Slurry wall and barrette excavation · Hydraulic and kelly-guided grabs, wall width and depth, closing force, grab weight, winch capacity, slurry support and when a cutter is needed
A diaphragm wall grab is a heavy clamshell bucket, hung from a crawler base machine on ropes or a kelly bar, that bites out rectangular trench panels for reinforced concrete diaphragm walls and barrette foundations, with the trench held open by supporting slurry. Ask three things first: what wall width and depth the grab must reach and how it is guided to stay vertical, what closing force and grab weight your ground needs, and when a cutter (hydromill) is needed instead for rock.
Rope-suspended hydraulic grabs and kelly-guided grabs for diaphragm walls and barrettes, with their crawler base machines. Bulk-material clamshell and orange-peel grabs for cranes, trench cutters (hydromills), excavator clamshell attachments and slurry plants are outside this page except where compared.
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01
SANY's SH500 hydraulic grab lists groove (wall) widths of 600–1,200 mm, a depth of 80 m, a maximum closing force of 165 t, grab weights of 15–25 t, main winches of 2 × 270 kN, an operating weight of 100 t and a 257 kW engine. The larger SH700 lists 600–1,500 mm widths, 80 m depth, 220 t closing force, 15–35 t grabs, 2 × 355 kN winches, 130 t and 300 kW. Its kelly-guided SR235-S-DW lists 500–1,200 mm widths, 35 m depth, 128 t closing force, 2.5–9 t grabs and 83 t operating weight. [2]
The FHWA drilled shafts manual (GEC 10) notes that clam systems for diaphragm wall panels and barrettes may have a hydraulically controlled guide system to maintain alignment. [1]
Editorial calculation: a panel 6 m long, 0.8 m wide and 40 m deep (assumed dimensions) holds 6 × 0.8 × 40 = 192 m³ of soil to be removed and replaced by slurry, then concrete; ask the supplier for the grab's bite length and volume, and plan slurry storage and treatment for at least the panel volume. [2]
Give the supplier the wall widths and depths, panel lengths, ground profile (soil, boulders, rock and its strength), groundwater, slurry type, verticality tolerance, site space and headroom, transport limits, base machine preference, and whether a cutter or chisel will also be needed.
02
FHWA's manual describes grabs (clams) and hydromills as non-rotary methods for constructing rectangular diaphragm wall panels; when used as a foundation an individual panel is called a barrette, which can be oriented to resist large horizontal shear and overturning forces as well as axial load and can be post-grouted. It states that barrettes are excavated under mineral slurry to keep the excavation stable, and that a hydromill (cutter, or hydrofraise) is used to excavate rock. [1]
The manual also notes that polymer slurries form no filter cake, which reduces their effectiveness in supporting coarse-grained soils and non-circular excavations such as barrettes and slurry wall panels, compared with bentonite. [1]
Editorial note: agree with the designer and supplier which slurry will be used, how verticality will be measured and corrected, and the point at which the grab will be replaced by a cutter or chisel in hard layers.
Grab excavation moves the ground beside the trench before any main excavation starts. Zhu's 2021 study of slurry trenching for concrete diaphragm wall panels gives a panel length range of 4 to 6 m and a bentonite slurry unit weight range of 1.05 to 1.25 g/cm³, and notes that slurry pressure on the trench faces is lower than the at-rest earth pressure, so the ground releases stress. It cites field observations in which trenching settlement accounted for 40 to 50% of total ground settlement during deep excavations supported by these walls, and Clough and O'Rourke's five-project summary in which average and maximum settlement next to the wall during trenching reached about 0.08% and 0.15% of wall depth. [4]
Editorial calculation: for an 80 m-deep panel (the depth SANY lists for its hydraulic grabs), 0.08% and 0.15% of wall depth correspond to about 64 mm and 120 mm of settlement next to the trench; for a 35 m kelly-guided wall, about 28 mm and 53 mm. These are illustrative figures from the cited ratios, not predictions for a site. [4] [2]
03
Bauer Maschinen's brochure for its DHG V diaphragm wall hydraulic grab (July 2023) states that contractors have been moving from mechanical to hydraulic grabs because hydraulic grabs lead on trench accuracy and ease of operation, and describes the DHG V as combining hydraulic accuracy with the strength and free-fall ability of a mechanical grab. One grab body covers a wide weight range through extensions, add-on weights and 4, 8 or 12 steering flaps. [3]
For verticality, the brochure describes the B-Tronic grab module: an inclinometer in the grab measures trench inclination in the x and y axes during excavation, data run to the cab over a cable on a hydraulic recoil reel, and an optional gyroscope with cylinder and flap position sensing adds z-axis deviation and shovel position; a separate survey measures final deviation. Compare grab weight with the base machine's winch rating and the slurry and rock conditions described above. [3] [2] [1]
Editorial calculation: a 34 t grab is about 333 kN of dead weight; SANY lists 2 × 270 kN main winches on its SH500 for 15–25 t grabs, so a heavier grab needs a base machine rated for it.
| BAUER DHG V | Range stated |
|---|---|
| Length | 2,400–3,800 mm |
| Width (wall thickness) | 600–1,500 mm |
| Hydraulic cylinder | 120 or 180 t (1,200–1,800 kN) |
| Grab weight | 15–34 t |
| Steering flaps | 4, 8 or 12 |
| Additional weights | Pairs of 0.5, 1.5 and 2.5 t |
| Options | Cleaner or chisel in the shovel; cutting edge or stop-end removing aid |
State wall thickness and depth, panel length, ground and rock strength and verticality tolerance, and ask for grab weight and cylinder force, steering flap count, deviation monitoring and the matching base machine winch rating.
04
Suppliers linked to this page list diaphragm wall grabs; each card links to the page reviewed.
The supplier reviewed lists hydraulic and kelly-guided grabs with trench cutters and rotary rigs; ask for wall widths and depth, closing force, grab weight and bite size, guidance and verticality control, winch capacity, base machine and transport dimensions.
05
This is a functional reference built from the sources cited; it is not one maker's design.
| Part | Role | Fix in the order |
|---|---|---|
| Grab body and jaws | Bite and lift soil. [2] [1] | Width; weight; bite. |
| Closing cylinders | Close the jaws. [2] | Closing force. |
| Guide system | Keep alignment. [1] | Guidance; correction. |
| Suspension (ropes or kelly) | Lower and raise grab. [2] | Rope or kelly. |
| Base machine and winches | Carry and hoist. [2] | Pull; weight; engine. |
| Slurry system (separate) | Support trench. [1] | Bentonite or polymer. |
| Bentonite slurry in the trench | Supports trench faces while the grab digs; 1.05–1.25 g/cm³ unit weight cited. [4] | Slurry density; level control. |
06
A diaphragm wall grab quotation needs values for your wall. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.
| Field | What it means and published values | Ask the supplier for |
|---|---|---|
| Excavation Width (meters) | E.g. 0.6–1.5 m. [2] | Widths available. |
| Excavation Depth (meters) | E.g. 80 m hydraulic; 35 m kelly-guided. [2] | Depth and basis. |
| Operating Weight (tons) | E.g. 83–130 t. [2] | Weight; ground bearing. |
| Bucket Capacity (cubic meters) | Bite volume. | Volume; bite length. |
| Closing Force (kN) | E.g. 128–220 t-force. [2] | Force. |
| Operating Pressure (MPa) | Hydraulic system. | Pressure. |
| Max Pull Force (kN) | Winch, e.g. 2 × 270 or 2 × 355 kN. [2] | Line pull. |
| Opening Width (mm) | Jaw opening. | Value. |
| Cylinder Stroke (mm) | Closing cylinders. | Value. |
| Operating Temperature (°C) | Climate. | Range. |
| Material Grade | Jaws and teeth. | Steel grade; wear parts. |
| Hydraulic Oil Flow (L/min) | Grab circuit. | Flow. |
| Grab weight and cylinder force | 15–34 t; 1,200–1,800 kN for 600–1,500 mm walls in one hydraulic grab range. [3] | Weight, force, flaps, monitoring. |
07
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Wall: [width; depth; panel length] Ground: [soil; boulders; rock strength; water] Slurry: [bentonite or polymer] Verticality: [tolerance; measurement] Grab: [hydraulic or kelly-guided; weight; force] Base machine: [winch pull; weight; engine] Site: [space; headroom; transport]
These companies list diaphragm wall grabs.
Lists hydraulic grabs (SH500, SH700) and the kelly-guided SR235-S-DW for diaphragm walls, with trench cutters.
Product scope checked 2026-10-11
Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.
SANY lists 80 m for its SH500 and SH700 hydraulic grabs and 35 m for its kelly-guided SR235-S-DW. [2]
FHWA's manual says a hydromill (cutter) is used to excavate rock. [1]
FHWA states barrettes are excavated under mineral slurry to keep the excavation stable. [1]
Bauer's DHG V brochure describes steering flaps and an inclinometer in the grab feeding B-Tronic, which displays x and y deviation in the cab during excavation, with an optional gyroscope for z-axis. [3]
Zhu (2021) cites average and maximum settlement during slurry trenching of about 0.08% and 0.15% of wall depth, and trenching making up 40–50% of total settlement in supported deep excavations. [4]
Sources checked 2026-10-12. FHWA's GEC 10 is a US federal engineering manual for drilled shafts and related foundations; SANY and Bauer Maschinen describe their own grabs; a 2021 Soochow University paper quantifies ground movement during slurry trenching.
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