岩土工程技术

Principle of Active Earth Pressure Calculation for Building Foundation Pit Side-wall

Liu Xu

2021, 35(3): 141-145,162. doi: 10.3969/j.issn.1007-2993.2021.03.001

[Abstract](90) [PDF 1269KB](46)

Abstract:
With the increasing and intensive use of underground space in urban construction, in recent years, some actual projects of geotechnical engineering design beyond the scope of the norms and standards are quite common. However, relevant national standards, industry standards and local standards are different in the specific provisions. The active earth pressure calculation of foundation pit side-wall involved in the relevant provisions of some codes and manuals are sorted out and summarized. The principle analysis of an engineering project case is carried out, which often appears recently but has not yet listed specific provisions in various codes. The calculation principle for this kind of working condition is put forward. The purpose is to sort out the terms of active earth pressure calculation on the side-wall of foundation pit clearly, and provide suggestions and supplements for the calculation principle of a working condition not listed in the specifications, so that the relevant problems in the geotechnical engineering design can be carried out clearly and reasonably.

Numerical Simulation of Groundwater Seepage in Suspended

Zhang Qinxi, Wei Meng, Wang Chengming

2021, 35(3): 146-150,156. doi: 10.3969/j.issn.1007-2993.2021.03.002

[Abstract](135) [PDF 2708KB](43)

Abstract:
The suspended water curtain is widely used in foundation pit engineering. GMS is used to simulate the indoor groundwater seepage model test. The numerical simulation results are compared with the test results to verify the reliability of groundwater numerical simulation software. Then on the basis of determining the accuracy of the software, the change rule of groundwater seepage in different shapes of foundation pit under the same insertion depth of suspended water stop curtain are further studied, providing reference for the actual engineering dewatering design. The results show that the numerical simulation is consistent with the actual monitoring of the water inflow outside the pit and the water level change outside the pit; for the foundation pit with different shapes, the increase of the curtain insertion depth has no obvious effect on the water level outside the pit, but under the same curtain insertion depth, the water inflow of the foundation pit with different shapes is quite different, specifically, the water inflow of the square foundation pit is the largest, the rectangle foundation pit is the second, and the water inflow of circular foundation pit is the least.

Stability Analysis and Treatment of a Graded Layered and Zoned Landslide

Zeng Peng, Jin Yuxiang, Zhong Zhihui

2021, 35(3): 151-156. doi: 10.3969/j.issn.1007-2993.2021.03.003

[Abstract](109) [PDF 6015KB](34)

Abstract:
A complex landslide in Guangdong Province is analyzed as a typical engineering case. Combined with the field deformation survey, engineering geological mapping and supplementary deep hole displacement monitoring, the landslide is divided into different grades, layers and zones, and the landslide characteristics and causes are analyzed. It is considered that the comprehensive effects of geological environment, engineering activities, rainfall and groundwater lead to the slope landslide. According to the characteristics of the landslide, the technical scheme of "vertical steel pipe group piles + inclined prestressed anchor cable crown beam" is put forward, which can provide reference for the treatment of landslide under similar geological conditions.

Design and Monitoring Analysis of a Soft Soil Deep Foundation Pit

Qiao Liping, Li Yundi, Huang Wenbin, Wang Yuan

2021, 35(3): 157-162. doi: 10.3969/j.issn.1007-2993.2021.03.004

[Abstract](93) [PDF 7752KB](50)

Abstract:
It has a high risk to excavate foundation pits in soft soil areas, and the impact of foundation pit excavation on adjacent subway tunnels must be strictly controlled in the subway security area. Therefore, the deformation control on designing of foundation pit support in subway security areas under soft soil conditions is highly demanded. The support design scheme of a deep foundation pit in Shenzhen's reclamation area and subway security zone is introduced in detail. The design scheme is analyzed and verified by rational element calculation and three-dimensional finite element calculation, and the calculation results are also compared with the monitoring data. The analysis shows that the form of occlusal piles + reinforced concrete support structure has high reliability in the application of deep foundation pits in soft soil. The monitoring data is applied to three-dimensional finite element to conduct inversion analysis, which can assist in the design and predict the deformation of the supporting structure and the adjacent subway tunnel, so as to adjust the supporting measures in engineering projects.

