The pipe twisting machine full casing construction method is a pile foundation hole-forming technology designed for complex geological conditions. Its core lies in replacing traditional mud wall protection with "pipe twisting machine resistance reduction + full casing hard wall protection" to solve hole-forming difficulties in special strata. It is widely used in pile foundation construction of major projects such as bridges and high-rise buildings.

I. Core Principle Utilizing the hydraulic drive of the pipe twisting machine, the steel casing realizes the "semi-rotation (15°-20°) + downward pressing" action, reducing the frictional resistance between the casing and the soil layer (by 30%-50% compared with the traditional static pressure method). The full casing wraps the hole wall throughout the process, and synchronously cooperates with a rotary drilling rig/grab bucket to remove the soil inside the pipe. After hole formation, the reinforcement cage is lowered and concrete is poured, while the casing is pulled out simultaneously with pouring according to the "speed-controlled casing pulling" process, ultimately forming a complete pile foundation.

II. Applicable Scenarios 1. Complex geological conditions**: Backfill layers, soft soil, quicksand layers, pebble and boulder layers (particle size ≤45cm), karst caves, high-water-level/strongly permeable strata. It can solve the problems of "hole collapse and necking" in traditional processes; 2. Sensitive areas**: Scenarios with high environmental protection/noise requirements such as urban areas and residential areas (construction noise ≤70dB during the day and ≤55dB at night, no mud pollution).

III. Brief Construction Process 1. Preparatory work: Site hardening (foundation bearing capacity ≥150kPa), equipment commissioning (no pressure drop in the hydraulic system of the pipe twisting machine), and casing inspection (100% flaw detection for welds); 2. Casing downward pressing: After pile position setting out, the pipe twisting machine clamps the first section of the casing (with alloy cutting edge), and presses it down with the "short footage, fast pipe twisting" method. V-groove welding is adopted when extending the casing; 3. Hole formation and pile formation: Soil extraction inside the pipe (rotary drilling rig for stable layers, grab bucket for pebble/boulder/quicksand layers), hole cleaning (sediment at the hole bottom ≤50mm), lowering the reinforcement cage followed by concrete pouring, and synchronously pulling out the casing according to the "speed-controlled casing pulling" process.

IV. Core Advantages 1. High hole-forming quality: The full casing isolates the hole wall from groundwater, eliminating the risks of mud skin and pile breakage. The pile bearing capacity is increased by 20%-30% compared with traditional mud wall protection, and the verticality deviation is ≤0.5%; 2. Strong stratum adaptability: It can penetrate pebbles with a particle size of 300mm, flow plastic soil, and multi-layer karst caves, expanding the applicable range by 60% compared with the traditional rotary drilling method; 3. Environmental protection and high efficiency: No need for mud pools, saving 20%-30% of the site area; no mud pollution, meeting the requirements of green construction.

V. Construction Efficiency - Hole-forming speed: 15-20m/h in stable soil layers, 8m/day in hard rock strata, 5-8m/h in complex quicksand/pebble layers, which is 30%-50% higher than traditional processes; - Single pile cycle: 45-60min/pile in soft soil layers, 90-120min/pile in complex strata (including karst caves and pebble layers), shortened by more than 50% compared with traditional processes; - Daily pile completion volume: 30-40 conventional piles can be completed per day with two-shift operation (12h per shift), and 12-15 large-diameter (2.5-3.0m) piles can be completed for large bridges and subway projects.