BASEMENTS DESIGN

Construction of basements for buildings can be very challenging if it is situated in CBD with underground services and tall buildings around the site. Temporary and permanent retention system is required to construct basements of buildings.

TYPES

Commonly adopted methods of basement construction are top-down method, bracing method and anchored method.
Top-down method is often used for constructing high-rise buildings in urban areas. It starts with constructing load-bearing foundation walls and laying a concrete ground floor on top of those walls. Then, a large (often complex basement) gets excavated beneath that ground floor. This method is in general expensive, but its major advantage is that building’s upper floors can be built while a basement is getting excavated.
Bracing method is more economical than the top-down method. This method offloads weight from the retaining wall and transfers it to horizontal struts, which are installed in front of the wall. This method does a good job of reducing strain on your retaining walls, although horizontal struts are not as strong and foolproof as a full concrete floor bolted to a foundation, which is what you would install in the top-down method. This method is more cost effective and less complex as compared to top-down, it is therefore preferred in most cases.
Anchored method involves installing strand anchors into the ground, which also run through the retaining wall. The anchoring force of the earth provides stability to the overall structure and allows excavation to proceed swiftly and safely. These anchors are mostly prestressed and are also called active anchors.

WHAT TO CONSIDER FOR DESIGN?

At the design stage, understanding the challenges of ground conditions, sensitivity of nearby assets, groundwater level and construction time is very important for the optimum design. It is also important to know the sequence of construction for the basement to adopt the best solution.
For shallow groundwater and soft ground conditions, D-Walls with temporary props can be considered better than secant piles with ground anchors. It will be difficult to achieve ground anchor capacity in soft ground as well as stop groundwater infiltration. It will however require thick D-walls and base slab to control hydrostatic pressure. The major advantages of this method are to facilitate construction of basements without impacting propping system and the props can be removed or adjusted as the construction progresses.
On the other hand, if the geology of the ground is hard rock and groundwater is not shallow, soldier piles with ground anchors may be considered better option.
It is, therefore, important to understand the ground conditions, depth of basement, groundwater levels, location of nearby underground or above ground sensitive services and adjacent buildings to decide the best solution of basement retention system. It is also important to have good groundwater management plan in place.
The most important is to have a thorough collaboration process between the engineers and specialised contractors from the design phase right through to construction.

GEOCONSOL SERVICES:

At GEOCONSOL, we deliver a tailored suite of the following services to accommodate project geology, complexity, diverse design solutions, and safety requirements.

• Preliminary review of the ground conditions
• Advice on additional geotechnical information required as per Project Specifications or Standards
• Advice on suitability of foundation type
• Tender design advice of foundations for buildings, bridges, retaining walls, noise walls, barriers, light poles
• Detailed design advice of foundations for buildings, bridges, retaining walls, noise walls, barriers, light poles
• Construction phase services including verification of ground conditions adopted in foundation design, insitu testing to verify ground conditions and reporting.
• Foundation design optimization
• Independent review of footings design by others
• Proof Engineering

GEOCONSOL, has certified resources to provide the above services.