Research outline

Technology Development for More Efficient, Accurate River Discharge Observation

Observation using remotely operated boat equipped with ADCP

Installation of non-contact current meter
Left: ultrasonic Right: radio wave

ADCP observation data
(River cross section; colored according to velocity)
(Kokaigawa River Kurogo Observatory, March 15, 2007)

Measurement of discharge, the volume rate of water flow which is transported through a given cross-sectional area per unit time, is an important operation to appropriately conduct river planning and management. PWRI has been involved in improvement of measurement procedures and devices in this area and recently paid attention to river discharge measuring sensors using ultrasonic technology, which has made a remarkable progress in the private sector. While evaluating individual sensors for observation accuracy, PWRI also aims to establish new observation technologies using those sensors to achieve more efficient, accurate discharge observation.

This article presents the development of a discharge observation method that uses an acoustic Doppler current profiler (ADCP) and non-contact current meter.

An ADCP is capable of 3D calculation of water current by radiating ultrasonic waves downward to the riverbed and observing their reflection. Because it calculates riverbed data in addition to 3D current velocity, it is also capable of calculating discharge while the device cross the river vertically to the water flow. PWRI verifies the observation accuracy of this type of sensors in search of safer and more reliable observation methods.

A non-contact current meter uses a sensor mounted on a bridge over a river to radiate ultrasonic or radio waves on the river surface to find the frequency variation of the reflected waves (Doppler effect), and calculates surface velocity based on that value. It allows unmanned, real-time observation by using information transmission devices, such as fiber optics.

ADCP-based observation facilitates an understanding of river flow structure in order to reproduce the river flow based on numerical calculation at the time of flood. A non-contact current meter can be used for real-time, continuous river-flow measurement. A combination of these technologies is expected to enable lower-cost, safer, and more accurate discharge observation.

(Contact: Hydrologic Engineering Research Team, ICHARM)

Development of Technology to Reinforce Existing Damaged Tunnels

Load-carrying capacity test of a tunnel reinforcement method
(Thin lining reinforcement is provided inside the inner-wall concrete of a full-size tunnel in order to check the load-carrying capacity.)

Method using steel and spray fiber reinforced mortar and its fracture mode

As the number of aging tunnels has increased in recent years, adequate technology for repair and reinforcement of damaged tunnels is demanded. So far, when a tunnel has been damaged by the effects of excessive pressure due to the weight of soil, etc., no thin reinforcement method with sufficient reinforcement effect expected was available. Accordingly, high-cost, large-scale construction was sometimes necessary in tunnels without ample space inside.
To address this issue, the Team conducted joint research with the private sector to develop thin inner lining reinforcement technology that ensures sufficient load-carrying capacity even when ample space is not available in tunnel.
To develop the new thin inner lining reinforcement technology, an experimental device installed in PWRI that accommodates full-scale tunnel concrete (size: 10 m in diameter, 30 cm in thickness) was used to find out how much load it can withstand and to verify the reinforcement effects by clarifying the fracture mode.
The four reinforcement methods developed include techniques in which a material with an improved deformation performance due to mixing short or specially-shaped fibers that use concrete or partially-thinned PCL (pre-cast concrete lining: a method in which concrete products are made in advance at a dedicated factory and transported to the site for installation).
These reinforcement methods have been confirmed by the full-scale test to provide the same or higher load-carrying capacity as that of concrete of an undamaged tunnel, even if the soil on the upper part of the tunnel becomes unstable and soil weight equivalent to a regulated height acts as a load on the tunnel concrete.
The reinforcement methods that have been developed will be applied to tunnels damaged by pressure due to excessive soil weight, verifying the effect of the reinforcement methods as well as the durability of the reinforcement.

(Contact: Tunnel Research Team)