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Community

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  1. Fore bearing
    It is the bearing of line when the first letter of line say AB is taken as origin. This is to be written as Fore Bearing (F.B).
    Back bearing
    It is the bearing of line when second letter of line say AB is taken as origin and this is to be written as Back Bearing (B.B).
    Theoretical difference between Fore Bearing (F.B) and Back Bearing (B.B) should be 180°.
    Local attraction
    If the difference between magnetic Fore Bearing and Back Bearing of a line is not exactly 180°, it may be due to presence of local attraction at one of both stations. If this difference is exactly 180° then both stations are free from local attraction. Local attraction may be due to following reasons.
    Overhead electrical wires
    Magnetic materials in the vicinity
    Practice problem
    In the following table observed Bearings are given, we will compute the corrected bearings and Internal Angles.
    Line
    Observed
    Correction
    Corrected
    F.B
    B.B
    F.B
    B.B
    AB
    70° 00′
    251° 00′
    A= +30′ , B= -30′
    70° 30′
    250° 30′
    BC
    328° 00′
    145° 00′
    -
    327° 30′
    147° 00′
    CD
    225° 00′
    71° 00′
    -
    257° 30′
    77° 30′
    DA
    139° 00′
    316° 00′
    -
    136° 30′
    316° 30′
    By observing the table, it may be noted that no line has a difference of exactly 180° between Fore Bearing and Back Bearing. In such a case, a line where the difference is closest to 180° is selected. Such a line is called line of least disagreement, for this line correction is assign to each of the two stations of that line with opposite sign. In the above table line AB is selected for error distribution. Now, we will compute internal angles from these corrected Bearings.
    A = (360° - 316° 30′) + 70° 30′ = 114° 00′
    B = 327° 30′ - 250° 30′ = 77° 00′
    C = 257° 30′ - 147° 30′ = 110° 00′
    D = 136° 30′ - 77° 30′ = 59° 00′
    Before computation of internal angles, you need to draw a rough sketch of scheme based on corrected bearings so that you can judge which angle is lying in which quadrant.
  2. Latitude and Departure
    In order to do start with Theodolite Traversing you should be familiar with the Latitude and Departure which are discussed briefly below,
    OA is the line with whole circle bearing equal to θ.
    OC = Latitude = lCosθ
    OB = Departure = lSinθ
    By using the above formulae for Latitude and Departure with whole circle bearing, calculator will be giving algebraic sign automatically for Latitude and Departure.
    For a closed Traverse ∑ of all Latitude is equal to zero and ∑ of Departure is also equal to zero.
    Consecutive co-ordinates
    When the Latitude and Departure are calculated at second point of a given line taking first point as a origin then it is called consecutive co-ordinates.
    Independent co-ordinates
    Independent co-ordinates are the Latitude and Departure of points of a traverse with respect to a common origin, so that all the values are +ve. These are used for plotting purposes.
    Bowdich Rule
    This rule is used to apply the correction in Latitude and Departure which states that correction in Latitude/Departure is equal to Length of Line multiply by Total correction in Latitude/Departure and then dividing by the perimeter.
    Traverse Table
    For the following traverse ABCD, I have applied the correction in Latitude and Departure using Bowdich rule.
    Line
    L (m)
    Bearing (° ′ ″)
    Latd.
    Depr.
    Corrections applied
    Consecutive co-ord.
    Independent co-ord.
    Latd.
    Depr.
    Latd.
    Depr.
    Latd.
    Depd.
    AB
    148
    115 30
    -63.27
    133.58
    -0.26
    -
    -63.98
    133.58
    500
    500
    BC
    172
    42 25
    126.98
    116.02
    -0.30
    -
    126.68
    116.02
    628.68
    616.02
    CD
    201
    205 30
    -181.42
    -86.53
    -0.36
    -
    -181.7
    -86.53
    444.90
    529.49
    DA
    202
    306 15
    119.44
    -162.9
    -0.36
    -
    119.08
    -162.9
    563.98
    366.59
    ∑
    723
     
