Study Of DDC Composite Foundation Bearing Capacity Under The Condition Of New Technology About Compaction Of Automation In The Construction

DDC method is a kind of traditional way of foundation treatment. Generally, the heavy tamping machine worked by manual operation, labor intensity, high security,ramming speed lags behind drilling. The old DDC of foundation treatment after filling rammer pile diameter often cannot meet the requirements because of construction, even400 mm into the hole diameter ram filled out the only 450 mm and depth of processing only 20 m. The DDC composite foundation under the condition of new technology about compaction of automation in the construction get rid of the old technology leads to heavy work operation, with the device itself low degree of automation, safe hidden trouble, ramming speed is slow, at the same time solve the compaction of diameter can’t meet the design requirements, the depth of the shallow foundation treatment and other key problems affecting the bearing capacity of foundation soil, currently 400 mm into the hole diameter, under the condition of new technology and demolition after can reach600 mm or 800 mm, processing depth increased to 40 m.Combined with the field test, to simulate the two aspects of the research importantly about the DDC composite foundation under the condition of new technology about compaction of automation in the construction by using the finite element software ABAQUS. First: the new technology compaction process and the plastic zone under the condition of the relationship between stress and strain. Second:the new technology under the condition of pile length, pile diameter, pressure around pile, pile body shell layer modulus to DDC change of bearing capacity of compoundfoundation. The results of the study as follows:(1)The field test of DDC composite foundation to prove: The new technology under the condition of DDC pile diameter and depth processing meet the design requirements, advance into the hole after compaction pile hole diameter of 400 mm to600~800mm, foundation treatment effect is good, high bearing capacity of composite foundation.(2)The construction of DDC method, the change of Plastic deformation is not proportional to the number of tamping, extension of plastic zone is not equal. With the increase of tamping times, the area of plastic deformation is larger will be formed obvious reinforcement area, the energy of tamp get through the obvious reinforcement of area to greater depths. The formation of obvious reinforcement of area can reduce the energy of tamp absorption from soil, make energy to more deep, thus increase the scope of foundation reinforcement. At the same time, the increase of plastic deformation of soil is not infinite, there is the largest number of tamping under certain lamping.Horizontal stress distribution in the depth direction can be divided into two parts. The first part of the bottom of the rammer and the edges of rammer, horizontal stress with depth increase rapidly decay, the decrement are mainly concentrated in the following 4L(L as a Rammer buried depth)scale. The second part is from the center of rammer 1D(D as a Rammer diameter), horizontal stress with depth increases after the first decreases, and the maximum horizontal stress in the tamping surface below 1.4 L.(3)DDC pile load bearing characteristic of composite foundation is closely related to material properties. The increase of pile Length on the DDC composite foundation under the condition of new technology about compaction of automation in the construction can obviously improve the depth of foundation treatment; The increase of pile diameter can effective improve the settlement and displacement of the composite foundation, at the same time can change the stress distribution of composite foundation;The increase of the pressure around pile and the formation of the Hard shell can not only greatly improve the DDC single pile bearing capacity, reduce the settlement of the composite foundation under the equivalent load, and can improve the bearing character of composite foundation, makes participate more in the upper load distribution of foundation soil, reduce the load sharing ratio of pile in composite foundation, thefoundation stiffness tends to uniform.