A cushion layer made of a certain thickness of granular material is placed between the foundation of the piling machine and the soil around and between the piles. Under load, since the modulus of the piles is much greater than that of the soil, the deformation of the soil surface between the piles is greater than the deformation at the top of the piles. The piles penetrate into the cushion layer, and with this change, the granular loose material continuously adjusts and supplements the surface of the soil between the piles. Thus, the foundation maintains contact with the soil between the piles through the cushion layer, and the soil between the piles remains functional, allowing its load-bearing capacity to be utilized. Therefore, whether a cushion layer is set beneath the foundation significantly affects the stress on the composite foundation.

For a long-spiral drilling rig foundation without a cushion layer, the load-bearing characteristics of the composite foundation are similar to that of a pile foundation. Under a given load, the piles bear more load, and over time, the piles settle to some extent, transferring part of the load to the soil. The load borne by the piles decreases over time, while the load borne by the soil increases. The load-bearing capacity of the soil between the piles is dependent on the settlement of the piles. If the pile ends are on a hard soil layer, the settlement of the piles is minimal. The load transfer from the long-spiral drilling rig piles to the soil is minor, making it difficult for the soil between the piles to exert its load-bearing capacity and not contributing effectively to the composite foundation.

The feed system is an important part of the drilling rig, directly affecting drilling efficiency, quality, and power consumption. The feed circuit generally includes three modes: throttling feed, pressure-balanced feed, and pressure-regulated feed. The pressure-regulated feed circuit can adjust the pressure on the drill bit, but it has a high system loss during decompression drilling and cannot control the feed speed. The back pressure in the pressure-balanced feed circuit causes system pressure loss and heating. The throttling speed control feed circuit can control the feed speed, and the presence of back pressure in the return oil makes the feed speed more stable, reducing the impact of drill speed fluctuations on the drill pressure. This minimizes the dynamic load on the cutting edge of the drill bit, thereby extending its life.