UNIT 29: GEOTECHNICS & SOIL MECHANICS
Table of content
Introduction
LO 1 Reviewing rock types, their formation and application within civil engineering
LO 2: Exploring and classifying soils to the current codes of practice
LO3: Analysis of soil properties determined by geotechnical procedures (M3)
LO4: Producing a proposal for addressing the identified geotechnical problems and weakness (M4) (D3)
Conclusion
Introduction
The study of this assignment will be emphasized upon the geo-technics and soil mechanisms. The assignment will be written form an assistant civil engineers point of view who is currently working within a large engineering firm. The assignment is aimed at exploring the rock types and the formation of the same under the uses of the civil engineering practices and the construction working patterns in order to analyze the role of the rock mass characterization for the designs of the buildings and even the roads and tunneling activities. Additionally, the assignment also accomplishes the classification of the soil along with the practices that would drive the effective facilitation of the ground and the site analysis in terms of the activities of soil sampling. This is found to be beneficial towards soil descriptions that are required for the contrition practices in Hong Kong. The discussion will be focused on preparing of report based upon the survey carried out during the survey and soil sampling for the construction sites. Therefore, the study will focus on reviewing the rock types, their formation and the uses within the civil engineering, exploration and classification of the soils as per the current codes of practices. Followed by, the properties of the soil types will be determined using the geotechnical procedures and proposal will be prepared which will be capable for identification of the issues and the weakness, which will be required to overcome in order, to successfully complete the study. Understanding of the various aspects present within the civil engineering project with reference to Hong Kong will be further, emphasized for bringing clarity to the project.
LO 1 Reviewing rock types, their formation and application within civil engineering
P 1 Discussion on the rock types classification and formation
The process of rock formation can be instigated through certain major aspects. There are a number of rocks present in the world and all of them possess different formational process and structures. This part would look into the process of formation of three major rock forms on the earth surface.
? Process of formation of igneous rocks
Igneous rocks are framed when liquefied shake cools and hardens. Liquefied rocks come in the form of magma. This magma is found to be present under the surface of the earth. It can likewise come out as a source of molten rock materials from under the surface of the earth and turns in solidified forms when it is discharged onto the surface of the earth. The magma is produced basically through the process of attributes that are produced and brought onto the surface of the earth during the volcanic eruption. However, the igneous rocks are produced under certain matters and states which are inclusive of different forms and manners (Riouxet al. 2016). For example, pumice is one kind of igneous rock that is produced based when the molten lava from beneath the earth's surface is trapped with water and the gas ejected also from the volcano. Similarly, different forms are derived giving rise to different attributes and characteristics.
Figure 1: Formation of igneous rocks
(Source: Osinski et al. 2018)
They have lower susceptibility to weathering as they are hard and smooth in nature. Yet they are weathered by the air and water. The igneous rocks are found majorly consisting of calcium. The rocks containing calcium is found to be more susceptible to weathering. The weathering process is both fair and quick. Thus, through the process of weathering of igneous rocks the soil receives high amount of calcium.
? Process of formation of sedimentary rocks
The sedimentary rocks are formed in a especial way. The rocks are developed when the materials that have been eroded from a number of sources finally settles down. The materials that are originally eroded are soil and other materials. The settlements are formed in a manner that is one on the top of the other. Thus, there is a formation of layer. Among the layers formed, the lower layer is trapped at the end and hence and feels the intense pressure and heat from the above layers on it (Schön, 2015). Hence, these layers usually develop into rocks under pressure, weight and heat. The examples of the sedimentary rocks are sandstone, shale, limestone, gypsum, conglomerate, etc. these rocks are majorly found in the deltas where the soils and other eroded materials are deposited in layers.
Figure 2: Process of formation of sedimentary rocks
(Source: Riouxet al. 2016)
Their susceptibility to weathering is low as they are placed above the earth surface. Water and air are the weathering agents. The rocks are usually characterised with fewer joints, fractures as well as bending. Therefore, they have greater resistant towards weathering. These rocks are therefore, produced with less massive fractures and allow the weathering agent to pass off well. On the other hand, due to less cracks the other weathering agents such as water is not allowed to enter into the spaces between the layers of the rocks.
? Process of formation of metamorphic rocks
Metamorphic rocks are those that have gone changes from the one form to the other. This is well signified by the name which contains metamorphosis that means change in form. Thus, the original form of metamorphic rock might be igneous, sedimentary or any other kinds of rocks. The changes in the rock form occurs when the rocks are lied or buried under high pressure as well as an extreme heat conditions below the surface of the earth. These rocks that turn in metamorphic are produced mainly due to the conditions that occur in the areas where the rocks are subjected to inundation due to movement of the tectonic plates (Han and Yu, 2016). The types of the metamorphic rocks can be understood from their examples, like gneiss, slate, marble, etc.
