CN105178336B - Method for determining ultimate bearing capacity of refuse dump with weak foundation base - Google Patents

Abstract

The invention discloses a method for determining the ultimate bearing capacity of a soil dump on a soft base. First, the ultimate bearing capacity formula of the _Prandell foundation is used to calculate the ultimate pile height when the triangular load on the side of the dump is not considered. The soil field slope angle β, slope height H ₉₀ + △H and the position of the slope surface line, respectively determine the functional relationship between the sliding moment increment △ _Mslip and △H, and the _anti- sliding moment △Mslip' and The functional relationship of △H, draw the △M _slip- △H and △M _anti- △H curves again, and judge whether the two curves intersect. If they intersect, the H ₉₀ +△H corresponding to the intersection point is the edge of the dump The limit pile height when the slope angle is β, the load corresponding to the limit pile height is the ultimate bearing capacity of the dump site on weak base, if there is no intersection point, the dump site has no limit pile height. The invention determines the limit pile height of the weak base dump from the perspective of the bearing capacity of the base, and can effectively avoid the instability of the dump due to insufficient bearing capacity of the base.

Description

A Determination Method of Ultimate Bearing Capacity of Weak Substrate Dump

technical field

The invention belongs to the field of open-pit mining, and in particular relates to a method for determining the ultimate bearing capacity of a soil dump on a weak base.

Background technique

Weak basement is an important factor affecting the stability of open-pit mine dumps. Under the condition of weak basement, when the height of the dump site reaches a certain critical value, ground drum will occur, which will induce the dump site instability. Landslides or slopes have occurred in soft base dumps such as Pingshuo Antaibao Open-pit Coal Mine, Baorixile Open-pit Coal Mine, No. 1, No. 2, No. 3, and No. Large deformation phenomena such as drums at the feet and cracks on the surface seriously threaten the safety of open-pit mines and affect the continuous normal operation. Insufficient base bearing capacity is an internal factor leading to the overall instability of the weak base dump. Therefore, the calculation of the base bearing capacity of the weak base dump is particularly important.

The ultimate bearing capacity formula of Plantel foundation is a classic method for calculating the bearing capacity in building foundation theory. Because of its simple calculation principle and convenient application, it is often used to calculate the ultimate bearing capacity of the foundation of the dump site. During the calculation process, the load of the dump site It is regarded as strip-shaped uniformly distributed load, and the distribution characteristic of triangular load of the dump site is not considered, so the theory is not perfect when applying this method to calculate the bearing capacity of the dump site base.

Contents of the invention

Aiming at the deficiencies of the prior art, the present invention improves the ultimate bearing capacity formula of Prandell's foundation, which can be used to determine the ultimate pile height of the weak base dump.

According to the distribution characteristics of the base load of the dump site, the specific steps of a method for determining the ultimate bearing capacity of the dump site with weak bases are as follows:

Step 1: Use the ultimate bearing capacity formula of Prandell's foundation to calculate the ultimate row height H ₉₀ when the triangular load on the side of the dump site is not considered.

Step 2: As the slope angle and height of the dump site change, the position of the slope line of the dump site changes, and when the slope height increases to H ₉₀ + △H, determine the sliding moment increments △ _Mslip and △H respectively The functional relationship between the _anti- sliding moment △M and △H produced by the side triangular load, △H is the height increment after the height of the dump site reaches H ₉₀ ;

Step 2.1, determine the functional relationship between the _sliding moment increment ΔM and the height increment _ΔH after the height of the dump site reaches H90;

Step 2.2, according to the slope angle β of the dump site and the slope height H ₉₀ + △H, determine the position of the slope line of the dump site;

Step 2.3, according to the slope line position of the dump site, determine the functional relationship between the _anti- sliding moment △M △M' produced by the lateral triangular load and the height increment △H after the dump site height reaches _H90 .

