Влияние жесткости угловых зон котлованов на перемещения подпорных стен в песчаных грунтах

So far, there have been a large number of diaphragm walls in the Yangtze River Delta as engineering examples of deep foundation pit maintenance structures in subway stations, but there is a lack of systematic research and summary on the deformation characteristics of ground connecting walls. This study aimed to clarify the deformation law of the diaphragm wall during the excavation of a deep foundation pit in a soft soil region. Based on the monitoring data of the diaphragm wall of the deep foundation pit of the Hangzhou metro station, the monitoring data of the deep foundation pits of 15 subway stations in Shanghai and Ningbo cities around Hangzhou were considered. Grouping and classification methods were used to analyze the similarities and differences in the deformation characteristics of the diaphragm wall in the three regions. The results indicate the following: the maximum lateral deformation of the diaphragm wall in Hangzhou increases linearly with the relative depth of the maximum lateral deformation. The maximum lateral deformation of the foundation pit in Hangzhou is 0.072% H∼0.459% H, with a mean of 0.173% H. The wall deformation in Hangzhou varies significantly with the depth of the foundation pit, but the influence of the depth of the foundation pit on the wall deformation is considerably less than that in Shanghai and Ningbo. The corresponding position of the maximum lateral deformation in the excavation depth increases linearly with the excavation depth of the foundation pit, and the corresponding position of the lateral deformation of the diaphragm wall in Shanghai is more affected by the excavation depth of the foundation pit. The lateral deformation of the diaphragm wall increases rapidly in the range of 0 H–0.5 H, and the maximum lateral deformation occurs at 0.5 H–1.1 H.

In order to explore the optimal lateral restraint system for long-span cable-stayed bridges under ultra-high performance concrete deck pavement. This paper takes a UHPC deck pavement cable-stayed bridge as an example, selects four different lateral restraint systems, calculates the stress of each key section of the cable-stayed bridge under the action of an earthquake, and then selects the optimal lateral Constraint system. The research results show that when ultra-high performance concrete is used as the bridge deck pavement, the increase in the quality of the bridge deck system will have a greater adverse effect on the seismic performance of the bridge. Compare the internal force response and displacement response at each key section of the bridge under four different lateral restraint systems under earthquake action. Compared with the other three systems, the internal force response and displacement response value of the horizontal cable system is smaller, and the energy dissipation and shock absorption effect is better. For cable-stayed bridges using ultra-high performance concrete as the deck pavement, in the selection of the lateral restraint system, a restraint system of cables is set between the towers and beams, which can better reduce the impact of the increase in the quality of the bridge deck on the seismic performance of the bridge, is the most reasonable horizontal restraint method. Considering the internal force and displacement response of the bridge structure and the safety of the support under the earthquake, the parameter selection of the cable support is k = 135000 kN / m and S = 0.4 m.

Water conveyance tunnels usually experience high internal water pressures and complex soil conditions. Therefore, shield tunnels with double-lining structure have been adopted because of their high bearing capacity. The effect of the interface between the segmental and inner linings on the bearing capacity has been widely investigated; however, the effect of soil on the internal water pressure bearing capacity has not been emphasized enough. Therefore, in this study, model tests and an analytical solution are presented to elucidate the effect of soil on the internal water pressure bearing capacity. First, model tests are conducted on double-lining models under sandy soil and highly weathered argillaceous siltstone conditions. The internal force and earth pressure under these different soil conditions are then compared to reveal the contribution of soil to the internal water pressure bearing capacity. Following this, an analytical solution, considering the soil—double-lining interaction, is proposed to further investigate the contribution of the soil. The analytical solution is verified with model tests. The analytical solution is in good agreement with the model test results and can be used to evaluate the mechanical behavior of the double-lining and soil contribution. The effect of soil on the bearing capacity is found to be related with the elastic modulus of the soil and the deformation state of the double-lining. Before the double-lining cracks, the sandy soil contributes 3.7% of the internal water pressure but the contribution of the soil rises to 10.4% when it is the highly weathered argillaceous siltstone. After the double-lining cracks, the soil plays an important role in bearing internal water pressure. The soil contributions of sandy soil and highly weathered argillaceous siltstones are 10.5% and 27.8%, respectively. The effect of soil should be considered in tunnel design with the internal water pressure.

