Subsidence

DOE-STD-1022-94

Ground water conditions,

Penetration resistance of the soil, e.g., Standard Penetration Test (SPT), Cone Penetration Test(CPT),

Shear wave velocity of the soil,

Evidence of past liquefaction,

Ground motion characteristics.

A soil behavior phenomenon similar to liquefaction is strength reduction in sensitive clays. Although this

behavior phenomenon is relatively rare in comparison to liquefaction, it should not be overlooked as a

potential cause for land sliding and lateral movements. Therefore, the existence of sensitive clays at the site

shall be identified.

5.5.4.2 Subsidence

Ground settlement during and after natural phenomena hazards due to dynamic loads, change of ground

water conditions, soil expansion, soil collapse, erosion, and other causes shall be considered. Ground

settlement due to the ground shaking induced by NPH can be caused by two factors: (1) compaction of dry

sands due to ground shaking, and (2) settlement due to dissipation of dynamically induced pore water in

saturated sands. Differential settlement would cause more damage to facilities than would uniform

settlement. Differential compaction of cohesionless soils and resulting differential ground settlement can

accompany liquefaction or may occur in the absence of liquefaction. The same types of geologic information

and soil data used in liquefaction potential assessments, such as the Standard Penetration Test (SPT)

N-value, can also be used in assessing the potential for differential compaction. Ground subsidence has been

observed at the surface above relatively shallow cavities formed by mining activities (particularly coal mines)

and where large quantities of salt, oil, gas, or ground water have been extracted, (Hatheway and McClure,

1979). Where these conditions exist near a site, consideration and investigation must be given to the

possibility that surface subsidence will occur.

5.5.4.3 Slope instability

Stability of natural and man-made slopes shall be evaluated when their failures would affect the safety and

operation of DOE facilities during natural phenomena hazards. In addition to land sliding facilitated by

liquefaction-induced strength reduction, instability and deformation of hillside and embankment slopes can

occur due to the ground shaking inertia forces causing a temporary exceedance of the strength of the soil or

rock. The slip surfaces of previous landslides, weak planes or seams of subsurface materials, mapping and

dating paleo slope failure events, loss of shear strength of the materials caused by the natural phenomena

hazards such as liquefaction or reduction of strength due to wetting, hydrological conditions including pore

pressure and seepage, and loading conditions imposed by the natural phenomena events shall all be

considered in determining the potential for instability and deformations. Various possible modes of failure

shall be considered. Both static and dynamic analyses shall be performed for the stability of the slopes.

The following information, at a minimum, shall be collected for the evaluation of slope instability:

Slope cross sections covering areas which would be affected the slope stability,

Soil and rock profiles within the slope cross sections,

Static and dynamic soil and rock properties, including densities, strengths, and deformabilities,

Hydrological conditions and their variations,

Rock fall events,