钻孔灌注桩桩头静态破碎原理与裂纹发展机理

静态破碎技术近年来在混凝土构筑物的拆除中得到了广泛应用,将该技术应用于钻孔灌注桩桩头的破除是一种新的破除方案,可以避免粉尘和噪音污染。为了分析桩头静态破碎过程中的应力分布和裂纹发展规律,利用RFPA^2D软件建立了桩头裂纹发展数值计算模型,得到了一些重要结论。研究结果表明：静态破碎是一个持续发展过程,当膨胀压达到混凝土抗拉强度,裂纹开始产生,随着膨胀压的增大,在尖端应力的作用下,裂纹得以继续发展；当膨胀孔直径为40mm时,在灌注破碎剂大约7h后膨胀压达到20MPa,混凝土开始产生裂纹；膨胀孔裂纹大致呈两条或三条形式发展,一条伸向最小抵抗线方向,其余指向相邻膨胀孔；直径为600mm和800mm的桩头在应力场分布和裂纹发展模式上差异不大。

Static Crushing Principle and Crack Development Mechanism of Bored Cast-in-place Pile

Static crushing technology has been widely used in the demolition of concrete structures in recent years. The application of this technology to the head breaking of bored pile is a new method, which can avoid dust and noise pollution. In order to analyze the stress distribution and crack development law in the static crushing process of pile head, the numerical calculation model of crack development of pile head is established by using RFPA^2D software, and some important conclusions are obtained. The research results show that the static crushing is a continuous development process, when the pressure reaches the concrete compressive strength, crack began to produce, with the increase of swelling pressure, in tip stress, under the action of the crack to continue development; When the diameter of the expansion hole is 40mm, the expansion pressure reaches 20MPa about 7h after the pouring of the expansion agent, and the concrete begins to crack. The crack in the expansion hole develops in two or three forms, one of which extends to the direction of the minimum resistance line, and the others point to the adjacent expansion hole. There is little difference in stress field distribution and crack development mode between 600mm and 800mm diameter pile heads.