Piling Operations — HSSG Foundation Contracting

HSSG Foundation Contracting holds the piling works contract for The Mukaab, executing the installation of 1,200 construction piles that will anchor the world’s largest building to stable substrate beneath the al-Qirawan desert site. As of September 2025, 1,000 piles have been installed, representing 83 percent completion of the piling program. This progress places the foundation work among the most advanced elements of the Mukaab’s construction, alongside the 86 percent complete excavation. Together, these two below-grade programs represent the critical-path foundation activities that must be completed before any superstructure work can begin — and, critically, they continue uninterrupted despite the January 2026 construction suspension that has paused all other Mukaab construction activities.

The 1,200-pile foundation system represents one of the most demanding piling programs in global construction history. While individual projects have installed more piles (large bridge foundations or offshore platforms may require thousands of smaller piles), the combination of pile size, load capacity, depth, and the geological complexity of the desert site places the Mukaab’s piling program at the upper limit of foundation engineering achievement.

Why 1,200 Piles

The Mukaab’s foundation must support a structure of extraordinary weight and geometric uniqueness. The 400-meter cube contains 1 million tonnes of structural steel — a quantity that, if concentrated at a single point, would exert a force of approximately 10 billion newtons on the ground beneath. Of course, the load is distributed across the cube’s 160,000-square-meter footprint, but even distributed, the bearing pressure is far beyond what the al-Qirawan site’s upper soil layers can support without excessive settlement.

The 1,200 piles transfer these loads through the variable upper soil layers — windblown sand, cemented sarooj formations — down to stable limestone and sandstone bedrock of the Arabian Shield that underlies the Riyadh plateau. Each pile acts as a structural column extending from the raft foundation above to competent rock below, with the load transfer occurring through a combination of end-bearing (the pile tip resting on rock) and shaft friction (the surrounding soil gripping the pile along its length).

The number 1,200 is determined by dividing the total structural load by the individual capacity of each pile, with safety factors applied. If each pile can safely carry, for example, 8,000 to 10,000 tonnes (a reasonable estimate for large-diameter bored piles bearing on rock), then 1,200 piles provide a total system capacity in the range of 10 to 12 million tonnes — sufficient to support the 1 million tonnes of steel plus the concrete floors, facade cladding, mechanical equipment, furnishings, occupancy loads, and the dynamic forces generated by wind on the cube’s massive flat faces.

Piling Specifications and Methodology

The 1,200 piles must be engineered to carry the extraordinary loads generated by the 400-meter cube structure. Each pile is bored or driven through the variable upper soil layers into the stable bedrock. Bored piling — the method most likely employed for piles of this diameter and depth — involves drilling a shaft through the soil using a rotary drilling rig, lowering a prefabricated steel reinforcement cage into the bored shaft, and then filling the shaft with structural concrete that bonds to both the reinforcement cage and the surrounding rock.

Pile diameters for structures of this scale typically range from 1.2 to 2.5 meters, with larger diameters providing higher individual load capacity. Pile lengths vary across the site based on the depth to competent bedrock, which is not uniform — geological variations in the Arabian Shield’s surface profile mean that some piles must penetrate deeper than others to reach the required founding stratum. Length variations of 10 to 20 meters across a 400-meter site are common in Riyadh’s geological context.

Reinforcement specifications — the number, diameter, and arrangement of steel reinforcing bars within each pile — are determined by the structural engineers based on the load combination that each pile must resist. Piles beneath the cube’s corners carry the highest loads due to the convergence of forces from the structural frame’s three orthogonal directions. Edge piles must resist both vertical loads from the building’s weight and lateral forces generated by wind pressure on the cube’s massive flat faces — each face presenting 160,000 square meters (400 meters by 400 meters) of wind resistance.

Corner piles experience particularly complex load combinations. The cube geometry concentrates lateral wind forces at the corners, where two perpendicular faces meet, creating combined horizontal force vectors that the foundation must resist without allowing the structure to slide or overturn. The pile layout at the corners is likely denser — more piles per unit area — than in the center of the footprint, where loads are predominantly vertical.

Load Testing and Quality Assurance

Each pile must be verified to confirm that it achieves the design capacity specified by the structural engineers. The standard verification approach in piled foundation construction involves two types of load testing: preliminary (or sacrificial) pile tests and working pile tests.

Preliminary pile tests are conducted on dedicated test piles that are loaded to failure or to a predetermined multiple of the design working load — typically 2.0 to 2.5 times the working load. These tests, conducted early in the piling program, verify that the design assumptions about soil and rock capacity are correct. If the test pile fails at a load lower than expected, the pile design must be revised — longer piles, larger diameters, or more piles — before production piling continues.

Working pile tests are conducted on a percentage of the production piles — typically 1 to 5 percent — to verify that the piles installed during production achieve the same performance demonstrated by the preliminary tests. These tests apply loads up to 1.5 times the design working load and measure the pile’s settlement response. Any pile that exhibits excessive settlement or fails to achieve the required load is rejected and must be supplemented with additional piles.

For the Mukaab’s 1,200-pile program, a 2 percent testing rate means approximately 24 working pile tests — each requiring the installation of reaction piles, load application using hydraulic jacks, and settlement monitoring using precision survey instruments over periods of 24 to 72 hours. The load testing program is itself a significant engineering undertaking, requiring specialized equipment, experienced personnel, and careful scheduling to avoid interfering with production piling operations.

