On January 2, 2026, the tragic collapse of Manzil Towers C in Nairobi’s South C estate claimed the lives of security guards Ali Adan Galgalo Abdi and Hassan Huka. While media headlines initially focused on municipal approvals and political finger-pointing, forensic structural engineers and investigators from the Directorate of Criminal Investigations (DCI) uncovered a far more calculated reality on the ground.
The disaster was not caused by an act of nature. Instead, it was the catastrophic result of technical shortcutting, forged geotechnical surveys, severely compromised concrete mixes, and structural overloading.
This third installment of our investigation examines the forensic engineering findings, breaking down the exact structural mechanisms that caused Manzil Towers C to pancaking down, and exposing the regulatory loopholes corrupt developers exploit to erect dangerous high-rises across Nairobi.
1. Forged Geotechnical Reports and the “Black Cotton” Hazard
South C, along with parts of Lang’ata and the broader Athi Basin, rests on expansive clay soil locally known as black cotton soil. This clay swells drastically during wet seasons and shrinks during dry spells, creating extreme differential movement.
Black Cotton Soil Mechanics vs. Multi-Story Load Demands
┌─────────────────────────────────────────────────────────────┐
│ HIGH-SWELL CLAY LAYER (Top 2-4 meters) │
│ • Volumetric expansion up to 30% when saturated with water │
│ • Requires deep foundation (Piles or Raft to bed-rock) │
└─────────────────────────────────────────────────────────────┘
↓
┌─────────────────────────────────────────────────────────────┐
│ FORGED GEOTECHNICAL REPORT (Manzil Towers Site) │
│ • Falsified soil bearing capacity (q_a) to save costs │
│ • Substituted deep pile foundations with shallow pad footings│
└─────────────────────────────────────────────────────────────┘
Standard engineering protocol mandates a site-specific geotechnical investigation before designing foundations for multi-story residential towers. Engineers drill core samples to classify soil strata and establish the allowable bearing capacity (q
a
), ensuring footings extend deep into stable weathered rock.
In court filings, state prosecutors revealed that the developers of Manzil Towers C circumvented this crucial step by fraudulently acquiring and presenting a forged geotechnical report alongside a falsified Environmental Impact Assessment (EIA) license.
By substituting deep-piled foundations with inadequate shallow pad footings on soft, expansive soil, the building’s foundation suffered from severe differential settlement. As the soil shifted under the immense weight of the rising floors, localized stress concentrations began cracking the ground-level support columns.
2. Concrete Compressive Strength Failure (f
ck
)
Reinforced concrete structures rely on two core materials working in tandem: concrete to absorb compressive forces and steel rebar to resist tensile forces.
For a multi-story residential building, Kenyan building codes (Code of Practice BS 8110 / Eurocode 2) require a minimum characteristic 28-day concrete compressive strength of f
ck
=25 N/mm
2
to 30 N/mm
2
(Class C25/30) for primary load-bearing columns.
1
Improper Water-Cement Ratio
Batching Phase
To reduce cement costs, contractors diluted the mix with excess water and fine river sand containing high silt content, raising the water-cement ratio (w/c) above 0.65.
2
Inadequate Curing Protocols
Construction Phase
Freshly poured ground-floor columns were not kept moist during the critical 14-day hydration period, losing up to 40% of their intended design strength.
3
Premature Formwork Removal
Curing Phase
Scaffolding and slab shuttering were stripped in as few as 4 days instead of 21 days, subjecting uncured ground columns to premature dead loads.
4
Critical Column Buckling
Failure Phase
Core samples tested after the collapse revealed actual concrete strength below 10 N/mm
2
—less than half the required safety margin—leading to explosive axial failure.
3. Rebar Omission and “Column Slenderness”
In addition to weak concrete, structural audits uncovered severe defects in steel reinforcement detailing:
Undersized Longitudinal Bars: High-yield steel rebar (Y20 and Y25) was substituted with thin, cheaper Y12 bars, drastically reducing column load capacity.
