Natural land slope

[Yann]

Hi,

I'm planning to excavate my backyard to get it level with my house. I'll use retaining walls on the sides. But I'm thinking of having a natural slope at the back between a flower bed (running along the back fence, 4m off it) and the excavated area.

We got sandy soil and the elevation difference between the excavated area and the flower bed will be 900mm.

Anyone can help me regarding what sort of slope gradient I should consider and how to stabilise the slope.

Thanks.

[Eli]

What distance is the 900 drop taking place over?

[Yann]

I'll try to clarify it...

I'll have the flower bed running from the back fence for 4m and 900mm above the level of the rest of the backyard. From this point I want a natural slope which bring me to the level of the rest of the backyard (so 900mm drop) as quickly as possible.

Hope it helps

[autogenous]

you want the angle of repose (natural ground fall) but you will need to stabilise it with grass or stone pitching

[echnidna]

absolute steepest angle 45 degrees

[journeyman Mick]

absolute steepest angle 45 degrees

With Yann's sandy soil, probably way less than that. I'd be inclined to get a shovel and dig some up and pile it in a heap to see what angle it will naturally end up at and then work to an angle about 5 - 10 degrees less.

Mick

[pharmaboy2]

for tht sort of thing, i'd go 45 degrees and plant a stack of agapanthas on the slope - if the soil is rich and you water well, aggies will stabilise it in a few weeks - and by a year a massive downpour should be fine

[Bleedin Thumb]

1:4 -(25 Deg) if you want it stable without using mechanical stabilisation techniques. IMHO a 45 deg slope is unstable and you should not attempt this.

If you want it steeper you could stabilise it by using jute meshing while plants establish, but you are always going to get into trouble with mulch sliding off and potential erosion.

BTW here are some angles of repose for sand. As you can see 45 deg is unrealistic. It should be noted that the Angle of Repose is not a stable slope but merely what the dry material will sit at.



<TABLE cellSpacing=0 cellPadding=3 width=500 border=1><TBODY><TR><TD colSpan=5>Angle of Repose Data Table



</TD></TR><TR><TD></TD><TD class=table-head align=middle colSpan=4>Angle of Repose (degrees)
<HR noShade SIZE=1></TD></TR><TR class=table-head2><TD>Material </TD><TD>First Pour </TD><TD>Second Pour </TD><TD>Third Pour </TD><TD>Average</TD></TR><TR><TD>Brown sand



</TD><TD>33



</TD><TD>33



</TD><TD>32



</TD><TD>32.7


</TD></TR><TR><TD>White sand



</TD><TD>34


</TD><TD>32


</TD><TD>33


</TD><TD>33


</TD></TR><TR><TD>Salt


</TD><TD>35


</TD><TD>35


</TD><TD>35


</TD><TD>35


</TD></TR><TR><TD>Sugar


</TD><TD>37


</TD><TD>35


</TD><TD>36


</TD><TD>35


</TD></TR><TR><TD>White rice


</TD><TD>40


</TD><TD>39


</TD><TD>39


</TD><TD>39.7


</TD></TR><TR><TD>Brown rice


</TD><TD>40


</TD><TD>43


</TD><TD>41


</TD><TD>41.3


</TD></TR><TR><TD>Lentils


</TD><TD>39


</TD><TD>34


</TD><TD>39


</TD><TD>37.1


</TD></TR></TBODY></TABLE>

[journeyman Mick]

BT,
looks like Yann's best bet is to replace his sandy soil with brown rice then.

Mick

[Bleedin Thumb]

Hmmm maybe if you don't mind mice.

For the life of me I don't know why they used those materials as a comparison....probably done by Uni students in the 70's