BEFORE SURFACE 

Leveling, is the work of leveling the ground of a construction project or a planning ground, from a ground with different high and low natural terrain. Flattening is the excavation of the highest land in the land that transports to the lowest areas and embankments on those low areas, to flatten the surface of that landform according to human predetermined owners ( predetermined design surface, taking into account the slope of surface drainage. As such, the ground leveling work usually includes excavation, soil transportation and soil embankment. In leveling work, first, construction land is mainly taken right inside the construction site. The amount of surplus or missing land must be contacted outside the site, often as a supplementary source or only a small amount, or even not available (such as when leveling and digging).

There are usually two types of ground leveling work: - Follow the conditions to control the level of ground level after leveling, without paying too much attention to the excess or lack of soil, - Follow the requirements of the volume of soil when leveling, including the following cases: leveling the volume of excavation with filling, leveling with the intention of leaving a volume of soil after leveling (digging more than filling) or deliberately adding an amount of pre-existing soil (more than digging).

Design and construction works san

- In both types of leveling work, the design of ground leveling requires the fact that the two steps are as follows: - San ground design (this step is to determine the volume of land to be constructed, the direction and distance of average soil transport from the excavated area to the embankment within the construction site.) - Design construction measures (design specific construction methods for ground leveling, after knowing the volume of construction and the distance to transport them while leveling)

The simplest case of leveling ground terrain is the case on the topographic map of the region, the contour lines are almost straight and simultaneously parallel. In this case, using a single section cut perpendicularly through all contour lines can represent the full elevation of all natural ground points on the area considered. Therefore, the determination of soil mass in this case is simply the calculation of the volume of each long run and the nearly constant section. This is called the method of determining soil mass by section.

The more complex case is that the contour lines are slightly curving but still relatively parallel. Then use a section that cannot fully represent all pitches of the entire natural terrain. In this case, it is necessary to divide the face area by planning the grid into a grid, along the direction of the contour line, with the distance of the meshes small enough to break the contour lines into relatively straight segments continuously and of equal length. Then the approximate ground in each grid is a plane created by mesh elevations. Mesh elevations are determined according to the way in the contour. The volume of each plot of land is calculated by the product of the average elevation of the meshes on the 4 corners of the plot with the projected area of ​​the grid. This is called the method of determining the amount of soil in a grid.

Where the most complex ground is when the contour lines are curved and not parallel, the distance between them changes constantly at every position. In this case, the grid can not accurately simulate the actual shape of the terrain, because in each complex natural ground, if it is referred to a plane, the error is very large (4 mesh points are on one quadrilateral, not flat. In this case, in order to accurately simulate the more realistic terrain, in each square the natural ground is roughly approximated by two inclined planes, (each creates 3 of the 4 grid elevations of the square), with a horizontal projection of two half squares, a right triangle with a hypotenuse is a diagonal of a square. Divide the grid by the diagonal of the plot, so that these diagonal lines are parallel to the direction of the nearest contour line, ensuring a more accurate realistic simulation. The volume of each triangle land plot is calculated by the product between the average altitude of the meshes in the three corners of the plot with the area of ​​the projected area of ​​the triangular grid. This is called the method of determining soil mass by triangular grid.

Determine the design ground after leveling

The level of leveling condition that controls the level of ground level after leveling: the investor usually controls before the average elevation of the surface, so the contractor does not need to calculate this elevation. Form of ground leveling according to the required volume of soil when leveling: Follow the condition of earthwork digging (outside soil volume V0 = 0): The volume of excavated soil must be equal to the volume of embankment soil. It also means that the total volume of land on the planned ground area, calculated from the hydrological surface upward, is redistributed on the same projected area, with the average elevation H0 compared to the water level.

