Measurement Management
Measurement management to measure and correct errors in design and construction or points that were unavoidable in design and construction is essential. Exact values for the physical properties of the ground that are substituted for structural calculation in large construction such as large foundation structures, bridges, tunnel excavation work, excavation work, sand dams, and skyscrapers have not been fully established until now. This is because the homogeneity of major strata and the hydraulic conditions of groundwater still remain as many variables. To solve this problem, it is too uneconomical to overcalculate the safety factor. In addition, if the construction is under the assumption of the average thinking conditions, this is very dangerous and may cause a large-scale accident. Therefore, Misung uses WIDAS (Patent No.: 10-1121215) to discover urgent danger signs and obtain important information for structures under construction other than the measurements required for the safety diagnosis being performed. It acquires data remotely in real time, and performs short-term and long-term measurement and management while constructing an intelligent damage assessment system by extracting frequency analysis and dynamic parameters through various sensors of WIDAS at the request of the client to improve the construction method.
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Kind Use Place Direction Tiltmeter Established in the nearby main structure and used as the data that measure and analyze the angle of tilt and transformation The structure and flat of surrounding structure Adhesion or bolting Crack gauge To measure closely the size and change of crack at the surrounding structure, ground, etc. and to grasp the velocity of crack creating and to provide other analysis of measure result with it Cracked part Establishing the crack ball at the both cracked parts and continuous measuring Vibration sound levelmeter After measuring the vibration and noise by excavation blasting and device movement and to use it for preventing from structure accident and civil affairs The surrounding structure and if need be Measuring if need be Seismic prospecting To investigate the void of the back of tunnel and to estimate the execution progressing and flowing direction of underground water The part within 1M or less both sides of joint on concrete execution Drawing up the average as the hammer for creating of seismic Strain guage To survey the stress displacement of structure and consult it to calculate the load carrying capacity Depending on measure place Divide into gauge for concrete and for steel and adhere with the moment adhesives Accelerometer To examine the accelerating force created after hitting structure and consult it to safety inspection Depending on measure place Fix with Bolting, or Set anchor Electric Theodolite To survey displacement and settlement amount of structure Depending on measure place Fix with Bolting, or Set anchor Ground horizontal displacement To survey the horizontal displacement, place, direction and size of neighboring ground on excavation and to valuate the stress of all part of earth structure The earth wall or back ground Above the depth of excavation blow antifreezing stratum Ground vertical displacement To grasp the change of settlement in each surrounding stratum and to decide the object and extent of reinforcement or to inspect the measurement data for the final settlement Around the surrounding structure or the back of earth wall Above the depth of excavation blow antifreezing stratum Ground water level meter To survey the level change of underground water and use it as the various measurement data and to analyze the causes of water level change and to establish the related counterplot The poor subsoil of the back of earth wall Above the depth of excavation blow the aquifer Pore pressure meter To measure the change of excess pore water pressure due to excavation and establish the related counterplot The poor subsoil of the back of earth wall Each depth of the weak stratum Surface settlement meter To measure the change of absolute settlement in ground surface and to compare it with the permitted settlement through surveying the velocity of settlement and predict the stability to establish the counterplot Around the surrounding structure or the back of earth wall Above the depth of freezing Earth pressure cell To measure the change of earth pressure and use it to grasp, analyze the stability of members The back of earth wall Depending of the kind of earth wall Load cell To measure the change of axal load like strut, earth anchor and use it to grasp, analyze the stability of members set anchor Excavation of each step Strain gauge After measuring the stress changing of all members in earth structure, all part in surrounding structure and executed concrete and to grasp the abnormal strain and to establish counterplot All sort of steel material Welding, adhesion, bolting
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The common principle of measurement
The measurement of initial value is practiced right after establishing the station, before the tunnel excavation affects enough and we must measure the total displacement. Also, we must be able to measure in the same section in order to explain in mutual aiding of measurement result of all measuring items.
