Pile foundation guides provide geotechnical recommendations to engineers in selecting the appropriate depth, type of pile, and necessary precautions based on different soil conditions. These recommendations are crucial in ensuring the foundation’s stability and preventing potential failures.
Pile foundations are usually suggested when a raft foundation is not feasible due to the excessive settlement caused by weak or compressible soil. In such cases, pile foundations offer a more reliable solution to support the structure’s weight and distribute the loads to a deeper and stronger soil layer.
The geotechnical recommendations provided in these guides are applicable to all types of pile foundations. They include factors such as the soil’s strength and stiffness, groundwater level, and the required load-bearing capacity. Based on these factors, engineers can choose the most suitable type of pile, such as driven piles or bored piles.
Moreover, these recommendations also outline the necessary precautions to be taken based on specific soil conditions. For example, in clay soils, precautions should be taken to prevent soil heaving during pile installation, while in soft or loose soils, special measures should be taken to maintain the pile’s verticality and prevent soil loss.
In summary, geotechnical recommendations in pile foundation guides play a crucial role in ensuring the stability and longevity of structures. These guidelines provide engineers with valuable insights into selecting the appropriate depth, type of pile, and necessary precautions based on specific soil conditions.
Geotechnical Recommendations for Pile Foundation
When constructing pile foundations, there are several geotechnical considerations that must be taken into account. Firstly, the base level of the piles needs to be determined based on the end resistance of the stratum and the settlement behavior of the soil under the pile group.
For the piles to develop full skin resistance, a soil slip of 5 to 10mm is sufficient, while a displacement of around 10% of the pile tip diameter is needed for full end bearing resistance. If the piles encounter shrinkable clays, allowances must be made for loss of frictional resistance and uplift due to swelling.
Stiff fissured clays require bored cast-in-situ piles or low displacement driven piles. Dense silts create high penetration resistance for driven piles, resulting in a low pile capacity due to soil disturbance during driving. Normally consolidated clays cause down-drag on bored cast-in-situ piles due to consolidation resulting from drainage occurring during boring.
In sand, the point resistance and skin friction of piles increase as the pile length increases. The increase in value is ten times the pile diameter for loose soil and 20 times for dense sand, and beyond a certain length, the values remain constant. For piles longer than 15 to 20 times the diameter, driven through weak strata into a thick, firm sand deposit, the point resistance increases with the depth of embedment up to a maximum value corresponding to 8 to 12 times the diameter of the pile.
In most cases, the capacity of a group of piles is equal to the sum of the capacities of individual piles in the group, except for bored piles in sand where the capacity is approximately two-thirds of the sum of individual capacities. It is essential to check for failure of the pile group as a single block.
Pile capacity can be calculated using various appropriate methods to establish upper and lower bound values. However, it is crucial to note that errors are significant when extrapolating results obtained from one soil deposit in one location or year to derive values for different deposits in other locations or other types of piles that involve different construction techniques.
Geotechnical Recommendations for Driven Piles
Driven piles are commonly used in construction to provide support to structures. When selecting the soil type for such piles, compact, loose, and medium dense cohesionless soils are preferred. These types of soils are considered more suitable for pile driving compared to cohesive soils. The reason for this is that the formulas used for pile driving are more reliable for cohesionless soils.
In the case of driven piles in stiff clays, large surface cracks can form during the process. As a result, the skin resistance of the piles may not be significant up to a depth of 1.8 meters from the top. It is important to take this into consideration when designing and installing driven piles in such soil conditions.
Geotechnical Recommendations for Bored Piles
The capacity of bore piles is more reliant on the method of construction compared to driven piles. When boring, the soil becomes more loosened, and this affects the capacity of the pile. In sands, the shaft friction values for bored piles may be only half of that for driven piles, while the ratio for end bearing resistance is about one-third. When concrete is placed without mechanical compaction while withdrawing the shell tube, the surrounding cohesionless soil can be considered to be in a loose condition. To minimize the number of piles required in each group, it is recommended to determine the highest possible capacity of the pile by considering the soil parameters, the bore log, and the appropriate type of pile. The capacity of the desired pile foundation can be calculated using the standard codes of the region. To achieve the best results, it is essential to follow these recommendations.