Underground pipelines are affected by their surrounding soils. When providing recommendations for a pipeline, geotechnical engineers consider the potential for settlement, liquefaction, or corrosion by the soil. They provide recommendations for pipeline design based on these and other factors.
Pipelines are supported and covered by earth materials. Proper selection and placement of the materials around the pipe is essential. Geotechnical recommendations are required for the material placed in the pipe bedding, pipe zone, trench backfill and the techniques used to place and compact each material.
Retaining walls may be used to support steep slopes when the earth materials lack adequate strength, or when there is not enough space for a slope. In order for a retaining wall to be stable, its design must include all of the loads that it will support. Converse’s engineers have provided geotechnical recommendations and parameters for the design of numerous types of retaining walls.
Cantilever retaining walls are usually constructed of concrete and include a large footing at the base of the wall. The space behind the wall is backfilled with compacted fill soil. Important considerations are the pressure exerted by the retained soil, the weight of the backfill, drainage behind the wall and compaction of the backfill.
Mechanically stabilized earth walls typically consist of interlocking masonry blocks with layers of synthetic geo-grid extending behind the wall into compacted fill. Drainage is not generally an issue, but the geo-grid material and spacing must be designed based on the correct loads and soil characteristics.
Soil nail and rock bolt walls use steel rods to stabilize a soil or rock slope. Depending on the geologic conditions and wall design, the rods may be held in place by friction, epoxy, or mechanical anchors. The exposed end of the soil nails or rock bolts may be treated cosmetically or a structural concrete facing may be required to retain the earth material at the slope face. The success of this type of wall depends on accurate characterization of the materials in the existing slope and appropriate geotechnical recommendations for the size, strength, spacing and placement of the soil nails or rock bolts.
Buildings and other structures may be supported on the ground by several different types of foundations. Shallow foundations include the spread footings used around the perimeter of most buildings as well as the thicker and more rigid mat foundations used in certain difficult soil conditions. Deep foundations include cast-in-place-drilled piles, driven piles and micropiles.
Engineers evaluate the site geology and project requirements and provide recommendations regarding which type of foundation are appropriate. They also provide essential information for the design and construction of the foundations. Depending on the project, these parameters might include how much load the ground will support, how far footings should extend into the ground, sizing for deep piles, or how far apart piles should be placed.
Most project sites are graded before construction of the improvements. The grading may transform the layout of the site, or it may return the site to something close to its original appearance. In either case, Converse’s engineers provide recommendations for site grading that will provide a stable surface with enough strength and stability to support whatever structures are planned.
The natural soil found at the surface of many sites is too soft to support buildings or other improvements. Remedial grading may be recommended to remove several feet or many feet of unsuitable earth materials. In many cases, the removed soil may be re-used as compacted fill. Occasionally, site conditions prevent the recommended remedial grading, so specialized ground improvement techniques, such as vibrocompaction, stone columns, or surcharging, are utilized.
Compacted fill is soil that has been moistened and compressed to a specified density. This process reduces the potential for the fill soil to settle or erode. Engineers provide specifications for how much compacted fill should be placed under buildings or other improvements and how the fill should be compacted.
Slopes may be constructed of compacted fill or cut into existing natural earth materials. Both fill slopes and cut slopes must be stable and resistant to erosion. Converse’s engineers and geologists evaluate slopes in design and in the field and provide recommendations to improve stability where needed.
Geotechnical engineers analyze the properties of earth materials at a project site and evaluate whether those materials meet the project requirements. They provide recommendations for how structures should be designed based on the underlying soils or rock. They also recommend earthwork to improve the ground conditions to meet the needs of the planned structures. Converse’s engineering team routinely provides geotechnical recommendations for building foundations, pipelines, bridges, tunnels, pavement and other structures.