Slope cutting & controlled blasting.
The construction methodology behind Malaysian slope formation. How slopes are cut, drilled, blasted, and stabilized in the right sequence so soil nails, rock bolts, and shotcrete go in safely. Mechanical excavation (hydraulic excavator, hammer breaker, rock saw, ripper attachment), controlled rock blasting (pre-splitting, smooth blasting, line drilling, cushion blasting, decking), hand-held cutting tools (jackhammer, chain saw rock cutter), top-down lift sequencing, blast vibration monitoring (PPV), Akta Bahan Letupan (Explosives Act 1957) and JKM/JBPM/PDRM permits, integration with soil nail / rock bolt / shotcrete installation. Aligned with BS 6164, FHWA-NHI-14-007, AASHTO LRFD, JKR Slope Engineering Manual. By Infraconcrete - CIDB G7 specialist geotechnical contractor.
Jump to a topic.
The single most important rule.
Slope cutting for soil nail or rock bolt installation must follow strict top-down sequencing in 2-3 m vertical lifts. Each lift is fully stabilized before the next is excavated. Skipping this sequence is the most common cause of slope failure during construction. The sequence works because the slope above each cut is supported by the still-stabilized lifts above, while the lift just exposed has temporary stand-up time before its reinforcement is installed.
| Step | Activity | Duration | Notes |
|---|---|---|---|
| 1 | Cut lift 1 (top) to design profile | 1-3 days | Mechanical or controlled blast; immediate face cleaning |
| 2 | Drill soil nail / rock bolt holes | 2-5 days | Per design pattern, with centralisers / packers |
| 3 | Install nails / bolts, grout, end plates | 1-2 days | Grout cure 24 hours minimum before face load |
| 4 | Apply shotcrete facing with mesh + drainage | 2-4 days | BRC mesh, weep pipes, chute drains |
| 5 | Cut lift 2 (next 2-3 m down) | Repeat | Only after lift 1 is fully stabilized |
| 6 | Continue top-down to slope toe | Project-dependent | Final lift integrates with toe drainage / toe wall |
The default method for residual soil and weathered rock.
| Equipment | Productivity | Best for | Limitation |
|---|---|---|---|
| Hydraulic excavator (20-50 ton, e.g. CAT 320, Komatsu PC300, Hitachi ZX350) | 50-200 m^3/hour | Residual soil (Grade V-VI), weathered rock (Grade IV) | Productivity drops to 10-20 m^3/hour in Grade III; uneconomic in Grade I-II |
| Hammer breaker attachment (Atlas Copco, Furukawa, Soosan) | 5-25 m^3/hour | Grade III-II rock (moderately to slightly weathered) | Productivity drops below 5 m^3/hour in fresh rock; tooth/chisel wear |
| Rock saw / wheel cutter (Tesmec, Vermeer, Saturn) | 15-40 m^3/hour | Vertical / steep cuts in Grade III-II rock; precision cuts | High capital cost; specialist tool |
| Ripper attachment (excavator-mounted) | 30-80 m^3/hour | Layered sedimentary rock (Crocker Formation, sandstone-shale) | Less effective in massive granite |
| Bulldozer with ripper (CAT D8/D9, Komatsu D275) | 100-300 m^3/hour | Mass earthworks, embankment cuts, soft to moderately weathered rock | Cannot do precise slope formation; for bulk only |
For tight access and precision finishing.
Common tools
- Pneumatic jackhammer (Atlas Copco / Chicago Pneumatic): 20-30 kg, 1-3 m^3/hour. For precision cleanup of cut face, removing loose material, trimming overbreak.
- Hand-held chain saw rock cutter (Stihl GS461, Husqvarna K970): Diamond chain, 30-60 cm cut depth. For trimming, slot cutting, mortar removal in stone work.
- Demolition saw (Stihl TS800, Husqvarna K1270): 14"-16" diamond blade, for narrow cuts, kerf cutting.
- Splitting wedges + hand chisels: Mechanical splitting of pre-drilled holes. Slow but quiet, used for vibration-sensitive sites.
- Hydraulic rock splitter (Darda, Teledyne): Cylinder + wedges in 50-100 mm pre-drilled holes. Splits 0.5-2 m^3 per cycle. Vibration-free alternative to blasting.
When hand tools are essential
- Tight urban sites where vehicles cannot access the cut face
- Final 100-300 mm trimming of mechanical / blast cut face
- Vibration-sensitive proximity (heritage buildings, hospitals, sensitive equipment)
- Night works or noise-restricted hours
- Crew working from suspended scaffold on steep / vertical faces
The economic and technical decision.
