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Dynamic Load Testing DLT

PDR-system used for special bridge project in Cartagena, Colombia

 

For the highway from Cartagena to Barranquila, Colombia, the approx. 6 km long bridge “Viaducto Gran Manglar” is built just north of Cartagena through a shallow lagoon with mangroves.

 

Mangroves are protected vegetation and therefore a construction method with minimal environmental impact was required. The contract was awarded to the Italian contractor Rizzani de Eccher who proposed to build the bridge from a launching gantry, using precast concrete elements.

 

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This very special construction method – developed by Canadian piling & equipment company Berminghammer - has a minimal impact on the surroundings, because the footprint of the construction work is the same as for the bridge itself: the gantry rests on the front end of the already completed part of the bridge and cantilevers to the location of the next pier. At the front of the gantry the piles for the next pier are installed, while at the back the main girders of the bridge deck are installed. These girders (just as all other construction materials) are transported over the already completed part of the bridge instead of through the lagoon, further reducing the environmental impact.

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Essential for this construction method is the verification of the foundation piles’ bearing capacity for each of the 129 piers within hours after installation, because the piles will have to bear their maximum design load 72 hours after driving. For this reason Rizaani chose to purchase Allnamics PDR-systems and AllWave software, and have their staff trained on site by Allnamics. This enabled Rizzani to perform PDA and subsequent signal matching themselves, with Allnamcis support (both on site & remote). Rizzani also contracted Allnamics to perform the dynamic monitoring of the test piles and the development and implementation of the pile driving and acceptance criteria.

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The construction method with the launching gantry allows the entire bridge to be built with precast pre-stressed concrete elements. For production of these elements – piles, pier caps and bridge girders – a complete precast yard has been built next to the northern abutment of the bridge. All elements are then transported to the rear of the gantry, using the already constructed part of the bridge.

 

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The launching gantry consists of 2 parallel truss bridges, and  rests on 2 main support beams that are placed on already installed piers.  From there the gantry cantilevers approx. 50 m, just past the loacation of the next pier.  Running over the top of the gantry are 2 cranes and at the front there is a leader system, equipped with a Berminghammer B6505-HD diesel hammer.

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The hollow concrete piles with a diameter of 1,0 m and a length of up to 55 m are driven in 2 sections that are jointed together with a custom designed mechanical splice . The cranes move the pile sections from the rear to the front of the gantry where it is placed into the leader. Next the leader  is erected vertically, after which the pile section is driven. Once the pile section is installed the leader is lowered back to the horizontal position sothe next pile section can be accepted.

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After all 6 piles for the pier have been installed, they are cut off and a precast concrete cap is mounted over the pile heads. Once a temporary support is placed between this pile cap and the gantry, the front main support can be moved to this new pile cap and the rear main support is also moved up one pier. Then when both main supports are in their new position, the whole gantry is moved one span forward (approx. 37 m), with the leader ending up just past the location of the next pier to be constructed. But before the piles for that pier are driven , the girders for the bridge deck are mounted up to the just finished pier.

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With the launching gantry working at its normal pace, this installation cycle takes 3 days. For that reason the piles will get their maximum design load after 72 hours, when the gantry with leader cantilevers just passed the freshly installed pier cap. In each cycle, the pile bearing capacity needs to be verified in time for that.

 

Rizzani started piling at the north end of the bridge in August 2016 and will soon start with a second gantry at the south end.

 

For dynamic pile monitoring on two fronts Rizzani has purchased a second PDR-system.

 

 

Video of Berminghammer.

 

New service – > Strain gauge monitoring

 

February 2017. After several succesful testprojects Allnamics adds this new monitoring technique to her portfolio of services: (dynamic) strain monitoring with strain gauges directly glued-on the (steel) surface.

 

Allnamics has been involved in (dynamic) strain gauge monitoring for a long time, mostly for PDA (Pile Driving Analysis) monitoring during impact driving of foundation piles. Because the sensors have to sustain severe dynamic loads during impact driving (accelerations up to than 1000 x gravity or more), the strain sensors are traditionally bolted in holes that are drilled in the pile wall.

 

However, drilling is not allowed or simply impossible in more and more cases. Allnamics has been able to solve this issue by glueing the strain gauge and its sensor cabling directly on the steel surface.

 

This technique has been succesfully used for PDA-moniotring during a pile driving test in Kinderdijk (NL) and during installation of monopiles for several offshore windfarms. The same technique, that in principle can also be applied for other sensor types or larger elements, has been used for a structural health monitoring project near Delfzijl (NL), with the sensors functioning for several months.

 

You want to learn more about this service?

 

Take a look at our product page strain gauge monitoring or contact us.

 

Dynamic Pile Testing for Amstel Towers Hotel in Amsterdam

 

In April 2016 Allnamics has performed PDA-monitoring and DLT-testing for our client Voorbij Funderingstechniek BV, for the Amstel Towers Hotel near Amstel station in Amsterdam. The tests were done on 51 m long precast concrete piles, driven in sections, with a mechanical joint.

 

PDA monitoring (Pile Driving Analysis) was done during full installation cycles of selected production piles. Main goal of the test was to check the tensile stresses during driving, in particular at the location of the mechanical joint.

 

DLT-monitoring (Dynamic Load Testing) was done during restrike (approx. 10 blows) on piles that had been installed a couple of days earlier. Main goals of this test were to check the strength of pile shaft and joint and the static bearing capacity  of the pile.

 

Both tests were performed with the in-house developed Allnamics PDR-system, fitted with combined strain and acceleration sensors, which were mounted near the pile head. The PDR reads and stores the monitoring data real time and transmits them with a wireless connection (by WiFi) to the field computer of the monitoring engineer. The wireless connection offers great advantages during upending and positioning of the pile and makes it possible for the monitoring engineer to do his monitoring job on a good location, at a safe distance from the pile and without traditional worries about the long cable getting stuck or damaged during handling or piling.

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Photo 1 : Monitoring with WiFi connection, at a safe distance from the pile

The tests showed that the tension stresses during driving were acceptable and that the available static bearing capacity is sufficient for the design loads of the piles.

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Photo 2 : no trouble with long cables during upending of the pile

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Photo 3 : pile and monitoring equipment at end of PDA