The instability of the land forces to reinforce security on the AP-8 motorway in Zaldibar and in the Ermua variant

The Department of Infrastructure and Territorial Development of the Provincial Council of Biscay has adopted new measures to improve highway safety AP-8 in Zaldibar and the Ermua variant, affected by the landslide collapse from Zaldibar on February 6.

As reported by the regional institution in a statement, “from the outset these measures have been coordinated with the Basque Government and subject to the priority objective of locating and recover the two missing people"And are carried out" in compliance with current regulations on safety and health at work. "

In addition to continuing to study new measures to strengthen the safety on the highway and the Ermua variant, the Provincial Council has worked in these eleven days “to know in depth the geotechnical characteristics of the landfill, to study and adopt measures to contain the mass of materials that he slid down the trough that flows into the highway, and in taking measures to keep the highway open to traffic safely for users ”.

From the foral institution they have pointed out that knowing the characteristics of the mass of waste, as well as the original land on which they are based, is “fundamental to assess and determine subsequent actions”. Therefore, geologists and engineers of the Department of Infrastructure and Territorial Development keep the mass of slides monitored from the morning of Friday, February 7.

This monitoring is carried out “simultaneously and in coordination” from a visual control post, by specialized technicians, and from a robotic topographic station that constantly takes the references of 19 witnesses (prisms) placed in key points of the landfill, explained the responsible Foral The station sends signals continuously to each of these prisms and the reception of the bounce allows to determine if movements occur at the millimeter scale.

For this Tuesday, February 18, work is scheduled to be completed to put into operation a second topographic station, which will allow "to have redundant information, strengthening the topographic control system."

The information obtained during these past eleven days has allowed technicians to improve topographic knowledge and the geotechnical characteristics of the landfill, "knowledge that will continue to expand as they get more information," said the Diputación.

In any case, the information obtained since last day 6 concludes that, "since then, there have been no significant displacements, although the mass of landfill slips is unstable."

That instability, he warned, "could manifest itself in the form of new landslides if environmental conditions change, mainly due to rain." Given the possibility of new landslides, the Diputación has adopted measures to contain the movement of the mass, "protecting the safety of the highway and therefore of the users."

As explained, last February 12 began the construction of a breakwater dam next to the road in the direction of San Sebastián, which requires an investment of 200,000 euros, and will be six meters high and 50 meters long. Additionally, the installation of a dynamic anti-avalanche screen, formed by a metal mesh capable of supporting large thrusts.

Based on the technical calculations made by the team of geologists and foral engineers, this mesh will have an area of ​​75 square meters and will be installed about 40 meters above the containment dam in an area with little slope, “the place where it will be more effective both for storage capacity and energy absorption ”.

The Provincial Council has already ordered the necessary material, which comes from Switzerland, and expects to have the dynamic screen installed by the end of this month of February. The estimated cost for its acquisition and assembly is about 75,000 euros. To install this mesh in the final part of the trough that flows into the highway, approximately 6,000 cubic meters of waste deposited at the head of the landslide must be previously removed.

In order to expedite this operation, the construction of the breakwater dam will be slowed down for a few days, as its base will serve as an operating platform for excavators and trucks. As explained by the regional officials, the construction of both barriers must be coordinated because access to the location of the barrier will be made from the point where the breakwater is being erected.

According to the calculations made, in the case of a new slippage of materials, the sum of the containment dam and the dynamic screen would provide a sufficient capacity to retain 7,700 cubic meters of spills, which is twice as much as the amount that fell to the Highway and the N-634 February 6. In any case, the technical teams continue to analyze “what other additional measures can be taken to increase the safety of the highway”.

Closing protocol

The detachment kept the traffic on the AP-8 and the Ermua variant cut off for fifteen hours, until seven in the morning on Friday, February 7, which generated significant traffic problems as it was two “priority” roads of the road network from Bizkaia. On the highway, traffic has been done since then by a two kilometer bypass in the Bilbao sense road.

This situation, with the road in the direction of San Sebastián closed to traffic, will remain as a safety measure until it is guaranteed that it can no longer fall on the highway. Therefore, the bypass, currently marked by cones, will be improved with the installation of New Jersey type concrete barriers to segregate the two directions of movement.

These works will be done at night, starting on Wednesday, and will require cutting the highway to traffic between 23.00 and 5.00 hours for five nights. Since the reopening of the highway to traffic, at dawn on February 7, the Department of Infrastructure and Territorial Development maintains an active protocol for the closure of the highway and the Ermua variant, prepared and coordinated with the Department of Traffic Department of Security of the Basque Government and with the Provincial Council of Gipuzkoa.

This protocol is activated when the landfill monitoring system warns of the possibility of slippage. At that time, a pre-alert is activated that mobilizes the necessary resources by the Provincial Council and Ertzaintza. If the technical team determines that the risk of detachment is real, the alert is activated, which implies “immediately” cutting the highway in both directions in the bypass.

This work, for which the participation of Ertzaintza agents and Interbiak personnel is currently planned, will be reinforced this week with the installation of automatic traffic lights. Also, in an alert situation, both directions of bypass circulation with surveillance personnel would be cut off. Once the detours were established, in Gerediaga and Eibar, the retained vehicles would be evacuated. The recommended alternative route would be signposted and would run along the Gerediaga - Elorrio highway and the Kanpazar stop.

In the Ermua variant, the same action protocol is established in the case of an alert, which involves taking traffic at the roundabouts of the toll road and San Lorenzo and diverting it along the N-634 through Ermua. Ep