Kaedah Pengukuran Utility Suvey

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Peralatan Pengesanan dan Penentududukan

Kaedah Pengukuran/ Perolehan Data untuk Pemetaan Utiliti

 PCL

• Total Station

 GPR

• GNSS

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Mengapa pepasangan utiliti bawah tanah perlu dikesan? •Bagi mengelakkan kemalangan yang melibatkan nyawa dan kemusnahan aset utiliti sedia ada. •Bagi mengelakkan pertambahan kos semasa kerja-kerja pengorekkan jalan. •Sebagai maklumat awalan sebelum kerja-kerja pengorekkan •Bagi memenuhi kewajiban pihak kontraktor.

Persediaan yang perlu sebelum memulakan kerja-kerja pengesanan utiliti 1. Dapatkan peta atau pelan utiliti bagi kawasan tersebut (maklumat awalan) 2. Perhatikan keadaan tempat semasa (keadaan tanah (basah/kering), pili bomba, gas valve dll) 3. Menilai keberkesanan pelbagai teknik pengesanan bagi mengesan pepasangan utiliti. JANGAN bergantung kepada satu teknik pengesanan sahaja.

Maklumat-maklumat yang diperlukan sebelum kerja-kerja pengorekkan dilaksanakan 1. Apakah maklumat utiliti yang tertanam di kawasan itu? (jenis, pemilik, material bahan, saiz dll) 2. Dimanakah kedudukan pepasangan utiliti tersebut? (alignment, direction) 3. Berapakah kedalaman pepasangan utiliti tersebut? (kedalaman utiliti ditanam)

Bagaimana Data Utiliti Diperoleh Pengesanan Untuk pepasangan (installation) sudah ditanam

Ukuran Terus Untuk pepasangan baru yang belum ditanam

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Bagaimana Data Utiliti Diperoleh Pengesanan

 Teknik Perolehan Geofizik Secara Pengesanan Untuk pepasangan (installation) sudah ditanam Libatkan pengesanan utiliti di bawah tanah secara non-invasive Menggunakan kaedah pengesanan geofizikal e.g PCL dan GPR Libatkan pengukuran tanda di permukaan diukur menggunakan peralatan ukur konvensional atau GNSS Hasil ukuran – tahap Kualiti “B”

Untuk pepasangan (installation) sudah ditanam

Ukuran Terus Untuk pepasangan baru yang belum ditanam

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Peralatan utama yang digunapakai bagi mengesan pepasangan utiliti bawah tanah: Electromagnetic Locater (Pipe and cable locater) Ground Penetrating Radar (GPR)

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Pengesanan Menggunakan Pipe and Cable Locator (PCL)  Mengandungi 2 komponen utama  Pemancar (transmitter)  Penerima (receiver)

 Terdapat pelbagai jenis PCL dengan berbagai saiz dan bentuk serta frekuensi boleh diperoleh dipasaran. Julat frekuensi yang biasa digunakan : 50 Hz ke 480 kHz  PCL berupaya mengesan pada ketepatan ± 10cm dan kedalaman pada ±5% daripada nilai sebenar

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Teknik pengesanan menggunakan prinsip radio detection  Menggunakan prinsip elektomagnetic untuk mengesan utiliti bawah tanah.

Prinsip Asas Operasi PCL Pemancar

Penerima

Arus elektrik yang mengalir pada bahan konduktor mengeluarkan medan magnet bulat di keliling konduktor.

 Koil penerima boleh digunakan untuk mengesan amplitud medan magnet Amplitud berubah bergantung kepada kedudukan dan arah penerima dalam medan magnet Amplitud paling tinggi apabila penerima berada tepat diatas bahan konduktor

 Digunakan untuk kesan bahan logam yang boleh mengeluarkan gelombang elektromagnet

Medan magnet

Pemancar keluarkan isyarat gelombang Isyarat gelombang jana medan magnetik Medan magnetik mengarahkan isyarat ke dalam penderia penerima 12

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Pengendalian PCL Adakah pengukur tersebut sedang mengesan kabel?

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Apakah yang sebenarnya dikesan?

….yang sebenarnya dikesan adalah medan magnet (magnetic fields)

? Apakah itu Medan Magnet?

Terdapat 2 kaedah bagi mengesan medan magnet iaitu secara;

1. Peak and 2. Null Medan magnet adalah arus yang dipancarkan oleh konduktor yang membawa arus.

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Peak Response

Peak Response

Null Response

Null Response

Null Response

LOCATING

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Locating

Pipe or Cable Direction

Pipe or Cable Direction

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Marking

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Frequency

BAGAIMANA MEMILIH FREKUENSI YANG SESUAI?