Step 3: Draw △M _slip- △H and △M _anti- △H curves respectively, and judge whether the two curves intersect. If they intersect, then the H ₉₀ +△H corresponding to the intersection point is the slope angle of the dump site is β The limit pile height at , the load corresponding to the limit pile height is the ultimate bearing capacity of the soft base dump, if there is no intersection point, the dump site has no limit pile height.

Advantages of the present invention:

Based on the distribution characteristics of the dump site load, the present invention improves the ultimate bearing capacity formula of the Plantel foundation, and proposes a method for determining the base bearing capacity of the dump site with weak bases, which makes up for the design of the dump site with weak bases in engineering Insufficiency in stability research. This method determines the limit pile height of the dump site with weak basement from the perspective of basement bearing capacity, which can effectively avoid the dump site instability caused by insufficient basement bearing capacity.

Description of drawings

Figure 1 is the mechanical model of the dump site based on the ultimate bearing capacity formula of Prandell's foundation;

Fig. 2 is the mechanical model of the dumping field of a kind of embodiment of the present invention;

Fig. 3 is the curve of ΔM _sliding -ΔH and ΔM _anti' -ΔH under different situations of an embodiment of the present invention, wherein (a) is ΔM _sliding -ΔH and ΔM _anti when β=60° '-△H curve, (b) is △M _slip- △H and △M _anti'- △H curve when β=45°, (c) is △M _slip- △H and △H when β=36° M _- anti'-△H curve, (d) is △M _-slip- △H and △M _- anti'-△H curve when β=16°;

Fig. 4 is a flowchart of a method for determining the ultimate bearing capacity of a dump site with a weak base according to an embodiment of the present invention.

detailed description

The specific embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings. In the ultimate bearing capacity formula of Prandell’s foundation, the force acting on the foundation is regarded as a uniform vertical load, as shown in Fig. 1. When calculating the bearing capacity of the dump site, the side of the dump site should be considered Effect of triangular vertical loads. From this aspect, the ultimate bearing capacity formula of the Prandel foundation is improved, and the mechanical model of the dump site in this embodiment is shown in Figure 2 .

The design slope angle of an open-pit mine dump is β=16°, the base is Quaternary silt and fine sand, and the weight of the waste is γ ₀ =18kPa; the internal cohesion of the base soil is c=2.1kPa; the internal friction angle of the base soil In this embodiment, the base width of the uniform vertical load is b=6m.

As shown in Figure 4, the steps of the method for determining the ultimate bearing capacity of the weak base dump in this embodiment are as follows:

Step 1: Using the ultimate bearing capacity formula of Prandell's foundation to calculate the ultimate row height without considering the triangular load on the side of the dump site is H ₉₀ , which is the limit height of the vertical slope.

H ₉₀ =P _u /γ ₀ =37.375/18=2.076m

Among them, P _u —the ultimate bearing capacity of the basement under the condition of vertical uniform load, kPa;

q—soil gravity on the upper part of the basement, kPa;

γ ₀ —weight of waste, kN/m ³ ;

in is the internal friction angle of the base soil, °;

c—cohesion of base soil, kPa;

b—basic width, m;

H ₉₀ — the limit height of the dump site calculated without considering the triangular load on the side of the dump site, m;

△H—height increment after the height of dump site reaches H ₉₀ , m;

β—Slope angle of dump site, °.

At this time, if the anti-slip moment M ₀ generated by the side triangular load corresponding to H ₉₀ is considered, the total _anti- slip moment M is greater than the _sliding moment M, and the base is in a stable state.

Step 2: As the slope angle and height of the dump site change, the position of the slope line of the dump site changes, and when the slope height increases to H ₉₀ + △H, determine the sliding moment increments △ _Mslip and △H respectively The functional relationship between the _anti- sliding moment △M and △H generated by the side triangular load, △H is the height increment after the height of the dump site reaches H ₉₀ . There is a linear relationship between △M _slip and △H, and a power function curve relationship between △M _resistance ' and △H (when is a cubic curve when is a quadratic curve), both of which are increasing functions with △H as the independent variable. When the height of the dump site continues to increase △H, the _sliding moment increases △Mslip, and the _anti- sliding moment increases △Mantis, and the _anti -sliding moment △Mantis generated by the corresponding side triangular load'=△ _Mantis +M ₀ , △ _Msliding It is equal to (△M _resistance +M ₀ ), which means that M _resistance and M _slip have reached a balance again, and the height of the dump at this time is its limit pile height.

