The overall finite element mesh is shown in Figure 4. See Figure 5 for elevated pile foundation, capping beam and continuous beam structure of expressway and Daguan Road in the East Ring Road, subgrade and pavement structure of expressway and guangzhou-shenzhen railway in Guangyuan, and grid of water pipeline and supporting structure. Among them, the diameter of the pipeline is DN 1800, and the pipe material is prestressed concrete cylinder pipe (PCCP). According to the longitudinal profile of the pipeline, the buried depth from the center of the pipeline to the surface is 6.38 meters ... Because the size, length and material of the elevated pile foundation of Donghuan Expressway and Daguan Road are unknown, it is determined according to the field investigation and engineering experience. In this model, the length of pile foundation is 22m, the diameter is 800mm, the height of bridge column is 7m, the diameter is 800mm, and the section of capping beam and continuous beam is 800mm×800mm；; ; The material is C30 concrete. According to the design scheme of water conveyance pipeline, an integral model considering soil layer, water conveyance pipeline, subgrade and pavement structure of expressway and guangzhou-shenzhen railway in Guangyuan, elevated pile foundation, continuous beam, capping beam and column of expressway and Daguan Road in the East Ring Road is established.
Among them, the pile foundation, continuous beam, capping beam and column of Donghuan Expressway and Daguan Road are simulated by beam element; The slab element is used to simulate the structure of water pipeline, subgrade and pavement of expressway and guangzhou-shenzhen railway in Guangyuan. The water, backfill concrete and undisturbed soil in the pipeline are simulated by solid elements. The calculated length of the whole model is103.2m along the pipeline cross section,180m along the pipeline longitudinal direction and 45m in the vertical direction. * * * There are 8 1626 units and 42,944 nodes. The soil adopts Mohr-Coulomb constitutive model. In terms of load, in addition to the self-weight of soil and structure, the load of subgrade and pavement structure of Guangyuan Expressway and guangzhou-shenzhen railway above the water pipeline, and the load of Daguan Road and Donghuan Expressway Bridge are also considered in the calculation. According to the current bridge load specification, the vertical linear load of the east ring expressway cover beam of this node is 462.5kN/m, and the pavement load of Daguan Road is 25kN/m2 after conversion. In terms of boundary conditions, the left and right sides and the bottom of the model are constrained with translation displacement degrees of freedom corresponding to the normal. On the other hand, the front face and the back face impose constraints on the so-called Y plane (that is, in addition to the freedom of normal translation, the freedom of rotation of the X axis and the Z axis is also constrained).
2 Calculation results and analysis
2. 1 Influence of pipeline water filling on guangzhou-shenzhen railway and its adjacent buildings.
In order to study the influence of internal water filling on the surrounding sensitive objects during normal operation of the pipeline, the whole project is calculated according to the water filling heights in the pipeline as 1/4D, 1/2D, 3/4D and D(D is the internal diameter of the pipeline, and the internal diameter of the pipeline at this node is 1.8m), and the results under different water filling conditions are obtained. When the water filling height in the pipeline is 1/4D, 1/2D, 3/4D and d respectively, the number of horizontal and vertical displacements of the East Ring Expressway structure is shown in Table 2 (excluding the structural displacement caused by the previous construction). The displacement distribution when the water filling height is d is shown in Figure 7. According to the data in Table 2, the horizontal and vertical displacements of adjacent structures such as guangzhou-shenzhen railway are increasing with the increase of water filling height of the pipeline, but even if the pipeline is filled with water, the horizontal and vertical displacements of adjacent structures are only 0. 14mm and 0.83mm, which is far from causing structural damage to the structure.
2.2 Influence of soil strength change under the pipeline on guangzhou-shenzhen railway and its adjacent structures.
Considering that the strength of the soil under the water pipeline may be reduced due to the leakage of joints and the vibration of traffic reciprocating load during the operation of the water pipeline. In order to study the additional stress and deformation of the pipeline caused by the change of soil strength of the bearing layer below the pipeline, the silty clay layer below the pipeline at this node (see Figure 8 for specific areas) was studied. Due to the coarse sand layer under the silty clay layer, the water stability is very good, and the possibility of soil loss and relaxation is very small, regardless of its strength reduction. The elastic modulus, cohesion and internal friction angle are reduced in equal proportion, and four groups of strength coefficients (namely, the strength coefficient is 1.0) are calculated on the basis of the original strength parameters.
Table 4 shows the whole model with different strength factors and the displacement of adjacent bridges and roads. Figure 9 and Figure 10 show the horizontal and vertical displacement distribution of the whole model at the joint when the soil under the pipe is not weakened and the strength parameter is weakened to 0.4 (that is, the strength index is reduced to 40% of the initial value). As can be seen from Table 4, when the strength parameters of the soil under the pipeline are reduced to 0.8 and 0.6 of the original model, the deformation of the whole model and adjacent structures is basically unchanged. However, when the soil strength parameter under the pipeline is reduced to 0.4 of the original model, the overall horizontal and vertical displacement is greatly increased compared with the original model, and the maximum value mainly appears in the soil area near the pipeline; However, the horizontal and vertical displacements of adjacent bridges and roads have increased, and the horizontal and vertical displacements are 0.80mm and 2.00mm respectively.
It can be seen that the strength reduction caused by the loss and relaxation of the silty clay layer under the pipeline has not had a destructive impact on the adjacent structures such as guangzhou-shenzhen railway, expressway in the East Ring Road, Daguan Road Elevated and expressway in Guangyuan. Because there is a relatively stable coarse sand layer under the silty clay layer below the pipeline, the risk of serious settlement of the whole pipeline is small. According to experience, due to the pipeline itself, it is unlikely that the soil strength under the pipeline will be reduced to 40%. It can be considered that the strength reduction caused by the loss and relaxation of the silty clay layer under the pipelines at the intersections of the second-phase trunk pipeline with guangzhou-shenzhen railway and expressway in Guangyuan has not damaged the structures of guangzhou-shenzhen railway, expressway in the East Ring Road, Daguan Road Viaduct and expressway in Guangyuan. Because there is a relatively stable coarse sand layer under the silty clay layer below the pipeline, the risk of serious settlement of the whole pipeline is small.
3 Conclusion
Based on the actual situation of the joint water supply project of the three rivers, such as Shaheyong in the northern water system of Guangzhou, this paper analyzes the influence of the reduction of foundation strength caused by pipeline water flow and pipeline leakage on the deformation characteristics of surrounding buildings. The research shows that (1) with the increase of water filling height of the pipeline, the horizontal and vertical displacements of adjacent structures are increasing, but even if the pipeline is filled with water, the horizontal and vertical displacements of adjacent structures are only 0. 14mm and 0.83mm, which is far from damaging the structure. (2) The strength reduction caused by the loss and relaxation of the silty clay layer under the pipeline at the intersection of the second-phase trunk pipeline and the adjacent structures such as guangzhou-shenzhen railway did not have a destructive impact on the adjacent structures such as guangzhou-shenzhen railway.
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