Frequency vs Range

Which Frequency ?

Low frequency = long range (minimum capacitance signal loss to ground). This frequency is better for connection and locating longer metal pipes or cables.

Radiodetection

 Frequency =  Range (Capacitance Effect)

Which Frequency ?

Higher frequency = shorter range (greater capacitive signal loss to ground). This frequency is better for induction onto small or short length conductors, such as telephone drops, CATV cables or street light cables.

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Pipe = Surface Area = Range Pipe = Surface Area = Range

Ground Moisture

Low Frequency Better Identification

Higher Frequency, Broader Peak

High Frequency Signal Coupling

Higher Frequency

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APPLICATION

Passive

Active There are two methods of signal detection.

Two types of Passive Signal

1. Radio Signal 2. Power signal

Passive Signal - Radio

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Passive Signal - Power 50/60Hz

Passive Sweep

Passive

Active There are two methods of signal detection.

DIRECT CONNECTION 29

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Direct Connection

Direct Connection

mA

Connection

Direct Connection

mA

A successful connection to the metallic pipe or cable will be indicated by a change in the transmitter audio or visual indicator. Always make the best possible connection for reliable signal.

Direct Connection

Direct Connection

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Signal Clamp

SIGNAL CLAMP

Signal Clamp

Signal Clamp

Signal Clamp

Higher Frequency

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INDUCTION 48

Induction

Induction

Induction

Induction - Signal Strength

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Induction - Identification

Active Sweep

Induction - Identification

Induction - Never Locate Near To The Transmitter.

Min 10 paces away from the transmitter.

Check the signal with the receiver.

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Induction : Re-Bar Interference

General Locating

During excavation, keep checking in the trench. This may show smaller conductors which were not detectable at ground level.

Problems Solving

GENERAL LOCATION

Locate A Death End Pipe, But NOT Pot End Cable!

Locate A Bend

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Locate A Submerge Pipe or Cable.

Locate A Tee.

Locate Problem: Re-bar

Connection

Remote ground = better range, less signal transfer.

Connection

Badly positioned remote ground causes more signal transfer. Always place ground rod away from adjacent utilities.

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Connection

Ground stake too close to target conductor: Less range, some signal transfer.

Metal fences may seem a convenient ground point, but might produce interfering signals. Always use an independent ground such as a screwdriver or ground stake.

Connection

LOCATOR LIMITATIONS

SIGNAL DISTORTION Grounding to a structure which is also grounded can produce multiple signals.

Distortion

Distortion 1 3

Peak

Null

This distortion varies depending upon the direction and magnitude of the current flow, causing a discrepancy between the peak and null aerial responses.

Current on one line may induce 'stray' signals to nearby conductors.

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Distortion

Unique Features For Cable Identification • DEPTH MEASUREMENT •CURRENTMEASUREMENT(CM) •CURRENT DIRECTION(CD)

Distorted field may appear to come from a different point.

Depth Measurement

HOW TO TAKE DEPTH MEASUREMENT?

Depth Measurement

Depth Measurement

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Distortion and Depth

Depth Measurement Peak Null

d

Peak Null

d

When there is a discrepancy between the aerial responses the following must be observed. 1. The Peak response will always be more accurate. 2. Push button depth estimation should not be used until the two responses agree.

Depth Measurement

Low Frequency Better Identification

Current Measurement(CM)

Signal Coupling: How to identify?

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Current Measurement(CM)

Current Measurement(CM)

Current Measurement(CM)

Current Measurement(CM)

Current Measurement(CM)

CURRENT DIRECTION(CD)

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Current Direction (CD)

Expected current direction indications and return signal path.

Current Direction(CD)

The target line is identifiable by Current Direction.

Current Direction(CD)

Current Direction(CD)

Current Direction (CD)

Penentuan lokasi  Menggunakan Alat penerima Global Navigation Satellite System (GNSS) – latest boleh menerima isyarat dari 3 system GNSS – GPS, GLONASS dan Galileo untuk menentukan lokasi.  Teknik pengesan utiliti tidak boleh „position‟ cuma „detect‟ kedudukan  Pengesan akan tanda dengan tepat kedudukan utiliti dan kemudian di ukur menggunakan GPS dan total station

Possible current direction indication on conductors.

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Ground Penetrating Radar

Basic concept of GPR

 GPR can be defined as a radar which able to detect buried objects and to characterize the subsurface structure and properties in a wide variety of applications.