If using the sectional method, the average elevation: H0 = ΣSi / B With ΣSi is the total area of ​​the section above the hydrological surface, of all soil ingots running along the contour line in the planned ground area. And B is the width of the planned area (perpendicular to the contours). If using the grid or triangular grid method, the average elevation is calculated as the ratio of the total volume of all grid cells, calculated from the sea level upward, with the total projected area of ​​the area planning. The total volume of all grid cells is calculated through mesh elevations, calculated from the hydrological surface. Case of grid grid: H0 = (ΣH (1) j + 2ΣH (2) j + 4ΣH (4) j) / 4m

In the case of triangular grid: H0 = (ΣH (1) j + 2ΣH (2) j + 3ΣH (3) j + ... + 6ΣH (6) j + ... + 8Σ H (8) j) / 3n. With H (1) j, H (2) j, H (3) j, H (4) j, ..., H (6) j, ..., H (8) j, are self elevation However, in grid squares, there are 1, 2, 4 squares gathered around, or natural elevations in the grid of triangles that have 1, 2, 3, ..., 6, ..., 8 triangles are gathered around. With m is the total number of squares in the planned area. And n is the total number of triangles in the planned area.

With the condition of leaving the ground behind, or adding the soil from outside when leveling (external soil mass V0 ≠ 0): the average height of the leveling ground is calculated by the average elevation when the leveling and leveling balance is added. or reduce the height difference due to the amount of soil added or lessened. If the outer soil mass V0 ≠ 0 has been predetermined, then the average elevation H0 is calculated by the following formulas: Case of grid grid: H0 = ((ΣH (1) j + 2ΣH (2) j + 4ΣH (4) j) / 4m) ± (V0 / (ma²))

In the case of triangular grid: H0 = ((ΣH (1) j + 2ΣH (2) j + 3ΣH (3) j + ... + 6ΣH (6) j + ... + 8 H (8) j) / 3n ) ± (2V0 / (na²)). With a is the distance of the meshes (next to the grid view). However, if only the entire surface is leveled according to the same level of H0 average, it is not possible to ensure drainage on the surface of the planning area (such as rainwater, ...). It is necessary to create planning areas into drainage slopes, with a predetermined slope. In order to correlate the volume of construction soil unchanged, the leveling of the leveling slope of the designed slope around the average elevation H0 must ensure the balance of excavation and embankment while adjusting the slope. At the focal points of each design slope, we get the correct design elevation equal to the average elevation H0, then adjust and reduce the design pitches on either side of each focal point, the high difference calculated according to the slope ratio, so as to ensure the condition of digging and balancing. The design elevation of the points on both sides of the design slope is:

htkj = H0 ± itkl0. With itk is the given design slope according to the design task (%), and l0 is the distance from the point of design to determine the design elevation to the design slope center. As such, it has been determined that the design surface is correct. Now at every location of the planning ground there are two levels: natural altitude (of natural ground htnj) and design elevation (of the design surface htkj). In addition, to ensure the stability of the roofs after leveling both the excavation and embankment, to avoid landslides after ground leveling, when designing the ground level, it is necessary to design the roofs. ta-luy circled around the design side after leveling, following the allowable slope. The slope allowed to be critical is the maximum slope that the ta-lug roof or excavated soil can have, without causing slippage of the earth's roof.

In the flat surface area, there will be boundaries between excavated areas with earthen areas, called O-O earthworks. This O-O boundary is the intersection of the natural terrain with the design face. Calculate workload  The hctj height of each point on the planned site is the difference between the natural elevation of that point and the design elevation of that point: hctj = htnj - htkj. A certain area of ​​the planned ground is a excavation area if all working elevations of the points in the area have a positive value of hctj> 0 (in that area, the natural ground is higher than the surface). design, and vice versa, the embankment area has the negative work height: hctj <0 (in that area, the natural ground is lower than the design level). Places with hctj = 0 are above the earthwork boundary. Thus, depending on the simulation method, we can determine the volume of working land, according to the characteristics of the simulation

With the cross-section method, the determination of the volume of excavated soil and embankment is simply the multiplication of the area of ​​the working area, which is the part between two lines: the natural ground elevation and the high road The ground level is designed after leveling, with the length of the soil ingots again (length along the contour line of the land plot to be leveled). If the area of ​​the work area is below the natural ground elevation, the volume of soil is excavated soil, whereas the area of ​​this area is located on the natural elevation, the volume of embankment soil. O-O excavation boundaries, in this method, are only intersections, on typical sections, of two roads: natural ground highways and ground level elevators designed after leveling.

