Study On The Method For Assessing The Situation Of Bridge Bored Piles Foundation In Service

As the main form of bridge pile foundation, bored pile is the most popular. When the pile is under construction, it is easy to form a pile of local constriction or expansion, segregation of concrete defects etc. And during the service period, by the influence of various factors, it is easy to cause the existing defects of the pile foundation to develop, and even the new damage, resulting in its bearing capacity to reduce, threatening the safety operation of the bridge. In order to ensure the safe operation of the bridge, it is very necessary to evaluate the current situation of the bridge foundation.But the nondestructive detection of bridge bored pile foundation in service has its own particularity:there are the platform and pier columns, beams, bridge panel on the upper part of the pile foundation of existing bridges. So it causes a large number of secondary reflection interference signals in the reflection wave method, leading to complex signal detection and much difficult of analysis; the service state of existing bridge and the natural environment restricts the operations and the detection range of the detection technology; pile size is generally larger, and three-dimensional effect impacts greatly. It does not necessarily satisfy the one-dimensional wave equation theory and vibration theory.This paper carries out the research on the method for assessing the situation of bridge bored piles foundation in service from the two aspects of bearing capacity and integrity, and focuses on the feasibility analysis of double velocity method, and puts forward integrity detection method of "Edge of pile cap or pile side exciting, pile side receiving (exciting and measuring are on different sides)" double velocity method. The main contents and conclusions of this paper are as follows:Firstly, discuss the bearing capacity evaluation theory of bridge pile foundation in service. The bearing capacity of pile foundation cannot be directly tested and evaluated, but it can be inferred indirectly through the appropriate theoretical analysis.Secondly, induct the status quo of disease and disease type of pile foundation, summarize concrete strength measuring method in bored pile foundation of bridges, and determine the two kinds of defects:shrinking diameter or expanding diameter, as the typical defect type. The low strain reflected wave method and its improvement are analyzed. It is considered that the double velocity method can be used as an important means to detect the integrity of bored pile foundation of existing bridge.Thirdly, use the finite element software ANSYS/LS-DYNA to establish complete pile and shrinking diameter or expanding diameter of the two types of defects defective pile model of a free pile top or pile top with upper structure(CAP), simulate pile stress wave propagation in three kinds of excitation modes of pile top, top edge of pile cap and pile side, to verify the feasibility of the method of double velocity, put forward integrity detection method of "Edge of pile cap or pile side exciting, pile side receiving (exciting and measuring are on different sides)" double veloity method.Fourthly, carry out the simulation of a practical engineering pile to prove that integrity detection method of "Edge of pile cap or pile side exciting, pile side receiving (exciting and measuring are on different sides)" double velocity method is feasible in large diameter pile.