The Design of Safety Monitoring System for Navigation Hubs Built in Plain Area

Abstract

Navigation hubs built in plain area usually have large space span and compact structure layout. Safety monitoring performance, especially the surface deformation monitoring performance, is sensitive to the monitoring distance and structure features. Thus the monitoring system should be elaborately designed to meet the requirement of accuracy and robustness. Conventional approaches for surface deformation monitoring are time-consuming and suffering from low accuracy. In this paper, the designing strategies and monitoring techniques for surface deformation monitoring in Jiepai Navigation Hub, a typical navigation-power hub built in plain area, are demonstrated. The monitoring result shows that the designed monitoring system has good performance both in accuracy and robustness. The designing strategy can serve as a reference for other similar projects built in plain area.

1 Introduction

Surface deformation monitoring is an essential part of safety monitoring system for waterway infrastructures. The deformation data serves as one of the most important bases for assessing structure running state. The accuracy and robustness of surface deformation monitoring system, however, depend strongly on monitoring approaches and structure features. Manual observation, GNSS and sensor monitoring are the three main methods for surface deformation monitoring in hydraulic engineering (Ding et al. 2022; Zhou et.al. 2022).

Manual observation using the total station and the electronic level is the most widely used method due to the low cost. However, navigation hubs built in plain area usually have large space span and complex structure layout. Monitoring accuracy can be easily reduced due to error accumulation along the long monitoring distance. Intervisibility between monitoring points and datum points may be destroyed by the complex structure layout. Moreover, manual observation is time-consuming and labor intensive, thus the real-time monitoring cannot be achieved.

GNSS, i.e. Global Navigation Satellite System, is a rapidly developing method in deformation monitoring area (Huang et al. 2018). This method is based on satellite positioning technology, deformation data is automatically computed from the distance between satellites and monitoring stations. The accuracy can hardly be influenced by space span or structure features. The cost of GNSS, however, is relatively expensive. Thus it is uneconomical to design a large number of GNSS monitoring stations for navigation hubs with large space span.

Sensor monitoring is another widely adopted monitoring approach (Yan and Li 2002; Li and Li 2002). The surface deformation is automatically measured by a set of sensors and then collected by the monitoring platform software, thus the real-time monitoring can be achieved. The cost for sensor monitoring is lower than GNSS method while the accuracy is relatively higher. Installation space, however, must be ensured for facility installation and maintenance.

Jiepai Navigation Hub, which serves as a key waterway project on Xinjiang River in east China, is a typical inland navigation hub built in plain area. Diverse structures including the navigation lock, the overflow dam, the flat slab dam, the sluice gates, the concrete dam, the earth dam and the hydro-power stations are assigned compactly along the long engineering axis. Difficulties are experienced when designing the surface deformation monitoring system. This paper introduces the designing strategies of surface deformation monitoring system for Jiepai Navigation Hub. Solutions to the difficulties including the low deformation monitoring accuracy for long-axis structures and the lack of construction space are stressed. Some representative monitoring results are also exhibited and analyzed. The designing strategy can be used as a reference for other similar navigation projects.

2 The Designing Strategy of Surface Monitoring System

2.1 Layout of the Project

The layout of the project can be seen from Fig. 1. Diverse structures are assigned across Xinjiang River between the left bank and the right bank. A road bridge is also built on the top of water retaining structures. The overall length of engineering axis is about 1.0 km. The project layout is complex and the monitoring distance is much longer than ordinary hydraulic infrastructures.

Fig. 1.

The layout of Jiepai Navigation Hub.

2.2 The Designing Strategy of Surface Deformation Monitoring System

According to the discussion in Sect. 1, GNSS method and manual observation method have significant disadvantages in economical cost or monitoring accuracy. Then sensor monitoring method turns to be an appropriate choice as the cost and the accuracy are satisfying. Two kinds of sensor systems, hydrostatic level system and tension wire alignment system are thus applied for vertical deformation monitoring and horizontal deformation monitoring respectively.

The navigation lock and the main water retaining structures, including the sluice gates, the flat slab dam and the overflow dam, are the primary monitoring objects. As the measuring points in tension wire alignment system should be built along a straight line, the monitoring system is divided into 5 independent sub-systems according to the structure feature. The sketch of the system can be seen in Fig. 2.

Fig. 2.

Sketch of surface monitoring system.

To give a detailed illustration, the designing detail for right lock wall is shown in Fig. 3. The right lock wall consists of 11 independent blocks. The water level in lock chamber varies significantly and frequently as ships keep driving through the navigation lock. The deformation of each block is of great concern as the blocks are in complex loading conditions. Thus sensors, including hydrostatic level sensors and tension wire alignment sensors, are placed near the center of block surface. The inverse plummet device and double-metal pipe device are employed as the horizontal displacement datum point and vertical displacement datum point respectively. All the sensors are connected into the safety monitoring platform, thus the deformation can be measured and collected automatically.

Fig. 3.

