AUTOMATIC DREDGING PROFILE AND CONTOUR CONTROL Jay Wise 1 ABSTRACT Phillips and Jordan, a leading excavating and disaster recovery contractor, was faced with the challenge to manage a civil contract involving creation of water storage ponds while simultaneously building development land elevation for the county of West Palm Beach through use of dredging. The objective was to dredge out several predetermined water storage ponds while sending the material through the dredge pipeline directly to the development area where excavating equipment was used to fill and grade 526 development hectares (1300 development acres) and adjacent mined out pits for Florida Power and Light. The biggest challenges where to adhere to the strict pond contours and meet the timeframe deadline. Kruse Controls, Inc. was subcontracted to develop an automation solution that would improve the dredge efficiency and control the cutter and ladder of the cutter/suction dredge to automatically follow the predetermined pond contours. Through the use of PLC control, RTK (Real-time Kinematic GPS) and Dredge location/logging software, the dredge 3.4 meter (11 foot) diameter cutter was automatically controlled to follow the actual predefined slope within + or 15.2 cm (6 inches). This feature eliminated over (or under) dredging and takes the guess work out of operator control. Keywords: Real time kinematic, global positioning system, elevation control, PLC, reclamation plan. INTRODUCTION When the Palm Beach County Water Authority purchased water storage rights from Palm Beach Aggregates, they specified the pond contours they required. There are six storage ponds on the property, ranging in size from 81 to 45 hectares (200 to 111 acres). Final depth will be 45 to 50 feet. The material - good quality shell and sand -- is being pumped about three miles away to a 504-hectare (1245-acre) development site, aided by two 3356 kilowatts (4500 horsepower) booster pumps. They are also filling an adjacent mined-out pit, which has been sold to Florida Power and Light. At the discharge, GPS-equipped bulldozers move the material into the final elevation and contour for the development property. Figure 1 is an aerial view of the project. The light green and dark, rectangular cells at top left are the ongoing project, which must be dredged to precise depth and side slopes. The dredge is pumping three miles to the small white rectangle at lower right center just under the inset photo. The largest dredged cell is 81 hectares (200 acres) and the smallest is 45 hectares (111 acres). Circle shows the dredge location and the inset is a close-up of the dredge and pipeline. 1 Kruse Control Inc., Office 443.460.0301, jwise@krusecontrols.com. 243
Figure 1. West Palm Beach water storage and development. Phillips and Jordan managed the contract to develop property land and create water storage pits in the West Palm Beach, Florida area. The operation is 32.2 kilometers (20 miles) west of Palm Beach on State Road 80, and is about 1416 hectares (3500 acres). The company recently purchased another 809 hectares (2000 acres) that will also be dredged. The task required dredging several ponds to make water storage while using the dredged material to fill nearby future development property. Each storage pond had specific county designs that Philips and Jordan had to adhere too (See Fig. 2). The designs included AutoCAD drawings with slopes and depths (See Fig. 1 for pond pit example) for the individual ponds. Additionally, the county imposed a time limit as well as bonuses for completion prior to time frame. The massiveness of the project and the need to create pre-determined profiles in the ponds, as well as a desire to optimize efficiency, led the company to seek an automation and management solution. They contacted Kruse Controls in July of 2005, and gave them the job. 244
Figure 2. Predetermined pond example. Prior to installing the automation system, the dredge operator was manually following the predetermined pond contours by watching the cutter depth and comparing it to the location predetermined depth as he swung the dredge and controlled the ladder and cutter speed. This was a very demanding and exhaustive task for the skilled operators. Additionally, the operator had to manually monitor two remote booster pump parameters as well as care for the cutter amps as not to stall the 1491 KW (2000 HP), 3.4 m (11 foot) cutter (See Fig. 3). Figure 3. Sam Houston dredge with 3.4 m (11 ft) cutter. 245
The automation included updating instrumentation and adding automatic control features to the existing Allen Bradley PLC system (See Fig. 4). New sensors and PLC code were installed to automatically monitor and control the cutter amperage and the booster pump pressures to relieve the operator of some of his demanding constant worries. Figure 4. Typical PLC. Dredgepack, a dredge location GPS logging software package, was installed along with a new software based graphical user interface to display parameters and real-time dredge plan view and profile view location of the dredge and ladder (See Fig. 5). Figure 5. Plan view of DredgePack showing the dredge to scale. 246
