- When does it make sense to lift a site
- Is drainage needed
- Removal of the fertile layer
- How to fill up the hill
- Whether tamping or rolling is necessary
- Black soil filling
- Protection against erosion, strengthening of the embankment on the slope
After acquiring building land, it often turns out that the relief and geology of the area are not quite suitable for long-term use and agricultural activities. We will talk about raising and leveling the ground, from marking to protective landscaping.
When does it make sense to lift a site
One of the worst geomorphological conditions is the rise of the groundwater level above the depth of soil freezing. In such areas, heaving is especially pronounced, which causes the need for complex types of foundations, for example, pile-grillage. Shallow foundations do not work in such conditions, and full deepening requires support on a soil layer 2.5-3 meters from the surface, above the foundation remains unstable and can be subject to precipitation due to high soil moisture.
This is not to say that geodetic site planning is a cheap method to get rid of soil problems. However, the usefulness of such a solution can be expressed economically in favor of the developer, if the raising of the ground eliminated the problems with waterproofing, insulation and stabilization of the foundation and the resulting costs. This is usually the case: planning allows for a cheaper, and most importantly, faster solution to the problem of poor geomorphology, significantly shortening the final shrinkage of the base. This solution is especially shown when building a log house or installing prefabricated foundations..
But raising the level on the site does not always solve the problem. With a steep slope (more than 5–7%), terracing should be performed, and not uplifting, and this is a completely different technology. On such slopes, even attracting special equipment for pouring bored piles costs less blood, and among the foundations this is one of the most difficult. The terrain may also simply not have a sufficiently dense layer of soil to support the building of the required mass on it. Raising the site in such an environment will do nothing at all, in any case, you will have to make the foundation floating.
Is drainage needed
Drainage systems are shown for artificially leveled areas with significant elevation differences, where, as we know, the problem cannot be solved by conventional uplift. However, the phenomena of erosion and washout can be expressed even on small slopes, therefore, the minimum filling and surface drainage will have to be done.
On both boundaries of the site, located along the slope, it is necessary to dig rain trenches, one of which (the lower one) receives water from the cross-section arranged along the upper border of the site. The bottom of the trenches is covered with rubble, and shrubs are planted along the slopes. Periodically, the trenches will have to be cleaned, usually the owner of the site has the one that is higher in level. In depth, the trenches should reach the upper aquiclude and cut it a little – about 20–30 cm. In order to less disturb the terrain, the depth of the trenches can be adjusted with hygroscopic material – the same rubble or construction battle.
If the direction of the slope and trenches diverge by more than 15?, You should be prepared for an increased flow of water. The bottom of the upper trench should be paved with bricks, even better with trays. In such areas, it makes sense to level the soil locally exclusively for buildings. In this case, the plot for the garden is simply protected from erosion by a trench across the slope, on the upper slope of which willow trees or several birches are planted. It is recommended to fill the bottom of the trench and its upper slope with crushed stone to prevent siltation.
Removal of the fertile layer
There is no point in covering the entire layer of the embankment with chernozem, just as there is no point in throwing clay over the fertile layer. The top layer will have to be removed to clean clay, and then put back in place. If only part of the site is to be leveled, the surplus soil is simply thrown into the adjacent area. If the site is planned completely, the work is carried out in two stages..
The excavation is carried out in order to eliminate the plastic washed-out layer between two dense layers, because the probability of the embankment sliding under its own weight is so great. The only exception is when the site is located simply in a lowland without a slope 20-30 cm below the adjacent territory. Here it is reasonable to limit ourselves to increasing the thickness of the fertile layer..
After exposure of the dense layer, a series of geodetic measurements is carried out. Knowing the configuration of the upper aquiclude, you can determine the required volume of soil and start importing it. In parallel, the volumes of crushed stone for filling are calculated and the arrangement of the drainage system is planned.