Controlled blasting is the right choice when (a) the rock mass is too hard for economic mechanical excavation and (b) the site is far enough from sensitive receptors to keep blast vibration within limits. Blasting is the dominant method for highway and rail rock cuts in Pahang interior, Genting Highlands, EKVE Genting Sempah portal approaches, ECRL Main Range tunnels, Pan Borneo mountainous sections, and similar federal infrastructure.
| Condition | Recommendation |
|---|---|
| Grade IV-VI residual soil / weathered rock | Mechanical only - no blasting needed |
| Grade III moderately weathered rock | Mechanical with hammer breaker - blast only if productivity uneconomic |
| Grade I-II fresh granite, hard limestone, indurated rock | Controlled blasting (pre-split / smooth blast for permanent face) + bulk blast for body |
| Sensitive receptors within 50-100 m | Mechanical or hydraulic splitting; blast only with strict PPV control |
| Sensitive receptors within 200-500 m | Reduced charge per delay, longer delay times, electronic detonators |
| Sensitive receptors greater than 500 m | Standard blast design with PPV monitoring |
Creating the slope face line.
Pre-splitting creates a clean fracture plane along the final slope face BEFORE the main bulk blast. A line of closely-spaced lightly-charged drill holes on the design face line is detonated first - the holes split between each other, forming a continuous crack along the face. The bulk blast behind it then breaks the rock without damaging the pre-split face.
Typical specification
- Hole diameter: 64-89 mm (2.5"-3.5")
- Hole spacing: 10-12 x diameter, typically 600-900 mm
- Charge per hole: 60-120 g/m of decoupled explosive (e.g. detonating cord 30-80 g/m, or specialty pre-split cartridges)
- Stemming: top 0.5-1.0 m, fine aggregate
- Initiation: instantaneous along the line (or in groups with very short delays)
- Inclined drilling for slope face matching design angle
Result
Clean slope face with minimal overbreak (typically 100-300 mm beyond design line). Tight rock mass behind is preserved for soil nail / rock bolt anchorage. Stable face suitable for shotcrete adhesion. Half-barrels of pre-split holes visible on the finished face are evidence of correct execution.
For Malaysian highway and rail permanent rock cuts, pre-splitting is mandatory per JKR Slope Engineering Manual. EKVE Genting Sempah portal cuts, ECRL Main Range tunnel approaches, and Pan Borneo Sabah Crocker Formation cuts all use pre-split as standard.
Trimming the face after the bulk blast.
Smooth blasting (also called perimeter blasting) achieves the same goal as pre-splitting but in the opposite firing order: bulk blast goes off FIRST, perimeter holes go off LAST as a trimming round. The bulk blast removes the body of rock; the perimeter shots clean up the face.
| Aspect | Pre-splitting | Smooth blasting |
|---|---|---|
| Firing order | Perimeter first | Perimeter last |
| Face quality | Excellent (face exists before bulk blast) | Good (depends on bulk blast control) |
| Drilling cost | Higher (closer spacing) | Lower |
| Best for | Final permanent face, critical slopes | Bulk excavation with reasonable face quality |
For Malaysian permanent rock cuts where rock bolts and shotcrete will be installed on the face, pre-splitting is preferred. Smooth blasting is acceptable for less critical bulk cuts where the face will be subsequently trimmed mechanically.
Removing the body of rock.
| Parameter | Typical range | Notes |
|---|---|---|
| Bench height | 3-15 m | Limited by drill rig reach + face safety |
| Hole diameter | 89-165 mm (3.5"-6.5") | Larger for harder rock and bigger benches |
| Burden (distance to free face) | 2.5-4.0 m | Approximately 30 x hole diameter |
| Spacing (hole-to-hole) | 3.0-5.0 m | Approximately 1.2 x burden |
| Sub-drill (below bench) | 0.5-1.5 m | To break hole bottom; 0.3 x burden typical |
| Stemming | 2-4 m | Top of hole; fine aggregate |
| Powder factor | 0.3-0.8 kg/m^3 | Lower for soft rock, higher for hard granite |
| Explosive | ANFO (bulk) or emulsion (wet holes) | Local Malaysian suppliers: Orica, Maxam, MSE Mining |
| Initiation | Electronic or non-electric (NONEL) detonators | Electronic: programmable delays, vibration control. NONEL: cost-effective. |
| Delay sequence | 17, 25, 42, 67 ms typical between rows | Controls fragmentation + vibration |
Keeping the neighbours and structures safe.
