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Exposed slurry wall of the World Trade Center at Ground Zero

A slurry wall is a civil engineering technique used to build reinforced concrete walls in areas of soft earth close to open water, or with a high groundwater table.[1] This technique is typically used to build diaphragm (water-blocking) walls surrounding tunnels and open cuts, and to lay foundations. Slurry walls are a "well-established" technology but the decision to use slurry walls for a certain project requires geophysical and other engineering studies to develop a plan appropriate for the needs of that specific location. Slurry walls may need to be used in conjunction with other methods to meet project objectives.[2]

Construction

[edit]
Sequence of constructing a slurry wall

While a trench is being excavated to create a form for a wall, it is simultaneously filled with slurry (usually a mixture of bentonite and water). The dense but liquid slurry prevents the trench from collapsing by providing outward pressure, which balances the inward hydraulic forces and also retards water flow into the trench. The density of the slurry mix must be carefully monitored and adjusted to produce the correct outward pressure to prevent the trench walls from collapsing.

Slurry walls are typically constructed by starting with a set of concrete guide walls, typically 1 metre (3 ft 3 in) deep and 0.5 metres (1 ft 8 in) thick. The guide walls are constructed near the ground surface to outline the desired slurry trench, and to guide the excavation machinery. Excavation is done using a special clamshell-shaped digger or a hydromill trench cutter, suspended from a crane. The excavator digs down to design depth (or bedrock) for the first wall segment. The excavator is then lifted and moved along the trench guide walls to continue the trench with successive cuts as needed. The trench is at all times kept filled with slurry to prevent its collapse, but the fluid filling allows the excavation machinery and excavation spoil to be moved without hindrance.

Once a particular depth of trench is reached, a reinforcing cage is lowered into the slurry-filled pit and the pit is filled with concrete from the bottom up using tremie pipes. The heavier concrete displaces the bentonite slurry, which is pumped out, filtered, and stored in tanks for use in the next wall segment, or it is recycled.

Slurry walls are successively extended to enclose an area, blocking water and softened earth from flowing into it. Once the concrete has hardened, excavation within the now concrete-wall-enclosed area can proceed. To prevent the concrete wall from collapsing into the newly excavated area, temporary supports such as tiebacks or internal crossbeams are installed. When completed, the structure built within the walled-off area usually supports the wall, so that tiebacks or other temporary bracing may be optionally removed.

History

[edit]

The slurry wall technique was first introduced in the 1950s during the excavations of the Red Line of the Milan Metro in Italy by the company ICOS (Impresa Costruzioni Opere Specializzate). This new technology became an important component of the top-down tunnelling method also known as Metodo Milano ("Milan method").[3]

Slurry wall construction was used in 1967–1968 to construct the "bathtub" that surrounded the foundations of most of the World Trade Center site in New York City.[4] In the 1980s, the Red Line Northwest Extension project in Boston was one of the first projects in the US to use the modern form of the technology, with hydromill trench cutters and the "Milan method". Slurry walls were also used extensively in Boston's 1990s Big Dig tunnel project.

Design

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The design of a slurry wall (diaphragm wall) includes the design of wall thickness and reinforcements. Thickness of a slurry wall in preliminary design is generally set to about 4-8% of the excavation depth. Slurry wall design is undertaken based on bending moment and shear envelope obtained from the stress analysis. In the design of such underground walls, width of the unit is considered as one meter, and the wall is analyzed under plane strain condition. Since the length-to-width ratio of excavations is generally large, plane strain conditions can be assumed.[5]

In a single-phase diaphragm wall, also known as a "cut-off wall", a binder (usually cement) is added to the supporting fluid so that the supporting fluid hardens without exchange.[6] One application for this type of construction is a landfill seal that is to be retrofitted later.

