Soil Engineering

Reinforced fill consists of reinforcement embedded in fill with facing. With backfilling material of clayey nature, it may pose problems to potential corrosion of steel reinforcement. The low permeability of cohesive fill materials tends increase the duration of contact between reinforcement and water and may cause corrosion problems. Moreover, consideration should be given if cohesive materials could also achieve the required compaction.

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.

Rockfall barrier is intended to absorb the energy of rockfall safety without the need of future regular maintenance. The net of rockfall barrier is best to be arranged like Olympic Rings with interlacing (called ringnet) and it has proved to be very effective in its energy absorption capacity.

The main function of post of rockfall barrier is to provide support to the net. Impacts to posts should not result in the collapse of the structure. In the event of directly impact of rocks with the posts, there is a break devise at the post’s base plate which is designed to allow the post from separating the base plate. In this way, it serves to protect the anchor of base plate from being damaged.

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 rockfall barrier has to serve basically the following two purposes:

(i) It has to be sufficiently high so that it would not be jumped over by rock boulders.
(ii) It has to resist the impact of rockfall without structural failure.

For rockfall energy greater than 2,500kJ, it requires the installation of earth dams, underpinning (stabilized) or even complete removal. For rockfall energy less than 2,500kJ, it can be resisted by rigid structures made of concrete or steel. However, the recent trend is that most of these rigid structures are replaced by flexible structures like flexible wire rope nets. For total work on barrier system, it is defined as force times displacement. The merit of flexible system lies in the small forces generated with large displacement when compared with larges forces with little displacement in rigid structures. As a result, the flexible structures can be designed with low impact forces leading to better and economical design.

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.

Rock dowels are passive reinforcing elements which need some ground displacement for activation. In installation of rock dowels, a hole is drilled and untensioned steel bars are inserted into the hole. When displacements along joints occur, rock dowels are subject to both shear and tensile stresses. The level and ratio of shear and tensile stress depends on the properties of the surrounding ground, the grout material filling the annular gap between the dowel and the ground and the strength and ductility parameters of the rock dowel itself. Moreover, the degree of dilation during shear displacement affects the level of stress acting within the dowel.

Rock bolts are tensioned once the anchorage is attained to actively set up a compressive force into the surrounding rock. This axial force increases the shear capacity and is generated by pre-tensioning of the bolt. The system requires a bond length to enable the bolt to be tensioned. In essence, rock bolts start to support the rock as soon as they are tensioned and the rock does not have time to start to move before the rock bolt becomes effective.

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.

The use of rock bolts can be dated back to Roman Empire and it was commonly believed that rock bolts pin surface rock (bedded rock strata or individual rocks) to more stable rock. With the insertion of rock bolt into rock slope, it increases the rock mass’s stiffness and strength with respect to shear and tensile loads. Axial force in rock bolts consist of a force component normal to joint plane which contributes frictional resistance, and a force component parallel to joint plane which contributes to dowel action.

Inclined rock bolts helps to stiffen shear and results in an increase in shear strength at smaller displacements. Rock bolts perpendicular to shear planes provide the lowest shear resistance. The optimal inclination of rock bolt is 30^o to 60^o based on past experimental works.

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.