Bored piles primarily carry static vertical loads when supporting a building. In designing such piles, the shaft resistance and end bearing are often estimated when determining the pile’s load-carrying capacity. To ensure satisfactory performance, the pile also needs to meet specific settlement criteria at working loads. One helpful aid in pile design is using numerical simulations. With advances in computing, access to numerical simulations has become widely available and often quite economical. This article highlights some practical aspects of numerical simulations which can be helpful in pile design.
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Author Archives : Hee Yang Ng, MIStructE, C.Eng, P.E.
Hee Yang Ng is a Principal Engineer with a building control agency in the Asia-Pacific region.
Reinforced concrete is a construction material widely used in many applications, including buildings, bridges, and other infrastructures. Due to its massive size and various redundancies, concrete structures are often considered solid, robust, and safe. However, there have been instances of concrete structure failures and collapses, many due to erroneous assumptions or oversight by the designers in evaluating the design situation or poor construction practices. This article highlights several design and construction situations that designers and builders should pay special attention to in order to prevent failures.
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Steel sections can be used as columns, beams, and struts to resist axial forces (tension/compression), moments, and shears. They may come in the form of open sections (such as ASTM A992 – Wide Flange W-shapes beams/S-shapes beams) or closed sections (such as Hollow Structural Section [HSS] tubing).
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Rapid transportation by metro has become an indispensable development for many modern cities. Due to the depth and length of the tunnels, these urban subway lines are often built using circular tunnel boring machines (TBM). Two common types of TBMs are slurry TBMs and earth pressure balance (EPB) TBMs. While the tunnel shield and completed segmental tunnel linings (usually discrete precast concrete panels assembled together or precast rings) are relatively safe, the TBM excavation process can be potentially dangerous. This article looks at some measures and good practices to avoid sinkholes (Figure 1) during closed-face tunneling. The intricacies of tunneling and TBMs are much broader than the overviews included here.
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Gentle slopes are usually stable. As the slope’s inclination angle increases, the risk of failure increases accordingly. This can be attributed to the instability of the soil mass when the geometry results in the soil strength being unable to provide adequate support and its natural tendency to achieve stability and equilibrium. Failures in slopes usually occur in the form of soil movement, where the unstable mass topples or slides downwards or sideways to achieve stability.
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A Brief Summary
Bored piles, also referred to as auger-cast piles, are large-diameter cast-in-place concrete piles used commonly to support buildings when column loads are high. The design of bored piles requires the designer or the project’s geotechnical engineer to estimate the load-carrying capacity of the pile based on the ground conditions at the project site. One way to predict the pile capacity is by carrying out calculations using soil parameters obtained from site investigation data. While many pile design methods are highly empirical, pile capacity can also be affected by other factors such as the method of installation, quality of workmanship, and construction materials used. Therefore, pile load testing is an essential aspect of pile design that should not be overlooked.
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Preventing Damage Caused by Ground Loss and Water Loss
Deep excavation projects in highly urbanized and built-up environments must be designed and constructed with additional care. The design of these projects needs to deal with lateral wall movement, ground settlement, ground loss, and subsurface water pressure changes, all of which can lead to damage to adjacent structures (Figure 1). Damage can be in the form of cracks on non-structural walls (appearance), jammed windows and doors or dysfunctional services (functionality), and, in severe cases, cause structural members to be distressed (safety). Work suspension limits, usually for building settlement and inclinometers, may be breached. The project team could potentially face delays, claims, and additional costs due to expensive rectification work.
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Three-dimensional (3-D) volumetric construction is also known as concrete modular construction or Prefabricated Prefinished Volumetric Construction (PPVC). This construction method involves the stacking of rectangular factory-finished modular components on-site to form a complete building, similar to Lego® bricks. Joints are typically grouted with special interfacing details. To achieve speed and high productivity, the components have to be substantially completed with minimal site work. This article looks at some of the key design considerations and strategies that designers need to think about when using this type of construction method.
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The Nicoll Highway excavation shoring construction collapse occurred in Singapore on April 20, 2004, around 3:30 pm. The accident deeply impacted Singapore’s local construction industry. Many regulations were tightened up through this incident, such as appointing qualified geotechnical engineers for deep excavation works and requiring authority submissions for temporary construction. The collapse resulted in four people killed and three injured. Several project parties were charged in court, and project completion was delayed.
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A Comparison of Three Design Codes
Foundations for a building are required to support the structure so that it remains safe and functional, and so that they meet serviceability limits. Buildings with excessive cracking and movement (e.g. total settlement, differential settlement, tilt, etc.) are alarming and not acceptable. …