You see, the ratio of a circle's circumference to its diameter is what's known as an irrational number, one that can never be expressed as a ratio of two whole numbers.
A bulldozer is a powerful vehicle with a caterpillar track on it, so it means that the wheels act kind of in a long caterpillar-like tread, and those treads move in a long circular motion rather than just in a circular motion.
That's right, March 14th, or 3.14, the day we celebrate the fascinating mathematical constant Pi, the ratio of a circle's circumference to its diameter.