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Strain increases in pi 'Strains stiawn are tensile. before excavation` line. Following these findings, West Gas deaded to implement mitigating measures immediately. Before implementation of these measures, the area of the landslide was surveyed so that the landslide extent could be accurately defined and the course of the landslide plane interpreted. Following this survey, the pipe alignment across the landslide and the surrounding area was sur- veyed with the pipe locator. This survey indicated clearly dis- tinct displacement of the line by ap- proximatefy 9 ft downhill in the direc- tion of landslide movement, and two distinct line Flexures at both bound- aries of the landslide. It became evi- dentthat considerable deformations of the landslide occurred .n the spring of 1985 and very probably during earlier years, causing such significant dis- placement of the line. Emergency relief. An emergency re- iiei of strains and stresses in the pipe was pedormed at the end of May 1981. Stress reiiei was accomplished by a trench excavated uphill from the line with a backhoe. To reduce the risk of line failure during the excava- tion, the pressure in the line was decreased from 420 psi to 50 pv. The excavation was performed, starting in the central part of the landslide, in approximately 2 days. An immediate effect of strain relief was evident when the line displaced verv rapidly uphill trOm iI5 Orlgindl location. This displacement reached a maxr mum of nearly } ft. Fit. i shows the distinct flexure of the line at the r.; a is shown on Fig. }. Strain Gauge I showed the lowest stress reiiei of 1,430 µ-,trains. ~.vhile Gauges ?and 1 showed considerably high strain relief of 2,110 and 1,314 µ-;trains. r?spectivey. With an assumption of an average stram reiiei of I,i21 µ-strains, total stress relief can be calculated. Total reiiei or the decrease of longi- tudinal stresses in the pipe by the excavation reached nearly 5?.000 psi. ,Maximum decrease of stresses is even higher; it may have attained values higher than 60,000 psi. Longitudinal strain decreases moni- tored during the excavation provide information on stresses in the line induced by landslide deformations. It is evident that landslide deforma- tions, between the time of line instal- lation and that of excavation, induced longitudinal stresses in the line on the ordec of 12,000 psi. This is considera- bly more than the yield strength of the pipe (42,000 psi). Stability analyses. With regard to these findings, West Gas decided to replace the line section across the landslide. Stability analyses of the landslide area and analyses of possible remedial measures indicated that fairly difficult and costly methods of stabilization would be necessary to secure the long-term safety of the line if it remains buried. for this rea- son, West Gas only replaced the line section across the landslide and in- stalled it above- ground, on horizon- tal support mem- bers, to prevent line failure in case of re- peated, major land- slide deformations. It is expected that in a case of major landslide deforma- tions, the line will slide on the horizon- tal support mem- bers. The integrity of the line would prob- ably be endangered in a case of large, sudden, catastroph- ic deformations of the landslide. Even ii such a case cannot be ruled out, its probability i5 fairly low. The original set of Pipeline flexure caused by landslide de- formations IFIg. 5). boundary of the landslide aher exca- vation of the stress relief trench. Strains in the line were continuously monitored during the excavation. The strain relief caused by the excavation