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Article

Force and Deformation Characteristics of Large-Scale Zoning Excavation in Soft Soil: A Case Study in Hangzhou

by
Gang Lin
1,2,
Zhaorui Lin
3,*,
Yi Zhao
2,
Changjie Xu
3,4,5,
Feng Sun
6,
Yun Duan
3 and
Tao Fang
3,4
1
College of Civil Engineering, Zhejiang University of Technology, Hangzhou 310014, China
2
Zhejiang Province Geological & Mineral Engineering Investigation Institute Co., Ltd., Hangzhou 310014, China
3
Institute of Geotechnical Engineering, School of Civil Engineering and Architecture, East China Jiaotong University, Nanchang 330013, China
4
State Key Laboratory of Performance Monitoring Protecting of Rail Transit Infrastructure, East China Jiaotong University, Nanchang 330013, China
5
Research Centre of Coastal and Urban Geotechnical Engineering, Zhejiang University, Hangzhou 310015, China
6
China Railway Siyuan Survey and Design Group Co., Ltd., Wuhan 430061, China
*
Author to whom correspondence should be addressed.
Appl. Sci. 2024, 14(14), 6358; https://doi.org/10.3390/app14146358
Submission received: 21 June 2024 / Revised: 16 July 2024 / Accepted: 17 July 2024 / Published: 21 July 2024
(This article belongs to the Special Issue Structural Mechanics in Materials and Construction)
Browse Figures
Figure 1
<p>Schematic diagram of ‘New World’ foundation pit.</p> "> Figure 1 Cont.
<p>Schematic diagram of ‘New World’ foundation pit.</p> "> Figure 2
<p>Layout of field monitoring points.</p> "> Figure 3
<p>Schematic diagram of the finite element model. (<b>a</b>) Model size. (<b>b</b>) Condition 1. (<b>c</b>) Condition 2. (<b>d</b>) Condition 3. (<b>e</b>) Condition 4. (<b>f</b>) Condition 5.</p> "> Figure 4
<p>Horizontal displacements of diaphragm wall during excavation to the bottom of the foundation pit. (<b>a</b>) 3A10-1 sub-pit. (<b>b</b>) 3A10-1 sub-pit. (<b>c</b>) 3A10-2 sub-pit. (<b>d</b>) 3A10-2 sub-pit. (<b>e</b>) 3A10-2 sub-pit. (<b>f</b>) 3A5 sub-pit. (<b>g</b>) 3A8 sub-pit.</p> "> Figure 5
<p>Deep horizontal displacements of the soil. (<b>a</b>) 3A10-1 sub-pit. (<b>b</b>) 3A10-1 sub-pit. (<b>c</b>) 3A10-1 sub-pit. (<b>d</b>) 3A10-2 sub-pit. (<b>e</b>) 3A5 sub-pit. (<b>f</b>) 3A8 sub-pit.</p> "> Figure 6
<p>Monitoring results of surface settlement. (<b>a</b>) The side of Yuantai Building. (<b>b</b>) The north side of sub-pit 3A10-1. (<b>c</b>) West side of sub-pit 3A10-1.</p> "> Figure 7
<p>Changes in bending moments of diaphragm walls during the excavation. (<b>a</b>) Diaphragm walls of 3A10-1 sub-pit. (<b>b</b>) Diaphragm walls of 3A10-2 sub-pit. (<b>c</b>) Diaphragm walls of 3A5 sub-pit. (<b>d</b>) Diaphragm walls of 3A8 sub-pit.</p> "> Figure 8
<p>Horizontal displacements nephograms of pre-built diaphragm wall at the western edge of the sub-pit.</p> "> Figure 8 Cont.
<p>Horizontal displacements nephograms of pre-built diaphragm wall at the western edge of the sub-pit.</p> "> Figure 9
<p>Horizontal displacement of the pre-built diaphragm wall at the southern edge of the pit.</p> "> Figure 9 Cont.
<p>Horizontal displacement of the pre-built diaphragm wall at the southern edge of the pit.</p> "> Figure 9 Cont.
<p>Horizontal displacement of the pre-built diaphragm wall at the southern edge of the pit.</p> ">
Versions Notes

Abstract

:
The zoning excavation method is fully employed to control the deformation of foundation pits constructed in urban soft soil areas. However, the similarities and differences in forces and deformations between foundation pits excavated by the zonal method and those excavated by the conventional method still need to be further explored. In this study, the deformation was monitored and analyzed by taking the zonal excavation of a foundation pit of the ‘New World’ project in Hangzhou City as the research object. The measured results showed that the pre-built diaphragm wall for the first excavated foundation pit restricted the deformation of the first excavated diaphragm wall. The presence of extensive construction and unloading activities also changed the deformation pattern of the soil. Further, finite element simulations were carried out. The simulation results revealed that excavating the foundation pit first caused displacements in the pre-built diaphragm wall. The displacements transmitted by non-adjacent pits through the pre-built diaphragm wall were small and were concentrated at the junction of the two sub-pits. Adjacent foundation pits caused large displacements of the pre-built diaphragm wall with similar displacement patterns. The results of the study can provide effective guidance for foundation pit excavation in soft soil areas in the future.