    +1.28
    +0.17
    -1.28
     
    0
    +0.17
     
     
    As you can see, correction was not applied in Departure as the error was too small to be neglected. Using Bowdich rule we can apply correction in Latitude and Departure for respective line
  3. The following points should be kept in mind while selecting pipe for a certain water supply system,
    Carrying capacity.
    Durability.
    Fire cost.
    Maintenance cost.
    Type of water to be conveyed.
    1. Cast iron pipes (C.I)
    Most widely used for the city water supplies.
    Average life is 100 years.
    Corrosion my reduce its capacity by 70%.
    Must be lined with cement or bitumen.
    C = 130 for new pipe.
    C = 100 for old pipe (Selected for Design).
    "C" is the Hazen Williams Coefficient known as HWC. It is the important term used in the design of water distribution system.
    2. Steel pipes
    Contains less carbon than Cast Iron pipes.
    Frequently used for trunk mains.
    Difficult to make connections hence seldom used for water distribution systems.
    Much Stronger and lighter than Cast Iron pipes.
    Cheaper than Cast Iron pipes.
    Cannot withstand vacuum, hence collapse.
    Highly susceptible to corrosion, hence high maintenance charges are required.
    3. Ductile pipes
    Similar to Cast Iron pipes except increased ductility.
    Ductile iron is produced by adding a controlled amount of Mg into molten iron of low sulphur and phosphorous content.
    Stronger, tougher and elastic than Cast Iron pipes.
    More expensive than Cast Iron pipes.
    4. Galvanized iron (G.I) pipes
    Manufactured by dipping Cast Iron pipe in molten zinc.
    Resistant to corrosion.
    Mainly used for plumbing.
    5. Concrete pipes
    Usual size of Reinforced Cement Concrete pipe is 400mm dia. and above.
    Not subjected to corrosion.
    Manufactured at or near site.
    Average life is 75 years.
    C = 138 to 152.
    6. Asbestos cement pipes (A.C)
    Sizes are 100mm to 600mm dia.
    Average life is 30 years.
    Immune to actions of acids, salts, soil and corrosion.
    Less cost for laying and jointing.
    Less plumbing cost due to less friction.
    C = 140.
    Asbestos Cement pipes are economical and are generally preferred to use in the design of water supply systems.
    7. Poly vinyl chloride pipes (PVC)
    Mainly used for domestic plumbing.
    Easy to install and easy to handle.
    Cheaper in material cost
    Weak to sustain load.
    Only available 350mm dia size.
    Expected life is 25 years.

  4. Technical terms in leveling and equipment

    Surveying · Community · 12/23/2025 09:50 AM

    Leveling equipment
    a) Level
    There are different types of Levels as follows,
    1. Dumpy level
    It is the type of Level in which whole body of level is cast in one unit.
    2. Tilting level
    Still being used, Level can be tilted in vertical plane with the help of tilting drum.
    3. Automatic level
    In this type, the line of sight becomes horizontal when the Level is within certain limits. This system provides the works on the principal of gravitation.
    b) Staff
    It is the graduated rod of maximum 5m length usually available in telescopic form. The gradations are both in feets and meters. Smallest graduation in feet is 0.01 ft or 1/100 ft and smallest division in meters is .005m.
    Technical terms in leveling
    1 - Sights
    A reading taken from a level on staff is called sight.
    2 - Back sight (B.S)
    It is the first sight taken after setting of the instrument.
    3 - Fore sight (F.S)
    It is the last sight taken before shifting the instrument.
    4 - Intermediate sight (I.S)
    These are sights taken between F.S and B.S.
    5 - Line of collimation
    It is the straight line joining the intersection of cross hairs and optical center of object glass.
    6 - Level line
    It is the curved line equidistant from the center of earth at all points.
    7 - Horizontal line
    It is the straight line tangent to observer position. The of collimation obtained by a carefully leveled instrument is a horizontal line.
    8 - Reduced level (R.L)
    It is the level of a point with respect to a certain datum whose level is taken as zero.
    9 - Datum
    It is a certain reference level to which levels of all other points are referred
    i.e in Pakistan Datum is mean sea level (MSL) at Karachi.
    10 - Change point (C.P)
    It is the last position of staff after which the instrument was shifted.