Analysis on Quality Problems of Post-grouting Bored Pile in Deep Sand Stratum

Chen Zhixin, Peng Manhua, Zhang Haishun

2021, 35(3): 163-167,195. doi: 10.3969/j.issn.1007-2993.2021.03.005

[Abstract](94) [PDF 2819KB](49)

Abstract:
A quality accident of post-grouting bored pile in deep sand stratum is discussed as an example. Based on field test data and field investigation, the causes of quality accident are analyzed from the aspects of design, investigation and construction. The analysis results show that the main causes of the quality accident are improper holing and hole cleaning technology, unreasonable grouting amount, grouting speed, grouting device and the insertion depth of grouting pipe. In view of these reasons, solving measures are put forward. Reverse circulation technology and twice grouting technology should be adopted when post-grouting bored pile is cleaned in deep sand stratum. At the same time, reasonable grouting amount should be ensured, and consistency between grouting pipe and hole forming depth should be checked. The research results can be used as reference in the design and construction of similar pile foundation engineering of post-grouting bored pile in deep sand stratum.

Application of a Multi-level Support System in Deep Foundation Pit of Bridge Pier

Liu Xuyang, Feng Xiaola, Xiong Zonghai, Zhang Zhefei

2021, 35(3): 168-173. doi: 10.3969/j.issn.1007-2993.2021.03.006

[Abstract](78) [PDF 7331KB](33)

Abstract:
The construction work platform of Wuhan Xinhe Bridge Pier 11 is small in size. The soil pressure and water pressure next to the foundation pit are unevenly distributed and the strength of the soil is low. In order to reserve a certain space for the foundation pit support and bridge pier construction, the technologies of a variety of foundation pit support design schemes are compared. According to local conditions, a double-row steel sheet pile is adopted combined with soil filling between the piles to form a cofferdam externally; the transition zone in the middle is reinforced by high-pressure jet grouting piles to form a construction road; a multi-level support system for deep foundation pits supported by double-row piles and three steel pipes is adopted inside.Through the collaborative calculation module for three-dimensional calculations and Plaxis 2D finite element calculation and analysis, it is found that this transition system can strengthen the soft soil and play a good deformation control effect. Combined with the results of the pile displacement monitoring, the superiority of the multi-level support system is proved. This system can reduce the force of the internal support, reduce the deformation of the soft soil, and solve the construction in the soft soil area of the riverside with heavy equipment. The problem of insufficient space can also provide a reference case for similar projects.

Analysis of Subgrade Slope Stability in Cold Region Based on Rock and Soil Water-physical Properties

Wang Guoai, Cao Jun, Du Yaohui

2021, 35(3): 174-178. doi: 10.3969/j.issn.1007-2993.2021.03.007

[Abstract](63) [PDF 2378KB](16)

Abstract:
The stability of subgrade slopes in cold regions is analyzed based on the water-physical properties of rock and soil. The stability of the subgrade in the cold area is mainly affected by the coupling effect of water and temperature, that is, the freeze-thaw cycle and the thawing process. The rock slope is mainly affected by freeze-thaw cycles, which causes freeze-thaw damage, reduces its strength and causes instability. Due to the change of the water phase, the soil slope softens and swell-shrink, accordingly its cohesion, internal friction angle and strength decrease. Its slope stability coefficient is closely related to the melting depth and the saturation of the melting layer.

Modeling Method of Complex Layered Foundation Rock Mass

Li Jin

2021, 35(3): 179-184. doi: 10.3969/j.issn.1007-2993.2021.03.008

[Abstract](66) [PDF 4417KB](29)

Abstract:
The characteristics of rock engineering are obviously different due to the influence of diagenetic conditions, geological tectonics, metamorphism and weathering. In the practical engineering application, considering the stress distribution and convenient calculation, the relatively complex rock mass should be simplified. Within the scope of a project, to obtain geotechnical design parameters objectively and evaluation of engineering properties, reasonable engineering simplification is the basic premise to realize the foundation calculation. Taking a certain nuclear power project as an example, by means of a large number of experiments and tests, merge and simplify the rock strata with similar engineering properties, the characteristics of complex layered rock mass have been revealed. The engineering practice shows that the rock mass of the site presents obvious inhomogeneous characteristics, and the division of the engineering geological unit according to the rock group and weathering intensity to divide the engineering geological unit does not reflect the difference of lithology; According to the acoustic and mechanical experiment data of various types of rock mass, the engineering geological section is carried out according to the lithological combination, which conforms to the engineering practice.

