OFF THE BEATEN PATH
Every Sunday, dirt roads throughout Baja beckon me. My trusty grandson, Gabriel and I find some of the most secluded, beautiful places in Baja…Allow us share our experiences with you. If you have a great spot off the beaten path, let me know, we’d love to check it out and share.
The Road to El Cardonal in the East Cape- JUST ONE EXAMPLE
A sigh of relief from East Cape residents, OR Is it?
A relatively new road between Las Barilles and El Cardonal is a 17 km. 2 lane road that heads north of Las Barilles through the mountains to the beachfront town of El Cardonal on the Sea of Cortez. It was built as an alternative to the 11 km, rouged dirt road along the coastline and to make development and delivery of goods in that area more accessible.
Up until very recently, this new road was a veritable hazard even during daylight hours, and a death trap after dark. Many sections of this road literally collapsed into steep canyons leaving, not potholes, but chasms where whole cars could disappear off the cliffs without warning. In addition, the ancient, soft sand / rock composites (called semi-lithified sand, caused from either alluvium sediment movement -run off from mountains or ancient seashores) making up the excavated and filled road sides, were cut and filled at angles exceeding 80 degrees and collapsed in many places over the road bed itself. This falling rock and sand condition eliminated the two lane status of the road in many places, causing drivers to hug the dividing line to make it through the debris covering both sides of the road. In many instances, these avalanches occurred in dangerous curves where on coming traffic could have easily caused an accident.
Well, recently, the government finally made some repairs to the collapsed roadsides and cleared the debris off the road beds. Hallelujah! But East Cape residents and visitors - don’t get too excited yet. This is a temporary fix AT BEST.
Mexico has been a member and a participator in many international engineering and science societies for decades. The last I knew the basics of physics don’t change when you cross the border of any country of the world, including Mexico, so engineers and scientists have long participated in sharing of research, data and standards around the world. The soil here in Baja and it’s properties are not unique or outside of the international sciences of geology and soil mechanics. None of these scientific principals or safe roadway construction standards are new to Mexico’s engineers and builders. In fact Mexico is noted for learning from the earthquake of the 1980’s in Mexico City regarding the importance of soil stability when founding structures. But, you really don’t have to be an architect, engineer or soil mechanics expert to recognize the issues of roadway construction here in the Baja, the evidence from poorly built and designed roads are all around us. It may be annoying and even frustrating to be driving along one of Los Cabos’ urban streets after a rain and end up swerving to avoid the resulting potholes, additional evidence of poor roadway design and construction, but it is quite another matter when life and safety is put at risk from these practices where whole lanes of a highway slide down an unstable manmade hillside. Why will this road fail again?
First , some Basic Soil Mechanics 101 for Novices: 1) *Natural angle of repose is defined as “the angle made by the inclined plane from the horizontal surface such that the body lying on the inclined plane is at rest just at the verge of sliding down along the inclined plane.” It is an angle that each material seeks with the forces of gravity. This angle can increase with proper compaction, but every type of soil or composite soil has an angle that is “safe” for natural and manmade cut and fill conditions and the soil needs to be tested to
determine this angle. Sand, however, is a material that has a very low angle of repose; dry, unconsolidated usually between occurs between 30 - 37 degrees, depending on the grain size. Think of a sand castle. Without water present or a “glue” such as silt or clay, the dry material seeks a fairly low angle to come to rest, a function of friction between the tiny particles making up your dry sand castle. When you build your castle from moist sand, the angle increases dramatically, especially with the compaction you give it patting the soil in place. But once dry, the castle will eventually collapse to the angle of repose of the particles it is made from. If you add pebbles and stones in the mix, the time to collapse speeds up from the added weight on the tiny particles. If you take a garden hose to your castle, the sand quickly “melts” no matter how much you have compacted it, making the mix a fluid seeking level, as is the physics of fluids. This is true for this naturally semi-lithified sand with rubble materials too. It is what this roadway is built on and through. Semi lithified means semi-converted to a more cohesive rock, but it is not fully converted, so therefore still susceptible to its finer grain components. See Fig. 1 The excavations through the mountains that previously collapsed (and will again), a “debris avalanche” (the geotechnical name for it), occurred in slopes exceeding 12 feet high, in fact in areas well over 50 feet high (that is a 5 story building). This material, although safe to cut at an angle of ¾:1 when temporary and under 8 feet, is highly unstable at the permanent heights they have been cut and when unprotected from the elements. Even truck vibrations will affect the material these cliffs are made from, as well as rain, wind, seismic activity and the upward lift of the mountains they are occurring within. When no other option is at hand, slopes such as these need to be structurally underpinned along its face and the exposed material protected from the elements with gunite, rock lining or even planting where the angles and soils allow.
