ACE060

What is limit state?

A Limit State is a condition of a structure beyond which it no longerfulfils the relevant design criteria. Involved ULS and SLS

What is a function of a pile?

A Pile transfer the load from the structure to a soil layer with sufficient strength and stiffness.

What is the observational method? Describe the steps?

A recommended approach is to accurately predict key quantities to be compared against values monitored during construction Produce accurate prediction- Deformations, stresses, porepressures 2. Set trigger levels (in advance): The crucial aspect for the Observational Method is to set in advanceallowable limits that cannot be exceed during construction• So called trigger levels 3. Plan modifications (in advance)- Clear idea of what to do when thetrigger levels are exceeded 4. Monitor the structure and the soil

What is a non-displacement technique?

A volume of soil is removed before inserting an equal pile volume, also called replacement pile. -CFA pile

What are action in piling?

Actions are known before a calculation is performed. It is a generalization of the more familiar concept load which basically accounts for applied forces to structures. For example permanent loads, self-weight of buildings, winds, goods etc.

What is active earth pressure?

Active pressure is the condition in which the earth exerts a force on a retaining system and the members tend to move toward the excavation.

Design methods for ULS (Indirect method). What is alpha method?

Alpha method is a total stress method that uses the undrained shear strength and an empirical factor alpha

What is the earth pressure at rest?

At rest earth pressure is the pressure that soil exerts on a structure when the soil is at rest. This pressure is caused by the weight of the soil above the structure and the weight of the soil below the structure.

Discuss benefits and downsides of doing field tests

Benefits: Realistic soil behavior, identification of soil properties, Uncertainties and variability Downsides: Cost and time, site limitations, interpretation challenges.

Design methods for ULS (Indirect method). What is beta method?

Beta method is an effective stress method that uses the vertical effective stress and an empeirical factor beta that is based on the strength properties in the soil and pile type.

How can we calculate the wall deflections?

By solving a differential equation and using a diagram.

What is control monitoring?

Construction = control monitoring Reduce uncertainties resulting from the design process Pro-actively address potential design scenarios Demonstrate performance to client. The monitoring method refers to the practice of collecting and analyzing data from various instruments and sensors installed in or around geotechnical structures or natural soil deposits.

What is the ultimate bearing capacity and what distinguishable modes of failure can be identified for shallow foundations?

Defined as the least pressure (Loading) to cause shear failure in the soil beneath the foundation. Failure is assumed to take place along a distinct failure surface. Three distinguishable modes of failure have been identified.

How do we determine a new a and/or b for a new pile type?

Determining the appropriate values of "a" and "b" for a new pile type typically involves a combination of field testing, laboratory testing, and empirical correlations.

What kind of pile installing techniques are there?

Driven (Solid and open-ended displacement piles) Bored (Auger, CFA - continuous flight auger) Vibrated (Sheet piles, Steel tubular piles) Jacked (Solid and open-ended displacement piles) Screwed (Helical)

How can we measure effective stress in the ground? Hint: you need to measure twoproperties

Effective stress can be measured using a spade cell and a tool for water pressure: best field application is the BAT probe

Describe some possible approaches for geotechnical modelling

Empirical model: Based on experience, More reliable data = more robust model. Theoretical model: A mathematicval model with differential and algebraic equations. A better understanding of reality based on calibrating existing theories and laboratory data. Numerical model: computational simulation of geological scenarios

What is a tension crack? How can we calculate that in an undrained material?

In geotechnical engineering, a tension crack refers to a type of crack or fissure that develops in a soil or rock mass due to tensile stresses (draghållfasthet). These cracks occur when the tensile strength of the material is exceeded, causing it to fracture and separate. Tension cracks are commonly associated with slope instability and can have significant implications for geotechnical analysis and design. Calculated with z0=2*cu/gamma

How do we obtain characteristic values in Geo?

In geotechnical engineering, characteristic values are obtained through statistical analysis of the available data. These values represent the properties or parameters of the soil or rock that are used for design and analysis purposes. It is important to note that the process of obtaining characteristic values involves some level of engineering judgment and may vary depending on the specific project and available data

What is the deterministic approach?

