Keywords: gravel slope, monitoring systems, soil nailing method, erocomat, stabilization treatment, stability analysis.

Gravel is common soil deposit in Taiwan. Consequently, many infrastucture construction projects have to treat slope corrosion and sliding problems in gravel deposits. This study adopts data obtained from site investigations between the Ku-Kang and Mei-Shan interchanges of the Third Southern Freeway. Conventional treatment techniques such as polyathylene strip and thin layer hydrograsser methods, do not function very well for preventing slope corrosion and sliding. An effective method of preventing slope corrosion and sliding is required.

This study aims to find the optimal approach of preventing slope corrosion and sliding on gravel slopes, appraise the methods treating gravel slopes, identify the strongest effect on the gravel slope stability, and establish a system for monitoring index values of the gravel slopes.

This study utilizes the Third Southern Freeway 277K+800 - 277K+860 for the case study of the gravel slopes. Stabilization treatment methods (erocomat, press soil nail + erocomat, put soil nail + erocomat) are used on the site. However, the factors influencing the stability of gravel slope must be identified in order to select a new method of treating slope problem. This study aims to determine the factors affecting gravel slopes , such as slope height, slope gradient, soil cohesion c, friction angle , and rainfall. The associate monitoring systems for factors such as inclinometer probe, loading cell, strain gage, settlement point, and erosion tank are also set up on site for comparison.

FLAC software is used to analyze the stability of the gravel slope under different conditions, including normal conditions, heavy rainfall, and earthquake conditions. FLAC is also used to determine the most significant factors during the heavy rainfall and analyze the failure mechanism of gravel slope with different treatment methods of soil nail+erocomat. The software is also used to simulate the observation points at the grid nodes of instrument points on analysis net, and compared to the monitoring data of monitoring systems on site. Finally, FLAC is used to find the inclinometer monitor index values, as the factor safety values near 1 of the gravel slope of Third Southern Freeway.

This study reaches the following conclusions:

1. Failure on all gravel slope sites results from shallow plane failure or arc slipping.
2. Soil nailing can reverse failure depth in the gravel slope.
3. Heavy rainfall is the strongest factor affecting the stability analysis of a gravel slope.
4. The gravel slope with soil nailing system plus heavy rainfall condition, the failure mechanism becomes a circular rotational failure.
5. The appraisal of the treatment methods of the gravel slopes indicates that the press type soil nail+erocomat is the safest and most economical and ecologically beneficial treatment.
6. A gravel slope monitoring system is established to monitor index values on the gravel slope of Third Southern Freeway.

The results of this study will provide a helpful in reference for the maintenance of the gravel slope of Third Southern Freeway and the nearby region practical projects.

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