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See also

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References

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Slurry wall

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from Grokipedia
A slurry wall is an impermeable, structure constructed in a narrow, deep excavated in or soft ground, utilizing a clay-water to stabilize the excavation sides during and prevent collapse or inflow. The , which forms a on the trench walls, is displaced by tremie-placed mixed with , creating a durable barrier with low permeability, typically less than 10⁻⁷ cm/s. This technique, also known as a diaphragm wall, enables the of walls up to 100 feet deep and is essential for projects in challenging subsurface conditions near water tables or unstable soils. In , slurry walls serve dual purposes as both structural elements and environmental controls. Structurally, they act as retaining walls for deep basements, tunnels, and excavations, stabilizing lateral earth pressures and protecting adjacent structures from settlement, as demonstrated in landmark projects like the World Trade Center "bathtub" in 1967 and the Boston Tunnel's extensive slurry wall system. Environmentally, they function as cutoff barriers to contain groundwater contamination, prevent pollutant migration from landfills or hazardous sites, and divert non-aqueous phase liquids (NAPLs), often integrated with pumping systems and impermeable caps for long-term efficacy. Backfill variations, such as soil-bentonite or cement-bentonite mixtures, allow customization for permeability needs without concrete, extending their use in remediation efforts. The slurry wall method originated in the mid-20th century, with early applications in drilled shaft construction post-World War II and widespread adoption for pollution control by the 1980s, as outlined in U.S. Environmental Protection Agency guidelines. Construction requires precise equipment like hydraulic clamshell excavators or vibratory beams, site-specific geotechnical planning, and to ensure integrity, including keying into low-permeability layers by 2-3 feet. Advantages include adaptability to varied soil types, cost-effectiveness for linear barriers, and longevity when properly maintained, though challenges like management and potential panel joints necessitate rigorous monitoring.

Overview

Definition and Purpose

A slurry wall is a barrier constructed within a narrow, deep excavated in or soft ground, where a stabilizing —typically a mixture of clay and —is used to support the trench walls and prevent collapse during . This technique allows for the creation of impermeable or structural barriers in challenging subsurface conditions, such as high areas or unstable soils. The resulting wall serves as a permanent element once the is displaced by and or by impermeable backfill. The primary purposes of slurry walls include acting as impermeable barriers to control and contain contaminants, preventing migration into adjacent areas. They also function as retaining walls for deep excavations, providing lateral support to stabilize surrounding soil during of basements, tunnels, or in urban settings. Additionally, slurry walls can serve as structural , bearing vertical loads from overlying structures while resisting seismic and lateral forces. Basic components of a slurry wall consist of the excavated , the supporting that exerts hydrostatic equal to or greater than the surrounding , and a backfill that displaces the slurry to form the final hardened wall. In structural applications, reinforcement cages are placed within the trench for tensile strength. The , often composed of approximately 5% by mass in , plays a crucial role through its thixotropic properties, behaving as a when pumped or agitated but gelling into a semi-solid state when static to maintain trench stability. This dual behavior ensures safe excavation depths without caving, while the forms a low-permeability on the trench walls.

Types

Slurry walls are primarily classified by their functional roles into cutoff walls, structural walls, and hybrid walls. Cutoff walls are designed to impede and seepage, commonly applied in foundations and levees to enhance impermeability and prevent subsurface contaminant migration. Structural walls serve as load-bearing elements, providing lateral support and retention for deep excavations such as building basements and underground parking structures. Hybrid walls integrate both functions, offering seepage control alongside structural stability, often in projects requiring multifaceted subsurface barriers like combined management and foundation support. Variations based on materials further distinguish slurry wall compositions, tailored to specific permeability and strength needs. Soil-bentonite slurry walls, a traditional type for applications, use a mixture of excavated and to form a low-permeability, flexible barrier suitable for non-structural applications. -bentonite walls incorporate into the for enhanced and durability, making them ideal for semi-structural uses where moderate load-bearing is required. Soil-bentonite walls mix excavated site with , promoting cost efficiency by utilizing local materials while achieving low permeability for purposes. Slurry walls also vary by depth and geometry to suit project demands. Permanent deep walls can extend beyond 100 meters, supporting long-term like high-rise foundations in challenging geologies. In contrast, temporary shallow walls, typically under 30 meters, provide interim support during construction phases before permanent structures are installed. Geometrically, straight panels form continuous linear barriers for straightforward alignments, whereas keyed interlocking panels feature overlapping or dovetailed joints to ensure watertight seals and structural continuity in irregular terrains. In European contexts, the term "diaphragm walls" is often used synonymously with structural slurry walls, emphasizing their composition and role in deep foundation engineering.