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The general standard of the interval of sidetrack
2-1) Surveying of the surface
1) The surveying of surface settlement is operated to confirm the stability of tunnel and surrounding ground
2) The general ground of station interval (vertical-sectional) based on earth heightThe relation between earth height(H) and excavation depth of tunnel(D) Interval of the station (m) 2D < H 20 - 50 D< H < 2D 10 - 20 H < D 5 - 10 3) The cross-sectional measurement extent must be within the wide limit out of influence of the ground settlement due to tunnel excavation and the station space of the section in the direct influence must be 5m or less
2-2) Measurement of internal cavity deformation and archcrown settlement
1) It must be laid in the same section as the place of ground settlement.
Tunnel entrance Earth height (H < 2D)
(D;side to tunnel)The progressing step of construction Hard rock without fractured zone like faults 20m 20m 50m 이하 Safe rock creating plasticity bearing 20m 20m 30m 이하 Weathering rock, soil 10m 10m 20m 이하 2) In case that the good and similar qualified grounds continue, we must increase the interval.
3) In case that geologic change is great, we must decrease the interval.
2-3) The sidetrack of table section (B measurement)
It is the main aim that we grasp the ground behavior and inspect the plan of initial step or the propriety of planning design from it to reflect the blow content in design and execution.
⊙ This is practiced at the initial step of execution.
⊙ We make it a rule to establish the measurement section in the representative geologic section
1) We make it a standard to practice on every 300-500m in ground condition.
2) To decide in consideration of the size of tunnel or ground condition.
ⓐ In case of being able to omit the B measurement
- Case that the length of tunnel is short (200m or less), the tunnel of similar ground condition is constructed near.
- Case that the ground is safe to have no problems with execution.
ⓑ Case that the B measurement is operated.
- Case of altering the plan largely by the change of ground condition
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The establishment of measuring instruments and the interval
The effectiveness of the whole measurement depends on the establishment of measuring instruments. So the instrument must be established carefully, correctly to achieve the aim in the required place and protected sufficiently for fear that they should be damaged during measuring period, and also established at the place able to be approached. As for deciding the place of measurement, inspect the association of items, arrangement of instruments in all section and the direction of tunnel l profile to grasp the relationship among the items. At this time, the standards of estimating are the geological profile, the pattern of timber, surrounding building and obstacles.
1-1) The main parts of deciding the measuring place are like the following. ① We must understand the relationship between the behavior of ground, timber like rock bolt axial force, earth strain, shotcrete stress measurement and the common measurement like the inner void displacement measurement. Besides we must consider it to estimate and use the measurement result in initial construction of all pattern of timber. But we must arrange the instruments in the place excavated at the depth of 1D∼3D after altering the timber pattern for avoiding the mutual interference.
② Select the place that cause the large-sized fault, fractured zone, ground destructing or the troubled spot such as the settlement due to excessive construction and inclining points.
③ As for the predictable declination pressure and the special construction like the double path tunnel, the arrangement of the measuring instrument is not bound by the symmetrical arrangement and should be selected after considering the propriety in each construction step.
④ After starting construction, we must alter the measurement place as the timber pattern of plan is altered.
1-2) The measurement place of each measuring item is like the following.
We make it a rule to measure in the same section and accomplish in the representative section measured the earth displacement, shotcrete stress essentially. The measurement of relative strain between walls is based on the horizontal course of traverse and add the diagonal course of traverse at need to grasp the influence of the declination pressure. In case of the large displacement like the poor subsoil, we must narrow the profile measurement interval and in case of slight displacement like the good ground, widening the interval.
1-3) Earth displacement, rock bolt axal force, shoetree stress in the pit.
When the initial step of construction, the ground condition and the timber pattern change, we must measure.
1-4) Surface settlement, earth settlement, earth horizontal displacement, structure behavior survey out of a pit Decide after considering the three-dimensional behavior as access of the blind end.