  5. Methods of rock reinforcement in tunnels

    Geotechnical engineering · Community · 12/17/2025 01:36 PM

    Rock support for tunnels and underground cavern design is a demanding and very complex task. In principle, the problem can be approached from two directions: The first way is to define the relationship between geo-mechanical properties of the rock mass and the support methods used. This is mostly based on the utilization of statistical and empirical data gathered in similar conditions. The second way is to estimate the deformation characteristics of the rock structure, and then the related effect on supporting structures. This method typically requires very good rock property and rock mass property data.
    The most important factors affecting rock reinforcement method and design are:
    Geological factors, such as rock mass structure.
    Dimensions and geometry of excavated space.
    Location and direction of caverns in the rock mass.
    Excavation method.
    Use and expected lifetime of space.
    Common support methods in underground construction work are:
    Bolting.
    Sprayed Concrete.
    Steel Arches.
    Concrete Lining.
    Grouting.
    1. BOLTING
    Rock bolting is one of the most common methods of rock reinforcement. The main principle of bolting is to reinforce loose rock or fractured in-situ rock to precent caving or spalling, and to assist the rock mass to form its own self-supporting structure. Bolts can be divided into three categories according to the way they behave in the rock, for example, grouted bolts, mechanically anchored bolts and friction bolts.
    1.1. Cement-grouted bolts
    Cement-grouted rebar is still the most inexpensive and widely used rock bolt, because it is simple and quick to install and can be used with or without mechanized equipment. Correctly installed, a cement-grouted bolt gives rock support for years.
    The grout cement provides protection from corrosion. Special galvanized and/or epoxy coated bolts can be used in extremely severe conditions.
    The major disadvantages of the cement-grouted bolt is its relatively long hardening period. The grout takes between 15-25 hours to harden; therefore, it does not provide immediate support. When immediate support and/or pre-tensioning is needed, a grouted wedge-type or expansion-shell bolt can be used. Mixing additives in the grout can reduce the hardening time, but it also increases bolting cost.
    The water/cement ratio considerably affects the quality of installed bolts. The best water/cement ratio is 0.3 (w/c). This grout density can be easily used and maintained when using mechanized bolting equipment.
    1.2. Resin-grouted bolts
    Resin-grouted bolts give the required support relatively quick due to a short hardening time. When correctly installed with full-length grouting, the resin-grouted bolt is considered to give permanent support with a life span of 20 to 30 years.
    By using resins with two different hardening times, with faster one at the bottom of the hole and another that is slower at the stem, the bolts can be pre-tensioned. The same can be done for short-time support by only bottom-grouting the bolt.
    1.3. Cable bolts
    Cable or steel strained bolts are used to bind and secure large volumes of rock around large caverns. Cable bolts can be used both before and after excavation, and also used for preventing rockslides in mountain slopes and quarries.
    The anchor itself is a steel strand, typically two strands of 15.2 mm in diameter, with typical bolt length being between 10-25 meters.
    Today, with mechanizes equipment, the installation and grouting of cable bolts of any length is fast and efficient, and the cable bolt's bearing capacity clearly exceeds capacity of rebar steel bolts. Its lack of efficient protection against corrosion limits its extensive use in permanent rock support.
    1.4. Mechanically anchored bolts
    Mechanically anchored bolts are usually wedge or expansion-shell bolts that are point-anchored at the bottom of the hole.
    The bolt has an expanding anchor at its end. After insertion, the bolt is either rotated or pressed/hammered against the bottom of the hole. This expands the wedged end and anchors the bolt firmly to the end sides of the hole. To install anchored bolts successfully, the hole size must be accurate, and the rock must be relatively solid.
    Wedge or expansion-shell bolts are typically meant for temporary rock support. Together with cement grouting, it provides both immediate and long-term support.
    1.5. Friction-type bolts
    Typical examples of friction-type bolts are the split-set and Swellex bolts. Both are quick and easy to install and give instantaneous support. They cannot, however, be used for long-term reinforcement.
    The split-set bolts is hammered into the hole, which has a slightly smaller diameter than bolt. Using the correct hole size for a specific bolt diameter is essential for successful installation. Split set bolts are very suitable for layered formations. The Split-set bolts provide immediate support but only for fairly short period of time. A disadvantage is that the split-set cannot be effectively protected against corrosion. The life span can somewhat be extended by using cement grouting. The Swellex bolt has a longer life span than the Split-set. It is installed by applying high-pressure water to bolt after inserting it to the hole. The high pressure expands the bolt to its final dimensions in the hole, therefore enabling it to utilize the roughness and fractures in the bolt hole surface. As with the Split-set bolt, poor corrosion protection limits this bolt.
    1.6. Equipment for bolt installation
    Development of mechanized equipment began as early as the 1970s. Today there is a wide selection of fully mechanized equipment, and a wide variety of different methods for bolt installation. The main factors affecting the choice of method are usually tunnel size, number of bolts to be installed and work cycle arrangement at this site.
