Civil Engineering projects releated to geological aspects

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TYPES of the Civil Engineering Projects with respect to the Geological Aspects and Investigations:
(i) Structures in which the basic problem is concerned with the foundation only e.g. tall buildings, bridges, long walls, etc.
(ii) Structures which are constructed in and from the earth i.e. fills e.g. under-fills and back-fills of the highways, motorways, railways, tunnels, bridges, culverts, dams & reservoirs, retaining walls, etc.
(iii) Structures which are concerned with the stability of earth slopes e.g. embankments, mounds, levees, etc.
(iv) Structures which are concerned with water-tightness problems – where the geology of water-tightness of the site is involved e.g. rivers, lakes, canals, reservoirs, catchment-areas, etc.
(v) Projects concerned with Ground-water and Hydro-geology
e.g. accessories of dams, reservoirs, rivers, canals, drains and foundations of the bridges
Effects of WATER on the site and foundation of a Civil Engineering Project:
 Special consideration is given to the effects of surface-water and of a big channel or source of water existing near a proposed Civil Engineering Project and effects of the sub-surface water in and under its foundation that is likely to affect the project in the future
Water reduces the Load Bearing Capacity of the foundation of a Civil Engineering Project and causes the deterioration of the cement and concrete structures too
 Projects existing in or close to the water e.g. accessories of dams, reservoirs, rivers, canals and foundations of the bridges as well as the projects to be laid on and inside the ground that is likely to be affected with the water during the heavy rains, e.g. highway, motorway, railway, runway, tunnel, foundations, etc are designed against the worst and aggressive condition of the water i.e. against the heavy rains, rainy season, floods, etc likely to exist
around and under a Civil Engineering Structure in the future
 Reccy and Ground-Surveys of the proposed site are carried out (and the site is observed) in the event or just after the event of heavy rains, floods, etc as well as in the maximum dry condition of the site in order to find out the load bearing capacity of the ground in the two extreme climatic conditions and to find out the difference between the dryness and soaking of the ground and hence the behavior and characteristics of the ground in these extremes conditions
 Similarly the Structures (i.e. Structural Members) and Foundations of the tall Civil Engineering Structures e.g. tall buildings, tall bridges, tall dams, etc are designed against the worst and aggressive conditions of earthquakes, winds, hurricanes, any other storm, etc likely to damage a Civil Engineering Structure in the future  
 History and information about the floods, earthquakes, winds, hurricanes, any other storm, etc of the nearby Civil Engineering Projects are also checked and studied
Geological Investigation of the ground for Final Design:
 After having selected the site on the basis of preliminary Geological Investigation (i.e. carrying out reccy, geo-surveys, taking the ground-samples and testing the collected samples in the lab), detailed and final Geological Investigation is carried out
 For this purpose, additional and detailed boring and testing of the ground is carried out:
(i)  In-Situ Soil Testing (is carried out in order to find out in-situ behavior and characteristics of the ground) – These tests will be studied in good detail in Soil Mechanics
(ii) Detailed boring of the sub-surface rock only – Rotary Drilling and Coring is carried out
Depth of the ground-boring depends upon the type, size, life, purpose and area of the structure to be built
In many situations and projects, the final and practical decisions  
are made more on the basis of results of the field tests than results of the same ground-samples tested in the lab
Important Field Tests (Field Tests are also known as In-Situ Tests) Equipment of the first Four Tests is known as Penetrometer:
Standard Penetration Test (SPT)
Static Cone Penetration Test (CPT)
 Dynamic Cone Penetration Test (DCPT)
 Cone Penetrometer using Physical Phenomena
 Vane Shear Test
 Bearing Capacity Test
 
(i) Standard Penetration Test (SPT): Soil boring reports are not considered complete without the result of this test – a very important test
This test is carried out by driving a Standard Split Spoon Sampler (3 to 5 ft long, usually 3 ft long) inside an already made bore-hole, by usually a hydraulic hammer weighing 50 to 100 kg, usually 65 kg, dropping it through a height of half to one meter, usually ¾ of a meter i.e. 750 mm
The number of blows for every 75 mm penetration is counted until the sampler penetrates a depth of 450 mm. The result is divided into three sets of blows usually for every 150 mm penetration.
First set is neglected; second and third sets are reliable and taken into account. Number of blows for the last 300 mm are called N value for SPT. Chart showing N value for sand and soil:
N Value        Consistency        Unconfined Compressive                         Strength
0 – 4             Very loose sand    Nil
10 – 30         Medium sand        Nil
> 50            Very dense sand    Nil
0 – 2             Very loose soil    Nil
4 – 8             Medium soil        10 N (=10 kN/m2)
8 – 15             Stiff soil        13.5 N
> 30             Very hard soil        > 20 N     (ii) Static Cone Penetration Test (CPT): Used for soft clays, silts and fine-sands only. In this test, pressure, denoted as Q(CPT) (usually expressed in kgf /cm2) required to push the cone of this equipment into the soil, is measured. This test is also known as Dutch Cone Penetration Test (but not called as DCPT which is Dynamic Cone Penetration Test)  Number of b
(iii) Dynamic Cone Penetration Test (DCPT):
Equipment consists of penetrating cone with Apical Angle of 60O
50 mm cone dia test without circulating bentonite, for simple investigation
65 mm cone dia test with circulating bentonite, for detailed investigation
50 mm cone dia test same as Standard Split Spoon Test i.e. SPT
65 kg hammer drops through 750 mm height
Number of blows for the cone to penetrate 300 mm is taken as Dynamic Cone Penetration Value: ND
Blows count is taken for every 100 mm penetration of the cone



About the author

muhammad-bilal-310

i am a student of civil engineering takes much interest in this field

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