The construction of a building can be considered as production with temporary factory. The building site being the ‘factory’ in which the building contractor will make the product on site. Site layout can be defined as site space allocation for material storage, working areas, units of accommodation, plant positions, general circulation areas, and also access and egress for deliveries and emergency services.

The site layout would be focusing on construction project of a building and the elements on what it should have. The building site have to be carefully controlled so that:

• The operatives of construction have the right machinery in the most advantageous position.
• The materials stored with care so that they are readily available and not interfering with general site circulation.
• An adequate storage spacing for construction materials on site.
• Site accommodation and complete facilities for construction workforce..

Knowledge of The Site

It is important to acquire the knowledge of the project site before setting out the site layout. The knowledge about the project site can be obtained from:

• Contract Document
• Site Investigation
• Information from Local Authority

Knowledge from Contract Document
Plant Schedule
– This can be prepared in the form of a bar chart and method of statements showing the requirements and utilization on which will help in deciding the right equipment and the space for plant accommodation will be needed on site.

Material Schedule
– The basic data can be obtained from the bill of quantities. The contractor can predict the delivery periods and the amount or size of the site space and/or accommodation required.

Labor Summary
– Basic data obtained from the bill of quantities and pre-tender bar chart programmed to establish the number of sub-contract trades required. Also the quantity and type of site personnel accommodation required.

A Set of Hand Auger for Soil Sampling

Knowledge from Site Investigation
Access to Site
– All information regarding on-site and off-site access, road and rail facilities, distances involved and bridge weight or height limitations on approach routes.

The Workforce
− About the travel distances, availability of local trade contractors, specialist contractors, local rates of pay and facilities to be provided, examples site accommodation, catering, health and safety equipment, and so forth.

Temporary Services

The Common Services Trench

– Available and adequate power and water supplies together with rates of payment or services already on site, diversion required and the time element involved in carrying out any necessary diversion together with cost implications.

Security Matters
– Local vandalism and pilfering record (history if needed), security contractors facilities, need for night security, fencing hoarding requirements to prevent trespassing and to protect the people in the vicinity.

Site Clearance and Demolition
– The neighboring properties, preservation orders, trees, demolition problems and special insurance considerations.

Ground Composition
– All the general site conditions such as nature of soil, classification of soil, height of water table, flooding risks, tidal waters, site elevation, and so forth.

Knowledge from Local Authority
From the planning, highways, building departments
– Permission to develop the project site.

To ascertain the viability of the proposal
– Access roads and facilities are adequate.

Proposed alteration and improvement are acceptable
– Follow the given outline for approval.

The detail planning of construction application is necessary for authority approval…

Planning Site Layouts

When planning site layouts the following must be taken into account:

• Site Activities
• The Efficiency
• Facilities and Accommodation

Site Activities
The time needed for carrying out the principal activities can be estimated:

1. the data obtained previously for preparing the material such as concrete where the rate of placing concrete will be determined by the output of the mixer,
2. labor requirements, example speed of transporting the mix to the appropriate positions.

Alternatives which can be considered are:
– Provide more than one mixer, regulated supply of ready mix concrete or on large contracts, pumping the concrete to the placing position.

All alternatives methods for any activity will give different requirements for staff numbers, material storage, access facilities and possibly plant types and numbers.

Efficient Handling and Storage of Materials

The Efficiency
To achieve maximum efficiency the site layout must aim at maintaining the desired output of the planned activities. This will depend largely upon the following factors:
• Avoidance, as far as practicable of double handling materials.
• Walking distance are kept to a minimum to reduce the non productive time spent in covering the distance between working, rest and storage areas.
• Avoidance of loss by the elements;
– provide adequate protection for unfixed material on site, thereby preventing time loss and cost of replacing damage materials,
– Proper store keeping arrangements to ensure that the materials are of the correct type, in the correct quantity and are available when required.
• Avoidance of loss by theft and vandalism;
– provide security arrangements by having adequate hoardings and fences.
• Avoidance of loss due to pilfering by site staff;
– provide adequate system of stores’ requisition and material checking procedures.
• Minimizing on-site traffic congestion;
– plan delivery arrivals,
– provide adequate parking facilities for staff cars and mobile machinery when not in use,
– provide sufficient turning circle room for the type of delivery vehicles likely to enter site.

Facilities and Accommodation
The main contractor is obliged to provide a safe, healthy place of work and safe system of work, plant and equipment which are not a risk to health as well as environment:

• A safe and healthy place of work,
• Safe access and egress from place of work,
• Safe and efficient system of work,
• Safe items of plant and equipment,
• Suitable and adequate training, supervision and instruction in the use of equipment,
• Suitable and appropriate Personal Protective Equipment (PPE),
• Material and substances which are safe to use.