History

Origins and Early Development

The slurry wall technique, also known as the diaphragm wall method, was developed in during the late 1940s by the engineering firm Impresa Costruzioni Opere Specializzate () as a means to facilitate deep excavations in unstable, water-bearing soils during urban infrastructure projects. This allowed for the of vertical barriers by excavating trenches filled with slurry to prevent soil collapse, marking a significant advancement for subway and foundation work in challenging ground conditions. The method's conceptual roots trace back to 19th-century caisson techniques employed in bridge foundation construction, where pressurized air or mechanical supports stabilized deep excavations below the , though the introduction of bentonite-based for chemical and hydrostatic stabilization represented a breakthrough. ICOS applied for patents on the slurry wall process toward the end of the , building on observations that bentonite suspensions could effectively maintain trench stability without traditional . The first full-scale implementation occurred in 1950 for deep foundation elements in , with widespread early adoption across in the for subway systems and post-war reconstruction efforts. Initial development faced significant challenges related to slurry stability, particularly in the trial-and-error refinement of mixtures to counteract infiltration and ensure consistent hydrostatic support during post-World War II rebuilding projects in . These efforts involved iterative testing to address variability in types and pressures, laying the groundwork for the technique's evolution into more standardized applications in subsequent decades.

Modern Advancements

Slurry wall technology was first adopted in the United States in the 1960s, with a landmark application in the construction of the World Trade Center's foundation "bathtub" in 1967, which utilized the method to create a watertight barrier in soft soils near the Hudson River. Further adoption in the 1970s marked expanded use, particularly with applications in the Washington Metro system, where guide walls were introduced to align excavations precisely and hydraulic clamshell excavators enhanced trench digging efficiency in urban settings. This integration allowed for deeper and more stable underground structures amid challenging groundwater conditions, facilitating the expansion of subway infrastructure without extensive dewatering. In the , advancements included the development of polymer additives for slurries, which improved stability by enhancing and reducing in permeable soils, thereby minimizing risks during excavation. By the , computerized real-time monitoring systems emerged, enabling precise control of pressure through data loggers and sensors to maintain hydrostatic balance against earth pressures, reducing construction uncertainties. The technology spread globally in the late , with widespread adoption in , such as for Tokyo's subway expansions in the , where diaphragm walls supported deep excavations in dense urban environments. Following 1990s U.S. Environmental Protection Agency regulations under the program, slurry walls gained prominence in , serving as low-permeability barriers to contain contaminants at hazardous sites. As of 2025, modern innovations include the integration of (BIM) for slurry wall design, allowing 3D simulations to optimize panel layouts and predict geotechnical interactions for greater precision. Drone-assisted inspections have also become routine for trench monitoring, providing high-resolution aerial data to detect instabilities or defects without human entry into hazardous areas. Additionally, sustainable slurries incorporating biodegradable polymers have been developed, offering environmental benefits by degrading naturally post-construction while maintaining stability during use. These advancements have collectively improved efficiency in excavation and . By 2020, slurry walls had seen extensive construction worldwide across numerous civil and environmental projects, underscoring their scalability.

