Measuring Anchor
MEASURING ANCHOR
User Manual
(Sisgeo S.r.l. - 05/06 Rev. 1)
SISGEO S.r.l. Tel.+39-02 95764130 Cap. Soc. 99.000 Euro int.versato Via F. Serpero, 4/F1 Fax +39-02 95762011 Cod. Fisc. e P.IVA. n. 10732420152 20060 Masate – (MI) E-mail:[email protected] VAT No.:IT 10732420152 Italy http://www.sisgeo.com Trib. Milano: 333230 - REA: 1413159
Contents
Introduction……………………………………….1
Measuring anchor………………………………..2
Assembling procedure…………………………..3
Grouting procedure………………………………4
Taking readings…………………………………..5
Maintenance……………………………………...6
Service and repair………………………………..7
______1
Introduction
______
Chapter 1: Introduction
Application
Measuring anchor is a device used for strain and stress evaluation in rock mass. Measuring anchors are generally used in monitoring of slope stability, in measuring strain around walls and tunnels, for safety control during tunnelling or underground excavations, in the control of foundation settlement of retaining walls, bridge piers and abutments.
General description
The measuring anchor consists of a steel hollow rod in which up to four stiff steel small diameter rods are inserted and fixed (see next figure)
DBS.doc 1-2
Chapter 1: Introduction
DBS.doc 1-3
Chapter 1: Introduction
The bottom end of each rod is anchored internally at different length within the annulus connected at selected locations inside the measuring anchor. After the installation the measuring anchor is subject to change in length due to the soil influence. This change in length is detected by each steel measuring rod and reflects the relative movement of rock at the anchor section locations. The steel rod transmits this movement at the top of the measuring anchor where, using a dial gauge or an electric displacement transducer for each rod, is measured.
Data interpretation
Data interpretation and evaluation of the phenomena to be monitored are performed in accordance with the number of measuring points installed in each measuring anchor. As an example, in the following is presented the set of formulas for data interpretation on measurements performed using a two measuring rods anchor. The relative change in length of each measuring rod is evaluated with the following formula:
ΔLr(i) = (Lt – L0) (i)
Where:
ΔLr(i) = relative change of position of rod (i) at time (t);
Lt = reading at time (t);
L0 = zero reading at initial time (t0).
In addition, the average strain between two rod attachment points is given by:
ΔL/L = (ΔLr(2) - ΔLr(1) )/ L21
ΔLr(2) = relative change of position of rod (2) at time (t);
ΔLr(1) = relative change of position of rod (1) at time (t);
L21 = distance between attachment points of the two rods.
Average strain can be converted to approximate value of stress using a composite modulus of the measuring anchor and grout around it.
DBS.doc 1-4
______2
Measuring anchor
Chapter 2: Measuring anchor
Measuring anchor
The measuring anchor is supplied, for easier transportation partially unassembled, with the anchor tubes and the measuring rods having different length according to the required number of measuring points. For each measuring anchor the following components are supplied: • anchor tube; • couplings with centring/anchoring rings; • measuring rods; • protective conical tip; • top cap; • measuring rod caps; • measuring gauge with calibration checking jig.
Anchor tube
Each tube has equal length to allow the measuring at the requested level.
Measuring rods
Preassembled measuring rods are nominal OD 6mm steel rods supplied in the required length. Each measuring rod is screwed to a centring ring fixed by grains to the coupling. Each anchoring ring is provided with a number of holes to permit free guided movement of adjacent measuring rods. In the following text we also refer to them as "inner rods".
Conical tip
A conical steel tip is supplied for easier installation and measuring anchor protection.
Measuring anchor 2-2
Chapter 2: Measuring anchor
Upper Terminal
On the upper anchor tube is mounted a stainless steel adaptor for the direct reading or for mounting the electric measuring head.
Direct reading measuring unit
The measuring unit consists of a mechanical dial gauge with resolution 0.01mm and available in 0- 10mm ranges. The measuring unit includes a plate, used to facilitates the measurement, to be mounted on the measuring rod of the dial gauge. A reference jig for zero check and adjustment of the dial gauge is also provided.
Top cap
When not used the upper terminal cap is protected with a removable cap which prevents inflow of material and moisture.
Electric measuring head
In case of remote reading up to four 10mm stroke vibrating wire, displacement transducers can be mounted on the surface rod cap. The transducers are housed in a stainless steel cap and a single cable will bring the signal of the transducers to the remote location.
