**6.4 Grassing**

Grass species suitable for use are locally available in abundance and the type to be introduced can be decided by the horticulturist attached to the project. The grass is provided and nourished as a cover over the backfill. The roots of the grasses serve as the fiber reinforcement to the loose backfill and as well provide infiltration channels into the fill. This may prevent clogging of the interstices by oxides and clays suspended in the runoff. In addition, it adds to the esthetic value of the drain.


#### **Table 1.**

*Properties of various soil types obtained from laboratory studies.*

*A Drainage System for Road Construction on Flat Terrain DOI: http://dx.doi.org/10.5772/intechopen.105019*

#### **Figure 5.**

*Drawdown versus time curve with varying backfill materials.*

**Figure 6.**

*The regression graph for varying backfill materials.*

#### **6.5 Gang way**

Situations may arise where the trenchless drain must be bridged. This is mainly in residential areas in which case crossings to serve as entrances to housing units must be provided. This may require placement of precast concrete slabs over the drain and will be limited specifically on the required position.

#### **6.6 Comprehensive outline**

In special consideration of all the input variables, a hypothetical design of trenchless drainage system on a road section is illustrated in **Figure 7** while the plan of the sketch drawing is shown in **Figure 8**. The alignments and relative locations of the features are defined in the drawing.

## **7. Construction method**

The construction of trenchless drain in a road project simply involves trenching, backfilling and grassing.

**Figure 7.** *Hypothetical design section of a trenchless drainage system on a road profile.*

**Figure 8.**

*Plan view of a hypothetical trenchless drainage system in residential district.*
