Geotechnical Engineering Foundation Design

How we built over a live sewer for the extension element for our CIAT Awards shortlisted project.    Building over a sewer can be risky. The weight of a new structure can crush the pipe, leading to serious damage and costly repairs from the local water authority. To avoid this, we had to get creative. 💡    This sort of work is controlled under the Building Regulations and building over an existing sewer is only allowed if the building work 'is constructed or carried out in a manner which will not overload or otherwise cause damage to the drain, sewer or disposal main either during or after construction.'   First, I mapped out the existing drains and manholes to understand the depth and size of the pipes. We discovered they were over 2 metres deep, which meant we needed a specialised foundation system to bypass them.    After considering several options, I decided on piled foundations. This method uses deep "stilts" to transfer the building's weight well below the sewer pipe, ensuring no pressure is placed on it. This not only dealt with the risk to the sewer but also proved to be a safer, faster, and more cost-effective solution than the alternative which was 3m deep trench foundations.    The choice of roof structure also had an impact on the piled foundations and how they interacted with the sewer pipe. I proposed a cut timber roof supported off a steel ridge beam. This roof structure was designed to move loads to the long gable side wall of the extension [running parallel to the pipe] so the two short walls [on top of the pipe] were not as heavily loaded, this therefore reduced the loads above the sewer and the risk of the sewer being damaged. If trussed rafters had been used the loads would have been moved to the short walls thus increasing the loads on the existing sewers below. This detail was key to protecting the underground infrastructure.    To make this project even more interesting the piling sub-contractors who had been quite helpful pre-construction decided to change their T&C’s a week before installation. The Clients weren’t really happy with this late change so I helped source alternative piling sub-contractors at short notice who managed to turn things around in enough time. Was slightly stressful for a couple of weeks but we just about made it without any delay or cost changes.    We also had CCTV surveys completed before + during + after the building work to check the condition of the drains. This helped us identify if the drains were in good condition or if they had become damaged during the building work and needed some remedial repairs.    So, that’s how we successfully built over a live sewer.    I can’t stress how important the initial survey work is before design work is started, as this vital information will inform the initial and final design.    Wish me luck for the actual Chartered Institute of Architectural Technologists (CIAT) Awards event tomorrow in London, I’ll keep you posted! 😎