working on each grid, including squares or triangular networks, will see that there are 3 types of grid: The type of umbrella has all altitudes working at positive mesh hctj> 0, which is the type of cell that is completely located in the excavation zone; The type of cell has all the altitudes working in the negative mesh hctj <0, which is the type of cell that is completely in the embankment area; The type of cell containing both meshes has a medium and negative negative altitude, with both meshes hctj> 0 and meshes with hctj <0, which is the type of umbrella that lies on the OO earthworks boundary (excavation and cut boundary these boxes). For two types of cells that are entirely in the excavation area or embankment area, the work volume, (calculated equally but contrary to the mark: the digging box is positive and the offset is negative), equal to the product between the average height of 3 (case of triangle) or 4 (square case) the height of work in the grid at the corner multiplied by the projection area of ​​the grid.

· Grid: Vi = (hct1 + hct2 + hct3 + hct4) a² / 4 · Triangle network: Vi = (hct1 + hct2 + hct3) a² / 6 With Vi being the workload in each grid, hctj is the working height at the jth mesh of the grid.   Umbrella triangular grid across the O-O line

With the type of cell lying across the OO boundary: if the grid grid, the workload in each square is calculated as a combination of two common triangles, so we only need to consider the grid triangle only. In this case, it is certain that one of the 3 peaks of the grid will have a working height (called this peak work height is hct1) in contrast to the working altitudes at the other two peaks (hct2, hct3). The O-O earthworks boundary divides the considering triangle into two halves:

The hct1 elevation of the working soil mass is in the form of a triangle pyramid (VchópΔ) with hct1 height, and is calculated through the projection area by SOO1. Through trigonometric transforms SOO1 becomes dependent on the altitudes of work in the grid: SOO1 = (hct1) ²a² / 2 (hct1 + hct2) (hct1 + hct3). Therefore, VchópΔ = (hct1) ²a² / 6 (hct1 + hct2) (hct1 + hct3). How to calculate the remainder of the triangle grid grid on the O-O boundary

On the hct2 and hct3 working altitudes, the volume of V1 is calculated by adding an intermediate V2, created by assuming a high elevation of the natural ground adding a high difference hct1. The intermediate image V2 combines with the VchópΔ shape, forming a triangular prism whose height is hct1. Calling the calculation of the large pyramid above the level of the O-O earthworks boundary is: Great contribution = V1 + V2.

Add VchópΔ to us: V = V large cap + VtΔ = V1 + V2 + VΔΔΔ = V1 + V pillar. Inferred: V1 = VchópΔ + VchópΔ-V cylinder. With V cylinder = a²hct1 / 2. And V-tip big = (2hct1 + hct2 + hct3) a² / 6. Thus, the volume of excavated or filled soil of the triangular grid is located on the earthwork boundary, which is one of two volumes: VchópΔ, V1.

After calculating the volume of soil needed to work inside the planed ground, it is necessary to determine the volume of excavated or filled soil of the lodged roofs located around the edge of the leveling ground. These masses are also classified into two types: ta-peach mass and taut mass. The working soil of these two types is compensated with each other, taking the soil in Tauyao to cover it. However, in most cases, these two volumes are often unequal, then the amount of earth we have or excess (actually just in the calculation) is assumed to bring up the whole The excess leveling surface (including on the surface of the roofs of the lugs) or peeling off the ground in a level goes evenly to a certain thickness (including on the roof of the roof) to compensate if it is missing. Then the design surface, and the amount of earthwork calculated and the earthwork boundary will change. New design side is parallel to the old design surface. The problem of san becomes a level with a different amount of V0, and must be repeated many times until the digging balance is reached. Therefore, in practice, there are often few pure leveling and leveling problems.

Ground leveling under the control conditions before the average elevation H0, the ground level of the design has been predetermined, the volume of working land is also calculated completely like the form of leveling according to volume requirements: that is the volume Clamp between two natural ground and rear design san. Landfill