Foundation Engineering in Desert Conditions

Foundation Engineering in Desert Conditions

The Mukaab’s foundation system must support the weight of the world’s largest building on desert terrain in the al-Qirawan district of northwest Riyadh. The foundation design encompasses 1,200 construction piles, an excavation of 40 million cubic meters, and a raft foundation described as the world’s largest. These elements must work together to transfer the loads from 1 million tonnes of structural steel and 2 million square meters of floor area safely into the desert substrate while maintaining dimensional stability over the building’s design life.

Geotechnical Conditions

The al-Qirawan district sits on the Arabian Shield, a stable craton of Precambrian crystalline rock overlain by varying depths of sedimentary deposits and desert soils. The geotechnical conditions at the Mukaab site include surface layers of windblown sand and silt, intermediate layers of cemented sand and gravel (locally called “sarooj”), and deeper limestone and sandstone formations.

Desert soils in the Riyadh region present specific challenges for foundation engineering. Collapsible soils — formations that maintain apparent strength when dry but lose bearing capacity dramatically when wetted — can occur in arid environments where soil structures have developed without the consolidating effect of regular rainfall. While Riyadh receives minimal rainfall, the introduction of water through construction activities, utility leaks, or landscape irrigation can trigger settlement in susceptible soil layers.

Piling System

The 1,200 construction piles being installed by HSSG Foundation Contracting anchor through the variable upper soil layers into stable rock formations below. As of September 2025, 1,000 of these piles have been installed, representing 83 percent completion of the piling program.

The piles for the Mukaab must handle extraordinary loads. Unlike a conventional tower where pile loads are concentrated under a relatively compact core, the cube form distributes loads across a 400-by-400-meter footprint. Corner piles carry the highest loads due to the convergence of structural forces from the mega-frame system. Edge piles must resist both vertical loads and lateral forces from wind loading on the cube’s faces.

Excavation Program

The excavation of 40 million cubic meters of earth represents one of the largest earthmoving operations in construction history. To contextualize this volume, it exceeds the total excavation for the Panama Canal expansion project. As of the latest reports, 86 percent of the excavation has been completed, with over 10 million cubic meters of earth moved.

All excavated material is being repurposed rather than sent to landfill, aligning with the project’s sustainability commitments. Uses for the excavated material include fill for other construction sites within the New Murabba development, raw material for concrete aggregate, and landscape grading for the development’s 25 percent green space allocation.

The construction of a temporary bridge crossing King Khalid Road connects the excavation site to material handling areas, reducing an estimated 800,000 truck movements on public roads. This infrastructure demonstrates the logistical scale of the foundation operations.

The World’s Largest Raft Foundation

The raft foundation — a continuous concrete slab distributing loads across the full building footprint — will be the largest ever constructed. For a 400-by-400-meter footprint, the raft covers 160,000 square meters. The concrete volume required for a raft of this size, at appropriate thickness for the Mukaab’s loads, represents a significant fraction of Riyadh’s annual concrete production capacity.

Raft Foundation Design Challenges

The raft’s design must accommodate the non-uniform load distribution created by the cube geometry. Unlike a conventional tower where the heaviest loads concentrate under a central core, the Mukaab’s mega-frame structural system delivers peak loads at the cube’s corners and edges, where columns from three orthogonal faces converge. Corner column reactions — the forces transmitted from the superstructure to the foundation at each of the cube’s four base corners — exceed those at interior columns by factors of 3-5, creating stress concentrations in the raft that require localized thickening or reinforcement intensification.

The concrete specification for a raft foundation of this scale must address both structural performance and constructability in Riyadh’s extreme climate. Summer temperatures exceeding 50 degrees Celsius accelerate cement hydration, reducing working time for fresh concrete and increasing the risk of thermal cracking as the heat of hydration combines with ambient heat to create temperature differentials exceeding 70 degrees Celsius between the raft’s core and surface. Mass concrete techniques — including chilled mixing water, ice replacement for a portion of the mix water, fly ash or slag cement substitution to reduce heat generation, and embedded cooling pipes circulating chilled water through the fresh concrete — are essential for pours of this thickness.

The concrete volume required for the raft represents a sustained demand on Riyadh’s ready-mix concrete supply chain. With batching plants typically producing 100-200 cubic meters per hour, continuous pours for raft sections may require coordinated supply from 10-15 plants operating simultaneously, with GPS-tracked mixer trucks managing delivery schedules that prevent both supply gaps (which create cold joints that weaken the raft) and excessive queuing (which causes concrete to exceed its working time before placement).

Load Transfer Mechanisms

The interaction between the raft foundation and the 1,200 piles creates a piled-raft foundation system — a composite structure where both the raft’s bearing on the soil and the piles’ transfer to deep strata contribute to supporting the 1 million tonnes of structural steel above. The relative contribution of raft bearing versus pile support depends on the soil stiffness, pile spacing, and load magnitude, with pile support typically dominating under the heaviest column loads and raft bearing contributing more significantly in lightly loaded interior zones.

The piled-raft interaction requires three-dimensional finite element analysis that models the raft as a flexible plate, the piles as discrete structural elements, and the soil as a continuum with depth-varying stiffness properties. The AtkinsRealis geotechnical team has developed models containing thousands of elements to capture the stress distribution across the 160,000-square-meter footprint, validated against pile load test data from the site investigation program.

Settlement Monitoring and Long-Term Performance

A structure weighing over 1 million tonnes of steel alone — with additional mass from concrete floors, facade cladding, building contents, and the water stored for the fire suppression systems — will induce measurable settlement in even the most competent foundation materials. For the Mukaab, differential settlement between adjacent pile groups must be controlled to within millimeters per meter of span to prevent cracking of rigid architectural finishes, misalignment of elevator guide rails, and distortion of the facade cladding system.