𝐋𝐨𝐠𝐢𝐜𝐚𝐥 𝐈𝐧𝐟𝐫𝐚𝐬𝐭𝐫𝐮𝐜𝐭𝐮𝐫𝐞 & 𝐑𝐞𝐭𝐚𝐢𝐧𝐢𝐧𝐠 𝐖𝐚𝐥𝐥 𝐂𝐨𝐧𝐬𝐭𝐫𝐮𝐜𝐭𝐢𝐨𝐧 𝐒𝐞𝐪𝐮𝐞𝐧𝐜𝐞🛣️ progression of constructing a mountain hairpin road with retaining walls: terrain excavation → structural earth retention → engineered backfill → pavement construction → drainage → safety installations. 📌 𝐒𝐮𝐫𝐯𝐞𝐲 & 𝐆𝐞𝐨𝐭𝐞𝐜𝐡𝐧𝐢𝐜𝐚𝐥 𝐈𝐧𝐯𝐞𝐬𝐭𝐢𝐠𝐚𝐭𝐢𝐨𝐧: ✓ Topographic survey ✓ Establish Road alignment. ✓ Geotechnical investigation. ✓ Bearing capacity verified. ✓ Slope stability evaluated. 📌 𝐂𝐨𝐧𝐭𝐫𝐨𝐥𝐥𝐞𝐝 𝐄𝐱𝐜𝐚𝐯𝐚𝐭𝐢𝐨𝐧: ✓ ControlledExcavation. ✓ Loose materials continuously removed. ✓ Design formation levels maintained. 📌 𝐓𝐞𝐦𝐩𝐨𝐫𝐚𝐫𝐲 𝐒𝐥𝐨𝐩𝐞 𝐒𝐭𝐚𝐛𝐢𝐥𝐢𝐳𝐚𝐭𝐢𝐨𝐧: ✓ Rock bolts systematically installed. ✓ Shotcrete protection uniformly applied. ✓ Wire mesh securely anchored. ✓ Temporary drainage channels constructed. ✓ Slope movements continuously monitored. 📌 𝐑𝐞𝐭𝐚𝐢𝐧𝐢𝐧𝐠 𝐖𝐚𝐥𝐥 𝐅𝐨𝐮𝐧𝐝𝐚𝐭𝐢𝐨𝐧𝐬: ✓ Competent founding strata exposed. ✓ Foundation excavation accurately trimmed. ✓ Lean concrete blinding provided. ✓ Reinforcement correctly installed. ✓ Foundation concrete properly cured. 📌 𝐑𝐞𝐭𝐚𝐢𝐧𝐢𝐧𝐠 𝐖𝐚𝐥𝐥 𝐂𝐨𝐧𝐬𝐭𝐫𝐮𝐜𝐭𝐢𝐨𝐧: ✓ Structural reinforcement securely fixed. ✓ Concrete placement continuously monitored. ✓ Construction joints properly treated. ✓ Wall alignment accurately maintained. ✓ Design strength fully achieved. 📌 𝐃𝐫𝐚𝐢𝐧𝐚𝐠𝐞 𝐒𝐲𝐬𝐭𝐞𝐦 𝐈𝐧𝐬𝐭𝐚𝐥𝐥𝐚𝐭𝐢𝐨𝐧: ✓ Perforated collector drains installed. ✓ Granular drainage blanket provided. ✓ Geotextile filter layers placed. ✓ Weep holes uniformly constructed. ✓ Surface runoff effectively diverted. 📌 𝐄𝐧𝐠𝐢𝐧𝐞𝐞𝐫𝐞𝐝 𝐁𝐚𝐜𝐤𝐟𝐢𝐥𝐥𝐢𝐧𝐠: ✓ Approved granular backfill utilized. ✓ Layer thickness strictly controlled. ✓ Compaction density consistently achieved. ✓ Moisture content properly maintained. ✓ Wall surcharge carefully minimized. 📌 𝐑𝐨𝐚𝐝 𝐅𝐨𝐫𝐦𝐚𝐭𝐢𝐨𝐧: ✓ Formation level accurately trimmed. ✓ Weak zones properly improved. ✓ Subgrade uniformly compacted. ✓ Crossfall correctly established. ✓ Formation quality thoroughly verified. 📌 𝐒𝐮𝐛𝐛𝐚𝐬𝐞 & 𝐑𝐨𝐚𝐝 𝐁𝐚𝐬𝐞: ✓ App. aggregates properly placed. ✓ Layer thickness controlled. ✓ Compaction requirements satisfied. ✓ Surface tolerances verified. ✓ Load distribution uniformly achieved. 📌 𝐁𝐢𝐧𝐝𝐞𝐫 𝐂𝐨𝐮𝐫𝐬𝐞: ✓ Prime coat uniformly applied. ✓ Binder mix correctly paved. ✓ Asphalt temperature monitored. ✓ Longitudinal joints compacted. ✓ Surface profile maintained. 📌 𝐀𝐬𝐩𝐡𝐚𝐥𝐭 𝐖𝐞𝐚𝐫𝐢𝐧𝐠 𝐂𝐨𝐮𝐫𝐬𝐞: ✓ Wearing course uniformity. ✓ Ride quality consistently achieved. ✓ Surface texture adequately provided. ✓ Compaction density attained. ✓ Finished levels verified. 📌 𝐑𝐨𝐚𝐝 𝐅𝐮𝐫𝐧𝐢𝐭𝐮𝐫𝐞 & 𝐒𝐚𝐟𝐞𝐭𝐲: ✓ Safety barriers installed. ✓ Traffic signs positioned. ✓ Pavement markings. ✓ Reflective studs embedded. ✓ RSA compliance verified.

“Standing on Stones” — The Japanese Ishibadate Technique 🪨🏯 Have you heard of Ishibadate? It’s a centuries-old Japanese building practice where wooden pillars are placed directly on stone bases (plinths), without rigid fastenings. At first glance it looks simple. But its elegance is in the subtle engineering. 🔍 What Is Ishibadate & Why It Matters • Ishibadate means “pillar on stone.” Columns rest on stone foundations, shaped precisely so they match the uneven stone surface. This allows a snug contact without bolts or nails. • The wooden posts are carved (scribed) to follow the stone’s contours, which gives a tight fit that allows a little movement. • These pillars aren’t anchored rigidly; they can shift, slide, or lift slightly over the stones during seismic movement. That means the building absorbs and dissipates earthquake energy rather than forcing it through fixed connections. 📐 Engineering & Environmental Advantages • Flexible response to earthquakes: Because the base is not fully rigid, structures built with Ishibadate handle quick, sharp tremors much better. • Moisture & decay prevention: Since wood is lifted off the ground atop stones, it avoids direct contact with soil moisture, reducing rot and insect damage. • Repairability: Damaged pillars can be lifted/removed and replaced without disturbing the stone base — the foundation remains intact. 🌍 Modern Relevance & Inspiration As someone always exploring how tradition meets innovation, I find Ishibadate deeply inspiring. It’s proof that ancient wisdom can still guide us in: • Building in seismically active zones • Designing structures that age gracefully • Choosing construction methods that are repair-friendly, resilient, and sustainable 🎥 by agathusstudios (IG)

