9.3.1 Testing during execution can comprise three different categories of tests:
- a) soil nail load tests to verify the ultimate pullout resistance and creep characteristics of the soil nails;
- b) material tests to verify the ultimate pullout resistance and creep characteristics of the soil nails;
- c) face stability assessment tests to evaluate the stand-up time of the ground during excavation.
9.3.2 Soil nail load tests
22.214.171.124 The frequency and procedures for soil nail load testing should be based on a consideration of the consequences of failure, as defined in EN 1990 and EN 1997.
126.96.36.199 Table 1 describes the principal types of soil nail load tests, their purpose, when they are required and actions to be taken in the event of a non-compliant test result. Annex C gives guidance on test procedures, acceptance criteria and the equipment to be used for soil nail load tests. Table 2 suggests the frequency of soil nail load tests based on the Geotechnical Category.
188.8.131.52 Sacrificial test nails are the preferred method to validate the resistance of a soil nail. Length of the nails may be de-bonded as described in Annex C.
184.108.40.206 If load tests are conducted on production nails, consideration should be given to downgrading the capacity, and additional nails may be installed to provide sufficient resistance and long-term stability.
220.127.116.11 The test procedures and locations of test nails shall be agreed.
18.104.22.168 Test nails, wherever possible, should be evenly distributed throughout the body of the soil nail works to assess nail performance across the site.
NOTE Active and passive zones are functions of particular limit equilibrium analyses and are not helpful for execution. The key issue during testing is to ensure that local boundary effects do not result in overestimating bond and therefore it is desirable to de-bond the head of the nail a sufficient distance from the reaction system. A minimum de- bonded length is 1 m.
|Type of Soil Nail Load Test|
|Purpose of test||Sacrificial nail test||Production nail test|
|to verify the ultimate soil nail to ground bond resistance used in the design
(1) the bond in the passive zone;
(2) the bond in the active zone;
(3) the bond along the entire length of the nail.
|to demonstrate satisfactory soil nail performance at a load designated by the designer.
The test is performed on the entire length of the nail.
|When tested||Before, during or after production works.||During or on completion of production works.|
|Type of nail used||Sacrificial||Production|
|Action taken in case of non-compliant test result||Review soil nail installation method and/or consider alternative soil nail length and layout.||Consult designer for action to be taken and approval to continue.|
|Comments||If necessary at each different soil layer||Caution should be exercised when testing production nails not to overstress the nail to grout bond or cause damage to corrosion protection.
When a structural facing is used the test nail should be debonded within the zone of influence of the facing.
|Test type||Suggested Minimum Frequency of Load Tests|
|Sacrificial nail test||Production nail test|
|Geotechnical Category 1: negligible risk to property or life.||Optional||Optional|
|Geotechnical Category 2: no abnormal risk to property or life.||If no comparable experience of soil type: a minimum of three sacrificial nails with at least one sacrificial nail per soil type.
Where direct experience exists then sacrificial nail tests are optional.
|2 %, min. three tests.|
|Geotechnical Category 3: all other structures not in Category 1 or 2.||A minimum of five sacrificial nails with at least two sacrificial nails per soil type.||For number of nails:
3 %, min. five tests.
|NOTE 1 Geotechnical Category of structure as defined in EN 1997.
NOTE 2 Test nails should be evenly distributed throughout the structure.
NOTE 3 The frequency of testing is a suggested minimum.
NOTE 4 Where sacrificial nail tests are carried out the number of production nail tests can be reduced on a pro-rata basis.
NOTE 5 For spacing, less then 0,8 m, a group test of four nails is recommended.
9.3.3 Material tests
22.214.171.124 These clauses are relevant to the testing of materials produced during the execution soil nailing works such as grouts, sprayed or cast in-situ concrete.
126.96.36.199 Grout shall be sampled and tested in accordance with the requirements set out in EN 196-1 to ensure compliance with the characteristic strengths and other properties specified in the design. Grout in the annulus between a corrugated sheeting and a bar should be tested according to EN 445, taking EN 446 and EN 447 into consideration.
188.8.131.52 Testing of sprayed concrete should include tests on constituent materials (grading, moisture content, etc.), samples from preliminary test panels and from the completed works. Where sampling involves coring of the completed works, then reinstatement shall be carried out as necessary. Test methods shall be in accordance with EN 14488 (all parts).
184.108.40.206 Concrete shall be sampled and tested in accordance with the requirements set out in EN 206-1.
220.127.116.11 The sampling and testing of other materials shall be in accordance with Clause 6.
9.3.4 Face stability tests
18.104.22.168 Where soil nail execution involves excavation and there is uncertainty about the stability of the ground at the proposed face angle, then face stability assessment tests should be undertaken. It is important to note that face stability assessment tests are not precise and are only intended to give an indication of face stability.
22.214.171.124 The test involves the excavation of a trial pit to a batter and depth equal to the slope angle and bench height used in the design. The width of excavation should not be less than twice the bench height and the period of observation should be representative of the anticipated time between the installations of rows of nails.
126.96.36.199 Where possible, these tests should be undertaken before execution of the works. Where soil nail execution involves excavation to significant depths and in varying strata, then consideration should be given to carrying out additional tests as execution proceeds or as changing ground conditions are encountered.