Apart from legislative necessities, the main area of concern will be sizing, equipping and assigned a location to the various units of accommodations such as:

• Mess Hut or quarters
• Toilets and washing area
• First aid and medical rooms
• Offices – Contractor’s supervisory staff, Clerk of works, Reception of material or security
• Lock up store for materials and tools
• Storage compound for major materials such as aggregate, sand, cement
• Timber store and formwork fabrication area
• Reinforcement store and fabrication area
• Scaffold and misc. store
• Sufficient vehicle parking areas
• Plant and machinery area such as tower crane, concrete deliveries, sand and cement storage, and site mixer
• Fencing or hoarding to mark boundary
• Great services and welfare
• Site Identification for workers and visitors

Site Layout for Building Construction

The site layout can be divide into several sections such as the main gate, hoarding fencing, uncovered storage area, covered storage area, car park, site office, access road / traffic in site, tower crane, workers mess, sign board, guard house, workshop for machinery, and material or soil stockpile.

The Conclusion

The planning of a site layout in practice will depend upon a number of factors such as the time and money. The need for careful site layout and site organization planning becomes more relevant as the size and complexity of the construction operation increases, and especially where spare site space is very limited.

Read More Constructive Posts:

• Construction Life Could Be Fun
• Who Else Working With The Civil Teams?
• In The Minds Of The Builders
• Article: Civil Construction and Engineering

Technology is a wonderful thing especially in today’s world. Things we once though impossible are now realities thanks to technology. Whether it is sharing music online, chatting with friends across the globe in real time, driving an electronically powered car, or able to build an awesome skyscraper buildings as we are seeing things that didn’t exist a few years ago.

The same holds the truth for our professional and advanced modern world. When you were studying engineering, you probably learned the latest and greatest ways of doing your work. You had access to the most up-to-date research and materials during your time in school. Since then, things may have changed dramatically and there is now an even better way of accomplishing your work. For this particular reason, engineering continuing education should be a crucial part of your career. By realizing the impact it would be towards the workforce supplies due to shortage, this is recommended to continue the engineering generation’s years to come by replacing the veteran with the young engineers.

Apart from the fact that engineering continuing education keeps you armed with the best tools available, it is often mandated by law through accreditation. Furthermore, many states require the engineers to keep current certifications. These certifications are only available by completing continuing education courses. Finding the right civil engineering course will ensure that you stay ahead of the game and maintain the ability to be the best engineer you can be for future generations.

Engineering continuing education courses obviously differ according to your specialty especially in civil engineering where the sub-divisions separate from another. Civil engineers will complete much different courses than would an electrical engineer. The common thread in all of these courses is time. You will need to invest a good amount of time and of course money in completing the required courses. By selecting the right course, however, will minimize headaches and wasted steps that will eventually leads to failure.

For more convenient purpose, select a course that is close to your work or home. Courses that cause you to drive significant distances would promote bad attitudes, resentment, and lack of concentration. A course located close to home is more convenient and will allow you to spend more time in your personal life, with family, less time on the road, and be able to focus more without being fatigue quite often.

Selecting a course that is taught via the Internet which is online education would be one good option if possible or offered. Many agencies provide engineering continuing education courses in an online setting. Class participants can log in remotely from home, work, at Starbucks, or even on vacation. Online courses do require participants to maintain a certain level of self-motivation and discipline where the courses are the ultimate in terms of flexibility and user-friendly with less pain for study.

Another thing to look for in a civil engineering study program is through recommendations. Talk to co-workers to find out which courses they recommend. Chances are, they have tips, advices, and guidelines that will help guide you to the perfect program. If possible, take a course with a co-worker whereas you may both benefit from an additional accountability and teamwork in workforce.

In the end, you will gain valuable knowledge and training from an engineering continuing education program. Before you begin to enroll, you may feel like you are signing up for pointless busy work. By the end of your coursework, however, you will discover new techniques and other useful information that will help you succeed in boosting your profession to much higher level. Learning is always a good thing and becomes essential for advancement of technology. [ Photo from Flickr ]

Read More Constructive Posts:

• Article: Civil Engineering News
• In The Lifes of Engineering Students
• Video: Civil Engineers – What Say You?
• Article: Supporting Facts of Engineers Shortage
• Are We Having Enough Civil Engineers?

Concrete mix designs is best defined as a process in selecting suitable ingredients, which is cement, aggregate, sand and water, and determining their relative proportions to give the required strength, workability and durability.  A design mix, which is a performance specification stating required strength and minimum cement content but leaving the grading and details of the mix design to be work out.

Objective of Mix Design

Concrete Mixer – Drum type 140L

Two main objectives for concrete mix design:

• To determine the proportions of concrete mix constituents of; Cement, Fine aggregate (or normally Sand), Coarse aggregate, and Water.
• To produce concrete of the specified properties.
• To produce a satisfactory of end product, such as beam, column or slab as economically as possible.

Theory of Mix Design

The Process of Mix Design
The method of mix design applied here is in accordance to the method published by the Department of Environment, United Kingdom (in year 1988).

There are two categories of initial information required:

1. Specified variables; the values that are usually found in specifications.
2. Additional information, the values normally available from the material supplier.

Reference data consists of published figures and tables is required to determine the design values including;

• Mix parameters such as target mean strength, water-cement ratio and concrete density.
• Unit proportions such as the weight of materials.

The design process can be divided into 5 primary stages. Each stage deals with a particular aspect of the mix design:

Stage 1: Determining the Free Water/ Cement Ratio
i) Specify the required characteristic strength at a specified age, f_c
ii) Calculate the margin, M.