 The GPR is a device used for non-invasive scanning and precise detection of underground utilities. GPR is composed of a receiver and transmitter antenna, a control unit, battery supply and a survey cart

Basic concept of GPR

Basic concept of GPR

 Generally, when the survey cart moves on the site surface the transmitting antenna send polarized, high frequency electromagnetic (EM) waves in the ground. Because of different existing inhomogenities in the ground, e.g. soil layers, underground utilities, stones, gravel, cavities and other anomalies, part of the EM waves is reflected from the dielectric boundary between different materials and other part is refracted and goes to the deeper layer

Frequency selected

Attenuation, α

GPR image

0.001

 General character of EM field phase velocity and attenuation with frequency illustrating the ‘ GPR plateau’(Annan, 2002)

GPR Plateau

1

1000

Frequency (MHz)

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Teknik Pengesanan menggunakan Pengesanan Menggunakan Ground Penetratin/Probing Radar (GPR)

GPR Limitations  The factors affecting the GPR performance and should be consider are the design of a GPR (hardware), target types, material of the target and the surrounding (environment)

 Teknik radio detection tidak boleh digunakan untuk kesan bukan metalik termasuk paip air dan gas plastik, paip di perbuat dari tanahliat dan cable gentian.  GPR berfungsi dengan menghantar microwave kedalam tanah dan proses pantulan balik dari pelbagai lapisan yang diterima oleh akan menghasilkan imej dalam bentuk hyperbola.  Imej perlu dibuat interpretasi

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Teknik Pengesanan menggunakan Pengesanan Menggunakan Ground Penetrating/Probing Radar (GPR)

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Operasi Pengesanan

Jarak Selang Pengesanan B

BM

(xB , yB )

GPR Mula 1

GPR Henti 4

(x1 , y1)

(x4 , y4)

GPR Mula 5

Lubang Ujian

Laluan PCL

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Kabel (sedang dipasang)

(x11 , y11)

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A

(xA , yA)

(x2 , y2)

GPR Henti

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(x3 , y3)

(x12 , y12)

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(x10 , y10)

2

Laluan GPR

PCL

Laluan GPR

Laluan GPR

(x5 , y5)

Kesan setiap 20m Garis Rentas Garis lintang Arah pergerakan Lihat muka 11 garis panduan

GPR Mula Tanda Cat (GPR) Tanda Cat (PCL) Air

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(x6 , y6)

GPR Henti

Stesen Kawalan Elektrik Telekomunikasi

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Pelbagai Jenis Antena GPR

Bagaimana Data Utiliti Diperoleh Pengesanan Untuk pepasangan sudah ditanam

Ukuran Terus

Dari kiri ke kanan:

Sistem Antenna GPR.

Untuk pepasangan baru yang belum ditanam

1,500, 900, 550, 400, 300, 200, 120, 100, 80 MHz

Kelas Antena

Frekuensi Antena

Frekuensi Tinggi

> 1000 MHz

Kedalaman Pengesanan < 0.5 m

Frekuensi Sederhana Tinggi

400 – 600 MHz

0.5 m – 1.5 m

Frekuensi Sederhana Rendah

200 – 400 MHz

1.5 m – 2.0 m

Frekuensi Rendah

< 200 MHz

2.0 m – 3.0 m

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Kaedah Ukuran Terus

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Lubang ujian

 Libatkan pengukuran kepada utiliti yang terdedah  Menggunakan peralatan ukur konvensional  Ukuran lubang ujian  Ukuran terus sebelum pepasangan utiliti ditimbus  Hasil ukuran – data utiliti pada tahap Kualiti “A”

Backoe Penggalian menggunakan alat asas Ekskavasi hampagas

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Peralatan Ukuran Terus

Perbandingan Pengesanan & Pengukuran Terus

Kegunaan

Tahap Kualiti

Peralatan

Pengesanan

Kaedah

Pepasangan Tertanam

B

Pengukuran Terus

Pepasangan baru belum ditanam

A

PCL GPR Total Station GNSS Total Station GNSS

Ketepatan (relatif)

Kos (relatif)

Rendah

Tinggi

Masa Perolehan Data (relatif) Lama

Tinggi

Rendah

Cepat

 Sesuai mulakan pemetaan utiliti secepat mungkin  Penggunaan kaedah pengukuran terus terbaik bagi pepasangan baru  Penggunaan kaedah pengesanan kaedah terbaik untuk pepasangan sedia ada

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