1-5) The example of the general interval of measurement are like the following.Condition Portal of tunnel 2D or less of soil Initial step of construction The progressing step of construction Rock (Hard rock, soft rock, weathered rock) 10m 10m 20m 30m Soil 10m 10m 10m ~ 20m 20m When measuring ground subsidence, the measurement interval in the tunnel end direction
The relation between soil(h)and tunnel depth (D) Interval of station 2D < H 20 - 50 D< H < 2D 10 - 20 H < D 5 - 10
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The managed standard of BIDO construction in Japan
This establishes the managed standard on the measurement result of internal displacement about the tunnel of 10m diameter length and manages as 2 steps
::: The managed of BIDO construction in Japan :::Level of attention I Level of attention II Internal displacement Displacement velocity Internal displacement Hard rock 2 ~ 3cm 3 days continuously with 5mm/day 3 ~ 5cm Talus 2 ~ 3cm 3 days continuously with 5mm/day 5 ~ 7cm Soil sand soil 2 ~ 3cm 3 days continuously with 5mm/day 3 ~ 5cm Cohesive soil 3 ~ 5cm 3 days continuously with 5mm/day 5 ~ 7cm Swelling ground 10cm 3 days continuously with 5mm/day 20 ~ 30cm Counterplot Estimate situation of measuring result field synthetically and decide counterplot. Measure many times and execute carefully Establish counterplot altering the construction method, adding the supplementary method, and adding the timber -
The standard of management of Alberg tunnel in Austria
This establishes the ideal internal displacement within 3 ∼ 4% of rock bolt the maximum permissible of internal displacement within 10% of used rock bolt or 10% of tunnel diameter. And this establishes the time of adding rock bolt from measuring result as when the relative displacement (d10) of 10 day after excavation is 150mm and more, or the displacement (d10')in the tenth day is 10mm/day and more, and also the time of second composite construction as when the relative displacement for 30 days, 100 days after excavation is 7mm or less (d′= 0.23/day).
※ Concrete stiffness for second composite construction as internal displacement velocity is like the following
1) 0 ∼ 1mm/30day or 0 ∼ 0.03mm/day : 200kg/cm2
2) 1 ∼ 3mm/30day or 0.03 ∼ 0.1mm/day : 240kg/cm2
3) 3 ∼ 5mm/30day or 0.1 ∼ 0.17mm/day : 320kg/cm2 -
The standard of management of industrial structure in France
This establishes the absolute displacement of tunnel archcrown about at the 50 ∼ 100㎥ area to the standard. In general, the maximum permissible strain depends on the earth‘s height but usually, about 1/1000 of the height. However, deciding the maximum permissible strain must contain the consideration of ground behavior enough. The permissible displacement a day is about 1/5 ∼ 1/4 of whole permissible displacement when going through the blind end, and it declines to 1/20 after a week and the final displacement velocity must be accepted completely.
::: The standard of management of industrial structure in France :::Earth height (m)Archcrown maximum permissible strainHard rockPlasticity10 ~ 501 ~ 22 ~550 ~ 1002 ~ 610 ~20100 이상6 ~ 1220 ~ 40
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The phenomenon under execution and the proper step
Section The phenomenon under execution Step A Step B In case of finishing as relatively simple alteringIn case of requiring the relatively large altering including adding timber memberExcavation and nearby ground Portal of tunnel is not stable - Shorten the length of excavation
- Excavate with the core left
- Setting up the striped sheet pile and mini-pipe roof- Use the stabilization method of tunnel portal
- Improve the groundFalling in the portal of tunnel - Shorten the excavating time and operate the shoetree in early stage
- Execute the falling- proof steel (the striped sheet pile, mini-pipe roof)
- Drain off for 1 excavating place- Put the timber member steel in
- Improve the groundThe industrial water comes out from the part which to cut off or the water capacity increases. - Hasten the hardness of shoetree
- Draining control for the part which to cut off
- Execute the fine- grained mesh.
- Execute the drain sheet- Operate draining method (weep drain boring, deep well point)
- Improve the groundshotcrete rock bolt Due to the rack of the bearing value of ground, the settlement becomes more - Excavate not to touch the bearing ground.
- Make the shoetree of lower part thick and increase the bearing area- Increase the rock bolt.
- Shorten the bench length and recognize early.
- Execute the invert.
- Improve the groundFlat expansion - Construct the invert in early stage - Construct the rock bolt in the invert
- Shorten the bench length and recognize early.
- Do as minibench methodThe concrete floats or comes off - After excavating, cut off early.
- Put the mesh in.
- Remove the water pressure..
- Increase the thickness of shoetree- Set up the rock bolt or execute the adding bolt. The crack or shear breaking of concrete - Put the mesh in.
- Make the sleet in shoetree- Execute the adding bolt with the longer than the beginning.
- Put the timber member of steel in. (If necessary, to the next construction)
- Use the strong internal forced bolt.