Layout of measuring points for right lock wall.

2.3 Solution to the Lack of Construction Space

The above designing strategy successfully guarantees the feasibility and accuracy of the monitoring system as the sub-system are independent and the measuring distances are reduced to no more than 200 m. Difficulties, however, such as lack of construction space still exist. Auxiliary facilities are thus needed. The implementation of overflow dam monitoring system is a typical example. As can be seen from Fig. 4(a), sensors are placed on the top of the pier with narrow space. No passageway is available for sensor installation. To solve the above problem, a steel auxiliary bridge is designed. The sketch can be seen from Fig. 4(b). U-bars are fixed on the both sides of the piers and the auxiliary bridge is placed on the U-bars. Bearing capacity is examined by calculation and in-situ testing. Figure 4(c) shows the completed bridge. The passageway for installation and maintenance is thus ensured.

Fig. 4.

Layout of sensors and auxiliary bridge for overflow dam.

3 Working Principles of the Monitoring System

3.1 The Hydrostatic Level System

The hydrostatic level system is built according to the principle of connected vessels. As can be seen from Fig. 5, the sensors are connected by tubes and filled with fluid. At the initial moment, the surface of the fluid in each sensor are at the same elevation. The fluid height is measured and recorded as h₀, …, h_i, …, h_n respectively. Thus we have:

$$ H_{0} + h_{0} = H_{i} + h_{i} = H_{n} + h_{n} $$

(1)

where H stands for the structure elevation. At the current moment, the structure experienced some deformation, and we have:

$$ H_{0}^{*} + h_{0}^{*} = H_{{\text{i}}}^{*} + h_{{\text{i}}}^{*} = H_{{\text{i}}}^{*} + h_{{\text{i}}}^{*} $$

(2)

where the superscript “*” stand for the current moment. Eq. (2) can be rewritten as:

$$ \begin{aligned} \left( {H_{0} + \Delta H_{0} } \right) + \left( {h_{0} + \Delta h_{0} } \right) = & \,\left( {H_{i} + \Delta H_{i} } \right) + \left( {h_{i} + \Delta h_{i} } \right) \\ = & \,\left( {H_{n} + \Delta H_{n} } \right) + \left( {h_{n} + \Delta h_{n} } \right) \\ \end{aligned} $$

(3)

With:

$$ \Delta H = H_{0}^{*} - H_{0} ;\;\Delta h = h_{0}^{*} - h_{0} $$

(4)

Thus the vertical deformation of the ith measuring point can be obtained:

$$ \Delta H_{i} = \Delta H_{0} + \Delta h_{0} - \Delta h_{i} $$

(5)

where $\varDelta H_0$ is measured by double-metal pipe device (datum point), $\varDelta h_0$ & $\varDelta h_i$ are measured by “sensor 0” and “sensor i” respectively.

Fig. 5.

Sketch of hydrostatic level system.

3.2 The Tension Wire Alignment System

The tension wire alignment system is made of deformation sensors, datum points (inverse plummet device), and tension wire device. The system is assigned into a straight line and the tensioned wire goes through each sensor. As can be seen from Fig. 6, the relative horizontal displacement ($\varDelta S_i$) between the wire and the structure is measured by the ith sensor. The true deformation then can be obtained with the correction of datum points ($\varDelta S_{j1}$, $\varDelta S_{j2}$).

Fig. 6.

Sketch of tension wire alignment system.

4 Monitoring Performance

To evaluate the performance of the designed system, some typical monitoring results are demonstrated and analyzed. The monitoring data of sensor 5–7, which locate on the middle part of the right lock wall blocks, are chosen. Deformation curves are plotted and shown in Fig. 7. As can be seen from the figure, the deformation curves are smooth with slight perturbations. The vertical displacements of the 3 sensors are very close, indicating that no inhomogeneous vertical deformation occurs between blocks. The horizontal displacements, however, are different. The maximum difference between neighboring block can reach 4 mm. The result implies that the horizontal stiffness of the lock wall blocks have slight difference though they have the same structure formation.

The deformation increments between adjacent measuring times, as can be seen, are no more than 1 mm. The accuracy of GNSS method, however, is about 2.5 mm and 5 mm for horizontal deformation measuring and vertical deformation measuring respectively. Thus the designed monitoring system exhibits its advantage in accuracy.

Fig. 7.

Deformation curves of typical blocks in right lock wall.

5 Conclusions

Surface deformation monitoring system designing is challenging for navigation hubs built in plain area, due to the long engineering axis and the complex structure layout. In this paper the monitoring system designing strategy of Jiepai Navigation Hub is demonstrated. The whole system is divided into 5 independent sub-systems according to the structure feature. The monitoring distances are thus reduced to appropriate values. By comparing different monitoring methods, the sensor method is chosen as the main monitoring approach. The problem of lacking construction space is solved introducing auxiliary facilities. The monitoring results indicate satisfying performance of the designed system. The designing strategy can serve as a reference for other similar projects built in plain area.