Topic :- BBS of Pile Foundation 👷Pile Foundation ➡️A pile foundation is a type of deep foundation that transfers structural loads from a building or other structure to a deeper soil or rock stratum with greater load-bearing capacity. Piles are essentially long, slender members made of materials like concrete, steel, or timber, driven or drilled into the ground to provide support. 👷Types of Pile Foundations 🚧Pile foundations can be classified based on various criteria, such as their function, material, and installation method. Here are some common types: 👷1. Based on Function: 🚧 End-bearing Piles: These piles transmit the load to a strong, load-bearing stratum located at a considerable depth below the ground surface. 👷 Friction Piles: These piles develop their load-carrying capacity primarily through skin friction between the pile surface and the surrounding soil. 👷2. Based on Material: 🚧 Timber Piles: Made of wood, often treated to resist decay and insect attack. They are relatively inexpensive but have limited load-bearing capacity and durability. 🚧 Concrete Piles: Made of concrete, either precast or cast-in-place. They are strong, durable, and versatile, suitable for a wide range of soil conditions and loads. 🚧 Steel Piles: Made of steel, offering high strength and slenderness. They are commonly used in situations where high loads or space constraints are a concern. 🚧 Composite Piles: Combine two or more materials, such as concrete and steel, to optimize their properties. 👷3. Based on Installation Method: 🚧 Driven Piles: Installed by driving them into the ground using a hammer or other impact device. 🚧 Bored Piles: Formed by excavating a hole in the ground and then filling it with concrete. 🚧 Screw Piles: Installed by rotating a helical blade into the ground. 🚧 Sheet Piles: Interlocking elements driven into the ground to form a continuous wall, often used for excavation support or water barriers. 👷Choosing the Right Pile Foundation 🚧The selection of the appropriate pile foundation depends on various factors, including: 🚧 Soil conditions 🚧 Load requirements 🚧 Environmental considerations 🚧 Cost 🚧 Construction constraints 👷A geotechnical engineer can assess the site conditions and design the most suitable pile foundation for a specific project.

🌍 Strong Foundations – Key Points - Invisible strength: The true stability of buildings lies beneath the ground, not in the bricks we see. - Different soils, different solutions: There’s no single foundation type that works everywhere. - Zapata (footing): Best for light loads on firm ground. - Deep foundations (piles): Used for heavy loads or soft soils. - Franki pile: Has a widened bulb at the base, acting like an anchor for extra capacity. - Screw/propeller pile: Twists into the soil while concrete is poured, combining strength and efficiency. - Material choice matters: Using the wrong cement or foundation type can be the most costly and dangerous mistake. - Steel tubes & prefabricated piles: Designed for extreme loads and impact resistance. - Geotechnology: The art of defying gravity by designing foundations that adapt to soil conditions. - Silent giants: Skyscrapers stand tall thanks to hidden foundations working invisibly beneath our feet. - Knowledge = security: Engineering wisdom is the foundation of every great project. --- Strong Foundations Explained | Civil Tech Time 🏗️ Foundations are the backbone of any structure. Choosing the right type depends on soil condition, load requirement, and construction method. This visual explains the most commonly used shallow and deep foundations in civil engineering, clearly and simply. 🔹 Isolated Footing – Used for light loads and shallow depths 🔹 Tube Pile – Large diameter pile with steel cage for heavy loads 🔹 Precast Pile – Driven into the ground, ideal for soft soils 🔹 Franki Pile – Enlarged base formed in-situ for higher load capacity 🔹 Continuous Flight Auger Pile – Drilling and concreting done simultaneously for weak soils 📘 Learn civil engineering concepts visually with CIVIL Tech Time Simple • Practical • Site-oriented

