Earthworks Material Repurposing

The Mukaab’s 40-million-cubic-meter excavation generates an enormous volume of earth that, in a conventional project, would be trucked to landfill at significant cost and environmental impact. Instead, the New Murabba Development Company has committed to repurposing all excavated material, creating a circular material flow that eliminates landfill disposal while reducing demand for virgin construction materials across the 19-square-kilometer development. This zero-landfill commitment transforms what is typically a cost center — excavation disposal — into a material asset that directly serves the project’s broader construction requirements.

To appreciate the scale of this repurposing effort, consider that 40 million cubic meters of material, if loaded into standard dump trucks carrying 20 cubic meters each, would require 2 million truckloads. Laid end to end, those trucks would stretch from Riyadh to London and back. The decision to repurpose this material on-site rather than transport it to external disposal facilities eliminates not only the environmental impact of disposal but also the logistical burden of millions of heavy vehicle movements through Riyadh’s road network — a burden partially addressed by the temporary bridge crossing King Khalid Road that has already eliminated 800,000 truck movements from public roads.

Geological Composition of Excavated Materials

The al-Qirawan site’s geological profile produces multiple material types, each with distinct physical properties and repurposing applications. Understanding this composition is essential because different materials serve different construction purposes, and the repurposing strategy must match material characteristics to end-use requirements.

The uppermost layers consist of windblown Aeolian sand — fine-grained, unconsolidated material deposited by prevailing winds over millennia. This sand is characteristic of the Arabian Peninsula’s desert environment and can vary in depth from several meters to more than ten meters depending on local topography and wind patterns. Aeolian sand has relatively low bearing capacity in its natural state but serves effectively as fill material when properly compacted and moisture-conditioned.

Below the sand lies cemented desert formations known locally as sarooj — a natural conglomerate of sand, gravel, and calcium carbonate that has bonite over geological time through mineral precipitation. Sarooj formations vary widely in strength and composition, ranging from weakly cemented material that can be excavated with conventional equipment to heavily indurated formations requiring hydraulic breakers or controlled blasting. This material’s natural cement content makes it valuable for certain fill applications and, when crushed, as aggregate for concrete production.

The deepest excavation layers encounter limestone and sandstone bedrock of the Arabian Shield — the ancient geological platform underlying the Riyadh plateau. These rock formations provide the stable substrate into which the Mukaab’s 1,200 foundation piles are anchored. Excavated rock from these deeper layers is the most valuable repurposing material, as crushed limestone and sandstone produce high-quality concrete aggregate that meets structural specifications.

Repurposing Channels

The excavated material is directed into multiple repurposing channels based on its geological classification, physical properties, and the construction requirements of the broader New Murabba development.

Site grading and fill. Sandy materials serve as fill for site grading across the New Murabba masterplan. The 18 planned neighborhoods require level building platforms, road subgrades, and landscape contours that consume large volumes of fill material. Using on-site excavation output for this purpose eliminates the need to quarry and transport fill from external sources. The 19-square-kilometer development area requires tens of millions of cubic meters of fill to establish the finished grades specified in AtkinsRealis’s masterplan design — a volume that aligns with the excavation output, creating a rough balance between material generation and consumption within the project boundary.

Site grading with excavated material requires careful geotechnical control. Fill placement must follow engineered specifications for layer thickness, compaction effort, and moisture content to achieve the bearing capacity required for building foundations and road subgrades. Quality control testing — typically including field density tests, moisture content measurements, and compaction verification — must be performed at specified intervals throughout the fill placement process to ensure that repurposed material meets the same engineering standards as virgin fill from commercial quarries.

Concrete aggregate production. Rock materials can be crushed for use as concrete aggregate. Given the Mukaab’s enormous concrete demand — the world’s largest raft foundation alone requires tens of thousands of cubic meters of concrete — on-site aggregate production reduces both cost and the environmental impact of aggregate trucking. Crushed limestone from the deeper excavation layers meets the gradation and strength requirements for structural concrete aggregate when processed through standard crushing and screening equipment.

The concrete demand across the full New Murabba development is staggering. With 104,000 residential units, 9,000 hotel rooms, 1.4 million square meters of office space, 980,000 square meters of retail, and extensive infrastructure including roads, bridges, and underground systems, the total concrete volume will reach millions of cubic meters over the project’s 17-year construction timeline. On-site aggregate production from excavation spoil reduces the project’s demand on regional quarries and the associated trucking distances from quarry to batching plant.

Landscape fill and topsoil. Landscape-grade materials contribute to the 25 percent green space allocation that defines New Murabba’s commitment to urban greenery and biodiversity. The development’s parks, walking paths, cycling routes, and planted areas require topsoil substrate, drainage layers, and contour fill to create the landscape forms specified in the masterplan. While natural desert soils typically require amendment with organic matter and nutrients to support plant growth, the base fill and drainage layers beneath landscaped areas can use unmodified excavated material.

The green space program encompasses significant landscape infrastructure. Riyadh’s climate — with summer temperatures exceeding 45 degrees Celsius and annual rainfall below 100 millimeters — demands irrigated landscapes with species selected for heat and drought tolerance. The excavated material provides the physical foundation for these landscapes, with drainage layers of coarse-graded crushed rock overlaid by amended topsoil layers supporting plant root zones. The integration of landscapes with local ecosystems and wadis, as specified in the masterplan, requires careful grading to direct stormwater flows and create microclimates that support biodiversity.

