Research results

Estimating the shear strength behavior of weak layers in rock mass

Figure 1: Weak layer in rock mass

Figure 2: A shear strength simulation model

Figure 3: Results of simulating shear strength behavior of weak layer

Weak layers such as faults and joints occasionally are contained in rock mass (Figure 1). Because such weak layers have relatively low strength compared to the surrounding rock mass, they can interfere with construction. Ordinarily, in-situ shear tests are conducted to accurately ascertain shear strength of rock mass. However, because in-situ shear tests require shaping-such as cutting out a block of rock mass with a base area of 60 x 60 cm and height of 30 cm from an adit-they are costly in terms of both time and expense. Moreover, when weak layers are intercalated in rock mass, it is often difficult to conduct the test mass shaping due to softness. This limits the cases in which in-situ shear test can be used.

To address this problem, the Geology Research Team developed a new shear strength simulation model that is based on interlocking of the rock joint surfaces. The concavo-convex shape of joint surface of weak layer is relatively easy to be obtained. The simulation model sequentially displaces upper and lower concavo-convex profiles of irregular surface of weak layer in increments of 0.5 mm (Figure 2). It results that overlapping concavo-convex shape profiles predicts an area of shear resistance locations and estimates shear strength (Figure 3).

The application of this new simulation model to geological surveys of foundation rock for dams and slopes, etc., will improve the reliability of shear strength evaluations. It will by supplement conventional in-situ shear tests and help to reduce test costs.

(Contact: Geology Research Team)

Effects of Installing Wind/Snow Protection Facilities at Ports
- Improvement in Work Efficiency in Cold, Snowy Regions -

Removing fish from nets in a cold environment at a port in winter

Removing fish from nets (after the installation of wind protection facilities)

Graph showing improvement in work efficiency
Pegboard: a test to insert pegs in holes
Tapping: tapping a counter with an index finger

Wind/snow protection facilities at ports
People working at harbors and fishing ports in cold, snowy regions like Hokkaido are exposed to extremely severe conditions, including freezing temperatures, strong winds and snowstorms. Under these poor working conditions there are concerns for a decrease in work efficiency and safety issues including freezing pavements, diminished attention and effects on health of elderly people. In order to improve the severe working conditions in winter, wind/snow protection facilities are installed close to quay walls of ports.

Work efficiency improved by wind/snow protection facilities installed at ports
Wind/snow protection facilities installed at ports have been said to have effects on improvements in sanitary control, working environments and the like. Since there were no specific numerical measurements to show the effects, research has been conducted to quantify improvements in working environments and work efficiency.
Experiments to determine the relationship between WCI (Wind Chill Index: a heat factor to appropriately express psychological responses such as wind-chill temperatures of people working in cold environments) - calculated from wind speeds and air temperatures - and work efficiency were conducted and the results shown in a graph on the right were obtained. With this graph, it has become possible to estimate the difference in work efficiency based on the temperature at site and differences in wind speeds before and after the installation of wind/snow protection facilities.
A reduction in working hours can be calculated by multiplying the improved rate of work efficiency by the working hours, and quantification of improvement effects of wind/snow protection facilities installed at ports has become possible.

Creation of guidelines for wind/snow protection facilities at ports
Guidelines describing basic concepts for research, planning and designing of wind/snow protection facilities to be installed at ports were created to help the smooth implementation of the process for those who wish to build such facilities. Improvement effects of wind/snow protection facilities that can be envisaged are categorized and included in the guidelines. The outcome of research by CERI - Quantitative Evaluation Methods for Improvement of the Working Environment and Work Efficiency - is also included in the guidelines.

(Contact: Port and Coast Research Team,CERI)