Figure 3: Formation of metamorphic rocks
(Source: Xuanjunet al. 2018)
Metamorphic rocks are mainly susceptible to the mechanical erosion or weathering types. These are also known as physical weathering and are weathered based on the physical functioning of a number of physical forces such as exfoliation, thermal expansion, etc.
P 2. Analysis of the discontinuous nature of rock mass and characterization of the designing and construction purposes (P2) (M1) (D1)
The discontinuous nature of rock masses tends to the heterogeneous and anisotropic in nature as per the information obtained from the study carried out by the civil engineering. The term discontinuity used within the geotechnical engineering tend to refer to the surface or the plane which marks the changes which takes place in the physical or chemical process in a rock mass or soil (Fu, et al. 2016). The rocks are found to be different from most of the materials used in the process of engineering which consists of the fractures of one type or another and render the discontinuous structure. The rock mass hence, is the total in-situ medium comprising of the bedding planes, joints, fields, and the other structural features. The analysis of the characterization of the rock masses for design and construction purposes are required to detailed examination of the weathering profile and characteristics of discontinuity (Tuckey, and Stead, 2016). Effect of weathering is crucial as observed found within the tropical climate as the various properties might get changed depending upon the original material and the process it undergoes during formations. Other aspects of discontinuity this, is able to reduce the mass strength of the rocks. The uncemented sediments refers to the materials such as the sands and the loose aggregate usually gathered from the unconsolidated sediments from the lakes, rivers and the ones coming from the sea (Zhang, 2016). Overviewing of the works carried out by the civil engineers related with designing, construction and maintenance of the physical environment along with building infrastructure for the needs of the public. In context with the civil engineering construction project initiated in Hong Kong it is found that the geographical landscape of Hong Kong mainly is formed rom reclamation of land from the ocean and mountainous regions. The occurrence of various issues is thus, the constructions which are being carried out involves risks which would further cause disruption on the new construction of bridges and tunnels. Taking the case study of the transport infrastructure in Hong Kong, such us the international links, water and sanitation and energy it has been found that the building of tunnels through the mountainous regions and the bridges connecting the cities are difficult. The cross-harbour tunnels which links the Hong Kong Island with Kowloon are not actually being cut through the rocks under sea but are immersed tube designs are constructed in floated positions on the surface of the water before it gets sunk. Thereby, it can be said that while addressing the different issues faced by the civil engineers are selecting the appropriate rocks which will be able to be used for carrying out the process of construction so that it will be able to provide safety and security to the populations residing within the regions. Although issues also occur due to the uncemented sediments which tend to deteriorate the bridges and tunnels which are being constructed are required to be used after proper examining of the location and using the rocks which will be able to survive the natural calamities and damages.
LO 2: Exploring and classifying soils to the current codes of practice
P3. Detailed exploration of the methods and techniques used in ground and site investigation, soil sampling, soil descriptions and soil classification to current codes of practice
The site characterization tends to refer to the process of collection of important data about the appraisal of data, assessment and representing the same with the use of maps in order to eliminate the hazards in the ground underneath the site which cannot be known (Arnold, 2016). Overview of the study tend to show that the sources of information which are available to the engineer comprises of geological maps, topographic maps, aerial photographs, groundwater information soil survey maps, and reports of the existing site investigation. Along with this the civil engineers also required to examine thoroughly about the local history literature river and coastal information and metrological records as well (Lai, Derobert and Annan, 2018). The process of soil sampling soil profiling is found to be the outcome of the site investigation and vertical sections which is used to show the scaling of the sequence of the thickness or the strata of the soil profiles. The sampling of soil is found to be of two types such as the disturbed sample and the undisturbed sample. The disturbed sample shows that the soil sample consists of as borehole which is being excavated within it due to which it is known as the disturbed soil samples. On the other hand, the undisturbed samples are found to be driving a core into the ground and is required to be removed carefully. In the first stage it is given two coats of paraffin wax on both sides and secondly it is placed in an airtight container. As per the current codes of practice the site investigation report is the final outcome of the exploration program which is being carried out and consists of the following aspects discussed as follows:
1. Preamble: This section will be presenting a brief summary of the location of the sites, date of investigation, and the other details which will be able to give clarity to the report.
2. Description of the site: This section is important as it will be shedding light upon the particular area or site of construction where the instructions are planned to be carried out. It will be helpful for determining whether the location will be open area or a redevelopment site of any old foundations. A map will be used for identification of the locations and for proper positioning of the any boreholes put down and will be included within the report.
