Moving piles
Unexpected movement of the pile is another indication of a problem that needs to be addressed before work can continue.
Lateral movement of previously driven piles
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If a previously installed pile moves laterally when a new pile is driven in, soil displacement may be the culprit. However, soil damage on adjacent slopes may be the cause. Solutions include changing the sequence of pile driving or re-driving the installed piles. You can also reduce ground movement by pre-drilling pile locations.
Piles out of alignment tolerance
Piles are designed to take into account a certain amount of alignment tolerance. It is based in part on the type of material of the pile. If the pile moves outside of this tolerance, it may be related to a hammer pile alignment control problem or soil conditions. There are several ways to adjust the hammer pile alignment control. For example, you can use a template or pile gate. Use a pile gate to guide the pile into the guide. There may also be obstacles near the surface. Removing the obstruction will change the soil and may reveal other soil problems below. The engineer will need to evaluate the soil and determine the next step.
Pile Obstacles
Solutions for dealing with pile obstacles vary depending on the depth of the obstruction. Obstacles may expose contaminated soils.
Shallow Pile Obstacles
If you encounter a shallow obstruction within three feet of the working slope, you may only need to remove it without significant impact to the surrounding soil.
Deep Pile Obstructions
When the obstruction is located beyond three feet or below the water table, excavation is usually not a viable solution. In this case, the pile location may be pre-drilled. Deep pile obstructions may require an engineer to provide a remedial design. Deep obstructions can reduce the calculated bearing capacity. In such cases, additional piles may be required.
Concrete Piles
Concrete piles are subject to various types of cracking. The direction, location and severity of the cracks provide clues to the cause. Common problems and solutions for concrete piles include
Localized Cracking - Pile Driving Made Easy
If easy pile driving can cause partial horizontal cracking in concrete piles, check hammer pile alignment. Another possible cause is excessive tension and bending of the combination.
Complete Horizontal Cracks - Easy Pile Driving
In cases where easy piling results in a complete horizontal crack in the concrete pile, the calculated tensile stresses may be off. If the tensile stress is too high, increase the buffer or reduce the length of the hammer blow. If too low, it may be related to poor hammer performance.
Complete horizontal crack in hard drive
Complete horizontal cracks during hard driving require you to calculate the tensile stresses along the length of the pile. If they are high, you may need heavier ram. if they are too low, the seismic may be higher than expected.
Pile monitoring with fiber optic sensors allows you to measure stresses along the entire length of the pile during pile driving. This provides greater accuracy compared to standard monitoring. Please note that cracks found early can be repaired with epoxy. Otherwise, they may end up in the pile.
Spalling near the pile head
When spalling (cracking or crushing) occurs near the pile head, you need to determine the pile head stress for the number of strikes observed compared to the allowable stress. One of the causes of damage near concrete pile heads is inadequate pile pad cushioning. Adding a pile pad is the solution to high stresses. However, if your calculations indicate low stresses, there are several potential causes. These include hammer performance and alignment issues, as well as poor pile quality.
Image credit: Jacobs Demolition and Carting
Steel and wood piles
There are several things that can cause steel pile heads to warp or wood pile heads to split or divide. These include.
Incorrect size or shape of the head
Inadequate strength of the steel
Uneven pile heads
Incorrect lashing
You can use metal tips or boots to protect the stake. Use them together with straps near the top of the pile to prevent splitting.
If you still have problems, calculate the stress on the pile head. Reduce the number of hammer blows to reduce the number of strikes; increase the number of high blows. However, you may need to choose a different hammer - or even a different pile type.
Hammer problems
Sometimes pile driving hammers are the source of problems. An example is when the field stroke of a diesel hammer is less than 90% of the calculated stroke. In this case, plunger friction may be the cause. If the observed strike count is less than the calculated value, the soil resistance may be lower than initially estimated. If they are similar, use a lower combustion pressure to align the hammer strikes.
Wave analysis data problems
You may encounter data problems when using a wave analysis software program to predict pile behavior. If you enter wave analysis data without listing the specific hammer you are using, use the same type of hammer. It should have a similar energy rating and plunger weight. You will need to modify its data to fit the application. In some cases, there is no hammer that matches the drive stress and drag limits. It may be that the calculated stresses and number of strikes are too high. One option is to increase the material strength - or make design changes. Perform a heavy blow or static load test to confirm capacity.
Wrap it up
Piling sounds simple - hammer the post into the ground. But it's a complex process that requires extensive testing and accurate calculations. Choosing the right pile material and equipment for the soil and load-bearing capacity depends on it. Several issues can arise in this area. Preparation and contingency planning are key to keeping a piling project on schedule and within budget.