Wuhe Station of the Shenzhen Metro Line 5 is close to Bulong highway. The top level of road embankment is higher seven to nine meters than the ground level, resulting the foundation pit bearing the unsymmetrical loaded. In this paper, the deformation features of unsymmetrical-loaded foundation pit's enclosure structure are systematically studied based on field test, and the stability of retaining structure about the horizontal displacement and internal force of the diaphragm wall was evaluated reasonably. The results shows that the deformation of top of the diaphragm wall inclined towards the inside of the enclosure structure with shallow excavation depth, and the displacement of diaphragm wall near highway is larger than that of far from highway due to the load from high road embankment. However, the deformation of top of the diaphragm wall far from highway moves towards the outside of the enclosure structure after the excavation depth up to one threshold, and the deformation increases with the increasing of excavation depth. Moreover, under the same conditions about construction procedures and excavation depth, the moment of the diaphragm wall near highway is larger than that of the diaphragm wall far from highway, also the maximum moment of the diaphragm wall near highway is deeper than that of the diaphragm wall far from highway. Therefore, different supports of the enclosure structure should be considered for design and construction.

Building natural period, T, is a key character in building response for wind and seismic induced forces. In design practice, the period, T, is either estimated from empirical relations proposed by the design codes or determined from analytical or numerical models. The effect of the soil-structure interaction is usually neglected in the design practice and analysis models. This paper uses a sophisticated finite element simulation to investigate the effect of soil-structure modeling on the fundamental period of RC buildings subjected to wind and seismic induced forces. A typical interior building frame has been imitated using the frame element for beams and columns with constrains to model the almost-rigid diaphragm nature for floors and roof while a three-dimensional element has been adopted for the raft foundation and the soil mass. Different sandy soils have been considered. Standard Penetration Test, SPT value, has been taken as an identification index for soil nature. All other soil properties have been estimated based on well-accepted correlations. After applying the gravity dead and live loads, and eigenanalysis has been achieved to show how soil flexibility affects the effective stiffness of the structure and the corresponding natural period. Finally, the results are used to introduce a correction factor to modify the natural period estimated from a linear analysis with ideal supports to reflect the aforementioned effects.

Foundation pit envelope and foundation pit excavation solution design is a multidisciplinary problem that could be linked to a series of safety issues in the geotechnical engineering of an actual construction project. Moreover, the construction of large deep foundation pit in soft soil often faces greater risks and challenges as the support structure deforms more easily and unpredictably. In order to improve the deformation prediction of deep foundation pit engineering precision and efficiency and to ensure that the construction of deep foundation pit engineering is safe and efficient, in this article the traditional MSD (mobilizable strength design) theory research and analysis, combined with the Jinan formation characteristics of a tunnel in JInan, and new parameters were introduced to the original MSD method theory: the wall itself within the bending strain energy U and support compression elastic potential energy of V. A new law of conservation of energy is constructed, and finally, an optimized MSD method has been proposed, this method is shown in the article. Finally, the results of foundation pit deformation calculation were compared among the optimized MSD method, finite element calculation method, and field monitoring data analysis method, so as to demonstrate the reliability of the prediction system of optimized MSD method and finite element analysis method. The results show that, by optimizing the MSD calculation method, the horizontal displacement of the retaining wall varies depending on the excavation depth of the foundation pit and the form of internal support with the overall peak value of displacement between 0∼0.2% H (H being the excavation depth); the deformation of retaining wall increases gradually with the increase of excavation depth of the foundation pit, and the peak position of deformation gradually moves down with the excavation of foundation pit. The trend of these changes is consistent with the results of the finite element method and field data analysis method, proving that the optimized MSD method is reliable in predicting the deformation of the foundation pit under specific stratum conditions.

