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Why are the wires in some gabion walls designed in hexagonal patterns with doubly twisted joints?

Gabions are wire mesh boxes which are filled with stones and they are placed in an orderly pattern to act as a single gravity retaining wall. Lacing wires or meshes are designed to hold the gabion boxes together. Most of the wires are zinc-coated or PVC coated to prevent the steel wire from corrosion. Moreover, it is common that the wires are fabricated in hexagonal patterns with doubly twisted joints to avoid the whole gabion mesh from disentanglement in case a wire accidentally breaks. Owing to the nature of gabion filling materials, they are very permeable to water.

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They have particular application in locations where free water drainage has to be provided. Moreover, gabions are capable of accommodating larger total and differential settlements than normal retaining wall types so that they are commonly found in locations where the founding material is poor.

wires-of-gabion-walls

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

How to carry out water control for sheet pile walls?

Ground water flow into excavations constructed by sheet pile walls should be minimized in order to save the cost of the provision of pumping systems or well points to lower the water table inside the excavation.

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How could counterforts in counterfort retaining wall assist in resisting earth pressure?

Counterforts are used for high walls with height greater than 8 to 12 m. They are also used in situations where there is high lateral pressure, i.e. where the backfill soils are heavily surcharged.

The counterforts tie the base slab and wall stem together and they act as tension bracing which strengthen the connection between wall and base slab. The counterforts help to reduce bending moment and shear forces induced by soil pressure to the retaining wall. Moreover, it also serves to increase the self-weight of the retaining wall which adds stability to the retaining wall.

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This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

What is the function of mortar in brick walls?

A typical brick wall structure normally contains the following components:
(i) a coping on top of the brick wall to protect it from weather;

(ii) a firm foundation to support the loads on the brick wall; and

(iii) a damp course near the base of the brick wall to avoid the occurrence of rising damp from the ground.

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Bricks are bedded on mortar which serves the following purposes:
(i) bond the bricks as a single unit to help resist lateral loads;

(ii) render the brick wall weatherproof and waterproof; and

(iii) provide even beds to enhance uniform distribution of loads.

brick-wall

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

How does pressure distribution vary under rigid and flexible footings?

For thick and rigid footings, the pressure distribution under the footings is normally assumed to be linear. If uniform and symmetrical loadings are exerted on the footings, the bearing pressure is uniformly distributed. However, if unsymmetrical loads are encountered, then a trapezoidal shape of bearing reaction would result.

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For flexible footings on weak and compressible soils, the bearing pressures under footing would not be linear. As such, a detailed investigation of soil pressures is required in order to determine the bending moment and shear forces of the structure.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.