ENG4070 - Geotechnical Engineering 4 Assessment Answer

1.A

End bearing piles : -

Feasibility : - Loads in this pile are thought to pass through a smaller tip and thicker layers of soil support the pile's bottom. The pile can be found on the top of transition layers between strong and weak layers. In this case, the pile behaves as vertical structure which transfers load to strong layer and total capacity of an end bearing pile is considered to be the bearing capacity multiplied by area of pile tip. Factor of safety is to be considered to be calculated for the diameter of the pile.

Benefits: -  End-bearing piles are critical structural elements for large structures such as factories, stadiums, and bridges. Topsoil would be unable to support these structures without end-bearing piles. End-bearing piles must pierce the firm strata (e.g., the rock) by at least three times the diameter of the pile to achieve their full benefit. Except when passing through air or water, end-bearing piles do not encounter buckling inability in weak soil (Somja &Goyet ,2018).

Drawback : - The disadvantages of this foundation include the requirement of heavy machinery and time for construction installation and the development of negative skin friction.

pile resistance capacity calculation for end bearing piles: -

q_t = (q_c1 + q_c2 ) / 2

where, q_c1 = cone resistance average of pile tip considering depth of end bearing pile-( 0.7D to 4D)

q_c2 = the minimum cone tip resistance of 8D above the tip of the pile

D = depth of the end-bearing pile

friction piles : -

Feasibility: - When there is loose soil beneath a structural foundation, friction piles are enlarged to a depth where the frictional force on the piles' sides is equivalent to the weight applied to the piles. When solid foundation strata are available at a deeper depth, a friction pile is typically used (Hansen,2018). The friction pile is a type of underground system that is used to build foundational and heavy structures such as bridges that can support the topsoil. The load in a friction pile can support itself directly along its length.

Benefits : -  Friction piles provide force resistance between the pile surface and the adjacent soil, allowing the load to be transferred to the superstructure. The force is due to the formation of a specific pile length or the entire length based on the subsoil strata situation. The static friction must be required to support the superstructure for the nature of the foundation. To calculate the friction pile capacity multiplied by the surface area developed by frictional force per unit area The skin friction developed at the surface must be thoroughly evaluated with a reasonable safety factor in mind (Wehnert & Vermeer ,2021).

drawbacks: -

1. Driving through the stones and large rocks quickly damages a pile.
2. Marine borers can attack pilings in saltwater.

calculation for pile capacity for friction pile:

Q = (2C 1C2 )1/2 =

 where: Qu = load capacity at its ultimate state

C1 = fitting line slope

 C2 = y-intercept of the straight line.

Justification of adopted foundation : -

As the southern side span of Barton pier, Humber bridge is 530 metres long, 300 metres west of Barton Haven, with the anchorage approximately 30 metres inshore (Decourt,2017). Soft alluvial deposits are to be underlined in boulder clay, gravel, or sand where the tower and anchorage are considered and below the bed depth of 30 m and are heavily fissured on the tower at the end bearing pile to resist the fissures due to the clay layer. The piers are concrete structures that support the towers. Barton Pier is about 500 metres from the river's south bank (Dewaikar & Pallavi,2019).

B .

The main site investigation is geophysical surveying which employs non-invasive or minimally invasive methods to map properties of soil or characteristics over a larger area than boreholes, sampling, and trial pits alone can achieve economically in barton pier of humber bridge. Geophysical data, in conjunction with sample preparation and in-situ tests, can be used to map the variability of surveys in barton pier of humber bridge, which are always put in place and construed by experts. Measuring electrical resistance usually entails inserting metal probes into the ground and measuring the transitional resistance. This method can determine the distribution of material type and the level of groundwater boundaries. Ground penetrating radar uses electromagnetic pulses to penetrate the ground. The reflected wave measurements indicate the location of object boundaries of ground stratigraphy. In general, 10 - 20m in sand and 1 - 3m in saturated clay. Magnetometers - Can be measured from the ground surface or through probes such as the CPT and is used to detect the presence or location of unexploded ordinance (UXO). Because the friction sleeve in the CPT is not rigidly connected to the cone tip, pore pressure, it can be used to calculate the corrected cone resistance, qt. For force equilibrium at the cone tip, u2, and pore water pressure measured at the sleeve as per British geological survey. The seismic cone penetrometer test is a well-established method for determining soil stiffness (SCPT) (Ahmed &Pise ,2019).

A standard CPT cone is supplemented with one or more sets of gps receivers in this method (accelerometers). By striking a vertically loaded beam at the surface, compression (P) and shear (S) waves are generated in the soil media. The shear stiffness is calculated using elasticity theory, which directly relates the shear wave velocity to the small strain shear modulus: There are two methods for calculating the speed of the waves.

