How do I know that my piles are cast right?

We have done the piling. Now what? Can we immediately start constructing over the piles?

No! Wait…Before doing that, first we should ensure that the piles we have just cast are really capable enough to take that big responsibility…. This process is called testing of piles.

There are different types of tests commonly practiced in completed piles. Let us understand what they are. The tests done on piles are broadly classified into two based on the purpose of the tests: Please remember – what we are mentioning below is specific for cast-in-situ concrete piles only.

               

    A. Tests to make sure that the piles are cast correctly and are homogeneous in nature. Here we make sure that the piles;

a.       Are cast without any breakage or discontinuity

b.      Are straight without any bend or inclination

c.       Have reached till the expected depth

d.      Does not have any defects such as bulging / caving / necking / soil inclusion or voids.

·    B. Tests to ensure that the piles can carry the expected load when put into action. These tests are called load tests.

In this lesson let us see the first case. Let us see how to check whether the piles are cast correctly.

Piles are buried structure - that means, once done, it is not possible to visually inspect them to verify whether they are cast correctly. Hence we need to resort to some other techniques to gather information about the correctness of the piles. The tests used for this purpose are generally termed as Pile Integrity Test.

Pile Integrity Test is also known as low strain dynamic test. The principle is very simple. When we apply a small impact at the top of the pile, it produces a compression wave. This wave travels down through the shaft of the pile and reflects at points where there are any discontinuity or change is strata due to any defects of pile such as caving, necking etc. we measure the time taken by the wave to reflect back, and analyse the whole process with help of computer to determine the quality of the pile. What we should keep in mind is that this method is NOT used to assess the strength of the concrete or load carrying capacity of piles. This is purely a substitute for visual inspection.

Now, let us go a little more deep into the process and methodology for these tests.

There are no guidelines specified for pile integrity test in Indian Standards (IS) – hence we follow ASTM D5882 for conducting and monitoring the tests. 

There are two commonly used methods for testing the pile integrity.

1. Pulse Echo Method (PEM): Here, the pile head motion is measured as a function of time. This record is then evaluated for pile integrity.
2. Transient Dynamic Response (TDR) method: In this method, the pile head motion and force is measured as a function of time. These data are then evaluated for pile integrity.

Before going into the process in depth, let us understand the apparatus that are used for the integrity tests.

• Apparatus for applying impact: A hand held hammer. This would ideally be with hard plastic tip so that it can induce short force pulse without damaging the pile surface.
• Apparatus for velocity measurement: Accelerometer. It is placed near pile head with its sensitive axis parallel to the pile axis using a suitable thin layer of bonding materials such as wax, vaseline etc to correctly measure axial pile motion.
• Recording unit: The signals from the sensors are transmitted to an apparatus for recording analysing and displaying data.
• Force measurement: in TDR method, the hammer (impact devise) shall be capable of measuring the impact force as a function of time.

Let us now see how the test works:

In the case of cast in situ concrete piles, the tests are generally conducted after 7^th day or when the concrete achieve 75% of the design strength. The pile head surface is made accessible, clean from debris or loose particles. Proper pile top preparation is essential for successful application of this method. The motion sensors are fixed at the selected locations away from the edge of the pile head. The location to fix motion sensors (transducers) may be prepared smooth by grinding using a hand grinder. For piles with diameters more than 500mm, the accelerometers shall be attached at more than three places so that the integrity evaluation is possible from each localized sections of the pile. The accelerometers are attached at the top of the pile (not at sides). The impact is then applied at top of the pile with the hammer at a location which is not more than 300mm from the accelerometer.

Generally, the tests are done using a Pile Integrity Tester, which is a small and compact testing unit that is used for testing and analysing data. When the impact is applied to the pile top, a low stress wave is transmitted to the pile. And this will result in generation of a very low strain to the pile. The acceleration generated by the impact is recorded in the accelerometer and converted in to velocity form. Reflections from pile toe, pile discontinuities, cross-sectional changes, soil resistance changes, the wave speed through the pile etc., are graphically displayed on the recording device screen.

