(i) Pipe piling and soldier piling

Pipe piling and soldier piling are earth retention techniques involving the construction of retaining walls using steel casings (in the case of pipe piling) or steel H-piles (in the case of soldier piling). They are often used in deep excavations (e.g. basement construction). Typically, the work process involves installing steel piles at regular intervals along the planned excavation perimeter. The steel piles are then reinforced with grout.

(ii) Grouting and grout curtain construction

Grouting is the filling of void spaces with grout material, which is applied as a thick emulsion and hardens over time. A hydraulic grout pump and a grout tube are typically used for inserting the grout material. Grouting and grout curtains are used to form barriers to seal joints, reinforce steel and/or protect foundation works from water seepage. Soldier pile and pipe pile retention walls constructed by our Group also include the construction of grout curtains behind such walls.

(iii) Groundwater control

Groundwater control involves the application of geotechnical works to lower down groundwater levels at a work site to create suitably dry working conditions for excavation activities. The exclusion of groundwater may either be permanent (in which case a wall is constructed using steel sheet piles and grouting to cut-off the flow of groundwater) or temporary (where a dewatering well and a sump pump are used to drain the groundwater).

(iv) Pumping test administration

A pumping test system is a controlled field experiment for estimating the hydraulic properties of an aquifer system _ an underground layer of water-bearing permeable rock or unconsolidated sediment (e.g. gravel, sand or silt). A pumping test involves pumping groundwater from a well (normally at a constant rate) and measuring water levels in the pumped well and any nearby wells (observation wells) during and after pumping. Data gathered from a pumping test is used by hydrogeologists to assess aquifer characteristics (e.g. its ability to store and transmit water).

(v) Pre-boring

Pre-boring is the process of drilling a bore hole into the ground to prepare a site for foundation works by breaking down any hard obstructions (e.g. rocks) and to help determine the appropriate founding levels. The number and diameter of pre-bored holes required in each project depend on, among other things, the nature of the foundation and overlying construction, the type of pile to be formed and the ground conditions. Typically, a boring rig, together with a hydraulic hammer drill or a hydraulic rotator, is used to sink a temporary casing into the ground. The excavated hole is then refilled with gravel, sand and silt before the temporary casing is retrieved using a crane.

(vi) Mini piling

Mini piling involves sinking a permanent casing into a pre-bored hole (generally not greater than 400 mm in diameter). One or a bundle of reinforcement steel bars are placed in the middle as load-bearing element, then grouted with cement to form a mini pile. Mini piles are generally used for supporting lower loads, and may be used on confined site areas with difficult access, limited working space, congested environment or low headroom. They may also be used for underpinning or strengthening existing structures. The diagrams below illustrate the general structure of a mini pile:

In a typical mini piling project, a boring rig is used to drive a permanent steel casing together with a bundle of steel bars into a hole through soil and bedrock and/or other obstructions. The fine soil and rock fragments in the hole are then removed by an air compressor. The steel casing will be left in the ground permanently. Subsequently, cement grout is pumped through grout tubes to fill the cavity in between the bars. The following diagram illustrates mini piling:

(vii) H-piling

H-piles are steel structural beams driven into a pre-bored hole (generally between 610 mm to 800 mm in diameter) and grouted with cement to form a pile. Due to their strength and durability, H-piles are generally used for supporting heavier loads than the mini pile, and may be utilized for driving in dense or very stiff materials that other piling would have difficulty penetrating. H-pile is used in construction projects including buildings, bridges, highways, amongst others. They are sometimes used in conjunction with sheet piles for additional lateral stiffness and bending resistance. The diagram below illustrates the general structure of an H-pile:

In a typical H-piling project, a boring rig is used to drive a temporary steel casing together a socketed H-pile to the required depth and into a sufficiently strong bedrock layer. The diameter and the depth of the borehole are highly specific to the ground conditions, loading conditions and nature of the construction project. Air compressors are used to remove fine soil and rock fragments from the hole. Subsequently, the void spaces in the hole are filled up with grout material while the temporary casing is gradually extracted. The following diagram illustrates H-piling: