Geosynthetic Sand Containers

Site preparation and underliner. Excavate to firm base material over the full revetment length, remove rocks, stumps and protrusions, backfill cavities with compacted sand, and shape the slope to the design batter, toe and crest elevations before any container is placed - the profile cannot be reshaped afterwards. Lay a nonwoven filter underliner over the full slope and toe trench in a shingle pattern, upper panel beneath lower so downslope flow passes over the joint, with 500 mm minimum overlap on stable subgrades and 1,000 mm on soft or variable ground.

Toe embedment. Placement begins at the toe and proceeds up the slope, with the first container set along the front line, long dimension parallel to the shoreline, establishing the datum for every course above. Toe embedment depth is the single most important design decision: scour at the toe removes lateral support and drives forward rotation and progressive collapse of the whole structure. USACE Coastal Engineering Manual and CIRIA Rock Manual guidance recommends embedding the toe container to a minimum of 1.8 times the significant wave height below design water level. Verify against project design wave height before proceeding.

Filling and closure. Containers are filled on site to approximately 80 % of theoretical volumetric capacity. Overfilling prevents units conforming to each other and destroys interlock; underfilling creates voids that concentrate hydraulic pressure at joints. Fill must be clean, well-graded sand free of sharp debris, organics and material finer than the container's O90 opening size. Fill bottom corners fully without creasing before closing. Closures require a double seam - straight pass followed by zigzag or overlock in UV-stabilised yarn. Single straight-seam closures are not compliant for structural coastal applications.

Stacking and compaction. Successive courses are laid in stretcher bond, each container offset half a bag length from the layer below - never stacked in vertical columns, which create continuous joints that open under repeated hydraulic loading. After a minimum run of three containers, level and compact the course with the back of the excavator bucket or a plate compactor before the next is placed. Double-layer configurations provide around 17 % greater stability than single-layer of the same grade under equivalent wave conditions. Check face alignment against setting-out pegs at every course to prevent progressive drift.

Crest, backfill and sign-off. Crest containers take wave run-up and overtopping in addition to direct attack and are placed last with the greatest care. Bench the rear profile to receive each course, folding the underliner back over completed sections and overlapping at each bench to prevent flanking flow behind the structure. Complete the crest fill, taper off with compacted backfill to design elevation, and level the exposed face with sand. Every stage is documented under IAGI-aligned QA/QC with photographic sign-off before the next course is placed.