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Soil Engineering

Where should be the direction of gunning in shotcreting?

During the construction of shotcrete, it is aimed at gunning the full thickness in one single operation and this helps to reduce the occurrence of possible delamination and formation of planes of weakness. Moreover, the nozzles should be held about 0.6m to 1.8m from the surface and normal to the receiving surface. The reason of gunning perpendicular to the receiving surface is to avoid the possible rebound and rolling resultingfrom gunning at an angle deviated from the perpendicular. The rolled shotcrete creates a non-uniform surface which serves to trap overspray and shotcrete resulting from the rebounding action. This is undesirable because of the wastage of materials and the generation of uneven and rough 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.

Which one is better, bentonite slurry and polymeric slurry?

For the construction of diaphragm walls, bentonite slurry is commonly used to form a filter cake on walls of trenches to support earth pressure. The use of bentonite solely is based on its thixotrophic gel viscosity to provide support.

Though the cost of polymer is generally more expensive than bentonite, the use of polymer is increasing because polymer is generally infinitely re-usable and very small amount of polymer is normally required for construction works. The disposal cost of bentonite is quite high while the disposal of polymer can be readily conducted by adding agglomerator.


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 reinforcement function in embankment built on soft clay?

The factor of safety for the embankment constructing on soft clay is minimum at the end of construction. After that consolidation takes place, thereby increasing the shear strength of foundation soils. Reinforcement is normally introduced to maintain the stability owing to the following reasons:

(i) The reinforcement at the clay surface, which is capable of carrying tensile forces, generates shear stresses to resist the lateral deformation of clay and improves its bearing capacity.

(ii) The reinforcement could also hold in equilibrium the lateral trust developed by the fill above so that it reduces the stresses which tends to cause failure of clay foundation.


(iii) The reinforcement has a tendency to drive the failure mechanism deeper in the soft clay, which should possess higher shear strength because its strength generally increases with depth.

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.

Assessment of Ground Water using GIS and its importance in Trenchless Technology

Korukonda Vinay

This paper describes the results of a ground water potentiality assessment and its importance in the field of trenchless technology. Water plays a vital role in the development as well as for depletion of any activity in the area . Thus, the availability of surface and ground water governs the process of planning & development of any activity. The surface water resources are inadequate to fulfill the water demand. Productivity through groundwater is quite high as compared to surface water, but groundwater resources have not yet been properly developed through exploration. Keeping this in view, the present study attempts to identify and understand groundwater potential zones of the study area using GIS. The methodology includes the construction of groundwater potentiality map using Geographical Information System (GIS) to protect the groundwater resources in the study area and to formulate recommendations to reduce the water scarcity. The ground water potentiality of the area has been assessed through integration of the relevant layers which include geomorphology, geology, slope and land use/ land cover, in ArcGIS environment. Criteria for GIS analysis have been defined on the basis of ground water conditions and appropriate weightage has been assigned to each information layer according to relative contribution towards the desired output. The ground water potential zones map generated through this model was verified with the yield data to ascertain the validity of the model developed and to find its corresponding influence in the subsurface constructions.

What are the rationales of Observational Method in geotechnical works?

The idea of Observational Method was first discussed by Peck in the Rankine Lecture in 1969. The Observational Method is commonly adopted in geotechnical works in construction phase, though it is also feasible in design stage.

In essence, in the conforming design by engineers during planning stage, the design is usually based on over-conservative approach or most unfavourable conditions owing to a lack of precise and actual site information. During subsequent construction, with precise site information and condition available the Observational Method is adopted in which the original design is revised based on most probable conditions with instrumentation monitoring. If the monitoring results show that performance of the revised design approaches the limit of acceptable level of risk, then it shall be reverted to planned modification which is based on most unfavourable conditions and hence the level of risk is lowered back to the original design. Otherwise, the revised design shall continue and this results in cost reduction without comprising safety of works.


However, care should be taken in implementing Observational Method when rapid deterioration of the site may occur so that there is insufficient time for carrying out the planned modification. For instance, rapid deterioration can result from development of high pore water pressure in heavy rainfall or burst watermain.

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.