Why is dry density required

Procedure for testing soil compaction

Since the plate diameter and a constant factor are also included in the measurement result, the values ​​must be illustrated using an example: For an Ev2 = 45 MPa (the usual requirement for the subsoil in road construction), the load plate may be in the course of the second load at 1, Lower the 5 t load by only 1 mm.

Dynamic plate load test according to TP BF-StB Part B 8.3

With the lightweight drop-weight device, the dynamic deformation module can be determined, a key figure that is used to quantify the deformability of the floor under (short-term) load effects. Compared to its static counterpart, the dynamic plate load test is a fast process that does not require a heavy load. For this purpose, the test point is loaded abruptly via a load plate (also with a diameter of 30 cm) and a drop weight. An electronic sensor measures the sinking of the plate, from which the dynamic deformation module Evd is calculated in the evaluation unit.

This value is not directly comparable with the static deformation module (Ev1 or Ev2). Due to the short-term shock load, the measured values ​​are influenced by the water content and the grain size composition in a different way than in the - about one hour - static plate load test. The short test duration of a few minutes per measurement, however, enables a large number of tests to be carried out quickly, so that this method is mainly used to prove the uniformity of large areas. Since specifications for Evd are rarely included in performance texts, the measurement results must be converted into Ev2 values ​​when using the light drop-weight device. Because of the uncertainties involved in this conversion, not all clients want to accept this verification procedure.

Subsoil inspection

All the test methods presented so far have a decisive disadvantage: They only provide results (with reasonable effort) for the top soil layer up to a depth of 50 cm. In the case of backfills or critical substrates that reach deeper, a simple, but therefore less precise, method is recommended.

Drift sounding according to DIN EN ISO 22476-2

This test is used to estimate the compaction of deeper layers of soil. The lightweight ram sounding device used for this purpose (often also called Künzelstab - but then actually provided with a smaller tip) consists of a ram with a 10 kg drop weight and an extendable steel rod with a standardized probe tip. At the test point, the probe is driven vertically into the ground. The number of blows required for each 10 cm penetration depth is counted. To illustrate this, the punch numbers are shown in a sounding diagram as horizontal bars.

The penetration resistance depends - unfortunately - not only on the compaction, but also on the type of soil and water content. Therefore, in order to assess the result, a comparative sounding is usually necessary on undisturbed terrain with the same soil type and with the same soil moisture. The interpretation of the punch numbers based on their depth sequence can also provide interesting conclusions, but requires great experience and precise knowledge of the "history of the soil".

Tips for practice

The measuring devices described above are only rarely available on landscaping construction sites and many also shy away from the costs of using them. Nevertheless, one should not completely forego the control of the paving quality. In addition to consequential damage, there is also a risk of sanctions on the part of the client, because self-monitoring tests are usually agreed as an ancillary service in the contract. The following examples name some simple test options that can also be used on small construction sites:

  • Documentation of compaction: It is even common in road construction to confirm that the machine operator has worked on all areas in the specified number of transitions with the compaction device provided in accordance with the written work instructions.
  • Compaction attempt: At the end of the compaction work, the last strips are drawn diagonally / transversely to the previous working direction. This makes it easier to see whether this will result in further densification.
  • Driving attempt: When driving over the compacted area, depending on the vehicle weight / tires, only small marks may appear. The depth of the acceptable tire tracks is to be determined according to the subsequent load.
  • "Boot heel test": In the static plate pressure test, the depression is measured at a compressive stress of 200 kN / m² under the load plate. Approximately the same pressure arises if you stand with 80 kg "live weight" on an area of ​​40 cm² (e.g. roof batten section 5 cm x 8 cm or a comparable large shoe heel). For the typical road construction requirement of 45 MPa, the indentation during loading by the load plate may not exceed 1 mm. As a result, there should be practically no imprint in the boot heel test.
  • Construction iron probing: For a rough preliminary test, a long cord can be hammered into the ground instead of the ram probe. Experience makes the landscaper "instinctively" cautious when hardly any physical effort is required.

Please also think of documenting your tests with photos, entries in daily reports or the construction site diary. Because when problems arise later, as is so often the case: "Only those who write will stay!"

literature

literature

Dörken, W. & Dehne, E. (2002): Basic building in examples - Part 1. - Werner Verlag, Düsseldorf

www.eng.hokudai.ac.jp/labo/geomech/ISSMGE%20TC202/proctor.html - accessed on January 5, 2016

de.wikipedia.org/wiki/Ralph_R._Proctor - accessed on January 5, 2016

Standards and regulations (selection)

ATV DIN 18300: General Technical Contractual Conditions for Construction Services (ATV) - Earthworks - Edition 2015-08 (German Institute for Standardization e.V. - DIN) Berlin.

DIN 18121-1: Investigation of soil samples - Water content - Part 1: Determination by oven drying - Edition 1998-04 (German Institute for Standardization e.V. - DIN) Berlin.

DIN 18122-1: Subsoil, investigation of soil samples - State limits (consistency limits) - Part 1: Determination of the flow and roll-out limit - Edition 1997-07 (German Institute for Standardization e.V. - DIN) Berlin.

DIN 18123: Subsoil, investigation of soil samples - Determination of the grain size distribution - Edition 2011-04 (German Institute for Standardization e.V. - DIN) Berlin.

DIN 18125-2: Subsoil, investigation of soil samples - Determination of the density of the soil - Part 2: Field tests - Edition 2011-03 (German Institute for Standardization e.V. - DIN) Berlin.

DIN 18127: Subsoil, investigation of soil samples - Proctor test - Edition 2012-09 (German Institute for Standardization e.V. - DIN) Berlin.

DIN 18134: Subsoil - Tests and experimental devices - Plate pressure test - Edition 2012-04 (German Institute for Standardization e.V. - DIN) Berlin.

DIN EN ISO 14688-1: Geotechnical exploration and investigation - Designation, description and classification of soil - Part 1: Designation and description; German version EN ISO 14688-1 - Edition 2013-12 (German Institute for Standardization e.V. - DIN) Berlin.

DIN EN ISO 14688-2: Geotechnical exploration and investigation - Naming, description and classification of soil - Part 2: Basics for soil classifications; German version EN ISO 14688-2 - Edition 2013-12 (German Institute for Standardization e.V. - DIN) Berlin.

DIN EN ISO 22476-2: Geotechnical exploration and investigation - Field investigations - Part 2: Ramming soundings; German version EN ISO 22476-2 - Edition 2012-03 (German Institute for Standardization e.V. - DIN) Berlin.

TP BF-StB Part B 8.3: Technical test specifications for soil and rock in road construction - Part B 8.3: Dynamic plate load test with a light drop-weight device - Edition 2012 (Research Association for Roads and Transports eV - FGSV) Cologne.