The test involves collection of several blows during the stage of testing. All such similar blows are averaged before display. If there are any random signals, they will get cancelled by this averaging technique. The signals are also exponentially amplified. Low strain signals generated due to hammer impact are often damped by skin friction. For long piles with high skin friction, reflections from pile toe may be small. By amplifying the records exponentially with time, this will enhance the identification of relevant reflections that have low energy.

Discontinuities, cross-sectional changes, material property changes etc cause reflections of the generated waves. Such reflections are measured and checked for each pile. Thus, any defect in the pile shaft can be easily detected. By measuring the travel time of any such reflection, the location of defect in the pile can also be located. The wave speed is determined from the response of the pile toe. This measured wave speed by itself is an important test result, from which the general condition of concrete can be estimated.

 

The result is generally displayed in the form of a graph with depth in one axis and amplitude in other. Let us assume that the speed of the compression wave is V m/s, and it takes ‘t’ seconds to reflect back from the toe or any irregularities within the pile. It means, the time taken to travel from the origin to the point of irregularity is t/2. With this information the depth of pile can be determined using the formula d = t/2 X V. Thus, by measuring the response time, the pile depth or / and the depth at which the anomalies occurred can be judged correctly.

Next, let us look at the load tests done on concrete piles.

Environmental Clearance for construction projects - How to make a Project Proposal?

In the last post we studied about environmental clearance, and what are the processes involved in obtaining one for your construction project. I repeat - construction projects which include construction and town planning projects alone, which come under item 8 in the schedule. Other than construction projects, there are several other classifications for projects which need environmental clearance, like mining, offshore explorations, refinery, metallurgical industries, fertilizer industry, nuclear power plant, leather industry, chemical industry, distillery, airports etc and the processes are slightly different for those when compared to projects under item 8 of the schedule.

As we studied before, the clearance process starts with submission of a project proposal to the SEIAA. Now, let us see what constitutes a project proposal.

PROJECT PROPOSAL

The project proposal submitted to the SEIAA seeking environmental clearance for construction projects includes the following.

1.       Conceptual plan

2.       Duly filled up Form -1 as mentioned in the Annexure –I of the notification S.O 1533.

3.       Duly filled up Form – 1A, in case of construction projects, that falls under item-8 as per the notification.

4.       Supporting documents.

CONCEPTUAL PLAN

All projects do have impact on their environment. The impacts of a project to its environment is multi dimensional – to the flora and fauna, the air, water, soil and ecology as a whole, besides other impacts to the livelihood and the social, cultural and economical life of the natives and the local community. The aim for making it mandatory for larger projects to obtain environmental clearance is to reduce the impact and adverse effect it imparts to the environment.

The conceptual plan is a detailed study report prepared after an extensive study about the environment where the project under consideration is proposed to be established. The study is to be carried out by an accredited agency on behalf of the project proponent.  The environmental conditions before the implementation of the project and expected impact after the project establishment are studied in detailed.  This would generally include the following activities.

·         Recording the environmental conditions before the start of the project. This includes analysis of soil, water and air samples for determining the level of contaminations and chemical composition. Current level of noise pollution also will be determined.

·         Studying the traffic volume before the project implementation and estimating the impact of the project on the local traffic issues.

·         Studying and recording the impact on the environment  due to the following:

• Impact on land environment – due to excavation, cutting of trees, bringing in earth from outside, disposal of excavated earth, disposal of debris and garbage , removal of top soil etc.
• Impact on water environment – due to drawing subsurface water, reduction in water table, disposal of waste water etc.
• Impact on air environment – due to construction debris, smoke, use of diesel generators, volatile organic compounds, chemicals etc.
•  Impact on ambient noise level – due to operation of machines during construction and operation stage.
• Impact on flora and fauna: due to removal of trees and top soil.

