"Domestic equipment with exceptional power, most inspiring to the national spirit" — Jintai SMC method drilling rig successfully applied at its 500th construction site. Recently, Zhengyu Kechuang received good news from the Huamahu Pumping Station Capacity Expansion Project Department in Ezhou. First, high praise for the Jintai SMC method drilling rig's strong capability in handling complex strata; second, appreciation for the construction contractor Zhengyu Kechuang, which achieved a diaphragm wall of excellent anti-seepage quality using the Jintai SMC method.

Site photo of the Huamahu Pumping Station project

The Huamahu Pumping Station Capacity Expansion Project is an important component of the Hubei International Logistics Core Hub Huamahu Water System Comprehensive Treatment Phase II Project (Lot 1), mainly including a drainage pumping station (design flow 96m³/s), a gravity drainage sluice (design flow 63m³/s), Huamahu Port expansion excavation, Zhonggoutao regulating sluice, etc. The pumping station consists of 4 units and adopts siphon-type outlet pipes crossing Changda Dike into the Yangtze River.

The Huamahu Pumping Station Capacity Expansion Project is a Class II large (2) water conservancy project. The main buildings including the main pump house, auxiliary plant, inlet/outlet pools (including wing walls on both sides), trash racks, and gravity drainage sluice are all Grade 2, while the remaining secondary buildings are Grade 3.

The pumping station foundation pit project is classified as Grade I in importance. The cutoff wall is constructed using the SMC method, with a wall thickness of 800mm, the wall penetrating 0.5m into the moderately weathered rock layer, an effective wall length of 33m, and a general excavation depth of 6.75m to 16.20m, with the pumping station area excavated to 18.50m.

SMC wall observed during excavation

Construction Challenges

01. Adjacent to river channel, relatively soft geology

This project is adjacent to the Huamahu River channel, with abundant groundwater systems and relatively soft geology. The site involves cross-operation of multiple equipment with crowded working surfaces, and many large construction machines have high requirements for the construction site. Zhengyu Kechuang has extensive construction experience on complex terrain and possesses multiple Jintai SMC method drilling rigs of various models, capable of handling various strata with ease.

Equipment selection and procurement stage: For narrow working areas, the more flexible SC-45 crawler-type equipment can be selected; for areas with relatively soft geology, the Jintai SC-55/SC-60 walking-type equipment with larger and more stable pile frames can be used for construction.

Final equipment selection for the Huamahu Pumping Station project: The SC55 dual-wheel mixing drilling rig is more suitable for on-site construction at the Huamahu Pumping Station project.

02. Wall must penetrate into moderately weathered rock

Rock penetration difficulty has always been a "chronic problem" in quality control of bottom-seated cutoff curtains. The Jintai SMC method drilling rig can cover depths from 30m to 65m and effectively perform milling and mixing in dense sand layers, large-diameter cobble layers, and soft rock strata within 10 MPa. For the design requirement of penetrating 0.5m into moderately weathered rock at the Huamahu Pumping Station project, the Jintai SMC dual-wheel mixing equipment can handle it with ease.

Typical cross-section of the Huamahu Pumping Station project

03. Wall integrity

The milling head of the SMC method is equipped with sensors for collecting various data. Operators control the verticality of the mast through the touch screen to adjust the attitude of the milling head and adjust the descent speed of the milling head, thereby effectively controlling the verticality of the trench within 3‰; the wall surface is flat (panel wall).

In addition, the mixture formed by the combined action of milling, cutting, mixing, air, and slurry is in a boiling state. The consolidated wall is uniform and dense; the panel connections are complete milling joints (not limited by the completion time of the previous panel wall, whereas conventional deep mixing walls cannot be socketed or overlapped due to excessive time between the front and rear panels, and can only be butt-jointed, requiring additional anti-seepage treatment of the butt or overlap joints). The joint surfaces have "no cold joints" and can achieve seamless connection, forming a seamless wall with strong integrity and good anti-seepage performance.

Why the SMC Method Becomes Mainstream

To meet the high requirements of current water conservancy and civil engineering projects for deep anti-seepage (cutoff), deep foundation pit support, earth retention, and ground improvement, Shanghai Jintai Engineering Machinery Co., Ltd. launched the national "948" project — "Research and Application of Hydraulic Milling Deep Mixing Diaphragm Wall Machine" in September 2009. Through the introduction of foreign advanced technology and equipment, and after digestion and absorption, a new type of construction equipment and process combining the characteristics of hydraulic dual-wheel trench cutters and traditional deep mixing technology was successfully developed and researched — the hydraulic milling deep mixing diaphragm wall machine and its construction process [abbreviated as SMC process], which won the Second Prize of the National Science and Technology Progress Award. This equipment has unique Chinese characteristics and conforms to China's national conditions. It not only provides an alternative to the CSM method piles invented in Germany, but also has a broader construction scope than SMW method piles and TRD method piles. The Jintai SMC method SC series drilling rigs SC35, SC45, SC50, SC55/65 have been successfully applied in 500 construction projects nationwide. The Jintai SMC method drilling rig is developing with the trend and will continue to be mainstream construction equipment in fields such as foundation pit anti-seepage, water-stop curtains, and ground improvement in the future.