Study On Water Resistance Piles And Compaction Piles Foundation Treatment On Deep Layer Strong Collapsible Loess

Relying on the Baoji-Lanzhou passenger dedicated line,in the view of the problem on subgrade slope foot`s water infiltration and roadbed deformation or failure in the deep layer loess area,this paper puts forward to create design which is to set continuous the high pressure block water jet grouting pile and combined with compaction pile composite foundation between the high rail base slope foot position and the drain.This method can avoid the conventional foundation treatment method in the deep layer of collapsible loess area,while in the process of high cost,time consuming and difficult disadvantages,in order to control of subgrade slope toe basal loess collapsibility deformation caused by water seepage.Without considering the loess itself under the premise of crack development and the underground water level change,rainfall and soil on the collapsible loess partition index were analyzed and summarized,through the method of numerical simulation,it is concluded that the different collapsible loess infiltration depth of partition.Through the indoor model test and numerical simulation method,considering working three conditions which is the deep layer of collapsible loess foundation,compaction pile composite foundation and block water+the compaction pile composite foundation,subgrade slope rainfall precipitation infiltration in the process of wetting front of subgrade base and development situation of wet areas and the settlement of roadbed foundation in different observation position variation characteristics,and get the following conclusion.?1?The impermeability of water soil material is affected by age,cement incorporation ratio and initial hydraulic gradientIt by laboratory experiments.Cement-soil material saturated remodeling loess pervasion ability is strong,the permeability coefficient is saturated remodeling loess 102¹03 times,in 10%mixture ratio,age 28 days,minimum permeability coefficient is 2.23×10^-7 cm·s-1,to meet the requirements of as seepage control material,the most economical cost.?2?Without considering the change of groundwater level,rainfall becomes the main factor affecting the seepage and destruction of subgrade.The results obtained are analyzed according to precipitation and soil parameters of collapsible loess subdivision:influence of rainfall infiltration extends to 5m below the surface,saturated soil generally reach to 2 m above,subgrade waterproof seepage need to focus on the treatment of soil within 5 m below the surface.?3?Through the indoor test method,the bearing capacity of the natural loess foundation with deep layer and strong collapsibility is low.According to model similarity ratio 1:50,deformation maximum can reach 28 mm.In practical engineering,it can not be used directly as the high iron foundation;In the experiment,when the slope of the subgrade slope of the natural loess subgrade was seepage,the seepage flow of the soil under the basement was serious and the development of the humid region was severe due to the unimpeded water constraint.The area can reach 790 cm2,the diffusion distance of wetting front can be up to 27 cm,the area of humid area under the actual base is up to 198.75 m2,and the wetting front has a diffusion distance of 13.5 m.The actual subsidence deformation on both sides of the roadbed can reach 235 mm,and the soil is cracked and the whole structure is badly damaged.When unsaturated,the bearing capacity and deformation condition of natural loess do not meet the specification requirements;In the process of water immersion,the subgrade of the subgrade is restricted by unimpeded water,and the wet area develops rapidly,and the deformation of wet subsidence is very large,which can not be used directly in the project.?4?The compacted pile composite foundation can effectively improve the bearing capacity of the natural loess foundation,and the settlement amount is 4.7mm when the foundation slope is not immersed in water.When the actual processing depth is 8¹0 m,it meets the requirement of high speed railway foundation bearing deformation.When water seepage and seepage slope foot range in the range of compaction pile treatment,water permeability resistance ability effect is improved,the development of wetting front and wet area under basal more slowly,from natural soil seepage time extending;With the increase of seepage flow,the seepage range expanded and the water resistance capacity of the extruded pile decreased gradually.The forward distance and wet area of the wetting front in the basement increased significantly,and the deformation of the roadbed was obvious.The further diffusion of wetting front and wetting area can be further inhibited by increasing the depth of pile foundation.Compaction pile composite foundation is still in the process of subgrade slope infiltration the collapse deformation happens is larger,the actual maximum subsidence of up to 200 mm,can meet the specification of high railway base post-construction settlement is less than 15 mm.Only by increasing the processing depth of the compacted pile can not control the deformation of the base loess.?5?In the composite foundation of water resistance and compaction pile,the bearing capacity and deformation control are satisfied when the foundation slope is not submerged.When the water was immersed,the seepage path of the seepage water of the slope was changed due to the constraint of the water resistance pile,and the seepage from the direct to subgrade base was changed to infiltration of the subgrade base by the water resistance pile.With the increase of the processing of water resistance of pile length,seepage path,experiment basement bottom soil wetting front advancing distance from 27 cm to 2 cm,actual wetting front position by basement under 13.5 m to 1 m,wet area smaller area of 198.75 m² to 1.25 m².The development of the wet area was suppressed,the settlement amount was controlled,and the treatment depth of the water resistance pile reached 20 m,and the actual settlement value of the roadbed met the requirements of the standard 15mm.The depth of pile foundation treatment can be reduced by increasing the treatment depth of water resistance pile.The effect of water resistance and water resistance on the composite foundation is better than that of compacted pile composite foundation.?6?Through strength subtraction,the three kinds of working conditions,embankment slope toe drain seepage and stack subsidence deformation numerical simulation analysis,block water+compaction pile composite foundation under the change of seepage control effect is superior to natural background and compaction pile composite foundation during the 60 h rainfall.Setting the block water pile can ensure subgrade base wetting front location which is limited in the pile lateral resistance of water,and improve roadbed ground water seepage resistance performance,while the collapsible deformation of embankment settlement can greatly reduce range from more than 250 mm to 15 mm at the same time.Taking into account the control of seepage,the waterproof and deformation of bearing capacity,water retaining and compaction pile composite foundation effectively improves the performance of deep collapsible loess.develop the soil environment,ensure the stability of road base and strongthen the safety and durability of the operation of high-speed rail lines.Baoji-Lanzhou Passenger Dedicated Line has been operated for one year,the line is operating normally and the sedimentational value after construction meets the specification requirements.It is hoped that the research in this paper will have implication on the future treatment of deep collapsible loess foundations.