Thursday

CRACK TREATMENT OF THE ASPHALT BINDER COURSE

Main Break Water(MBW) access road occurs several cracks on the asphalt binder course. The road cracks are monitored and investigated with specialist from RDA Research & Development. This report describes the reason and remedial method of the cracks based on the investigation and consultation.

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MBW access road structure consists of fallowing cross section and the core samples have been taken on the cracks.

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According to core sample data, can be observed that the crack was started from CBM and reflected to the binder course surface.


CRACK INVESTIGATION

The crack survey carried out for the entire road and investigation detail summarized as an attached sheet. Core samples were taken from the jointly selected locations with the engineer. MBW access road cracks were categorized into two types based on crack surface appearance.

  • Transverse cracks
  • Longitudinal cracks

Transverse cracks

Transverse cracks were occurred as a perpendicular to the road center line. These cracks are reflecting from the CBM layers.

  • According to core sample data, can be identified the fallowing crack types was happened.
  • Some of cracks were occurred from CBM 2st layer and reflected to the binder course surface.
  • Other cracks are started from CBM bottom layer (1st layer) and reflected to the binder course.

Longitudinal cracks

Longitudinal cracks were occurred as a parallel to the road centerline and which was happened due to the reflection of the CBM longitudinal joint. 


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PROPOSAL FOR REPAIR OF CRACK

Proposal of the crack repairing method is introduced by specialist from RDA Research & Development.


Three conditions for reflection cracks on CBM :

  • Cracks in the base layer must be wide enough to generate stress conditions in the asphalt surface.
  • There is no method available to relieve the stress concentrations.
  • The asphalt is brittle enough to crack due to upwards propagation of the stress concentration.

In most cases, reflection cracks are narrow (less than 3mm) and will not adversely affect the performance of the pavement. But all the cracks on MBW access road will be treated to prevent from the possibility of propagation.

As per the specialist’s proposal, Geo-Fabric material will be applied along the cracks of the binder course before laying the wearing course in accordance with manufacturer’s instructions.

CRACK REPAIRING

Proposed Material

  • Polyfelt (PGM-G 50/50) to be used, material details is in Appendix

Manpower

  • Supervisor
  • Skilled Labours
  • Unskilled Labours

Sequence

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Methodology

Identify the crack locations and properly cleaning by air compressor.

Bring the notification to the site representative of the Engineer.

The binder surface is thoroughly cleaned and free from all the traces of dust and any of unsound materials.

Cut the Ploy paving Fabric (PGM 50/50) for required length of the crack and 0.5m offset from the crack as following the sketch.


Friday

Foundation Part 02

Excavation For Pile Cap
Shoring is provided around the proposed pile cap with 600mm working space. Excavation is carried out up to certain level by using backhoe. Then excavation was carried out manually. Excavation is very difficult below ground water level. De watering system should be provided.
clip_image002 Excavation With Jcb
clip_image004 Shoring Is Provided
Difficulties in excavation below the ground water level.
  • Difficult to remove the soil
  • Need continuous de watering process
  • Density of soil will increased
  • Erosion or collapse of the sides of the excavation



Pile Hacking
Pile is casted up to above required level. Then it is broken up to required level. This is known as pile hacking. Top concrete is weaken so pile should be casted above required level. Normally height above required level, it is equal to the diameter of the pile. But during the concreting ensure the concreting whole pile, normally concreting the ground level. Then excavate soil and pile should hacking required level.

 

Pile Hacking Process

Pile was hacked by using Air breaker. Pile hacking can be carried out by using two methods.
1) Start to pile hack from top of the pile.
2) Break at above required level.
Second method is suitable for if large length to be hacked. For other cases first method is used. In second method pile is hacked horizontally up to reinforcement gage at just above required level. Then pile is connected to the crane. Reinforcement bars are cut. And small force is applied horizontally by crane or JCB. At this stage pile should break fully. To reference the pile cutting level the cutoff level marked on existing reinforced bar of pile.
There were used main three of tools to hacking piles. All are working with air compressor.
1. Driller – To making hole on pile, it make crack along the hole
2. breaker - To break the pile components as small peaces
3. chipper - To level the break surfaceclip_image006
clip_image008Pile Breaking With Breaker

Eccentricity Of Pile

After the hacking piles the eccentricity of piles was taken. Actual co-ordinate of the centre of the pile sometimes, which may vary from co-ordinate, which is according to the drawing.
Eccentricity of pile = (Actual co-ordinate) – (co-ordinate according to the drawing)

Determination Of Centre Of Pile

The geometrically method as shown in the figure, pile center was obtained most possible position. Most of times the casted pile or reinforcement cage of pile not in actual circle, but we were take the most probable circle shape in cut surface
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Plan view of pile
If pile is regular shape, we find centre of pile by triangulation method.
If pile is irregular shape, we find centre of reinforcement gage by triangulation method.