1. Introduction

The safety of foundations in soft soil areas is of great concern to academics and engineers [1,2]. As a precursor activity in building construction, the foundation pit is a kind of hidden temporary project with great safety risks [3,4,5]. Especially in soft soil areas, due to the weak bearing capacity of the soil [6,7], foundation pits often face problems such as excessive deformation [8,9,10], exposing the project to great safety risks. Significant engineering accidents due to design errors or construction impacts have been reported in the literature. Problems such as the excessive settlement of surrounding structures, the uplift of foundation pit bottom, and the failure of supporting structures [11,12,13] adversely affect the safety and normal operation of the city and even cause considerable economic losses.
To solve the safety problems of urban foundation pits from a design perspective, a number of research works have attempted to reform the design theory from the design perspective [14]. The theory of non-limit state soil pressure [15,16,17,18,19,20,21,22] was developed and applied to develop an accurate displacement-controlled foundation pit design theory. The p-y curve methods [23,24,25], which introduce advanced principal models, are likewise ap-plied in the field of foundation pits. These methods attempt to replace the traditional stability control design theory that is represented by the equivalent beam method. These theories represent important innovations and breakthroughs in the field of foundation design, but they still have their limitations. On the one hand, the uniqueness and regionality of geotechnical engineering bodies [26] make it extremely difficult to find accurate and popularized methods. On the other hand, an increasing number of technical methods have been applied to cope with the deformation control requirements of urban engineering [7]. The corresponding design theories are difficult to update and solve simultaneously.
Analysis of specific projects in a particular area is clearly necessary [27,28,29,30]. Com-pared with theoretical research methods, although the research work on specific projects cannot be fully generalized, the results can provide data support and experience accumulation for subsequent projects [31,32]. The implementation effectiveness of some advanced construction techniques can also be effectively followed [33,34,35]. Through field monitoring or in-site tests [27,36,37,38,39], engineers can build up a knowledge of the specific site and construction mode, and the measurement results can also provide effective information for calculation and design methods. Finno et al. [40,41,42] and Hashash et al. [43] have carried out the field monitoring of deep foundation pits in Chicago, Crispin et al. [44] carried out a field monitoring study of deep foundations in the British Library, and Boonyarak et al. [45] carried out a field study of clay deep foundations in the Bangkok area. These are outstanding examples of site monitoring work carried out on deep foundation projects. However, the results of conventional monitoring tools are usually incomplete, and researchers are only able to analyze a relatively limited number of data points. Monitoring items are also influenced by actual construction site conditions and construction disturbances. Therefore, appropriate numerical simulations can often be complemented with field monitoring [46,47,48] to improve the engineers’ overall understanding of the construction situation. For a foundation pit with strict deformation control, engineers employ commercial finite element software [49,50,51] or a self-developed program [52,53] to carry out calculations and checks to ensure that the force and deformation during the foundation pit construction are in line with the requirements. For example, Russo et al. [54] carried out a 3D numerical simulation study of the Chiaia station of the Naples Metro Line 6 to predict and control the deformation of a deep foundation pit in order to safeguard the safety of the adjacent Basilica Santa Maria degli Angeli. Abdi et al. [55] and Hsieh et al. [56] applied Plaxis3D V20 software for finite element analysis to investigate the deformation of internally braced deep foundation pits in several adjacent buildings in the Taipei area. This sort of technical means provides an important guarantee for engineering safety. Based on the results of finite element analysis or field monitoring data in certain regions, some scholars [57,58,59,60,61] also analyzed and fitted them by mathematical means, achieving region-specific research conclusions that can be further promoted and applied.
This study was performed based on a foundation pit of the ‘New World’ project. This deep foundation pit is located in soft soil in Hangzhou City, with significant characteristics of a large excavation depth and many sub-pits. Detailed field monitoring of the foundation pit was carried out to investigate the influence of zonal excavation on the deformations of diaphragm wall and soil. A 3D finite element model of foundation pit was established to investigate the change of the internal force of diaphragm wall and the displacement of the pre-built diaphragm wall by excavating the foundation pit first. The study summarizes the qualitative law of force and deformation of the foundation pit due to proximity overloading and zonal excavation, which can guide the design and construction of subsequent zonal excavation of foundation pits in soft soil areas.