M = k x s     ….. [ F1 ]

where;
k = A value appropriate to the defect percentage permitted below the characteristic strength.  [ k = 1.64 for 5 % defect ]
s = The standard deviation (obtained from CCS 1).

CCS 1: Approximate compressive strength (N/mm2) of concrete mixes made with a free-water/cement ratio of 0.5

iii) Calculate the target mean strength, f_m

f_m =   f_c + M     ….. [ F2 ]

where;
f_m = Target mean strength
f_c = The specified characteristic strength

iv) Given the type of cement and aggregate, use the table of CCS 1 to obtain the compressive strength, at the specified age that corresponds to a free water/cement ratio of 0.5.

CCS 4: Relationship between compressive strength and free-water/ cement ratio.

v) In figure CCS 4, follow the ‘starting line’ to locate the curve which passes through the point (the compressive strength for water/cement ratio of 0.5). To obtain the required curve representing the strength, it is necessary to interpolate between the two curves in the figure. At the target mean strength draw horizontal line crossing the curve. From this point the required free water/cement ratio can be determined.

Stage 2: Determining the Free-water Content

CCS 2: Approximate free-water contents (kg/m3) required to give various levels of workability.

Given the slump or vebe time, determine the free water content from table CCS 2.

Stage 3: Determining the Cement Content

Cement Content = Free Water Content / Free-water or Cement Ratio     ….. [ F3 ]

The resulting value should be checked against any maximum or minimum value that may be specified. If the calculated cement content from F3 is below a specified minimum, this minimum value must be adopted resulting in a reduced water/cement ratio and hence a higher strength than the target mean strength. If the calculated cement content is higher than a specified maximum, then the specified strength and workability simultaneously be met with the selected materials; try to change the type of cement, the type and maximum size of the aggregate.

Stage 4: Determining the Total Aggregate Content

This stage required the estimate of the density of fully compacted concrete which is obtained from figure CCS 5. This value depends upon the free-water content and the relative density of the combined aggregate in the saturated surface-dry condition. If no information is available regarding the relative density of the aggregate, an approximation can be made by assuming a value of 2.6 for un-crushed aggregate and 2.7 for crushed aggregate.

CCS 5: Estimated wet density of fully compacted concrete.

With the estimate of the density of the concrete the total aggregate content is calculated using equation F4:

Total Aggregate Content = D – C – W     ….. [ F4 ]

where;
D = The wet density of concrete ( in kg/m³)
C = The cement content (in kg/m³)
W = The free-water content (in kg/m³)

Stage 5: Determining of The Fine and Coarse Aggregate Contents

This stage involves deciding how much of the total aggregate should consist of materials smaller than 5 mm, i.e. the sand or fine aggregate content. The figure CCS 6 shows recommended values for the proportion of fine aggregate depending on the maximum size of aggregate, the workability level, the grading of the fine aggregate (defined by the percentage passing a 600 μm sieve) and the free-water/ cement ratio. The best proportion of fines to use in a given mix will depend on the shape of the particular aggregate, the grading and the usage of the concrete.

CCS 6: Recommended proportions of fine aggregate according to percentage passing a 600 μm sieve.

The final calculation, equation F5, to determine the fine and coarse aggregate is made using the proportion of fine aggregate obtained from figure CCS 6 and the total aggregate content derived from Stage 4.

Fine Aggregate Content = Total Aggregate Content x Proportion of Fines ….. [ F5 ]

Coarse Aggregate Content = Total Aggregate Content – Fine Aggregate

Procedures of Mixing

Production of Trial Mix

1. The volume of mix, which needs to make three cubes of size 100 mm is calculated. The volume of mix is sufficient to produce 3 numbers of cube and to carry out the slump test.
2. The volume of mix is multiplied with the constituent contents obtained from the mix design process to get the batch weights for the trial mix.
3. The mixing of concrete is according to the procedures given in laboratory guidelines.
4. Firstly, cement, fine and course aggregate are mixed in a mixer for 1 minute.
5. Then, water added and the cement, fine and course aggregate and water mixed approximately for another 1 minute.
6. When the mix is ready, the tests on mix are proceeding.

Slump Test apparatus for Concrete Workability

Tests on Trial Mix

1. The slump tests are conducted to determine the workability of concrete.
2. Concrete is placed and compacted in three layers by a tamping rod with 25 times, in a firmly held slump cone. On the removal of the cone, the difference in height between the uppermost part of the slumped concrete and the upturned cone is recorded in mm as the slump.
3. Three cubes are prepared in 100 mm x 100 mm each. The cubes are cured before testing. The procedures for making and curing are as given in laboratory guidelines. Thinly coat the interior surfaces of the assembled mould with mould oil to prevent adhesion of concrete. Each mould filled with two layers of concrete, each layer tamped 25 times with a 25 mm square steel rod. The top surface finished with a trowel and the date of manufacturing is recorded in the surface of the concrete. The cubes are stored undisturbed for 24 hours at a temperature of 18 to 22⁰C and a relative humidity of not less than 90 %. The concrete all are covered with wet gunny sacks. After 24 hours, the mould is striped and the cubes are cured further by immersing them in water at temperature 19 to 21^oC until the testing date.
4. Compressive strength tests are conducted on the cubes at the age of 7 days. Then, the mean compressive strengths are calculated.