·         Establishing an Environment management Plan for construction and operation phases of the project. The Environment management plan includes;

• Waste management plan
• Pollution management plan
• Traffic management plan
• Landscaping and green management plan
• Energy management plan, including utilization of renewable energy resources.
• Water management plan including rainwater harvest, recharge and reuse.
• Disaster and hazard management plan

FORM-1 (view the form here)

Form -1 is the basic application form for environmental clearance. The following details are to be mentioned in the Form-1 by the applicant.

·         Basic information on the project, including size, location, name, cost etc of the project.

·         Details about the activities involved during construction, operation and decommissioning of the project, which will cause physical changes in the locality.

·         Details of use of natural resources for construction or operation of the project – like sand, water etc, especially non renewable.

·         Details of use, storage, transport, handling or production of substances or materials which are harmful to human health or environment.

·         Production of solid wastes during construction or operation or decommissioning.

·         Details about release of any pollutants / hazardous material to air.

·         Details of generation of noise and vibration and emission of light and heat.

·         Risk of contamination of land or water from release of pollutants into the ground or into sewer, surface water, ground water etc.

·         Risk of accidents during construction or operation of the project, which could affect human health or the environment.

·         Factors like consequential development that could lead to environmental effects or the potential for cumulative impacts with other or planned activities in the locality.

·         Environmental sensitivity of the project.

FORM – 1A (view the form here)

Form-1A is applicable for only those construction projects which are listed under item 8 of the schedule.

In this form the proponent is expected to explain about the project in detail for the relevant queries.

a.       Land environment:

a.       Details about the use of land prior to and after the development.

b.      List of project requirements including area statements, water consumption, power requirement, connectivity, community facilities, parking needs etc.

c.       Impact of the project to the adjacent structures.

d.      Land disturbance due the construction, like erosion, subsidence and instability.

e.      Quantities of earth work involved, transport of fill materials from outside the site.

f.        Details of water supply, waste generation and handling during the construction period.

g.       Details on how low lying and wetlands are affected.

h.      Details of construction waste and debris causing health hazards.

b.      Water Environment

a.       Total water requirement for the project with breakup, sources of water, Quantity expected from each source and water balance chart.

b.      Capacity (yield / flow) of source of water.

c.       Quality of water other than municipal supply.

d.      Pollution load from the waste water generated.

e.      Facilities for rain water harvesting.

f.        Impact on runoff characteristics.

g.       Tapping of ground water- water table, recharging capacity, approvals for taping ground water.

h.      Preventive actions from construction runoff water polluting the land and aquifers.

i.         Management of storm water within the site.

j.        Sanitary arrangements for construction workers.

k.       Onsite facility for collection, treatment and safe disposal of sewage.

l.         Details of dual plumbing system.

c.       Vegetation

a.       Influence of the project on the local biodiversity.

b.      Extent of clearing and modification of vegetation.

c.       Measures to minimize the likely impacts on site features.

d.      Fauna

a.       Displacement of terrestrial and / or aquatic fauna, or creation of barriers for their movement.

b.      Direct / indirect impact on avifauna of the area.

c.       Measures taken to mitigate the adverse impact on fauna.

e.      Air environment.

a.       Possibility of increased atmospheric concentration of gases.

b.      Impacts on generation of dust, smoke etc.

c.       Details of parking and impact of increased traffic volume on the present level of transport infrastructure.

d.      Internal road and movement details.

e.      Traffic noise and vibration.

f.        Impact of sets and other equipments on noise level and vibration.

f.        Aesthetics

a.       Impact of the project on the view, scenic amenity or landscape.

b.      Adverse impacts from new construction on the existing structures.

c.       Local considerations for urban form & urban design.

d.      Any special / significant features in the vicinity of the proposed site, including anthropological or archeological sites.

g.       Socio economic aspects.

a.       Changes to the demographic structure to the local population.

b.      Existing social infrastructure around the proposed site.

c.       Impacts to the local communities.

h.      Building materials

a.       Building materials produced with energy efficient process.

b.      Measures to minimize the impact to the environment due to the transport and handling of building materials.

c.       Extent of use of recycled materials for construction.

d.      Processes for collection, segregation and disposal of garbage generated during the operation phase of the project.

