Plate Load Test

Comparative Studies between the Plate Load Test (PLT) and other Devices

Best practice in compaction quality assurance for pavement and subgrade materials – National Asset Centre of Excellence (NACOE) – Queensland Department of Transport and Main Roads and the Australian Road Research Board (ARRB) – P60

The acceptance of earthwork and unbound pavement construction in Australia currently relies mostly on density testing and CBRs for Quality Assurance (QA).

Though its National Asset Centre of Excellence (NACoE) research program, Queensland’s Department of Transport & Main Roads sponsored a vital ARRB research project to update test methods acceptable for use for QA of pavement and subgrade materials. This state-of-the-industry study assessed test methods that have the potential to:

(a) reliably provide a direct measure of the strength or in-situ modulus value; and
(b) offer significant time savings in turnaround time of test results.

Methods evaluated included Light Weight Deflectometer’s (LWD’s), PANDA® Instrumented DCP, Clegg Hammer, DCP and Plate Load Testing (PLT). Specifically, the devices evaluated included the Zorn Light Weight Deflectometer, the Anix Instrumented Plate Load Test and PANDA® Instrumented DCP.

In earthworks testing, using density ratios is applied widely in quality control. There are currently many different measuring devices which can provide a more accurate measurement of design parameters (strength or stiffness) and can provide a more direct route for parameter assessment (i.e. limit need for any inclusion of generic relationships).

Comparisons of density with alternative in-situ testing show the latter provides significant benefits to the industry. Accuracy is not the same as precision, and industry’s reliance on density places an emphasis on precision rather than accuracy, data usability or timeliness of results.

This research has found density measurements are, although precise, not very accurate due to poor correlation with the results of other modulus or strength-based tests.

Presenters:

• Dr Jeffrey Lee – ARRB
• Dr Burt Look – FSG – Geotechnics + Foundations
• Dr David Lacey – FSG – Geotechnics + Foundations

The most important Technical Standards for values required for the Deformation Modulus, in Germany, are:

• “Zusätzliche Techni­sche Vertragsbedingungen und Richtlinien für Erdarbeiten im Straßenbau” (Additional Technical Terms of Contract and Guidelines for Earthworks in Road Construction) ZTV E-StB 09,
• “Zusätzliche Technische Vertragsbedingungen und Richtlinien für Aufgrabungen in Verkehrsflächen” (Additional Technical Terms of Contract and Guidelines for Excavations in Traffic Areas) ZTV A-StB 97/06
• “Zusätzliche Technische Vertragsbedingungen und Richtlinien für den Bau von Schichten ohne Bindemittel im Straßenbau” (Additional Technical Terms of Contract and Guidelines for the Construction of Courses without Binder in Road Construction) ZTV SoB-StB 07.

In accordance with ZTV E-StB, quality control is carried out according to a statistical test plan. In this method, the statistical distribution of the inspection criterion being examined is determined within an inspection lot on a random sampling basis. The decision as to whether the inspection lot is accepted or rejected is made on the basis of the results of the random sampling.

This method can be applied to any kind of ground.

The application of this method is particularly advisable in the following cases:

• with large inspection lots
• with inspection lots for which the uniformity of the compaction is to be evaluated
• with inspection lots on which test procedures requiring little time are used and whose results are available immediately

The statistical method should also be used for sample compactions.

In the statistical method, one inspection lot is assessed each time. An inspection lot is a layer of compacted ground that has been processed under uniform conditions and for which there is a uniform requirement. The area of the inspection lot should be precisely specified.

The test is carried out on a random sampling basis in which the position of the test points in the testing area is to be determined by means of a random selection process. The scale of the random sampling (n) depends on the size of the inspection lot.

The arithmetic average ( ) and the standard deviation (s) are calculated on the basis of the results (xi) of the random sample.

In the case of a 10% minimum quantile TM (degree of compaction, deformation modulus), the quality number Q is generated on the basis of  and s (3).

At the acceptance of the construction work, the inspection lot will be accepted if Q≥k, where k is the acceptability constant in accordance with Table 1; otherwise the inspection lot will be rejected. It must then be brought into a condition that meets the requirements by the contractor. In the case of a rejection, the entire area of the inspection lot must be rejected.

Table 1: Scale of random sampling and acceptability constant for a single plan for the inspection of variables depending on the size of the inspection lot 

The requirements mentioned below refer to the 10% minimum quantile TM in accordance with ZTV E-StB.

In the case of a road surface for heavy to medium traffic on a frost-proof subgrade or subbase, a deformation modulus of at least Ev2 = 120 MN/m² is required on the formation level. For light traffic, a deformation modulus of at least Ev2 = 100 MN/m² is required.

In the case of a frost-susceptible subgrade or subbase, a deformation modulus of at least Ev2 = 45 MN/m² must be proven on the formation level.

In the case of a frost-susceptible subgrade or subbase, Ev2 ≥ 70 MN/m² must be the case on the formation level after professional soil improvement has been carried out.

