The quality of slurry plays an important role in the quality of diaphragm walls. Firstly, if a thick slurry cake is formed in the interface between slurry and in-situ soil, it has a tendency to fall off during concreting works and it mixes with freshly placed concrete. Moreover, large thickness of slurry cake would reduce the concrete cover and affect the future durability performance of diaphragm 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.

The most ideal situation is to supply each tremie pipe with a single concrete truck. However, if only one concrete truck is available, all the fresh concrete in the truck should not be placed in one single tremie pipe.
With all fresh concrete placed in one single tremie pipe while the others left void, then due to the huge supply of concrete to the tremie pipe, a small concrete hump may form at the base of the tremie pipe and it is likely that it may collapse and trap the slurry inside the diaphragm walls. Therefore, the fresh concrete should be evenly shared among the tremie pipes to avoid such occurrence.

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.

Grouting can be implemented in two common modes, namely compaction grouting and fracture grouting. For compaction grouting, high viscosity grout is commonly used for injection into soils. Upon reaching the soils, the grout would not penetrate into soil spaces. Instead it forms a spherical bulb and remains as a homogeneous mass. The formation of bulb displaces the nearby soils.

Fracture grouting involves the use of low viscosity grout. Upon injection, the grout would split open the ground by hydraulic fracturing and penetrate into the fractures. Similarly, soils are displaced during the process.

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 critical depth of piles are normally assumed as 10-20 pile diameter deep and is the depth beyond which the resistance is constant and is equal to respective value at critical depth.

The critical depth is a fallacy which comes from the failure to interpret the results of full and model-scale pile tests. In full-scale test, the neglect of presence of residual loads renders a measured load distribution to be
linear below the so called “critical depth”. Residual loads refer to loads that are induced in piles during and after installation of piles.

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 type of connection between piles and pile caps affects the load carrying capacity of pile groups. The fixity of pile head into pile cap, instead of pinning into pile cap, enhances higher lateral stiffness of the pile groups. For instance, for the same deflections, a cap with fixed connected piles can sustain far more loads than that of pinned connected piles. To satisfy the criterion of fixed connection, the minimum embedded length of piles into pile caps should be at least two times the diameter of piles.

Moreover, the fixed connection of piles at pile caps allows significant bending moment to be transmitted through the connections when compared with pinned connections.

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.