Assume Two Construction Sites: Site A And Site B

Assume Two Construction Sites Site A And Site B Based On the Geotech

Assume two construction sites: Site A and Site B. Based on the geotechnical report, the dominant soil type is GP at Site A and CL at Site B. The soil will be excavated before the installation of the foundation. Answer the following questions based on the information provided:

Paper For Above instruction

Question 1: Determine the soil categories at sites A and B, the meanings of the symbols GP and CL, and identify which soil type is frictional and which is cohesive.

According to the classification table in Figure 2.3 of the referenced textbook, soils are generally categorized into coarse-grained and fine-grained types. GP, or Granular Peat, falls under coarse-grained soils, while CL, represented as Clay, belongs to fine-grained soils. Coarse-grained soils like GP typically exhibit high permeability, allowing water to flow easily through, and are associated with frictional behavior due to the granular nature of soils such as gravel and sand. Fine-grained soils like CL display lower permeability and tend to be cohesive, as clay particles cling to one another, creating shear strength primarily through cohesion.

The symbol 'GP' stands for Granular Peat, a coarse-grained, permeable, and frictional soil. Conversely, 'CL' indicates Clay, a fine-grained, low-permeability, cohesive soil. In terms of mechanical behavior, GP (coarse-grained) is frictional—its shear strength primarily derived from friction between particles—whereas CL (clay) is cohesive—its shear strength mainly resulting from the attraction forces (cohesion) between clay particles.

Question 2: Regarding excavation processes, identify which soil type might naturally hold in place during shallow cuts and rank bracing systems for deep excavations.

For shallow cuts above the water table, the coarse-grained soil at Site A (GP) is likely to be stable and may not require extensive support because coarse soils generally have high internal friction and permeability, aiding in self-support during shallow excavations. Fine-grained soils such as CL at Site B, especially if saturated, tend to be less stable and more prone to sloughing or collapse, thus often requiring support even during shallow cuts.

When considering deep excavations where support systems are necessary, the preference should lean towards systems that minimize space usage and support clutter. Ranking these bracing systems from most to least preferable based on these criteria: the Tieback system provides the most space efficiency and less clutter, making it most preferable; Raker supports offer good support with moderate space requirements; Cross-lot bracing, while very effective, tends to occupy more space and can create more obstruction, making it less desirable in tight sites. Therefore, the order from most to least preferable is: 3) Tieback, 2) Raker, 1) Cross-lot.

Question 3: Considerations for dewatering during deep excavation below water table.

a) Comparing soil permeability, the site with the higher permeability will allow water to flow more readily. Based on typical classifications, Site A (GP—granular soil) is more permeable than Site B (CL—clay). Therefore, Site A's soil permits faster water movement due to larger particle sizes and pore spaces.

b) Dewatering is more likely to be required at Site A because higher permeability facilitates water ingress into the excavation zone, potentially raising water levels during excavation. Effective dewatering strategies would be necessary to maintain a dry working environment, especially for granular soils like GP. At Site B, clay's low permeability naturally restricts water flow, reducing the need for extensive dewatering systems, unless the clay becomes saturated or fractured. Nonetheless, if the water table is high or the excavation is deep, dewatering might become necessary at both sites.

Question 4: Estimating bearing capacity and foundation choices for a multi-story building.

a) Based on the data from Table 2.6, the soil at Site A (GP) is generally expected to have a higher bearing capacity compared to Site B (CL). Granular soils like gravel and sand typically offer higher bearing capacities due to their dense particle arrangement and frictional strength, while clay soils tend to have lower and more variable bearing capacities influenced by moisture content and consolidation history.

b) Given that a bedrock layer is present at a relatively shallow depth, the most appropriate foundation type is an end-bearing deep foundation, such as a pile or shaft foundation, which transfers loads directly to the bedrock, providing high load capacity and stability. The structural engineer would likely recommend piles driven or drilled down to reach the rock layer, ensuring the load-bearing capacity and stability requirements are met efficiently.

c) If the bedrock lies at a significantly greater depth or is inaccessible, alternative foundation options include continuous deep foundations like piles or drilled shafts extending into competent soil strata or bedrock if available. If neither is feasible, the engineer may consider deep foundations with soil improvement techniques, such as soil stabilization or preloading, or utilize mat foundations (mat slabs) that distribute loads over a larger area of weaker soils, potentially coupled with ground improvement methods to enhance the soil's bearing capacity.

References

• Das, B. M. (2017). Principles of Foundation Engineering. Cengage Learning.
• Bowles, J. E. (1996). Foundation Analysis and Design. McGraw-Hill.
• Craig, R. F. (2004). Soil Mechanics. Spon Press.
• Tomlinson, M. J., & Woodward, J. (2006). Pile Design and Construction. Taylor & Francis.
• French, C. (2015). Geotechnical Engineering: Principles and Practices. CRC Press.
• Coduto, D. P. (1999). Foundation Design: Principles and Practices. Prentice Hall.
• Hansom, J. (2011). Geotechnical Site Characterization. McGraw-Hill.
• Holtz, R. D., Kovacs, W. D., & Sheahan, T. C. (2011). An Introduction to Geotechnical Engineering. Pearson.
• Das, B. M., & Sobhan, K. (2017). Principles of Geotechnical Engineering. Cengage Learning.
• Lee, K. L., & Chang, Y. C. (2009). Soil Dynamics and Geotechnical Earthquake Engineering. Springer.