Construction Process

Site Preparation and Planning

Site preparation for a slurry wall begins with comprehensive geotechnical assessments to evaluate subsurface conditions and ensure stability during . This involves conducting borings at regular intervals, typically every 15-50 meters along the proposed alignment, using methods such as hollow stem auger drilling to collect samples for laboratory analysis of composition, strength, and permeability. table levels are also determined through piezometer installations and pumping tests to assess hydrostatic pressures and potential inflow risks that could destabilize the excavation. These surveys inform the overall wall depth, which must key into an impermeable to prevent seepage beneath the barrier. Planning elements include the design and installation of guide walls, which are shallow concrete or timber trenches, typically 0.5-1 meter wide and 1-3 meters deep, positioned along the slurry wall alignment to provide precise panel positioning and support for excavating equipment. The panel layout is engineered as a series of interlocking segments, usually 2-6 meters in length and 0.6-1.5 meters in width, arranged to form a continuous barrier with overlaps of 0.3-0.5 meters to ensure hydraulic tightness. Equipment selection focuses on machinery suited to site-specific conditions, such as hydraulic grabs or clamshell excavators for trenching and high-shear mixers for preparation, with mobilization plans accounting for access and working platform stability. Regulatory compliance is addressed by obtaining necessary permits, including environmental approvals for disturbance and waste handling under frameworks like the Clean Water Act Section 404, to mitigate ecological impacts. Prior to excavation, the supporting is prepared and off-site to verify its properties. is typically mixed at 3-6% by weight in water to achieve a thixotropic suspension capable of stabilizing trench walls. is evaluated using the Marsh funnel test, targeting 30-50 seconds for outflow of one of slurry, ensuring adequate suspension without excessive density that could hinder concreting. These preparatory steps establish a robust foundation for the subsequent phases, minimizing risks of collapse or misalignment.

Excavation and Slurry Support

The excavation phase of slurry wall involves digging narrow, deep trenches to form the wall's panels, typically 0.6 to 1.5 meters wide and up to 100 meters deep, using specialized equipment to ensure precision and stability in various conditions. Common tools include the clamshell excavator, a grab-like device suspended from a crane that removes in bites, suitable for depths exceeding 80 feet in softer grounds, and the hydromill trench cutter, which employs rotating drums with cutting teeth for continuous excavation in denser or rocky , allowing faster progress while mixing with . Recent advancements as of 2025 include automated hydromill systems for enhanced verticality control and production monitoring. Trenches are excavated panel by panel, often in an alternating sequence to maintain stability between adjacent sections, with continuous circulation of introduced early to support the open excavation. The support mechanism relies on the hydrostatic exerted by a bentonite-water , which balances the lateral and forces to prevent collapse. The , typically at a of 1.02 to 1.10 g/cm³, creates a column that exerts proportional to its height and specific , exceeding the soil's active while a thin forms on the walls to seal against loss and enhance stability. Excavated soil particles are suspended and removed through systems, where the is pumped out, cleaned via desanders and desilters to separate sands and silts, and recirculated back into the , maintaining its supportive properties throughout the process. Initial placement often uses a tremie pipe to ensure uniform distribution without air pockets, particularly in deeper excavations. Real-time monitoring is essential to verify slurry integrity and trench stability, with checks conducted at least twice per shift on parameters such as level (maintained 1-3 feet above ), , (typically 8-10 to ensure activation), and content (kept below 4% to avoid excessive ). These tests, performed using tools like Marsh funnels for (35-50 seconds), hydrometers for , and ASTM-standard sieves for , allow immediate adjustments, such as adding or , to counteract variations from influx or environmental factors. Recent sensor-based systems as of 2025 enable automated real-time tracking of these parameters. This rigorous oversight ensures the trench remains open and stable until the subsequent backfilling stage.

