Annex E
(informative)
Examples of anchor testing methods
E.1 General
In clause 9 reference was made to the three classes of test commonly adopted in connection with anchors. These are:
a) Test Method 1: The anchor is loaded in incremental cycles from a datum load to a maximum test load. Displacement of the anchor head is measured over a time period at the maximum load in each incremental cycle;
b) Test Method 2: The anchor is loaded in incremental cycles from a datum load to a maximum test load or to failure. The loss of load at the anchor head is measured over a period of time at the lock-off load and at the maximum load in each incremental cycle;
c) Test Method 3: The anchor is loaded in incremental steps from a datum load to a maximum test load. The displacement of the anchor head is measured under maintained load at each loading step.
The essential loading procedures for Test Methods 1, 2 and 3 are shown in Figures E.1, E.2 and E.3.
E.2 Test Method 1
E.2.1 Investigation Test - Loading Procedure
The anchor should be loaded to failure (Ra)or to a proof load (Pp) which should be limited to 0,80 Ptk or 0,95 Pt0,1k whichever is the lower.
The anchor should be loaded to the maximum test load in a minimum of six cycles, see Figure E.1.
The load cycles and minimum periods of observation are given in Table E.1.
Where creep displacements are monitored the maximum load in each cycle should be held for a minimum of 15 min for loads less than Pp and 60 min at Pp in non-cohesive soils or 180 min in cohesive soils. This time should be extended until the creep displacement rate at that load is approximately constant.
E.2.2 Suitability Test - Loading Procedure
The proof load required for the working anchor should be:
Pp ≥ 1,25P0 or Pp ≥ Rd
whichever is greater.
The load in the tendon should not exceed 0,95 Pt0,1k.
The load cycles and minimum periods of observation are given in Table E.1.
The anchor may be loaded to the maximum test load in a minimum of five load cycles by the omission of the first cycle in Table E.1.
The maximum creep displacement rate, ks, at proof load should be no greater than 1 mm, where Investigation Tests have been carried out. Where failure (defined as ks = 2 mm) has not been confirmed by Investigation Tests then the value of ks at proof load should not exceed 0,8 mm.
E.2.3 Acceptance Test - Loading Procedure
The anchor should be loaded to proof load (Pp) by a minimum of three equal increments. The anchor should then be unloaded to a datum load Pa and again reloaded to lock-off load (P0). The proof load should be a minimum of 1,25 P0 but should be no greater than 0,9 Pt0,1k.
NOTE The load-extension curves may provide additional information about the ground and behaviour of the anchor components in the ground.
The monitoring period should be not less than 5 min at proof load.
The following limit should apply:
— the creep displacement rate ks should not exceed 0,8 mm at proof load and 0,5 mm at lock-off load.
Higher values of ks (up to 1 mm at proof load) are recommended if they have been proven to be acceptable by previous Investigation Tests.
E.2.4 Measurement of Creep Characteristics
The increment of anchor head displacement relative to a fixed point should be measured at the end of specified time intervals for load increments indicated in Table E.1. The creep rate should be determined after a constant creep displacement rate, ks, is measured over two time intervals.
ks is defined as follows:
ks = (s2 – s1)/log(t2/t1)
where
s1is the head displacement at time t1;
s2is the head displacement at time t2;
t is the time after application of load increment.
The creep rate limit is the maximum displacement creep rate permitted at the specified load level (see E.2.2 and E.2.3).
Measurements of anchor head displacement should be made, at the times indicated below while maintaining a constant load.
The successive monitoring times (in minutes) at the maximum cycle load levels as shown in Table E.1 are as follows:
1 → 2 → 3 → 5 → 10 → 15 → 20 → 30 → 45 → 60.
Where periods of observation are shorter than 60 min the sequence is curtailed as indicated in the Table E1.
Key
- 1 Applied load in % Pp
- 2 Datum load Pa
- 3 Anchor Displacement
