1, Overview of rotary drilling rig construction
Rotary drilling rig is a pile driving machinery used for drilling holes in building foundation engineering. It has the advantages of fast construction speed, good hole quality, low environmental pollution, flexible and convenient operation, high safety performance, and strong applicability. It has become a drilling machine. Rotary drilling rig is the main drilling equipment for bored pile construction. It is a highly integrated pile foundation construction machinery that adopts an integrated design, a tracked 360 ° rotating chassis, and a mast type drill rod. It is generally a fully hydraulic system. A special barrel shaped drill bit that can directly extract soil and slag without connecting long drill rods. Injecting grout into the hole during drilling to maintain the height of the mud inside the hole can greatly shorten the drilling time. Equipped with automatic verticality control and automatic return control, ensuring the verticality and position of the hole. The bucket drill causes minimal disturbance to the borehole wall during the soil lifting process. There are overflow holes around the bucket drill, and the overflowing mud can protect the wall.
2, Rock fragmentation
At present, there are three main methods of rock fragmentation in construction: impact rock fragmentation, grinding rock fragmentation, and shearing rock.
Impact rock breaking: According to theoretical analysis, only when the pressure acting on the rock exceeds 30% to 50% of the uniaxial compressive strength limit of the rock, will the rock break smoothly. Therefore, multiple impacts between the drilling tool and the rock before the pressure reaches the fracture strength limit of the rock can cause the rock to fracture and reduce its strength. When the strength of the rock decreases to a certain extent, the rock can break. The commonly used equipment currently is an impact hammer.
Grinding rocks: Under very small pressure loads, the frictional force generated by the contact between the rotating drill bit and the rock is used to break the rock (this method is actually a grinding action). This method has a slower rock crushing speed, finer rock crushing particles, and severe drilling tool wear. The commonly used equipment in the current market is the forward (reverse) circulation drilling rig.
Shear rock: According to the Cullen Levy criterion, the shear strength limit of rock is only about 10% of the compressive strength limit, so shear method is a good way to crush rock. For construction equipment mainly using rotary drilling, if pressure is applied to the drilling tool during drilling, the cutting teeth of the drilling tool can cut into the rock (when the rotary drilling rig is used for hard rock construction, the matching cutting teeth are used as the main), and then under the action of rotational torque, the rock can be sheared and broken.