Pile Caps

Pile caps are usually constructed of concrete to such depth as will ensure full transfer of load to piles, at the same time, resist punching shear. Since it is almost impossibility to bore or drive piles exactly vertical. The pile cap should be large enough in plan to accommodate any deviation in the final position of the pile heads.
imageConcreted Pile Cap
image  Section Of Pile Cap

Pile Cap Re- Design

Sometimes piles are not installed at correct position. That deviation is over to allowable limit that make additional moment in the structure. Due to above problem pile cap dimensions have to re-design. In our site the pile cap F6 2P1A of piles are shifted over the allowable limit. Therefore its pile cap was redesigned.
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Re-bar arrangement and spacing between bars are not changed. Additional reinforcement is taken by pro-rata basis from earlier one.

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TENDERING, ESTIMATING AND QUANTITY SURVEYING – Tendering Methods & procedures:

Tendering Methods & procedures:
Methods of Contractor Selection:
The selection of a contractor to carry out construction works in a project is a very important matter.
A wrong choice may lead to an unhappy client / contractor relationship.
It also may end up with dissatisfied client and sometimes even with an insolvent contractor.
The client’s professional advisers should find a contracting company;

That is financially stable / and has a good business record.
For which the size of project is neither too small nor too large.
That has a reputation for good quality workmanship and efficient organization.

There are three principal methods for choosing a contractor:
(a) open tendering,
(b) selective tendering,
(c) nomination.

Open Tendering
Initiated by client’s architect/ quantity surveyor advertising in newspapers and/or inviting contractors to apply for tender documents and to tender in
competition for carrying out the work. Usually a deposit is required to discourage irresponsible applicants, the deposit being returnable on the submission
of the tender.
Advantages –
There can be no favoritism.
Can get the maximum benefit from competition.
An opportunity is provided for any capable firm.
Disadvantages –
There is a danger that a firm inexperienced in preparing tenders may submit the lowest tender.
There is no guarantee that the lowest tenderer is sufficiently capable or financially stable.
Total cost of tendering is increased.

Selective Tendering
A short list drawn up of contractors who are considered to be suitable to carry out the proposed work.
Names may be selected from an approved list or ‘panel’ maintained by the client.
It is recommended that the number of tenderers should be limited to between five and eight, depending on the size of the contract.
If the firms on the list are all reputable, well established and suitable for the proposed work, then the selection is resolved into a question of price only.
Advantages –
Ensures that only capable and approved firms submit tenders.
Reduce the cost of tendering.

Disadvantages – 
Cost level of the tenders will be higher due to less competition and also due to the higher caliber of the tenderers.
Nomination
Sometimes referred as ‘single tendering’.
It is a special case of selective tendering where the short list has only one name.
Used when the client has a preference for a particular firm, often because it has done satisfactory works for him before.
Competition is eliminated and that will lead to a higher price.
Contract sum will be arrived by a process of negotiations.
When a large project is to be carried out in successive phases, a combination of selective tendering and nomination is employed –
this is sometimes called “serial tendering”.

*The contractor is chosen for the first phase by means of selective competitive tendering.
*The accepted tender forms the basis of payment for the resulting contract.
*The tender is also used for the second and later phases, provision being made for so doing in the initial contract by the inclusion of a
formula for updating prices.
The purpose of serial tendering is to gain the benefits of continuity.
*The contractor for the first phase of the project will have his site organization set up, his offices and storage huts, etc., already in
use and plant of various kinds on the site.
*When the second phase commences, these facilities will be already available.
It allows smooth transition with less additional expenses.
*In addition, the contractor’s workforce will be familiar with the details of the construction after building the first phase, and it helps to
work more speedily and efficiently.