In geotechnics, a deterministic approach refers to a method or analysis that relies on known parameters and assumptions to predict the behavior of soil or rock formations. It assumes that the input parameters and conditions are precisely known and can be used to determine the response or outcome without considering uncertainties or variability.

What are resistance in piling?

It can relate to a number of different failure does for example the structural capacity of a pile or the geotechnical bearing capacity of a pile. It can also be expressed as a maximal deformation for example the settlement.

what are the types of reliability index levels? And which ones are used in geotechnics?

Level 0 - deterministic calculations: Global safety factor level 1 - Semi probalistic: uncertainty parameters are modellen by one characteristic value for load and resistance. Level 2 - Approaximation: Uncertain parameters are modellen by mean values and the standard deviations. Level 3 - Numerical: Uncertain quanities are modellen by their common distribution functions level 4 - Risk based: consequence times probability of failr Level 0 and 1 are used in geotecnhics

How can load eccentricity be accounted for?

Load eccentricity in shallow foundations refers to the situation where the applied load is not uniformly distributed over the foundation's width, resulting in an uneven load distribution. Following things can be done: Soil improvement, reinforcement and size or shape adjustment.

What is Passive earth pressure?

Passive pressure is a condition in which the retaining system exerts a force on the soil.

Describe the relation between effective stress, shear strength. What is the difference between the peak strength and the strength at critical state?

Peak strenght is the highest force which can be applied, while the critical state is where we have no additional change in volume and constant stress. Shear strength is a function of effective stress

What kind of shallow foundation settlements are there? Three components

Primary consolidation settlement is the major component (Sc): Gradual and time-dependent settlement (Months-years) Immediate elastic settlement (Si): Once the load is applied, the settlement undergoes stress and deformation Longterm (Creep settlement) (Ss)

What is the reliability index?

Reliability is often represented by a reliability index (beta) which is a probability of failure.

What is the main focus for failure when designing pile grooups for SLS and ULS?

SLS: Ensure the foundation does not undergo excessive displacement ULS: Collapse

Which wall type can be easily re-used in multiple temporary projects?

Sheet pile wall

What kind of failure mechanism is there for lateral capacity in piles? Short and long piles

Short piles > Rigid rotation of the entire pile from centre Long piles > Formation of a plastic hinge at the depth of "critical" below soil surface

What is the servicability limit state?

Situations where deformations, settlements, vibrations and local damage of the structure in normal use where the loads ceases the building to malfunction. Higher probability of occurrence than ULS. SLS is usually settlements, deformation or cracks in the structure calculationsbased oncharacteristic values of material properties (as the partial factors are 1.0)

Explain how the flexibility of the wall affects the distribution of the earth pressures

Steel sheet pile walls are muchmore flexible than gravity walls orRC walls, and therefore deflectmore under load. This leads to a redistribution ofearth pressure behind the wall, withhigher values where the responseis relatively stiff (i.e., smallerdeflections) and lower valueswhere the response is relativelyflexible (i.e., larger deflections). In soils, this stress transfer isknown as arching

What are an retaining structure? Give an example

Structure that prevents the soil to fail or fall in the excavation -Cantilever walls -Piling wall -Gravity wall -Anchored wall

What is hydrauilic uplift?

The bottom of an excavation might heave or rise ff the groundwater pressure in the underlying cohesionless material.

What is the distinction between a shallow and deep foundation?

The choice between shallow and deep foundations depends on factors such as soil conditions, the weight and type of the structure, and local building codes and regulations. The distinction between shallow and deep foundations lies in the depth at which they are constructed to support a structure Shallow foundations are constructed near the surface and spread the load over a larger area, while deep foundations are installed at greater depths to transfer the load through weak upper layers to more competent lower layers. Shallow foundations are suitable for lighter structures and shallow bearing capacities, whereas deep foundations are used when the soil near the surface is unable to support the load or for added stability

What are the neutral plane in piling?

The concept is based upon ongoing settlements in the ground. These can be for example caused by external actions such as ground water lowering but also creep deformations. In the case of settlement the piles are subjected to down drag. The neutral plane defines the depth of where down drag changes into friction strength. At the neutral plane the friction stress is zero. This is where the resistance and the action effect are the same. The neutral plane can be considered the safe side.

