About This Project
Murphy Surveys was contracted by an engineering consultancy following an incident where a culvert running below the railway embankment was struck twice during stabilization works following a land slip. The sheet pile wall and anchor both struck the culvert in two different locations and we were required to ascertain if the design of the stabilisation structure was at fault or if the problem lay with the poor as-built information supplied by another contractor.
-We were required to verify the position of the design in relation to the OS grid and datum together with the originally supplied as-built information. This was achieved by using Realtime Kinematic GPS to set up a baseline and verify the existing site control which was used for setting out purposes.
-We needed to determine if the anchors had been installed to the correct angular position in both the horizontal and vertical axis as well as the position and alignment of each individual sheet pile. Laser scanning was used to survey the sheet piles which were recessed behind the capping beam and associated anchor positions which extended from the structural support beam.
-An as-built of the culvert running below the site was also required. Due to the confined space access of the structure, we opted to use a laser scanner to pick measure the alignment and levels within the culvert.
-Our findings determined that the overall project grid was approximately 1.2m out of position based on comparisons between the supplied controls and our GPS results.
-From the scan data we were able to give an indication of the angular position of the anchors as they entered through the sheet pile wall and into the embankment. Due to the very short length of the anchor that was exposed we could only provide an indicative direction of the drill but it was enough to confirm the general direction. A CAD drawing showing the anchor position in 3D was produced to show this information in plan and an isometric view with angular measurements.
-The scan data from the culvert allowed us to pick up the position and the size of an obstruction within the culvert. This was caused by earth falling through a hole created by the sheet pile striking the top of the culvert. The original as-built position of the culvert showed that the alignment, horizontal position as well as the crown levels were incorrect. This was the primary cause of the clash between the sheet pile wall design and anchor 13 which struck the culvert further down.
Poor as-built information can cause costly problems later during the design and construction phase. It is important to use a competent and experienced survey company