- If necessary, get in the compression member between plates to increase the ability of bolt's displacementTimber member of steel The stress of timber member of steel increases and bucking buckle comes out. - Increase the bolts in the joint, fasten the shoetree - Execute the adding bolt with the longer than the beginning.
- Use the timber member steel in the next best construction and make the sleet in shotcreteSettlement of fiducial mark and ground Because fiducial mark settlement and ground settlement becomes large, settlement velocity increases - Mend the ground like long mini pipe roof.
- Shorten the time excavation to timber.
- Press the ground in early stage shortening the 1 excavation place.
- Excavate with the core left- Shorten the bench length and make recognition of invert early.
- Change to temporary-invert or temporary- rod method.
- Improve the groundGround displacement The ground strain is large and looser and the area is wider. - Shorten the time excavation to timber.
- Hasten the construction of rock bolt- Execute the adding bolt with the longer than the beginning.
- Put the timber member of steel in.
- Shorten the bench length and recognize early.
- Change to method of minibench or temporary invertInternal displacement Internal displacement is larger and displacement velocity increases. - Shorten the time excavation to timber.
- Hasten the construction of rock bolt.
- Shorten the bench, 1 excavation place of invert.
- In case of putting crack in shoetree, make sleet.- Execute the adding bolt with the longer than the beginning.
- Shorten the bench length and recognize early.
- If necessary, get in the compression member between plates to increase the ability of bolt's displacement
- Change to method of minibench or temporary invert
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Factors considered on selecting the measuring item
1-1) Whether the structure in the extent of influence of excavation exists or not, the foundation of contiguity structure and the condition of building.
1-2) Explanation of uncertainty under the design
- In expectation of large error of measurement like the side pressure and hydraulic pressure which can be external force condition under design calculating.
- In expectation of large displacement of external force condition due to constructive execution at the nearby location.
- In case of small safe factor under making a comparison between the design measurement and the permissible error. -
The common measuring item
Measuring item Measuring instrument Ground horizontal strain Inclinometer Ground water level and pore pressure Water level meter, Piezometer Ground vertical strain ROD, MCS extensometer Fiducial mark and horizontal strain Settlement plate Earth pressure on wall Total press cell, Load cell, Jack-out pressure cell Measuring axal force of anchor Load cell, pull instrument of the test Measuring strut strain factor Strain gauge Measuring the slope of contiguity structure Tiltmeter, Electric theodolite Measuring the crack of contiguity structure Crackmeter, Crack ball Vibration and noise Blasting vibration measuring instrument Foundational elements, various stakes Strain gauge, Accelerometer
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Factors to be considered when selecting measurement items
The base of measuring management is that we accomplish the various measurements systematically, plan the result of measurement and reflect it in execution, and also alter the planned execution to the proper one in the building field. And it is the main aim of measurement that we manage the safe and economical construction. So the proper management and index classified by steps are essential
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The establishment of standard value of measuring management
We must establish the standard value of strain velocity, strain acceleration, allowable acceleration, allowable stress and strain permissible for the stability of ground including the contiguity structure. And we must compare them with the plan or structural calculation, if the occasion required, it is necessary to establish the standard of work operating, notice, and regular standard. -
Establishing the measuring instrument and repair
In consideration of process and work order, we decide the place, time of establishment Establishing the measuring instrument and station is operated as fast as possible. The instrument out of the pit is established before progressing of blind end (face) We must prevent the measuring instruments and station from damage by blasting or the work out of pit. We had better mark the number of rock bolt for blast testing. We must consider the means of waterproof and dampproof about the instrument affected by the damp easily. The automatic measuring instrument is required the protection of cable and data logger. etc. The depository of data telegraphed from the automatic measurement must be kept away from the humidity, rainy weather, excessive sunlight. The wholly responsible person must accomplish the management of maintenance and repair of instruments. Then we attach the stress-strain gauge, the humidity must be removed completely. The attaching place of stress-strain gauge must be even. -
Measurement
We must operate by observing the basic order and measure in precision suitable to the aim. We must understand the strain or measuring result with the data of all conferences in the building field. As the final value is commonly decided from the displacement between 1-2 days after excavation, it is important to compare with the standard value and inspect and the precision is required. If the measuring result is close to the standard value, we must increase the measurement frequency and, at the same time, decide the counterplot. -
Data arrangement
If finishing the measurement, we must draw up the graph at once the tendency of measuring result. But if something wrong, we must measure again at once. We must write dearly about the distance from the face and execution time as for the data arrangement. If there are many stations and measurement has accomplished for long-term, we must control the data with computers and store it in the disk. We must draw up the graph of overall measurement table, strain time, strain degree which show the relationship between the measuring result and geological condition well.
