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<br />Precautions Concerning Reliance on <br />Physical Methods <br />Although physical techniques may be the only means for <br />protecting existing land uses in hazard areas, sole <br />reliance on them may create a f:l1se sense of security. <br />An event of greater severity than that for which the pro- <br />ject was designed may occur, or a structure may fail due <br />to aging, changing conditions, or inadequate design. The <br />result could be catastrophic if the hazard zone has been <br />developed intensively. <br /> <br />Design Considerations and Physical <br />Mitigation Methods <br /> <br />When designing control measures, it is essential to look <br />well beyond the landslide mass itself. A translational <br />slide may spread over great distances if the bedrock <br />surface is sufficiently inclined and the shear resistance <br />along the surface remains lower than the driving fooce. <br />Debris flows can frequently be better controlled if <br />mitigation efforts concentrate on stabilizing the source <br />area. An understanding of the geological processes and <br />the surface and growxI-water regimes, under both <br />natural and human-imposed conditions, is essential to <br />any mitigation planning. <br />Some factors that determine the choice of physical <br />mitigation are: <br />. type of movement (e.g., fall, slide, avalanche, <br />flow), <br />. kinds of materials involved (rock, soil, debris), <br />. size, location, depth of failure, <br />. process that initiated movement, <br />. people, place(s) or thing(s) affected by failure, <br />. potential for enlargement (certain types of failures <br />[e.g., debris flows, translational slides] will enlarge <br />during excavation), <br />. availability of resources (funding, labor fooce, <br />materials), <br />. accessibi1ity and space available for physical <br />mitigation, <br />. danger to people, <br />. property ownership and liability. <br /> <br />The physical mitigation of landslides usually consists <br />of a combination of methods. Drainage is used most <br />often; slope modification by cut and fill and/or but- <br />tresses is the second most often used method. These <br />are also, in general, the least expensive methods. <br />The various types of physical mitigation methods are <br />listed in Table 7. Descriptions of these methods are pro- <br />vided in Appendix 3. <br /> <br />32 <br /> <br /> <br />Table 7. <br /> <br />ical mitigation methods. <br /> <br />MITIGATION METHODS FOR <br />SLUMPS <br /> <br />4) <br />5) <br />6) <br />7) <br />8) <br />2. E <br /> <br />; <br />'1 <br />, <br />j <br />I <br />i <br />, <br />.i <br />!, <br />