Technical Note-Water Seepage Through Piles

TECHNICAL NOTE ON WATER SEEPAGE THROUGH PILES Jamal Abdul Nasser Street-RA167 State of Kuwait

Technical note to investigate the water seepage through the bored cast in situ piles (1200mm dia.) of the foundations belonging to the Jamal Abdul Nasser Street Project- RA167, in the state of Kuwait. Technical note investigates the problem, analyzes and discuss & suggests preventive measures.

TECHNICAL NOTE ON WATER SEEPAGE THROUGH PILES

INTRODUCTION. A technical note to investigate the water seepage through the bored cast in situ piles (1200mm dia) of the foundations belonging to the Jamal Abdul Nasser Street/RA167 project, in the state of Kuwait. It has been observed that in certain piles in the above mentioned project, water is seeping through the piles at the cut off level. The water was reportedly seeping through the interface between the concrete and steel (permanent casing/rebar/sonic tube). All the piles reported with this phenomena belongs to the same area, which is identified as Sector H (Hospital Ramps). This technical note attempts to investigate and explain the phenomena along with suggesting solutions to avoid occurrence of such issues in the future.

DISCUSSION ON THE OBSERVED PHENOMENA. As stated above the water in the affected piles was seeping through the interface between the concrete and steel. This can be explained through capillary action and thereby suggesting the presence of micro pores in the interface between concrete and steel. It appears that the ground water table in the Sector H is higher than compared to the other sectors. After the commencement of the dewatering system, a temporary- localized drawdown is induced around the pile, thereby creating a positive pressure in the top of the pile, which assists the water seepage. What is worth noting here is the presence of micro pores along the interface between concrete and steel.

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TECHNICAL NOTE ON WATER SEEPAGE THROUGH PILES

A NOTE ON THE CONSTRUCTION SEQUENCE. The piling activities in the project are carried out from a working platform which is on an average 4.0 meters above the Cut of Level (COL) of the piles. During the piling operations no dewatering works are carried out in the vicinity of the piles. During the pile bore excavation, the stability of the bores are maintained using polymer slurry. The casting of the piles are done under wet conditions (slurry displacement method) using a tremie pipe. After the construction of all the piles in a pier, dewatering system (Well Points System) is commenced to aid the excavation works. After the excavation for pile cap construction, the top of the pile is hacked down till the cut off level, using appropriate means. The top of the pile is levelled at the COL for subsequent works. It is at this stage, the seepage of water is reported. It is to be noted here that neither the seepage of water is reported in all the piers nor all the piles in a pier, suggesting that the piling methodology in general is not responsible for the occurrence. The occurrence of the water seepage can only be attributed to the concrete quality and workability, which is discussed in the next section of this literature.

DISCUSSION ON THE EFFECTS OF CONCRETE The concrete mix for the piling works are specifically designed in order to achieve enhanced characteristics in terms of homogeneity and segregation resistance. Concerning workability, the concrete should be of a consistency class S4 or S5 (European Standard EN: 206-1:2000). The use of a concrete of such consistency, together with the enhanced characteristics described previously, is generally adequate enough to ensure a tight contact between the concrete 3

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TECHNICAL NOTE ON WATER SEEPAGE THROUGH PILES and the surface of the steel casing and reinforcement bars, thus avoiding any rise of groundwater once the dewatering system is in place.

As per the reported procedures followed on the site, it is evident that the concrete upon reaching the site is subject to a slump test. As reported, it takes around one hour for the concrete to reach the site since its batching and the casting begins on an average after 1 hour and 15 minutes post batching. After passing the slump test the concrete is allowed for pile casting. It is a possibility that during the casting of the piles affected with water seepage, there was a sudden or progressive loss of concrete workability beginning or during the concreting process. It is also observed that in the casting of some piles in this sector, during the pouring of the first truck mixer itself, the concrete was displacing upwards the steel cage and permanent casing (which are hung on the temporary casing with steel rebar), thereby confirms the possibility that the concrete lost its workability soon after the commencement of casting. When the concrete losses its workability gradually or progressively during the casting process, there is a need of continuous upward and downward movement of the tremie pipe which further risks the quality of the piles. This loss of workability during the casting process is the main cause of reduced bonding between the concrete and the steel surface, thus leading to micro pores through which the water seeps under favourable conditions. This can happen in any of sector of the project, but since the water table is reportedly higher in sector H, the seepage is occurring. These micro pores need not be evident in the Non Destructive Tests such as Cross Hole Sonic logging and or Low Strain Pile Integrity tests.

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TECHNICAL NOTE ON WATER SEEPAGE THROUGH PILES PREVENTIVE MEASURES AND SUGGESTIONS The following measures can be adopted to minimize/eliminate the occurrence of water seepage through the piles:1. Effort should be taken to reduce the interval between the Batching time and casting time. 2. Slump tests should be conducted by qualified personnel and immediately before the pouring.

3. The Mix design should be re-evaluated to study the effect of various components of the concrete and workability over time. 4. Regular inspection should be carried out in the batching plant to ensure the use of right and approved raw materials. The properties of the raw materials has a huge impact on the quality of the concrete. Necessary adjustments need to be done in the mix design taking into account the variations in the raw material properties. 5. Re-dosing of the admixtures on site, in case the concrete is reported to have low slump after reaching the site, should not be permitted. Re-dosing of the admixtures require qualification and competence of the concrete technicians. Since neither can be evaluated practically on the site, such practices should be discouraged. 6. The performance of the concrete also relies heavily on the quality of the admixture used. Proper study of the various kind and brands of admixture should be done by qualified personnel.

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