Before starting any construction in hilly or semi-rural areas like Petang, Badung, understanding the ground profile is essential. Indo Soil was commissioned to conduct a comprehensive soil and slope investigation for a planned development in Desa Carang Sari, Kecamatan Petang, Kabupaten Badung. The study was carried out between December 3–20, 2023, and included deep borehole drilling, SPT testing, topography measurement, and slope stability analysis.

This project, initiated by PT Graha Tunggal Nusamandiri, required accurate data to ensure the site’s safety, structural stability, and compliance with foundation engineering standards.

Why This Site Required Detailed Investigation

Petang is a highland area in North Badung, known for its undulating topography and complex soil layers. These conditions make foundation design especially sensitive to soil consistency and slope safety. As a result, this investigation aimed to determine:

• Soil bearing capacity for shallow and deep foundations

• Groundwater level and geological layering

• Slope stability and risk zones

• Topographical characteristics across the buildable area

Field Testing and Methodology

The scope of work included:

• 4 Boreholes, each reaching depths of up to 30 meters, with Standard Penetration Testing (SPT)

• 3 Cone Penetration Tests (CPT/Sondir) to assess cone resistance and local shear strength

• Topography survey to determine elevation gradients

• Slope analysis on 4 cross-sections near borehole locations

This multi-layered approach was necessary due to the combination of slope terrain and anticipated multi-level structures.

Soil Findings and Recommendations

Soil Profile

The soil investigation revealed a mix of clay loam, marine clay, and young sedimentary rock (cadas muda) at deeper levels. The top layers ranged from soft to medium consistency, gradually transitioning into harder strata suitable for anchoring foundations.

The SPT results showed increasing N-values with depth, suggesting improving soil strength below 5 meters. Most boreholes hit stiff soil and rock layers between 9–11 meters, making bore piles a suitable recommendation.

Groundwater

No significant groundwater table was encountered within the tested depth (up to 30 meters), minimizing concerns for water intrusion or buoyancy effects during foundation placement.

Foundation Bearing Capacity

Based on the borehole and CPT data, the recommended bearing capacities for 30 cm diameter bore piles were within the range of 50–56 tons, depending on the location and depth.

This makes bore piles ideal for supporting mid-rise villas, small resorts, or other residential buildings expected in this area. For shallow footings, allowable bearing capacities at 1–1.5 meters ranged between 0.5–1.3 kg/cm², which may be suitable only for lightweight structures.

Topography and Elevation Overview

The elevation mapping across the site showed gentle to moderate slope variation. These changes in elevation were taken into account during the slope section analysis. While overall terrain appeared manageable for residential construction, localized grade changes above 15% would require proper retaining structures and drainage systems to prevent erosion or sliding.

This topographical information is not only vital for site grading but also affects cut-and-fill calculations and building orientation.

Slope Stability Analysis

One of the critical components of this investigation was the slope safety factor analysis. Four slope sections were analyzed using borehole and soil strength data. All four sections produced stability factors above the minimum threshold for safe construction, though reinforcement and drainage systems are recommended in steeper zones.

Slope safety becomes even more crucial in high-rainfall areas like Petang, and incorporating retaining walls or proper swales can significantly improve long-term stability.

Conclusion and Next Steps

The investigation at Carang Sari provides a comprehensive understanding of both the subsurface and surface conditions. With proper foundation design and consideration for slope protection, the site is deemed feasible for development.

We’ve provided the client with:

• Full soil stratification and SPT data

• CPT resistance values and bearing capacity guidance

• Recommendations for foundation type and depth

• Elevation charts and slope reinforcement suggestions

Final structural decisions should be made by a certified civil or structural engineer using this data as the design baseline.

Build Safely with Indo Soil

At Indo Soil, we support responsible development in Bali’s unique landscapes by delivering field-proven, regulation-compliant soil and slope analysis. Whether you’re planning a hillside villa in Petang or a beachfront resort in Nusa Dua, we’re here to ensure your project starts with solid ground data.

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