Sains Malaysiana 54(6)(2025): 1465-1475

http://doi.org/10.17576/jsm-2025-5406-03

 

Utilizing Gravity Surveys for Subsurface Feature Identification in Foundation Planning

(Menggunakan Tinjauan Graviti untuk Pengecaman Ciri Subpermukaan dalam Perancangan Asas)

 

NORDIANA MOHD MUZTAZA^1,6,*, THANATH GOPALAN², NUR AMANINA MAZLAN², JAMALUDIN OTHMAN³, NAZRIN RAHMAN⁴, NAJMIAH ROSLI⁴, ROSLI SAAD^1,4,6, FARID NAJMI ROSLI^1,4, ATHIRAH ROSLI⁴ & YASIR BASHIR⁵

 

¹School of Physics, Universiti Sains Malaysia, 11800 USM, Pulau Pinang, Malaysia

²Mass Rapid Transit Corporation Sdn Bhd Headquarters, Tingkat 5, Menara I & P1, 46 Jalan Dungun, Bukit Damansara, 50490 Kuala Lumpur, Malaysia

³SubMAP Geophysical Services Sdn. Bhd, A-5-10, Empire Tower, SS16/1, 40750 Subang Jaya, Selangor, Malaysia

⁴Global GeoExperts Sdn. Bhd., 737-6-5, Kompleks Sri Sg Nibong, Jalan Sultan Azlan Shah, 11900 Bayan Lepas, Pulau Pinang, Malaysia

⁵Geophysical Engineering, Istanbul Technical University, Istanbul, Turkey

⁶Pusat Geokejuruteraan Tropika (GEOTROPIK), Aras 2 Blok D03, Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia

 

Diserahkan: 12 Jun 2024/Diterima: 28 Mac 2025

 

Abstract

Understanding the distribution and extent of solution features such as cavities and pinnacles in limestone bedrock is crucial for anticipating potential challenges and planning appropriate foundation solutions. This study employed microgravity surveying to complement available borehole data and map karst features, particularly cavities, within the limestone bedrock. The survey was conducted on a 5 m × 5 m grid interval, establishing a total of 91 stations. Reduced Bouguer and residual anomalies were contoured and plotted using the GEOSOFT Oasis Montaj Mapping system. Anomalies of interest were further analyzed through 2-D gravity modeling using PotentQ software to determine the dimensions of the causative bodies. The survey results, presented as Bouguer, residual, and Bouguer anomaly horizontal gradient maps, showed a small range of gravity values (-9.24 to -9.10 mGal), indicating minimal variation in limestone bedrock topography. Gravity highs were associated with shallow limestone bedrock, while isolated gravity lows suggested the presence of cavities. Horizontal gradient maps highlighted peaks corresponding to the edges of these cavities and potential channel-like features. Borehole data corroborated the microgravity findings, with bedrock encountered at depths between 9.6 m and 12.3 m indicating deeper bedrock towards the south. The 2-D gravity modeling suggested a sediment-filled cavity approximately 7 m thick and 15 m wide in an east-west orientation, aligning well with borehole data. The combined use of borehole data and microgravity surveying proved effective in characterizing subsurface karst features, providing valuable insights for foundation planning leading to safer and more efficient construction practices.

Keywords: Anomaly; Bouguer; cavities; limestone; microgravity

 

Abstrak

Pengetahuan tentang taburan dan ciri larutan seperti rongga dan puncak batu kapur adalah penting untuk meramal potensi cabaran dan merancang pembinaan tapak yang sesuai. Kajian ini menggunakan survei mikrograviti untuk melengkapkan data lubang bor yang sedia ada dan memetakan ciri karst, khususnya rongga dalam batuan kapur. Survei dilakukan dengan sela grid 5 m × 5 m, berjumlah 91 stesen. Anomali Bouguer yang dikurangkan dan baki digambarkan menggunakan sistem pemetaan GEOSOFT Oasis Montaj. Anomali yang menarik dianalisis lebih lanjut melalui pemodelan graviti 2-D menggunakan perisian PotentQ untuk menentukan dimensi jasad yang menjadi punca. Keputusan survei yang diketengahkan sebagai peta anjakan Bouguer, baki dan gradien mendatar anjakan Bouguer mendedahkan julat kecil dengan nilai graviti (-9.24 hingga -9.10 mGal), menunjukkan variasi minimum dalam topografi batuan kapur. Anjakan graviti tinggi dikaitkan dengan batuan kapur cetek, manakala anjakan graviti rendah menunjukkan kehadiran rongga. Peta gradien mendatar menunjukkan puncak yang sepadan dengan tepi rongga ini dan ciri potensi berbentuk saluran. Data lubang bor mengesahkan penemuan mikrograviti dengan batuan kapur dijumpai pada kedalaman antara 9.6 m dan 12.3 m menunjukkan batuan kapur yang lebih dalam ke arah selatan. Pemodelan graviti 2-D menyarankan keberadaan rongga berisi endapan dengan ketebalan kira-kira 7 m dan lebar 15 m dengan orientasi timur-barat, sejajar dengan data lubang bor. Penggunaan data lubang bor dan survei mikrograviti terbukti berkesan dalam pencirian karst di bawah permukaan, memberikan maklumat penting untuk perancangan tapak yang lebih selamat dan cekap dalam amalan pembinaan.

Kata kunci: Anomali; batu kapur; Bouguer; mikrograviti; rongga

 

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*Pengarang untuk surat-menyurat; email: mmnordiana@usm.my