Gravel areas where there is little traffic. Globally, far more roads are surfaced with gravel than with concrete or tarmac; Russia alone has over of gravel roads. Both sand and small gravel are also important for the manufacture of concrete. Large gravel deposits are a common geological feature, being formed as a result of the weathering and erosion of rocks. The action of rivers and waves tends to pile up gravel in large accumulations. This can sometimes result in gravel becoming compacted and lithified into the sedimentary rock called conglomerate. Where natural gravel deposits are insufficient for human purposes, gravel is
Silt fence inserting the silt fence fabric into the slot with a moving pivot, while the machine is moving forward. This step is followed by mechanical soil compaction, setting of fence posts, and attaching the fabric. Silt fence fabrics (geotextiles) tested in laboratory settings have shown to be effective at trapping sediment particles. Although there have been few field tests of silt fences installed at construction sites, these tests have shown generally poor results. (Effectiveness testing involved measurements for both total suspended solids and turbidity.) Other studies and articles about silt fence usage and practice document problems with installation and maintenance, implying