The settlement monitoring system employs precision survey points embedded in the raft foundation and structural columns, measured by automated total stations and satellite-based positioning systems that detect movements of less than 1 millimeter. The monitoring program begins before construction loading commences — establishing baseline readings — and continues throughout the building’s operational life, creating a multi-decade record of foundation performance that validates the geotechnical models and provides early warning of any anomalous movement.

The Riyadh climate’s thermal cycling between near-freezing winter nights and 50-degree-Celsius summer afternoons creates additional foundation performance considerations. Thermal expansion of the raft concrete itself — a slab covering 160,000 square meters — generates edge movements that must be accommodated by slip layers between the raft and the underlying prepared subgrade. The interaction between thermal raft movement and pile-head fixity creates bending moments in the uppermost portion of each pile that add to the structural demands from superstructure loading.

Desert-Specific Foundation Risks

The Riyadh region’s geological profile introduces foundation risks specific to arid environments. Sabkha deposits — salt-rich soil formations common in the Arabian Peninsula — can cause heave and chemical attack on concrete when salt crystallization pressures develop during wetting-drying cycles. While the al-Qirawan site is elevated relative to the sabkha-prone coastal lowlands, the presence of sulfate-bearing soils in the sedimentary layers requires sulfate-resistant cement (Type V or equivalent) in all below-grade concrete to prevent the expansive chemical reactions that can disintegrate conventional Portland cement concrete over decades.

Groundwater management adds another dimension to the foundation engineering. Although Riyadh’s water table is generally deep — typically 30-50 meters below surface in the central plateau — the excavation of 40 million cubic meters to depths approaching or exceeding the water table may encounter perched water tables or seasonal groundwater fluctuations that require dewatering during construction. The dewatering system must lower groundwater levels sufficiently to permit dry working conditions for pile installation, raft reinforcement placement, and concrete pouring, while monitoring adjacent structures and infrastructure for settlement caused by groundwater drawdown. The temporary bridge crossing King Khalid Road, which eliminates 800,000 truck movements on public roads, demonstrates the logistical sophistication applied to every aspect of the foundation program — a level of planning essential when the margin for error in a $50 billion project approaches zero.

Pile Load Testing and Quality Assurance

The quality assurance program for the Mukaab’s 1,200 piles employs multiple testing methods to verify that installed piles meet design capacity requirements. Static load tests — where a test pile is loaded to 150-200 percent of its design capacity using hydraulic jacks reacting against kentledge (dead weight) or adjacent anchor piles — confirm the load-settlement relationship assumed in the piled-raft analysis. Given the scale of the piling program, HSSG Foundation Contracting performs static load tests on a statistically representative sample of piles distributed across the 160,000-square-meter footprint to capture any spatial variation in ground conditions.

Dynamic load testing using Pile Driving Analyzer (PDA) equipment provides rapid verification of pile capacity during installation. High-strain dynamic testing measures the pile’s response to a hammer impact, and signal matching analysis (CAPWAP) derives the pile’s static capacity from the dynamic measurements. This method enables testing of a much larger percentage of piles than static load testing alone, providing comprehensive quality assurance across the full 1,200-pile array.

Integrity testing using cross-hole sonic logging (CSL) or thermal integrity profiling (TIP) verifies that each pile’s concrete shaft is free from defects — necking, soil inclusions, or voids — that could reduce the pile’s structural capacity below design requirements. For a building carrying 1 million tonnes of structural steel, a single defective pile that fails under load could trigger differential settlement affecting the mega-frame structural system above, making pile integrity verification a critical quality gate in the $50 billion construction program.

Waterproofing and Below-Grade Protection

The below-grade structure — extending multiple levels beneath ground level within the 40-million-cubic-meter excavation — requires waterproofing systems that protect against both groundwater ingress and the occasional flash flooding that Riyadh’s rare but intense rainfall events can produce. Tanked waterproofing systems using multi-layer membrane applications (typically bentonite clay sheets, high-density polyethylene membranes, and crystalline admixtures in the concrete itself) create redundant barriers against water penetration. The AtkinsRealis specification requires waterproofing performance guaranteed for the building’s 100-year design life — a durability standard that demands material selection, installation quality, and protection details exceeding standard commercial basement construction. The below-grade spaces housing climate control mechanical plants, fire pump stations, electrical switchgear, and data centers cannot tolerate water ingress that might disable the systems serving 2 million square meters of occupied space above.

Thermal Effects on Foundation Performance

Riyadh’s extreme temperature range — from near-freezing winter nights to summer afternoon peaks exceeding 50 degrees Celsius — affects foundation performance in ways unique to desert mega-structures. The raft foundation’s upper surface, exposed to ambient temperature through the building’s ground floor during construction and partially insulated during operation, undergoes thermal cycling that induces curling stresses at the raft’s edges. These curling stresses — caused by the temperature differential between the raft’s sun-heated upper surface and its cooler underside resting on thermally stable subgrade — can create edge lift or center lift conditions that modify the contact pressure distribution between raft and soil, altering the load-sharing ratio between raft bearing and pile support.

The 1,200 piles themselves experience thermal effects at their heads where they connect to the raft. Column base reactions fluctuate as the superstructure’s 1 million tonnes of steel expand and contract with daily and seasonal temperature cycles, creating variable loads on individual piles that must remain within design capacity under all thermal loading combinations. The AtkinsRealis foundation design envelope incorporates these thermally-induced pile load variations across the full annual temperature range, ensuring that the piled-raft system maintains the dimensional stability required by the mega-frame structural system above — stability measured in millimeters across a foundation spanning 160,000 square meters in one of the world’s most demanding desert construction environments.

For related analysis, see piling operations, structural design, and construction timeline.