3. Borehole journals: These journals help in listing down the materials which will be encountered during the boring. It will be best represented in sectional forms for determining the depth where the different materials can be met with in much easier ways.
4. Description of the laboratory soil tests: This is another vital aspect present within it as this will help in effectively conducting the tests along with laboratory sheets, which will be capable of determining the particle size distribution about the curves, liquid limit plots and the other necessities.
Evaluation of the geo-guide, geo-space and general specification for understanding the techniques used for ground investigation works (M2)
Geo-guide techniques used for ground investigation works: The geotechnical guide helps in representing about the recommended standards of good practices for conducting the site investigation in Hong Kong. The use of the geo-guide is emphasizes the information for conjunction in reference with the companion document (Koo, Kwan and Sze, 2016). Setting of the standards of the geotechnical standards are considered to be useful as it helps in providing up to date information about the changes which are being made or the existing information being revised.
a) The techniques, which is present within the geotechnical guide about the foundation design and construction refers to the global FOS approach for piling against the failures within the lateral resistance, tension and compression.
Figure 4: FOS approach for piling against the failures within the lateral resistance, tension and compression
Source: (Randolph and Gourvenec, 2017)
b) The temporary excavation published within the geotechnical guides helps in reviewing the global FOS approach for the excavations done against the ultimate failures such as by sliding, uplifting and overturning.
Figure 5: FOS approach for excavations done against the ultimate failures such as by sliding, uplifting and overturning
Source: (Xu, 2015)
c) Soil nails or soil nailing is one of the approaches, which are being used for slope stabilization within Hong Kong. This technique is being used during installation of soil nails and controlling of grouting, initiating good practices within the designing of steel soil nails for soil cut slopes and is helpful (Sharma, Samanta and Sarkar, 2019).
Thus, from the above it can be said that evaluating the geoguide used for investigating about the groundwater investigation can be carried out using the methods discussed. The methods will be useful for determining the water carrying services and identify the leakage along with the risks associated with landslides and boulder falls form the natural terrain.
Figure 6: Recommended Interim Societal Risk criteria in context with landslides and boulder falls form the natural terrain
Source: (Cruden, 2017)
General characteristics:
The importance of considering the general characteristics lies underneath the fact that it is useful for describing the bedding types or the arrangements of the beds and the spacing among the bedding planes. This helps further is useful for assuming the requirements and taking actions for conducting the orientation, surface textures and the openness of the groundwater and its level, which will be packed or will be impacted during the period of construction. It is evident that the bedding of the Hong Kong soils is found to be limited with the marine deposits and the alluvial soils.
Geo-space and general specification for understanding the techniques used for ground investigation works:
Geo-space techniques used for ground investigation works: The geophysical methods refer to the methods, which are being used for locating the depth of the solid rock, resistivity and seismic methods, locating the shallow deposits as well. The use of the geo-space techniques are hence, considered to be useful for groundwater investigation (Peng and Peng, 2018). Overview of the study determines the various geophysical methods, which are present such as the magnetic method, gravimetric method, seismic method, geothermal method, electrical method and the radioactive method. Using these methods will be useful for getting accurate details about the groundwater and its properties within the construction sites.
Figure 7: Gravimetric method
Source: (Blick, Freeden and Nutz, 2017)
Figure 8: Geothermal method
Source: (Aretouyap, Nouck and Nouayou, 2016)
Figure 9: Electrical method
Source: (Aydin, et al. 2018)
The purpose and objectives for the groundwater investigation, supplementary investigation within the construction sites in Hong Kong
The purpose and objectives for the groundwater investigation, supplementary investigation within the construction sites gives information about the hilly terrain in Hong Kong, which further, denotes about the formation of large number of slopes and retaining walls, which are manmade. It also shows data that the walls designed before 1977, by following the thumb rule were prone to landslides and are capable of surviving under heavy rain. The need and requirements of for the supplementary investigation within the construction sites are necessary for obtaining results about the past history and the methods used which was beneficial at the same time will be able to determine the changes occurring within the groundwater.
P4. Classification of solids from soil particle size, soil types, specific gravity and plasticity indices with the current codes of practice (D2)
The importance of classification of solids from the particles sizes, soil types, specific gravity and the plasticity indices will be required, to be marinated in appropriate manner as this will lead to accomplishing the global sustainable goals in effective manner. In context with the references to the concepts and the design carried out by the civil engineers during the process of designing must be sustainable form of infrastructures at the same time using less material consumption. The incorporating of the advanced systems, software and the processes will be another advantage although the infrastructure made such as the construction of roads, bridges, railways and tunnels constructed within Hong Kong consists of several hazards due to the improper geographic location for residency. The occurrence of natural calamities such as earthquakes, floods and landslides happens from time to time within less duration. The classification of the solids from the soils types are required to be examined carefully by the civil engineer before initiating the process of construction. The overview of the distribution of rocks and soils in Hong Kong as per the Geological Survey is found to have published series of 1:20,000 scale geological maps of Hong Kong depicting the different distribution of rock types, faults and superficial deposits.