How Do Structures Transfer Their Base Shear to Soil, and Why Is It Crucial? Understanding how lateral loads move through a structure and into the soil is a basic but often overlooked part of structural engineering. This knowledge is essential for checking an important assumption in our structural analysis: the fixed base model. This approach simplifies structural analysis by assuming that there is no movement at the soil level, which makes calculations easier. However, this can lead to significant discrepancies between analytical predictions and the actual behaviour of structures. This assumption is no longer the most efficient approach and may not be safe either. Mechanisms of Lateral Load Transfer to Soil: Many engineers are familiar with vertical foundation movements related to uplift forces and soil bearing capacity. However, the lateral movements of the foundation and their effects on structures are less frequently discussed. Here is a brief description of the mechanisms through which foundations transfer lateral loads to the soil: • Friction: This is the resistance that occurs as the foundation moves relative to the soil. • Passive Resistance: Lateral forces push the foundation against the soil through elements like ground beams and engage the soil to provide resistance (via minor axis bending of beams). • Piles: These function by pushing against the soil, utilizing a mechanism similar to passive resistance described above. Slab on Grade as a Transfer Floor: In scenarios where these mechanisms under lateral resisting elements are inadequate, how well the foundation system is connected becomes vital. This is particularly true if there are missing tie beams or insufficient reinforcement in the slab on grade. Recognizing the slab on grade as a crucial “transfer floor” is essential for addressing these issues. Here are strategies to enhance foundation design and performance: • Reinforcement: A diaphragm analysis of the slab on grade is crucial. It should include reinforcement details similar to those in suspended floors, often determined through methods like grillage analysis (refer to Section 5 - Appendix C5D of the NZ seismic assessment guidelines). • Tie Beams: These are essential for providing both passive resistance and functioning as diaphragm ties, facilitating load transfer across the foundation. • Ductile Reinforcement: Using ductile reinforcement in the slab is essential to maintain tensile capacity and manage large strains. • Connections: Strong connections between the slab on grade, lateral resisting elements, and footings are crucial for effective load transfer. By designing the foundation floor to function effectively as a diaphragm, we significantly enhance the building's efficiency and resiliency to withstand lateral forces. Keep an eye out for a future post, where I will discuss soil-structure interaction modelling and lateral assessment of piles. #structuralengineering #earthquakeengineering #seismicdesign #resilience

Strong Foundations: Choosing the Right Type for Safe & Sustainable Structures 🏗️ A structure is only as strong as its foundation. Selecting the correct foundation system depends on soil condition, load requirements, construction constraints, and project economics. The image highlights some of the most commonly used shallow and deep foundations in modern construction. Here’s a detailed breakdown 👇 1️⃣ Isolated Footing 🔹 Type: Shallow foundation 🔹 Used for: Individual columns 🔹 Suitable soil: Good bearing capacity soil 🔹 Key features: Simple design and execution Economical for low to medium-rise buildings Load transferred directly to soil through footing base 📌 Common in residential and small commercial buildings. 2️⃣ Tube Pile (Cast-in-Situ Bored Pile) 🔹 Type: Deep foundation 🔹 Used for: Heavy loads 🔹 Suitable soil: Weak or variable soil strata 🔹 Key features: Large diameter piles Steel reinforcement cage Load transfer through skin friction and end bearing 📌 Ideal for bridges, high-rise buildings, and industrial structures. 3️⃣ Precast Concrete Pile 🔹 Type: Deep foundation (Driven pile) 🔹 Used for: Soft soils and marine works 🔹 Key features: Factory-controlled quality Driven into ground using pile hammers Faster installation 📌 Widely used in ports, jetties, and infrastructure projects. 4️⃣ Franki Pile 🔹 Type: Special deep foundation 🔹 Used for: Very high load-bearing requirements 🔹 Key features: In-situ pile with enlarged bulb/base Excellent load capacity Minimal settlement 📌 Best suited for heavy structures where settlement control is critical. 5️⃣ Continuous Flight Auger (CFA) Pile 🔹 Type: Bored pile 🔹 Used for: Urban & vibration-sensitive areas 🔹 Key features: Drilling and concreting done simultaneously Low noise and vibration High productivity 📌 Preferred in congested cities and near existing structures. 🔑 Key Takeaway There is no one-size-fits-all foundation. Proper geotechnical investigation and engineering judgment are essential to select the most efficient, safe, and economical foundation system. “Strong foundations don’t just support structures — they support trust, safety, and longevity.” 💬 Which foundation type have you worked with the most? #CivilEngineering #Foundations #Construction #GeotechnicalEngineering #StructuralEngineering #Infrastructure #SiteEngineering