2. Project Overview

The foundation pit of the Hangzhou ‘New World’ project is located in the core area of Wangjiang New Town in the Shangcheng District of Hangzhou City, and the surrounding environment is very complicated. Figure 1 shows an aerial view of the layout of the foundation pit and the ongoing excavation for the project. It was worth noting that the protected historic building, the Yuantai Building, shown in Figure 1, was relocated back during the foundation pit construction, which brought significant loads, while the adjacent constructed basement limited the deformation on one side of the foundation pit. To control the deformation of the surrounding buildings during the foundation pit excavation, the foundation pit was extensively excavated in zones, with a total of 17 sub-pits. Each sub-pit was excavated layer by layer from top to bottom. Supporting piles or diaphragm walls were first driven prior to excavation, followed by the layer-by-layer excavation and erection of supports. The dense sub-pits somewhat increased the cost and led to a reduction in the integrity of the basement, which was a sacrifice made in the project to control deformation. The number, excavation depth, and support forms of the foundation pit are listed Table 1. Among them, the concrete support was poured by C35 concrete, with the main cross-section size of 800 mm*900 mm, and the steel support was mainly supported by a combination of H400*400*13*21 steel sections.

3. Methodology

3.1. Field Monitoring

To effectively control the deformation of the foundation pit, the deformation monitoring equipment of the supporting structure and soil was deployed at the project site. The lateral deformations of the diaphragm wall or the supporting pile were measured by the inclined pipes pre-buried in the structure. The lateral displacement of the soil was measured by the inclined pipes buried in the soil, and the surface settlement was measured by the magnetic settlement meter. Figure 2 shows the arrangement of the main monitoring points of the foundation pit.

3.2. Numerical Simulation

The 3D commercial finite element software Plaxis 3D was used to establish the 3D finite element model of the foundation pit of the ‘New World’ project. Figure 3 illustrates the established finite element model. The size of the model was 310 m in length, 300 m in width, and 80 m in thickness. The distance of the foundation pit edge from the model boundary was more than three times the excavation depth of the foundation pit, which could effectively guarantee that the calculation of the model was not affected by the boundary effect.
The model mesh was set to be ultra-fine. The tetrahedral elements were used to simulate the soil and the built-up underground structure, while plate elements were used to simulate the support piles and the diaphragm wall of the foundation pit. Point-to-point anchors were used to simulate the supports in the foundation pit, and interface elements were used to simulate the interaction between the support structure and the soil. A total of 422,376 elements were generated in the foundation pit model.
The established model used the HSS small strain constitutive model to simulate the constitutive relationship of the soil and the Hoek-Brown failure criterion to the simulate the constitutive relationship of the strongly and moderately weathered rocks. According to the actual conditions of the project site and laboratory test results of on-site soil samples, the physico-mechanical parameters of typical soil profiles at the project site could be obtained, as shown in Table 2.
The simulation of the foundation pit excavation was carried out according to the on-site construction sequence, which was divided into five batches and constructed with interval jump excavation. The specific construction steps and the simulation of the construction process are displayed in Table 3. It was worth noting that the model simulated the unloading and reloading of huge loads caused by the Yuantai Building by applying the removal and reapplication of face loads at the same time as the excavation. The model applied this face load after geo-stress equilibrium and removed the face load after the construction of condition 2. After the completion of the construction of sub-pit 3A10-2, the face load representing the Gentai Building was applied to the corresponding location on the construction site.

