921392 Exploration of seepage paths around a rock fill dam using radon tracing and multivariate analysis of water quality Shiozaki, I; Kitamura, T; Kojo, H; Nakajima, S Proc 6th International Congress International Association of Engineering Geology, Amsterdam, 6-10 August 1990 V2, P1235-1242. Publ Rotterdam: A A Balkema, 1990

Seepage paths around the Terayama rockfill dam have been examined using a radon 222 tracer and by water quality analy- sis. The foundation and left bank are mainly rhyolite and tuff, the right bank andesite, tuff breccia, and lake sediments. Seep- age and groundwater level were monitored at various sam- piing sites before and after reservoir filling. The change with time of 6 ions formed the basis of the water quality analysis. Flow paths obtained by regression analysis of water quality data and from tracer tests were in good agreement.

Hydraulic structures

921393 Geotechnical aspects of headcutting in emergency spillway channels Palmerton, J B; May, J H; Banks, D C Bull Assoc Engng Geol V28. NI, Feb 1991, P89-94

Observations of severe headcutting at moderate fows in spill- way channels,with the potential for undercutting failure of the structures, prompted reexamination of the processes causing channel erosion. Flume experiments simulating flow over overfalls indicated that flow causes a pressure drop beneath the nappc of the overflowing water, which results in the plume being pushed by atmospheric pressure towards the face of the overfall, with resultant reverse scour. This pressure drop is more predominant at low to moderate discharge rates.

921394 Chesil Sea Defence Scheme. Paper !: concept, design, and construction Hook, B J; Kemble, J R Inst Civ Engrs Proc V90, Ptl, Aug 1991, P783-798

Past flooding of areas of the landward side of the natural shin- gle barrier of Chesil Beach has prompted improvement of the sea defences. A new toe has been added to the existing sea wall. Gabion mattresses and slope regrading have been used to stabilise and raise the crest of the bank. A sheet pile cutoff wall driven at sensitive areas to underlying clay. and a large box culvert to collect and drain water percolating through the beach complete the scheme.

921395 Utilization of the Qattara depression in the western desert of Egypt Esbeck-Platen, H H V Proc 6th International Congress International Association o f Engineering Geology, Amsterdam, 6-10 August 1990 V2, P1417-1422. Publ Rotterdam." A A Balkema. 1990

The utilisation of the Qattara depression for such purposes as hydroelectric power generation is considered. A total of eight water conveyance routes from the Mediterranean to the depression have been studied. There are five aquifer systems of importance in an area of almost 300km long by 145km wide. The constraints to the economical utilisation of this depression range from long conveyance distances and presence of unfavourable geological conditions for construction of tunnels or canals in unconsolidated soils to problems due to the ele- vated topography (50-250m above sea level).

51A

Slopes

See also: 921011, 921252, 921260, 921280, 921464

921396 Landslides on fluidlike zones in the deposits of glacial Lake Hitchcock, Windsor County, Vermont Ohlmacher, G C; Baskerville, C A Bull Assoc Engng Geol V28, NI, Feb 1991, P31-43

Slope failures in the lake deposits around Lake Hitchcock in 1984 took the form of blocks of material moving downslop¢ on a layer of fluidlike material. They were associated with high pore pressures resulting from an extended period of above average rainfall, culminating in prolonged intense precipita- tion. Water contents exceeding liquid limit led to the forma- tion of the fluidlike zone, the block material being held together by vegetation. The slides had well developed head scarps and were bounded by lateral boundary shear planes or en echelon tension fractures.

921397 Effects of root reinforcement on soil-slip patterns in the Transverse Ranges of southern California Terwilliger, V J; Waldron, L J Bull Geol Soc Am VI03, N6, June 1991, P775-785

Effect of roots on shallow soil slippage was studied on unsta- ble hillsides covered by chaparral, prescription burned chapar- ral, and grassland. Large undisturbed samples were taken and direct shear tested. Roots were decayed from smaller samples and strength of the unreinforced soil determined. Absolute and relative contributions of the roots to soil strength are sig- nificant. The distribution of reinforcement for each vegetation type is discussed. A 3D analysis of slope stability for the root reinforced soil is developed which gives realistic results.

921398 September 5, 1987, landslide on the La Grande River, James Bay, Quebec, Canada Lefebvre, G; Rosenberg, P; Paquette, J', Lavallee, J G Can Geotech J 1/28, N2, April 1991, P263-275

The major landslide occurred at a site previously identified as high risk. Site conditions, decreasing grain size from surface sands to silty clays at depth, were well documented from an earlier boring. The soils are normally consolidated and subject to strong underdrainage. Stability analysis indicates the role of the groundwater regime on stability conditions of high riverbanks. The concept that regression after the initial deep seated slide is controlled by the undrained shear strength of the weakest layer is also supported.

921399 Extent and effects of mass wasting in Ghana Ayetey, J K lnt Assoc Engng Geol Ball N43, April 1991, P5-19

Mass wasting of soil and rock masses is found throughout Ghana. The general geology is outlined and landslide-prone areas illustrated. Causes of failures are examined: structural discontinuities, textural properties of soils, weathering and groundwater, rainfall and vegetation, and undercutting. Reach and velocity of slides are analysed. Formation of scree slopes and the economic consequences of the slides are considered. Corrective or preventative measures are discussed. A case example is presented where corrective measures were designed after examination of the failure mechanism.

1992 Pergamon Press plc. Reproduction not permitted