How do we compare Rowe cell and Oedometer apparatus?

The advantages of using Rowe cell over oedometer apparatus are:

(i) It possesses the control facilities for drainage and for the measurement of pore water pressure.

(ii) It is capable of testing larger diameter soil samples. Hence, more reliable data can be provided by using Rowe’s cell because of the relatively smaller effect of structural viscosity in larger specimens.

(iii) Rowe cell uses hydraulic loading system which is less susceptible to the effect of vibration than oedometer apparatus.

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.

Is it worthwhile to carry out tests on particle density of soil particles for geotechnical design?

Particle density of soils is defined by the ratio of soil particle mass and soil particle volume. Depending on soil types, the range of variation of soil particle density varies not significantly, i.e. by 4%. Therefore, it may not be worthwhile to order laboratory tests and incur additional expenditure just to determine the particles density by recognizing that the variation of particles density is not significant.

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 purpose of adding hydrogen peroxide in sedimentation analysis?

There are two major techniques of particle size distribution:

(i) Sieve analysis – for soil particles larger than 60?m they can be separated by this method.

(ii) Sedimentation analysis – for soil particles smaller than 60?m, they are too small to be sieved by sieve analysis. Instead, the particle size distribution is worked out from the rate of settlement of soil particles suspended in water by Stoke’s law.

In sedimentation analysis, the soil under testing is firstly boiled with little distilled water to wet and break up the particles. After that, hydrogen peroxide is added to remove any organic material. Then the whole mixture is allowed to stand still for a night and then boiled again to remove hydrogen peroxide.

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.

Why is multiple packer test instead of single packer test sometimes adopted in testing permeability of rock?

Packer test is used in unlined drillholes in rock to test the permeability. In single packer test, the hole is drilled to the bottom of first test section and the top of the test section is sealed off by a packer. Water is then delivered to the test section and it is kept at constant pressure and the flow is measured.

In highly fractured rock there is a high chance that water tends to leak around the packer which gives inaccurate result. As such, multiple packers are adopted instead in which three sections of the drillhole are sealed up and water is pumped to them at equal pressure. This eliminates the tendency for water to flow around the packers from the middle section.

Hence, a more accurate result could be obtained by measuring flow from the middle section alone.

Illustration of multiple pack

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.

Testing of Concrete Blocks

By
Er. Kaushal Kishore ,
Materials Engineer, Roorkee

INTRODUCTION
Concrete can be converted into precast masonry units such as Hollow and Solid normal and light weight concrete blocks of suitable size to be used for load and non-load bearing units for wallings. Use of such concrete blocks are more appropriate in region where soil bricks are costly, poor in strength and are not available. Depending upon the structural requirements of masonry unit, concrete mixes can be designed using ingredients available locally or if not found suitable then with in the most economical distance. The concrete mix used for normal hollow and solid blocks shall not be richer than one part by volume of cement to 6 parts by volume of combined room dry aggregates before mixing. Hollow concrete blocks for normal work used in masonry when reinforced is used shall not be leaner than 1 part cement to 8 parts room dry sand by volume. The mixes are designed with the available materials to give overall economy and the required properties of the products. The hollow load bearing concrete blocks of the standard size 400 x 200 x 200 mm will weight between 17 and 26 kg (1063 to 1625 kg/m3) when made with normal weight aggregates. Normal weight blocks are made with cement, sand, gravel, crushed stone and air-cooled slag. The grading for sand used in Hollow concrete block shall be as given below:
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