Using Numerical Methods to Examine Geotechnical Problems of Masonry Structures

Geotechnical analytical models are made for presenting the stress, deformation analysis, and settlement of the soil. The soil must be modeled in an advanced manner in order for the structural failure mechanisms to be observed. In this post, I am going to write about a research paper I found on the research gate that acknowledges and explains a model created using numerical analysis for geotechnical problem determination for the Abu Serga Church in Cairo, Egypt. Numerical and experimental analysis is used to characterize stress-strain analysis and subsoil deformation of the soft clay underneath the church. 

 

Abu Serga Church

The subsoil is composed of plastic silty clay layers mixed with fine to medium sand layers and the groundwater table is at 1.8 m depth. The geotechnical properties are summarized in the table given below;

Geotechnical Characterization of the soil layers underneath the Abu Serga Church

Church has a flood problem before a dam was constructed on the Nile River in 1971. But the floods caused loading and unloading of the subsoil for hundreds of years. the vertical effective stresses in the clay soil and its bearing capacity also changed with the rising and falling water table. Along with this problem, many cracks were observed on the superstructure of the church, because of the soil settlement and foundations movements undergoing a shear failure. A 3-dimensional model is implemented to analyze long-term creep deformations. To analyze the consolidation, a numerical model is produced based on assumptions, conditions, and simplifications. The main goal here is to find a suitable method for strengthening. 

Differential vertical displacement patterns in the bearing silty clay soil.

3D Finite Element discretization of the PLAXIS model and deformed generated mesh. 

References;

https://www.researchgate.net/publication/346041012_Numerical_Analysis_of_Geotechnical_Problems_of_Historic_Masonry_Structures

Building on a Site That Is "Pretty Much a Pool", What to Consider?

In this post, I will be writing about an off-the-grid getaway house that would ideally be located near Medellin, Colombia. But the soil study shows that the site is almost like a pool, having a high water table and thick layers of loose soil. These properties would provide little to no capacity for supporting heavy objects. The ground is made of silty sand, any design would be at risk for seismically-induced settlement dues to liquefication which would cause vertical settlement and lateral spreading. Also, there were some clays present on the site, and if this clay type is expansive then during rainy seasons, clayey soil would cause swelling which would cause an unwanted movement.

Project Site

The solution suggested was a floating slab- a flat layer of concrete resting on top of the soil, supported by vertical concrete piles beneath the outer edges. This solution has two problems;

1)It would damage the environment

2)Budget would be extremely high. 

When local geotechnical engineers were consulted, two alternatives popped up. The first one was deep foundation. This foundation type involves driving long piles into the ground to reach the more stable layers of earth below. Another solution was ground improvement, which would reduce the damage caused by liquefication.  This solution has many types; the first one would be the vibro-replacement stone column technique. Achieved by using a heavy vibrating weight to drill deep into the ground and create columns of compacted rock that support the earth around them. The second one would be deep soil mixing, achieved by using heavy equipment to mechanically combine weak soil and cementitious slurry.  At this point, the design process is continuing since these solutions are not perfectly sustainable or safe for the site. Further exploration is being done to develop the design.

Eco Shelter Rendering

Black and White Elevation Image

Source:

https://www.archdaily.com/585854/ask-arup-how-to-build-on-a-site-that-is-pretty-much-a-pool?ad_source=search&ad_medium=search_result_all

Impact Crater on Mars: Analyzing Its Morphology Using Slide2 and RS2

In my previous post, I mentioned the impact crater located on Mars. In this post, I will be talking about analyzing its morphology with software widely used by foundation engineers. This impact craters morphology is categorized as PPR (Peripheral Peak Ring). PPRs occur on craters having a diameter between 4 and 200 km when instabilities occur on the rim causing a crater deformation and a part of the rim to detach and slide into the crater. In the Department of Geoscience at the University of Calgary, there was a study to create a model for PPRS targeted to describe, characterize it. Jason Nycz, who was doing the research for this project, inversely modeled and analyzed the formation as a transversal block slide in Slide2 using the topographic inputs from DEM (Digital Elevation Models) and reasonable rock parameters. This research supplied much information about the strength parameters for the uppermost layers of the Martian crust. The model is created conditions and constraints (position, height, and shape of the crater) Three Phases of Modelling:

1. Modelling the crater before the PPR was formed. 

2. Detachment of the PPR from the crater rim, sliding laterally and downward toward the crater center. The result is an intermediate step in the formation of the PPR.

3. Transform the intermediate profile into the observed one.

Initial input model in Slide2

Slide2 model imported to RS2

Finite element analysis results in RS2

References:

https://www.rocscience.com/about/news-events/ocscience-goes-to-mars-using-slide2-and-rs2-to-advance-research-on-impact-crater-morphology

https://www.rocscience.com/documents/pdfs/rocnews/fall2011/Slope-Failure-Impact-Crater-on-Mars.pdf

Retaning Wall Collapsed During Foundation Excavations, the Building Next to the Construction Site Evacuated.

 On 25 February 2021, a construction site in Artvin Borçka had an incident concerning retaining walls. The excavator that was digging the site was under the wreckage, but the operator managed to get out of the machine unharmed. Fortunately, no other person was injured. The building which had its retaining walls collapsed was evacuated for security reasons. Rigid walls used for supporting soil laterally so that it can be retained at different levels on the two sides are called retaining walls.

The most common reasons for failure are,

• lack of proper reinforcement
• improper drainage behind the wall
• foundation footing problems
• settlement expansion of the soil
• overloading the wall
• construction errors or other design errors. 

For this case, the problem was caused by the excavator because they should have calculated the foundation that the retaining wall was settled in. At this point, they should either demolish the building or they should reinforce the wall with a curtain of piles of curtain grouting.

Source: 

https://www.trthaber.com/haber/turkiye/artvinde-istinat-duvari-coktu-14-katli-bina-bosaltildi-559646.html

https://sites.google.com/site/metroforensics3/causes-of-retaining-wall-failure-or-collapse