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Though there are a variety of views about premised theory as the nature of the ground that is excavated in NATM is so complex and diverse, in present time, the standardized theory; able to be said, "This is the NATM theory" has not been established yet.
Therefore, until now, the plan of timbering exercised before construction, that is, a prearranged plan usually means "Decision of empirical dimensioning". And also the calculation shows a marked trend to be used as a mean that examines properties of the established section and apprehends earth behavior predicted from now on. Actually, the execution in building site is also being done like this.
And also a prearranged plan is sometimes adopted in actual construction through monitoring of tunnel test at the special case, but generally, it is common that the plan is operated by "the observation method": corrects it accord with the measurement under execution and at the present time, such planning method is considered as the most economical and rational one, whether is safe or not also depends on observation method.
In case view, NATM may be naturally the method that contributes to the security of ground and tunnel by the method controlled pressure release, so the measurement is the core of NATM.
In general, for the construction of desirable tunnel structure, their conditions-security of structure itself, protection of nearby structures and long -term keeping of tunnel function- is required, and in the case of rock tunnel, it is desirable to measure first the tunnel and the displacement nearby base rock to estimate the security of tunneling structure itself because if the security of tunnel is kept, the neighboring structures seem to be relatively secure.
However, in the case of downtown tunnel, as the tunnel plan is established aiming at the protection of nearby structure than at the security of structure itself, the measurement of tunnel is also accompanied with the diverse measurement of substitution such as surface, earth tunnel and nearly structures considering this condition. And the direction of execution and countermeasure have to be established according to the result.
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The plan of tunnel measurement
Before the execution, measuring plan applied to planning and execution must be established in consideration of the result of examination and the size of tunnel. Besides the effective and economical measuring item, method and gauge must be selected and operated without interference in construction as possible.
Establishment of plan as steps is like the following.The measurement is divided into the common (A) and representative (B) point measurement and (A) measurement is the usual measurement for security of the ground around tunnel and planned execution of which space is 20-50M. (B) measurement is the measurement operated in representative point for the planning and execution of behavior of ground, rock, bolt, lining, non-excavated section and future plan. If classifying these into the purpose of measurement, they are like the following
·Measurement of displacement : Internal displacement measurement, arch crown settlement survey.
·Measuring of displacement range : Measurement of ground displacement, rock bolt axial force measurement, ground or surface settlement survey, measurement of tunnel seismic velocity, measurement of ground horizontal displacement.
·The measurement of timber effect : Rock bolt axial force or pullout test, lining-stress measurement.
Among the items of measurement above, the item that corresponds with the aim in consideration of relationship between the condition of ground nature of section and nearby structures must be selected and enforced. -
The selection of the measuring item
Among various measuring items, we usually execute like the following in measurement for NATM execution management.
2-1) Measurement A (General measurement)
① Observation · investigation of under ground (tunnel)
② Measurement of internal displacement
③ Settle measurement of Archcrown
④ Pull-out test of rock-bolt
2-2) Measurement B (Measurement on representative location)
⑤ Measurement of fiducial mark or ground settlement
⑥ Measurement of shotcrete stress
⑦ Measurement of ground displacement
⑧ Measurement of rock-blot axial force and load measurement
⑨ Measurement of ground horizontal displacement
⑩ Measurement of tunnel seismic velocity
The range of the fiducial mark settlement measurement and the station arrangement plan of ground settlementThe cross section of measurement
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The aim
The measurement of bridge must be operated and accompanied with the intensive examination of long-term settlement and scour of pier, deflection transformation and crack of upper structure or tension condition of inside wire in case of P.C Box structure, besides it should include grasping the damage condition of bridge. And also the long-term measurement about the main tower like cables stayed bridge, suspension bridge and tension of cable is necessary. Moreover, the information of measurement must be provided so that we can examine and evaluate fast, exactly the durability of bridge by the dynamic and static load such as the function of bridge and deterioration of material for construction. So it is the aim that the proper control is taken, keeping from the accident and find planning the scientific and systematic management of bridge.
