岩土工程技术

Deep Foundation Pit Security Risks and Accident Case Analysis

Zhou Yucheng, Guo Yuelong

2012, 26(6): 271-276. doi: 10.3969/j.issn.1007-2993.2012.06.001

[Abstract](28) [PDF 969KB](6)

Abstract:
This paper points out the main risks of three pit supporting types-soil nailed wall (composite soil nailed wall), piles (wall) anchor and inner support in the design and construction in Beijing, and proposed measures to cope with.Through accident analysis, the paper describes the relationship of risks and accidents.In aspect of pit supporting design, construction, supervision, teaching and research, this paper has important reference value.

Research and Development of Underground Cavity Detection Technology in City Road

Jia Hui, Chen Changyan, Sun Zhengwei

2012, 26(6): 277-281. doi: 10.3969/j.issn.1007-2993.2012.06.002

[Abstract](132) [PDF 754KB](28)

Abstract:
This paper illustrates the importance and necessity of underground cavity detection in city road, briefly generalizes the foremost technologies at present and their classification and characteristic, Focuses on ground-penetrating radar technology status, problems and future trends.

Cause Analysis of Uneven Settlement of Certain Building

Cao Ruina, Zhang Haidong

2012, 26(6): 282-285,291. doi: 10.3969/j.issn.1007-2993.2012.06.003

[Abstract](51) [PDF 793KB](9)

Abstract:
This paper calculated and analyzed the difference settlement of a building, the un-treated sounding areas of the building have extra load is the main reason for the situation.Meantime, this paper also discuessed the issues as different foundation type, backfilling time, and the cement mixing piling construction in the new backfilled area issue, etc.

Quantitative Research of the Structural Parameters of Loess Under the Plane Strain Conditions

Wang Xiaofeng, Shi Huaiqing, Wang Donghong

2012, 26(6): 286-291. doi: 10.3969/j.issn.1007-2993.2012.06.004

[Abstract](28) [PDF 956KB](5)

Abstract:
Due to its natural loess large gap between the particles and particles cemented with each other,and thus have a significant structural。Structural changes significantly influence their mechanical properties and stability of soil。Such as slope,tunnel,embankment,excavation and other problems of practical engineering plane strain used in the theory are mostly based on established remolded,it does not take into account the soils structural。This paper analyzes the engineering properties of loess,Quantitative study of the structural remodeling of loess and loess difference between the mechanical behavior,establish the soil strength and stability analysis of the deformation theory,Improve the system of soil mechanics,guidance the engineering practice。

Fuzzy Comprehensive Evaluation of Highway Tunnel Collapse Risk

Weng Qineng, Li Biao, Zeng Longquan

2012, 26(6): 292-296. doi: 10.3969/j.issn.1007-2993.2012.06.005

[Abstract](44) [PDF 654KB](5)

Abstract:
The highway tunnel collapse in tunnel construction is the most common disaster accidents, so the tunnel for the risk assessment is particularly important, through the collection of highway tunnel landslide case history information; and comparing various factors relative to the important degree of highway tunnel collapse, find out the seven effects in the main risk factor for the class of surrounding rock, groundwater conditions, buried deep, large span, bias, blasting disturbance, construction management level, and then based on the fuzzy comprehensive evaluation method and frequency analysis method to determine the risk factor evaluation matrix and the corresponding weight, get the fuzzy comprehensive evaluation model, the model according to the specific situation of tunnel and the concept of fuzzy mathematics the tunnel risk assessment results, in the example verified, with the higher the objectivity and practicability.

Research on Standard Value of Ultimate Shaft Resistance for Fragile Intermediary Weathered Bedrock

Zhan Kaiyu

2012, 26(6): 297-299,305. doi: 10.3969/j.issn.1007-2993.2012.06.006

[Abstract](56) [PDF 646KB](9)

Abstract:
This paper presents a calculation formula and puts forward the value range of standard value of shaft resistance for fragile intermediary weathered bedrock because it needs to be provided when the pile was placed at the fragile intermediary weathered bedrock, but there was no value recommended of it in technical code of building pile foundations.And the value range of standard value of shaft resistance for fragile intermediary weathered bedrock was validated by engineering practice.The results show that the value range of standard value of shaft resistance was 1 400~5 400 kPa for soft rock and it was 5 400~21 700 kPa for hard rock under dry drilling, and it was 1 200~4 600 kPa for soft rock and it was 4 600~18 500 kPa for hard rock under mechanical hole building.And the engineering property of fragile intermediary weathered extremely soft rock is similar to strong weathered soft rock, the fragile intermediary weathered soft rock is inferior to compacting gravel, the fragile intermediary weathered relatively soft rock is similar to compacting gravel, the fragile intermediary weathered relatively hard rock is better than compacting gravel.