The Calculations

Here is one example of calculation from one of the mix design obtained from the laboratory. We have to fill in all particulars in the concrete mix design form with some calculations…

CCS 3: Relationship between standard deviation and characteristic strength.

Firstly, we specified 30 N/mm² at 7 days for the characteristic strength. Then, we obtained the standard deviation, s from the figure CCS 3. So, s = 8 N/mm².

From the formula F1, k = 1.64 for 5 % defect. The margin, M is calculated as below:
M = k x s = 1.64 x 8 = 13.12 N/mm²

With the formula F2, target mean strength,  f_m is calculated as below:
Target mean strength, f_m = f_c + M
= 30 + 13.12 = 43.12 N/mm²

The type of cement is Ordinary Portland Cement (OPC). For the fine and course aggregate, the laboratory’s fine aggregate is un-crushed and for coarse aggregate is crushed before producing concrete.

Then, we obtain the free-water/ cement ratio from table CCS 1. For OPC ( 7 days ) using crushed aggregate, water/cement ratio = 36 N/mm².

After that, from the figure CCS 4, the curve for 42 N/mm² at 0.5 free-water ratio is plotted and obtained the free-water ratio is 0.45 at the target mean strength 43.12 N/mm².

Next, we specified the slump test for slump about 20 mm and the maximum aggregate size we used in laboratory is 10 mm. For the specified above, we can obtained the free-water content from table CCS 2 at slump 10 – 30 mm and maximum size aggregate 10 mm, the approximate free-water content for the un-crushed aggregates is 180 kg/m³ and for the crushed aggregates is 205 kg/m³. Because of the coarse and fine aggregates of different types are used, the free-water content is estimated by the expression:

Free-water Content, W
= ²/₃ W_f + ¹/₃ W_c
= (²/₃ x 180) + (¹/₃ x 205)
= 188.33 kg/m³

where,
W_f = Free-water content appropriate to type of fine aggregate
W_c = Free-water content appropriate to type of coarse aggregate

Cement content also can obtained from the calculation with the expression at F3:
Cement Content, C = Free Water Content / Free-water or Cement Ratio
= 188.33 / 0.45 = 418.52 kg/m³

We assumed that the relative density of aggregate (SDD) is 2.7. Then, from the figure CCS 5 with the free-water content 188.33 kg/m³, obtained that concrete density is 2450 kg/m³. The total aggregate content can be calculated by:

Total Aggregate Content = D – C – W
= 2450 – 418.52 – 188.33 = 1843.15 kg/m³

The percentage passing 600 μm sieve for the grading of fine aggregate is about 60 %. The proportion of the fine aggregate can be obtained from the figure CCS 6, which is 38 %. Then, the fine and course aggregate content can be obtained by calculation:

Fine Aggregate Content
= Total Aggregate Content x Proportion of Fines
= 1868.74 x 0.38 = 700.40 kg/m³

Coarse Aggregate Content = Total Aggregate Content – Fine Aggregate
= 1843.15 – 700.40 = 1142.75 kg/m³

The quantity per m³ can be obtained, which is;
Cement                                       = 418.52 kg
Water                                          =  188.33 kg
Fine aggregate                        =  700.40 kg
Coarse aggregate (10 mm)  =  1142.75 kg

The volume of trial mix for 3 cubes
= [(0.1 x 0.1 x 0.1) x 3] + [25% contingencies of trial mix volume]
= 0.006 + 0.00075
= 0.00375 m³

The quantities of trial mix = 0.00375 m³, in which is;
Cement                                      = 1.57 kg
Water                                         = 0.71 kg
Fine aggregate                       = 2.61 kg
Coarse aggregate (10 mm) = 4.29 kg

The Results of Mix Design

Slump Test = True Slump of 55 mm…

All the 3 concrete cubes produced were then cured for 7 days. After that, the compressive cube test is carried out. The results are as follows:

For cubes after 7 days of curing, compressive strength should not be less than 2/3 target mean strength.
= 2/3 × 43.12 = 28.75 N/mm² < 33.9 N/mm²

After 7 days of curing, the compressive strength of concrete cubes produced by the mix design method pass the specific strength requirements.

Discussions Upon Mix Design

Although our compressive strength passes the specific requirements, we still identified several factors which contribute to the lacking of compressive strength of concrete mixes produced in the experiment. However, the main factor is the condition of aggregates whether it is exposed to sunlight or rainfall.

When the free water/cement ration is high, workability of concrete is improved. However, excessive water causes “honey-comb” effect in the concrete produced. The concrete cubes become porous, and hence its compressive strength is well below the design value. Other possible reasons include over compaction, improper mixing methods and some calculation errors.

Few suggestion upon several steps to avoid the problems previously faced:

• All the raw materials, which is cement, aggregates, and sand should be protected from precipitation or other elements which may affect its physical properties.
• The quantity of ingredients may be adjusted if necessary, theoretical values are not always suitable.  For example, if the aggregates are wet or saturated, less amount of water should be added, vice versa.
• Compaction should be done carefully, as either under or over-compaction will bring significant negative effect on the concrete produced.

