Therefore, this paper summarizes the general contents of earthwork quantity and the problems easily overlooked in calculation, and puts forward some suggestions to solve the problems existing in earthwork calculation in design documents, which can be used for reference by peers and make earthwork budget work more reasonable. The compilation method of highway engineering design drawings in China is different from that of general construction projects. As the basic data of project cost, engineering quantity is usually calculated by designers when completing drawings. Before compiling the project cost, the cost engineer should be familiar with the design drawings and check the engineering quantity. How to correctly design the chart and extract the engineering quantity as the basic data of valuation is the key to compiling the project cost, and there are many engineering quantity items to be extracted. This paper only discusses the extraction of earthwork.
Subgrade earthwork is the main engineering quantity in highway engineering. In highway design and route scheme comparison, subgrade earthwork quantity is one of the main technical and economic indexes of highway design. When compiling the project budget, it is necessary to accurately calculate the earthwork quantity of subgrade, which has become one of the conditions for compiling a reasonable project cost.
A, generally extracted from the earthwork content.
(1) The quantities of bottom filling, excavation, earth borrowing, earth filling and valuation of the subgrade itself have been clearly reflected in the subgrade earthwork calculation table and earthwork calculation table per kilometer.
(2) During the renovation of borrow pits, spoil piles, berms, crushing platforms and subgrade, the excavation amount of borrow pits shall be priced according to the spread-in fill; The stacking amount of spoil piles is priced according to excavation; The excavation amount of the crushing platform should be included in the excavation amount.
(3) The earthwork volume of unpaved intercepting ditch and drainage ditch shall be included in the excavation volume.
(4) Earthwork volume of foundation pit excavation and filling of structures such as bridges and culverts.
(5) Soft foundation treatment, including excavation of soft soil, replacement of fill, preloading of fill and other earthwork operations.
(6) The earthwork operation of changing the river course can be priced according to the earthwork operation of subgrade.
(7) If technical measures such as soil replacement are needed for zero-filling and zero-digging subgrade, it includes earthwork operations of transporting original soil and soil replacement.
Second, the problem of easy negligence.
When extracting quantities according to the design chart, it is necessary to carry out various statistical analysis and summary work, check the subgrade earthwork calculation table, and check whether the fill calculation outside the design section is complete. The following earthwork quantities are reflected in the design charts and data, and should be determined according to the requirements of construction organization design, and priced in the subgrade fill quantities.
(1) Remove the topsoil or compact the basement in sporadic filling sections, tamp (compact) the cultivated land before filling, and backfill it to the original ground elevation. Topsoil removal varies according to different site conditions and should be listed according to the number of construction organizations; And should calculate the amount of backfill to the original ground elevation after removing the topsoil. For the compacted sections before zero filling and cultivated land filling, the ground will sink after rolling, and the amount of backfilling to the original ground elevation should also be proposed by the designer. It is recommended to use the following formula to calculate:
h=P/C ①
Q=F h ②
Among them, H is the natural soil settlement caused by compaction; P is effective, 2, generally calculated by 12 ~ 15t roller (p = 6.6/-2); C is the sedimentation coefficient resistance of soil, 2, which can be obtained according to the look-up table of undisturbed soil; Q is the increased filling quantity, m3; F is the ground area of compacted natural soil before filling, m2; H is the settlement, m. The calculated increased fill volume should be included in the estimated volume.
(2) Due to road subsidence, it is necessary to increase earthwork filling. Subgrade will naturally settle, even in the case of compaction, due to the natural conditions, there will be different degrees of settlement, and the settlement of high embankment, especially high embankment on soft foundation, will be more obvious, which requires that the fill must have a certain amount of reserved settlement, which can be calculated according to settlement theory or regional experience and included in the valuation volume.
(3) In order to ensure the compactness of subgrade edge, the amount of earthwork required for filling should be widened. When filling embankment, in order to ensure sufficient compactness of subgrade edge, embankment should generally be filled beyond the design width during construction. When mechanical rolling is used, the widening filling width of each side of the embankment depends on the filling height of the embankment, which is usually 20-50㎝. JTJ033-95 "Technical Specification for Highway Subgrade Construction" clearly stipulates: "The width of embankment fill should be wider than the design width of each side fill layer, and the compaction width should not be less than the design width, and finally the slope should be cut". "When repairing the surface of embankment slope, the width of overfilling on both sides should be cut off". Because this part of the earthwork increased by extensive filling is very large, it is obviously unreasonable not to include this part of the increase in the budget preparation. In general, the earthwork volume that needs to be filled in a wide range can be calculated according to the following formula:
Wide fill volume = total length of fill edge × average slope length × wide fill thickness
This part of the engineering quantity should not be included in the valuation volume, but the expenses incurred should be spread into the unit price of filling the valuation volume. There are still several problems in the calculation of earthwork quantity of design section when extracting engineering quantity according to the data of design chart.