Panel Installation and Concreting

Once the slurry-filled for a panel is fully excavated, cages are lowered into place to provide tensile strength to the wall. These cages, typically fabricated from with a yield strength of 400-500 MPa, are assembled off-site and installed using mobile cranes to ensure precise positioning within the . The is designed with adequate cover—usually at least 75 mm—to protect against and facilitate proper encasement, maintaining structural integrity under load. Concreting follows immediately after reinforcement placement to minimize the time the trench remains open, with high-slump concrete (200-250 mm) pumped through tremie pipes starting from the trench bottom. This method ensures the denser concrete displaces the lighter bentonite slurry upward in a controlled manner, preventing segregation and voids while forming a uniform panel. The displaced slurry is collected, cleaned to remove contaminants, and recycled for subsequent panels, promoting efficiency and environmental management. Tremie pipes, typically 250-300 mm in diameter, are embedded at least 5-10 m into the fresh concrete to maintain flow stability during placement. Adjacent panels are joined for structural continuity using keying or overlapping techniques, such as installing temporary stop-ends that create interlocking profiles or cutting into the previous panel's fresh with hydro-milling tools. Post-concreting, any residual on the or walls is cleaned to ensure bond quality. The mix is specifically designed for low permeability, with a water-cement below 0.45 to enhance and resistance to ingress. Panels cure for 7-28 days to reach the required compressive , typically 30-40 MPa, before adjacent excavations proceed.

Design Considerations

Materials and Properties

Slurry walls primarily utilize , a clay, as the key component in the supporting slurry during construction, prized for its ability to form a viscous, thixotropic fluid that stabilizes excavations. This clay's swelling properties in create a gel-like structure enabling it to exert hydrostatic against walls and prevent collapse. Bentonite slurries also exhibit low permeability, often on the order of 10^{-7} cm/s, which minimizes inflow and supports the formation of a low-permeability on excavation surfaces. To enhance slurry performance, additives such as polymers are incorporated to improve stability, reduce loss, and extend hydration time, particularly in challenging conditions or contaminated sites. These polymers increase the slurry's shear resistance and prevent premature of excavated materials, ensuring consistent trench support. For instance, such as have been standard since the late , and environmental concerns have driven innovations toward more sustainable alternatives, such as starch-based or cellulose-derived polymers, which degrade naturally without long-term impact. In structural slurry walls, the permanent barrier consists of high-strength with a typically between 30 and 50 MPa, reinforced by to provide tensile capacity and . Admixtures, including superplasticizers and accelerators, are added to the mix to optimize workability in the confined environment, allowing for proper placement and consolidation without segregation. reinforcement is protected against through coatings, which form a barrier to moisture and chlorides, extending the wall's in aggressive subsurface conditions. Key properties of these materials ensure the wall's functionality as both a structural and impermeable element. The slurry develops gel strength providing temporary shear resistance during excavation. Once concreted, the resulting wall achieves an impermeability coefficient (k) less than 10^{-8} m/s, effectively containing groundwater and contaminants while maintaining structural integrity under load.

Structural and Geotechnical Analysis

Geotechnical analysis of slurry walls primarily involves evaluating to ensure stability during and after construction. Finite element methods (FEM) are widely employed to model the complex interplay between the wall and surrounding , accounting for nonlinear behavior, excavation stages, and support conditions. These simulations predict deformations, stresses, and potential failure modes, such as basal heave or wall buckling, by incorporating parameters like modulus and . A typically ranging from 1.5 to 2.0 is applied to passive resistance and overall stability to address uncertainties in properties and loading. Structural design focuses on calculating internal forces in slurry walls, treated as cantilever or propped elements depending on embedment depth and bracing. For unpropped cantilever walls, the maximum bending moment at the point of rotation is approximated by M=KaγH36M = \frac{K_a \gamma H^3}{6}, where KaK_a is the active earth pressure coefficient, γ\gamma is the soil unit weight, and HH is the wall height, derived from earth pressure distribution assuming active conditions above the dredge line. Shear forces are determined from equilibrium, with design capacities verified using reinforced concrete principles, such as ϕVn=ϕ(Vc+Vs)\phi V_n = \phi (V_c + V_s), ensuring the wall resists lateral earth pressures without excessive deflection. Propped configurations reduce moments by up to 50% compared to cantilevers, but require iterative analysis for prop reactions. Permeability assessment verifies the wall's effectiveness in controlling seepage, particularly for applications. Darcy's law, q=kiAq = k i A, quantifies flow through the wall, where qq is discharge, kk is (typically ≤10−6\leq 10^{-6} cm/s for soil- mixes), ii is the hydraulic gradient, and AA is the cross-sectional area. This equation integrates and backfill contributions to ensure minimal leakage, with lab tests confirming low permeability under imposed gradients. Material properties, such as content, directly influence kk values input into these models. Seismic design incorporates wall flexibility to mitigate dynamic loads, following standards like ASCE 7 or Eurocode 8 in , which specify response spectra and factors for retaining structures. Simulations using software like PLAXIS model pseudostatic or dynamic responses, evaluating acceleration-induced pressures and wall cracking under events like the Northridge earthquake (magnitude 6.7). These analyses ensure the wall maintains integrity with minimal lateral deformation, often less than 1.5 cm in flexible configurations.

