Power shovel, backhoe and steel roller

(i) Power shovel (front shovel)

            boom
          _/\_
        _/    \   dipper stick
   cab /       \__
 [____]         [bucket] digs upward/forward
 [=tracks=]

Basic parts: crawler base, revolving deck with cab and engine, boom, dipper (stick), and bucket with a hinged bottom door. Operation: the bucket is crowded forward into the bank and lifted upward, curling in material; the machine swings, and the door is opened to dump into a truck. Application: digging above the track level (hillside, borrow pits, quarry), loading trucks, in hard and rocky soil with high output (bucket 1-5 m$^3$). It is not suitable for digging below its own level or for wet ground.

(ii) Backhoe (hydraulic excavator)

           boom
        __/\___ stick
       /        \
 [cab]/          \__bucket (teeth face machine)
 [==tracks==]

Parts: undercarriage (tracks or wheels), swing platform, boom, stick, bucket, hydraulic cylinders. Operation: the boom is lowered, the bucket is extended out and pulled toward the machine to dig; it is curled, lifted, swung and dumped. Application: trenches for pipes and cables, foundation pits, basement excavation, below-grade digging, ditches, demolition and loading trucks. Its 360-degree swing and precise control make it the most common site excavator.

(iii) Three-wheel steel roller

      [seat]
   ___|_____|___
  (   ) front guide wheel (steel drum)
   (  rear drive wheels - two big steel drums )

Parts: one front steering drum and two large rear drive drums, engine, frame, water spray and scrapers, ballast. Operation: it makes repeated passes at 3-6 km/h, with overlap, from the edges toward the centre; the weight is 8-12 t (ballast can be added). Application: compaction of granular sub-base, base course and macadam, initial rolling of asphalt, giving a smooth surface. Not suited to cohesive soils for deep compaction.