4. Analysis and Discussion

4.1. Field Monitoring Results of Foundation Pit

4.1.1. Monitoring Results of Diaphragm Wall

Figure 4 shows the monitoring results of the horizontal displacement of diaphragm wall during the excavation to the bottom of the foundation pit at the project site. The monitoring points in Figure 4a were mainly located in the northern section of the diaphragm wall of sub-pit 3A10-1, and the displacements of the wall at this location showed a typical parabolic pattern. Among them, the ZQT7 and ZQT9 monitoring points were located in the middle of this segment of the wall. The monitored maximum horizontal displacement was close to or even reached the monitoring warning value of 45 mm, which might be due to the fact that the road near this segment of the wall was subjected to loads from passing dump trucks as well as heavy equipment for a long period of time. At the project site, the construction workers reinforced the soil of the foundation pit, which limited the further development of foundation pit deformation and ensured the construction safety. The monitoring points of ZQT5 and ZQT11 were located at the edges of the wall and were affected by the shading effect of foundation pit corners, and the measured values at these points were much smaller than these at the monitoring points of ZQT7 and ZQT9.
The monitoring points in Figure 4b were primarily located in the western diaphragm wall of sub-pit 3A10-1, which was affected by the pre-built diaphragm wall of the adjacent sub-pit, and this segment of the wall was all within the influence of the foundation pit corner effect. Compared with Figure 4a, the monitoring values at the monitoring points in Figure 4b were consistent with the measured values at the monitoring points of ZQT5 and ZQT11 and were much smaller than those at the monitoring points of ZQT7 and ZQT9. This further verified that the zonal excavation fully utilized the foundation pit corner effect and could effectively limit the horizontal deformation of the foundation pit. Similarly, this could be demonstrated from the monitoring results of sub-pit 3A5 (Figure 4f) and sub-pit 3A8 (Figure 4g). It is not reasonable to simplify the zonal excavation of the foundation pit into a two-dimensional plane strain problem for design calculation, which will greatly overestimate the horizontal deformation of the foundation pit with zonal excavation.
Figure 4c–e illustrates the horizontal deformation of the southern diaphragm wall in sub-pit 3A10-2 as it was excavated to the bottom of the foundation pit. Monitoring points ZQT38 and ZQT39 showed maximum displacement values at the top of the wall, and the wall experienced a cantilevered dislocation pattern. The other five monitoring points also underwent large displacements at the top of the wall, although they still showed a parabolic displacement pattern. This may be attributed to the overall relocation and transfer of the Yuantai Building prior to the excavation and construction of sub-pit 3A10-2, and the large-scale load removal resulted in the displacement at the top of the diaphragm wall towards the foundation pit. This served as a reminder that deep foundation pits requiring large-scale load transfers may cause a change in the deformation pattern of the foundation pit support structure due to the unloading, and that engineers should not judge the possible deformation of the support structure based on the form of the support structure alone.

4.1.2. Monitoring Results of Deep Horizontal Displacements of the Soil

Figure 5 shows the deep horizontal displacement in the soil as the foundation pit was excavated to the bottom of the foundation pit. The monitoring points in Figure 5a were located behind the north segment of the diaphragm wall of sub-pit 3A10-1, and the monitoring points in Figure 5b were located behind the west segment of the diaphragm wall of sub-pit 3A10-1. The deep displacements of the soil at different locations showed a parabolic pattern with a large center and two small ends. Except for the monitoring point CX8, where the deep displacement was much smaller than the displacement of the diaphragm wall, the displacements at the other points were closer to the displacements of the diaphragm wall at the approach location. This may be due to the disturbance of the end of the inclinometer tube at monitoring point CX8 by the site construction, which resulted in an overall deflection of the tube towards the outside of the foundation pit. The comparison of the soil displacement pattern and wall deformation pattern at the same locations revealed some differences in the horizontal displacements. The maximum displacement depth of the soil of the north ground wall is lower than the maximum displacement depth of the wall, and the maximum displacement depth of the soil of the west ground wall is higher than the maximum displacement depth of the wall. In fact, the soil was composed of fragmented soil particles, and this difference may be due to soil deformation along the length of the diaphragm wall during the deformation of the diaphragm wall. The difference in the roughness between the supporting wall and the soil may cause a difference in the horizontal deformations of the soil. Due to the use of zonal excavation, the active zone on the west side of the diaphragm wall was pre-built with several diaphragm walls, which limited the deformation of the soil along the length of the diaphragm wall. This was why the maximum depth of burial of the soil displacement of the west ground-connecting wall was slightly higher than the maximum depth of burial of the wall displacement.
Figure 5c shows the deep soil displacements in the area between the Yuantai Building and the sub-pit 3A10-1. With the exception of monitoring point CX31, which was farther away from the Yuantai Building, the monitoring points for the shallow soil generally orientated towards the outside of the foundation pit and had a certain “push-back displacement”. As a result of the relocation of the Yuantai Building, the foundations at the base of the building were strengthened, and a ring beam foundation was fabricated. In fact, this reduced the width of the shallow active zone behind the diaphragm wall, so that the shallow soil was pushed back under the action of the diagonal struts.
Monitored deep displacements of the soil behind the diaphragm wall of sub-pits 3A5 (Figure 5e) and 3A8 (Figure 5f), CX2, CX3, and CX30 showed a similar trend to the aforementioned sub-pits. CX38 and CX26 were close to sub-pit 3A10-1, and foundation pit excavation affected the deformation monitoring at both points. The monitoring results were very discrete, which did not allow for a reliable pattern to be developed.

4.1.3. Monitoring Results of Surface Settlement

Figure 6 illustrates the surface settlements around the foundation pit during the excavation of sub-pit 3A10-1. The surface settlement in the vicinity of the Yuantai Building is presented in Figure 6a. Monitoring points DBC 28–31 were located at the surface between the foundation pit and the building. Due to the limited distance, only two monitoring points were set up at DBC 28–30 and only one monitoring point was set up at DBC 31. It was observed that the surface settlements at monitoring points DBC 28–31 were all smaller than those at the other three monitoring points, and that the soil in some areas produced a small uplift due to the combined effect of the foundation pit excavation and the Yuantai Building. This justified the interpretation of the deep displacement of the soil at this location. The shallow soil formed a “silo” shape between the rigid foundation pit enclosure and the reinforced foundation of the Yuantai building, and the compression of the loads and supports caused this part of the soil to rise towards the surface. As the Yuantai building was subjected to large loads, the soil settled under the loads, and the surrounding soil may experience some uplifts under the action of the sliding surface. This was also a possible cause of the surface uplift. Monitoring points DBC 26, 27, and 32 all produced a relatively large settlement. However, the settlements at the fourth measurement point of all three monitoring locations were smaller than those at the other points, which also supported the idea that the loads of the Yuantai Building caused the upward displacement of the surrounding soil.
Figure 6b illustrates the surface settlement behind the diaphragm wall on the north side of sub-pit 3A10-1. Consistent with that reported by Hsieh and Ou (1998), the displacement at this location essentially showed a notch-type distribution pattern. The surface settlements behind the diaphragm wall on the west side of sub-pit 3A10-1 are illustrated in Figure 6c, with a “triangular” pattern at the three monitoring points DBC 19, 20 and 22. This may be due to the large horizontal lateral displacement at the top of the wall at this location and the uniform settlement at monitoring points DBC 23 and 25. The dense stacking of materials at this location at the construction site may contribute to this phenomenon.

4.2. Finite Element Simulation Results

4.2.1. Comparison of Simulation Results with Monitoring Results

The comparative analysis of the simulation results with the monitoring data is a reliable means to verify the validity of the finite element model. The simulated horizontal displacement of the diaphragm wall was compared with the monitoring results to validate the established finite element model. Figure 4 shows the comparison between the simulation results and the monitoring results. Most of simulation results and monitoring simulations had similar dislocation patterns and displacement amplitudes, with good agreement. The results for monitoring points ZQT41 and 43 did not match well. The construction loads of the relocation of the Yuantai Building changed the dislocation pattern of the diaphragm wall at these two monitoring points. However, the numerical simulation did not fully describe this construction process, which may be the reason for the error at this point. Table 4 extracts the maximum deformation values of the monitoring data and numerical simulations for each monitoring location and provides the error analysis expressed in percentage. It can be observed that most of the monitoring locations have errors within 25%. In comparison, pit 3A10-1 and pit 3A8 better simulated the deformation of the pit with most of the computational errors within 15%. Collectively, the finite element models developed for the main points involved in the monitoring can effectively simulate the process of pit excavation.

4.2.2. Bending Moments of Diaphragm Wall

For the design of the foundation pit support structure, the bending moment of the support structure is an important parameter that engineers concern and which determines the reinforcement and economy of the support structure. Figure 7 shows the variation of bending moments during stepwise excavation of four sub-pits 3A10-1, 3A10-2, 3A5, and 3A8. As the foundation pit excavation proceeded, the bending moment of the diaphragm wall gradually increased, and the bending moments were mainly located in the excavation surface or in the area above the excavation surface. It was worth noting that in sub-pit 3A10-1, the bending moment of the diaphragm wall on this side was significantly larger than the other two walls on either side due to the influence of the Yuantai Building. As a result of the unloading of the loads imposed by the Yuantai Building and the excavation of the foundation pit in the original active area, the wall on this side showed a negative moment below the excavated surface of the foundation pit.

