Recently, a Shanghai Jintai SZ80-35 full casing drilling rig appeared at the pile foundation project site of the Shenzhen ICBC Tower constructed by China Construction Third Engineering Bureau. This brand-new SZ80-35 full casing drilling rig began its first attempt at using the "secant pile" technique for foundation pit retaining construction.
　　As a new type of building foundation pit retaining structure, the "bored secant pile" has achieved successful experience in some cities in China. The "bored secant pile" is named for its form of piles interlocking with each other and continuously forming a wall. Using this type of pile for foundation pit retaining has the advantages of small environmental impact, reliable quality, and low cost, thus having certain promotional value.
　　Construction data shows that the geological structure of this section is mainly backfill soil, sandy clay, and mudstone, with the backfill layer containing gravel of varying particle sizes. Engineer Yang, the person in charge of on-site equipment, introduced that the "secant pile" constructed by the SZ80-35 has a diameter of 1.2 meters and a depth of 33.5 meters. Such strata and pile type are extremely compatible with the SZ80-35 drilling rig. The drilling time for a single pile is about 120 minutes, and the user is quite satisfied with this construction efficiency.
　　The SZ80-35 full casing drilling rig is one of the most versatile products in the Shanghai Jintai series, with the following features:
　　1. The main machine adopts an electro-hydraulic power source with a total power of 440KW; the power head and winch unit are driven by independent motors;
　　2. The chassis is a hydraulic walking structure with low ground pressure; the mast is a three-point support structure with high stability;
　　3. It has two sets of power heads: the upper power head drives the drill pipe with a torque of 36 ton-meters (a rotary joint can be installed for conveying compressed air or concrete); the lower power head drives the casing with a torque of 60 ton-meters. The two power heads are driven separately, providing strong drilling capacity with powerful torque;
　　4. It has four sets of fully hydraulically driven winches, and the main winch has a follow-up function;
　　5. The interior of the mast adopts an "X" reinforcement structure, and the 900x100mm rectangular guide rail can provide a lifting force of 125 tons and meet the transmission of strong torque;
　　6. In terms of the control system, various electro-hydraulic parameter monitoring and detection devices for each working component are installed. All operations can be completed by handles combined with corresponding buttons, which is simple and convenient;
　　7. In practical applications, the SZ80-35 main machine can be equipped with various devices such as continuous flight augers, down-the-hole hammers, hydraulic hammers, multi-axis drilling machines, and milling mixing drilling rigs according to geological conditions and construction method requirements, to achieve multifunctional expansion of the equipment;
　　As early as June last year, in the "Shanghai Riverside Passage Cross-River Tunnel Project", the contractor used the Shanghai Jintai SZ80-35 full casing drilling rig for tension pile construction, successfully achieving mudless construction under soft soil geological conditions, and smoothly passed the review and acceptance by Shanghai Construction Group, Shanghai Tunnel Engineering Co., Ltd., Shanghai Foundation Engineering Group, and other departments, providing a new possibility for mudless construction of cast-in-place piles in Jiangsu, Zhejiang, and Shanghai regions. This successful implementation of secant pile construction will further expand the application fields of the SZ80-35.