The Conclusion

1. By using the concrete mix design method, we have calculated the quantities of all ingredients, that is water, cement, fine and coarse aggregate according to specified proportion.
2. The concrete produced did not fulfill the compressive strength requirements due to several reasons.  Furthermore, some steps mentioned above should be taken into consideration to overcome this problem.

Standard reference for the mix design is as accordance to British Standard;
BS 5328: 1981 : Methods of Specifying Concrete including Ready-Mixed Concrete

Read More Constructive Posts:

• The Facts About Concrete

In today’s topic, I’m expanding the previous topic regarding geotechnical investigation in construction or civil engineering project. Nevertheless, by taking a different twist of presentation with this series of 8 nos. of videos obtained from world’s most famous media stream, Youtube.

Recap: Site or geotechnical investigation is a process of site exploration consisting of boring, sampling and testing so as to obtain geotechnical information for a safe, practical and economical geotechnical evaluation and design.

Basic Operation of Soil Investigation

The basic operation of rock core drilling performed at site…

Geotechnical Investigations of Enlarged Cotter Dam

Canberra Engineering Excellence Awards 2009 Entrant Details…

AnuLab SPT Test at MG Road Agra for Soil Bearing Capacity

The standard penetration test (SPT) is an in-situ dynamic penetration test designed to provide information on the geotechnical engineering properties of soil. The test procedure is described in the Indian Standard IS: 2131-1981 British Standard BS EN ISO 22476-3 and ASTM D1586. The Standard Penetration Tests aims to determine the SPT N value, which gives an indication of the soil stiffness and can be empirically related to many engineering properties. The test is conducted inside a borehole. A ’split spoon’ sampler is attached to the bottom of a core barrel and lowered into position at the bottom of the borehole. The sampler is driven into the ground by a drop hammer weighing 68 kg falling through a height of 76 cm. The number of hammer blows is counted. The number required to drive the sampler three successive 150mm increments is recorded. The first increment (0-150mm) is not included in the N value as it is assumed that the top of the test area has been disturbed by the drilling process. The SPT N is the number of blows required to achieve penetration from 150-450mm. The hammer weight, drop height, spoon diameter, rope diameter etc. are standard dimensions. After the test, the sample remaining inside the split spoon is preserved in an airtight container for inspection and description. (By ANULAB Agra)

To Build a Tower: Part 1 – GeoTechnical Drill

The first first step in designing a radio tower is the foundation. This requires determining the quality of soil where foundation will be built & installed. Soil test was done by a radio-controlled drilling rig. This test went 40′ in depth, with samples “spooned” every 5′. This site was designed for Mid-Atlantic Broadband Cooperative (mbc-va.com), by RAF Wireless (rafwireless.com). It will be a 192′ monopole, located in Appomattox VA & will support Last Mile fiber connectivity for Digital Bridge’s WiMAX deployment around Appomattox, called BridgeMAXX.

Water Water Everywhere – Civil Engineering @ University of Limerick

This video clip shows Year 2 Civil Engineering @ University of Limerick students undertaking a site investigation as part of a geotechnical study. The Problem Based Learning (PBL) project involves the design of an earthen dam that could be used to store water or hold back flood-waters. The work involves the assessment of on-site soils for use in the construction of an impermeable dam and the analysis and design of the dam and supporting ground. The design is verified by construction and testing of a trial embankment on the site. Visit University of Limerick for more information on our course.

Geoprobe Direct-Push Sampling – Soiltest Italia

The direct-push approach for characterization of the shallow unconsolidated sub-surface is a rapidly developing methodology that deploys hydro-geological, geotechnical, and geophysical tools in the sub-surface. Direct-push methods for deployment of various sampling instruments in the subsurface present a viable alternative to traditional drilling. Soiltest Italia is specialized in geological surveys for environmental purposes.

CPT (Cone Penetration Test) – Soiltest Italia

Soiltest Italia is the foremost contractor for onshore in-situ soil testing in Italy. An acknowledged specialist in CPT, Soiltest Italia also offers a worldwide consultancy and training service. The cone penetration test is an in situ testing method used to determine the geotechnical engineering properties of soils and delineating soil stratigraphy. CPT test methods are governed by ASTM standard D-3441 “Standard Test Method for Deep, Quasi-Static, Cone and Friction-Cone Penetration Tests of Soil.” CPT is a geotechnical technique for determining soil strength parameters of near surface soils to depths of approximately 60 m.

Fehmarnbelt Fixed Link Geotechnical Investigations

Jens Kammer, a Project Manager of Geo-technology at Femern A/S, provides information on geotechnical investigations necessary for the planning of the Fehmarnbelt Fixed Link a video by Femern A/S. For further information on the project, visit our websites at Femern.

Hopefully the 8 numbers of videos will gives you some clue and further understanding on how site investigations are performed at site. To geotechnical…cheers…

Read More Constructive Posts:

• The Elements of Site Investigation
• Foundation In GeoTechnical Perspective

Site investigation is a process of site exploration consisting of boring, sampling and testing so as to obtain geotechnical information for a safe, practical and economical geotechnical evaluation and design. Generally it is an exploration or discovery of the ground conditions especially on untouched site.