PPV limits per BS 7385-2 / Malaysian guidance
| Structure type | PPV limit (mm/s) |
|---|---|
| Heritage / unreinforced masonry / glass facade | 5-7 |
| Residential (typical) | 12-15 |
| Industrial / RC structure | 25-50 |
| Pipelines (steel, RC) | 50-100 |
| Within construction site (no occupied buildings) | 100+ |
Frequency-dependent: lower limits for low-frequency vibration (under 4 Hz typical for far-field response).
Prediction formula (USBM RI 8507)
D = distance from blast (m)
W = max charge per delay (kg)
K, B = site-specific from trial blasts
Typical K = 100-500, B = 1.4-1.8 for granite
Site-specific K and B determined by trial blasts with seismograph monitoring. Blast design adjusted to keep PPV at the nearest receptor below the limit.
The Malaysian regulatory framework.
| Permit / approval | Authority | Lead time |
|---|---|---|
| Explosives Storage License | JBPM (Jabatan Bomba dan Penyelamat Malaysia) | 4-8 weeks |
| Explosives Transport Permit | PDRM (Polis Diraja Malaysia) | 2-4 weeks |
| Akta Bahan Letupan 1957 compliance | JMG (Jabatan Mineral dan Geosains Malaysia) | 4-8 weeks |
| Blasting Plan approval | Project consultant + JKR / LLM / authority | 2-4 weeks |
| Local council notification | DBKL / MBPP / MBJB / etc. | 2-4 weeks |
| Environmental compliance (EIA conditions) | DOE (Department of Environment) | Typically pre-existing for project |
| Pre-blast structural survey | Independent surveyor / consultant | 1-2 weeks per round |
Total lead time from project award to first production blast: typically 6-12 weeks. Permits cannot be rushed; programme allowance is essential.
The cut face becomes the working face.
Slope cutting is rarely an end in itself - it's the first step in a multi-trade sequence that ends with a fully stabilized, faced, drained, and monitored slope. Coordination between the cutting / blasting crew and the stabilization crew is the difference between a smooth project and a delayed one.
| Stabilization system | Cut face requirement | Typical hand-off time |
|---|---|---|
| Soil nailing with shotcrete facing | Trimmed to design profile, loose material removed, surface roughness for shotcrete adhesion | 24-48 hours after cut, with weather protection |
| Rock bolting with mesh or shotcrete | Pre-split / smooth-blast face, scaling of loose blocks, kinematic check for wedges / planes | 24-72 hours after blast (longer for large rock falls clearance) |
| Shotcrete on raw rock face | Loose material scaled, water-cleaned to remove dust, drainage weep pipes pre-installed | 24-48 hours after cut + cleaning |
| Ground anchors + capping beam | Cut face for anchor head zone, foundation level for capping beam, drilling platform | 5-14 days (longer due to deeper drilling + grouting) |
| Rock netting (drape mesh) | Scaled and cleaned face, ridge for top tie-back installation, toe trench | 3-7 days after cut |
| Rockfall barriers (above slope) | Foundation excavation for posts, anchor zones, working bench | Independent of slope cutting; pre-cut installation possible |
Codes and references.
| Topic | Reference |
|---|---|
| Blasting design | BS 5607 (use of explosives), USBM RI 8507 (vibration prediction), ISEE Blasters' Handbook, FHWA-NHI-14-007 Chapter 11 |
| Vibration limits | BS 7385-2, USBM RI 8507, DIN 4150-3 (Germany), Malaysian DOE / JKR guidance |
| Slope cutting sequence | JKR Slope Engineering Manual, FHWA-NHI-14-007, Hong Kong GEO Geoguide 1 |
| Earthworks | BS 6031, JKR/SPJ Section 2 |
| Rock excavation | BS 6164, FHWA-NHI-09-010 (tunnel methodology), AFTES (French Tunnelling) |
| Explosives regulation Malaysia | Akta Bahan Letupan 1957, JBPM regulations, PDRM transport rules, JMG approval |
| Pre-blast survey | BS 5228-2 (noise + vibration on construction sites), Malaysian construction industry practice |
Cutting & blasting questions.
What's the cutting sequence for soil nail / rock bolt installation? +
When does blasting become necessary? +
Pre-splitting vs smooth blasting? +
What PPV limits apply? +
What permits are required for blasting in Malaysia? +
Slope cutting or blasting job needs engineering?
Send the geometry, soil / rock report, and constraints (sensitive receptors, schedule, lift restrictions). Same-day response from the engineering team. We work as specialist contractor under your consultant or as design-build lead. CIDB G7, ISO 9001:2015. Track record across federal expressway, rail, and hillside development scopes.