The Experiment Research Of Vertical Bearing Mechanism On The Composite Pile In East Of Henan Province

As a new-style composite pile, the concrete-cored DCM pile bears the load under the work ofconcrete core and cement-soil, the load transfer path is concrete core—Inner and outer coresfriction—cement-soil outer core—pile-soil friction—soil, the transfer method is very complex. In Thisarticle, we used the soil in the east of Henan Province as raw materials to research the strength developmentof cement soil mixed with cement, Fly Ash-Calcium-Sulfur (FCS), cement-FCS, cement-sand,cement-gypsum by laboratory experiments, then research the relationship of load-settlement and the axialforce distribution by indoor model pile experiments. Main achievements are concluded as follows:1. Research of the strength development of cement soil. Through experimental study ofsingle-doped cement showed: with the increase of cement content, the strength of cement-soil increased byleaps and bounds, Cement content of10%or less for the first stage,14%to18%for the second stage,22%to26%for the third stage, the strength changed little in each segment but much between segments. FCSsystem can stimulate the activity of fly ash at room temperature and atmospheric pressure very well asF:C:S=77:20:3,but Compared with cement, the strength remains low. When use cement: FCS=1:2togethercan improve the strength of cement soil about80%under the same circumstances cement content or reducethe amount of cement about50%with the same strength. The experiment of cement-soil with sand showedthat the strength was first decreases and then increases as sand increased and reached the lowest value at15%, so we suggested that about35%is appropriate. Gypsum incorporation can significantly improve theearly strength of cement soil, but harmful to the late strength and high gypsum content is harmful toconstruction, so we suggested that about2%is appropriate.2. Experimental study of indoor on vertical bearing capacity of the composite pile. Take twokinds of inside and outside of the core length ratio of0.7and1.3to production of eight model piles withcement, cement-FCS, cement-sand, cement-gypsum. The experimental studies have shown that: theload-settlement curve of composite pile has an obvious turning point and all the failure types were groundfailure type, it refers to the shear failure of pile-soil interface or plastic failure of pile end soil layer. With along concrete core the load can be effectively passed down and maximize the pile side friction, under thesame load, the settlement is less than the short concrete core pile. With the same cement-soil outer core, the long concrete core pile bearing capacity relative to the short concrete core pile can be increased by50%to80%.In the vertical loads, due to the elastic modulus of the inner core is much larger than the outer core, theconcrete core will bear most of the load and then transmitted to cement-soil by frictional contact with theinner and outer surfaces of the core, finally transmitted to the soil around the pile by pile-soil interface ofthe friction. FCS can effectively stimulate the activity of fly ash, the effect of one cement and two FCS isequal to two point five cement. The bearing capacity of composite pile can be increased by about10%withsand. The gypsum can slightly reduced the bearing capacity of composite pile. The Axial force is next bigsmall along the pile and at the top of the pile for short pile within the following5to25cm range of axialforce decreased to50%of total load and then slow down, the axial force decreased to50%at the following5to40cm top of the long pile. With the load increased, the axial force of the upper half of the compositepile decreased rapidly, the load transmitted to pile tip accounts for about5%of the total load, so thecomposite pile is friction pile, we can put the end bearing capacity as safety margin value. The unit sidefriction of inner-outer cores interface and pile-soil interface showed a decreasing trend after the firstincreases. The main factors affecting the pile capacity have the strength of cement soil, pile stiffness, soilsqueezing effect and the proportion of the inner and outer core, improve the strength of cement soil and soilsqueezing effect can increase the side friction, improve the pile stiffness and proportion of the inner andouter core can let the load effectively pass down.3. Useing cylindrical cavity expansion theory to research the influence of composite pile to thesoil around the pile show: the Radial stress and radial displacement of the soil around the pile decreasesrapidly with increasing radial distance,the hoop stress decreases from the pressure into tension and thentends to zero.