Earthwork & Grading
Exponent’s engineering geologists and geotechnical engineers are specialists in characterizing subsurface conditions, determining the history of site grading and their effects on stability, and evaluating the performance of cut or fill slopes and compacted fill through monitoring and computer analysis.
Infrastructure is a vital component of our modern society. The reliability of our infrastructure is based, in part, on the stability of the ground on which it is founded and the earth with which it is built. Virtually all new infrastructure projects and land development involve modification of the ground surface topography by grading—the excavation, hauling, and placement of rock or soil material—to create building pads, roadway subgrade, and foundations. Grading and earthwork are typically the least expensive and most reliable means of improving relatively shallow weak or compressible soil conditions by removal and replacement of the suspect material. Examples include the removal of landslide shear zones and replacement with compacted earth material (called a “shear key”) or when volumes of collapsible soil are removed and recompacted as engineered fill.
Earthwork or grading can create soil instability problems when substandard grading design or poor workmanship occurs. Typical grading-related problems include differential performance at cut-fill transitions; landslides created by filling at the head or cutting at the toe of a natural slope; soil and rock creep; settlement, differential settlement, seismic compression, or heave of fills; heave of expansive bedrock in cuts; and diversion of surface drainage. Grading a site can exacerbate existing stability problems and mask natural topographic indications of potential hazards such as existing landslides or sinkholes. Cut slopes that are too steep can fail and undermine properties or structures at the top or threaten persons or property beyond the toe of the slope. Cuts can also intercept zones of groundwater, which can cause problems ranging from nuisance seepage to slope instability. The construction of fills without proper subgrade preparation, drainage, keying, benching, moisture conditioning, and compaction can result in fill settlement or slope failures. Use of unsuitable soil or other fill materials or other fill materials such as expansive clay, steel slag, or ash fly in near-surface fills can result in cracking of structures, slabs and pavements constructed on the fill. Uncontrolled (dumped) fills typically are susceptible to severe settlement, erosion, slumping, and mudflows or debris flows and can impose unanticipated surcharges on buried pipelines or downslope cuts. Such fills can block watercourses, causing sedimentation and posing a risk of upstream and downstream flooding.
Exponent services include:
- Field investigation of failures of graded sites
- Analysis of ground movement or slope failure causes
- Determination of relative contribution of factors controlling settlement or slope failure
- Emergency response and evaluation of slope failure hazards and damage to buildings and structures
- Analysis of dam and levees performance and failure
- Development of conceptual repair recommendations