2020

LVM to Study the Suitability of Wooden Piles for the Construction of Forest Roads on Low Load-bearing Soils

JSC “Latvia's State Forests” (LVM) has started work on a study on an alternative and innovative approach to forest road construction on low-bearing soils – the use of wooden piles to cross local but relatively deep peat inclusions.

When performing engineering geological research in the course of the design of forest roads, it is often found that there are local peat inclusions in the planned forest road route. Crossing them requires significant material investment in the stabilization of the ground surface, on which the pavement foundation and pavement can be built. The simplest solution is not to plan the construction of forest roads in such places. However, there are situations when due to various restrictions the construction of forest roads in another place is not possible, so an alternative is needed to build a forest road, for example, in order to cross peat inclusions.

LVM, together with construction project developers, has found various solutions for crossing local peat layers up to a depth of 3.5 metres.

Researching the experience of other countries on how to cross relatively deep peat inclusions – from 3.5 metres to 8 metres – it was found that wooden piles are often used. Thanks to this innovative technology, the structure of the forest road does not deform after construction and it ensures the intended load-bearing capacity.

In the autumn of 2021, LVM plans to build a forest road in West Vidzeme region, crossing a swampy territory, where the thickness of the problematic peat layer in a length of 250 metres is from 3.1 meters to 4.8 metres. Therefore, LVM plans to use wooden piles, the design solution of which is also suitable for timber trucks with a total weight not exceeding 52 tonnes. This forest road will also create preconditions for the management and protection of the forest massif. The technical solution and the constructed forest road will comply with the requirements of the LVM-approved regulations “Technical Regulations for the Design of Forest Infrastructure Facilities” concerning the forest road pavement durability requirements. When crossing such a peat section, the load-bearing capacity of the forest road must ensure that freight traffic with a load of 10 tonnes per axle can move on it, while the total weight of a vehicle unit must not exceed 52 tonnes.

LVM will conduct a study to find out how durable and stable such a solution is, as well as to further investigate the efficiency of wooden piles at different peat depths; it is also important to record the stability of the peat section of the built forest road and possible deformation dynamics. During the research, data on the stability of the developed design solution or possible deformation in places where the depth of the peat layer exceeds 3 metres will be regularly collected.

Based on these data, it is planned to determine how stable and durable the chosen wooden pile solution is for crossing local peat sections, what interrelationships can be observed depending on the intensity and seasonality of forest road use. 

It is planned to observe the section of wooden piles built in the peat layer for two years; the start of the monitoring programme is planned for autumn 2021.