HSSG Foundation Contracting’s quality assurance documentation for each pile includes drilling logs recording the soil and rock conditions encountered during boring, reinforcement placement records confirming that the correct cage was installed at the correct depth, concrete placement records including volume poured and concrete strength test results, and pile integrity testing data (typically using cross-hole sonic logging or thermal integrity profiling) that verifies the structural soundness of the completed pile.

HSSG Foundation Contracting

HSSG Foundation Contracting operates as a specialist foundation contractor in the Saudi Arabian market. The award of the Mukaab piling contract represents one of the largest foundation contracts in the Kingdom’s construction history, commensurate with the project’s $50 billion scale. Specialist foundation contractors like HSSG focus exclusively on below-grade structural work — piling, diaphragm walls, ground anchors, and dewatering — developing deep expertise in the geotechnical conditions and construction practices specific to their operating region.

The Saudi Arabian foundation contracting market is demanding. The Kingdom’s geological diversity — from the soft sands of the Eastern Province to the volcanic basalt of the Harrat region to the limestone and sandstone of the Central Province — requires foundation contractors to be adaptable across a wide range of soil and rock conditions. HSSG’s experience in the Riyadh area provides familiarity with the specific geological conditions at the al-Qirawan site, including knowledge of the Arabian Shield’s rock quality, the depth variations of competent bedrock, and the behavior of the cemented sarooj formations that overlie the rock.

The piling program commenced in Q2 2024. Achieving 1,000 pile installations by September 2025 — approximately 15 months — translates to an average installation rate of roughly 67 piles per month, or approximately two to three piles per working day. For large-diameter bored piles requiring drilling through variable geology, reinforcement cage placement, and concrete pouring, this rate suggests that HSSG has deployed multiple drilling rigs operating simultaneously across the 400-meter-square site. A single bored piling rig typically completes one to two piles per day depending on depth and ground conditions, implying that HSSG operates three to four rigs concurrently.

Piling and the 2026 Suspension

The January 2026 construction suspension applies to work “beyond soil excavation and pilings,” explicitly exempting the foundation work from the pause. This exemption reflects the critical-path nature of foundation operations — piles must be installed and verified before any superstructure work can begin. By continuing piling operations during the suspension period, the project preserves the option to resume superstructure construction without the delay of restarting foundation work.

The exemption also reflects practical construction logic. Foundation work is sequential and path-dependent. Each pile location must be excavated, drilled, reinforced, and concreted in a specific sequence that cannot be interrupted and restarted without significant cost and quality penalties. Partially completed piles — shafts that have been drilled but not yet concreted — can collapse if left open, destroying the investment in drilling and requiring redrilling. Mobilized piling equipment that sits idle accumulates standby costs without productive output. The economic case for continuing piling operations through the suspension is compelling.

The remaining 200 piles represent approximately three to four months of work at the installation rate achieved during 2024-2025. Completion of the full 1,200-pile program would ready the site for the raft foundation — the massive concrete slab that will tie the pile heads together and distribute the Mukaab’s loads across the full pile grid. The raft foundation is itself an unprecedented structure — the world’s largest — requiring its own design finalization, formwork construction, reinforcement placement, and concrete pouring program before structural steel erection can commence.

Connection to the Raft Foundation

The 1,200 piles are not independent structural elements; they function as a unified system connected through the raft foundation. The raft — a reinforced concrete slab potentially several meters thick — transfers loads from the Mukaab’s steel mega-frame columns to the pile heads, distributing forces across the entire pile grid rather than concentrating them at individual pile locations.

The raft foundation design must account for the complex load distribution pattern of the cube geometry. Unlike a conventional tower, where loads concentrate at the building’s core and perimeter columns, the Mukaab’s cube form generates loads at the intersections of its three-dimensional structural grid. The raft must be thick enough and sufficiently reinforced to transfer these loads laterally to adjacent piles without cracking or excessive deflection.

The concrete volume required for the world’s largest raft foundation is substantial — potentially exceeding 100,000 cubic meters, depending on the raft’s thickness and extent. Pouring this quantity of concrete requires careful planning to manage heat of hydration (the exothermic chemical reaction that occurs as concrete cures), which can cause thermal cracking in thick concrete elements if not controlled through cooling systems, mix design optimization, and pour sequencing.

Geological Context — The Arabian Shield

The Arabian Shield — the ancient Precambrian geological platform underlying the Riyadh plateau — provides the stable bedrock into which the Mukaab’s piles are anchored. This geological formation, composed primarily of metamorphic and igneous rocks overlain by sedimentary limestone and sandstone, has been stable for hundreds of millions of years and provides the load-bearing capacity required to support the world’s largest building.

The depth to competent rock varies across the al-Qirawan site, influenced by the geological history of erosion, deposition, and cementation that has shaped the Arabian Peninsula’s surface over geological time. Site investigation data — obtained through boreholes, geophysical surveys, and laboratory testing of soil and rock samples — informed the pile design, establishing the founding depth for each pile based on the rock quality at its specific location.

For independent reference on desert foundation engineering practices, see publications from the International Society for Soil Mechanics and Geotechnical Engineering.

Piling Operations — HSSG Foundation Contracting