2) Loads, bearing capacity and distribution through soil: Again, every soil and composite soil has its own specific load bearing capacity. Pure sand being the hardest to compact, but it generally can withstand about 3000 pounds per square foot (relatively low in comparison to rock). Engineering standards use an angle of 45 to 60 degrees as the angle loads naturally distribute throughout the underlying soil. When you have a material such as sand or uncompacted or improperly compacted fill with a fairly steep angle, the loads on top of the pile, cannot sufficiently distribute the load. Compacted fill for any structure, including road beds, is an internationally recognized requirement for the stability of any structure. Roads receive an incredible amount of load and vibration from traffic. When the terrain does not allow for a wide shoulder or an adequate load distribution angle, it should be underpinned with a retaining wall or grade beam, both of which, should founded in stable material such as bedrock or compacted fill. No underpinning is in place on these roads. The pavement comes within a foot or less of the top of the extreme slopes in many areas. In the case of this road, it is not a matter of whether it will fail or not, but rather of when failure will occur. As most failures occur suddenly without notice, hopefully it won’t be you and your family driving along when it occurs! See Fig. 2
3) Permeability and erosion: A basic principal of erosion states that permeable soils (those that have finer grains and spaces between particles allowing water to enter, are more susceptible to erosion. Sand is highly permeable and the cut hillsides will melt with each rain. The repaired holes are constructed on non-compacted fill at very steep angles where no laid asphalt cover has been placed over these massive holes. One good rain and that is that for those repairs! Aside from washing away the non-compacted fill repair with rain water and drainage from other paved surfaces, the probability is that it will be undermine additional feet below the pavement as well. Water always seeks the easiest path down hill.
Soil mechanics and engineering is rather complex with other topics such as liquifaction, creep, bedding planes and slippage to consider, but the above principals are easy to comprehend, especially with pictures. And “fixes” to unusual situations have been documented, tried and tested worldwide. So, how are these roads being built and maintained disregarding the basics of sound engineering practices here in Baja California Sur? Well without getting political, the funds for most new paved roads are obtained from a combination of county (Los Cabos or La Paz), State of BCS and federal government funds. Whether or not the design drawings are done in compliance with internationally recognized standards and testing procedures is unknown, but apparently, little to no inspections from these funding sources is in place. Continued funding apparently is not contingent on the contractor’s performance with regards to the compliance with drawings and specifications, if they exist at all. In fact, when I interviewed several contractors who have worked on public works projects, one contractor told me that, cutting corners is a Mexican cultural past time. He further stated that with no one there to assure the work is completed correctly, so it is an easy past time as well. He stated that most contractors bidding and doing public work in Baja know that they will get paid if they deliver a product, any product, and that they have a built in new job 3 to 5 years later when their work fails and needs to be repaired!
So El Cardonal and Los Barilles, enjoy it while you can.
See figures below
[As the load under a footing spreads out, pressure on the soil diminishes. Soil directly under the footing takes the greatest load, and therefore should be thoroughly compacted.]
Figure 2: Load distribution