B4 Ground investigation
The term ground investigation refers specifically to the investigation of subxsurface soil, rock and groundwater conditions, either through intrusive methods (principally boreholes and trial pits and the associated soil/rock sampling and testing) or surface and borehole geophysics. Ground investigation methods are described in numerous textbooks including more recently Clayton et al. (1995), Simons et al. (2002), Cornforth (2005) and Bond & Harris (2008), for example.
Ground investigations for low-cost roads can often be low on the priority list. They are sometimes seen to be costly and time consuming, providing little information of any value. However, if planned and implemented correctly, they can yield valuable information when compared to the cost of design.
Ground investigations are undertaken for new roads to determine:
typical soil and rock profiles to calibrate and augment the terrain models, terrain classifications and field mapping referred to earlier (Sections B2 & B3);
specific soil and rock profiles in the case of deep cuts for site-specific design;
foundations for structures, such as bridge piers and abutments and large retaining walls;
depth and geotechnical composition of existing landslides and the design of remedial works; and
material type and depth for borrow areas.
landslides that were not stabilized during construction; and
new landslides and road failures that have occurred since construction.
Figures & Tables
This book provides a complete guide to the study, design, construction and management of landslide and slope engineering measures for mountain roads, with an emphasis on low-cost. The geographical focus of the book is on the tropics and sub-tropics, but is also highly relevant to other regions where heavy rain, steep slopes and weak soils and rocks combine to create slope instability. The causes and mechanisms of landslides are described, and the hazards they pose to mountain roads are illustrated. Methods of desk study, field mapping and ground investigation are reviewed and illustrated, with an emphasis on geomorphological and engineering geological techniques. The design and construction of alignments, earthworks, drainage, retaining structures, the stabilization of soil slopes and rock slopes, and the control of erosion on slopes and in rivers and streams are covered. Slope management as part of road maintenance and operation is reviewed, and procedures for risk assessment and works prioritization are described.