Mechanics Studies on Composite Soil Nailing for Supporting Foundation Pit

Wang Tao, Xiong Chuanxiang

2012, 26(6): 300-305. doi: 10.3969/j.issn.1007-2993.2012.06.007

[Abstract](34) [PDF 832KB](7)

Abstract:
In order to discuss the mechanical mechanism of composite soil nailing wall supporting foundation pit in practical projects, it was based on discrete element method of PFC^2D, and the introduction of particle flow theory and development of particle flow in mesoscopic numerical simulation technology, to conduct the mechanics studies about its mechanism from mesoscopic aspect for composite soil nailing supporting.The particle flow code model for composite soil nailing supporting was established by discrete element method, which compared with nailing supporting only and cement-soil pile supporting only, there were much difference about axial force and its distribution between composite soil nailing supporting and nailing supporting only.Whats more, the distribution of bending moment and shear stress is different from cement-soil pile supporting only.So, the results show it offers a new approach and method for mechanism study of composite soil nailing wall supporting foundation pit by using discrete element method.

Monitoring and Countermeasure of Heritage Building Subsidence Caused by Closer Deep foundation Excavation

Zhang Shanggen, Li Keming

2012, 26(6): 306-308. doi: 10.3969/j.issn.1007-2993.2012.06.008

[Abstract](21) [PDF 627KB](6)

Abstract:
Cracks of wall were found in the Heritage Building because of deep foundation excavation.The monitoring scheme and countermine such as protected groundwater level, increase rigidity of reinforced concrete supports and dynamical predication model for building settlement were also forward.., the Heritage Building was safety during the construction of the very closer foundation pit.

Correlation Study of Physical and Mechanical Properties of Soft Soil in Tianjin

Li Yupeng, Guo Jinjing, Yu Hui

2012, 26(6): 309-312. doi: 10.3969/j.issn.1007-2993.2012.06.009

[Abstract](24) [PDF 671KB](11)

Abstract:
Method of least squares was used to determine the relevance among physical and mechanical properties of soft soil in Tianjin. The results showed that there were good relevance among initial void ratio, coefficient of compressibility and water content; natural water content and void ratio,so, water content can be used to estimate certain physical and mechanical properties. The regression equation between liquid limit and plastic index was:I_P=0.43(W_L-10.8), which is different form other plasticity charts. Meanwhile, it is different from Casagrande's plasticity chart which can be described as I_P=0.73(W_L-20). Soil region should be taken into consideration during soil classification.

Support Design and Monitoring Results Analysis of Deep Foundation Pit of Hankou Railway Station

Li Jiansheng, Yu Tingxin

2012, 26(6): 313-316. doi: 10.3969/j.issn.1007-2993.2012.06.010

[Abstract](27) [PDF 780KB](6)

Abstract:
The formation property of the foundation pit was poor.The upper was mucky silty clay and the lower was silt.The surrounding architectural environment was complex.According to formation and the surrounding environment, support scheme of bored piles, steel supports and high pressure jet grouting piles was made.Monitoring based on standard played an important role in guiding excavation.Monitoring results which were analyzed and compared with calculated value showed that support design of the foundation pit was reasonable.The results provided reference for other foundation pit design and monitoring.

Deep Foundation Pit Security Risks and Accident Case Analysis

Zhou Yucheng, Que Liedong, Xu Chao

2012, 26(6): 317-320. doi: 10.3969/j.issn.1007-2993.2012.06.011

[Abstract](22) [PDF 801KB](7)

Abstract:
A new type of long spiral mixing jet grouting pile is introduces which is mainly used for pit waterproof curtain and soil reinforcement.This paper summarized the relationship of pile diameter with the soil and construction parameters.The experimental research results not only provides guidance on construction parameters,but also suggests constructing the long spiral mixing jet grouting pile first then constructing the reinforced concrete revetment pile.This article provides an important reference for the foundation pit support and groundwater control design.

Application of Ground Penetrating Radar in the Survey of Hidden Karst for Subway Foundation Pit

Cheng Cifeng, Li Pengfei

2012, 26(6): 321-323. doi: 10.3969/j.issn.1007-2993.2012.06.012

[Abstract](20) [PDF 683KB](8)

Abstract:
Geological conditions of subway foundation pit bottom should be taken care of to guarantee the safety of construction and operation of subway in karst area.It has shown that geology method should be given the first place together with other auxiliary methods considering the features of subway construction.This paper described principle,technology character of GPR and practical working Method and using an application of the successful detection of the karst in a foundation pit of Wuhan metro Line 2 as example, confirms the effectiveness and feasibility of the method in the exploration of hidden karst in foundation pit.The technique is worthy of wide application with further improvement.

2012 Vol. 26, No. 6