i.         Energy Conservation.

a.       Details of power requirements, source of supply, backup source etc. Energy consumption per sq.ft of the built up area.

b.      Type and details of power backup.

c.       Characteristics of glass planned to use.

d.      Passive solar architectural features.

e.      Shading effect for heating / cooling

f.        Energy efficient space conditioning, lighting and mechanical systems.

g.       Thermal characteristics of building envelop, roof, external walls, fenestration, U and R values of the materials used.

h.      Precautions against fire hazards with emergency plans.

i.         Rate of air infiltration into the building.

j.        Utilization of non conventional energy technologies for overall energy consumption.

j.        Environment Management Plan

EMP consists of all mitigation measures for every activity undertaken during the construction, operation and the entire life cycle of the project to minimize the adverse environmental impacts.

ATTACHMENTS TO THE PROPOSAL

The following attachments also have to be submitted as part of the project proposal.

1.       Site map

2.       Map showing the surrounding features of the site within 500m.

3.       Site levels and contours to suitable scales.

4.       Soil test report

5.       Contour map with natural drainage.

6.       Water balance chart.

7.       Physical, chemical biological test results of water.

8.       Dual plumbing system drawings.

9.       List of trees and vegetations affected by the project.

10.   Traffic management plan.

11.   Layout plan in suitable scale showing landscape drawing with details of tree plantation, water bodies etc.

12.   Background air quality levels.

13.   Details of energy conservation measures.

Next: What is Environmental Impact Assessment?

Environmental Clearance for construction projects in India - What is it and how can we obtain one?

INTRODUCTION

As per EIA notification S.O 1533 dated 14/09/2006, by Ministry of Environment and Forests (MOEF), obtaining prior environmental clearance from the concerned regulatory authority before the commencement of work has become mandatory for all developments which meet certain criteria specified in the notification. Obtaining clearance is mandatory for certain expansion / modernization works also.

All projects are classified into category ‘A’ or ‘B’, of which clearance for all category ‘A’ projects are to be given by the MOEF, and clearance for category ‘B’ projects are granted by the State level Environment Impact Assessment Authority (SEIAA). In the absence of SEIAA in any state, the MOEF will be considered as the regulatory authority. The category B is again subdivided in to ‘B1’ and ‘B2’, where projects under category ‘B1’ require a proper Environmental Impact Assessment. The categorization of projects are given here.

In Kerala, the State level Environment Impact Assessment Authority (SEIAA) and State Expert Appraisal Committee (SEAC) were formed by central government vide a notification S.O 2484(E) dated 3^rd November 2011. The Directorate of Environment & Climate change, Thiruvananthapuram (located at Pettah) is designated to act as the Secretariat of the SEIAA and SEAC. SEIAA is a three member committee, with chairman, member and a member secretary. The SEIAA bases its decisions on the recommendations of the State Expert Appraisal Committee (SEAC), which also was formed by the same notification. SEAC has currently 14 members, and their term is three years from the date of notification. SEACs meet at least once every month.

CLEARANCE PROCESS – Specific for Construction / Township development projects (under item 8)

The procedure for obtaining the environmental clearance for construction projects is as mentioned in the central government notification SO1533 dated 14/09/2006.

1.    A project proposal with an application in the prescribed format as Form-1 & (or) Form-1A as in the annexure II of the notification to be submitted along with a conceptual plan to the regulatory authority before starting any construction activities at site. This application is scrutinized in detail by the SEAC, and determines whether the project falls in category B1 or B2. All projects in category B1 require an Environmental Impact Assessment.

2.    Within 60days of receiving the application and Form-1 from the proponent, the SEAC will convey the terms of reference (TOR) addressing all relevant environmental concerns for the preparation of Environmental Impact Assessment report.