Road and infrastructure subgrade. The development’s road network — serving 400,000 eventual residents and connecting to Riyadh’s arterial system via King Khalid Road and King Salman Road — requires substantial quantities of subgrade material beneath pavement surfaces. Properly graded and compacted excavation material serves this purpose, providing the load-bearing platform upon which road pavement structures are constructed. The requirement for different subgrade specifications across varying road classifications (arterial, collector, local, pedestrian) means that the material grading and compaction requirements vary across the road network.

Environmental and Sustainability Impact

The zero-landfill commitment reduces the project’s environmental footprint across multiple dimensions. Eliminating landfill trucking avoids the 800,000 truck movements that disposal would require for the earthworks phase alone. This reduces diesel consumption, exhaust emissions, road wear, noise, and traffic congestion in the surrounding Riyadh neighborhoods — an impact that extends beyond the project boundary to benefit the broader urban environment.

The ESG (Environmental, Social, and Governance) dimensions of the earthworks repurposing program align with NMDC’s broader sustainability commitments. A memorandum of understanding signed between NMDC CEO Michael Dyke and Princess Nouf bint Muhammad bin Abdullah Al Saud focuses on developing innovative solutions for ESG strategies and sustainability. The earthworks repurposing program provides concrete evidence of these commitments in action — not as aspirational targets but as operational practices integrated into daily construction activities.

Reduced demand for virgin construction materials has cascading environmental benefits. Every tonne of aggregate produced from on-site rock is a tonne that does not need to be quarried from a separate location, eliminating the land disturbance, dust, noise, and habitat destruction associated with commercial quarrying. Every cubic meter of fill sourced from the excavation is a cubic meter that does not require opening a new borrow pit in the desert. Over the life of a 40-million-cubic-meter excavation, these avoided impacts are substantial.

Carbon Footprint Reduction

The transportation component of the earthworks repurposing strategy delivers measurable carbon dioxide emission reductions. A single loaded dump truck trip of 20 kilometers (a conservative estimate for the distance to a commercial landfill in Riyadh’s outskirts) produces approximately 15-20 kilograms of CO2 equivalent in diesel emissions. Multiplied by 2 million potential truckloads, the avoided emissions from eliminating landfill transportation reach 30,000 to 40,000 tonnes of CO2 equivalent — a meaningful contribution to the project’s overall carbon footprint reduction.

This calculation does not include the avoided emissions from reduced quarrying operations, reduced virgin aggregate transportation, or the energy savings from not operating commercial landfill facilities. When these secondary emission reductions are included, the total avoided carbon footprint of the earthworks repurposing strategy is significantly larger.

The repurposing approach also contributes to New Murabba’s alignment with Saudi Vision 2030 sustainability objectives. The Kingdom has committed to reducing carbon emissions and promoting sustainable development practices as part of its long-term economic diversification strategy. Projects that demonstrate practical, quantifiable sustainability measures — rather than aspirational statements — provide evidence that Vision 2030’s environmental commitments are being implemented at the project level.

Material Processing Operations

The repurposing strategy requires on-site material processing infrastructure of considerable scale. Crushing plants capable of reducing excavated rock to concrete-grade aggregate operate continuously during active excavation phases, processing hundreds of tonnes per hour to keep pace with the earthmoving equipment feeding them. These plants — typically comprising jaw crushers for primary reduction, cone crushers for secondary sizing, and vibrating screens for gradation separation — occupy dedicated processing zones within the site boundary, connected to the excavation face by internal haul roads and to stockpile areas by conveyor systems or additional truck routes.

Screening operations separate excavated materials by particle size, directing fines (sand-sized particles) to fill stockpiles, medium-grade material to road subgrade stockpiles, and coarse rock to the crushing plant feed. This sorting process occurs at multiple points: at the excavation face where operators visually classify material during loading, at intermediate processing areas where mechanical screens separate size fractions, and at stockpile locations where quality control testing verifies that material meets the specification for its intended use. The logistical complexity of managing multiple material streams across a 400-meter-square excavation site, with each stream destined for a different end use within the 19-square-kilometer development, demands dedicated materials management staff and real-time tracking systems.

The concrete batching plants that will serve the broader New Murabba construction program can be located within the development boundary, adjacent to aggregate stockpiles produced from excavated rock. This co-location eliminates the truck transport between quarry and batching plant that constitutes a major cost and emission source in conventional concrete supply chains. With concrete demand across 104,000 residential units, commercial buildings, and infrastructure running to millions of cubic meters over the 17-year construction program, the cumulative savings from on-site aggregate production are substantial.

Quality Control and Engineering Verification

The repurposing of excavated material for structural applications — concrete aggregate, road subgrade, building platform fill — requires rigorous quality control that would not be necessary if the material were simply disposed of in landfill. Each repurposing channel imposes specific engineering requirements that the material must satisfy.

Concrete aggregate must meet gradation specifications (the distribution of particle sizes), strength requirements (measured by crushing value tests), durability standards (resistance to weathering, chemical attack, and alkali-silica reaction), and cleanliness standards (limits on clay, silt, and organic content). These requirements are defined in Saudi building codes and international concrete standards, and every batch of aggregate produced from excavated rock must be tested to confirm compliance before it is used in structural concrete. A single batch of substandard aggregate incorporated into the world’s largest raft foundation could compromise the structural integrity of the entire foundation system.

Fill material for building platforms and road subgrades must achieve specified compaction densities, measured by field density tests conducted at regular intervals during placement. The relationship between moisture content and achievable density varies by material type, requiring laboratory testing (Proctor compaction tests) to establish the optimum moisture content for each material source. In Riyadh’s arid climate, achieving optimum moisture often requires water addition during compaction — a resource cost that must be balanced against the material’s engineering performance.

For independent context on sustainable construction practices in the Gulf region, see reporting from Construction Review Online and Fast Company Middle East.

Earthworks Material Repurposing