Describe is the p-y method?

The p-y method is a used approach for analyzing the lateral response of piles in soil. It is particularly useful for determining the distribution of lateral forces and deflections along the length of a pile due to soil-structure interaction.

What is a displacement technique?

The pile pushes the soil away during installation -Auger screw pile (Auger screwed in the soil to remove material - bored)

What is LRFD? Load and resistance factor design

The principle that resistance (strenght) of various materials are scaled down by some factor while loads are scaled up by some factor. It means reduced strenght and increased loads.

What is the ultimate limit state (ULS)

The situations involving safety, such as collapse of a structure, or any other type of failure, where risk of danger to people or ecomic loss Deformation in the ground causing failure in the supported structure, have a low probability of occurrence for well designed structures.

Discuss the different stress distributions below a flexible and stiff footing on clay and sand.

The stress distribution beneath a shallow foundation depends on the foundation's flexibility (flexible or stiff) and the type of soil (clay or sand). In general, a flexible footing on clay or sand causes more deformation and results in a relatively uniform stress distribution, with higher stresses near the center of the footing gradually decreasing towards the edges. A stiff footing, on the other hand, has less deformation and leads to more concentrated stress distribution beneath the footing. The stress distribution is triangular for a stiff footing on clay or sand, with maximum stress directly below the center of the footing. Lateral soil pressures are generally higher in clay compared to sand, while sand exhibits lower lateral pressures due to its permeability. It's important to consider various factors and consult a qualified engineer for accurate stress analysis and foundation design.

Describe the t-z method?

The t-z method is an analytical approach used to analyze the axial load-settlement behavior of piles in cohesive soils. It focuses on the relationship between the applied axial load (t) and the settlement (z) of the pile. Time - (z) Settlements

What are action effects in piling?

There are not know before a calculation and is one of the most important part of the calculation process. This is which effect that can happen once the action is applied to the structure for ex failure mechanism (Settlement)

What is undrained shear strength? In which soils and under which conditions does itemerge?

Undrained shear strength refers to the shear strength or resistance of a soil in undrained conditions, where the excess porewater pressure cannot dissipate. It is a fundamental property of soils that indicates their ability to resist shear deformation when subjected to rapid or undrained loading conditions. Undrained shear strength refers to the shear strength or resistance of a soil in undrained conditions, where the excess porewater pressure cannot dissipate. (ex clay)

Why do we use a surcharge load in the stability analyses?

We use a surcharge load in stability analyses of retaining walls to account for additional loads or pressures imposed on the soil surface above the retaining wall. The surcharge load represents any external loads, such as building loads, vehicle loads

What are some methods to help balance the retaining wall? Give example

Whaler: Structure element that aims to distribute the forces between retaining wall and strut/anchor and is acting along the retaining wall Strut/anchor: Structure element that aims to transfer forces/loads. Could be pre-stressed. Struts are more stiffer than anchors. Anchors are to be put into a bedrock, otherwise it is questionable if the anchor can be sufficiently controlled.

Which processes affect the magnitude (Size or characteristics) of the undrained shear strength that emerges?

When the water content cant flow out of the material, it will therefore be part of the strength.

Can we calibrate sensors to minimise the impact of precision (repeatability)?

Yes, it can help with minimizing the impact of precision or repeatability errors associated with sensor measurements.

What is the probalistic approach?

a probabilistic approach recognizes that geotechnical parameters exhibit natural variability and uncertainties. Rather than assigning fixed values, probability distributions are used to represent the range of possible values for each parameter. This allows for a more realistic representation of the inherent variability in soil or rock properties and other factors. In probalistic approach all variables f(x) = z = 0 requires a probalistic model ex properties, loads, uncertainties etc.

What is critical state?

critical state is where we have no additional change in volume and constant stress.

Difference between lower bound and upper bound theorems

two types of solutions can be constructed tocalculate the failure load (semi-) analytically:• Lower bound approach - safe theorem: equilibrium distribution of stresses Upper bound approach - unsafe theorem: distribution of displacements& deformations