4.2.3. Disturbance Analysis of Pre-Built Diaphragm Walls

For a foundation pit with a zonal excavation, the diaphragm wall construction for each sub-pit was carried out first. The displacement disturbance of the pre-built diaphragm walls by the first foundation pit excavation may directly affect the subsequent pit excavations.
Figure 8 illustrates the horizontal displacement nephograms for sub-pits 3A5-2, 3A6, and 3A7 during the excavation to the bottom of the foundation pit for conditions 2 and 3. In condition 2, the pre-built diaphragm wall at the junction of sub-pit 3A6 and 3A7 displaced towards the east side of the foundation pit due to the excavation of sub-pit 3A10-1. As a result, the diaphragm wall on the east side of the sub-pit produced a maximum displacement of 2.4 mm at the junction of sub-pits 3A6 and 3A7. As the post-excavation pit is not adjacent to the excavation area, the horizontal displacement at the junction of sub-pits 3A5-2 and 3A6 was significantly smaller than that at the junction of sub-pits 3A6 and 3A7. The displacement trend of the diaphragm wall on the west side of the pit was identical to that on the east side, with only a difference in the depth of the diaphragm wall. In condition 3, the excavation action of sub-pits 3A10-2 and 3A8 together resulted in a maximum displacement of 15 mm at the junction of sub-pits 3A6 and 3A7. Under the influence of the excavation of sub-pit 3A5, the center of the pre-built diaphragm wall of sub-pit 3A5-2 showed a large bulging belly-type deformation, with a maximum deformation of 6 mm.
Similarly, the same condition was observed in the diaphragm walls of sub-pits 3A1-1 to 3A5-1 (Figure 9). During the zonal excavation, the pre-built diaphragm walls may be affected by constructed sub-pits. These deformations might be transmitted through the diaphragm walls orthogonal to the foundation pit enclosure structures under construction and acted on the foundation pit at a greater distance. This horizontal displacement effect was mainly on two non-adjacent pits, and the effect of the displacement was usually small. The difference was that the excavation area adjacent to the pre-built diaphragm wall produced a more significant deformation effect on the pre-built diaphragm wall. Pre-built diaphragm walls may exhibit deformation patterns similar to those of excavated foundation pits. Whether the larger deformation of pre-built wall affects the effectiveness of the support for the excavated sub-pit deserves to be investigated from an engineering perspective during the design and construction stages.

5. Conclusions

This paper presents a field monitoring and numerical modelling study based on the ’New World’ project in Hangzhou. Field monitoring work measured and analyzed the horizontal displacement of the diaphragm wall, the deep horizontal displacement of the soil behind the wall, and the surface settlement of the soil during deep foundation pit excavation in soft soil area. Based on a finite element model validated by monitoring results, the bending moment of the diaphragm wall and the influence of the first excavated pit on the pre-built diaphragm wall were analyzed. The main conclusions are as follows:
(1)
The zonal excavation of foundation pit did not affect the displacement pattern of diaphragm wall, but it would limit the degree of deformation. Peripheral loading and unloading may change the displacement pattern of the diaphragm wall. Under the parabolic dislocation mode of diaphragm wall, the deep horizontal displacement pattern of the soil behind the wall was similar to that of the diaphragm wall, and the soil deformation along the length of the wall led to difference in the horizontal displacements of the wall and soil.
(2)
Construction and consolidation operations around the foundation pit may form a finite soil zone, which may affect the deep deformation pattern of the soil. Large-scale loading and relocation-induced unloading would result in upward displacement of the soil layer in the area surrounding the loading zone and cause bending moment in the diaphragm wall below the excavation surface.
(3)
The first excavated foundation pit would affect the displacement of the support structure of the unexcavated foundation pit. Non-adjacent pit excavation transferred displacement through the pre-built diaphragm wall, resulting in a small displacement effect. Adjacent pit excavations would cause the pre-built diaphragm wall to deform in a similar manner to its supporting structure, resulting in a larger displacement effect.
This paper demonstrates the force and deformation characteristics of excavation in soft ground sub-pits, highlighting the effects of pre-built diaphragm walls subjected to pre-excavation. It can provide guidance for deformation control of soft soil zonal excavation in Hangzhou area.

Author Contributions

Conceptualization, G.L.; methodology, Z.L. and Y.Z.; software, G.L. and Z.L.; validation, F.S. and Y.D.; formal analysis, C.X. and T.F.; data curation, F.S.; writing—original draft preparation, G.L. and Z.L.; writing—review and editing, Y.Z.; visualization, Y.D. and T.F.; supervision, Y.Z.; funding acquisition, C.X. and T.F. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Key R&D Program of China, grant number 2023YFC3009400; the National Natural Science Foundation of China, grant numbers 52168048 and 52238009.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