Achieving superior burn resistant and mechanical properties of Ti40 alloy by laser solid forming

Code of practice for design and construction of under reamed pile foundations: IS 2911 (Part-III)—1980 presents one table in respect of safe load for bored cast in situ under reamed piles in sandy and clayey soils including black cotton soils, stem dia. of pile ranging from 20 to 50 cm and its effective length being 3.50 m. A comparative study, was taken up by working out safe pile capacity for one 400 dia., 3.5 m long bored cast in situ under reamed pile based on subsoil properties obtained from soil investigation work as well as subsoil properties of different magnitudes of clayey, sandy soils and comparing the same with the safe pile capacity shown in Table 1 of that IS Code. The study reveals that safe pile capacity computed from subsoil properties, barring a very few cases, considerably differs from that shown in the aforesaid code and looks forward for more research work and study to find out a conclusive explanation of this probable anomaly.

Taking the water-rich sand and pebble geology deep foundation pit of Jinfu Station of Chengdu Metro Line 6 as the research object, combined with the ladder excavation method of slotting, utilizing finite difference software FLAC 3D as well as on-site monitoring result, the deformation law of the diaphragm wall during the dynamic excavation of the foundation pit is analysed, and the influence of the relative stiffness between the vertical and horizontal walls of the foundation pit on the lateral deformation of the retaining structure is discussed. The results show that while using the ladder excavation method of slotting, the maximum lateral displacement of the underground diaphragm walls decreases gradually with the excavation depth of the foundation pit, which occurs at the intersection of the middle point of the oblique excavation line and the step distance section of the transverse excavation. Additionally, the lateral displacement increases closer to the excavation section. The lateral displacement of the envelope enclosure mainly depends on the relative constraint stiffness of the vertical and horizontal underground diaphragm wall of the foundation pit. The use of the ladder layered excavation method of slotting can effectively reduce the lateral displacement of the underground diaphragm wall. The simulated result and on-site monitoring result are nearly the same. These results can provide a corresponding theory and engineering basis for the selection of excavation methods for the same type of sand and pebble stratum foundation pit.

The integration of underground single structure and retaining structure is a new type of foundation pit support, and its working performance needs to be further studied. The physical model test was carried out on the diaphragm wall structure of “two walls in one” in this paper. The soil settlement and the earth pressure of the outside of the foundation pit and the stress of the integrated supporting structure were analyzed when the excavation depth is different. The analysis showed that the settlement of soil behind the wall gradually increased with the increase of excavation depth of the foundation pit. when it was 1H e away from the diaphragm wall, the maximum of soil settlement occurred, which was 0.08%H e (H e is the maximum excavation depth). With the increase of excavation depth, the state changed from static to active. Under the same condition, the bending moment of the wall increased first and then decreased with the depth. The reverse bending point is near 1.23H e .

Basement-addition for existing building plays a crucial role in alleviating urban land shortage. However, the disturbance induced by basement-addition construction to the stability of the building foundation and superstructure has not been well understood. The objective of this paper is to investigate the performance of typical structural components involved in a basement-addition project. They include the columns in the superstructure, the strip foundation beneath the columns, and the piles used for reinforcing the strip foundation during excavation. A three-dimensional finite element model is established, using a basement-addition project of an existing building as a case example. The calculated results by the finite element model align well with the measured data, confirming the model’s validity. Based on this, the stress and deformation characteristics associated with the selected structural components during basement-addition construction are investigated. The findings indicate that the stress and deformation characteristics of the structural components are highly sensitive to the depth of the foundation pit excavation, with these characteristics intensifying as excavation depth increases. The excavation of the initial soil layer has the most significant impact. Upon completion of the excavation, the maximum settlement values for the strip foundation (SF), column foot, and pile are -18.6 mm, −13.79 mm, and −16.1 mm, respectively. The underground diaphragm wall (UDW) exhibits maximum vertical and horizontal displacements of 7.6 mm and 18.1 mm, respectively. The pile primarily experiences compressive internal forces, with its axial force showing little sensitivity to excavation depth. The pile’s maximum bending moment, shear force, and axial force are 21.2 kN·m, 34 kN, and −2,481 kN, respectively. The internal forces and deformations of structural components demonstrate distinct spatial distribution patterns, with values increasing closer to the foundation pit’s center. Therefore, it is crucial to enhance monitoring of the displacement and internal forces of the central components of the foundation pit to prevent engineering accidents. These research findings will contribute positively to the design optimization and construction guidance of similar engineering structures.