     Negotiated Contracts:
  1. This may be done using bills of quantities / schedules of rates.
  2. The rates and prices are discussed and agreed until eventually a total price is arrived.
  3. Usually negotiation will be conducted between the contractor’s quantity surveyor and the project quantity surveyor.
  4. One party will usually price the tender document first of all, then the other party go through the rates and prices ticking off those which are acceptable.
  5. When agreement is reached, a contract will be entered between the client and the contractor.
  6. This process is sometimes called Single stage negotiation.
In this procedure, absence of competition usually results in a higher price.
Therefore, with a view to gaining the benefits of competition as well as the advantages of negotiation, a process of limited competition for the
selection of contractor, followed by negotiation with him on the details of his tender, is used.
This process is usually known as two-stage negotiation.
In the first stage tenderers are informed of the second stage intention and are asked to tender on the basis of
Schedule of rates consisting of the main/ significant items only.
Prices for the main preliminary items;
Construction program showing estimated times.
Labor and plant resources/ construction methods.
Details of all labor rates / material prices / discounts, etc.
Discussion with each of the tenderers may be conducted in order to clarify their proposals.
Having selected a contractor at the end of the competition stage, negotiation will follow on the basis of a detailed tender document as in
single stage negotiation.
Two-stage negotiation is the method normally used to select a contractor to carry out management contract, in which the general contractor
does little or none of the construction work himself but organizes sub contractors to do the work.

Tender Document:
The number and nature of tender documents will vary with the type of contract.
They will include some or all of the following;
Conditions of Contract:
This document sets out the obligations and rights of the parties.
  1. Bills of Quantities.
  2. Specifications.
  3. Drawings:
Normally general arrangement drawings will be provided.
Tenderers are not normally given working drawings.
Full descriptions of the work are incorporated in the bills or specifications.
Tenderers are informed that they can inspect drawings not supplied to them at the architect’s office.


Form of Tender:
This is a pre-printed formal statement, often in the form of a letter, in which tenderer fills in, in the blank spaces, his name and address and the sum
of money for which he offers to carry out the work shown on the drawings and described in the bills of quantities or specifications.

Return Envelope:
Each tenderer should be supplied with a pre-addressed envelope clearly marked “Tender for  - name of the project”.
This will ensure that tenders are recognized as such when received and will not be accidentally opened.
Tenderers should be asked to acknowledge in writing receipt of the tender document.

Tendering Procedure:
Preliminary Enquiry:
It is recommended practice (not always followed) to send, about a month beforehand, to each of the firms from whom it is proposed to invite a tender, a
preliminary inquiry, to ascertain that they are willing to submit a tender.
This avoids the situation of contractors declining to tender, or if they prefer not to decline, submitting a ‘cover price’, i.e. a price which is high enough to
be well above the lowest tender.
Sufficient information about the project should be given in the preliminary enquiry letter to enable each contractor to decide whether he is in a position to
meet the terms.  

Period for Preparation of Tenders:
It is important that tenderers are given sufficient time to make all necessary enquiries from suppliers, sub-traders, etc. and the date for return of tenders
should be fixed so as to allow for the amount of work likely to be involved in preparing tender.
Four weeks is recommended as a minimum period, although it is possible, in exceptional cases, for less time to be adequate.
A time of the day should be specified as the latest time for tenders to be received on the date fixed.
Any tenders arriving later should be returned.

Parity of Tendering:
It is important that all tenders should be based on the same information.
All the tender documents must be identical.
A tenderer may telephone the architect / project quantity surveyor about an item in the bills of quantities or a clause in the specification. He may question
the accuracy of a quantity or unavailability of a specified material in the market.
Such queries must be answered and must be dealt with promptly.
But, whatever the reply given to the enquirer must be communicated to all other tenderers, immediately by telephone and then confirmed in writing.
The same procedure must be followed if an error is discovered or if it is decided to extend the time for the receipt of tenders.
The tenderer should be asked to confirm in writing the receipt of every written communication of additional or varied information.

Opening of Tenders:
A formal procedure should be followed for opening tenders to eliminate any suspicion or irregularities.
No tender must be opened before the latest time for submission.
As little time as reasonably possible should be allowed to elapse before opening tenders and they should all be opened at the same time.

Notifying the Tenderers:
As soon as possible after opening of tenders, all tenderers should be informed, then each tenderer will know whether his tender is successful or not
and be able to judge his future commitments.
This is a duty of often falls to the project quantity surveyor.

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