In other words the main purpose of site investigation is to determine within practical limits, the depth, thickness, extent and compositions of each subsoil stratum, the depth and type of rock, the depth and composition of groundwater, the strength, compressibility and hydraulic characteristics of soil strata required by geotechnical engineers. Sometimes it is also known as geotechnical investigation.

The Importance of SI

• To study the general suitability of the site for an engineering project.
• To enable a safe, practical and economic design to be prepared.
• To determine the possible difficulties that may be encountered by a specific construction method for any particular civil project.
• To study the suitability of construction material (soil or rock).

Why Have To Perform SI?

SI is essential for every construction project. This sketch should do the trick...

Obviously, it is a part of geotechnical processes in preliminary stage.

Lack of geotechnical processes will lead to a:

• Failures where many case histories are available.
• Significant delay and increase in construction costs when the design has to be revised or amended.

Generally the elimination of the SI will not safe the cost of the project thus it only comprises from only 0.1% to 5% of the project cost. In fact most frequent claims in civil engineering contracts are on the basis of inadequate SI or obstructions resulting in extra costs which could not reasonably have been foreseen by an experience contractor.

Wok Procedure for SI
Steps of work involved in site investigation:

1. Desk study to collect all the relevant data and information,
2. Reconnaissance of site works,
3. Planning program after reviewing the above,
4. Ground or soil exploration includes boring, sampling and testing,
5. Laboratory testing (also field if necessary),
6. Preparation and documentation of SI report,
7. Engineering design stages,
8. Review during construction and monitoring.

Planning of SI Works
Surface Investigations:

• Site inspection to assess general site condition if there is any anticipated problems that might arise during the construction later on.
• Usually the engineer is required to inspect the site to appreciate actual site and ground problems with particular reference to terrain, vegetation, swamps, water runoff, stratigraphical formations where it is exposed.

Sub-surface Investigations:

• Ground or soil investigation by means of boring, sampling, testing, and etc. And also as to determine the stratigraphy and pertinent properties of soil underlying the project site.

Site Reconnaissance
A reconnaissance is a preliminary examination or survey of a job site. First step is to collect and study any pertinent information already available. After collecting and studying the data available, the engineers should visit the site in person, observe thoroughly and interpret what is seen. Results of reconnaissance help to determine the scope of subsequent soil exploration. It is important to locate any underground utilities to assist in planning and carrying out subsequent subsurface exploration.

A few generalizations of reconnaissance:

• Details on the ground surface for an early observation,
• Topographical characteristics, e.g. flatland, hilly, swamps or pit area,
• The possible location of the ground water tables (GWT),
• Interviewing the local residents for further information,
• Taking a lot of photographs of the proposed site.

Steps of Soil Exploration
Soil exploration consists of:

• Boring: Refers to drilling or advancing a hole in the ground. The test would include hand auger, motorized hand boring (wash boring), deep boring (rotary drilling), and/or trial pits.
• Sampling: Refers to removing soil from the hole. The samples can be classified as disturbed or undisturbed sampling. Disturbed samples are usually used for soil grain-size analysis, determination of liquid limit, specific gravity of soil as well as compaction test and California bearing ratio (CBR). The undisturbed samples are collected at least every 1.5 m and if changes occur within 1.5 m intervals, an additional samples should be taken.
• Testing: Refers to determining the properties from the soil. The test can be perform either at laboratory or at field. Laboratory testing would normally be moisture content, sieve analysis, liquid limit, compaction test, CBR and so forth. Field test would include Standard Penetration Test (SPT), Cone Penetration Test (CPT) and Vane test.

One of SI method; Rotary wash boring...

Record of Soil Exploration
It is important to keep complete and accurate records of all data collected. Boring, sampling and testing are often costly. A good map giving specific locations of all boring should be available. All boring should be identified and its location documented by measurement to permanent features. And all pertinent data should be recorded in the field on a boring log sheet.

Soil data obtained from a series of test boring can best be presented by preparing a geologic profile:

• Arrangement of various layers of soil,
• Ground water table,
• Existing / proposed structures,
• Soil properties data (e.g., Standard Penetration Test values).

The profile was prepared with data obtained from the boring, sampling and testing of each borehole from selected points.

Geotechnical Report Guideline
Here is the comprehensive guidelines for SI report:

• Table of Contents: Summery of content details included in the geotechnical report.
• Executive Summary: Brief to the point summary not exceeding one page of findings and design recommendations.
• Terms of Reference: Outline terms of reference and scope, identify requesting source. Find out geotechnical requirements from the project manager, structural engineer or the geometric designer at the beginning of the assignment and keep track of changing requirements thus terms of reference.
• Background Information/Review of Existing Data: Provide site description. Describe, topography and geology (in terms of engineering significance and engineering properties), seismic ground motion data, lab data, ground water and drainage information. Provide location map, National Topographic Series 1:50,000 map reference, e.g. 92B/12, Longitude and Latitude, Universal Transverse Mercator coordinates if possible. Provide plan profile where applicable, site history if available.
• Site Investigation: Describe what is needed in light of existing information, provide specific rationale for the scope and methods of site investigation to make it possible for reviewers to assess the adequacy of the investigation. Describe what was carried out. Show location of test holes or pits or geophysical lines if any. Include field observations at the site, soils and existing conditions.
• Laboratory Testing: List the tests done and present the results using standard format.
• Evaluation and Analysis: Discussion of the site investigation and laboratory test results and their implications on the proposed facility or the stability of the site investigated. The seismic assessment should be provided. Describe analyzes performed, assumptions, parameters and methods used (use two methods for analyzing slope stability or calculating bearing capacities where practical). Provide foundation or slope design information in terms of both static and dynamic (seismic) design if required and state what safety factors are in place. Provide anticipated range of settlement for foundations and fills, and Factor Of Safety of fill. Apply your field observation of the site conditions and existing foundations if any, on your choice of foundation type.
• Sand and Gravel Sources / Disposal Areas: Provide legal description, status (Crown, lease, etc.). Describe potential sand and gravel sources, tested or estimated material properties and projected quantities. Describe investigation methodology. Provide recommendations on waste or surplus material disposal areas.
• Design Recommendations, Including the Design of Pavement Structures: Point out possible foundation and construction difficulties, effects on the existing adjacent structures and suggest methods of overcoming these difficulties, recommend the preferred type of foundation, describe why and suggest possible alternatives (value engineering) where possible. Refer to findings of field investigation, lab test findings and analyzes the results. Point out that the geotechnical engineer should be given appropriate opportunity to review the geotechnical aspects of the completed design prior to construction.
• Discuss Predicted Effects of The Recommended Work on The Environment (water quality, etc.): Provide recommendations on mitigation measures. Provide specifications and special provisions for construction contract. Provide cost estimates for the recommended work.
• Literature References: Provide a list of references used in the preparation of the report.
• Appendices: Correspondence Soils and rock core logs (make sure standard disclaimers are included with the logs in contract drawings), test hole location plan, design profile for new roads, pit development plan, drawings, plan and profile, and also photos.
• Quality Control of Work: Reports must be signed and stamped both by the author and the reviewer. It is the responsibility of the author and the reviewer to determine the appropriateness and accuracy of input data and the correctness of the computed results. Use of computer programs does not free the Professional Engineer or the Professional Geo-scientist from this responsibility.

Drilling a borehole at site...

Summarizing
Scope of site investigation works when planned by different engineers tend to be varied because there are an infinite number of conditions to be met and the process of planning also leaves many areas where individual judgment and experiences must be applied. It is also impossible to attempt to provide an exhaustive step by step guidelines applicable to all possible cases. It should be realized that there is a possibility that any site investigation may leave some area unexplored or overlooked. The main risk in foundation design is the uncertainty involving in predicting soil conditions which may change with environment. The more site investigation the more it will reduce the margin of uncertainty but the time and cost requirement will be exorbitant.

Therefore the extent and the cost of Site Investigation should be such that risk is at an established acceptable level to the designer and also comply to the accepted code of practice.

Read More Constructive Posts:

• Video: Geotechnical Investigation at Site
• Foundation In GeoTechnical Perspective

A structure that is composed of a number of bars pin connected at their ends to form a stable framework is called a truss. It is generally assumed that loads and reactions are applied to the truss only at the joints. A truss would typically be composed of triangular elements with the bars on the upper chord under compression and those along the lower chord under tension. Trusses are extensively used for bridges, long span roofs, electric tower, and space structures.

Trusses are statically determinate when the entire bar forces can be determined from the equations of statics alone. Otherwise the truss is statically indeterminate. A truss may be statically (externally) determinate or indeterminate with respect to the reactions (more than 3 or 6 reactions in 2D or 3D problems respectively). The support reactions and related diagrams covered in previous post…

Members subjected to forces; Tension and Compression.

For trusses analysis, it is assumed that:

• Bars are pin-connected.
• Joints are frictionless hinges.
• Loads are applied at the joints only.
• Stress in each member is constant along its length.

The objective of analyzing the trusses is to determine the reactions and member forces. The methods used for carrying out the analysis with the equations of equilibrium and by considering only parts of the structure through analyzing its free body diagram to solve the unknowns.

Method of Joints

The first to analyze a truss by assuming all members are in tension reaction. A tension member is when a member experiences pull forces at both ends of the bar and usually denoted as positive (+ve) sign. When a member experiencing a push force at both ends, then the bar was said to be in compression mode and designated as negative (-ve) sign.

In the joints method, a virtual cut is made around a joint and the cut portion is isolated as a Free Body Diagram (FBD). Using the equilibrium equations of ∑ F_x = 0 and ∑ F_y = 0, the unknown member forces could be solve. It is assumed that all members are joined together in the form of an ideal pin, and that all forces are in tension (+ve) of reactions.

An imaginary section may be completely passed around a joint in a truss. The joint has become a free body in equilibrium under the forces applied to it. The equations ∑ H = 0 and ∑ V = 0 may be applied to the joint to determine the unknown forces in members meeting there. It is evident that no more than two unknowns can be determined at a joint with these two equations.
CCS: Figure 1: A simple truss model supported by pinned and roller support at its end. Each triangle has the same length, L and it is equilateral where degree of angle, θ is 60° on every angle. The support reactions, R_a and R_c can be determine by taking a point of moment either at point A or point C, whereas H_a = 0 (no other horizontal force).

