application of integrated geophysical technique for the mapping

Application of Integrated Geophysical Technique for the mapping of old Foundation Pilings at Penang Sentral, Butterworth, Pulau Penang Malaysia.

Mohd Nawawi and Amin E. KhalilPPSF, Universiti Sains Malaysia

overview

• Problem statement• Site Layout• Planned Geophysical techniques• Methods overview• Survey layout.• Results

Problem Statement

The site under investigation is planned for new development project at Pulau Pinang state. 20 years ago another project was established at the site. However, the project as cancelled and the buildings were removed and the foundations was buried. These buried foundation piles decelerated the construction of the new project. This is motivation of the present work.

Site Layout

Phase 1

Parking

Taxi area

Bus area

Site Layout (cont.)

The site is a connection center where various land and marine transportation exist. These facilities are:1- The ferry that connects Penang island with the mainland.2- The railway station (KTM) that connect the state with other Malaysian states.3- Rapid Penang bus station.4- Asphaltic roads and a flyover bridge.

FerryR. Penang

Planned Geophysical methods

Foundation Piles can be detected through these properties:

1. Density contrast.2. Shear wave velocity.3. Magnetic properties due to iron bars.4. Resistivity5. Dielectric constant

Planned Geophysical methodsHence the following Methods was proposed

1.Gravity.2.Magnetic gradiometer3.Multichannel Analysis of Surface

waves.4.Time domain electromagnetic5.Ground Penetrating Radar GPR

Gravity CG-5 autogra

v

Although density contrast exist between concrete piling and surrounding soil, the area is too noisy that we couldn’t carry out a reliable gravity survey. As a result the gravity method was excluded from the survey

Magnetic gradiometer

Preliminary test showed good results confirmed by field inspection. Example in figure shows high anomaly at Profile 1.

MASW (Multichannel analysis of surface waves).

Two problems when test MASW at the site. These problems are the high noise and low resolution of the method. Hence, the method was excluded

GPR

The method gave good result as shown in the figure.

Methods Used

1- Magnetic Gradiometer

2- GPR

Magnetic Gradiometer

The technique uses measurements from two proton magnetometer aligned vertically at a spacing of 1m. The subtraction gives the vertical gradient of magnetic field. The gradiant enhances the near surface anomaly.

GPR

The technique produce profiles similar to seismic reflection profile. An electromagnetic pulse is sent to the subsurface, the reflected energy from anomalous surfaces is then recorded at the receiver at near zero offset.

Survey Layout

Grid points at 5m separation.

Results

Results (cont.)

conclusion

• Old foundation piling decelerate the establishment of new development project

• Near surface geophysical methods were employed to solve the problem.

• Magnetic gradiometer and GPR showed good example for detecting old foundation piles.

• Other methods couldn’t be applied because of the site conditions

جزيال شكراTerima KasihThank you