Soil Engineering

For rocks with widespread fractures, individual blocks resulting from these fractures may fall out and as a result slope failure may occur. Rock reinforcement (e.g. rock dowels, bolts or anchors) is installed to bolt through the discontinuities in rock to enhance the rock to behave as a single unit. With the bolting across block interfaces, the stresses would be altered within the rock mass. For untensioned rock dowels, they may be subjected to tensile forces arising from rock movement. Other than the provision of rock reinforcement, shotcreting is another method to reinforce the rock. It functions by griping the rock together and maintaining the small blocks which hold the large blocks in position.

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.

Sometimes there is a cavity in rock slopes which is caused by previous rock falls. Concrete buttress, together with the use of rock dowels, could help to stabilize the rock slope.

The buttress serves to avoid local toppling of rock face. Moreover, it keeps protects the unstable rock and keep it in place. The presence of buttress also helps hold up the overhang. The size of buttress should be large enough to support the weak rock. In case the surface on which the buttress is founded is not normal to the resultant forces exerting on the buttress, buttress is tied to rock surface by using rock dowels to avoid the occurrence of sliding.

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.

Hydroseeding is the provision of grass seed mixed with fertilizer and nutrient by spraying. The grass seed shall grow and the root of grass serves as reinforcing fiber to hold tightly the surface soils.

Turfing is the direct application of grass with developed roots on slope surface. The already-developed grass is expected to grow easier when compared with hydroseeding. The roots of grass shall extend onto soils to strength the overall surface.

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.

A sprig is a part of stem with crowns and roots which is cut from a rhizome or stolon. Sprigging is a type of vegetative planting by placing sprigs in spaced intervals in holes. With proper transplantation and maintenance, a sprig is capable of growing as a plant. The cost of sprigging is moderate and vegetation is expected to grow for around six months. However, this method requires high manual input and is labour intensive.

Turfing is the direct application of vegetation with developed roots. The cost of turfing is high when compared with sprigging. However, it is the quickest way to get vegetation. Within a month mature-looking vegetation is ready for use.

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.

Vegetation in slopes could modify the soil moisture condition in two ways:

(i) Soil moisture is absorbed by roots of vegetation and the water is transpired to its root;
(ii) It intercepts the rainfall by reducing the amount of rainwater penetrating into the slope.

Both processes, i.e. evapotranspiration and interception effected by the presence of vegetation contribute to dry soil conditions. Moreover, evapotranspiration results in soil suction in unsaturated soil slopes, which further improves the shear strength of soil. As such, it tends to delay the time of saturation in slopes and this essentially improves the slope stability.

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.