How to fill up the hill
To create the embankment, a swollen tough-plastic clay, loam or sandy loam is used. The ability of the bedding to pass water is determined by geomorphology: if, with an abundance of water, it is impossible to fill up a tightly rammed terrace, or if the filling is carried out over a porous layer, the embankment should have limited water flow. It is optimal if the bearing capacity of the clay corresponds to the underlying layer, so do not be lazy to take samples.
In places where the site plan rises more than 30–40 cm above the adjacent territories, it is necessary to carry out retaining dumping with road crushed stone of fraction 70–90 cm. It is also used in surface drainage. Crushed stone is dumped immediately after excavation under the formed side. The width of the dump at the bottom should be at least half the height of the crushed stone shaft. On the sides of the site along the slope with rubble, you can immediately form the bottom of drainage trenches.
The supports with a height of more than a meter are covered with geotextiles, which are immediately pressed down with a small layer of clay. After that, the imported soil is started and distributed over the site. The easiest route for laying is starting from the shaft laid from the place of entry of the equipment to the opposite point, and then into the dump in both directions.
It is not recommended to fill more than 0.7–0.8 meters of clay embankment at a time. If it is necessary to raise more, wait for heavy rain or give the embankment time to winter. But with the use of ramming and excavating equipment, you can quickly fill in more impressive dumps..
Whether tamping or rolling is necessary
It is optimal if the imported clay is sequentially unloaded completely at the upper level of the dump, and then collides with the bucket into the unfilled areas. This is how a high-quality compaction occurs, in which the final shrinkage takes place in one or two wetting..
The rammer is used when a high speed of work is required, for example, when the optimal time for filling an embankment is limited by season or weather. With alternate compaction, layers of clean clay can be poured in 0.6-1.0 layers one after the other without preliminary wetting. Note again that only swollen clay is suitable for tamping, dry clay will not accept waterproof properties until swelling and subsequent compaction.
Layers of 30–40 cm can be compacted by rolling, but wheeled vehicles are poorly suited for these purposes. A crawler excavator is irreplaceable if the site is raised to a height of more than a meter, in other cases it is wiser to resort to manual delivery and leveling, and entrust the compaction to precipitation.
Note that it is often not necessary to manually tilt the site. Under the influence of the movement of surface water, the fresh embankment will eventually assume a natural slope. With an abundant flow of water, sometimes it is even necessary to slightly raise the embankment in the lower part of the slope in advance.
Black soil filling
If you hurry up and bring chernozem before the final compaction of the clay, erosion will quickly have its destructive effect and the site will greatly lose its fertility. Unfortunately, only plowing the soil in spring and autumn saves from such a phenomenon, and even then partly.
It is better to sprinkle chernozem or a fertile layer dry and not roll it, preferably manual distribution and leveling of the soil. Technique must deliver chernozem in the reverse order than the one in which the clay was poured. The area is filled from the edges to the central access trench. At the end of the backfill, it is filled.
This is the most time-consuming stage of raising the site: in addition to the fact that it is necessary to level the soil not only in one plane, but also with uniform compaction, the upper bulk layer may not be uniform. Usually, before unloading the black soil, formwork is mounted, the foundation is cast and waterproofed, then sprinkled with crushed stone. Embankments of surface backwater are also arranged before the formation of a fertile layer.
Protection against erosion, strengthening of the embankment on the slope
In addition to backfill and drainage, there are other ways to prevent soil erosion. Of these, the most famous and quite effective is planting along the upper and lower boundaries of the planned site of plants with a developed root system, and in the upper part – actively absorbing water.
Shrubs are planted along the slopes of drainage trenches to strengthen their walls. Plants from blackberries and rose hips to reeds are suitable here: they do not create much shade and at the same time they pump water out of the soil well. From the upper tier, in addition to birch and willow, you can use undersized elderberry and sea buckthorn. On steep slopes, it is recommended to strengthen the embankment with geogrids and an underground drainage network..
But with a small difference in ground level, filling and protective landscaping will be quite enough.