Study On The Load-bearing Property Of Auger Bored Cast-with-pressure Concrete Pile In Thick Sand Ground

Long auger bored cast-with-pressure concrete pile is developed use of a new type of reinforced concrete pile in recent years. This pile use the long spiral drilling, filed pumping concrete, under the cage followed, can avoid hole collapse and the hole bottom sediment thickness exceed the standard, the construction quality is reliable, can pass through the thick sand layer, the saturated soft loess, silt and mucky soil and other special soil. As a new type of pile can effectively solve difficult hole in special stratum, the bearing capacity of the pile foundation construction speed is slow to security issues, there are still many theoretical and practical problems need to study and solve.Combined with the engineering example, analysis and research of the long spiral drilling in thick sand layer grouting pile under the vertical load bearing performance is thoroughly analyzed by using the finite element software ABAQUS, get some help to improve and perfect the pile design and construction of the main conclusions, as follows:(1)A research in different pile length and pile diameter thick long auger bored cast-with-pressure in sand filling pile bearing capacity in thick sand ground shows that: in the same vertical load, the length and pile diameter of long auger bored single pile is larger, the settlement is smaller; and with the increase of length and pile diameter, the trend of decreasing gradually slowly; in addition, along with the increasing of length and diameter, the same depth of the pile axial force is smaller and smaller, and the longer the pile diameter the greater the decline; in addition, pile side friction curve have different numbers of “peak” while the pile length is different, but the different pile diameter pile have the same number; the longer the pile, the smaller the tip resistance of load sharing ratio and the bigger the side resistance load sharing ratio, while the bigger the pile diameter, tip resistance of load sharing ratio is greater, the side the load sharing ratio of the resistance is smaller.(2)The different elastic modulus of concrete thick pile of long auger bored cast-with-pressure in sand filling pile bearing capacity research shows that: in the same vertical load, the pile body concrete elastic modulus is larger,the pile top settlement is smaller, and with the decrease of the strength of concrete, the settlement of the pile top and the trend of increase gradually accelerated; In addition, different loading of pile top axial force of pile down along the pile depth gradually decreases with increase of basically the same, and the pile body elastic modulus of concrete, at the same depth of the pile axial force; In addition, different pile concrete elastic modulus of pile side friction curve "peak" the same number, the position of "peak" are basically the same, but the maximum value of side friction of pile in pile bottom, and with the increase of pile modulus, the maximum pile side friction resistance value increases.(3)Reinforcement cage depth under different thickness of long auger bored cast-with-pressure in sand filling pile bearing capacity research shows that: in the initial loading, under the cage at a depth of 1/4 pile length, the axial force is 1302.6kN; under the cage at a depth of 1/2 pile length, the axial force is 825.9kN; under the cage at a depth of 3/4 pile length, the axial force is 429.7kN; the depth to the next cage pile, axial force is 98.5kN, and with the increasing depth of the cage at the same depth, the axial force of pile is smaller and smaller.(4)Long auger bored cast-with-pressure concrete piles in thick sand layer of single pile and the ordinary single pile bearing characteristics of the comparative study shows that: compared with the ordinary single pile, long spiral bored pile can reduce the 37%~63% of the settlement of the pile top; the same cross section, long auger bored pile axial force less than the ordinary pile. When the load on pile top is small, two types of pile axial force are little difference, when the load on pile increases to a certain value, the axial force of pile will change greatly, the bottom of the pile axial force of section difference even reached at 50%; at the same depth of pile side friction resistance, the side friction resistance of ordinary pile is smaller; pile end resistance and load sharing ratio to long spiral drilling is small, the load sharing ratio of side resistance is large.(5)Different length of pile in thick sand layer of long auger bored cast-with-pressure bearing characteristics of pile groups research shows that: under the same vertical load, the longer the pile of pile group foundation,the smaller the pile top average settlement. The effect of pile length pile group foundation, along with the increase of the average top settlement of the pile, the average friction resistance of pile side is gradually increasing. Under the action of vertical load, the pile length is longer, the same average side friction of pile end corresponding to the average settlement is smaller. At the top of the pile under the same average settlement, pile length is longer, the average side resistance is larger. The length of the pile is longer, the average load sharing ratio is smaller, the average side resistance load sharing ratio is greater.(6)Long auger bored cast-with-pressure in thick sand layer filling pile and the bearing characteristics of pile groups of ordinary pile comparative study shows that: compared with the ordinary pile under the same vertical load, the long auger bored cast with pressure concrete pile of the top average settlement is smaller; with the same side friction resistance, long auger bored of group piles corresponding to the average settlement of pile end is smaller; under the average settlement at the top of the pile conditions, long auger bored pile of the average side resistance is greater; ordinary pile under the same pile end resistance corresponding to the same average settlement at the top of the pile is smaller; the average sedimentation under the same conditions, the average top resistance of the pile of long auger bored pile is bigger.