Holland is famous for its strong dikes. In 1995 the dikes proved their strength once again, when the water level in the rivers caused the government to evacuate part of the population. Luckily, at the end the dikes prove to be strong enough to resist the high water levels and immense pressure that was created. They didn’t break.
Dike builders and construction workers are involved in the construction process, the reparations and maintenance of the dikes. In the Netherlands are little over 45 professional dike builders; the number of construction workers that work under them exceeds that.
LaborThe work of the dike builders mainly consists out of manually placing natural stones or concrete columnar elements on the slopes of dikes and other banks Examples of these elements are:
- Columnar basalt blocks
- Vilvoord stone
- Doornik stone
- Maas stone
- Lessines stone
- Nordic and Drenthe blocks
- Basalton® columnar concrete blocks
- Pit-polygon columnar blocks
- Betonblokken systeem Leendertse
- Haringman blocks
- Square concrete blocks (in Dutch: ‘diabool betonblokken’)
- Hexagonal concrete blocks
- Groynes in the rivers
Construction, maintenance and repair.
Generally a shift consists out of two to five persons. Depending on the work (construction, repair, slope steepness, soil type, size stone sorting etc.) between 15-20m2 basalt can be placed on the slope every day. For basalton and other concrete elements the m2 that has to be done by hand is double due to the mechanical tools used at the preparation of the soil. When working along the North Sea coast working hours can range between 05:00 and 19:00 depending on the tides. Dike construction projects in the Northern part of the country are not affected by the tides but by the changing water levels. In the southern river area (on the east of the delta area known for its delta works) both the tide and the changing water level are of influence on construction process.
ConstructionAfter the core of the dike is completed and tamped, the revetment can be applied on the slope. Most of the time geotextile is first applied on the clay layer before placing a filtering layer. This layer can consist of:
- Rubble stone
- Brick rubble
- Phosphorus Slag
- Silex stone
- Steel slag
The elements are placed perpendicular on the slope by the dike builder. When working with natural stones the dike builder has to take into account the different sizes and shapes. To obtain a flat surface of the slope, each stone is placed individually. When the upper surface of a stone shows great unevenness, the dike builders can even it with a pickaxe. The dike builder has to be able to pick stones individually to connect well with the next one. The Dike builders get more skilled in the practice of placing stones in place, by rolling and lifting in the course of time.
Nowadays new slopes are being covered with concrete elements such as:
Basalton®, a combination columnar concrete stones with 6 to 9 surfaces
So called Hydroblocks® and pit-polygon columnar stones
In new construction projects, these factory-made concrete elements for the slopes are usually mechanically put in place. Yet even about 5% of handwork is required at the corners expansion joints, closures in gaps and stairs.
RestorationIn case of restoration of the slopes (maintenance and repair), the present elements have to be loosened and removed first. To do so the help of a hydraulic crane is often called in. After filling, leveling or possibly applying a new filter layer or filter construction, the stones are first cleaned of any dirt or other substance and then replaced in their position..
Working conditionsThe labor takes place in the open air. The work floor is almost always on an inclined slope. Except outer banks of dikes, which are fairly flat (1:15 to 1:20). The inclination of the slopes can vary between 15 º (1:4) to 45 º (1:1). Not only the inclination, but also the stability, type of soil and the evenness of the substrate are different at almost every construction site. In case of extremely difficult terrain the tools and building materials sometimes have to be manually transported to the construction site. Though, whenever possible a hydraulic crane or wheelbarrow is used to help the workers.
Physical strainThe physical demand of the dike builder is very high when stones have to be placed manually. This is caused mainly by the weight and poor handling of the columnar stones, the uneven and inclining slopes and the pace of work. The columnar stones of basalt weigh between 10 and 150 kilograms, the weight of concrete basalton columnar stones ranges from 25 to 90 kilograms. The heavier stones are maneuvered into place by rolling and lifting. This is being done in a typical bent posture. The dike builder always works from the bottom up, with his back uphill. The transportation of the columnar stones and other materials is primary done by machines; sometimes the dike builder has to do this by his self. A skilled dike builder is able to roll and lift the stone to the place where they have to be placed. Then he stands straight in front of his work with his feet in the right position. Finally he places the stones into position. In this way the physical stress is lowest. Lifting stones with rotated pelvis and stooped posture leads to (too) much physical stress. The amount of columnar stones moved on a daily base when working with basalton is higher than working with basalt; this is due to the height of the basalton columnar stones. An average of 300 to 350 basalt stones can be placed in position while the number of basalton stones is approximately double. Mechanical placing basalton and other concrete slope elements is also being done nowadays. The concrete columnar stone packages are placed into position with the help of a hydraulic crane with a clamp. The advantage of placing stones mechanically is that the physical strain is limited but that the dike builders craftsmanship stays indispensable.
StressTime pressure is uncommon, in case of emergency repairs though there could be time pressure. Working schedules are sometimes irregular, caused by the water levels and weather conditions. The dike builder is a pioneer, that’s why they work in groups of 2 to 5 people more or less isolated from civilization, sometimes assisted by a hydraulic crane and its operator
Measures and solutions:The mechanization of placing stones by hydraulic cranes with clamps enormously reduces the physical strain of the worker. On slopes not to steep this method can be applied very well. Repair work is done mostly by hydraulic crane nowadays. Removing damaged stones (partially) became much easier and physically less heavy with the arrival of these machines
The toolset of the dike builder traditionally consists of:
- crowbar, used for moving elements by punching and pushing
- pickaxe, used for smoothening the surface of the stone.
- small rake, used to scrape the filtering layer till equal heights of the stones are achieved.