Wednesday, November 21, 2012

Type of Loads - Deep Foundations.

Loads applied to deep foundations consist of vertical forces and horizontal forces. These forces are resisted by the soil through bearing and friction. Therefore, the pile capacity analysis should be performed to determine that foundation failure by bearing or friction will be avoided, and load-displacement analysis performed to determine that foundation movements will be within acceptable limits.

(1) Load distribution. Loads on a deep foundation are simulated by a vertical force Q and a lateral force T, Figure 3-1. These vertical and horizontal forces are considered separately and thcir individual effects are superimposed. Unusual cross sections should be converted to a circular cross section for analysis when using computer programs such as CAXPILE (WES Instruction Report K-84-4) or AXILTR.

(2) Construction influence. Construction methods, whether for driven piles or drilled shafts, influence pile capacity for vertical loads through soil disturbance and pore pressure changes.

(a) Driving resistance. A wave equation analysis shall be performed for driven piles to estimate the total driving resistance that will be encountered by the pile to assist in determining the required capability of the driving equipment.

(b) Structural capacity. Total stresses that will be generated in the deep foundation during driving or by vertical and lateral loads will be compared with the structural capacity of the foundation.

Fig. 3-1 Loading support of deep foundation.

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