The main automation feature included integrating the DredgePack software to the PLC through use of custom OPC communication drivers. Additional modifications were incorporated into the DredgePack software to discern the difference in + or depth from the county supplied predetermined pond profile and the actual cutter depth. The system used Trimble RTK for position, heading, elevation and pitch which were resolved in the DredgePack software drivers to give exact location of the dredge ladder trunnion. Through the use of a draft transmitter and ladder inclinometer, the PLC was able to communicate the cutter X and Z offset from the ladder trunnion point, thus giving DredgePack the actual final elevation and location of the cutter tool. The software modification allowed DredgePack to send real-time exact deviation in 10ths of an inch of the cutters nearest point from the predetermined pond profile. This calculation actually took the cutter shape and size as well as the cutter angle into account for accurate positioning. The PLC code would react to the deviation as a process variable and control the hydraulic ladder proportional valve accordingly (See Fig. 6). Figure 6. Simulation of automatic contour ladder control. The operator could configure the DredgePack real-time logging software to depict actual cutter depths as colors or shades to represent the cut profile. In Figure 7, the dredge is swinging to a starboard side slope as can be view by the lighter brown shade (the chart is designed to show the lighter shade at shallower depths. This is operator customizable). The tow line can be seen slightly to the left of the plan cut line. As the dredge swings starboard towards the predetermined slope, the ladder automatically and accurately follows the contour and raises then descends again when swinging away from the slope in the port direction. 247
Figure 7. Shows actual pond slope in brown shades. This feature also works well when the dredge is facing a slope or corner. Phillips and Jordan explained that through the use of good internal management and the automation as well as the production reporting system, the operation production increased from 497,000 cubic meters (650,000 cubic yards) per month to 994,000 cubic meters (1.3 million cubic yards) per month. Additionally, the pond slope accuracy was improved to completely eliminate the need to fill over dredging or re-dredge upon final survey. Figure 8 shows a cross section cut of the actual survey versus the predetermined pond plan. The lighter line is the predetermined plan and the red line is the actual slope cut by the automation. It is noted that the actual cut, although it followed the slope, did not go down to the bottom of the plan. This is due to a feature built into the automation which allows for the operator to enter a manual offset above the final plan elevation so it will dig in steps. Figure 8. Shows accuracy of automatic controlled slope. 248
Figure 9. Zoom out of the dredge in a single pond. Note the swing and plan line patterns as well as the slopes. CONCLUSIONS Phillips and Jordan was able to exceed the county deadline and accuracy requirement with the automatic ladder slope control and real time data collection for immediate system evaluation and progress. This automation feature can be setup on any dredge. The level of existing controls of the dredge dictates the amount of modifications required to install the necessary equipment. In order to automatically control the ladder elevation, a PLC (programmable logic controller) system must be installed. The PLC (and internal algorithm code) is the heart of the Profile Control feature. PLCs today come in very small footprint packages. The PLC system will have to interface with a real time digging display and recording software package such as DredgePack. This software will reside on a computer (should be industrial grade computer on dredge) and connect to a GPS system (preferably RTK) which will update real time coordinates of the dredge trunion position and heading to the PLC through the software communication drivers. The PLC has input and output modules which need to be wired to devices on the dredge such as a ladder inclinometer (gives analog value of the ladder angle), draft transmitter (optional, gives analog value of the dredge draft), pitch and roll sensors (optional, gives analog value of the dredge deck heave), ladder up limit switch (gives discrete input to PLC upon upper limit) and proportional electric over hydraulic valves (controls speed and direction of ladder winch through PLC). With the input devices, the PLC calculates the actual location of the cutter bottom (or excavator tool) and compares the location and elevation with the desired profile or contour, which can be derived from AutoCAD or many other formats, and entered into the real time digging software package. The PLC code will constantly correct the position of the ladder through the hydraulic proportional valve (or VFD Drive if electric dredge) to force the cutter bottom to follow the desired contour as the dredge swings and moves. An elevation offset can be entered if the operator wants to dig the pattern above or below the contour. 249
If RTK (real time kinematic) is not incorporated as the GPS receivers, it will be necessary to use a tide gauge or tide stick to offset elevation for depth. This technology can be used to allow automatic elevation control for dredging channels, permitted reclamation plans, marinas, environmental and restoration plans. The use will assure accuracy and avoid filling or over dredging fines. 250