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<br />002870 <br /> <br />This was an old metastable slide that was reactivated in the head scarp area <br />as a direct result of residential development. Development caused: 1) <br />loading of the top of the landslide, and 2) a change in the ground water <br />regime. <br /> <br />Community Impact <br /> <br />The greatest impact in the community is the loss of twelve to fourteen homes <br />located on the landslide. There is a risk of personal injury associated with <br />the possibility of a sudden foundation collapse, or explosion of a ruptured <br />gas line caused by the slow deterioration of the bearing support for the <br />buildings and the presence of large open tension cracks. Also at risk are the <br />city-owned and private utilities beneath Santa Clara Avenue. <br /> <br />Mitigation <br /> <br />Several conceptual engineering solutions oriented toward stabilization of the <br />upper portion of the landslide were explored at a preliminary level and <br />discounted due to the construction cost compared to an assumed present or <br />anticipated value of the property and improvements. <br /> <br />Given the state of distress of the majority of the structures and the <br />estimated cost of a suggested conceptual stabilization plan, it was concluded. <br />there was no cost effective way to allow long-term continued residential use <br />of the lots north of Santa Clara Avenue east of address 1154. Furthermore, <br />any structures remaining on the site would severely constrain implementation <br />of any stabilization plan intended to save the street and utilities. <br /> <br />Options for dealing with the slide include: 1) removing the houses north of <br />the scarp and regrading the slope to unload the upper landslide area, increase <br />slope exposure to sunlight, decrease slope angle, and improve slope drainage. <br />The installation of a monitoring system set back from the head scarp would <br />serve as an early warning system should retrogressive slope failure begin; 2) <br />installing a drainage gallery and/or cut-off wall to divert subsurface water <br />away from the slope. The net result of these methods would be to minimize the <br />threat of continued slope failure and the resulting loss of the utilities <br />beneath Santa Clara Avenue. <br /> <br />3461/1-8 <br /> <br />- 85 - <br />