure exceeds 30 m,it is recommended to use the composite structure of horizontal high-pressure rotary jet grouting pile steel pipe for advanced reinforcement.When the water pressure reaches 30-40 m,89mm steel pipe can be used.When the water pressure is greater than 40 m,108mm steel pipe should be used.It is recommended that the water pressure should not exceed 70 m.(3)Before the reinforcement of horizontal high-pressure rotary jet grouting pile,it should be supplemented by drainage in the tunnel or surface pumping measures to maintain the moisture content of surrounding rock below 18% for horizontal high-pressure rotary jet grouting pile;(4)The advance reinforcement of horizontal high-pressure rotary jet grouting pile should be supplemented by radial grouting and locking bolt to reinforce the tunnel side wall,so as to ensure the stability of surrounding rock at the side wall and support rotary jet arch shed. |
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