Figure 10: Bedrock geology of the offshore and onshore areas of Hong Kong
Source: (Kwong, Jiao and Chan, 2016)
The overview of the study shows that the sedimentary which are formed from the fragmented particles of the materials or the rocks which are been transported with the various natural processes as by gravity, wind, air, ice or the chemical precipitates. The soil types depend upon the characterization of the rocks and types of soils available within the particular regions. In context with the Hong Kong it was being found that nature of the types of rocks available are mainly igneous which are formed by the solidification of magma. On the other hand, the plasticity indices are being noted from the particle distribution size and from conducting t5he laboratory tests performed by following the laboratory tests. The plasticity properties are being evident from the simultaneous presence of silts and clay within the fine particles of soils. The distribution of the particle sizes can be observed present within the soils of Hong Kong contained thirty five percent of boulders or cobbles rather the fine particles of soils. Another example of the soil, which comprises of high amount of plasticity, is the black soil. The black soil types are expansive which are basically for due to the high chemical weathering. It exhibits large amount of swelling and shrinkages as huge amount of montmorillonite is present within it.
Figure 11: Table determining that the plasticity is based upon the liquid limit
Source: (Hobbs, et al. 2019)
Hence, it can be said that the plasticity of the soil refers to the property, which continuously undergoes deformation without permanently rupturing it.
LO3: Analysis of soil properties determined by geotechnical procedures (M3)
P5. Evaluation of how the properties of soil can be determined, including content of moisture, density, shear strength, compressibility, specific gravity, liquid and plasticity indices, California bearing ratio
The analysis of the soil properties determines that the processes used within the geotechnical methods within the engineering helps in understanding the different properties of soils. The definitions of soil are directly obtained from the field exposures as well from the excavations form the samples recovered from the excavations or from the borehole. The geotechnical procedures of soil, which can be used for determining the properties of soil, are discussed as follows:
Moisture content of the soil: The moisture content of the soil refers to the ratio of the weight of water to that of weight of the solids within a given mass of soil. In context with the soils available in Hong Kong the soils present in the unsaturated zone above the water table undergoes seasonal fluctuations in the content of moisture. Thus, the types of soils available in the regions of Hong Kong are cohesive in nature, which are dry, moist and wet type. From this it can be said that these types of soils are not suitable for any types of construction as the developed structure will be hazardous in nature.
Density of the soil: Measuring the density of the soil is one of the important criteria as it will be able to reflect upon the ability of soil for functioning such as by providing structural support, solute movement and soil aeration along with the impact of the water. In context with the sample soils of the Hong Kong construction sites shows that no such N values are present due to which the N values are recorded directly. It is evident from the study that the N values of gravels and sands present rate being measured using the boreholes by using the Standard Penetration Tests.
Shear strength of the soil: Identifying the shear strength of the soils refers to the term used within the soil mechanics for determining the magnitude of the shear stress, which can be sustained by the soil. Therefore, the resistance of the soils tends to relate to the outcomes generated as a result of interlocking of the particles, frictions along with the concentration of bonding present within the particles which are bonded together. The shear strength of the soil can be measured using the formula as:
Compressibility of the soil: The compressibility of the soil refers to the capabilities of the soil for reducing the volume when subjected to the mechanical loads (Atahu, Saathoff and Gebissa, 2019). The compressibility of soils found to be undergoing the methods of decreasing the volume within the soil under externally applied loads or compression. In context with the scenarios of Hong Kong the tectonic joints is one of the examples, which are being formed due to the regional compression. The compressibility of the soils tends to differ due to the origins, faults or the folds, which leads to the symmetric arrangement.
Specific gravity of the soil: The specific gravity of the soils relates to the knowledge, which is considered to be an important part for calculating the properties present within the soil such as the degree of saturation, relationship of weight volume and the void ratio. This is one of the vital aspects, which can be used for evaluating the properties of soil (Barnes, 2016). The presence of colluvial soils or the mass wasting deposits are found within the regions of Hong Kong. These types of soil formation do not have any specific structures although consists of mixed accumulations of the fragments of rocks and soils which are deposited at the base of the natural slopes.