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The reason that the measurement is necessary
2-1) As nearly almost base supported condition of bridge is composed of the cast-in-place pile or P.C, P.H.C, steel pipe pile, it is necessary to observe settlement and scour continuously.
2-2) The possibility that the tension of steel may relax because of damage by dynamic load and time is able to be found in advance.
2-3) We find the dangerous, factors by the fatigue crack, steel corrosion, decline of friction stress of high tension bolt in advance.
2-4) We can examine the horizontal and vertical movement of upper abutment in advance.
2-5) We can establish the adequate counterplot awarding of the effect of earthquake and the degree of damage.
2-6) We can predict the vertical, horizontal relative movement of substructure of supporting point in advance.
2-7) Able to investigate, in advance, about the second stress or bending of reinforcement and edge of connecting plate welding in steel structure, and fin out the deflection condition and the degree of crack.
2-8) Able to predict the bending crack, diagonal tension crack, vertical crack and the damage of steel member in case of prestressing concrete beam in advance.
2-9) Able to predict the condition of over-vibration, damage and abrasion about the cable of cable-stayed bridge and suspension bridge in advance.
2-10) Able to percept the matter of fixing point of wire.
2-11) Able to investigate the vibration in case of vehicle's passing about supporting side of abutment and pier. -
Sectional measurement of long-term transformation
3-1) Primarily the 'strain gauge' is used as long-term measuring gauge is installed for the measurement of long-term transformation. As it is the vibration wire type, the electrical error doesn't matter. The vibration wire type doesn't have to be composed of electrical circuit. Therefore it is appropriate for long-term measurement. If considering the aim, effectiveness, economical efficiency of long-term measurement, the strain gauge sensor and mechanical type gauge had better be established together.
::: specification of strain gauge :::capability of analysis 0.1 microadian (0.02 arc second) sensor type vibration wire type ±60°analysis angle, 0.1micro/mv∼10deg/v/v mech: nical 5 * 10-6 strain output power : DRU power, Twin axal tiltmeter read possibility 3-2) The test of tensile force laxity state presumption
- Piano wire : To obtain the piano wire sample and investigate the yield point by tension to know the maximum and allowable of tension on basis of the analysis about the deflection and condition of P.C Box structure and to compare it with measurement result.
- After operating the creep test by the standard method of ASTM C512 and recording the temperature and humidity according to analysis about deflection and settlement condition of P.C structures, we compare it with loading and unloading test condition. -
Investigation of settlement and slope of pier
The vertically and lean items should be measured. The established tiltmeter must be examined and recorded with inspection and the behavior about all settlement and scour delivered to the pier when the upper structure receives the normal load, bending moment or shear must be investigated. Therefore both one-axal and two-axal tiltmeter can be applicable. As the tiltmeter unfolds and transforms with the high-unitary signal that cannot be measured easily with the common recording gauge thorough the perception device which detects the resistance by voltage disjointing circuit, it must take into account the electric circuit of inner amplifier and micro electron engineering.
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The initial measurement
5-1) The necessity of establishment of initial value
The initial condition must be established for long-term inspection and measurement of bridge and enforced according to the necessary technique of inspection and measurement about management of bridge repairing. Therefore the record of initial inspection and measurement is compared with the matter resulting from later inspection and measurement and the changing process of bridge must be analyzed.
5-2) The initial establishment of P.C tension condition and load test
To obtain the information about the first tension condition of P.C steel piano wire and inspect, measure the tension in state of unloading and keep it for the data of initial condition. The strain gauge and tiltmeter attached at P.C section record the strain and behavior of member. Therefore the initial value of establishment must be analyzed and compared with continuous inspection value. And also right after completion, the static and dynamic load test is operated and the records about this are also kept as the initial establishment value. The dynamic load test must be operated with the truck of which load is within 60% of total possible loading when the bridge is first grade and records the proper number of vibration, damping ratio, dynamic amplification condition and deflection. -
Example of measured machine institution