    Manual operation, the hand-held drilling and installation of bolts, is typically used in small drifts and tunnels where drilling is also performed by hand-held equipment, and there is a limited amount of bolting work.
    Semi-mechanized installation is still typical at tunneling work sites. The drilling jumbo is used for drilling bolt holes, and bolt installation is performed from the jumbo's basket boom or from a separate utility carrier or truck.
    With today's full mechanized equipment, one operator can handle the entire bolting process from drilling to grouting and bolt installation. The operator is positioned away from the unbolted area under a safety canopy that protects him from failing rock.
    Although safety is a major reason for the development of mechanized bolting equipment, the superior installation technique of mechanized bolting rigs also produces consistently higher bolting quality. Thanks to powerful cement mixers, pumps and effective grouting methods, the bolts are securely fixed and grouted to their full length, providing a sound reinforcement structure, even with long bolts.
    2. SCREENING
    Screening, which is the installation of wire mesh, is most typically used in underground mining, but also construction sites together with bolting and/or sprayed concrete. Screening is primarily performed manually by applying the wire mesh together with bolting of the tunnel. It can also be done by mechanized equipment, such as by having a screen manipulator on the bolting or shotcreting unit, or on a dedicated screening machine.
    3. SPRAYED CONCRETE
    Sprayed concrete, otherwise called shotcreting, is widely used support method in construction. It is used for temporary or long-term support, lining and backfilling. Usually, shotcrete is used together with bolting to obtain the best support or reinforcement. Shotcrete can be reinforced by adding steel fiber to the concrete.
    The most common forms of shotcreting are dry-mix and wet-mix methods. In the dry-mix method the aggregate, cement and accelerators are mixed together and propelled by compressed air. Water is added last through a control valve on spray nozzle. The dry method is suitable for manual shotcreting because the required equipment is usually inexpensive and small. On the other hand, dry method can pose a health hazards as it creates considerably more dust and rebound than the wet method. The quality also depends heavily on the shotcreting crew and may vary widely.
    In the wet mix method, aggregate, cement, additives and water are measured and mixed before transport. Today, wet mix is more widely used because it is easy to mechanize and the capacity can easily out-do the dry method. Rebound rate is low and the quality procedure is even.
    Critical factors in shotcreting are:
    Water/cement ratio.
    Grain size distribution of aggregate.
    Rebound ratio.
    Grain size distribution.
    Mix design.
    Nozzle design.
    Nozzle distance and angle.
    Layer thickness.
    Manual shotcreting has been largely replaced by mechanized shotcreting machines. With mechanized equipment, multiple capacities per hour can be reached, together with consistent and even quality of the concrete layer. Safety, ergonomic and environmental conditions are other important aspects of shotcreting. These factors are efficiently improved with mechanized shotcreting units.
    4. STEEL ARCHES
    Steel arches are common permanent support method for weak rock formations. These are usually installed in the tunnel immediately after each round, at the same time as rock bolting. Steel arches are also commonly installed during shotcreting to give temporary support before final concrete lining of e.g. traffic tunnels.
    5. GROUTING
    Grouting is the method in which a solidifying liquid is pressure-injected into the rock mass. The main purpose of grouting is to prevent ground water leakage into the tunnel, and to increase overall rock mass strength.
    In grouting, a chemical agent or cement mass is pressure-pumped into the drill-hole to penetrate fractured and fill cavities.
    In drill and blast tunneling, grouting is typically performed before (pre-grouting) or after (post-grouting) excavation.
    5.1 Pre-grouting
    Pre-grouting means that rock mass is grouted before excavation begins. Usually, pre-grouting is done from the tunnel, but in situations with low overburden it is also possible to do it from the surface.
    Probe holes are drilled to map possible fractures and register water flow. This helps to analyze the need for grouting. Later, grout holes are drilled in conical-fan shape in front of the tunnel face. Typical grouting fan length is 15-25 meters.
    After drilling, the grouting agent is pumped into the hole until leakage has reached an acceptable level. Tunnel excavation can begin once the grouting mass has settled.
    Grouting fans overlap each other so that in 15-meter-long grout holes, grouting is performed every second or every third round depending on the round length.
    5.2 Grouting after excavation (post-grouting)
    When grouting is done after excavation, grouting holes are drilled from the tunnel in a radial form. In good rock conditions with small water leakage, post-grouting is often adequate. Post-grouting enables better rock mass structure evaluation. On the other hand, water leakage blockage is more difficult because the water flow tends to flush away the grouting agent before it hardens.
    5.3. Grouting agents
    The grouting agents can be divided into two categories: Suspension and Chemical.
    Cement water or bentonite water suspension is the most typical in rock grouting because both are cost-effective and environmentally safe. The drawback is, however, a relatively large maximum grain size, which leads to poor penetration in small cracks. Penetration characteristics can, however, be improved by adding additives. Silicate-based chemicals are also used to speed up the hardening time.
    Chemical agents are silicate-based, resin polymers, polyurethane-based or lignin-based chemicals that typically penetrate very s cracks and have adjustable hardening times.

