Geotechnical Design Exam Review 2024 Graded A

Geotechnical Design Exam Review 2024 Graded A What are indicator piles. and how do they benefit the foundation design process? - Answer-Indicator piles are prototype piles that are constructed before the production piles. These prototype piles are typically evaluated using pile driving analyzers, load tests, or other means to evaluate their load capacity. The results of these evaluations are then used to guide the design and construction of the production piles. In many cases, the indicator piles also are used to support the structure. Many engineers believe the only disadvantage to over designing pile foundations is the additional cost of the pile materials. However, there is another important consequence of over design which can significantly affect construction cost and may even make the foundation impossible to build. What is this consequence and how can it be avoided? -Answer-In addition to increasing materials costs, over designed piles are more difficult to install, thus increasing labor and equipment costs. In some cases, the additional labor and equipment costs, as well as the associated delays in the construction schedule, can be dis proportionally large compared to the additional capacity gained. These unnecessary costs and delays can be avoided by more precise designs and by the used of the various techniques of verification and redesign during construction. These measures help assure the as built foundation has sufficient capacity and performance, without being excessively over designed. Under what circumstances would you most likely require integrity testing of newly- constructed drilled shaft foundations? -Answer-Integrity testing is especially important when using the slurry method of construction. Explain the difference between the active, at-rest, and the passive earth pressure conditions. -Answer-The at-rest pressure is that which acts on a wall that has not experienced any lateral displacement or rotation. In other words, it reflects the horizontal stresses that were present in the undisturbed ground. The active pressure is that which acts on a wall that has moved a sufficient distance away from the back fill to fully mobilize the shear strength of the soil. The passive pressure is that which acts on a wall that has moved a sufficient distance into the back fill to fully mobilize the shear strength of the soil. Which of the three earth pressure conditions should be used to design a rigid basement wall? Why? -Answer-A rigid basement wall should be designed using at-rest pressure because it has not moved enough to develop the active condition. A pre-stressed concrete pile is being driven into a saturated cohesive soil with a hammer blow count of 17 blows per foot of pile penetration. Unfortunately, the pile driving rig breaks down before the pile reaches the required depth of penetration, resulting in a 15-hour delay. Once the rig is repaired, pile driving resumes but the blow count is now 25 blows per foot. Explain the primary reason for this change in blow count. -Answer-Driving of the pile caused large shear stresses in the soil. Since the soil was a saturated cohesive soil, positive pore pressures were generated during driving and therefore decreased the effective stress and both the end bearing and side friction compared to static loading. During the delay, the soil had time to dissipate some of the excess pore pressure generated during driving and the affected soil was able to consolidate. The decrease in pore pressure and the consolidation increased the soil strength and thereby the pile capacity. This effect is known in practice as ground "setup" or ground "freeze". Sometimes pile driving contractors use predrilling when installing piles. This method consists of drilling a vertical hole that has a smaller diameter than the pile, then driving the pile into this hole. Could predrilling affect the side-friction resistance? Why? Is the diameter of the predrill hole important? Why? -Answer-Predrilling can definitely affect the side-friction resistance by loosening the soil and by reducing the lateral earth pressure. Both the size of the predrill hole and its depth are important. The danger in predrilling is that it can reduce pile capacity if the predrilling is too long or the diameter of the hole is much larger than the pile. Ideally, the hole diameter should be smaller than the pile diameter and the length should be kept to a minimum. Why is it important for drilled shaft contractors to place the concrete soon after drilling the shaft? What detrimental effects can occur if the contractor waits too long before placing the concrete? -Answer-There are two potential detrimental effects which can be caused by delaying concrete placement. The first is related to reduction in lateral earth pressure. The drilled shaft construction process will always decrease the lateral earth pressure around the shaft. The longer time sha