Geotechnical Investigation for Slab Settlement: Causes and Mitigation

Geotechnical Investigation for Slab Settlement A geotechnical investigation was undertaken to evaluate the causes of settlement and failure of the concrete slab, approximately 10 metres from the sea. The slab is 0.5m thick and underlain by 1.0m of backfill material, which has been observed to be porous and weakly compacted. Distress has been recorded in the form of sinking and cracking, necessitating a detailed understanding of subsurface conditions and the proposal of suitable mitigation measures to ensure long-term slab stability. Drilling and Sampling Procedures: The investigation included drilling fifteen boreholes to depths of 15 metres, with two additional boreholes extended to 40 metres for profiling the deeper subsurface. Drilling was executed using rotary techniques to recover both disturbed and representative samples for laboratory testing. Disturbed samples were used for classification and index property analysis, while representative samples enabled determination of soil strength and compressibility. In Situ Testing: To characterize the soils in their natural condition, Standard Penetration Tests (SPT) were carried out at 1.5 metre intervals within the boreholes. SPT provided N-values used to assess relative density, shear strength, and stiffness of the soils encountered. Samples retrieved during SPT were correlated with blow counts to refine soil classification and engineering interpretation. An Electrical Resistivity Tomography (ERT) survey was also undertaken to delineate variability in soil stratigraphy and to highlight groundwater influence beneath the slab. Subsurface Conditions: The stratigraphy is dominated by loose to medium dense sands intercalated with silty and clayey horizons and layers of completely to highly weathered sandstone. Marine sands are prevalent, highly pervious, and directly influenced by tidal fluctuations. The shallow groundwater table enhances washout and erosion of fines. The backfill immediately beneath the slab was particularly porous and uncompacted, creating preferential seepage paths and voids. Problem Diagnosis and Mitigation: Slab failure is attributed to uncontrolled backfill, groundwater ingress, and compressible marine sands. To mitigate, systematic grouting is proposed beneath the slab to depths of about 1.0m. Cementitious grouts will fill voids and seal the porous backfill, while microfine or chemical grouts will permeate finer sandy horizons. Compaction grouting may be applied to densify loose layers, and localized soil replacement with engineered fill can be considered. Improved drainage will further reduce tidal groundwater impact. Should settlement persist, micropiles may be installed to transfer loads to deeper sandstone strata.

In your case (hangar), the slab is not a structural element. Grouting, even with thin grout (W/C = 3/1), will not be effective unless applied under pressure, and applying pressure would risk demolishing the entire slab. Check the cracks within the slab to determine whether they are still active. If they are not, this indicates that the immediate settlement of the poorly placed backfill has already been completed. In that case, you can simply repair the non-structural cracks using epoxy resin.

A borehole log is a systematic and detailed record of the subsurface conditions encountered during the drilling of a borehole. It provides comprehensive information about the different soil and rock layers, their depth, thickness, composition, and hydrogeological characteristics, along with the construction details of the borehole itself. In essence, a borehole log serves as both a geological and an engineering document that guides groundwater development, geotechnical design, and environmental assessments. A typical borehole log begins with general header information, which includes the borehole identification number, location, drilling date, coordinates, and the names of the driller and supervisor. It also indicates the borehole dimensions such as inside and outside diameters, the total depth drilled, and the static water level at which groundwater is first encountered. These details provide a basic overview of the borehole and form the foundation for interpreting the data recorded. The core part of the borehole log is the lithological description, which records the sequence of soil and rock layers encountered at various depths. This description highlights the material type, such as sand, silt, clay, gravel, limestone, mudstone, or sandstone. It also includes grain size classifications (fine, medium, or coarse, often given in millimeters), the color of the material, its texture, and any notable mineral content such as quartz, mica, or biotite. Such information helps engineers and geologists understand the subsurface stratigraphy and assess the suitability of different layers for groundwater storage or engineering applications. Depth markers are indicated alongside, allowing a clear correlation between layer depth and lithological properties. In summary, a borehole log is a vital document that records subsurface geological and hydrological conditions as well as borehole construction details. It provides a reliable source of information for hydrogeologists, civil engineers, and environmental scientists, ensuring informed decision-making in water supply development, geotechnical projects, and environmental protection. Without borehole logs, subsurface investigations would lack the accuracy and detail necessary for safe and effective engineering practice.