In accordance with ZTV E-StB, the static plate loading test can be used as a substitute for determining the degree of compaction in accordance with Table 2 for coarse-grained soils and mixed-grained soils with a fine grain proportion of less than 15 % (m/m).

For allocation to the degree of compaction, the deformation modulus Ev2 must adhere to the lower limit given in Table 2, while the ratio Ev2/Ev1 must adhere to the upper limit given in Table 2.

If the Ev1 value has already reached 60% of the Ev2 value given in Table 2, higher Ev2/Ev1 ratios are also permitted.

Table 2:    Standard values for allocation of the static deformation modulus Ev2 and the ratio Ev2/Ev1 to the degree of compaction DPr for coarse-grained soils

For base courses without binder, the following applies in accordance with SoB-StB:

In the case of roads of German construction classes SV, I to IV, on a formation level with Ev2 ≥ 45 MN/m² a deformation modulus of Ev2 ≥ 120 MN/m² must be achieved on the frost protection layer.

On roads of German construction classes V and VI, the required value is Ev2 ≥ 100 MN/m.

On gravel and crushed stone base courses, the ratio of the deformation moduli Ev2/Ev1 must not be greater than 2.2 if a degree of compaction DPr ≥ 103 % is stipulated. With a degree of compaction DPr < 103 %, Ev2/Ev1 must be ≤ 2.5.

Ev2/Ev1 ratios higher than 2.2 or 2.5 are permitted if the Ev1 value is at least 0.6 times the required Ev2 value.

In the case of roads of German construction classes SV, I to IV the following deformation modulus Ev2 must be achieved on frost protection layers with Ev2 ³ 120 MN/m² depending on the thickness of the base course without binder:

• on gravel base courses: ≥20 cm: Ev2 ≥150 MN/m² and ≥25 cm: Ev2 ≥180 MN/m²
• on crushed stone base courses: ≥15 cm: Ev2 ≥150 MN/m² and ≥20 cm: Ev2 ≥ 180 MN/m²

In the case of roads of German construction classes V and VI, the following deformation modulus Ev2 must be achieved on frost protection layers with Ev2 ≥ 100 MN/m² depending on the thickness of the base course without binder:

• on gravel base courses: ≥20 cm: E v2 ≥120 MN/m² and ≥25 cm: E v2 ≥ 150 MN/m²
• on crushed stone base courses: ≥15 cm: E v2 ≥120 MN/m² and ≥20 cm: E v2 ≥150 MN/m²

Unlike with ZTV E-StB, these required values are not the 10% quantile but rather minimum values for which deviations should be evaluated as follows:

• With fewer than five individual values, each of the individual values must be equal to or exceed the required minimum values.
• With five or more individual values per inspection lot, one individual value in each case may fall below the required minimum value for the deformation modulus by no more than 10%.
• The permitted deviations only apply, however, if these individual values relate to the five measurement locations that are closest to each other in each case.

Other supported standards include:

• DIN 18134:2012-04, Baugrund – Versuche und Versuchsgeräte – Plattendruckversuch, Deutschen Institut für Normung (Germany) – describes how to set up and carry out the plate loading test
• CNR BU 146 1992-12, determinazione del MODULO DI DEFORMAZIONE, Consiglio Nazionale delle Ricerche (Italy)
• ÖNORM B4417:1979-12, Erd- und Grundbau; Untersuchung von Böden; Lastplattenversuch, Austrian Standards Institute (Austria)
• SN 670 317b:1998, Plattendruckversuch, Norme Suisse (Switzerland)
• TSC 06.720:2003, MERITVE IN PREISKAVE – DEFORMACIJSKI MODULI VGRAJENIH MATERIALOV, REPUBLIKA SLOVENIJA (Slovenia)
• NF P94-117-1:2000-04, Portance des plates formes – Module sous chargement statique à la plaque, Norme française (France)
• BS 1377 Part 9:1990-08 Methods for test for soils for civil engineering purposes. In-situ tests, British Standards + HD 25 PAVEMENT FOUNDATIONS (UK)
• UNE 103808:2006-02, Ensayo de placa de carga, Asociación Española de Normalización y Certificación (Spain)
• Standaardbestek 250 – Hoofdstuk 14.16, Samendrukbaarheidsmodulus (Belgium)
• Aflevering Proefmethodes – Hoofdstuk 50.01, Samendrukbaarheidsmodulus (Belgium)
• MSZ 2509-3:1989, Útpályaszerkezetek teherbíró képességének vizsgálata, Magyarország (Hungary)
• VVMB 606 – Bestämning av bärighetsegenskaper med statisk plattbelastning Sammanfattning (Sweden)

Credentials for Anix AX01 Plate Load Test

The Anix AX01 Plate Load Test series has been in production since 2004. A number of units are used in high speed railway construction in China.

To find out more, Contact Us.

The Anix AX01 Plate Load Test is manufactured by Anix GmbH of Meitzendorf, Hintern Hecken, 139179 Barleben, Germany www.anix.biz