Applications

Civil Engineering Projects

Slurry walls play a critical role in urban construction, particularly for creating deep basements beneath high-rise buildings where control and soil stability are essential. In projects involving unstable sandy soils, such as those in , diaphragm walls—commonly referred to as slurry walls—provide lateral support during excavation and form permanent structural elements. For instance, during the construction of the in the 2000s, slurry walls were installed to stabilize the foundation and enable the deep excavation required for the world's tallest building. In transportation , slurry walls are widely employed to support subway systems and tunnels by acting as cutoffs and retaining structures during cut-and-cover or launch box excavations. A notable example is the Rail Link (CTRL) in the UK, completed in the 1990s and 2000s, where extensive diaphragm walls were constructed for the Stratford Box—a subsurface structure integral to the connection to the —ensuring stability in water-bearing ground. Similarly, in New York City's Second Avenue Phase 1, slurry walls facilitated the construction of a large TBM launch box, allowing deep excavations approximately 60 feet without compromising adjacent . For dams and waterways, slurry walls serve as effective seepage barriers to prevent underflow and foundation erosion in embankment structures. These walls are excavated under slurry and backfilled with low-permeability materials like cement- mixes to create continuous cutoffs keyed into . More recent examples include the rehabilitation of Center Hill Dam in , where a massive slurry wall, over 2 feet wide and extending deep into karstic , was installed starting in 2014 to mitigate seepage and enhance long-term stability. In densely populated cities like New York, slurry walls are indispensable for enabling deep excavations adjacent to existing structures while minimizing settlement risks to surrounding buildings and utilities. This technique's ability to provide both temporary support and permanent has made it a standard in urban environments with high water tables and sensitive adjacencies.

Environmental and Hazardous Site Uses

Slurry walls serve as critical containment structures in environmental and hazardous site management, forming impermeable barriers to halt the lateral migration of contaminants from landfills, chemical spills, and waste disposal areas into surrounding ecosystems. These walls are constructed using bentonite-cement or soil-bentonite mixtures that achieve hydraulic conductivities as low as 10^{-9} m/s or lower, effectively isolating polluted zones and protecting adjacent resources. By redirecting or blocking subsurface flows, they comply with regulatory frameworks such as the U.S. Environmental Protection Agency's (RCRA), which requires robust containment to prevent off-site releases of hazardous substances at regulated facilities. A prominent application occurred during the remediation of the hazardous waste site in , in the 1980s, where a slurry wall was installed to encase approximately 21,000 short tons of chemical wastes buried in the abandoned canal, thereby containing and averting further contamination of local aquifers and the . This intervention, part of a broader federal cleanup effort under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), highlighted slurry walls' efficacy in stabilizing legacy pollution sites and restoring habitability to affected communities. Similar containment strategies have been deployed at modern landfills to prevent migration, ensuring compliance with RCRA Subtitle C standards for liner systems and monitoring. Beyond passive containment, slurry walls can incorporate remediation functions through designs like permeable reactive barriers, where the wall matrix includes zero-valent iron (ZVI) to facilitate in-situ degradation of contaminants such as chlorinated volatile organic compounds and . As contaminated water percolates through the ZVI-amended barrier at controlled rates, oxidative reactions reduce the contaminants' toxicity—for instance, converting to non-hazardous byproducts—while maintaining structural integrity. This hybrid approach enhances site cleanup efficiency, particularly at RCRA-permitted facilities requiring active treatment to meet groundwater protection standards. In high-risk scenarios involving radiological hazards, slurry walls have been applied to nuclear sites for containment.

