Study On Reinforcement Technology And Effect Of Sand Disturbed Stratum

Due to sand excavation of riverbed at a highway bridge,settlement of riverbed occurred,partial riparian collapsed,soil in the riverbed became loose,the soil above the sand pumping layer is in a state of settlement,which leads to disturbed stratum formation.Because of disturbed stratum,original design scheme changed into a new proposal of increasing pile diameter and length.When drilled in the land,reaming and guard barrel dropping often even though took a measure of drilling slowly and with high quality mud protection.Meantime,deep disturbed stratum,large reaming range and deep guard barrel dropping influence pile construction seriously.Based on a highway bridge,this paper determines the method of reinforcing stratum that under special geological conditions for sand excavation by high-pressure rotary jet grouting pile.The method of reinforcing stratum by high-pressure rotary jet grouting pile has perfect reinforced effect,and it also shows the great innovation and practicality;also,analysis of pile's vertical bearing capacity in reinforced condition could provide theoretical reference for practical engineering.Taking drilling and pile before and after disturbed stratum reinforcement into consideration,building the finite element model with standard and ABAQUS to analyze high-pressure rotary jet grouting pile's effect on stability of the hole,analyzing the pile's working characteristics which include axial force and side friction before and after reinforcement with high-pressure rotary jet grouting pile,determine pile's vertical bearing capacity under load.In particular,including the following several parts:(1)Based on actual engineering geology,putting forward two reinforcement schemes which include setting of steel casings and high-pressure rotary jet grouting pile for disturbed stratum.Comparing the advantages and disadvantages of two methods,considering their construction period,construction risk and construction quality,the method of reinforcingstratum by high-pressure rotary jet grouting pile is determined finally.(2)Calculating pile's vertical bearing capacity with standard according to geological exploration data and reasonable calculation parameters,then compared with the result of ABAQUS.The result shows that calculation parameters and numerical model selected are reasonable.(3)Using 3D finite element model of drilling that is in stratum before and after reinforced to analyze what will influence holes' stability through simulating excavation and applying mud load.The result shows that after reinforced,lateral displacement of drilling is smaller than reinforced before.So high-pressure rotary jet grouting pile has an efficient effect on hole wall stability.(4)Analyzing 3D finite element model of single pile before and after reinforced,it is easy to obtain vertical bearing capacity of pile by applying force and obvious characters of axial force,side friction and tip settlement of pile.Axial force of pile decreases gradually from top to tip;side friction plays a whole role especially in range of rotary jet grouting pile which is larger than before;Q-S curve shows that rotary jet grouting pile can improve vertical bearing capacity of pile to about 14.68%.(5)Building 3D finite element model of pile group before and after reinforced to calculate horizontal bearing of piles and obvious rotary jet grouting pile's effect on horizontal bearing of pile through analyzing character of pile's moment,horizontal displacement and Q-S curve.Data shows that after reinforced,horizontal bearing capacity of single pile improved to about 15.42%,and pile group's improved to about 15.17%.(6)Building 3D finite element model of pile group before and after reinforced to calculate vertical bearing capacity of pile group by applying force,to obvious characters of axial force,side friction and tip settlement of pile group.The data shows that,axial force appears along the whole pile,it reduces rapidly in the range of rotary jet grouting pile's top because of side friction increase;side friction is larger than reinforced before overall range;after reinforced,tip settlement decrease by 9.43 mm obviously;Q-S curve shows that rotary jet grouting pile can improve vertical bearing capacity of pile to about 16.57%;pile group efficiency increased to 0.913 after reinforced,which means that rotary jet grouting pile canreduce pile group effect and improve vertical bearing capacity efficiently.