Study on Water Level of Anti-floating Construction in Xi’an

Liu Jun, Luo Yunhai, Qiu Zuquan, Wang Xiaoyan

2021, 35(3): 185-188. doi: 10.3969/j.issn.1007-2993.2021.03.009

[Abstract](106) [PDF 1568KB](57)

Abstract:
The groundwater that has influence on the construction of the project in Xi'an is phreatic water, and its water level is mainly affected by the landform, water bearing stratum, meteorology, surface water system, surface water body, urban ecological water supplement and the precipitation of adjacent projects. Combined with engineering examples, the difference of the annual variation of groundwater level in different geomorphic units is put forward. At present, the groundwater is still in the overall slow rising period. The conclusion can provide the basis for anti-floating water level determination in the construction site.

Engineering Characteristics and Engineering Classification of Cenozoic Semi-diagenetic Rock Masses

Yang Xiaofang, Li Yuqian, Ma Bingwu

2021, 35(3): 189-195. doi: 10.3969/j.issn.1007-2993.2021.03.010

[Abstract](134) [PDF 4521KB](48)

Abstract:
Basic classifications and evaluations of the Cenozoic semi-diagenetic rock masses are carried out by using the engineering rock mass classification methods in the current codes, on the basis of analyzing and summarizing the geological and engineering characteristics of the Cenozoic semi-diagenetic rock masses. It is found that the engineering rock mass classification methods in the current codes have strong universality for most engineering rock masses, but the applicability for the special medium between "rock" and "soil" is not universal. It is difficult to highlight the engineering characteristics on the influence of the engineering construction. According to the theory of engineering geology, the applicability of the engineering rock mass classification methods in the current codes to the Cenozoic semi-diagenetic rock masses are further analyzed and evalerated. On the basis of summarizing the previous research on the engineering characteristics and classification of the soft rocks as well as the Cenozoic semi-diagenetic rock masses, the idea and suggestion of engineering rock mass classification evaluation of the Cenozoic semi-diagenetic rock masses is put forward.

Internal Force Test of Super-long Cast-in-place Pile Based on Optical Fiber

Zhang Huihai, Ma Lin, Shi Huaiqing, Wan Zaixin, Wang Donghong

2021, 35(3): 196-198. doi: 10.3969/j.issn.1007-2993.2021.03.011

[Abstract](70) [PDF 4189KB](43)

Abstract:
Focusing on the problem of insufficient design data for the super-long piles, field test of distributed optical fiber technology is conducted on the mechanical behavior of the ultra-long piles in a typical supporting project in northwestern China. The results show that the pile side resistance increases first and then decreases along the pile depth, and the critical depth of the pile side friction is 26 m. It is concluded that the range of pile side friction is 58 m from pile body to pile top. The research results can directly guide the design and optimization of pile length.

Dynamic Shear Characteristics of Anisotropic Calcareous Sand Under Cyclic Rotation of Principal Stress Axis

Yu Yanming, Liang Hui, Shen Yang, Ge Huayang

2021, 35(3): 199-204. doi: 10.3969/j.issn.1007-2993.2021.03.012

[Abstract](49) [PDF 1283KB](13)

Abstract:
In order to study the dynamic shear characteristics of anisotropic calcareous sand under the cyclic rotation of principal stress axis, a series of undrained tests on the cyclic rotation of principal stress axis under the anisotropic consolidation mode were carried out by GDS hollow cylinder torsional shear apparatus. It was found that the anisotropic consolidation mode aggravated the anisotropy in the microstructure of calcareous sand samples and made the generalized shear strain develop from "stable type" to "destructive type" under the cyclic rotation of principal stress axis. For the "stable type" tests, each strain component has a linear relation with the logarithm of the vibration times, thus the empirical formula of the axial strain ε_z and vibration times N of the "stable type" calcareous sand is obtained. With the increase of vibration times, the "destructive type" calcareous sand softens, and the dynamic shear modulus rapidly decreases after 10 vibration times. The softening index R_N is introduced to reflect the softening degree, and the empirical formula for the calculation of softening index R_N and vibration times N is obtained.

Grouting Reinforcement Treatment of Liquefied Foundation

Song Keying, Zhang Kai, Zhang Qi

2021, 35(3): 205-211. doi: 10.3969/j.issn.1007-2993.2021.03.013

[Abstract](73) [PDF 3552KB](38)

Abstract:
Taking grouting reinforcement treatment of liquefied foundation as an example, through the standard penetration test and the comparative analysis of the shear wave velocity of soil between piles before and after grouting, it can be seen that the shear wave velocity of foundation soil can be increased effectively by this method.It can significantly reduce the liquefaction index, and greatly reduce the environmental pollution and save time. It has a good promotion and application

2021 Vol. 35, No. 3