By Mirza Sabir Baig
A new road looks finished the day it opens. The asphalt is smooth, the markings are fresh and the potholes are gone. Then, within a season or two, a depression appears over a trench, cracks follow and the repair crew returns. The usual blame falls on the asphalt or the contractor. Often the real cause lies below, in layers that were covered before anyone checked them.
Asphalt does not carry a road. It spreads traffic loads onto the base and subgrade beneath it. If those layers are loose, the asphalt flexes with them and cracks. A thick surface over a weak foundation is like a strong table standing on soft ground.
The utility trench problem
Most urban roads are cut open many times for gas, water, sewer and cable lines. Each trench must be backfilled and compacted layer by layer. In practice this is slow, the trench is narrow, and the result is invisible once paved. If the backfill is not compacted to the specified standard, it settles under traffic, and the road above it follows.
This does not explain every damaged road. Heavy traffic, ageing and poor drainage also play a part. But uncompacted layers over utility trenches are a common and preventable cause.
Measure, do not assume
In German practice, compaction is verified rather than assumed. Two simple tests show the idea. Dynamic probing (Rammsondierung) checks how dense the soil is at depth. The plate load test (Lastplattendruckversuch) measures the bearing capacity of a compacted layer. Without such tests, “properly compacted” is only an opinion. Both cost very little compared with reopening a finished road.
Wet and clayey ground
Clay soils hold water and lose strength when wet. Building directly on them is a mistake. The usual remedy is to remove the weak soil and replace it with crushed stone such as limestone gravel, or to improve it with lime. The new material is then compacted properly. Lift thickness matters: in trenches, layers of about 15 cm, each compacted and checked before the next, give far better results than one thick layer. Drainage must also be addressed, because trapped water undoes good compaction.
The asphalt layers still matter
The base course (Tragschicht) and the wearing course (Deckschicht) do different jobs, and each needs a mix designed for its purpose. On routes with heavy goods traffic (Schwerlastverkehr), the aggregate grading and binder must match the loads. A mix that suits a residential street will rut and crack under trucks. The specified grain-size distribution should be the one actually delivered, which means testing it.
Information makes roads cheaper
An economical road is not the cheapest road to build. It is one designed for the ground it sits on. That requires subsurface information before design: soil type, groundwater level, existing utility records and a few investigation points along the alignment. Without it, designers either assume the worst and overspend everywhere, or assume the best and pay for repairs later. A modest investigation budget is cheaper than either mistake.
What should change
Three practices would help immediately:
- Mandatory hold points, so no layer is covered before it is inspected and tested.
- Test results tied to specific locations, with failed areas reworked and the rework recorded.
- Independent laboratory testing for work that becomes inaccessible after construction.
None of this requires advanced technology. It requires discipline in the places the public cannot see.
A road should be judged by how it performs years after opening, not by how it looks on the day. Pakistan will get longer-lasting roads when the layers under the asphalt receive the same attention as the surface.
