E.4 Test Method 3

E.4.1 Investigation Test - Loading Procedure

The anchor should be loaded to failure (R_a) or to a proof load (P_p) which should be limited to 0,80 P_tk or 0,90 P_t0,1k whichever is the lower.

The anchor should be loaded to the maximum test load by a minimum of six load steps, see Figure E.3.a).

The load steps and minimum periods of observation are given in Table E.3.

The minimum periods of observation can be reduced to 30 min if no significant creep occurs.

E.4.2 Suitability Test - Loading Procedure

The proof load required for the working anchor should be:

P_p ≥ 1,25 P₀ or P_p ≥ R_d

whichever is greater.

The load in the tendon should not exceed 0,90 P_t0,1k.

The anchor may be loaded to the maximum test load in a minimum of five steps by the omission of the first step in Figure E.3b).

The load steps and minimum periods of observation are given in Table E.4.

The maximum creep displacement (α) at the proof load level of Suitability Tests should be less than 0,8 mm per log. cycle of time (see Figure E.4) where Investigation Tests have not been carried out. Where Tests have been carried out then a at the proof load level of the Suitability Test should be less than:

• 1,2 mm/log time for a temporary anchor;
• 1,0 mm/log time for a permanent anchor.

In any case the proof load level of the Suitability Test for the project anchors should be not greater than P_c.

E.4.3 Acceptance Test - Loading Procedure

The anchor should be loaded from the datum load P_a to proof load P_p of 1,25 P₀ or R_d in a minimum of four increments. Then the proof load is maintained constant for at least 15 min.

After the proof load has been maintained for the desired period the contractor can carry out a partial or total unloading-loading cycle, see Figure E.3 c).

NOTE The load-extension curves may provide additional information about the ground and behaviour of the anchor components in the ground.

Where Test Method 3 is used in accordance with 9.4, the apparent tendon free length may be calculated from the datum load to the proof load curve using the method shown in Figure E.3 c). Where there is significant friction in the free length a partial cycle may be performed and the apparent tendon free length calculated from the established no-friction curve to determine ΔP and Δs.

The displacement due to creep at proof load should be measured between the 3^rd and 15^th min. The corresponding α should be less than:

• 1,2 mm for permanent or temporary anchors without Investigation Tests;
• 1,5 mm for permanent anchors with Investigation Tests;
• 1,8 mm for temporary anchors with Investigation Tests.

E.4.4 Measurement of Creep and Characteristic Load

Creep and characteristic loads should be measured and evaluated as follows:

— the increment of anchor head displacement relative to a fixed point should be measured at each step of loading at different times;

— the creep displacement a should be determined at each step of loading as indicated in Figure E.4. The creep displacement a is defined as the slope of the anchor head displacement versus log. time curve at the end of each loading step;

— the anchor resistance R_a is the load corresponding to the vertical asymptote of the a versus load curve. If the asymptote cannot be determined, it is considered that R_a is the load corresponding to an a value equal to 5 mm, see Figure E.5;

— the critical creep load P_c should be determined as indicated on Figure E.5. The critical creep load is the load corresponding to the end of the first linear part of the α versus load curve. Where it is difficult to determine P_c accurately an alternative resistance P_c' is determined as indicated in Figure E.5 and P_c is defined by:

P_c = 0,9 P_c'

Measurement of creep displacement should be made at the times indicated below, after each change in load. The periods of observation for each step are:

• investigation test - 30 min or 60 min;
• suitability test - 30 min or 60 min;
• acceptance test - not less than 15 min at proof load.

The successive monitoring times (in minutes) at each step are as follows:

1 → 2 → 3 → 4 → 5 → 7 → 10 → 15 → 20 → 30 →45 → 60

a) Investigation test	b) Suitability test

Key

• 1 Applied load in % of P_10.1k
• 2 Anchor displacement
• 3 Applied load in % of P_p
• 4 Proof load
• 5 Anchor displacement

c) Acceptance test

Key

L_app=A_t · E_t · Δs/ΔP(1 – f)

Key

• 1 Creep displacement

Key

• 1 Slope
• 2 Applied load

E.5 General tables for loading procedure. Test methods 1, 2, and 3