Engineers can't completely stop earthquakes, but they can significantly reduce their devastating effects on buildings and infrastructure. 1. Understanding the Enemy: Seismic Design • Earthquake Loads: Engineers design buildings and structures to withstand specific earthquake forces based on location and seismic risk. • Building Codes: Strict building codes in earthquake-prone areas ensure structures are designed and built to withstand ground shaking and potential soil liquefaction. • Seismic Resistance: This involves: * Stronger Materials: Using high-strength steel and reinforced concrete that can withstand significant stresses. * Reinforcement: Adding steel reinforcement to concrete structures to increase their ability to resist bending and shear forces. * Ductility: Designing structures to be flexible and bend rather than break under seismic loads. * Shear Walls: Installing stiff walls to resist lateral forces and prevent the building from collapsing. 2. Mitigating the Impact: Advanced Technologies • Base Isolation: This involves separating the building from the ground with flexible layers that absorb seismic energy, preventing it from transferring to the structure. • Tuned Mass Dampers: These are heavy weights strategically placed in buildings to absorb and reduce vibrations, especially during high-frequency seismic waves. • Energy Dissipation Devices: These devices are installed to absorb and dissipate energy from earthquakes, reducing the forces transmitted to the building. 3. The Limits of Engineering • Unpredictable Nature: Earthquakes are unpredictable events, with varying intensities and ground motions. • Mega-quakes: While engineering has made significant progress, even the most advanced designs may not be able to withstand the extreme forces of a very large earthquake. The Goal: • Reducing Damage: The aim isn't to stop earthquakes, but to reduce their impact. Engineers strive to make structures more resilient, minimizing damage, loss of life, and disruption. • Building Resilience: Engineering solutions play a crucial role in creating earthquake-resistant infrastructure, helping communities better prepare for and recover from seismic events. While engineers can't completely prevent the swaying of buildings during earthquakes, they can greatly mitigate its devastating effects through innovative design, construction, and technology. It's a continuous effort to protect lives and property in earthquake-prone regions. #Seismicdesign #Earthquake #Construction #Infrastructure #Civilengineering #Structure #Baseisolation #Buildingcodes #Shearwalls #Ductility

Foundation Design! Whether you’re supporting a massive industrial winch or a simple steel warehouse, everything starts with what’s happening beneath the surface. Designing a foundation isn't just about pouring concrete; it’s about a high-stakes handshake between the structure and the earth. Here is a look at the technical reality of foundation design: 1. You can’t design what you don’t understand. This is where we collaborate with Geotechnical Engineers to peek into the black box of the site. Through rigorous geotech investigations, we determine: • The Soil Profile: Are we dealing with stiff clays, collapsible sands, or rock? • Safe Bearing Pressure: Knowing exactly how many kN/m^2 the soil can take at SLS (Serviceability) and ULS (Ultimate) Limit States to prevent those dreaded sinking feelings. • The Water Table: Because nothing ruins a design like unexpected buoyancy or pore water pressure. 2. Once the geotech report is in, the structural analysis begins. We aren't just looking at gravity; we’re fighting forces from every angle: • Balancing vertical P loads with Mx and My moments. • Ensuring Factor of Safety (FoS) against Overturning and Sliding. If the winch pulls at a 30° angle, that foundation better stay put! • Optimizing rebar to handle the flexural design moments and punching shear. 3. A design is only as good as its execution. As structural engineers, we have to be loud and clear on the drawings about Compaction Specifications. Specifying a "G5 material compacted to 95% Mod AASHTO" isn’t just a suggestion—it’s the difference between a rigid base and a structural nightmare. If the compaction isn't right, that 150 kPa bearing pressure you counted on? It's gone. Foundation design is the ultimate team sport between soil mechanics and structural integrity. It might be buried underground where no one sees it, but it’s the most important part of the project. #CreatingRealityForALiving #StructuralEngineeringMadeEasy #StructuralEngineering #CivilEngineering #Geotechnical #FoundationDesign #EngineeringLife #ConsultingEngineers #SBANGWANA