Geotechnical engineers use analytical reports like the subsurface soil investigation and water table map data to help them decide how to proceed on a construction project, whether it is for building a new school, redeveloping along the highway, or expanding a business. The information they gather allows them to advise architects and developers about potential foundation issues or problems with the soil or water in an area. These specialists help solve problems with existing structures and foundations too. https://lnkd.in/eSqRFSgW #KagaoanEngineering #GeologicalEngineers #GeotechnicalEngineers

Makarios Geotechnical Dynamics: One of South Africa’s Leading Geotechnical Contractors Johannesburg, South Africa – Makarios Geotechnical Dynamics has rapidly established itself as one of the premier geotechnical contractors in South Africa, renowned for its technical expertise, advanced equipment fleet, and proven ability to deliver large-scale ground improvement and soil stabilization solutions across multiple industries. With one of the largest dynamic compaction fleets in the country, Makarios is uniquely positioned to tackle some of the most challenging geotechnical conditions in Southern Africa. Their capability to carry out dynamic compaction to depths of up to 12 metres and deploy high energy impact compaction (HEIC) rollers makes them a contractor of choice for developers, municipalities, and mining companies alike. Broad Capabilities, Proven Performance Makarios offers a full suite of geotechnical contracting services, including: Dynamic Compaction – Deep densification for problematic soils, sinkhole mitigation, and mine rehabilitation. High Energy Impact Compaction (HEIC) – Fast, efficient large-area soil stabilization. Compaction Grouting – Targeted sinkhole rehabilitation and cavity filling. Piling & Lateral Support – Auger, CFA, micro piles, and slope stabilization solutions. Geotechnical Investigations – DPSH testing, auger trials, drilling, and plate load tests. These solutions have been successfully applied across projects in infrastructure, mining, power, residential, commercial, marine, and environmental rehabilitation sectors. Notable projects include sinkhole remediation at Khutsong, dynamic compaction works at Waterkloof AFB, and large-scale ground improvement for commercial developments such as Dayizenza Plaza. Safety, Quality, and Innovation at the Core Makarios is committed to delivering safe, efficient, and cost-effective geotechnical solutions. The company’s track record demonstrates not only technical innovation but also a strong focus on on-time project delivery and strict adherence to quality and safety standards. A Trusted Partner for South Africa’s Future South Africa’s expanding infrastructure and industrial projects demand contractors who can solve complex geotechnical challenges. Makarios Geotechnical Dynamics has proven itself as a reliable, innovative, and highly capable partner—earning recognition as one of the best geotechnical contractors in the country. --- 📢 About Makarios Geotechnical Dynamics Makarios Geotechnical Dynamics is a specialist South African contractor providing geotechnical construction services, ground improvement, and soil stabilization solutions across civil, mining, energy, and infrastructure sectors. 🌐 Visit: www.makariosgd.co.za

Attention Geotechnical Engineers! Are you working on excavation projects and looking to improve the prediction of soil movements? Do constitutive models, dewatering, and soil calibration spark your interest? ✅ look no further and read the full article by our expert Richard Witasse Here’s what you’ll explore: 1️⃣ Strain dependency of soil stiffness – soils don’t behave with constant stiffness, and advanced models (like Hardening Soil with small-strain stiffness in PLAXIS ) show how stiffness changes with strain, giving more realistic predictions of excavation. 2️⃣ Calibrating constitutive model parameters – with the SoilTest module available in PLAXIS and acting as a virtual lab, you can simulate triaxial, oedometer, and shear tests to efficiently calibrate model parameters of your soil constitutive models against lab data. Beyond calibration, the Soil Test facility serves as an interesting learning tool for students and young engineers. 3️⃣ Accurate dewatering modelling – essential in deep excavations below groundwater. PLAXIS enables realistic simulation of dewatering by coupling groundwater flow with soil deformation using either a steady-state or fully transient approach. Dewatering wells, recharge systems, and cutoff walls can be explicitly included in the model using hydraulic boundary conditions and time-dependent functions that reflect pumping schedules. Whether you’re an experienced professional or a young engineer, this blog will give you practical insights to make your geotechnical analyses more reliable. 🔴 For more details, check the blog on : https://lnkd.in/dA2g7nqj 🔴 For more resources on excavations, check the comment section Follow me for more PLAXIS tips and don't forget to hit that notification bell

