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Stadium Hemsbach – A new sports landscape with an artificial turf pitch is being created
By Marc Lukowski, S. Lukowski + Partner, Darmstadt
The sports facilities at Hemsbach, Germany, were originally a natural grass pitch with a cinder circumference running track, clay and grass surfaces as well as a further clay pitch and a full size natural grass pitch. A section of untended grass was used as a kick-around play area. Many years of use solely for football by the club brought about a new way of thinking. With participation from the population the city decided to create a sport and leisure centre for all sectors of the population and all generations on this enormous area near the Wiesensee Lake.
Implementation of this project was carried out in two construction phases. Construction of the sport facilities was started mid May 2015 followed by construction of the surrounding leisure-time facilities which was started in autumn of 2015 and accompanied by the landscape architects Schelhorn Landschaftsarchitekten from Frankfurt am Main, Germany.
At the site of the existing cinder running track and grass pitch, competition facilities similar to the Type C grade with full-sized artificial turf pitch and polymer-surface running track was installed.
The field and track athletics area of these competition facilities are made up of a 400-lap circular track (4 lanes) with an integrated sprint track on the west side which can also be used as a 110-m-hurdle track. The southern segment area, like the pitch, was given an artificial turf surface and can be used as a warming-up and goal training area. The northern segment, like the running track, was given a polymer surface and is used for field athletics. A long-jump pit with two approach tracks is planned while the existing high-jump pit will continue to be used and relocated to this area.
A cast-liquid, waterproof polymer coating, 15 mm thick was installed as per the standard DIN 18035, part 6. Despite the high installation costs, the low maintenance costs and longer working life are advantages of a cast-liquid surface compared to water-permeable surfaces.
The artificial turf system was installed according to the standard DIN 18035, part 7 with a green artificial turf system with 40-mm-long fibers and pol filling. The surface made of stabilised polyethylene was laid on a further waterproof elastic layer, ensuring that long-term elasticity and energy absorption is provided. The surface was cast on-site with a finisher.
Small artificial turf pitch
The existing grass training pitch was replaced with a small artificial turf pitch. This pitch lies in an almost east-west direction and has a total area of 54 x 74 metres. Taking into account the open areas in front of the ball nets, this means a total playing area of 50 x 70 metres. The construction of the artificial turf system corresponds to that of the large playing field.
The main entrance to the sport areas remains as it was previously and entry is gained through the gate at the end of the carpark so the south-west of the small playing field. The new artificial turf pitch borders on the existing concrete paths on its southern side. This path will be maintained but requires comprehensive adjustments due to the gradient situation.
Along the northern side of the small playing field there is only a 50-cm-wide stone strip defining the edge of the mowing and maintenance area. At the top end, a two-metre-wide strip behind the run-out area and the ball nets was laid in concrete paving slabs. The circumference running track has a maintenance path, also made of concrete paving slabs running its whole length, which is also as for standing places for spectators and includes the storage space for mobile junior-size goal nets. In the area of the existing stadium seating, the paved area was continued right up to the lower edge of the terraced seats. To the left and right of the buildings the paths were changed slightly and a maintenance path to the playing areas leads through a double gate in the spectator entry gate.
The scope of usable playing surface was reduced so that the construction measures of the renovation work did not create a need for more parking spaces.
Fencing and ball nets
At the top edge of the full-size artificial pitch, 5 and 6 metre high ball nets were installed covering practically the whole width of the pitch to prevent interruptions and possible injury to players when both pitches are used at the same time.
Along the whole length of the running track, spectator barriers made of steel piping (height approx. 1 metre (were installed) with openings approx. 1 metre wide allowing access to the pitch and the player dugouts. Access for maintenance vehicles is gained through a double barrier gate at the west side of the running track. To prevent vandalism and misuse, the whole playing areas are surrounded by a boundary fence. The existing outer fence of the sports centre were made use of and expanded. At the western side a new length of fence was necessary to close off the sports facilities from the rest of the leisure-time activity area.
At the start of the planning work, the club requested installation of an LED flood lighting system for the competition and small pitches. After clarification regarding the surrounding residential area and evaluation of the possibilities of installing an LED system, the Ingenieurbüro Teichelmann IBT Company, was given the task of drawing up an expert report. In accordance with the results of this inquiry, two 20-metre-high floodlight masts were installed on the west side of the pitch and three similar masts on the eastern side with an additional 18-metre-high mast at each apex of the running track to the north and south. Due to the light emission values, the system requires use of a total of 17 vertical floodlights with halogen-metal vapour lamps which are also fitted in some places with shades and screens to reduce the light emission for the neighbours. For the smaller playing field, a system of four 16-metres-high masts, each with a floodlight, was sufficient. It was decided against use of LED floodlights however, to prevent unavoidably exceeding the light emission values and for financial reasons.
