Page 68 - Geotechnical Engineering Soil and Foundation Principles and Practice

Soils That Are Sediments
Soils That Are Sediments 63

Surcharge loads usually are piles of soil that can be moved to successive
building sites in a complex. Another option is to store all building materials
on a site footprint slab; then as the structure is built the weight stays the
same. Surcharging is common where a new highway must cross soft, compressible
terrain. Surcharging can save money but requires time, and owners see time as
money. It therefore is important to be able to predict the time that will be required
and monitor the progress of settlement. A method described later in this book
shows how to predict future settlement from measurements made over a period
of time.

4.3 GRAVITY DEPOSITS

4.3.1 Talus

Steeply sloping heaps of rock fragments at the bases of rock outcrops are called
talus or scree. The rubble deposits have fallen off and slid down to a marginally
stable, relatively steep slope angle, Fig. 4.1. The deposits tend to be cone-shaped
with the apex pointing to the source.

The stability of a talus slope is readily measured by simply walking on it, as the
weight of a foot can start things sliding. For obvious reasons such a slope is not
a satisfactory foundation but it sometimes cannot be avoided, particularly when
building roads in mountainous areas. In that case vibration or blasting may be
used to cause the deposit to settle into a more comfortable slope angle, while
recognizing that more scree will be on the way. As mountainous areas usually are
earthquake areas, a good shake may accomplish the same thing until the next
shake that may be bigger.

Figure 4.1
Road constructed
across a talus
slope where there
was not much
alternative,
Karakorum
Highway, Pakistan.

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