Distributed piles are often installed in the foundation pit in sandy soil before dewatering. Hydraulic conductivity should be estimated considering the block effect of piles on groundwater seepage. Research shows that the effective medium theory (EMT) could be used to calculate the equivalent hydraulic conductivity (k eq) of a heterogeneous medium with other material inclusions. In order to verify the applicability of EMT in an aquifer with piles, an experimental investigation is conducted. In this experiment, a sandy soil is considered as an aquifer and polyvinylchloride pipes are adopted as piles. Piles are distributed in rectangular and triangular layouts. The relationship between k eq of the aquifer and the volume replacement ratio is plotted for these two layouts. The results indicate that EMT could well predict k eq for the cases with the rectangular layout; however, for triangular layouts, the prediction becomes poor. To provide a better prediction of k eq of the aquifer with piles distributed in a triangular layout, a modified EMT (MEMT) is proposed, in which a correction factor is adopted considering different layouts of piles. The MEMT can provide better k eq predictions for an aquifer with piles in the triangular layout pattern than those obtained using the EMT.

For modern urban construction in the compacted conditions of new sites, the question of the stability of soil massifs under existing buildings is relevant. The intensity of development of possible deformations largely depends on the mutual location of the base of the previously erected foundation and the pit for the new building. The article provides a methodology for determining the area of influence of the pit on the soil foundations of adjacent buildings, depending on the type of enclosing structures and the depth of the pit used. The impact zone was calculated for the pit using protective structures in the form of Larsen sheet piles, bored piles and a diaphragm wall. Corresponding zones of influence of a pit excavated to different depths using different types of pit construction are graphically determined. The scientific result can be explained by the fact that the idealized model of the influence zone takes into account the conditions under which the boundary of the influence zone of a new building can be limited to a distance at which the calculated value of additional subsidence of the soil massif or the base of the existing structure of the surrounding building does not exceed 1 mm. The dimensions of the influence zones are determined at different pit depths, which roughly correspond to the location of the one-, two-, and three-level underground structures of the building. Increasing the depth of the pit to two underground floors increases the zone of influence by 24-31% for the considered types of pit enclosure, and up to three floors - by 14-17%. It was established that the nature of the change in the zone of influence is similar for different types of enclosure structures, and the transition from rigid to flexible functioning of the pit enclosure depends on the ratio of the enclosure's rigidity and the excavation depth. As a practical result of the research, it can be used when choosing the type of construction of the pit to prevent the negative impact of the construction works of the new construction on the surrounding buildings. Keywords: underground construction, pit, concrete, piles, impact, modeling, optimization, parameters

The internal forces in stiffeningwalls are usually determining by numerical methods. Extreme values of forces and displacements can be achieved without significant problems. The numerical model is always labour-intensive; therefore, it is not used for single-family or multi-family buildings with a simple wall layout. To calculate efficiently internal forces in such walls uses an analytical model. Eurocode 6 (prEN 1996-1-1: 2019) does not provide specific guidelines for determining geometrical characteristics and procedures for calculating the values of internal forces in the stiffening walls. The use of numerical methods and other reliable methods was allowed. The paper presents the adaptation of the total stiffness method to determine internal forces in a building with a simple wall system. The method was based on dividing the masonry wall with openings into pillars, lintels, bottom sprandels and flanged walls. The analytical results were compared with linear-elastic FEM calculations. It has been demonstrated that flexural stiffness, shear stiffness and localization of rotation centre (RC) had a crucial impact on masonry structure.

Taking a foundation pit in Nanjing as the background, a numerical model was established to simulate the dynamic process of foundation excavation by 2D finite element software. The influences of different factors on the displacement of the lateral shield tunnel during the foundation pit excavation are studied. The research indicates: when a foundation pit excavation is needed on the side of a shield tunnel, we should select the area in which the tunnel is buried deeper, control both the excavation volume and the distance between tunnel and pit, and try to avoid the excavation depth close to the buried depth of the tunnel. On the basis of numerical calculation, the protection range of the shield tunnels is determined according to different excavation depth of the foundation pits and different buried depth of the tunnels.