The floodlight switching system makes it possible to illuminate either the whole pitch or just either half of the pitch so that an economic solution is always possible as required. In order to reduce the danger of the masts being struck by lightning, the masts themselves as well as all newly erected metal fences and barriers are grounded using an equipotential bonding system. This was created using a grounding band of stainless steel installed in the ground around the whole playing area. In addition, the masts were also fitted with step voltage protection (wire meshing squares made of stainless steel bands in the foundations). This can however only reduce the danger of lightning striking but cannot prevent it. Outdoor sports fields should be evacuated in all circumstances during storms. Both playing fields were also equipped with training lights of at least 80 Lux lighting strength. The field athletic areas and the southern segment fitted with artificial turf can also be illuminated in such a way that they can be used for training purposes.
Due to the unsuitable subsoil conditions and the high groundwater level, natural draining of rainwater is not possible. This made it necessary to connect the drainage system of the playing areas to the standard drain system to allow rainwater to drain off.
The artificial turf systems are water permeable meaning that surface water is absorbed into the construction system and then runs into the drainage system. A rain channel was installed along the inside edge of the running track and to remove surface water from the polymer and artificial turf surfaces. An open channel system was chosen to keep cleaning simple. This also made it possible to keep the system at the same height through all intersections of the different segments and playing field areas to the running track. The 5-cm-high raised edge required by competition regulations for field and track athletics was not installed. As far as possible, the surrounding paved areas were laid with an outside camber so that any surface water flows onto the surrounding area where an approx. 1-metre-wide recess was built to allow the water to slowly seep away.
According to the results of a subsoil examination, the substrate is practically impermeable for water so installation of a drain system according to DIN 18035 to allow homogeneous drainage of the playing surfaces was necessary. At a distance of every 6 metres, drain feed lines were laid and filled with seepage packing of gravel or gravel sand. These all intersected at a drainage collection point at the ends of the pitches. Further drainage lines were laid along the inside of the running track and in the area of the clay shot-put pit. Use of corrugated plastic perforated full or semi-drain pipes and installation of drain packages where water can be absorbed, a slowing effect of the run-off and distribution of water into the substrate can be achieved along the flow lines of the draining system. This means that according to the construction of the drainage system, short-term storage of the run-off and reliable draining of the remaining amount into the main drains. Maintenance and access manholes were installed to allow revision and cleaning work to be carried out.
The playing behaviour of an artificial turf system can be optimised by watering. In addition, the temperature of the playing surface, which in summer can be higher than 50 °C, can be reduced. Near the full-sized pitch a relatively new irrigation system was already installed and it was considered using this pipe system. Following a pressure check, this idea was abandoned however, to prevent later damage and comprehensive repair work being necessary under the newly laid artificial turf surface.
The underground irrigation system is run in sections by an electrical control device. The small artificial pitch was also installed with an extension of the irrigation system with additional sprinklers. The control systems for irrigation as well as floodlighting for both pitches are operated centrally from a key control panel in the technical building near the small pitch.
The two goals on the full-size pitch are installed in sleeves and can be removed. The junior-size goal nets are hung in mobile frames which are fitted with safety weights during use to prevent them falling over. Storage areas for these mobile goal nets were paved at the edge of the pitch and outside the running track. At the full-sized pitch, two dugouts with benches for substitute players were built. The existing terraced seating was kept and renovated in places by the club. A beech hedge was planted in the area between the two playing fields to achieve an optical division between the two pitches. At each end of this hedge, trees were planted to provide shade for school classes for example, during their sport lessons.
In front of the hedge and oriented towards the running track is a seating area. To make the sports facilities seem less technical and to create a mutual link to the bordering open playing area, shell-limestone blocks were positioned along the path and in the greenery of the wall. A woodchip jogging trail (Finnenbahn) was built around the open play area. At its highest point along the eastern wall and the competitive running track, a view can be gained of the whole sports facilities. Individual Robinia or locust trees hold the slope and provide additional "hurdles".
Particular challenges were faced during the construction work due to the extremely difficult and inhomogeneous subsoil formation combined with a very high groundwater level. The foundations for the floodlights in particular required comprehensive static and ground-mechanic calculations in order to ensure a safe and stable footing. Stabilising measures were also required for creation of the base grade for installation of the playing surfaces and paths. Following weeks of drought and dryness, a series of rainy days at the end of the summer prevented complete installation of the artificial playing surfaces. This work had to be stopped in November 2015 due the weather conditions and was then completed in spring of 2016.
Despite the overall difficult building conditions, a very good cooperation between the owner (building authorities and ISEK), the building company Strabag Sportstättenbau GmbH from Dortmund and the planning offices S. Lukowski + Partner, allowed a very good result to be achieved which will provide pleasure for the citizens and athletes of the city of Hemsbach for a long time to come.
More information is available at www.SL-plan.de
Photo: S. Lukowski + Partner