Recently, excavation is underway at the foundation pit project site of a building in Futian, Shenzhen. The secant piles serving as the foundation pit retaining system have become visible. Project manager Mr. Wang pointed at the completed secant pile wall and said: "I didn't expect such good results—these piles look beautiful!"

 

    The project's foundation pit adopts a secant pile design, with a pile diameter of 1.2 meters and a depth of 25 meters. The excavation depth of the foundation pit is 22–23 meters, and the design calls for five basement levels. The total number of secant piles for the entire foundation pit is 790, and about 90% of the piles need to be embedded into slightly weathered granite, with the maximum embedment reaching 5 meters and an average of about 1 meter. In the early stage of construction, the contractor used a casing oscillator together with a rotary drilling rig. Because the casing oscillator was inefficient at installing casings, and the selected rotary drilling rig could not meet the design requirements for rock penetration, the client decisively introduced a Bauer BG30 rotary drilling rig in order to expedite the schedule.

 

    The Bauer BG30 rotary drilling rig is equipped with a winch crowd system and, paired with a casing driver, can use the casing driver to install casings. At most, it can independently install and extract casings about 22 meters long. Combined with the superior rock-penetration capability of Bauer rotary drilling rigs, within six months after mobilization, the Bauer BG30 rotary drilling rig completed the construction of nearly 600 piles with guaranteed quality and quantity. It lived up to expectations and helped the project contractor recover the construction schedule.

 

    Because secant piles can penetrate rock and can flexibly adjust pile depth according to the undulations of the rock surface, they have certain advantages over diaphragm walls under specific conditions and broad market prospects. This construction method places high demands on drilling rigs, requiring high-torque, high-quality equipment, and the characteristics of Bauer rotary drilling rigs can be fully brought into play. With the continuous promotion of the secant pile technique, Bauer drilling rigs will certainly bring more considerable economic benefits to users.