Inadequate Stirrup Spacing: Transverse ties (links) meant to prevent main rebar from buckling outward under heavy axial loads were spaced 300 mm apart instead of the required 150 mm.
High Column Slenderness Ratio: Ground-floor columns were built too narrow relative to their height, making them vulnerable to lateral buckling under axial loads:
Slenderness Ratio (λ)=
b
l
ef
Where l
ef
is the effective length of the column and b is the cross-sectional width. When λ exceeds allowable thresholds without increased steel reinforcement, columns fail suddenly without warning.
Comparison: Code Standard vs. Defective Site Reality
┌──────────────────────────┬──────────────────────────┬──────────────────────────┐
│ Metric │ BS 8110 Code Standard │ Manzil Towers Site Real │
├──────────────────────────┼──────────────────────────┼──────────────────────────┤
│ Concrete Strength f_ck │ 25 – 30 N/mm² │ < 10 N/mm² (Failed) │
│ Longitudinal Rebar │ Y20 / Y25 High-Yield │ Y12 / Y16 Substandard │
│ Stirrup Link Spacing │ 150 mm c/c │ 300 – 350 mm c/c │
│ Geotechnical Survey │ Deep Core Drilling │ Forged / Falsified │
│ EIA Environmental Status │ Approved NEMA License │ Unlicensed Construction │
└──────────────────────────┴──────────────────────────┴──────────────────────────┘
4. The “Add-a-Floor” Strategy: Structural Overloading
A common practice in Nairobi’s rapid urbanization is unauthorized vertical expansion.
The original approval for land reference LR No. 209/5909/10 was intended for a lower-density residential building. However, the developers pushed construction upwards, adding additional residential floors beyond the foundation’s design limits.
The total design axial load (P
u
) on a ground-floor column increases linearly with every additional floor added:
P
u
=1.4G
k
+1.6Q
k
Where G
k
is the total dead load (self-weight of concrete slabs, masonry walls, tiles) and Q
k
is the live load (occupants and furniture).
By adding unapproved upper floors using dense, solid concrete blocks rather than lightweight hollow blocks, the total dead load (G
k
) exceeded the ultimate bearing capacity of the ground columns by over 180%.
5. How Rogue Developers Bypass National Construction Authority (NCA) Checks
How did a multi-story building constructed with forged documents, weak concrete, and missing rebar proceed to near completion in South C?
In criminal charge sheets filed by the ODPP, prosecutors named public officials—including former National Construction Authority (NCA) Regional Coordinator Bowen Kwambai Kanda—accusing them of failing to verify documentation or enforce stop-work notices.
┌─────────────────────────────────────────────────────────────────┐
│ THE 4-STEP REGULATORY BYPASS PLAYBOOK │
├─────────────────────────────────────────────────────────────────┤
│ 1. Submission of Borrowed Engineering Seals │
│ • Using registered engineers’ stamps without their knowledge │
│ to gain initial plan approvals. │
│ │
│ 2. Fake On-Site Compliance Boards │
│ • Mounting project boards displaying fake NCA registration │
│ numbers to deter field inspectors. │
│ │
│ 3. Night & Weekend Concrete Pours │
│ • Casting structural slabs outside official business hours │
│ to evade mandatory council inspections. │
│ │
│ 4. Ignoring Statutory “Stop Work” Orders │
│ • Continuing work behind high iron sheets despite red │
│ compliance warning marks sprayed on perimeter walls. │
└─────────────────────────────────────────────────────────────────┘
Technical Summary: Preventing the Next Disaster
The collapse of Manzil Towers C demonstrates that structural failures are rarely caused by a single defect. They are the cumulative outcome of forged geotechnical reports, compromised materials, rebar omissions, and deliberate overloading.
To prevent recurring tragedies across Nairobi, industry regulators must enforce mandatory digital verification of structural stamps, conduct random core-drilling tests on active sites, and enforce strict criminal prosecution against developers who tamper with building safety standards.
DPP approves manslaughter charges over Manzil Towers collapse
This report provides important context on the legal actions taken by the ODPP following the structural investigation into the Manzil Towers collapse.