3.    The final EIA report (for those projects under category B1) and environmental management plan shall be submitted to SEAC, and this will then be taken for a presentation meeting before the SEAC. The project proponent is also required to attend the presentation meeting of SEAC, and shall make a presentation on the salient features of the project, the related environmental issues, proposed environmental management plans. The representative of the project proponent shall also respond to the queries / suggestions which the committee may raise during the discussion. Based on this meeting, the SEAC makes categorical recommendations to the regulatory authority concerned (SEIAA) for grand of prior environmental clearance on stipulated terms and conditions. Before the presentation meeting, the project proponent shall distribute one copy each of the full set of proposal to all the members of the SEAC at least 15days in advance to the date of meeting.

4.    Once the environmental clearance is obtained from the regulatory authority, it is mandatory for the proponent to submit half-yearly compliance reports in respect of the stipulated prior environmental clearance terms and conditions, in hard and soft copies to the regulatory authority concerned.

APPOINTMENT OF CONSULTANTS

The proponent can appoint an environmental consultant for conducting the impact assessment and preparing the report as well as the detailed proposal for submission. The consultant can also attend the SEAC meeting as an authorized representative of the proponent. In such case, the consultant shall be an accredited consultant by the Quality Council of India (QCI). Also, the representation should be through an irrevocable POA (Power of Attorney) executed and formally registered with the sub registrar.

Next: What makes a project proposal complete?

Next case….The cube test on 28th day also failed…..

When we consider concreting at site and their respective cube tests, there are four possible combinations as listed below.

1. Concrete is strong; cube is also strong.

2. Concrete is weak; cube is also weak.

3. Concrete is strong; but cube is weak.

4. Concrete is weak; but cube is strong.

We normally consider the first two possibilities while analyzing cube test results, the third and fourth possibilities are generally being neglected. The third option, however, does not harm the structure. But the option four….well…it is better to be optimistic in such situations.

When you get reports indicating that the 28th day cube tests are failed, remember that it is something serious. It cannot be treated just like in the case of 7th day test failure. As we have discussed already, 28th day cube tests are considered as the deciding criterion for acceptance of the concrete.

Before going deep into our scenario of cube failure, let us quickly see how the cube results are generally interpreted as per IS code.

According to IS 456 2000 Cl 16.1, two conditions are to be met for accepting a concrete after cube test.

For concrete of grade M20 and above,

1. The average strength of a group of four consecutive test results should not be less than the greater of fck+4 N/mm2 or fck+0.825σ where σ is the standard deviation established.
2.  Individual cube strength should not be less than fck-4 N/mm2

Let us analyze this with an example.

The following are the 28th day cube test results of four M40 concrete samples. 45, 43, 42 and 47 N/mm2. The average strength of these samples is 44.25 N/mm2 .

Now, the first condition is that this average should not be less than the greater of fck+4 N/mm2 or fck+0.825σ. Let us assume a standard deviation (σ) of 5 N/mm2, as per table 8 of IS 456 for M40 concrete.


Thus the minimum strength should be the greater of 40 + 4 = 44N/mm2 or 40 + 0.825 x 5 = 44.125 N/mm2 , ie 44.125 N/mm2 .



The first condition is met.


The second condition is that no individual test result should have values less than fck–4 N/mm2 . in our case it should not have values less than 36N/mm2.


We meet the second condition too. So the concrete sample is acceptable.


Now, let us go back to our problem of failure of cubes on 28th day test.


If the cubes do not have the required minimum compressive strength, and thereby failed, the following actions are to be taken urgently.


1. Stop all activities on the member under question.
All further construction on the members under question need to be suspended immediately to prevent further damage to the structure.


2. Test the compressive strength of the structural member under question.
This step is to clarify whether the member itself is weak, or just the cube. There are different methods for testing this like core testing and Non–Destructive tests including rebound hammer test, ultrasonic pulse velocity test, pullout test, probe penetration tests, maturity test etc. These tests will be explained in another post. If it is found that the member under question is not having the required compressive strength, the stages mentioned below to be considered.


3. Test the load carrying capacity of the member.
Load tests also can be carried out on the members to decide on their load carrying capacity. This can be normally done on flexural members by applying a load equal to DL+1.25LL for a period of 24hrs. The deflection is noticed at the end of 24hrs and then the LL part is removed.