If you're working on excavation projects, don’t miss Richard Witasse’s article on making your geotechnical analysis smarter with PLAXIS, covering soil stiffness, model calibration and dewatering. https://lnkd.in/dA2g7nqj

Help!! A 7-bedroom duplex just collapsed to the ground..... This could be you the moment you take the decision to neglect Site Investigation before building your dream home. WHY SITE INVESTIGATION SAVES BUILDINGS Every building must stand on the ground. Whether it is on a simple pad foundation, pile foundation or even a bamboo platform, it's ultimate support will be from the ground. While this is is true, unfortunately, not every ground is stable enough to carry different kinds of buildings. But do you know what ground is stable and what ground is not? I daresay your answer is NO, except you're an Engineering Geologist "Who has previously tested that area". Previously tested because not even the most skilled Engineering Geologist can guess the subsurface layers accurately by just looking at it. Yet in many projects in this modern 21st century, Site Investigations are skipped by LEARNED people just to save money - and this has oftentimes caused the untimely destruction of the said infrastructure leading to loss of lives and finances - the same one you wanted to save. Soil Investigation is the process of studying the soil and rock properties beneath the proposed construction site. It involves various tests including the Dynamic Cone Penetration test, Standard Penetration Test, Cone Penetration Test and a number of laboratory analyses to determine the properties and behavior of the subsurface layers, and ascertain its load bearing capacity to ensure that the proposed project does not suffer any Earth related casualties in the future such as cracks, tilts and worse, collapse. These tests are able to reveal accurately, the soil conditions at the proposed site, and the knowledge of this utilized to give proper recommendations on how the construction should proceed from foundation design to the entire structure design load. Usually, the cost of Site Investigation is less than 1% of the total project budget, but a neglect of this seemingly insignificant 1% can bring the entire building down to its own "Knees". This goes forward to imply that good geology equals safe engineering. Therefore, when you think of constructing any structure at all, no matter how small, remember to call on an Engineering Geologist before anyone else because while The Civil Engineer is able to make your building come to "LIFE", the Engineering Geologist ensures that your building is able to "LAST" for ages. So from your own Point of View, have you ever seen a building that collapsed due to bad soil? And do you think soil Investigation before construction should be made compulsory? Video Source: Daily Post #engineeringgeology #soilinvestigation #siteinvestigation #geotechnicalengineering #civilengineering #youngengineeringgeologist #womeninengineeringgeology #womeningeosciences #buildingcollapse #

🌍 How Deep Do We Go in Geotechnical Engineering? 1. Shallow Investigations (0–30 ft / 0–10 m) For small buildings, retaining walls, or light infrastructure, shallow borings and test pits are often enough. The focus here is on soil strength, groundwater level, and near-surface conditions. 2. Moderate Depth (30–100 ft / 10–30 m) For mid-rise buildings, roadways, or bridges, it is the skilled and knowledgeable engineers who often drill to these depths, showcasing their professional expertise and importance in the geotechnical process. Standard Penetration Tests (SPT), Cone Penetration Tests (CPT), and lab samples help determine bearing capacity, settlement potential, and soil layering. 3. Deep Foundations (100–300 ft / 30–90 m) High-rise towers, dams, tunnels, and critical infrastructure often require borings well beyond 100 feet. The goal is to understand deep soil strata and ensure piles or caissons reach stable bearing layers. 4. Mega-Projects (>300 ft / 90 m and beyond) For subways, tunnels, offshore wind turbines, or major dams, borings may extend hundreds of meters. Investigations here also include rock coring, seismic surveys, and advanced lab testing.