B. Describe the in situ and laboratory tests that would be useful for designing your foundations for the pier. You must link these to your foundation choice.

For high-quality triaxial testing, undisturbed samples must be obtained, which can be difficult in some deposits (e.g., sands and sensitive clays). Consolidation of samples in the lab to in situ stresses in the ground is dependent on knowledge of the lateral stress coefficient, k0, which is difficult to define; . The response of a tiny part of soil may not portray the behaviour of the entire soil mass in materials with major characteristics within the macro-fabric, such as fissuring in stiff clays and fracturing in rocks (Mirza,2017). During the SI phase, in situ testing involves the direct measurement of soil properties at the site. In situ testing can overcome some of the limitations of laboratory testing, complement it, and provide a quick assessment of key parameters. This Section provides a high-level overview of a variety of in-situ testing procedures. In situ tests frequently apply rather complex stress and strain changes to the soil, making interpretation of the test results difficult.

Cone penetration test

 In its most basic form, the CPT is a 60° cone jacked into the ground from a rig on the ground surface. The forces acting on the cone are measured and used to provide data about the soil. the average stress, QC, on the cone itself (referred to as cone resistance), the average stress, fs, acting on a friction sleeve behind the cone (referred to as sleeve friction), and the pore pressure at some location near the cone tip. The CPT test is performed by jacking the cone into the ground and screwing together a series of rods at the ground surface. A light trailer-mounted rig is appropriate for shallow jacking in soft soils. However, during investigations, the CPT is launched from a specially designed vehicle known as a cone truck. The use of a cone truck has the advantage of allowing technicians to perform the testing within the truck itself, and the truck can house any necessary computing or other equipment required to log the test results. The truck reacts to the force used to drive the cone, so the maximum jacking force is restricted by the mass of the truck.

3.C

The Humber Bridge requires repairs after it was discovered that a portion of the Barton Tower is not functioning properly. Officials discovered a problem with the two A-frames that secure the road to the south bank tower and say repairs are needed to keep them from becoming 'unserviceable.' The 3.8-meter-tall structures are intended to allow the bridge to adapt to changes in traffic, wind, and temperature. However, it was found last year that the few near Barton tower are not functioning properly and are under increased stress. The Humber Bridge, as a large structure, experiences significant induced longitudinal movements due to thermal, wind, and traffic loading - up to a range of nearly 2m .

REFERENCES

L. Decourt (2017), “Behavior of Foundations under Working Load Conditions,” Journal of Soil Mechanics and Geotechnical Engineering, 17(12),pp. 453-488
Link - https://citeseer.ist.psu.edu/showciting?cid=6495307
J. B. Hansen (2018), “Discussion on Hyperbolic Stress-Strain Response, Cohesive Soils,” Journal for Soil Mechanics and Foundation Engineering, 89(12), pp. 241- 242
https://ascelibrary.org/doi/10.1061/JSFEAQ.0000542
F. Ahmed and P. J. Pise (2019), “Pile Load Test Data-Interpretation & Correlation Study,” Geotechnical Journal, 17(20) , pp. 443-446.
https://www.sciencedirect.com/topics/engineering/pile-load-test
M. Wehnert and P. A. Vermeer (2021), “Numerical Analysis of Load Test on Bored Piles,” Journal in Geomechanics”, 14(23), pp. 1-6.
https://www.semanticscholar.org/paper/Numerical-analyses-of-load-tests-on-bored-piles-Wehnert/222c119ba1453a472d6066cb4282230a82d85706
D. M. Dewaikar and M. J. Pallavi (2019), “Analysis of Pile Load Tests Data,” Journal of Southeast Asian Geotechnical Society, 6(4),pp. 27-39
link - https://opac.library.iitb.ac.in/cgi-bin/koha/opac-search.pl?q=au:%22Dewaikar%2C%20D.M%22
U. A. A. Mirza (2017), “Pile Skin Friction in Clays,” International Journal of Offshore and Polar Engineering, 7(1), pp. 538-540.
https://www.semanticscholar.org/paper/Pile-Skin-Friction-In-Clays-Mirza/47c033c4dd8a83c914e534a8c6184de5adc0ed32
H. Somja, V.V. Goyet (2018), A new strategy for analysis of erection stages including an efficient method for creep analysis, British geotechnical society publication, 30 ,2871–2883.
link - https://www.semanticscholar.org/paper/A-new-strategy-for-analysis-of-erection-stages-an-Somja-Goyet/00de193c96bb6528827d7ff3410d73195ab1fde9

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