Study On Double Row Reinforcement Jet Grouting Pile Supporting Pit Stability

At present, the use of underground space development and get an unprecedenteddevelopment， the design and construction of foundation pit level improvecontinuously, excavation method is more and more advanced, the supporting methodalso all kinds, new supporting structure are endless. Double row reinforcement jetgroutin, in the jet grouting pile and double row pile supporting development on thebasis of mature, through the in jet grouting pile on in two rows of steel pipe, form acomposite support structure, solve the construction problems of insufficient over theline, to ensure the construction safety smooth.In this paper, guangzhou science cityroad tunnel engineering electric power circle the double row reinforcement jetgrouting pile as the background, with the current study is less, there is no criterioncan to be taken an examination, with reference to general SMW pile constructionmethods, general SMW methods to pile, jet grouting pile and double row pile methodof study,for this new supporting structure for research, for the subsequent engineeringdesign and research to provide the reference.Methods according to the design of pile SMW checking methods, the use ofrelying on the phosphor tongjishuguang soft is engineering analysis, the result canmeet the safety requirements, and is designed to provide parameters is roughly same,also found that all safety coefficient is not high, when construction must be strictlyaccording to the design depth excavation and supporting in time. Foundation pitexcavation near the surface of pile soil and the bending moment horizontaldisplacement bigger, design should be considered when the bottom of foundation pitare strengthened, and the largest occurred in the basal below shear in certain depth,show that the reinforcement pile soil, improve the shear capacity is very necessary.Based on FLAC-3D to establish the two row reinforcement jet grouting pilefoundation pit supporting model, the calculation results show that the maximumhorizontal displacement of foundation soil in the basal happened near, the pilemaximum bending moment distribution in the basement and nearby, the calculatedresults and checking the similar design. On the rigid connection of former and backpile, in the second way support (3.5m depth) in foundation pit level rigid connectionsoil displacement is relatively small, rigid connection position appropriate is set inthe second word in support. From the soil horizontal displacement control, reasonablearrangement of the pile length of former and back pile when the pile length forcorolla12m; Before and after the pile length is not equal, advised by their short formafter long before decorate; the foundation soil reinforcement, choose the reinforcement of priority basement way.Based on FLAC-3D consider under the action of soil arch calculation results,When engineering design conditions reasonable pile spacing shoulds not be greaterthan5d (d is the reinforcing steel pipe diameter);When the local surface overload for25kPa, biggest pile spacing should be not exceed5d; When the local surfaceoverload for50kPa, the biggest pile spacing should be not more than4d; In the pilespacing for6d, ground overload for10kPa conditions friction angle of pile soil more than26°to increase between horizontal displacement the impact is small; whenthe reduced to16°,horizontal displacement between pile soil increased obviously;Pile diameter of the maximum principal stress arch effect is small, practical projectsnot only on pile diameter increase to improve support ability.The foundation pit excavation in soil regional support horizontal displacementand ground surface settlement greatest influence soil horizontal displacement offoundation pit depth development form and stiffness of the support structure has thevery big relations, steel sheet pile and reinforced jet grouting pile because of pilebody stiffness smaller, the basement excavated plane horizontal displacement is nearother parts. In considering water pressure, crown beam, ground overload andconstruction factors conditions, this paper reinforcement jet grouting pile simulationresults and monitoring, design a similar checking, the research result has certainreference value to the project.