Study On Mechanical Properties And Engineering Application Of Micro-pile-soil Nail Composite Support Structure

The micro-pile composite soil-nail support structure is a type of composite support structure,which is generally composed of micro-piles,crown beams,soil-nails,surface layers,original soil and other parts,forming a certain shear,tensile,and bending resistance,a composite support system of pressure resistance.The system is suitable for the situation where the soil is loose and has poor ability of self-support,the deformation of the foundation pit has certain control requirements,or the slope top has a large construction load.Because of its low cost,simple and fast construction,low requirements for site operation surface,and can meet certain safety performance,it has been widely used and developed in construction engineering.Recently,the micro-pile composite soil-nail supporting structure has been applied in actual engineering.At present,there is no mature calculation system.In the design of foundation pit supporting engineering,the micro-pile,soil-nail,crown beam,The influence of the deformation of the soil inside and outside the foundation pit and other factors has not taken into account the impact of the construction load on various factors.Therefore,it is of great practical significance to study the mechanical characteristics of the micro-pile soil-nail composite supporting structure during construction to verify the safety and applicability of this type of supporting structure.This article takes the foundation pit project of a health industrial park in Changsha as the background,calculates,designs and verifies the foundation pit supporting scheme using the rational structural design software,and combines the MIDAS GTS finite element software to support the micro-pile soil nailing structure system.The mechanical properties during the construction process were studied and some meaningful conclusions were obtained.Overall deployment of the actual application of the project to provide a certain reference value for similar projects in the future.Here are the main research purposes of this article:(1)Type selection and design of micro-pile soil-nail composite support structure.Detailed analysis of topography,stratum lithology,hydrogeological conditions,according to the characteristics of the back side of the foundation pit as an urban municipal road,no sloping space,etc.Refer to relevant design requirements and specifications,and scientifically select and design the foundation pit support plan.Using the software for designing the supporting structure of deep foundation pits,adding parameters such as slope line,soil layer,overload,soil-nails,flower tubes,etc.,the results of the uplift bearing capacity of the foundation pit support are calculated and designed.(2)Research on deformation and mechanical characteristics of micro-pile soil-nail composite supporting structure during construction.The deformation displacement of the crown beam,micro-pile,soil-nails,and the soil inside and outside the foundation pit all increase with the increase of the excavation depth.The deformation displacement of the crown beam is much smaller than that of the foundation pit without support;At the bottom,the maximum vertical displacement is near the top of the pile;the horizontal and vertical deformation displacements of the soil nails are basically linear,located at the end of the soil-nails;the deformation of the soil outside the foundation pit is mainly settlement,from the foundation The edges gradually increase and then gradually decrease,forming a funnel shape;the soil in the foundation pit basically shows uplift.(3)Study on the effect of construction excavation on the slope of foundation pit.With the gradual increase of the excavation depth,the horizontal and vertical deformation of the slope gradually increased,but the deformation value of the slope in the four working conditions of foundation pit excavation is less than the standard alarm value,indicating that the micro piles,soil-nails,crown beams The interaction of equal support structures can effectively limit the deformation of the slope.(4)Study on the deformation and mechanical characteristics of the micro-pile soil-nail composite support structure under the influence of construction load at the pit side.After the construction load is increased,the crown beam is deformed horizontally toward the inside of the foundation pit,and the vertical deformation is reduced,and the relationship between the main stress line shape of the crown beam is increased.The lateral deformation is reduced,the main tensile stress of the micro-pile fluctuates in a certain interval,and the main compressive stress is linearly increased.After the construction load is increased,the soil-nails have horizontal deformation inside the foundation pit,vertical deformation decreases,and the soil-nail axis Both the force and the main tensile stress showed a linear growth trend;the vertical deformation of the soil outside the foundation pit showed a linear growth trend with the increase of the construction load,and the vertical deformation of the soil inside the foundation pit was less affected by the construction load.