Rotary Bored Piling Rig

Overview

A rotary bored piling rig drills the deep, large-diameter holes that become cast-in-place concrete pile foundations for buildings, bridges, retaining walls and quays. It is a crawler base machine carrying a tall vertical mast. A Rotary Drive Head runs up and down that mast and spins a long Telescopic Kelly Bar, and at the bottom of the kelly bar a soil or rock cutting tool grinds its way into the ground. The rig bores the shaft, the spoil is lifted out, a reinforcement cage is lowered, and concrete is placed to form the pile. Because the same machine can change tools and bore diameters from 0.6 m up to 3.0 m and depths from 30 m to 90 m, one rig covers a wide range of ground conditions and pile sizes.

The machine balances three jobs at once: it must stand stably on soft or graded sites, it must turn the tool with very high torque, and it must hold the bore exactly vertical so the finished pile carries load as designed. Operating weights run from about 60 t for compact rigs to 150 t for the largest, and the Counterweight on the upper frame offsets the overturning moment of the mast and tooling reaching out ahead of the tracks.

Undercarriage and Upper Frame

The Crawler Undercarriage is an extendable crawler base. The two Track Frame assemblies can be pushed out on Track Gauge Cylinder cylinders to a wide working gauge for stability and pulled in narrow for road transport. Each track frame carries a sealed Track Chain, bolt-on Grouser Track Shoe grousers, support rollers, an idler tensioned by a Coil Spring, and a Travel Drive Unit planetary gearbox driven by a Hydraulic Motor.

The Upper Frame sits on a Slew Ring Bearing and slews a full 360 degrees on twin Swing Drive units. The rotating deck carries the powerpack, the winches, the counterweight, and the foot of the mast. The mast hinges on the Mast Pivot Bearing and is raised to vertical and trimmed for rake by the Mast Luffing Cylinder luffing cylinders.

Powerpack and Hydraulics

Everything on the rig is hydraulic, so the Diesel Powerpack is the heart of the machine. A turbocharged Diesel Engine of 150-450 kW drives a Pump Drive Gearbox distributor gearbox, which splits power between two variable-displacement Variable Main Pump units and a smaller Auxiliary Gear Pump for the pilot controls. Oil is drawn from the Hydraulic Reservoir and metered to each actuator through the load-sensing Main Control Valve Block block, whose Proportional Spool spools and Relief Valve Cartridge cartridges set the flow and protect the circuits. A Cooler Pack keeps the oil and engine within temperature during long drilling shifts, and Pressure Sensor feedback lets the control system hold torque and crowd limits.

Mast, Rotary Head and Kelly Bar

The Leader Mast is a box-section leader 18-30 m tall built from high-strength Mast Box Section weldments. Twin Head Guide Rail rails guide the rotary head carriage, and the Crowd Cylinder crowd cylinder, working through the Crowd Rope System reeving, pushes the head down with the crowd force needed to keep the tool cutting.

The Rotary Drive Head is where torque is made. Several Rotary Head Motor motors feed a sealed Rotary Head Gearbox built around a Gearbox Housing and stacked Helical Gear Pair reductions, summing their output to 100-450 kNm. That torque passes through the Kelly Drive Sleeve into the Telescopic Kelly Bar. The kelly is telescopic: 3 to 5 nested Kelly Bar Section sections slide through Kelly Guide Bushing guides and lock with Kelly Interlock Stop interlocks so torque passes down while the bar extends to reach full depth. The Kelly Swivel at the top links the bar to the hoist rope, and the bottom carries a Tool Coupling bayonet for fast tool changes.

Winches and Drilling Tools

The Main Winch raises and lowers the whole kelly and tool string. Its grooved Winch Drum is driven by a planetary Winch Gearbox and held by a spring-applied Multi-Disc Brake when the load stops. A separate Auxiliary Winch handles casing, reinforcement cages and tooling at the bore using its Load Hook.

The Drilling Tool Set set is chosen for the ground. A helical Drilling Auger fitted with carbide Auger Cutting Tooth picks cuts soil and lifts spoil on its flights. A Drilling Bucket with a hinged Bucket Bottom Flap scoops wet or loose material and is emptied beside the hole. For rock, a Core Barrel with Roller Cutter cutters ring-cuts a core. In unstable ground a Casing Tube holds the bore wall open until concrete is placed.

Materials and Operation

The structural members, mast, car body and counterweight frame are welded from S355 and high-strength S690 steel. Gears and drive shafts use case-hardened alloy steels such as 18CrNiMo7-6 and 42CrMo4, and the cutting teeth carry tungsten carbide inserts that resist abrasive soils and rock. From the Operator Cab, the operator works two Pilot Joystick pilot controls while the Rig Control Unit computer logs depth from the Depth Encoder and reads lean from the Inclinometer inclinometers, showing both on the LCD Panel so the pile stays vertical.

Variants and Use

Compact rigs near the 60 t and 100 kNm end suit urban sites with restricted headroom and lighter pile loads, while large rigs at 150 t and 450 kNm bore the deep, wide piles needed for bridge piers and high-rise cores. Rigs are also set up for related methods such as continuous flight auger and double rotary cased drilling by swapping tooling and adding a casing oscillator. Across all variants the bored pile method is favoured where piles must be large, deep and quiet to install, since the soil is removed by drilling rather than driven aside by impact.