Authors Gang Lin and Yi Zhao were employed by the company Zhejiang Province Geological & Mineral Engineering Investigation Institute Co., Ltd. Author Feng Sun was employed by the company China Railway Siyuuan Survey and Design Group Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Applsci 14 06358 g001aApplsci 14 06358 g001b
Figure 1. Schematic diagram of ‘New World’ foundation pit.
Figure 1. Schematic diagram of ‘New World’ foundation pit.
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Figure 2. Layout of field monitoring points.
Figure 2. Layout of field monitoring points.
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Figure 3. Schematic diagram of the finite element model. (a) Model size. (b) Condition 1. (c) Condition 2. (d) Condition 3. (e) Condition 4. (f) Condition 5.
Figure 3. Schematic diagram of the finite element model. (a) Model size. (b) Condition 1. (c) Condition 2. (d) Condition 3. (e) Condition 4. (f) Condition 5.
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Figure 4. Horizontal displacements of diaphragm wall during excavation to the bottom of the foundation pit. (a) 3A10-1 sub-pit. (b) 3A10-1 sub-pit. (c) 3A10-2 sub-pit. (d) 3A10-2 sub-pit. (e) 3A10-2 sub-pit. (f) 3A5 sub-pit. (g) 3A8 sub-pit.
Figure 4. Horizontal displacements of diaphragm wall during excavation to the bottom of the foundation pit. (a) 3A10-1 sub-pit. (b) 3A10-1 sub-pit. (c) 3A10-2 sub-pit. (d) 3A10-2 sub-pit. (e) 3A10-2 sub-pit. (f) 3A5 sub-pit. (g) 3A8 sub-pit.
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Figure 5. Deep horizontal displacements of the soil. (a) 3A10-1 sub-pit. (b) 3A10-1 sub-pit. (c) 3A10-1 sub-pit. (d) 3A10-2 sub-pit. (e) 3A5 sub-pit. (f) 3A8 sub-pit.
Figure 5. Deep horizontal displacements of the soil. (a) 3A10-1 sub-pit. (b) 3A10-1 sub-pit. (c) 3A10-1 sub-pit. (d) 3A10-2 sub-pit. (e) 3A5 sub-pit. (f) 3A8 sub-pit.
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Figure 6. Monitoring results of surface settlement. (a) The side of Yuantai Building. (b) The north side of sub-pit 3A10-1. (c) West side of sub-pit 3A10-1.
Figure 6. Monitoring results of surface settlement. (a) The side of Yuantai Building. (b) The north side of sub-pit 3A10-1. (c) West side of sub-pit 3A10-1.
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Figure 7. Changes in bending moments of diaphragm walls during the excavation. (a) Diaphragm walls of 3A10-1 sub-pit. (b) Diaphragm walls of 3A10-2 sub-pit. (c) Diaphragm walls of 3A5 sub-pit. (d) Diaphragm walls of 3A8 sub-pit.
Figure 7. Changes in bending moments of diaphragm walls during the excavation. (a) Diaphragm walls of 3A10-1 sub-pit. (b) Diaphragm walls of 3A10-2 sub-pit. (c) Diaphragm walls of 3A5 sub-pit. (d) Diaphragm walls of 3A8 sub-pit.
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Figure 8. Horizontal displacements nephograms of pre-built diaphragm wall at the western edge of the sub-pit.
Figure 8. Horizontal displacements nephograms of pre-built diaphragm wall at the western edge of the sub-pit.
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Figure 9. Horizontal displacement of the pre-built diaphragm wall at the southern edge of the pit.
Figure 9. Horizontal displacement of the pre-built diaphragm wall at the southern edge of the pit.
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Table 1. Excavation depth and support for each sub-pit of the project.
Table 1. Excavation depth and support for each sub-pit of the project.
Foundation Pit No.Foundation Pit Excavation DepthForms of Foundation Pit Support
3A115 mA total of three supports, the first support using concrete support, the second and third support using section steel support.
3A2
3A3
3A4
3A1-19 mA total of two supports, the first support using concrete support, the second using section steel support.
3A2-1
3A3-1
3A4-1
3A5-1
3A5-2
3A6
3A7
3A518 mA total of four supports, the first support using concrete support, the second, third and fourth support using section steel support.
3A818 mTotal of three braces, all concrete braced.
3A9
3A10-1
3A10-2
Table 2. Soil parameters.
