The Challenge
A 62 MWp fixed-tilt project on a Mediterranean hillside had average slopes of 18% with localized zones exceeding 30%. An initial flat-terrain layout placed rows uniformly across the site, but slope analysis flagged 34% of the total area as exceeding the 15% slope limit for standard fixed-tilt racks. The conventional options were expensive: mass grade the entire hillside, or sacrifice a third of the site capacity.
The engineering team needed to determine whether terrace grading could recover the excluded zones while keeping earthwork volumes manageable and cut/fill balanced on-site.
Site Conditions
PVX.Cad mapped the terrain and classified slopes before any layout work began:
Slope distribution:
| Slope Range | Percentage | Area (m2) | Status |
|---|---|---|---|
| 0-10% | 28.4% | 112,300 | Buildable without grading |
| 10-15% | 37.2% | 147,100 | Buildable with minor grading |
| 15-25% | 24.8% | 98,100 | Requires terrace grading |
| 25-35% | 7.9% | 31,200 | Requires heavy terrace or exclusion |
| >35% | 1.7% | 6,700 | Excluded (access roads, drainage) |
The site had uniform soil conditions (medium-firm clay and weathered limestone), which simplified the cost model but did not reduce the slope challenge.
Two Approaches Compared
Approach 1: Mass Grading to 15% Maximum Slope
PVX.Cad applied full-terrain smoothing with a 15% target maximum slope across the entire site.
- Total cut: 89,400 m3
- Total fill: 82,100 m3
- Net excess: 7,300 m3 (off-site removal)
- Cost: $612,000
- Buildable area: 100% of original boundary
Mass grading achieved full buildability but at high earthwork volume. Cross-section analysis showed cut depths exceeding 2.5 m in the steepest zones, with several benches requiring retaining structures.
Approach 2: Terrace Grading with Adaptive Row Orientation
PVX.Cad generated terrace platforms following the natural contour lines, with row orientation adapted per terrace to maximize GCR within each level. Terraces were designed with 3:1 slopes between levels, eliminating the need for retaining walls.
- Total cut: 41,200 m3
- Total fill: 39,800 m3
- Net balance: 1,400 m3 (virtually balanced on-site)
- Cost: $298,000
- Buildable area: 92.4% of original boundary (recovering 38% of previously excluded zones)
The terrace approach accepted a small capacity reduction (losing the steepest 7.6% of the site) in exchange for dramatically lower earthwork. Row orientations varied by up to 12 degrees across terraces, which PVX.Cad handled by generating independent rack configurations per terrace level.
Full Comparison
| Approach | Method | Cut (m3) | Fill (m3) | Cost | Buildable Area |
|---|---|---|---|---|---|
| 1 | Mass grading to 15% | 89,400 | 82,100 | $612,000 | 100% |
| 2 | Terrace grading + adaptive rows | 41,200 | 39,800 | $298,000 | 92.4% |
Cost Model
Unit costs based on site soil conditions:
- Excavation: $2.80/m3
- Fill placement and compaction: $4.50/m3
- Off-site hauling: $3.50/m3
- Terrace shaping (per linear meter): $8.50/m
- Indirect site costs: 10% of direct earthwork
| Comparison | Savings |
|---|---|
| Approach 2 vs 1 | $314,000 |
Key Findings
- $314,000 saved by switching from mass grading to terrace grading with adaptive row orientation.
- 54% reduction in earthwork volume from 89,400 m3 to 41,200 m3.
- Cut/fill virtually balanced on-site (1,400 m3 net vs 7,300 m3 off-site removal with mass grading).
- 38% of previously excluded area recovered for rack placement through terracing.
- No retaining walls required. 3:1 inter-terrace slopes stayed within natural angle of repose.
- 7.6% capacity trade-off accepted. The steepest zones were excluded rather than graded at extreme cost. This was a conscious engineering decision, not a software limitation.
- Both scenarios were generated and compared in a single AutoCAD session using PVX.Cad.
Designed with PVX.Cad and PVX.View.