Select a diaphragm wall grab with a jaw width corresponding to the specified wall thickness, because panel thickness is governed by the excavating grab width [S5].
Typical diaphragm wall thicknesses range from 600 mm to 1500 mm [S2].
Width Matching Controls Panel Thickness
The grab forms the trench profile, so its jaw width dictates the diaphragm wall panel thickness [S5]. Soiltec likewise describes the excavating system as a clamshell bucket with the same thickness as the wall being built [S8]. The width is therefore an equipment parameter, not a dimension to be determined independently after procurement.
Stein gives a typical range of 600–1500 mm and states that thicknesses up to 2000 mm are feasible [S2]. These ranges cover the usual market offerings, but the project-specific structural design remains the controlling document.
Mechanical slurry wall grabs are opened and closed by rope, while hydraulic grabs are opened and closed by hydraulic cylinders [S3]. Jaw width governs the trench and panel thickness; opening describes the bucket movement available during excavation, not the wall thickness.
Compare the Three Relevant Dimensions
Three dimensions govern equipment interpretation: jaw width determines panel thickness, jaw opening determines bucket travel, and panel length determines excavation passes [S3][S5].
For a 1000 mm wall, specify the 1.00 m grab-width arrangement. Stein’s guide-wall schedule illustrates the same disciplined approach with wall widths of 0.60, 0.80, 1.00, 1.20, and 1.50 m, paired with guide-wall widths of 0.635, 0.835, 1.035, 1.235, and 1.535 m [S2].
Use the Nominal Thickness and Clearances
A jaw width of 1.00 m normally corresponds to a nominal 1000 mm wall, not an unlimited tolerance. The specified thickness should be reconciled with excavation deviation, guide-wall setting-out, panel joint geometry, and the concrete section accepted by the designer [S2][S5].
The guide wall must be slightly wider than the excavation in the Stein arrangement: each listed guide-wall width is 35 mm greater than its associated wall width [S2]. This 35 mm difference is a documented dimensional arrangement, but it should not be copied as a universal clearance without checking the selected grab and guide-wall design.
The published range of 600–1100 mm for diaphragm wall thickness demonstrates that even nominal thicknesses vary by project [S4]. For procurement, record the wall thickness in millimetres, the corresponding jaw width in metres, and the applicable construction tolerance separately. Do not select a grab solely by its maximum capability.
Panel Length and Multiple Bites
A long panel does not require a proportionally wider jaw. Panel length is generally much greater than the grab jaw size, so one panel is excavated through multiple bites [S5].
Panel dimensions also depend on ground conditions, excavation depth, panel position, and excavation equipment type [S4]. A minimum panel length is generally about 3.0 m, linked to the dimensions of the grab equipment [S6]. Consequently, jaw width and panel length should be specified as separate constraints.
A diaphragm wall grab is appropriate when reinforced-concrete wall panels must be excavated through stable or slurry support without a conventional trench excavation cycle. It is not a substitute for designing panel joints, reinforcement cages, stop ends, and the concrete placement method around the actual ground and groundwater conditions.
Equipment and Workflow Consequences
Jaw width affects more than excavation volume. A wider grab requires a larger opening in the guide wall, compatible suspension and handling arrangements, and suitable reinforcement and joint details. Stein specifies one to two grabs with widths corresponding to the panel arrangement, plus a diaphragm-wall chisel, plough, stop-end elements, tremie pipes, and supporting-suspension equipment [S2].
Hydraulic grabs can use flexible guiding strips on the grab frame to align the tool in the trench, while mechanical grabs use rope actuation and can increase closing force through multiple reeving [S3]. The sequence for each reinforced-concrete panel is excavation with support suspension, installation of stop-end pipes, insertion of reinforcement, and tremie concreting while support fluid is pumped out [S3].
For deeper excavation, the trench is protected by bentonite or another support fluid, and guide walls provide alignment and help prevent trench collapse [S4]. A correctly sized jaw does not remove the need to verify crane capacity, closing force, slurry performance, panel stability, and concrete volume.
Decision Rules by Project Type
For a 600–800 mm wall, use a grab in the corresponding 0.6–0.8 m width class rather than a machine merely capable of that thickness [S2][S3]. For a 1000–1200 mm wall, select the matching 1.0–1.2 m jaw class. For a 1500 mm wall, the 1.5 m width reaches the top of the common jaw range and requires close verification of crane, guide-wall, reinforcement, and joint arrangements [S2][S3].
For walls above 1500 mm, Stein states that thicknesses up to 2000 mm are feasible [S2]. Such a selection is a special-engineering case, not a standard catalogue substitution. Confirm the exact jaw configuration, panel geometry, handling system, and construction method before accepting the equipment offer.
For restricted sites, narrow panels of 2.5 m can be used where soils have low stability, high overhead constraints, or deep excavation conditions [S4]. Where stability permits, a longer panel may improve continuity and reduce the number of joints, but panel width must still remain compatible with the grab and excavation sequence.
Procurement Check Before Ordering
Issue the grab width against the approved wall thickness, not against a generic maximum. A compliant purchase description should state the nominal panel thickness in millimetres, the required jaw width in metres, and the permitted deviation. It should also identify the expected panel length and number of bites [S2][S5].
Request confirmation that the guide wall accommodates the selected jaw and panel arrangement, and verify that the slurry-wall grab has exchangeable jaws where the frame permits different trench widths [S3]. For alternative equipment approaches, the same basic discipline applies to a shield machine or rotary drilling rig: excavation width must match the intended structural element.
The trackable procurement signals are the approved wall-thickness schedule, the quoted jaw width in metres, and the maker’s dimensional drawing linking the grab, guide wall, stop ends, and panel arrangement [S2][S3][S8]. If any two of those documents show different thickness assumptions, hold the selection until the discrepancy is resolved.