If the maximum deflection is less than 40l2/D mm, where ‘l’ is the effective span in meter and ‘D’ is the overall depth in mm, the member is safe in flexural load.


If the deflection is more than 40l2/D mm, the recovery of deflection after the removal of LL is analyzed. If the recovery within 24hrs after the removal of LL is less than 75% of the deflection, the test is repeated after 72hrs. If the recovery in this case also is less than 80%, the structure is considered as unacceptable.


4. Determine the maximum load the member can take at the present condition.
Once we realize that the member is not strong enough to carry the designed load, the next process is to calculate the maximum load that can be safely transferred to the member. This can be obtained normally by studying the compressive strength of the cubes tested earlier, and the compressive strength of the cores taken from the member. The quality of concrete obtained by other N-D tests also needs to be studied before reaching a final value. Though not advisable, anyhow at this stage, we also need to consider the factor of safety assumed for the member by the structural consultant. Perhaps the assumed load combination during the design may not be the likely one at the given / changed scenario, and in such case analysis may be reviewed with a more likely load combination.


5. Redesign of members so as to distribute the excess load to other members in a safe way.
AND / OR
6. Strengthen the member under question using various strengthening methods.
OR
7. Removing the member under question and casting a new member with adequate strength.


Choice / combination between options 5,6 and 7 depends on various factors including severity of the case, time, cost, functionality, technical feasibility, aesthetics, workability, influence on other members and services etc. A detailed study considering all these factors is done before finalizing on a methodology to move forward.


Option 5 involves redesigning the members in and around the affected area in such a way that the load in excess to the load carrying capacity of the member under question is distributed to other members safely. Changes are made to any or all of the parameters like cross section area, percentage of reinforcement, concrete mix etc to meet the requirement. This could also include providing additional beams, columns and / or slabs for reducing effective spans and reducing load on the influence area. Architectural and services layout is also revised if required on the affected floors by relocating heavy equipments or assembly area away from the affected location.


Option 6 involves strengthening the weak member / members to take the original designed load. This is more convenient than redesign since in this method modification is mostly limited to the members that are weak, and hence is easy to keep a track on the process. However, the adaptability of this method depends on other factors also. There are various options to strengthen a weak concrete member, like,


Providing steel casing:
A steel casing is provided around the structure, especially columns, to make it a composite member to improve its structural performance.


Providing steel stiffeners:
Steel stiffeners are provided on the sides of the member to increase its load carrying capacity. The stiffeners are either bolted or epoxy bonded to the concrete member.


Providing Fiber Reinforced Polymer (FRP) sheet bonding:
A FRP sheet (basically with glass fiber - GFRP or carbon fiber- CFRP) with lesser thickness is wrapped around the surface of the concrete member and bonded with epoxy adhesive, so that the structural behavior is improved. This can also be provided in strips of suitable width, limiting to the area affected in case of slabs.


Providing Near Surface Mounted FRP reinforcement:
In this, FRP laminates (rigid plates) are bonded using epoxy polymer adhesive in the saw cutting made along the cover of concrete members. Once inserted, the laminated would be flush to the surface of the concrete member.


Sprayed concrete / shotcreting:
Reinforcement is drilled around the periphery of the member and shotcreting is done on the surface of the member to increase its cross section to modify the structural performance.


Attaching pre-tensioned cables to the concrete members :
This method is not so commonly used. This involves inducing the effect of pre-stressed member into the existing member.


Concrete Jacketing:
Jacketing involves covering the structural member at any or all sides with skillfully placed reinforced concrete. The reinforcement is welded to the existing reinforcement to impart proper bonding of jacket to the existing member. Jacketing increases the cross section area of the member and thereby improving its structural performance.


Option 7 would seem to be the easiest one, but there are several impediments with this method, like disposal of debris, practical difficulty in demolition without damaging other members, safety of the workmen, practical difficulty in shuttering and casting new member in the original position, quality control etc are a few hurdles to mention with this option.