  6. Types of sewers and sewer systems

    Environmental engineering · Community · 06/05/2025 05:18 PM

    Types of sewers
    1. Sanitary sewer
    It carries sanitary sewage i.e. wastewater from municipality including domestic and industrial wastewater.
    2. Storm sewer
    It carries storm sewage including surface runoff and street wash.
    3. Combined sewer
    It carries domestic, industrial and storm sewage.
    4. House sewer
    It is the sewer conveying sewage from plumbing system of a building to common/municipal sewer.
    5. Lateral sewer
    This sewer carries discharge from house sewers.
    6. Submain sewer
    This sewer receives discharge from two or more laterals.
    7. Main or trunk sewer
    It receives discharge from two or more submains.
    8. Outfall sewer
    It receives discharge from all collecting system and conveys it to point of final disposal.
    Types of sewer systems
    1. Separate system
    If stormwater is carried separately from domestic and industrial wastewater, the system is called separate system. Separate systems are favored when:
    There is an immediate need for collection of sanitary sewage but not for stormwater.
    When sanitary sewage needs treatment, but the stormwater does not.
    2. Combined system
    It is the system in which the sewer carries both sanitary and stormwater. Combined system is favored when:
    Combined sewage can be disposed off without treatment.
    Both sanitary and stormwater need treatment.
    Streets are narrow and two separate sewers cannot be laid.
    3. Partially combined system
    If some portion of storm or surface runoff is allowed to be carried along with sanitary sewage, the system is known as partially combined system.
    In urban areas of developing countries, mostly partially combined system is employed.
  7. History of electronic distance measurement
    In surveying distance measurements were always a challenge for surveyors specially when long distances were to be measured with high accuracy. In 1950 scientist tried to calculate the distance by using light beam to travel over unknown distance with measured time.
    Ordinary lights travel at a velocity of 186,000 miles per second, therefore the time taken will be very small to cover a short distance. This idea was soon dropped but the scientists succeeded in finding a low velocity light beam in form of Infra-Red Rays generated by solid state Gallium Arsenide Diode (GAD). This was put into laboratory experimentation in 1960 and finally instrument called Electronic Distance Measurement came into existence. Initially the instruments were very expensive but as the demand increased the price was within the reach of most professionals.
    Revolution in surveying due to EDM
    Modern EDM equipment contains hard-wired algorithms for reducing the slope distance to its horizontal and vertical equivalent. For most engineering surveys, Total stations combined with electronic data loggers are now virtually standard equipment on site. Basic theodolites can be transformed into total stations by add-on, top-mounted EDM modules. The development of EDM has produced fundamental changes in surveying procedures e.g.
    Traversing on a grandiose scale, with much greater control of swing errors, is now a standard procedure.
    The inclusion of many more measured distances into triangulation, rendering classical triangulation obsolete. This results in much greater control of scale error.
    Setting out and photogrammetric control, over large areas, by polar coordinates from a single base line.
    Deformation monitoring to sub-millimeter accuracies using high-precision EDM
    The latest developments in EDM equipment provide plug-in recording modules, capable of recording many thousand blocks of data for direct transfer to the computer. There is practically no surveying operation which does not utilize the speed, economy, accuracy and reliability of modern EDM equipment. For example, the EDM instrument Model # LEICA RM100 BUILDER POWER have the following particulars,
    Absolute circle reading
    Laser plummet
    Endless drives
    30x magnification
    Dual-Axis compensation
    High resolution LCD display
    Electronic laser distance measurement
    Graphic sketches
    EDM measurement with red laser on target
    Upload and transfer data
    Data editing and exchange
    Connectivity to 3rd party devices
    Hence, the advent of EDM equipment has completely revolutionized all surveying procedures, resulting in a change of emphasis and techniques. Taping distance, with all its associated problems, has been rendered obsolete for all base-line measurement. Distance can now be measured easily, quickly and with great accuracy, regardless of terrain conditions.

