technical_document for piling

ISLAMABAD PILING WORKS

TESTING OF PILES – METHODOLOGY

TECHNICAL SUBMISSIONS –PILING WORKS AT ISLAMABAD

TESTING OF PILES - METHODOLOGY

Table of Content

S. No. Topic Pg. No.

1 Dynamic Pile Load Test 1

2 Crosshole Sonic Logging 2

3 Sonic Echo Test 3



1. DYNAMIC PILE LOAD TEST

Dynamic pile load test is performed during the initial driving of piles and provides information

on driving hammer performance, driving stresses, pile integrity and capacity at the time of

testing.

1.1 Selecting the drop weight system

The first step is to select the most adequate drop weight system for load testing. The system

is determined by running software with the following inputs:

Subsurface information (in-situ strength of subsurface deposits etc.)

Pile characteristics (diameter, density, concrete & steel grade and depth)

The GRLWEAP® software, a wave equation analysis program developed by Pile Dynamics

Inc. USA, simulates the conditions and gives the most appropriate weight system for

dynamic pile testing.

1.2 Instrumentation of the pile

The second stage is the instrumentation of the pile. Two strain transducers and two

accelerators are installed near the pile head and two strain transducers and accelerators are

embedded near the base of the shaft or at any lower depth below the pile head. The

transducers and accelerators installed near the base are optional.

The accelerometers capable of measuring up to 10,000 g force will be used. The

accelerometers will be bolted with the pile concrete. The transducers should be able to

measure strains in range of 2000 times of the damping value.

1.3 Storage and processing of the data

The data obtained from the test is stored in the PDA® pile driving analysis software. The

data is analyzed by CAPWAP® software. The software determines the resistance

distribution, dynamic soil response and simulates a static load test. The test will be

performed in accordance with ASTM D4945.

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2. CROSSHOLE SONIC LOGGING

Cross hole sonic logging is a state-of-the-art method which employs the passage of

ultrasonic pulses through the concrete pile to ascertain its structural integrity and extent of

extent and location of defects.

The time taken by the pulse to generate and then intercepted and its strength gives a

measure of the concrete quality between transmitter and receiver. Concrete wave speed,

calculated by dividing the distance between the transmitter and the receiver by the first

arrival time also serves as a relative indicator of concrete quality. Non-uniformities such as

contaminated or soft concrete, honeycombing, voids and inclusions exhibit delayed arrival

times with reduced signal strength.

2.1 Equipment Required for CSL:

1. A computer based CSL data acquisition system for display of signals during data

acquisition, with a minimum 12 bit A/D converter with a sampling frequency of at least

50,000Hz, and recording of all pulse signals for full analysis and individual inspection.

2. Ultrasonic transmitter and receiver probes capable of producing records with good signal

amplitude and energy through concrete.

3. Four depth sensors to independently determine transmitter and receiver probe depths.

2.2 Procedure for CSL

Prior to CSL testing, the contractor should have a record of all drilled shaft lengths with

elevation of the top and bottom and the installation dates of all drilled shafts. The access

tubes shall be labeled for identification.

The Transmitter and the receiver are installed vertically through access pipes previously

placed in the shaft. The testing is carried out with the transmitter and the receiver at the

same level unless defects are indicated, in which case the questionable zone is evaluated

with angled tests.

The data gathered from the test shall be used to draw graphs which show relationships

between pulse first arrival time and depth, between pulse wave speed and depth and

between amplitude verses depth.

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3. PILE INTEGRITY TESTING

Sonic echo/impulse testing is conducted to determine the integrity and the length of deep

foundations. This test can be performed on drilled shafts or driven piles. The test involves

the striking of the shaft top with a hammer and a subsequent monitoring of the by a receiver.

Sonic echo testing is conducted with different frequencies to optimize reflections coming

from the bottom of the shaft and to reduce the effect of surface waves or reflections from a

discontinuity at a shallow depth.

The method adopted will either be the sonic echo method in which the analysis is performed

in the time domain or Impulse response method in which the analysis is performed in the

frequency domain.

The equipment will consist of the following parts:

a) A small instrumented impact device (hand held hammer).

b) A sensitive accelerometer: This sensitive accelerometer is handled carefully

c) Pile Integrity Tester (PIT).: This is the data processing and storage unit of the equipment.

3.1 TEST PROCEDURE

The Pile Integrity Tester (PIT) uses the small hand held hammer to generate a low

strain shock wave in the pile; the sensitive accelerometer temporarily attached to the

pile top then measures the response from the pile bottom or hidden defects along the

shaft

The accelerometer shall be fixed on a clean pile top area using a suitable bonding

material (that is, wax, Vaseline, etc.) in such a way to prevent slippage of the sensor

under hammer impacts. It is to be noted that the transducer axis of sensitivity shall be

aligned with the pile axis in order to measure correctly the axial pile motion.

The motion sensor (i.e. the accelerometer) shall be placed in general near the centre

of the pile. The low strain impact shall be applied to the pile head within a distance of

300 mm from the motion sensor.

Whenever it seems necessary, full details of the ground conditions, the construction

method and daily drilling conditions shall be made available by the contractor to the

PIT Engineer in order to facilitate the study and to give accurate results about the

integrity of the piles.

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