Ch. 7] SLIDES 135 



relative weakness and potential sliding, and it should be apparent that greater 

 clanger of sliding exists when they dip steeply toward the excavation than when 

 the inclination is in the opposite direction. Close jointing may impair the 

 shearing strength of an otherwise strong and competent rock. From these and 

 numerous other examples which might be cited, it should be apparent that 

 the influence of geology is very important. Hence the importance of corre- 

 lating the results of soil mechanics studies with a detailed knowledge of 

 geological conditions. 



SLIDES 



Landslides have always constituted a threat to engineering projects, 

 and they cause great annual property damage every year. They as- 

 sume greater importance in highway engineering than ever before be- 

 cause of the deeper cuts and excavations essential in modern construc- 

 tion practices. A large percentage of the literature is devoted to de- 

 scriptions of slide occurrences, but relatively little embraces studies 

 of the mechanics of slide movements and their classification. 



Ladd (1927, 1928) published analyses of slides and their relation- 

 ship to highways, particularly types occurring in West Virginia, Ohio, 

 and southern Pennsylvania. He classifies these as: flow-moment 

 slides; slope-adjustment slides; small-scale adjustment slides; struc- 

 tural slides; and slides involving artificial fills. In a later paper 

 (1935) he discusses slides in relationship to railway construction. 

 Here he sets up five major groups: (1) flows; (2) slope adjustments; 

 (3) subsidence; (4) structural slides; (5) clay ejection from clay- 

 filled caverns opened by cuts. Within these groups are 17 subdivi- 

 sions based on material type and structural control. Ladd's descrip- 

 tions and discussions of control methods are more effective than his 

 classification. 



The first distinctly scientific effort at a sound classification was 

 made by Sharpe (1938) . In this work Sharpe recognizes four principal 

 groups, which are divided into subdivisions as follows: 



1. Slow flowage 3. Sliding 



(a) Rock creep (a) Slump 



(6) Talus creep (b) Debris slide 



(c) Rock-glacier creep (c) Debris fall 



(d) Soil creep (d) Rock fall 



(e) Solifluction {e) Rock slide 



2. Rapid flowage 4. Subsidence 



(a) Earth flow Sinking over mines, caves, etc. 



(6) Mud flow 



(c) Debris avalanche 