Advantages and Limitations

Key Benefits

Slurry walls exhibit significant versatility in applications, adapting to a wide range of types, including soft clays, sands, and gravels, and enabling installations to depths exceeding 50 meters, which facilitates effective control in challenging environments such as waterlogged or contaminated sites. This adaptability stems from the use of soil-bentonite mixtures that conform to site-specific geotechnical conditions without requiring extensive site preparation. A primary benefit of slurry walls is their high impermeability, achieving values as low as 1 × 10⁻⁷ cm/s, which serves as an effective long-term barrier against ingress, with documented performance exceeding 40 years without degradation and no anticipated finite lifespan under proper . Recent advancements, such as self-healing geopolymer materials, further enhance durability by mitigating crack formation. Slurry wall construction promotes speed and safety by supporting deep excavations without the need for , thereby reducing worker exposure to hazardous conditions and minimizing disruptions to surrounding through low-vibration installation methods. This approach has been employed successfully in urban projects, such as remediation and underground barriers, where it outperforms traditional methods in efficiency. In terms of economic and environmental advantages, slurry walls offer cost savings compared to alternatives like sheet piling, particularly in urban settings where minimal noise and reduce ancillary expenses, while the use of recyclable bentonite-based slurries lowers overall environmental impact through reduced material waste.

Challenges and Drawbacks

One significant challenge in slurry wall construction is the high initial cost, which can be up to 4 times greater than that of sheet piling systems due to the need for specialized equipment such as hydraulic clamshell excavators or hydromills, extensive slurry mixing facilities, and skilled labor for precise panel installation. For example, in some regions like , costs range from $341 to $420 per linear meter, often higher than alternatives like sheet piling ($231-263 per linear meter) or driven piles ($263-368 per linear meter), making slurry walls less economical for smaller or less complex projects. This expense is exacerbated by the requirement for thorough site preparation and testing to ensure structural integrity. Technical risks associated with slurry walls include slurry contamination, which can compromise the bond between concrete and the surrounding formation, leading to weakened structural performance and potential failure zones. Residual or inadequate displacement during concreting creates micro-annuli or cracks at the interface, reducing shear bond strength and increasing the risk of fluid migration or leakage over time. Additionally, constructing slurry walls in fractured rock presents difficulties, as unstable fractures can cause collapse, slurry loss into voids, or uneven backfill distribution, necessitating specialized soil-cement-bentonite mixes to seal gaps and maintain permeability below 1 × 10⁻⁶ cm/s. Environmental concerns arise from bentonite slurry disposal and its potential to alter groundwater flow if not properly managed during construction. Used bentonite, often contaminated with soil or hydrocarbons, must be treated as hazardous waste if it contains more than 10% free liquid or pollutants, with improper disposal risking soil and water contamination through leaching of heavy metals or clogging of drainage systems. Contaminated groundwater can also interact with the slurry, reducing its stabilizing properties and potentially allowing unintended pathways for pollutant migration if the wall's hydraulic conductivity exceeds design limits. Excavation for slurry walls generates that can induce adjacent ground settlement, with reported displacements up to 25 in sensitive urban areas, particularly when using traditional mechanical excavators near existing structures. These may cause cosmetic or structural to nearby buildings. Since the , low-vibration hydromills have been adopted to mitigate this issue by using high-pressure water jets for cutting, reducing peak velocities to below 12 μm/s and minimizing settlement risks in densely developed sites.

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