Measuring anchor 2-3
______3
Assembling procedure
Chapter 3: Assembling procedure
Measuring anchor
In the following is presented the assembling sequence of the measuring anchor; all the anchor has to be assembled on the ground before the insertion into the borehole.
1. select the inner rods with both ends female threads. They are the rods to be screwed on the
centering rings.
2. mount one of this rods on the conical tip and insert the hole marked 1 into the centering ring
with two holes; on the hole 2 mount one of the remaining inner rods.
3. screw one anchor tube on the conical tip and mount the coupling on the other end. Rotate the
centering ring until it is possible to screw the grains on the coupling and fix it.
4. insert the centering ring with 3 holes into the two inner rods according to the stated coding and
screw a new inner rod into the thread 3.
5. mount the outer rod and the relative coupling and go on in the same way for the remaining
components. Do not forget to install the surface plate and the tensioning nut.
6. mount the upper terminal cap. There are two types according to the measuring technique.
A- If direct reading will be taken, it is enough to mount the component screwing on the anchor
tube and them inserting the centering ring and screw on the grains as usual.
B- If the electric heads has to be mounted, screw the stainless steel adaptor on the last anchor
tube; insert the centering ring and lock in place by the two grains;
- on each rod mount the eccentric transducer adaptor;
- screw on each vibrating wire transducer on the adaptor until all the 4 transducer are
mounted;
- insert the lower part of the protective cap and fix by the two lower screws and then insert
the upper coupling and lock the two screws;
Measuring anchor 3-2
Chapter 3: Assembling procedure
- pull up the transducer body of 3-4mm and lock it in place screwing the grain. Repeat this
operation for all the transducers;
- make the electric connection between each transducer cable and the multipolar cable. We
normally suggest to connect only one of the four thermistors of the transducers. To make
the electric connection use the special 3M connectors that are supplied;
- take the upper part of the S.S. protective cap and open the gland to pass through the
electric cable;
- mount this part of the cap on the coupling, lock it with the two screws and then screw the
gland.
Measuring anchor 3-3
______4
Installation and grouting procedure
Chapter 4: Installation and grouting procedure
Installation and grouting
Once the anchor has been assembled as described in the chapter 3, it can be installed into the borehole. Installation and grouting have to be performed according to the procedure used for normal anchors. Special attention and care has to be put in protecting the top cap and in sealing the couplings of the anchor bars and the grains used to fix the anchor section.
Measuring anchor 4-2
______5
Taking readings
Chapter 5: Taking readings
Taking readings
1. With dial gauge taking readings consists of the following steps: • remove the protective top cap from the upper terminal of the measuring anchor; • using the jig supplied with the measuring kit set the dial gauge to zero; • each measuring rod is identified by a number on the cap (rod number 1is the longest, rod number 4 is the shortest); • for each measuring rod: a) insert the gauge rod inside the upper terminal of the measuring anchor until it is in contact with the measuring rod; b) read the measured value at the dial gauge and annotate it; • remove the mechanical depth gauge from the measuring anchor; • replace the protective top cap on the measuring anchor.
2. With electric transducers connect the wires of each transducer to a Volta or Galileo readout unit, respecting the colour code, and take the reading following the instruction of the readout.
Note
The first set of measurements is, usually, defined "zero reading" and reflect the relative or absolute position of each measuring rod at the beginning of the phenomena to be monitored.
Measuring anchor 5-2
______6
Maintenance
Chapter 6: Maintenance
Measuring anchor maintenance
The measuring anchor is an assembled measuring system equipped with removable mechanical gauge or electric transducers. Handle the above mentioned gauge with care during transportation and measurement. Protective caps, and transportation case are provided for the components most exposed to shocks and severe environmental conditions. The measuring system required standard maintenance only. The cap of the measuring rod, where the gauge is temporarily installed, has to be cleaned before each reading. Clean the reference cylinder and the measuring rod cap using alcohol or spray lubricants. Be careful to not introduce soil particles inside the cleaning process. Regular cleaning of the dial gauge is also recommended.
Measuring anchor 6-2
______7
Service and repair
Chapter 7: Service and repair
Service and repair
Service and repair activities, on the components previously presented, are performed at the factory or by technically trained operators authorized from the factory.
Shipment
In case of shipment or transportation, protect the instruments from shocks with appropriate carrying case. Ship the instrumentation to:
SISGEO S.r.l. Via F. Serpero, 4/F1 20060 Masate (MI) Italy Attn. Service Department
Or: • call the nearest SISGEO representative; • call our Service Department at: phone +39-2-95764130, fax +39-2-95762011
Measuring anchor 7-2