Geotechnical engineering

College of Engineering Geotechnical engineering CE353 Semester 412 Quiz 4 By: Student Name Student ID Naif Khalid Aljarbou 362114822 Report on: Soil Settlement and Structure Safety Submission date: 29/3/2020 Instructor: Dr. Sherif ElKholy Page 1 of 8 Table of Contents 1. INTRODUCTION 3 2. THEORY 3 2.1. SOIL SETTLEMENT 2.1.1. WHAT IS SOIL SETTLEMENT 2.1.2. CAUSES OF SETTLEMENT 2.1.3. TYPE OF SOIL SETTLEMENT 2.1.4. VALUES OF EXPECTED SETTLEMENT AND ITS TIME DEVELOPMENT 2.1.5. CONSEQUENCES ON STRUCTURES 2.2. STRUCTURE SAFETY 2.2.1. WHAT IS STRUCTURAL SAFETY? 2.2.2. FACTOR OF SAFETY 2.2.3. FORMULA OF FACTOR OF SAFETY 3 3 3 4 5 6 6 6 6 6 3. CONCLUSION 7 4. REFERENCE 8 Page 2 of 8 1. Introduction In this course of CE353, the most important information of Geotechnical engineering was learned. And in this report I will talk about the Soil Settlement and Structure Safety. Which is an important to know about it at all as a civil engineering specially as a geotechnical engineering. As we know the soil settlement are caused by a load consolidating or causing displacement of the soil and because that settlement there is a structural safety that based on soil settlement and other. So, I will talk more about these topics below. 2. Theory 2.1. Soil Settlement 2.1.1. What is Soil Settlement Settlement is the downward movement of the ground caused by a load consolidating the soil below it or causing displacement of the soil. Settlement often refers to the downward movement of the ground around an excavated space, such as that for tunnels, shafts, or basements. And it’s usual for buildings to experience some degree of settlement within the first few years after construction. The extent to which this ground movement impacts upon buildings depends on several factors, which may include: • • • • Existing soil condition. Methods of construction. Size and depth of the construction works. Type of structure, its condition, and its foundations. [1] 2.1.2. Causes of Settlement For soil settlement there are many reason that make the settlement in the soil. And this settlement will damage the foundation and sometimes the building. Theses causes of settlement can occur from natural factor and man made mistake. And here is the most reason of causing settlement: • Extreme Weather Changes: Natural changes in the weather can also cause foundation settlement. Heavy downpours oversaturate the soil, making it become soft and heavy.[2] Page 3 of 8 • Soil Consolidation: soil plays a huge role in supporting. Contractors must use construction equipment to compact or consolidate the soil to best support the bottom. If fill soil is poorly compacted, or if it isn’t compacted at all, the soil can cause the structure above the surface to settle improperly. • Soil type: Some type of soil changes volume when its moisture content changes. And the soil shrinks in the dry summer and fall, when the rain quits falling as seen by cracks in ground. When the moisture returns to the soil during the winter and spring due to higher quantities of rain and snow, the soil swells back to its previous volume. [3] • Varying foundation depth: Foundations that are supported at different soil depths are likely to settle differentially. This condition is typical when a shallow foundation is placed near a deeper basement foundation or on sloping lots. • Changes in moisture content: The soil’s ability to support the load of a foundation settlement may be reduced by changes in moisture content within the soil. If soils are saturated, clays and silts may be softened. If soils are dried-out they have a tendency to shrink or contract. 2.1.3. Type of Soil Settlement Settlement of the foundation soil is a vertical displacement of the soil surface caused by the workload of the building. During and after the building construction, settlement of the foundation structure is considered normal and acceptable to a certain extent. Below in figure1 will show the soil settlement type which are uniform, tipping and differential settlement. [4] Figure1.Type of soil settlement of the foundation structure Page 4 of 8 2.1.4. values of expected settlement and its time development For calculation the value of settlement, there are three main categories that should be calculate it to estimate the total value which is ST = Se + Sc+ Ss. The three categories are: • immediate (elastic) settlement (Se), which caused by the elastic deformation of the dry, wet or saturated soil particles without any change in the moisture content. For the equation of the Se is known as: 𝑆" = ∆σB '()* ,* 𝐼. Where: - Se is the immediate settlement. - ∆σ is the net pressure applied. - B is the width of the foundation - 𝜇0 is the Poisson’s ratio of soil. - 𝐼. is the nondimensional influence factor. • Primary Consolidation Settlement (Sc), which caused as a result of volume change in saturated cohesive soil due to the expulsion of water within void space. For the equation of Sc is known as: 𝑆1 = H ∆ℯ 45 Where: - e7 is the initial void ratio. H is thickness of layer. ∆ℯ is the change of void ratio. • Secondary Consolidation Settlement (Ss), which caused as a result of plastic deformation of soil particles. @ 𝑆0 = 𝐶′: 𝐻 log ( A ) @B Ø Now after having all the three equation we can get the total soil settlement from this equation: 𝑆D = 𝑆" + 𝑆1 + 𝑆0 Ø And for the Time Rate Consolidation it’s calculate by this equation 𝑇G = HI @ J A KL Where: - 𝐻M NO is the maximum drainage path 𝐶G is coefficient of consolidation [5] Page 5 of 8 2.1.5. Consequences on structures Problems occur to the structure and have many forms of problems, like If there is a shift in the soil beneath the structure, or if one part of the structure has foundations on rock and another part on clay or embankment, the result is a change of the state of stress that is transmitted from the foundation to the structure, creating cracks in the walls. and here we will review some of pictures of these problems below in figure 2 & 3. Figure2.example of effect on structures 2.2. Figure3.example of effect on structures Structure safety 2.2.1. What is Structural safety? structural safety, is defined as the probability that failure will not occur or that a specified criterion will not be exceeded. 2.2.2. Factor of safety Factor of Safety is how much could a system withstand beyond the expected loads or actual loads. Factor of Safety is often calculated by using ratio of the ultimate load to the allowable load for a model or structural designing in construction such as bridges and buildings. 2.2.3. Formula of Factor of safety Here is the formula that calculate the factor of safety: Factor Of Safety = yield stress working stress Page 6 of 8 • A structure with a FOS of exactly 1 will support only the design load and no more. Any additional load will cause the structure to fail. A structure with a FOS of 2 will fail at twice the design load. 3. Conclusion At the end of this report, we can get that is the soil settlement is very important for a civil engineer to be know how can settlement occur and why. Also, should know how to avoid this problem as an engineering, because it’s has a really big problem which cause dangers to society and people. So, in this report the knowledge of soil settlement in general was talked about specially the type of soil, causes, consequences on structures with examples and the estimating value of expected settlement. Also, the Structure Safety was done with the factor of safety and how it’s calculated. Finally, I hope that everything is clear, understandable and admired as a scientific report. Page 7 of 8 4. Reference 1- https://www.designingbuildings.co.uk/wiki/Settlement_of_buildings visited on March 27, 2020 at 8:30 pm[1] 2- https://www.therealsealllc.com/what-exactly-causes-foundation-settlement visited on March 27, 2020 at 10:15 pm [2] 3- https://www.angieslist.com/articles/4-common-causes-foundation-settlement.htm visited on March 27, 2020 at 10:45 pm [3] 4- https://www.geotech.hr/en/differential-settlements/ visited on March 28, 2020 at 12:40 am [4] 5- Slides of lectures of Geotechnical Engineering. visited on March 29, 2020 at 1:24 am [5] Page 8 of 8