Earthwork for foundations

The earthwork for foundation has been done in order to facilitate hacking of piles, grouting and testing of piles and construction of pile caps. During this phase of work a Komatsu PC 200 hydraulic excavator was used for excavation and other related work for excavation such as filling material transportation, removal of hacking material, and aiding other tasks as shoring and dewatering.

Shoring

Shoring has been done to ensure the safe working environment for the workers and also to reduce the effect of disturbing the surrounding soil structure due to the deep excavations that was being carried out. H-girder with timber planks has been adopted as the shoring method in this construction project. The typical design is shown in the figure 2.1. The temporary bench mark has been utilized to assign the necessary levels. As the first step in the shoring installing process, the setting out of the shoring line was carried out. This was done utilizing the already established grid lines and marking the necessary offset so that at the end the front facing of the shoring will be aligned with this offset. The line was marked with a thread at the TBM level on the existing ground in between two poles driven in to the ground. Then the places of vertical H-girders were marked on the ground in 1 m intervals.Figure 1.1 - Typical detail for shoring

After that auguring was done using manually handled tools such as hand augur. This auguring process was carried out until the necessary depth was achieved. In case of meeting the sand layer below the water table where the auguring is unable to remove sand, a tool with a non-return valve was used to remove sand along with water. And also a PVC pipe of 200 mm diameter was installed when a sand layer was encountered to prevent the collapsing of internal walls.After reaching the depth TBM-4.0 the 150 x 75 H-girder was installed and the top was aligned to the level given by the thread. This was done either hammering the girder down or lifting it and filling the augur hole with some hard material to make the bottom hard and redoing the H-girder.Figure 1.2 - Auguring for H-girder installation

Then the Waller was welded on the outer side of the area to be excavated. A 200 x 100 girder was used as the Waller. While this was carrying out, marking of the supports were done. For this, another thread was used to mark an offset of 2.350 m from the previously marked line to accommodate the Waller bar and the horizontal support. The auguring was done as before up to a depth of 1.5 m from TBM. Then the H-girders for both the support structures has been installed and welded providing the splices to ensure the proper connectivity between the members to sustain in transferring the tensional loads. The rest of the shoring was done along with the excavation process.

Excavation

The excavation was done starting from the H-girder line so that the timber planks can be inserted. The timber planks used were of 50 mm thick mango wood. This is done in layers as shown in the diagram below (extracted from the respective method statement) and in parallel to that insertion of the timber planks was done. In this process, each of the timber planks were cut in to the necessary dimension after measuring the exact width between the H-girders to account for the deformations occurred while insertion. Figure 1.3 - Excavation process after shoring structure done

Dewatering

Due to deep excavations the seepage and surface runoff at rain causes collection of water inside the excavated areas making the soil condition worse than ever. Due to this, submersible pumps were used to pump out the collecting water. Each submersible pump was connected to the main pipe line with flexible pipes and the collected water was discharged to the environment after sending through a sedimentation tank and a filtration tank.

Formwork for foundation, columns, beams and slabs

Foundation

The substructure for the particular building was consisting of piles and hence the formwork for foundation can be considered as the formwork for pile caps. Excavation for the pile caps were deep and it was not efficient enough to use timber or steel for the formwork due to both constructability and strength wise issues. Hence it was used a permanent formwork out of blocks.

Figure 2.1 - Poor ground condition due to water seepage

Since the excavation depth was much below the ground water table, it was not possible to start the block work at once. Hence the existing ground was prepared with rock boulders and made the ground to the necessary level. Then a screed layer was done with further maintaining the level surface.

Figure 2.2 - After ground preparation was done

Due to the existing seepage at some places remedies for leakages through the screed layer was had to be taken.The procedure after that is stated below. Setting out for the block work was done on the screed layer. Since the structural drawing was issued without considering the allowance for the water proofing membrane, the setting out was done allowing a 10 mm per layer. The bock work was carried out using solid cement blocks of 200 x 190 x 390 with 1:6 cement sand mortar. The maximum height of block work carried out in a single day was 1.2 m. The top of the formwork was made to the level with the allowance for the water proofing membrane.With those steps, the formwork for the pile caps were finished.

Figure 2.3 - Setting-out for formwork

Figure 2.4 - Finished formwork

Columns

2.9.1 Introduction

In this project it was used to utilize conventional formwork but due to the effectiveness, the site management proposed of utilizing KumKang Aluminium formwork system. This was once used for a previous project by Sanken and it was available for the use. Selecting formwork items has done carefully since the parts were not fabricated for our project.

KumKang aluminium formwork system consists of 20 types of components including wall panels, slab panels, beam bottom slab panels as main components and wedge and round pin, wall bracket as connecting accessories.

2.9.2 Process

Setting out of columns is the first step in the process. This is done with the aid of the offset lines established earlier. Then the required wall panels are chosen to correctly size the column. Since the kicker was not casted along with the basement slab, two plywood pieces of 12 mm thickness and 100 mm width with the length equals to the width of the square column and another two pieces of the same plywood with the same width but the length 200 mm greater than the previous ones were nailed to the floor slab keeping the inner edge on the markings to aid installing the formwork panels. Then the formwork panels were erected and attached to each other so that they keep supporting each other to stand still. After fixing all four panels, the installation of supporting acro jacks and the chains or cables to pull were done retaining the verticality and the position which was identified with the 200 mm marking and the plumb bob lowered in to it. The allowance for the verticality was 5 mm at the bottom. And also GI pipes were fixed at 600 mm distance on each side with wall ties to prevent panel from buckling. With the inspection on correct installation and the approval by the consultant, the process is concluded. If any correction is necessary, it is done and again requested for inspection.

Figure 2.5 - Installation of formwork on plywood kicker

Figure 2.6 - Finished formwork erection

Figure 2.7 - Column formwork supported with acro jacks and pipe supports

Beams and slabs

Formwork for beams were done with laminated plywood panels and for slabs both laminated plywood and Kumkang formwork slab panels in combination are used. The laminated plywood were used to get the required finish without going for further work after concrete casting. The procedure that has been adopted for the erection of beam and slab formwork is as follows. First of all, the beam bottom level is marked on the column faces and the beam bottom panels which has been already fabricated is lifted up to the required level and supported on acro jacks Then the beam bottoms are levelled After that the side walls of the beams are installed according to the required depth and they are supported with 6 mm steel separator pairs fixed with butterfly washers Then the fabricated plywood slab panels or the Kumkang slab panels are installed with the provision of supports in the means of acro jacks/ pipe supports on T-jacks or scaffolding frames at necessary distances. When plywood panels are used, GI pipes were laid on top of the 4 x 4 timber additionally below the slab panels The slab is levelled to the required level and then the middle portion of large panels are raised 10 mm more to account for the deflection under load due to concrete pouring The inspection for the formwork is requested and the approval is obtained before starting reinforcement installation

Figure 2.8 - Kumkang Aluminum slab panels

Figure 2.9 - Beam bottom panel and supports

Figure 2.10 - Scaffolding supports for the slab panels

Page | 11