Step 2.1. Determine the functional relationship between the _sliding moment increment ΔM and the height increment ΔH after the height of the dump site reaches H ₉₀ .

Step 2.2. According to the dump slope angle β and slope height (H ₉₀ + △H), compare (H ₉₀ + △H)/tanβ with Determine the position of the slope line of the dump site, as shown by slope line 3 and slope line 4 in Figure 2.

Step 2.3, according to the slope line position of the dump site, determine the functional relationship between the _anti- sliding moment △M △M' produced by the lateral triangular load and the height increment △H after the dump site height reaches _H90 . The position of the slope line of the dump site will affect the functional relationship between △M _resistance ' and △H, so △M _resistance ' is calculated in two cases:

when $(h_{90}+\mathrm{\Δ}h)/ta\mathrm{no}\mathrm{\β}\≤\stackrel{\‾}{AI},$

when $(h_{90}+\mathrm{\Δ}h)/ta\mathrm{no}\mathrm{\β}>\stackrel{\‾}{AI},$

Step 3: Draw △M _slip- △H and △M _anti'- △H curves respectively, as shown in Figure 3, 1 is the △M _slip- △H curve, and 2 is the △M _anti'- △H curve. Figure 3(a) shows the intersection of the △M _slip- △H curve and the △M _resistance'- △H curve at the base of the dump site when the slope angle is 60°, and the intersection point is the limit heap height of 2.136m; Figure 3(b ) shows that when the slope angle is 45°, the △M _slip- △H curve and the △M _resistance'- △H curve of the dump site intersect, and the intersection point is the limit heap height of 2.326m; Figure 3(c) shows that when When the slope angle is 36°, the △M _slip- △H curve and the △M _resistance'- △H curve of the dump site are tangent, and the intersection point is the limit stack height of 3.186m; Figure 3(d) shows that when the slope angle When the slope is 16°, the △M _-slip- △H curve and the △M _{- anti'-} △H curve of the dump site do not intersect, and the anti-sliding moment is very large. △M is _slippery and increases infinitely with the increase of slope height, that is, the dump site can be infinitely high.

Claims (1)

1. a kind of determination method of weakness Based Earth Dump ultimate bearing capacity, comprises the following steps:

Step 1: calculate the limit not considered during the delta load of refuse dump side using your Formula of ultimate bearing capacity of shallow of Prandtl The a height of h of heap₉₀；

Step 2: with the high change of refuse dump slope angle and slope, the domatic line position in refuse dump changes, and slope height increases to h₉₀+ During δ h, determine slip moment increment δ m respectively_SlidingThe resisting moment δ m producing with the functional relationship of δ h, side delta load_Anti-′ With the functional relationship of δ h, δ h highly reaches h for refuse dump₉₀Height gain afterwards；

Step 3: draw δ m respectively_Sliding- δ h and δ m_Anti-'-δ h curve, judges whether two curves intersect, if intersecting, intersection point Corresponding h₉₀+ δ h is the limit height that refuse dump slope angle is during β, and the corresponding load of this limit height is weak substrate row Native field ultimate bearing capacity, if no intersection point, refuse dump does not have limit height；

It is characterized in that: described step 2 specifically comprises the following steps that

Step 2.1, determine slip moment increment δ m_SlidingHighly reach h with refuse dump₉₀The functional relationship of height gain δ h afterwards；

Step 2.2, according to refuse dump side slope angle beta and the high h in slope₉₀+ δ h, determines the domatic line position in refuse dump；

Step 2.3, according to domatic line position, determine the resisting moment δ m that side delta load produces_Anti-' highly reach with refuse dump To h₉₀The functional relationship of height gain δ h afterwards.