Table 2. Soil parameters.
Layer of SoilThicknessesγcφE
(m)(kN/m3)(kPa)(°)(MPa)
Miscellaneous fillings217.58.010.04
Sandy chalky soil318.96.332.68
Silt sand619.53.736.614
Chalky sand with sandy silt519.14.834.612
Sandy chalky soil418.96.332.68
Silty clay1118.79.127.46
Fine sand720.12.340.018
Boulder620.03.040.030
Cobble820.03.042.035
Strongly weathered rock322.035.025.038
Medium-weathered rock2524.0200.032.050
Table 3. Construction steps for finite element modelling.
Table 3. Construction steps for finite element modelling.
Construction NumberFoundation Pit No.Construction Step
Condition 1 Ground stress equilibrium
Load application and construction of diaphragm walls
Condition 23A10-1Excavate to −5 m
Erection support 1
Excavate to −11 m
Erection support 2
Excavate to −16 m
Erection support 3
Excavate to −18 m
Condition 33A5/3A8/3A10-2Foundation pit 3A5 excavated to −3 m, foundation pit 3A8 and 3A10-2 excavated to −5 m
Erection support 1
Foundation pit 3A5 excavated to −7 m, foundation pit 3A8 and 3A10-2 excavated to −11 m
Erection support 2
Foundation pit 3A5 excavated to −11 m, foundation pit 3A8 and 3A10-2 excavated to −16 m
Erection support 3
Foundation pit 3A5 excavated to −16 m, foundation pit 3A8 and 3A10-2 excavated to −18 m
Foundation pit 3A5 erection support 4
Foundation pit 3A5 excavated to −18 m
Condition 43A5-1/3A5-2/3A7/3A9Foundation pit 3A9 excavated to −5 m, foundation pit 3A5-1, 3A5-2 and 3A7 excavated to −3 m
Erection support 1
Foundation pit 3A9 excavated to −11 m, foundation pit 3A5-1, 3A5-2 and 3A7 excavated to −6 m
Erection support 2
Foundation pit 3A9 excavated to −16 m, foundation pit 3A5-1, 3A5-2 and 3A7 excavated to −9 m
Foundation pit 3A9 erection support 3
Foundation pit 3A9 excavated to −18 m
Condition 53A1-1/3A2/3A3-1/3A4/3A6Excavate to −3 m
Erection support 1
Foundation pit 3A2 and 3A4 excavated to −7 m, foundation pit 3A1-1, 3A3-1 and 3A6 excavated to −6 m
Erection support 2
Foundation pit 3A2 and 3A4 excavated to −11 m, foundation pit 3A1-1, 3A3-1 and 3A6 excavated to −9 m
Foundation pit 3A2 and 3A4 erection support 3
Foundation pit 3A2 and 3A4 excavated to −15 m
Condition 63A1/3A3/3A2-1/3A4-1Excavate to −3 m
Erection support 1
Excavate to −7 m
Erection support 2
Excavate to −11 m
Erection support 3
Excavate to −16 m
Table 4. Error table of maximum deformation for monitoring and numerical simulation.
Table 4. Error table of maximum deformation for monitoring and numerical simulation.
Pit NumberMonitoring PointMonitoring MaximumNumerical MaximumPercentage Error
mmmm%
3A10-1ZQT524.714.669.2
ZQT740.938.56.2
ZQT951.851.70.2
ZQT1122.524.38.0
ZQT2117.720.918.1
ZQT2222.222.30.5
ZQT2422.519.913.0
ZQT2521.818.021.1
3A10-2ZQT3112.911.413.2
ZQT3311.79.030.0
ZQT3516.710.756.1
ZQT3814.910.739.3
ZQT3912.113.410.7
ZQT4110.810.34.9
ZQT4313.210.921.1
3A5ZQT2710.29.013.3
ZQT2818.517.74.5
ZQT2910.27.437.8
ZQT5311.213.823.2
3A8ZQT320.015.826.5
ZQT1911.910.612.2
ZQT5217.718.75.6
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Lin, G.; Lin, Z.; Zhao, Y.; Xu, C.; Sun, F.; Duan, Y.; Fang, T. Force and Deformation Characteristics of Large-Scale Zoning Excavation in Soft Soil: A Case Study in Hangzhou. Appl. Sci. 2024, 14, 6358. https://doi.org/10.3390/app14146358

AMA Style

Lin G, Lin Z, Zhao Y, Xu C, Sun F, Duan Y, Fang T. Force and Deformation Characteristics of Large-Scale Zoning Excavation in Soft Soil: A Case Study in Hangzhou. Applied Sciences. 2024; 14(14):6358. https://doi.org/10.3390/app14146358

Chicago/Turabian Style

Lin, Gang, Zhaorui Lin, Yi Zhao, Changjie Xu, Feng Sun, Yun Duan, and Tao Fang. 2024. "Force and Deformation Characteristics of Large-Scale Zoning Excavation in Soft Soil: A Case Study in Hangzhou" Applied Sciences 14, no. 14: 6358. https://doi.org/10.3390/app14146358

APA Style

Lin, G., Lin, Z., Zhao, Y., Xu, C., Sun, F., Duan, Y., & Fang, T. (2024). Force and Deformation Characteristics of Large-Scale Zoning Excavation in Soft Soil: A Case Study in Hangzhou. Applied Sciences, 14(14), 6358. https://doi.org/10.3390/app14146358

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