(4) Quantity deducted from the pavement width of the filled section:
(1) The height of the fill within the width of the fill section is only calculated to the bottom of the road, that is, the total thickness of the road including the cushion should be deducted for the design of the fill section, and this thickness will be deducted or not in the design and construction of expressway and the first-class highway, which will affect a lot of quantities.
(2) When designing and calculating the earthwork volume of highway subgrade, the earthwork volume occupied by the passage is usually not deducted, but there are many such projects built on the expressway, and the subgrade fill volume should be appropriately deducted according to the actual situation of the construction project.
(3) In the soft soil foundation treatment area, it should be noted that when sand or gravel is used as cushion, the corresponding subgrade fill amount should be deducted to avoid repeated pricing.
(5) The number of trench excavation works should be included in the excavation quantities.
It is stipulated in the model bidding documents of domestic highway engineering that the compaction inspection of subgrade requires loosening and rolling the subgrade to achieve the specified degree of compaction. In expressway, the pavement structure layer, including cushion, is thick, and it is economical and reasonable to dig to the top of subgrade at one time, no matter from the aspects of engineering quantity calculation, construction arrangement and subgrade shaping. Therefore, it is stipulated in the technical specifications of the general tender documents that the excavation quantities of this part of the trench are included in the excavation quantities. In order to keep as consistent as possible with the contents of the pre-tender estimate, the number of trench excavation works will also be included in the excavation quantity when compiling the budget estimate and budget.
Third, the conversion coefficient.
The first chapter of Budget Quota for Highway Engineering (version 1992) states that "earthwork excavation is calculated according to the natural dense volume, and the volume after filling pressure (tamping) is calculated; Rock blasting is calculated according to natural dense volume. When the compaction volume of filling is taken as the engineering quantity and the natural compaction square is taken as the unit of measurement, the quota adopted shall be multiplied by the following factors. Therefore, when using the quota, we should pay special attention to the conversion relationship between the natural secret party and the compacted party, which cannot be ignored. The adoption of this conversion factor must be considered before the calculation and allocation of subgrade earthwork, that is, it cannot be simply allocated according to the cross section. The following examples illustrate the application of conversion factors.
Fourth, the problems in earthwork calculation
Because the quantity of earthwork determines the quantity of earth borrowing, spoil, land occupation and project cost, the earthwork items should be complete and the calculation should be accurate in the design chart data. However, in practical work, there are often some problems in the earthwork table, which brings some difficulties to the budget and budget personnel to extract earthwork.
1, there is no division between compacted side and natural side in earthwork allocation. Generally speaking, the section fill is calculated by compaction, and the section excavation is generally calculated by natural party. Most design documents directly take the users of cut and fill excavation as borrowers; The party with reduced excavation and utilization is regarded as the abandoned party; The digger and the borrower are the pricing parties. There is nothing wrong with the items calculated by this addition and subtraction, but the compacted side is different from the natural side. Therefore, the quantities of compaction side and natural side cannot be directly added or subtracted, and can only be calculated after conversion.
2. The list of earthwork projects is incomplete. The increased earthwork volume, such as tamping before filling cultivated land, clearing cultivated land soil, dredging and backfilling, widening on both sides of filled subgrade, etc., is often omitted. The increased earthwork volume of these projects generally accounts for 10% ~ 30% of the fill volume. Although there is no single column in the design drawing, it is indeed an inevitable engineering quantity in the project, and it is unreasonable to expect it to be listed. It should be listed at the end of the table in the form of table description, instead of column by column.
3. Improper earthwork calculation in artificial structure. Large structures such as interchanges, bridges and tunnels are generally listed as independent projects. Due to the lack of coordination between these independent projects and the personnel on both sides of the main line, it often leads to repeated calculation of earthwork or omission of both sides. The mileage length of some main lines and independent projects is not connected, which leads to an increase or decrease in earthwork volume compared with the actual situation. Other interchanges will be treated separately in the future, but the amount of earthwork is included in the main line, and there are similar problems in the quantities of drainage, protection and paving.
4. Lack of supplementary explanation of the earthwork list. Whether the above-mentioned items related to earthwork have been listed in the table, and the method of listing; Whether the excavation quantity includes the excavation of side ditches, drainage ditches and trenches; Whether the volume of pavement structure layer has been deducted from the fill quantity; The derived length and calculation method of artificial structure are often blank in the remarks column or explanation of design chart.
5. The earthwork calculation is not standardized. Some design documents calculate earthwork, but the distance between users and borrowers in each earthwork calculation section is different, the construction machinery and transportation machinery used are different, and the free transportation distance and grading distance of various transportation machinery are also different. So it is very complicated to accurately count the traffic flow. Although some design documents fill in the traffic volume in the corresponding columns, the filling methods are various and not standardized enough to reflect the actual situation. According to the requirements of the chart example, only fill in the average transportation distance.
The above content comprehensively expounds and analyzes how to calculate earthwork volume, which can calculate the actual value of excavated earthwork volume according to the current earthwork volume and the actual situation on site, which is helpful to determine the actual budget of earthwork volume and control the budget cost. The calculation of earthwork quantity must be carried out step by step in strict accordance with the calculation method, in order to get accurate values.