Here are some simple guidelines for this method:

1. Firstly draw the Free Body Diagram (FBD),
2. Solve the reactions of the given structure,
3. Select a joint with a minimum number of unknown (not more than 2) and analyze it with ∑ F_x = 0 and ∑ F_y = 0,
4. Proceed to the rest of the joints and again concentrating on joints that have very minimal of unknowns,
5. Check member forces at unused joints with ∑ F_x = 0 and ∑ F_y = 0,
6. Tabulate the member forces whether it is in tension (+ve) or compression (-ve) reaction.

CCS: Figure 2: The figure showing 3 selected joints, at B, C, and E. The forces in each member can be determine from any joint or point. The best way to start by selecting the easiest joint like joint C where the reaction R_c is already obtained and with only 2 unknown, forces of F_CB and F_CD. Both can be evaluate with ∑ F_x = 0 and ∑ F_y = 0 rules. At joint E, there are 3 unknown, forces of F_EA, F_EB and F_ED, which may lead to more complex solution compare to 2 unknown values. For checking purposes, joint B is selected to shown that the equation of ∑ F_x is equal to ∑ F_y which leads to zero value, ∑ F_x = ∑ F_y = 0. Each value of the member’s condition should be indicate clearly as whether it is in tension (+ve) or in compression (-ve) state.

Trigonometric Functions:
Taking an angle between member x and z…

• Cos θ = x / z
• Sin θ = y / z
• Tan θ = y / x

Method of Sections

The section method is an effective method when the forces in all members of a truss are being able to determine. Often we need to know the force in just one member with greatest force in it, and the method of section will yield the force in that particular member without the labor of working out the rest of the forces in the truss.

If only a few member forces of a truss are needed, the quickest way to find these forces is by the method of sections. In this method, an imaginary cutting line called a section is drawn through a stable and determinate truss. Thus, a section subdivides the truss into two separate parts. Since the entire truss is in equilibrium, any part of it must also be in equilibrium. Either of the two parts of the truss can be considered and the three equations of equilibrium ∑ F_x = 0, ∑ F_y = 0, and ∑ M = 0 can be applied to solve for member forces.

CCS: Figure 3: Using the same model of simple truss, the details would be the same as previous figure with 2 different supports profile. Unlike the joint method, here we only interested in finding the value of forces for member BC, EC, and ED.

Few simple guidelines:

1. Pass a section through a maximum of 3 members of the truss, 1 of which is the desired member where it is dividing the truss into 2 completely separate parts,
2. At 1 part of the truss, take moments about the point (at a joint) where the 2 members intersect and solve for the member force, using ∑ M = 0,
3. Solve the other 2 unknowns by using the equilibrium equation for forces, using ∑ F_x = 0 and ∑ F_y = 0.

Note: The 3 forces cannot be concurrent, or else it cannot be solve.

CCS: Figure 4: A virtual cut is introduce through the only required members which is along member BC, EC, and ED. Firstly, the support reactions of R_a and R_d should be determine. Again a good judgment is require to solve this problem where the easiest part would be consider either on the left hand side or the right hand side. Taking moment at joint E (virtual pint) on clockwise for the whole RHS part would be much easier compare to joint C (the LHS part). Then, either joint D or C can be consider as point of moment, or else using the joint method to find the member forces for F_CB, F_CE, and F_DE. Note: Each value of the member’s condition should be indicate clearly as whether it is in tension (+ve) or in compression (-ve) state.

Graphical Method (Maxwell’s Diagram)

The method of joints could be used as the basic for a graphical analysis of trusses. The graphical analysis was developed by force polygons drawn to scale for each joint, and then the forces in each member were measured from one of these force polygons.

The number of lines which have to be drawn can be greatly reduced, however, if the various force polygons are superimposed. The resulting diagram of truss is known as the Maxwell’s Diagram.

In order to draw the Maxwell diagram directly, here are the simple guidelines:

1. Solve the reactions at the supports by solving the equations of equilibrium for the entire truss,
2. Move clockwise around the outside of the truss; draw the force polygon to scale for the entire truss,
3. Take each joint in turn (one-by-one), then draw a force polygon by treating successively joints acted upon by only two unknown forces,
4. Measure the magnitude of the force in each member from the diagram,
5. Lastly, note that work proceed from one end of the truss to another, as this use for checking of balance and connect to other end.

CCS: Figure 5: A simple triangle truss with degree of angle, θ is 60° on every angle (a equilateral) and same member’s length, L on 2 types of support. Yet again, evaluating the support reaction plays an important role in solving any structural problems. For this case, the value of H_b is zero as it is not influence by any horizontal forces.
CCS: Figure 6: The procedure for solving this problem could be quite tricky and requires our imagination…sort of. It starts by labeling the spaces between the forces and members with an example shown above; reaction R_a and applied force, P labeled as space 1 and continue moving clockwise around the truss. For each member, take example between space 1 and 5 would be the member AC and so forth. Note: Choose a suitable scale for drawing the Maxwell diagram.

In conclusion, the truss internal reaction as well as its member forces could be determine by either of this 3 methods. Nonetheless, the methods of joints becomes the most preferred method when it comes to more complex structures…

Read More Constructive Posts:

• Shear Force and Bending Moment as Structural Basics
• The Basic Principles in Structural Mechanics