  8. Methods of booking and reduction of levels

    Surveying · Community · 06/05/2025 08:58 PM

    1. Using rise and fall method
    In this method booking is done in the following manner,
    B.S
    I.S
    F.S
    Rise
    Fall
    R.L
    Remarks
    2.570
    -
    -
    -
    -
    100.00
    A
    3.750
    -
    1.200
    1.370
    -
    101.37
    C.P
    -
    -
    3.750
    -
    0.70
    100.67
    B
    5.620
    -
    4.950
    1.370
    0.70
    -
    -
    1) On any page of book, the first reading is always a B.S and last reading is always a F.S. If you are not getting F.S as last reading on each page, then it means you have done mistake while booking readings.
    2) From the B.S next F.S is subtracted. If the answer is positive (+), it will be Rise and if the answer is negative (-) it be Fall and put that reading in respective box.
    3) In the above table, I have assumed that Reduce Level (R.L) of point A is 100.0 and you can see R.L of point B is 100.67, which shows that point B is .67 units higher than point A.
    In case of numerous readings, the check should be applied at the end of each page while booking reading,
    ∑ (B.S) - ∑ (F.S) = ∑ Rise - ∑ Fall = R.L of last point - R.L of first point; 5.620 - 4.950 = 1.37 - 0.70 = 100.67 - 100.00 = 0.67 = 0.67
    2. Using height of collimation method (H.O.C)
    For this method use the following formulas,
    R.L + B.S = H.O.C and H.O.C - F.S = R.L
    B.S
    I.S
    F.S
    H.O.C
    R.L
    Remarks
    2.50
    -
    -
    102.50
    100.00
    -
    1.75
    1
    1.95
    102.30
    100.55
    -
    -
    2.55
    -
    -
    99.75
    -
    -
    2.70
    -
    -
    99.60
    -
    2.95
    -
    3.10
    -
    99.20
    -
    -
    -
    2.75
    -
    99.40
    -
    7.20
    -
    7.80
    -
    -
    -
    All other considerations are same as Rise/ Fall method. Below check have applied,
    ∑ (B.S) - ∑ (F.S) = R.L of last point - R.L of first point = 7.2 - 7.8 = 99.4 - 100 = -0.6 = -0.6

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