Study on the Stabilization Mechanisms of Clayey Slope Surfaces Treated by Spraying with a New Soil Additive

The topsoil of a clayey slope is easily washed off by rain due to its loose structure. To protect the slope surface, in recent years, several types of non-traditional soil additives have been used by means of mixing with soil. In this work, a new organic polymer soil stabilizer, named aqua-dispersing-nano-binder (ADNB), was sprayed on the soil surface to stabilize the topsoil of a clayey slope. To understand the interaction between the polymer and soil particles during the infiltration process as well as the stabilization mechanism, infiltration tests, water stability tests and scanning electron microscopy (SEM) analyses were performed with different polymer contents. The infiltration tests showed that the infiltration rate of the polymer stabilizer in the soil was slower than that of water due to its characteristics of easy adhesion to soil particles, poor fluidity and large molecular volume. The maximum effective infiltration depth was achieved in the specimen treated with 2% ADNB, and the minimum was achieved in the specimen treated with 5% ADNB. The water stability of the soil increased with the content of the soil stabilizer in the soil aggregates with diameters of either 5–10 mm or 10–20 mm. The SEM analysis showed that the quantity of polymer decreased with infiltration depth; a polymer membrane was formed on the surface of the topsoil and chains were formed inside. The amelioration of the soil water stability may have been due to the bonding between soil particles and polymers generated after evaporation of water in the emulsion. The polymer stabilizer could be applied to improve the erosion resistance of the slope topsoil and reduce soil loss.

Influence of rainfall regime on hydraulic conditions and movement rates in the overconsolidated clayey slope of the Orvieto hill (central Italy)

The medieval town of Orvieto is built on the top of a pyroclastic slab overlying a gentle slope of overconsolidated clays. The clayey slope has been constantly affected by landslide phenomena in the form of slow movements and failure events, which in turn have periodically caused instability of the marginal areas of the pyroclastic slab. Since 1982 a number of Casagrande-type piezometers and inclinometers were installed in the northern slope of the Orvieto hill within the area that was involved in the huge Porta Cassia landslide in 1900. In this paper, after a brief description of the geology and the geotechnical properties of the slope, data obtained through the monitoring system are illustrated. Piezometric data are utilized to develop a conceptual model of the hydraulic conditions in the clayey slope, and inclinometer measurements are interpreted and correlated with the geotechnical ground profile and slope morphology to understand the present complex evolution of the clayey slope. Finally, the strong correlation among the rainfall regime, the piezometric levels, and the rate of movements is discussed, and the recurrence periods of critical cumulative rainfall on displacement trends are estimated on the basis of statistical methods.Key words: overconsolidated clays, slope movements, piezometric levels, rainfall.

A hydrochemical study of urban landslides caused by heavy rain: Scarborough Bluffs, Ontario, Canada

Scarborough Bluffs is a 15 km long stretch of the Lake Ontario shoreline east of downtown Toronto. This heavily urbanized area currently represents Canada's most serious erosion problem. The worst affected zone is 1.5 km long and lies along South Marine Drive where 50 m high bluffs are failing by shallow retrogressive failures of jointed glacial clays over underlying deltaic sands and clays. The erosion rate is about four times that for the coastline as a whole.Heavy rains in the Toronto area in August and September 1986 produced a spate of slope failures and mud flows. Particularly heavy storms on September 10 and 29 triggered extensive retrogressive slope failures at South Marine Drive. Hydrochemical investigations of discharge waters suggest that slope failure was caused by surface runoff on the bluff top recharging lower slope areas by infiltration through joints in the upper clay capping. Discharge of water from the lower slope is impeded by less permeable barriers in the deltaic stratigraphy at the site and by a cover of clayey slope debris. Data suggest that provision for adequate drainage of the bluff top, by interceptor drains, is a prerequisite for controlling slope behaviour in the area. Key words: slopes, erosion, groundwater, hydrochemical, recharge, drainage.