Liquid and plasticity indices of the soil: The liquid and the plasticity indices of the soil is another important feature, which is required to be emphasized upon, as it will help in evaluating the properties of the soil. Provided the plasticity index refer to the size of the range of water contents highlighting the presence of the plastic properties within the soil.
California bearing ratio or CBR of the soil: The evaluation of the properties of soil based upon the ratio obtained in percentage of the force per unit area which is required for penetrate the mass of soil along with using the standard circular plunger of 50 mm diameter with rate of 1.25mm/min.
LO4: Producing a proposal for addressing the identified geotechnical problems and weakness (M4) (D3)
P6. Designing of proposals for addressing the geotechnical, issues related with the embankments, bridge and road foundations
Preparing of the proposal is one of the necessities carried out within the geological investigation, as this will help the civil engineers for gaining deeper insights about the sites where the construction process will be beginning. The geological investigation will be carried out based on the nature of the engineering project undertaken and identification of the complexities present within the project. Therefore, the requirement for developing a geological model will be able to successfully carry out each of the processes and the uncertainties present within the same and the potential geological hazards. In the initial stages of developing the proposal, the requirements, which will be required for examining the sites, will be based upon the information obtained from the code of conduct. This will be advantageous, as it will involve fieldwork, interpretation, aerial photographs, geophysical and hydro-geological surveys. The accuracy of the developed model will be based on the following outcomes such that it will be able to provide a clear presentation of the concepts and the strategies, which will be used for initiating the project. The ground investigation will be emphasized upon as it will be able to assume the occurrence of the hazards or the uncertainties along with the risks associated with it.
Geotechnical issues related with the embankments:
Over viewing of hazard which took place on the, twenty-second of March 2013, during the heavy rainstorm it was found that due to the severe distress reinforced earth wall in Hong Kong. At the time of heavy rainstorm the wall was found to be under construction and was process of construction was near about completion. The distress was found to be hugely affecting upon the due pot the distress caused at the three localized areas along the wall forming as sinkhole within the backfilled soil masses. The issues which was determined from these particular incident that as the soil deposition was present near the surface of the drainage system the construction which was being made was not flexible and reliable.
Figure 12: Proper calculation of the design of embankments
Source: (Manic, et al. 2016)
Therefore, with the severe rain the changes within the water level flooded along with overflowing the debris followed by the road carriageway below at the same time. The issue related with the construction of embankments can be said was not undergo detailed investigations due to which all the requirements along with the code of conduct were not followed properly. Although this particular incident did not create any havoc among the individuals residing within the local communities but no harm was caused.
Geotechnical issues related with the bridge and road foundations:
The geotechnical issues which are evident during the construction of the bride and road was found that as Hong Kong is designed within the discontinuous types of rock masses along with the hilly and coastal regions tend to impact the constructions which are initiated (Morelli and Baldovin, 2015). The civil engineers are hence, required to carry out the investigations and select the designs, which will be flexible and will be able to provide safety and security to the individuals residing within the country during their travel.
Justification of the identified geotechnical weaknesses as designed in the proposal during the meeting: The weakness was identified in the initial stage as although the plan developed was hazardous based upon the location, which is Hong Kong. Therefore, even after implementation of the advanced technologies for designing and mechanism, during the construction the civil engineers will not be able to change the impact of natural disasters or hazards.
Conclusion
The study carried out in the sections above helped in clearing out the various aspects consisting within the geotechnical and soil mechanisms with reference to the scenario provided. Over viewing of the rock types, their classification and formations as a result of weathering processes helped in understanding that the nature of rocks changes depending upon the processes it undergoes. Thus, the study allows an insight on the prior activities that are associated with the techniques and methods present in the civil engineering substructures attempting to mitigate the hazards of earthquakes, associated with the excavation, load, haul and the complex foundations that are aligned with the principles and frameworks of civil engineering. The main aim is to evaluate the methods that fit the issues of ground and slope stability in the cases ad project occurring in Hong Kong. Therefore, these assessments primarily aim at driving the development of the site safety plan along with the risk assessment and the method statement for a given civil engineering activity. The necessity to understand the discontinuous nature of their rock mass tend to highlight the issues that are faced by the civil engineers during the planning, developing and initiating the construction process in context with the constructions carried out in Hong Kong. The necessity to understand the discontinuous nature of their rock mass tend to highlight the issues that are faced by the civil engineers during the planning, developing and initiating the construction process in context with the constructions carried out in Hong Kong. The information obtained from the code of practices helps in dealing with the investigation sites in effective manner and determines the suitability of the sites for proceeding the construction process. Hence, it can be said that the study was helpful in enhancing the skill and knowledge of the individuals in prosperous manner.